Reflective mask and semiconductor device manufacturing method

Abstract

A reflective mask capable of suppressing overexposure at the joints between patterns on a wafer and realizing highly accurate pattern transfer is provided. [Solution] A reflective mask is provided that has a substrate, a multilayer film disposed on one side of the substrate, and an absorption layer pattern disposed on the side of the multilayer film opposite the substrate, the reflective mask having a transfer pattern area having the absorption layer pattern, and a shading area disposed on the periphery of the transfer pattern area, which does not have the multilayer film or the absorption layer, and in which the substrate is exposed, and in a planar view, the shape of the boundary between the transfer pattern area and the shading area is rounded.

Description

[Technical Field]

[0001] The present disclosure relates to a reflective mask used in extreme ultraviolet (EUV) lithography and a method for manufacturing a semiconductor device using the same. [Background technology]

[0002] In recent years, EUV lithography, an exposure technology using EUV, has become a promising approach in the semiconductor industry due to the miniaturization of semiconductor devices. Reflective masks have been proposed as a mask for use in EUV lithography. A reflective mask includes, for example, a substrate, a multilayer film that reflects EUV light and is disposed on one side of the substrate, and an absorbing layer that absorbs EUV light and is disposed in a pattern on the opposite side of the multilayer film. In EUV lithography, EUV light incident on the reflective mask is absorbed by the absorbing layer and reflected by the multilayer film. The optical image reflected by the multilayer film is then transferred onto a wafer through a reflection optical system.

[0003] When transferring a pattern onto a wafer using a reflective mask, an exposure method called the step-and-repeat method is used. The step-and-repeat method involves sequentially moving (stepping) the wafer and repeatedly (repeat) exposing it. The exposure equipment that uses the step-and-repeat method is called a stepper.

[0004] When performing exposure using this step-and-repeat method, the transfer pattern areas where the absorber layer patterns are arranged on the reflective mask are usually transferred as close to each other as possible to extract as many chips as possible from the wafer. Furthermore, in the step-and-repeat method, an area slightly larger than the transfer pattern area is generally exposed. Therefore, areas where adjacent exposure areas on the wafer overlap are generated. Hereinafter, areas where exposure areas overlap are sometimes referred to as "multiple exposure areas." For example, in the case of a rectangular exposure area, the corners of one exposure area overlap with the other three exposure areas, resulting in four exposures.

[0005] In the multiple exposure region, multiple exposures are performed, and most of the exposure light is absorbed by the absorbing layer. Even if a single exposure does not substantially contribute to resolution, the exposure amounts may add up to an amount that contributes to resolution. As a result, an unnecessary pattern is formed, and a high-precision pattern cannot be obtained.

[0006] Furthermore, in a reflective mask, the exposure light is incident on the mask surface at a tilt of several degrees, usually around 6 degrees, from the perpendicular direction. Because the absorber layer has thickness, when the exposure light is incident at an angle, a shadow is cast by the absorber layer pattern itself. This effect is called the shadow effect. The degree of the shadow effect varies depending on the orientation of the absorber layer pattern relative to the exposure light, and affects the dimensions transferred to the wafer. The problem of this shadow effect has become particularly noticeable in recent years as patterns have become finer.

[0007] To suppress such a shadow effect, it is preferable that the absorbing layer is thin. However, if the thickness of the absorbing layer is thin, the absorption of exposure light by the absorbing layer decreases, which increases the problem of pattern defects in the multiple exposure region.

[0008] Therefore, as described in Patent Documents 1 and 2, for example, in a reflective mask, it has been proposed to arrange a light-shielding region on the periphery of the transfer pattern region to suppress reflected light from a peripheral region located on the periphery of the transfer pattern region, which forms a multiple exposure region. The light-shielding region is also called a light-shielding frame or a light-shielding band. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-69859 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-190979 Summary of the Invention [Problem to be solved by the invention]

[0010] The numerical aperture (NA) of the projection optical system lens in currently available EUV exposure tools is 0.33, and the reduction ratio in the x and y directions of the projection optical system is 4x. In contrast, EUV exposure tools with an NA increased to 0.55 have been developed, which achieves a reduction ratio of 4x in the x direction and 8x in the y direction of the projection optical system. For a given reflective mask size, when the NA is 0.55, the reduction ratio in the y direction is twice that of the x direction compared to when the NA is 0.33, and therefore the exposure area on the wafer is halved. In this case, as shown in Figures 18(a) and 18(b), two exposures are performed using two reflective masks 100A and 100B. At this time, it is necessary to stitch the pattern transferred by the reflective mask 100A and the pattern transferred by the reflective mask 100B together on the wafer 120. This technique is called stitching exposure. In stitching exposure, exposure is performed on the wafer 120 so that an exposure region 121a corresponding to the reflective mask 100A and an exposure region 121b corresponding to the reflective mask 100B partially overlap each other. As shown in Figures 19(a) and 19(b), each of the reflective masks 100A and 100B has a substrate 102, a multilayer film 103 that is disposed on one surface of the substrate 102 and reflects EUV light, and an absorption layer 105 that is disposed in a pattern on the surface of the multilayer film 103 opposite the substrate 102 and absorbs EUV light. As shown in Figures 18(a), 19(a), and 19(b), each of the reflective masks 100A and 100B has a transfer pattern region 111 in which the pattern of the absorption layer 105 is disposed, and a light-shielding region 112 that is disposed on the periphery of the transfer pattern region 111.

[0011] As described above, in a reflective mask, exposure light is incident from a direction tilted by several degrees, typically about 6 degrees, from the perpendicular direction to the mask surface. As shown in FIG. 19(a), when exposure light L1 is incident obliquely on a reflective mask, the EUV light reflected by the multilayer film 103 is absorbed by the absorption layer 105 and attenuated in the transfer pattern region 111. However, as shown in FIG. 19(b), when exposure light L1 is incident obliquely at the edge of the transfer pattern region 111, the EUV light reflected by the multilayer film 103 is not attenuated by the absorption layer 105, resulting in light leakage toward the light-shielding region 112. For example, as shown in FIG. 20, when the position of the boundary 113 between the transfer pattern region 111 and the light-shielding region 112 is set to 0, the reflectance is high at a distance d from the boundary 113 between the transfer pattern region 111 and the light-shielding region 112 toward the light-shielding region 112. In other words, the reflectance is high near the periphery of the transfer pattern region 111. 19(c), the absorption layer may be etched back during the formation of the light-shielding region, which may result in the multilayer film 103 being exposed at the edge of the transfer pattern region 111. In this case, light leakage is likely to occur, and the reflectance becomes even higher near the periphery of the transfer pattern region 111.

[0012] 21(a), in the wafer 120, a region 122a where the exposure dose increases is present on the periphery of the exposure region 121a in response to the increase in reflectivity near the periphery of the transfer pattern region 111 of the reflective mask 100A. Similarly, in the wafer 120, a region 122b where the exposure dose increases is present on the periphery of the exposure region 121b in response to the increase in reflectivity near the periphery of the transfer pattern region 111 of the reflective mask 100B. Hereinafter, the region on the wafer where the exposure dose increases on the periphery of the exposure region in response to the increase in reflectivity near the periphery of the transfer pattern region of the reflective mask may be referred to as a "high exposure dose region." In the overlapping region between the high exposure dose region 122a on the periphery of the exposure region 121a and the high exposure dose region 122b on the periphery of the exposure region 121b, the exposure doses may be added together to reach an amount that contributes to resolution. 21(b) is a graph illustrating the exposure dose at the line aa in FIG. 21(a), and FIG. 21(c) is a graph illustrating the exposure dose at the line bb in FIG. 21(a). As shown in FIG. 21(b), in the high exposure dose region 122a on the periphery of the exposure region 121a alone, even if the exposure dose increases, the resolution threshold T100 is not reached. However, as shown in FIG. 21(c), in the region where the high exposure dose region 122a on the periphery of the exposure region 121a and the high exposure dose region 122b on the periphery of the exposure region 121b overlap, the exposure doses may be added together and reach the resolution threshold T100. As a result, unnecessary patterns are formed at the joints between patterns on the wafer, which causes the problem of not being able to obtain high-precision patterns.

[0013] The present disclosure has been made in consideration of the above-described circumstances, and has as its main object to provide a reflective mask that can suppress overexposure at the seams between patterns on a wafer and achieve highly accurate pattern transfer. [Means for solving the problem]

[0014] One embodiment of the present disclosure provides a reflective mask having a substrate, a multilayer film disposed on one side of the substrate, and an absorption layer pattern disposed on the side of the multilayer film opposite the substrate, the reflective mask having a transfer pattern region having the absorption layer pattern, and a light-shielding region disposed on the periphery of the transfer pattern region, which does not have the multilayer film or the absorption layer, and in which the substrate is exposed, and in a planar view, the shape of the boundary between the transfer pattern region and the light-shielding region is rounded.

[0015] Another embodiment of the present disclosure provides a method for manufacturing a semiconductor device, which includes a step of performing stitching exposure using the above-mentioned reflective mask to form a pattern on a semiconductor substrate, wherein in the reflective mask, in a planar view, the shape of a corner in the shape of the boundary between the transfer pattern area and the light-shielding area is an arc shape, and the radius of curvature R1 of the arc shape satisfies the following formula (1): 0.58L≦R1≦4.22L (1) (In the above formula (1), L represents the overlap width of the transfer pattern region during the first exposure and the transfer pattern region during the second exposure. L is expressed as L=8M. M represents the overlap width of the exposure region during the first exposure and the exposure region during the second exposure on the semiconductor substrate.)

[0016] Another embodiment of the present disclosure provides a method for manufacturing a semiconductor device, comprising a step of performing stitching exposure using the above-mentioned reflective mask to form a pattern on a semiconductor substrate, wherein in the reflective mask, in a planar view, the shape of a corner of the boundary between the transfer pattern area and the light-shielding area is an elliptical arc shape, the ratio a1 / b1 of the major axis radius a1 to the minor axis radius b1 of the elliptical arc shape is 2, and the major axis radius a1 of the elliptical arc shape satisfies the following formula (2): 0.7L≦a1≦14.7L (2) (In the above formula (2), L represents the overlap width of the transfer pattern region during the first exposure and the transfer pattern region during the second exposure. L is expressed as L=8M. M represents the overlap width of the exposure region during the first exposure and the exposure region during the second exposure on the semiconductor substrate.) [Effects of the Invention]

[0017] The present disclosure provides an effect of suppressing overexposure at seams between patterns on a wafer and realizing highly accurate pattern transfer. [Brief explanation of the drawings]

[0018] [Figure 1] 1A and 1B are a schematic plan view and a cross-sectional view illustrating a reflective mask according to the present disclosure. [Figure 2] 1A and 1B are schematic diagrams illustrating an exposure method using a reflective mask according to the present disclosure. [Figure 3] 1 is a schematic plan view illustrating a wafer exposed using a reflective mask according to the present disclosure and a graph illustrating the exposure dose. [Figure 4] 1A and 1B are a schematic plan view and a cross-sectional view illustrating a reflective mask according to the present disclosure. [Figure 5] 1A and 1B are a schematic plan view and a cross-sectional view illustrating a reflective mask according to the present disclosure. [Figure 6] 1 is a schematic plan view illustrating a wafer exposed using a reflective mask according to the present disclosure and a graph illustrating the exposure dose. [Figure 7] 1 is a schematic plan view illustrating a wafer exposed using a reflective mask according to the present disclosure and a graph illustrating the exposure dose. [Figure 8] 10A and 10B are schematic plan views illustrating examples of the shape of the boundary between a transfer pattern region and a light-shielding region in a reflective mask according to the present disclosure. [Figure 9] 10A and 10B are schematic plan views illustrating examples of the shape of the boundary between a transfer pattern region and a light-shielding region in a reflective mask according to the present disclosure. [Figure 10]10A and 10B are schematic plan views illustrating examples of the shape of the boundary between a transfer pattern region and a light-shielding region in a reflective mask according to the present disclosure. [Figure 11] 10A and 10B are schematic plan views illustrating examples of the shape of the boundary between a transfer pattern region and a light-shielding region in a reflective mask according to the present disclosure. [Figure 12] 10 is a graph showing the relationship between the coefficient α of the overlap width L and the intersection angle θ1. [Figure 13] 1 is a schematic plan view illustrating the shape of the boundary between a transfer pattern area and a light-shielding area in a reflective mask according to the present disclosure, and a wafer exposed using the reflective mask according to the present disclosure. [Figure 14] 10 is a graph showing the relationship between the coefficient α of the overlap width L and the intersection angle. [Figure 15] 10A and 10B are schematic plan views illustrating examples of the shape of the boundary between a transfer pattern region and a light-shielding region in a reflective mask according to the present disclosure. [Figure 16] 10A and 10B are schematic plan views illustrating the shape of the boundary between a transfer pattern region and a light-shielding region, and the shape of the boundary between a light-shielding region and a non-transfer pattern region in a reflective mask according to the present disclosure. [Figure 17] 1A to 1C are process diagrams illustrating a method for manufacturing a reflective mask according to the present disclosure. [Figure 18] 1A and 1B are schematic diagrams illustrating an exposure method using a conventional reflective mask. [Figure 19] 1A and 1B are schematic diagrams illustrating an exposure method using a conventional reflective mask. [Figure 20] 10 is a graph showing the reflectance near the periphery of a transfer pattern area in a conventional reflective mask. [Figure 21] 1A and 1B are a schematic plan view illustrating a wafer exposed using a conventional reflective mask and a graph illustrating exposure dose. [Figure 22] 1A and 1B are schematic plan views illustrating the shape of the boundary between a transfer pattern region and a light-shielding region, and the shape of the boundary between a light-shielding region and a non-transfer pattern region in a conventional reflective mask. DETAILED DESCRIPTION OF THE INVENTION

[0019] Embodiments of the present disclosure will be described below with reference to the drawings and the like. However, the present disclosure can be implemented in many different forms, and should not be construed as being limited to the description of the embodiments exemplified below. Furthermore, to clarify the explanation, the drawings may show the width, thickness, shape, etc. of each part schematically compared to the actual form, but these are merely examples and do not limit the interpretation of the present disclosure. Furthermore, in this specification and each drawing, elements similar to those described above with reference to the previous drawings are designated by the same reference numerals, and detailed descriptions may be omitted as appropriate.

[0020] In this specification, when describing a mode in which another component is placed on a certain component, the term "above" or "below" is used, unless otherwise specified, to include both a case in which another component is placed directly above or below a certain component so as to be in contact with the component, and a case in which another component is placed above or below a certain component with another component interposed therebetween. Also, in this specification, when describing a mode in which another component is placed on the surface of a certain component, the term "on the surface side" or "on the surface" is used, unless otherwise specified, to include both a case in which another component is placed directly above or below a certain component so as to be in contact with the component, and a case in which another component is placed above or below a certain component with another component interposed therebetween.

[0021] The reflective mask and semiconductor device manufacturing method according to the present disclosure will be described in detail below.

[0022] A. Reflective mask The reflective mask of the present disclosure is a reflective mask having a substrate, a multilayer film disposed on one side of the substrate, and an absorption layer pattern disposed on the side of the multilayer film opposite the substrate, and has a transfer pattern area having the absorption layer pattern, and a shading area disposed on the periphery of the transfer pattern area, which does not have the multilayer film or the absorption layer, and in which the substrate is exposed, and in a planar view, the shape of the boundary between the transfer pattern area and the shading area is rounded.

[0023] FIG. 1(a) is a schematic plan view showing an example of a reflective mask according to the present disclosure, and FIG. 1(b) is a cross-sectional view taken along line AA in FIG. 1(a). As illustrated in FIGS. 1(a) and 1(b), the reflective mask 1 includes a substrate 2, a multilayer film 3 disposed on one surface of the substrate 2, a protective layer 4 formed on the surface of the multilayer film 3 opposite the substrate 2, a pattern of an absorbing layer 5 disposed on the surface of the protective layer 4 opposite the multilayer film 3, and a conductive film 6 disposed on the surface of the substrate 2 opposite the multilayer film 3. The reflective mask 1 also includes a transfer pattern region 11 having a pattern of the absorbing layer 5, and a light-shielding region 12 disposed on the periphery of the transfer pattern region 11, which does not include the multilayer film 3, protective layer 4, or absorbing layer 5, and in which the substrate 2 is exposed. In a plan view, the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 is rounded. In FIG. 1(a), the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 has rounded corners, that is, a so-called rounded rectangle.

[0024] In general, in stitching exposure, as shown in Figures 18(a) and 18(b), exposure is performed on a wafer 120 so that an exposure region 121a corresponding to a reflective mask 100A and an exposure region 121b corresponding to a reflective mask 100B partially overlap. Furthermore, in a reflective mask, the exposure light is incident from a direction tilted by several degrees, typically about 6 degrees, from the perpendicular direction to the mask surface. Therefore, as shown in Figure 19(b), at the edge of the transfer pattern region 111, the EUV light reflected by the multilayer film 103 is not attenuated by the absorption layer 105, resulting in light leakage toward the light-shielding region 112. For example, as shown in Figure 20, when the position of the boundary 113 between the transfer pattern region 111 and the light-shielding region 112 is set to 0, the reflectance is high at a distance d from the boundary 113 between the transfer pattern region 111 and the light-shielding region 112 toward the light-shielding region 112. In other words, the reflectance is high near the periphery of the transfer pattern region 111. 19(c), the absorption layer may be etched back during the formation of the light-shielding region, which may result in the multilayer film 103 being exposed at the edge of the transfer pattern region 111. In this case, light leakage is likely to occur, and the reflectance becomes even higher near the periphery of the transfer pattern region 111.

[0025] Therefore, as shown in FIG. 21(a), in the wafer 120, a high exposure dose region 122a where the exposure dose increases is present on the periphery of the exposure region 121a in response to the increase in reflectivity near the periphery of the transfer pattern region 111 of the reflective mask 100A. Similarly, in the wafer 120, a high exposure dose region 122b where the exposure dose increases is present on the periphery of the exposure region 121b in response to the increase in reflectivity near the periphery of the transfer pattern region 111 of the reflective mask 100B. In the overlapping region between the high exposure dose region 122a on the periphery of the exposure region 121a and the high exposure dose region 122b on the periphery of the exposure region 121b, the exposure doses may be added together and reach an amount that contributes to resolution. FIG. 21(b) is a graph illustrating the exposure dose at the line aa in FIG. 21(a), and FIG. 21(c) is a graph illustrating the exposure dose at the line bb in FIG. 21(a). 21(b), in the high exposure amount region 122a on the periphery of the exposure area 121a alone, even if the exposure amount increases, the resolution threshold T100 is not reached, whereas in the overlapping region of the high exposure amount region 122a on the periphery of the exposure area 121a and the high exposure amount region 122b on the periphery of the exposure area 121b, the exposure amount is added and may reach the resolution threshold T100, as shown in FIG. 21(c). As a result, unnecessary patterns are formed at the joints between patterns on the wafer, which causes the problem of not being able to obtain high-precision patterns.

[0026] In conventional reflective masks 100A and 100B, as shown in FIG. 16(a), the light-shielding region 112 is frame-shaped, and the boundary 113 between the transfer pattern region 111 and the light-shielding region 112 is rectangular in plan view. When the boundary 113 between the transfer pattern region 111 and the light-shielding region 112 is rectangular, as shown in FIGS. 19(a) and 19(d), the high-exposure-amount region 122a on the periphery of the exposure region 121a and the high-exposure-amount region 122b on the periphery of the exposure region 121b overlap linearly on the wafer 120. This results in a large overlap between the high-exposure-amount region 122a on the periphery of the exposure region 121a and the high-exposure-amount region 122b on the periphery of the exposure region 121b. Note that FIG. 19(d) is an enlarged view of the portion indicated by the line bb in FIG. 19(a).

[0027] In contrast, in the present disclosure, as illustrated in Fig. 1(a), the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 is rounded in plan view. Therefore, when stitching exposure is performed using two reflective masks 1A and 1B such that an exposure region 21a corresponding to the reflective mask 1A and an exposure region 21b corresponding to the reflective mask 1B partially overlap on a wafer 120, as illustrated in Fig. 2(a) and Fig. 2(b), it is possible to reduce the overlap between a high exposure amount region 22a existing on the periphery of the exposure region 21a and a high exposure amount region 22b existing on the periphery of the exposure region 21b on a wafer 20, as illustrated in Fig. 3(a) and Fig. 3(c). Specifically, the high exposure dose region 22a on the periphery of the exposure region 21a and the high exposure dose region 22b on the periphery of the exposure region 21b overlap in a dotted pattern, so that the overlap between the high exposure dose region 22a on the periphery of the exposure region 21a and the high exposure dose region 22b on the periphery of the exposure region 21b becomes smaller. Figure 3(c) is an enlarged view of the part along line cc in Figure 3(a).

[0028] FIG. 3(b) is a graph illustrating the exposure dose at the line cc in FIG. 3(a). Compared to when high-exposure-dose regions overlap linearly, when high-exposure-dose regions overlap in a point-like manner, the resolution threshold T1 is higher. This is because, when high-exposure-dose regions 122a and 122b overlap linearly as shown in FIG. 19(d), resist 131 is likely to remain during development. However, when high-exposure-dose regions 22a and 22b overlap in a point-like manner as shown in FIG. 3(c), resist 31 is less likely to remain during development. As a result, when high-exposure-dose regions 22a and 22b overlap in a point-like manner, resist 31 is less likely to be resolved, resulting in a higher resolution threshold T1. This makes it possible to suppress unintended pattern resolution at the joints between patterns on the wafer.

[0029] Therefore, when stitching exposure is performed using the reflective mask of the present disclosure, it is possible to suppress overexposure at the seams between patterns on the wafer, thereby achieving highly accurate pattern transfer. In particular, when the absorption layer is etched back during the formation of the light-shielding region, and the multilayer film is exposed at the edge of the transfer pattern region, it is possible to effectively suppress unintended pattern resolution.

[0030] Hereinafter, each component of the reflective mask according to the present disclosure will be described.

[0031] 1. Shape of the boundary between the transfer pattern area and the light-shielding area In the reflective mask of the present disclosure, the transfer pattern region is a region having a pattern of an absorption layer. The light-shielding region is a region disposed on the periphery of the transfer pattern region, does not have a multilayer film or an absorption layer, and exposes the substrate. In the present disclosure, the shape of the boundary between the transfer pattern region and the light-shielding region is rounded in plan view.

[0032] 16(a), in conventional reflective masks 100A and 100B, the shape of a transfer pattern area 111 in a plan view is usually rectangular. Therefore, in a plan view, the shape of a boundary 113 between the transfer pattern area 111 and a light-shielding area 112 is rectangular, and all corners are right angles.

[0033] In contrast to this, in the reflective mask of the present disclosure, the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 is rounded in plan view, as shown in Fig. 1(a) for example. In particular, it is preferable that the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 is a roughly rectangular shape with rounded corners in plan view.

[0034] As used herein, the term "rounded corner shape" refers to a shape in which the corners are not right angles, i.e., a shape in which the corners are cut off by straight or curved lines. Specific examples of rounded corner shapes include shapes in which the corners are cut off by curved lines, i.e., shapes with rounded corners, as shown in Figures 1(a) and 4(a), and shapes in which the corners are cut off by straight lines, as shown in Figure 5(a). A shape with rounded corners may have a circular or elliptical arc shape with outwardly protruding corners, as shown in Figure 1(a), or a circular or elliptical arc shape with inwardly recessed corners, as shown in Figure 4(a). The rounded corner shape may be one type, or two or more types may be combined.

[0035] 1(a), for example, in a plan view, the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 is a shape with rounded corners and an arc shape with the corners protruding outward. Therefore, when stitching exposure is performed on a wafer 20 using two reflective masks 1A and 1B so that an exposure region 21a corresponding to the reflective mask 1A and an exposure region 21b corresponding to the reflective mask 1B partially overlap each other, as shown in FIGS. 3(a) and 3(c), the overlap between a high exposure amount region 22a existing on the periphery of the exposure region 21a and a high exposure amount region 22b existing on the periphery of the exposure region 21b can be reduced. Specifically, the high exposure dose region 22a on the periphery of the exposure region 21a and the high exposure dose region 22b on the periphery of the exposure region 21b overlap in a point-like manner, resulting in a smaller overlap between the high exposure dose region 22a on the periphery of the exposure region 21a and the high exposure dose region 22b on the periphery of the exposure region 21b. Figure 3(c) is an enlarged view of the portion indicated by line cc in Figure 3(a). Figure 3(b) is a graph illustrating the exposure dose at the portion indicated by line cc in Figure 3(a). Compared to when high exposure dose regions overlap in a linear fashion, when high exposure dose regions overlap in a point-like manner, the resolution threshold T1 is higher. Therefore, it is possible to suppress unintended pattern resolution at the seams between patterns on the wafer.

[0036] For example, in FIG. 4(a), in plan view, the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 has rounded corners and an inwardly recessed arc shape. Therefore, when stitching exposure is performed using two reflective masks, as illustrated in FIGS. 6(a) and 6(c), the overlap between the high-exposure-dose region 22a on the periphery of the exposure region 21a and the high-exposure-dose region 22b on the periphery of the exposure region 21b on the wafer 20 can be reduced. Specifically, the high-exposure-dose region 22a on the periphery of the exposure region 21a and the high-exposure-dose region 22b on the periphery of the exposure region 21b overlap in a point-like manner, thereby reducing the overlap between the high-exposure-dose region 22a on the periphery of the exposure region 21a and the high-exposure-dose region 22b on the periphery of the exposure region 21b. FIG. 6(c) is an enlarged view of the portion along the line cc in FIG. 6(a). Figure 6(b) is a graph illustrating the exposure dose at the line cc in Figure 6(a). Compared to when high exposure dose regions overlap in a straight line, when high exposure dose regions overlap in a point-like manner, the resolution threshold T1 is higher. Therefore, it is possible to suppress unintended pattern resolution at the joints between patterns on the wafer.

[0037] For example, in FIG. 5(a), the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 in a plan view is a shape in which the corners are cut off by straight lines. Therefore, when stitching exposure is performed using two reflective masks, as illustrated in FIGS. 7(a) and 7(c), the overlap between the high-exposure-dose region 22a on the periphery of the exposure region 21a and the high-exposure-dose region 22b on the periphery of the exposure region 21b on the wafer 20 can be reduced. Specifically, the high-exposure-dose region 22a on the periphery of the exposure region 21a and the high-exposure-dose region 22b on the periphery of the exposure region 21b overlap in a point-like manner, thereby reducing the overlap between the high-exposure-dose region 22a on the periphery of the exposure region 21a and the high-exposure-dose region 22b on the periphery of the exposure region 21b. FIG. 7(c) is an enlarged view of the portion indicated by the line cc in FIG. 7(a). FIG. 7(b) is a graph illustrating the exposure dose at the portion indicated by the line cc in FIG. 7(a). Compared to when high exposure dose regions overlap linearly, when high exposure dose regions overlap in a dotted pattern, the resolution threshold T1 is higher, which makes it possible to suppress unintended pattern resolution at the joints between patterns on the wafer.

[0038] 1(a), it is preferable that the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 in plan view has rounded corners and has an arc shape or an elliptical arc shape with the corners protruding outward, because such a shape can be easily formed.

[0039] When the shape of the boundary between the transfer pattern region and the light-shielding region has rounded corners in a plan view and has an arc shape that protrudes outward, the radius of curvature of the corners is not particularly limited.

[0040] As described above, in stitching exposure, as shown in Figures 2(a) and 2(b), two reflective masks 1A and 1B are used to expose a wafer 20 so that an exposure area 21a corresponding to the reflective mask 1A and an exposure area 21b corresponding to the reflective mask 1B partially overlap. The overlapping width M between the exposure areas 21a and 21b on the wafer 20, as shown in Figure 2(b), can be converted to the overlapping width L of the transfer pattern areas 11 on the reflective masks 1A and 1B, as shown in Figure 8(a), depending on the reduction ratio of the projection optical system. When the NA is 0.55, the reduction ratio in the x direction of the projection optical system is 4 times, and the reduction ratio in the y direction is 8 times. For example, when the NA is 0.55, and the overlapping width M between the exposure region 21a and the exposure region 21b on the wafer 20 is 10 nm, the overlapping width L between the transfer pattern region 11 of the reflective mask 1A and the transfer pattern region 11 of the reflective mask 1B is converted to 80 nm. The overlapping width M between the exposure region 21a and the exposure region 21b on the wafer 20, i.e., the overlapping width L between the transfer pattern region 11 of the reflective mask 1A and the transfer pattern region 11 of the reflective mask 1B, is a value that can be selected appropriately.

[0041] When the overlap width between the transfer pattern area 11 of the reflective mask 1A and the transfer pattern area 11 of the reflective mask 1B is L, it is preferable that the radius of curvature R1 of the corner satisfies the following formula (3). R1≧0.5×L (3)

[0042] For example, when the NA is 0.55 and the overlap width M between the exposure areas 21a and 21b on the wafer 20 is 10 nm, the overlap width L between the transfer pattern areas 11 of the reflective mask 1A and the transfer pattern areas 11 of the reflective mask 1B is converted to 80 nm. In this case, R1≧0.5×80=40, and it is preferable that the radius of curvature R1 of the corner is 40 nm or more.

[0043] Figure 8(a) shows the case where R1 = 0.5 × L, Figure 8(b) shows the case where R1 < 0.5 × L, and Figure 8(c) shows the case where R1 > 0.5 × L. When R1 = 0.5 × L in Figure 8(a), the boundary 13 between the transfer pattern area 11 and the light-shielding area of reflective mask 1A and the boundary 13 between the transfer pattern area 11 and the light-shielding area of reflective mask 1B overlap at a point. When R1 > 0.5 × L in Figure 8(c), the boundary 13 between the transfer pattern area 11 and the light-shielding area of reflective mask 1A and the boundary 13 between the transfer pattern area 11 and the light-shielding area of reflective mask 1B overlap at a point, but the overlap is at an angle compared to the case where R1 = 0.5 × L in Figure 8(a). In contrast, when R1<0.5×L in FIG. 8(b), the boundary 13 between the transfer pattern region 11 and the light-shielding region of the reflective mask 1A partially overlaps the boundary 13 between the transfer pattern region 11 and the light-shielding region of the reflective mask 1B, resulting in a linear overlap. As described above, the reflectivity is high near the periphery of the transfer pattern region 11 in the reflective masks 1A and 1B. Therefore, the small overlap between the boundary 13 between the transfer pattern region 11 and the light-shielding region of the reflective mask 1A and the boundary 13 between the transfer pattern region 11 and the light-shielding region of the reflective mask 1B can reduce the overlap between high-exposure-level regions on the periphery of the exposure region on the wafer. Therefore, when R1≧0.5×L, unintended pattern resolution at the seams between patterns on the wafer can be further suppressed.

[0044] 9 to 11, when the intersection of the transfer pattern area 11 of the reflective mask 1A and the transfer pattern area 11 of the reflective mask 1B is defined as p1 and the angle formed by the tangent t1 at the intersection p1 of the transfer pattern area 11 of the reflective mask 1A and the tangent t2 at the intersection p1 of the transfer pattern area 11 of the reflective mask 1B is defined as the intersection angle θ1, the following formula (4-1) holds for the radius of curvature R1 of the corner, the overlap width L, and the intersection angle θ1. That is, the radius of curvature R1 of the corner is expressed by the following formula (4-2). L / 2=R1×[1-cos(θ1 / 2)] (4-1) R1=L / {2×[1-cos(θ1 / 2)]} (4-2)

[0045] Therefore, from the radius of curvature R1 of the corner, the overlap width L, and the intersection angle θ1, the radius of curvature R1 of the corner is expressed by the following formula (4-3): In formula (4-3), α is a coefficient of the overlap width L. R1=αL (4-3)

[0046] FIG. 9 shows the case where the intersection angle θ1 is 90°, FIG. 10 shows the case where the intersection angle θ1 is 60°, and FIG. 11 shows the case where the intersection angle θ1 is 120°. As shown in FIG. 9, when the intersection angle θ1 is 90°, R1 = L / {2×[1-cos(90° / 2)]} = L / {2×[1-cos45°]} ≒ 1.7L. As shown in FIG. 10, when the intersection angle θ1 is 60°, R1 = L / {2×[1-cos(60° / 2)]} = L / {2×[1-cos30°]} ≒ 3.7L. As shown in FIG. 11, when the intersection angle θ1 is 120°, R1 = L / {2×[1-cos(120° / 2)]} = L / {2×[1-cos60°]} ≒ 1.0L. Furthermore, although not shown, when the intersection angle θ1 is 30°, R1 = L / {2 × [1 - cos(30° / 2)]} = L / {2 × [1 - cos15°]} ≒ 14.7L. When the intersection angle θ1 is 150°, R1 = L / {2 × [1 - cos(30° / 2)]} = L / {2 × [1 - cos15°]} ≒ 0.7L. Figure 12 shows the relationship between the coefficient α of the overlap width L and the intersection angle θ1.

[0047] For simplicity, the above explanation assumes that the reduction ratios in the x and y directions are equal. However, as mentioned above, EUV exposure tools with an NA as high as 0.55 have been developed, and the reduction ratio in the x direction is 4x, the reduction ratio in the y direction is 8x, and the reduction ratio in the y direction is twice that of the x direction. Therefore, the arc shape with the radius of curvature R1 and intersection angle (θ1) of 90° on the reflective mask, as shown in Figure 13(a), becomes an elliptical arc shape on the wafer, with the width of the y direction component halved, as shown in Figure 13(b). Therefore, when the reduction ratio in the y direction is twice that of the x direction, the slope of the arc is halved compared to when the reduction ratios in the x and y directions are equal, and the intersection angle also changes. In Figure 13(a), when θ2 is the angle of arc A, |tan θ2| indicates the absolute value of the slope of arc A. Note that when θ2 = 0°, the inclination of arc A is on the y-axis, which is 0. When θ2 = 90°, the inclination of arc A is infinity. |tanθ2| also corresponds to the inclination of arc B symmetrically with respect to the x-axis. If the reduction ratio is different on the wafer, and the reduction ratio in the y-axis is twice that in the x-axis, the inclination of the arc is 1 / 2, which is expressed as |tanθ2| / 2. The angle of the arc on the wafer in this case can be calculated as arctan(|tanθ2| / 2). Therefore, when the arc angle θ2 on the mask is 45°, arctan(|tan45°| / 2) = 26.6°, and the arc angle on the wafer is 26.6°. Conversely, when the arc angle on the wafer is 45°, arctan(|tan63.4°| / 2) = 45°, and the arc angle θ2 on the mask is 63.4°.

[0048] Therefore, it is clear that the radius of curvature R1 of the corner must be smaller than when the reduction rates in the x and y directions are the same for the overlap width L. The radius of curvature R1 of the corner when the arc angle θ2 on the mask is 63.4°, i.e., the radius of curvature R1 of the corner where the intersection angle on the wafer is 90°, is R1=L / {2×[1-cos63.4°]}≒0.9L for the overlap width L.

[0049] Calculating similarly, the radius of curvature R1 of the above corner where the intersection angle on the wafer is 60° is R1 ≈ 0.69L. The radius of curvature R1 of the above corner where the intersection angle on the wafer is 120° is R1 ≈ 1.45L. The radius of curvature R1 of the above corner where the intersection angle on the wafer is 30° is R1 ≈ 0.58L. The radius of curvature R1 of the above corner where the intersection angle on the wafer is 120° is R1 ≈ 4.22L. Figure 14 shows the relationship between the coefficient α of the overlap width L and the intersection angle on the wafer.

[0050] 3(a) and 3(c), high exposure dose region 22a existing on the periphery of exposure region 21a and high exposure dose region 22b existing on the periphery of exposure region 21b partially overlap on wafer 20. Referring to Figures 13(a) and 13(b), when the intersection angle on the wafer is 90°, the overlapping area of high exposure dose regions 22a and 22b on wafer 20 is minimized.

[0051] Therefore, the intersection angle on the wafer is preferably 90±60°, more preferably 90±30°, and even more preferably 90°, because this makes it possible to reduce the intersection area where the high exposure dose regions 22a and 22b overlap on the wafer 20.

[0052] From the above calculations, the radius of curvature R1 of the corner where the intersection angle is 90° on the wafer is R1≈0.9L. The range of the radius of curvature R1 of the corner where the intersection angle is 90±30° on the wafer is 0.69L≦R1≦1.45L. The range of the radius of curvature R1 of the corner where the intersection angle is 90±60° on the wafer is 0.58L≦R1≦4.22L. Therefore, in terms of the preferred range of the intersection angle on the wafer, the radius of curvature R1 of the corner preferably satisfies the following formula (1), more preferably the following formula (1-2), and even more preferably the following formula (1-3). 0.58L≦R1≦4.22L (1) 0.69L≦R1≦1.45L (1-2) R1=0.9L (1-3)

[0053] The radius of curvature R1 of the corner varies depending on the overlap width L, which is a value selected as described above. For example, when the overlap width L is 80 nm to 1200 nm, the radius of curvature R1 of the corner may be, for example, 50 nm to 5000 nm, 60 nm to 1700 nm, or 80 nm to 1000 nm. Having a radius of curvature of the corner equal to or greater than a predetermined value can sufficiently suppress unintended pattern resolution at the seams between patterns on the wafer, as described above. On the other hand, having a radius of curvature of the corner equal to or less than a predetermined value can prevent the transfer pattern area from becoming excessively narrow.

[0054] Conversely, taking into account deformation of the shape due to differences in magnification, the reflective mask may be designed so that the above corners are arc-shaped on the wafer.

[0055] In the above case, the corner shape of the boundary between the transfer pattern area and the light-shielding area in the reflective mask is an elliptical arc shape with the ratio a1 / b1 of the major axis radius a1 to the minor axis radius b1 being 1. In the projection optical system, the reduction ratio in the x direction is 4x, the reduction ratio in the y direction is 8x, and the reduction ratio in the y direction is twice the reduction ratio in the x direction, so the major axis side is the y direction and the minor axis side is the x direction. The relationship between the overlap width M between exposure areas 21a and 21b on wafer 20 and the overlap width L between transfer pattern areas 11 of reflective mask 1A and transfer pattern areas 11 of reflective mask 1B can be set as L=8M on the major axis side and L=4M on the minor axis side. When the shape of the corner is reduced in both the x and y directions on the wafer and becomes an arc, the radius of curvature R1 of the arc can be replaced with the major axis radius a1 of the elliptical arc, and the range of the major axis radius a1 of the elliptical arc and the range of the minor axis radius b1, which is half the length of the major axis radius a1, can be determined. As described above, when the shape of the corner on the reflective mask is an elliptical arc, the shape of the corner on the wafer becomes an arc, so the specific derivation method can be the same as that for the case where the shape of the corner is an arc. Therefore, from the preferred range of the intersection angle on the wafer, the major axis radius a1 of the corner preferably satisfies the following formula (2), more preferably satisfies the following formula (2-2), and even more preferably satisfies the following formula (2-3). 0.7L≦a1≦14.7L (2) 1.0L≦a1≦3.7L (2-2) a1=1.7L (2-3)

[0056] The major axis radius a1 of the corner varies depending on the overlap width L, which is a value selected as described above. For example, when the overlap width L is 80 nm to 1200 nm, the major axis radius a1 of the corner may be, for example, 60 nm to 17000 nm, 80 nm to 4400 nm, or 140 nm to 2000 nm. By having the major axis radius a1 of the corner equal to or greater than a predetermined value, the effect of suppressing unintended pattern resolution at the joints between patterns on the wafer as described above can be sufficiently obtained. On the other hand, by having the major axis radius a1 of the corner equal to or less than a predetermined value, excessive narrowing of the transfer pattern area can be suppressed.

[0057] When the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 is a generally rectangular shape with rounded corners in a plan view, and the shape of the corners is an arc, the radii of curvature R1 of the four corners may be the same or different. Also, when the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 is a generally rectangular shape with rounded corners in a plan view, and the shape of the corners is an elliptical arc, the major axis radii a1 of the four corners may be the same or different.

[0058] Furthermore, when the shape of the boundary between the transfer pattern region and the light-shielding region in plan view has rounded corners and has an inwardly recessed arc shape, the radius of curvature of the corner is not particularly limited and can be considered to be the same as the radius of curvature of the corner when the shape of the boundary between the transfer pattern region and the light-shielding region has rounded corners and has an outwardly protruding arc shape.

[0059] Furthermore, when viewed in a plane, if the shape of the boundary between the transfer pattern area and the shading area is a shape in which the corner is cut off by a straight line, it may be a shape in which the corner is cut off by a single straight line, as shown in Figure 15(a), or a shape in which the corner is cut off by multiple straight lines, as shown in Figures 15(b) and 15(c).

[0060] 15(a) to 15(c), when the shape of the boundary between the transfer pattern region and the light-shielding region is a shape in which a corner is cut off by a straight line, the angle θ11 formed by the main side 13a and the oblique side 13c of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 is not particularly limited and is, for example, 30° to 60°. Also, the angle θ12 formed by the main side 13b and the oblique side 13d of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 is not particularly limited and is, for example, 30° to 60°.

[0061] 15(a) to 15(c), when the shape of the boundary between the transfer pattern region and the light-shielding region is a shape in which corners are cut off by straight lines, the distance c1 from the intersection of the main side 13a and the oblique side 13c of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 to the intersection of the extension of the main side 13a and the extension of the main side 13b is, for example, 100 nm or more and 1000 nm or less. Also, the distance c2 from the intersection of the main side 13b and the oblique side 13c or 13d of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 to the intersection of the extension of the main side 13a and the extension of the main side 13b is, for example, 100 nm or more and 1000 nm or less.

[0062] When the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 is a generally rectangular shape with rounded corners in a plan view, the four angles θ11 may be the same or different. Similarly, the four angles θ12 may be the same or different. Furthermore, the four distances c1 may be the same or different. Similarly, the four distances c2 may be the same or different.

[0063] Furthermore, when the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 is a roughly rectangular shape with rounded corners in a plan view, it is sufficient that at least two of the four corners in the portion where the transfer pattern regions 11 of the reflective masks 1A and 1B overlap during stitching exposure have rounded corners. Therefore, in the above case, of the four corners, the two corners in the portion where the transfer pattern regions 11 of the reflective masks 1A and 1B do not overlap during stitching exposure may or may not have rounded corners. In particular, it is preferable that all four corners have rounded corners.

[0064] 1(a) and 1(b), the reflective mask 1 has a non-transfer pattern region 14 arranged on the periphery of the light-shielding region 12. In plan view, the shape of the boundary 15 between the light-shielding region 12 and the non-transfer pattern region 14 is not particularly limited, but preferably has a rounded shape. Even at the edge of the non-transfer pattern region 14, if the exposure light is incident obliquely, the EUV light reflected by the multilayer film 3 may not be attenuated by the absorption layer 5, resulting in light leakage toward the light-shielding region 12. Therefore, similar to the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12, the shape of the boundary 15 between the light-shielding region 12 and the non-transfer pattern region 14 is also rounded, thereby suppressing unintended pattern resolution at the seams between patterns on the wafer.

[0065] The shape of the boundary 15 between the light-shielding region 12 and the non-transfer pattern region 14 is the same as the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 described above.

[0066] The shape of the boundary 15 between the light-shielding region 12 and the non-transfer pattern region 14 may be the same as or different from the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 .

[0067] In particular, it is preferable that the shape of the boundary between the transfer pattern region and the light-shielding region, and the shape of the boundary between the light-shielding region and the non-transfer pattern region, both have rounded corners and have an arc shape or an elliptical arc shape with corners that protrude outward, because such shapes can be easily formed.

[0068] 1(a), when the shape of boundary 13 between transfer pattern region 11 and light-shielding region 12 and the shape of boundary 15 between light-shielding region 12 and non-transfer pattern region 14 both have rounded corners and arc-shaped corners that protrude outward, radius of curvature R1 of the corner in the shape of boundary 13 between transfer pattern region 11 and light-shielding region 12 and radius of curvature R2 of the corner in the shape of boundary 15 between light-shielding region 12 and non-transfer pattern region 14 may be the same as or different from radius of curvature R1 of the corner. In particular, radius of curvature R1 of the corner is preferably equal to or smaller than radius of curvature R2 of the corner, and more preferably smaller than radius of curvature R2 of the corner.

[0069] FIG. 22 shows a case where, in the reflective masks 100A and 100B, in a plan view, the shape of the boundary 113 between the transfer pattern region 111 and the light-shielding region 112 and the shape of the boundary 115 between the light-shielding region 112 and the non-transfer pattern region are both rectangular and all corners are right angles. FIGS. 16(a) and 16(b) show a case where, in the reflective masks 1A and 1B, in a plan view, the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 and the shape of the boundary 15 between the light-shielding region 12 and the non-transfer pattern region are both shapes with rounded corners and have an arc shape protruding outward. FIG. 16(c) is an enlarged partial view of the d-d line portion of FIG. 16(b). In FIG. 16(a), R1 = R2, and in FIG. 16(b), R1 < R2. Compared with the overlap K100 between the boundaries 115 between the light-shielding region 112 and the non-transfer pattern region as shown in FIG. 20, the overlaps K1 and K2 between the boundaries 15 between the light-shielding region 12 and the non-transfer pattern region as shown in FIGS. 16(a) and 16(b) are smaller. Also, compared with the overlap K1 between the boundaries 15 between the light-shielding region 12 and the non-transfer pattern region as shown in FIG. 16(a), the overlap K2 between the boundaries 15 between the light-shielding region 12 and the non-transfer pattern region as shown in FIG. 16(b) is smaller. In particular, as shown in FIG. 16(c), the boundaries 13 between the transfer pattern region 11 and the light-shielding region 12 are likely to overlap at a point, and the boundaries 15 between the light-shielding region 12 and the non-transfer pattern region are also likely to overlap at a point.

[0070] Therefore, when the radius of curvature R1 of the above-mentioned corner is less than or equal to the radius of curvature R2 of the above-mentioned corner and further less than the radius of curvature R2 of the above-mentioned corner, it is considered that the resolution of unintended patterns can be more suppressed at the joints between patterns on the wafer.

[0071] Furthermore, when the shape of the boundary between the transfer pattern region and the light-shielding region and the shape of the boundary between the light-shielding region and the non-transfer pattern region both have rounded corners and an elliptical arc shape with the corners protruding outward, the major axis radius of the corner in the shape of the boundary between the transfer pattern region and the light-shielding region and the major axis radius of the corner in the shape of the boundary between the light-shielding region and the non-transfer pattern region may be the same or different. In particular, the major axis radius of the corner in the shape of the boundary between the transfer pattern region and the light-shielding region is preferably equal to or smaller than the major axis radius of the corner in the shape of the boundary between the light-shielding region and the non-transfer pattern region, and more preferably is smaller than the major axis radius of the corner in the shape of the boundary between the light-shielding region and the non-transfer pattern region. As described above, when the shape of the corner in the reflective mask is an elliptical arc, the shape of the corner on the wafer becomes an arc, which is thought to further suppress unintended pattern resolution at the seams between patterns on the wafer, as described above.

[0072] 2.Shading area In the present disclosure, the light-shielding region is a region that does not have a multilayer film or an absorption layer and where the substrate is exposed. In a reflective mask, if a protective layer or a buffer layer is disposed between the multilayer film and the absorption layer, the light-shielding region is a region that does not have the protective layer or the buffer layer.

[0073] The reflectance of the light-shielding region is not particularly limited as long as the exposure amount in the multiple exposure region of the wafer can be set to an amount that does not contribute to resolution when step-and-repeat exposure is performed using the reflective mask of the present disclosure. Specifically, the reflectance is preferably 0.5% or less.

[0074] The light-shielding region may be disposed on the outer periphery of the transfer pattern region. The light-shielding region may be disposed on a part of the outer periphery of the transfer pattern region, or may be disposed on the entire outer periphery of the transfer pattern region. In particular, in order to effectively suppress the occurrence of defective patterns in the multiple exposure region, it is preferable that the light-shielding region be disposed on the entire outer periphery of the transfer pattern region.

[0075] The shape of the light-shielding region may be any shape that allows the light-shielding region to be arranged on the periphery of the transfer pattern region, but is usually a frame shape.

[0076] The dimensions of the light-shielding area are not particularly limited as long as they can prevent the occurrence of defective patterns in the multiple exposure area, and are adjusted appropriately depending on the dimensions of the reflective mask, the dimensions of the exposure area when step-and-repeat exposure is performed using the reflective mask of the present disclosure, etc.

[0077] 3.Multilayer film The multilayer film of the present disclosure is disposed on one surface of a substrate and reflects EUV light in EUV lithography using a reflective mask of the present disclosure.

[0078] Materials commonly used for multilayer films in reflective masks can be used for the multilayer film. Among these, materials with extremely high reflectivity for EUV light are preferred, as this can enhance contrast when a reflective mask is used. For example, a Mo / Si periodic multilayer film is typically used as a multilayer film that reflects EUV light. Furthermore, examples of multilayer films that can achieve high reflectivity in a specific wavelength range include Ru / Si periodic multilayer films, Mo / Be periodic multilayer films, Mo compound / Si compound periodic multilayer films, Si / Nb periodic multilayer films, Si / Mo / Ru periodic multilayer films, Si / Mo / Ru / Mo periodic multilayer films, and Si / Ru / Mo / Ru periodic multilayer films.

[0079] The thickness of each layer constituting the multilayer film and the number of layers stacked vary depending on the materials used and are adjusted appropriately. For example, a Mo / Si periodic multilayer film can be a multilayer film in which 40 to 60 Mo and Si films, each about several nanometers thick, are stacked.

[0080] The thickness of the multilayer film is, for example, 280 nm to 420 nm. Examples of methods for forming the multilayer film include ion beam sputtering and magnetron sputtering.

[0081] 4.Absorbent layer The absorbing layer in the present disclosure is arranged in a pattern on the surface of the multilayer film opposite the substrate, and absorbs EUV light in EUV lithography using the reflective mask in the present disclosure.

[0082] The material for the absorption layer is not particularly limited as long as it can absorb EUV light, and examples thereof include Ta, TaN, a material mainly composed of Ta, Cr, and a material mainly composed of Cr and containing at least one component selected from N, O, and C. Furthermore, TaSi, TaSiN, TaGe, TaGeN, WN, TiN, etc. can also be used.

[0083] Examples of methods for forming the absorbing layer include magnetron sputtering, ion beam sputtering, CVD, and vapor deposition. Methods for forming the absorbing layer in a pattern typically include photolithography and electron beam lithography. Specifically, an absorbing layer is formed on a substrate on which a multilayer film has been formed, a resist layer is formed on the absorbing layer, the resist layer is patterned, the absorbing layer is etched using the resist pattern as a mask, and the remaining resist pattern is removed to form the absorbing layer in a pattern. Common methods can be used for photolithography and electron beam lithography.

[0084] 5.Protective layer In the present disclosure, a protective layer may be disposed between the multilayer film and the absorption layer. The protective layer is provided to prevent oxidation of the multilayer film and to protect the reflective mask during cleaning. When the outermost surface of the multilayer film is a Si film or a Mo film, the protective layer can prevent the Si film or the Mo film from being oxidized. If the Si film or the Mo film is oxidized, the reflectance of the multilayer film may decrease. When a buffer layer (described later) is disposed on the surface of the multilayer film opposite the substrate, the protective layer and the buffer layer are usually disposed in this order on the surface of the multilayer film opposite the substrate.

[0085] The material for the protective layer is not particularly limited as long as it exhibits the above-mentioned functions, and examples thereof include Si and Ru.

[0086] The thickness of the protective layer is, for example, 2 nm to 15 nm. The protective layer can be formed by a sputtering method or the like.

[0087] 6. Buffer layer In the present disclosure, a buffer layer may be disposed between the multilayer film and the absorption layer. The buffer layer is provided to prevent damage to the underlying multilayer film. By disposing the buffer layer, damage to the underlying multilayer film can be prevented when the absorption layer is pattern-etched by a method such as dry etching.

[0088] The buffer layer material should have high etching resistance. It is usually made of a material with different etching characteristics from the absorption layer, i.e., a material with a high etching selectivity to the absorption layer. The etching selectivity between the buffer layer and the absorption layer is preferably 5 or more, more preferably 10 or more, and even more preferably 20 or more. Furthermore, the buffer layer material is preferably a low-stress, highly smooth material. In particular, the root-mean-square roughness (Rq) of the buffer layer is preferably 0.3 nm or less. The method for measuring the root-mean-square roughness (Rq) will be described later. From this perspective, the buffer layer material preferably has a microcrystalline or amorphous structure. Examples of such buffer layer materials include SiO2, Al2O3, Cr, and CrN.

[0089] The thickness of the buffer layer is, for example, not less than 2 nm and not more than 25 nm.

[0090] The buffer layer can be formed by, for example, magnetron sputtering or ion beam sputtering. When Cr is used, it is preferable to form a Cr film on the multilayer film by RF magnetron sputtering using a Cr target in an Ar gas atmosphere.

[0091] When a buffer layer is disposed on the surface of the multilayer film opposite to the substrate, the exposed buffer layer may be peeled off after patterning the absorber layer. The buffer layer can be peeled off by a general method for peeling off a buffer layer, such as dry etching.

[0092] 7.Low reflective layer In the present disclosure, a low-reflection layer may be disposed on the surface opposite to the multilayer film of the absorbing layer, in order to increase detection sensitivity during mask pattern inspection.

[0093] The material for the low-reflection layer may be any material that has low reflectivity to the inspection light, such as tantalum oxide (TaO), oxynitride (TaNO), or tantalum boron oxide (TaBO). The thickness of the low-reflection layer is, for example, 5 nm or more and 30 nm or less.

[0094] 8. Substrate The substrate used in the present disclosure can be one generally used for reflective mask substrates, and a glass substrate is preferably used, for example. Glass substrates are particularly suitable as reflective mask substrates because they provide good smoothness and flatness. Examples of materials for glass substrates include quartz glass, amorphous glass with a low thermal expansion coefficient (e.g., SiO2-TiO2-based glass, etc.), and crystallized glass in which β-quartz solid solution is precipitated. Metal substrates such as silicon and Fe-Ni-based invar alloys can also be used.

[0095] To obtain high reflectivity and transfer accuracy for a reflective mask, the root mean square roughness Rq of the substrate is preferably 0.2 nm or less. The root mean square roughness Rq is measured using an atomic force microscope in accordance with JIS B0601:2013.

[0096] Furthermore, to achieve high reflectivity and transfer accuracy for reflective masks, the flatness of the substrate is preferably 100 nm or less. Flatness is a value indicating the surface warpage (deformation amount) indicated by TIR (Total Indicator Reading). This value is the absolute value of the difference in height between the highest point on the substrate surface above the focal plane, determined by the least squares method based on the substrate surface, and the lowest point below the focal plane. The flatness is measured over a 142 mm square area. The flatness is measured using an oblique incidence interferometer. An example of an oblique incidence interferometer that can be used is the UltraFlat manufactured by Tropel.

[0097] 9.Conductive Film In the present disclosure, a conductive film may be disposed on the surface of the substrate opposite the multilayer film. The conductive film is provided to allow the reflective mask of the present disclosure to be attached to an electrostatic chuck of an exposure tool. By providing such a conductive film, the reflective mask can be easily and firmly fixed to the exposure tool during exposure, thereby improving pattern transfer accuracy and manufacturing efficiency.

[0098] The material for the conductive film is not particularly limited as long as it is generally used for conductive films of reflective masks, and for example, metals or metal compounds such as Cr, CrN, etc., which exhibit conductivity, are used.

[0099] The thickness of the conductive film is, for example, not less than 30 nm and not more than 150 nm.

[0100] Examples of a method for forming the conductive film include sputtering, etc. When the conductive film is formed in a pattern, methods such as sputtering through a mask, photolithography, and electron beam lithography can be used.

[0101] 10.Applications The reflective mask of the present disclosure is preferably used as a reflective mask for lithography using EUV as exposure light.

[0102] 11. Reflective mask manufacturing method An example of a method for manufacturing a reflective mask according to the present disclosure is a manufacturing method including: a preparation step of preparing a mask blank having a substrate, a multilayer film, and an absorbing layer in this order; an absorbing layer patterning step of patterning the absorbing layer; and a light-shielding region forming step of removing the multilayer film and the absorbing layer around the periphery of a transfer pattern region having the pattern of the absorbing layer to form the light-shielding region in which the substrate is exposed.

[0103] 17(a) to 17(c) are process diagrams illustrating an example of a method for manufacturing a reflective mask according to the present disclosure. First, as shown in FIG. 17(a), a mask blank 20 is prepared in which a multilayer film 3, a protective layer 4, and an absorbing layer 5 are sequentially stacked on a substrate 2 (mask blank preparation step). Next, as shown in FIG. 17(b), the absorbing layer 5 is patterned to form a transfer pattern region 11 having the pattern of the absorbing layer 5 (absorbing layer patterning step). This results in a reflective mask intermediate 30 having the substrate 2, the multilayer film 3 formed on the substrate 2, the protective layer 4 formed on the multilayer film 3, and the pattern of the absorbing layer 5 formed on the protective layer 4, and having the transfer pattern region 11 having the pattern of the absorbing layer 5. Next, as shown in FIG. 17(c), the absorbing layer 5, the protective layer 4, and the multilayer film 3 are removed from the periphery of the transfer pattern region 11 to form a light-shielding region 12 in which the substrate 2 is exposed (light-shielding region formation step). In this manner, a reflective mask 1 having a light-shielding region 12 is obtained.

[0104] Each step in the method for manufacturing a reflective mask according to the present disclosure will now be described.

[0105] (1) Mask blank preparation process In the mask blank preparation step, for example, a commercially available mask blank may be used, or a mask blank may be fabricated.

[0106] (2) Absorber layer patterning process The method for patterning the absorbing layer has been described above in the section on the absorbing layer, and therefore the description thereof will be omitted here.

[0107] (3) Light-shielding area formation process The method for forming the light-shielding region is not particularly limited as long as it can partially remove the absorbing layer, the multilayer film, etc. and expose the substrate, and examples thereof include photolithography and electron beam lithography. Specifically, a resist layer is formed so as to cover the pattern of the absorbing layer, the resist layer is patterned, and the absorbing layer, the multilayer film, etc. are etched using the resist pattern as a mask to expose the substrate, and the remaining resist pattern is removed. As the photolithography and electron beam lithography, general methods can be used.

[0108] B. Semiconductor Device Manufacturing Method The method for manufacturing a semiconductor device according to the present disclosure includes a step of performing stitching exposure using the above-described reflective mask to form a pattern on a semiconductor substrate.

[0109] In the method for manufacturing a semiconductor device according to the present disclosure, stitching exposure is performed using the above-described reflective mask, which makes it possible to suppress overexposure at the seams between patterns on the semiconductor substrate and achieve highly accurate pattern transfer. In particular, when the absorption layer is etched back during the formation of the light-shielding region, and the multilayer film is exposed at the edge of the transfer pattern region, unintended pattern resolution can be effectively suppressed.

[0110] The reflective mask has been described in detail above in the section "A. Reflective Mask," so a detailed description thereof will be omitted here.

[0111] It is preferable that the reflective mask is designed so that, in plan view, the corner shape of the boundary between the transfer pattern area and the light-shielding area is an arc shape, and the radius of curvature R1 of the arc shape satisfies the following formula (1). 0.58L≦R1≦4.22L (1) (In the above formula (1), L represents the overlap width of the transfer pattern area during the first exposure and the transfer pattern area during the second exposure. L is expressed as L=8M. M represents the overlap width of the exposure area during the first exposure and the exposure area during the second exposure on the semiconductor substrate.)

[0112] Furthermore, it is preferable that the reflective mask is designed so that, in plan view, the corner shape of the boundary between the transfer pattern area and the light-shielding area is an elliptical arc shape, the ratio a1 / b1 of the major axis radius a1 to the minor axis radius b1 of the elliptical arc shape is 2, and the major axis radius a1 of the elliptical arc shape satisfies the following formula (2): 0.7L≦a1≦14.7L (2) (In the above formula (2), L represents the overlap width of the transfer pattern area during the first exposure and the transfer pattern area during the second exposure. L is expressed as L=8M. M represents the overlap width of the exposure area during the first exposure and the exposure area during the second exposure.)

[0113] The above formulas (1) and (2) have been described in the above section "A. Reflective Mask 1. Shape of the Boundary Between the Transfer Pattern Area and the Light-Shielding Area," so a description thereof will be omitted here.

[0114] As the semiconductor substrate, a general semiconductor substrate used in a semiconductor device can be applied, such as a wafer.

[0115] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure.

[0116] The present disclosure provides the following inventions. [1] A reflective mask having a substrate, a multilayer film disposed on one surface of the substrate, and an absorbing layer pattern disposed on the surface of the multilayer film opposite to the substrate, a transfer pattern region having a pattern of the absorption layer; and a light-shielding region that is disposed on the outer periphery of the transfer pattern region, does not have the multilayer film or the absorption layer, and in which the substrate is exposed; A reflective mask, wherein the shape of the boundary between the transfer pattern region and the light-shielding region is rounded in plan view. [2] The reflective mask according to [1], wherein the shape of the boundary between the transfer pattern region and the light-shielding region has rounded corners in plan view. [3] The reflective mask according to [1] or [2], wherein the shape of the boundary between the transfer pattern region and the light-shielding region is a generally rectangular shape with rounded corners in a plan view. [4] The reflective mask according to any one of [1] to [3], further comprising a conductive film on the surface of the substrate opposite to the multilayer film. [5] Further, a non-transfer pattern area is arranged on the outer periphery of the light-shielding area, A reflective mask according to any one of [1] to [4], wherein the radius of curvature R1 of the corner in the shape of the boundary between the transfer pattern area and the light-shielding area is equal to or less than the radius of curvature R2 of the corner in the shape of the boundary between the light-shielding area and the non-transfer pattern area. [6] A reflective mask according to any one of [1] to [5], wherein the shape of the corner of the boundary between the transfer pattern area and the light-shielding area is an elliptical arc shape or a circular arc shape, and the ratio a1 / b1 of the major axis radius a1 to the minor axis radius b1 of the elliptical arc shape is 2. [7] A method for manufacturing a semiconductor device, comprising a step of performing stitching exposure using a reflective mask according to any one of [1] to [6] to form a pattern on a semiconductor substrate, A method for manufacturing a semiconductor device, wherein in the reflective mask, in a planar view, the corner shape of the boundary between the transfer pattern area and the light-shielding area is an arc shape, and the radius of curvature R1 of the arc shape satisfies the following formula (1). 0.58L≦R1≦4.22L (1) (In the above formula (1), L represents the overlap width of the transfer pattern area during the first exposure and the transfer pattern area during the second exposure. L is expressed as L=8M. M represents the overlap width of the exposure area during the first exposure and the exposure area during the second exposure.) [8] A method for manufacturing a semiconductor device, comprising a step of performing stitching exposure using a reflective mask according to any one of [1] to [6] to form a pattern on a semiconductor substrate, A method for manufacturing a semiconductor device, wherein in the reflective mask, in a planar view, the shape of a corner in the shape of the boundary between the transfer pattern area and the light-shielding area is an elliptical arc shape, the ratio a1 / b1 of the major axis radius a1 to the minor axis radius b1 of the elliptical arc shape is 2, and the major axis radius a1 of the elliptical arc shape satisfies the following formula (2): 0.7L≦a1≦14.7L (2) (In the above formula (2), L represents the overlap width of the transfer pattern area during the first exposure and the transfer pattern area during the second exposure. L is expressed as L=8M. M represents the overlap width of the exposure area during the first exposure and the exposure area during the second exposure.) [Explanation of symbols]

[0117] 1...Reflective mask 2... Substrate 3...Multilayer film 4...protective layer 5...Absorption layer 6...Conductive film 11...Transfer pattern area 12...shading area 13 ...Boundary between transfer pattern area and light-shielding area 14...Non-transcribed pattern region 15 ...Boundary between light-shielding area and non-transfer pattern area

Claims

1. A reflective mask having a substrate, a multilayer film disposed on one surface of the substrate, and an absorbing layer pattern disposed on the surface of the multilayer film opposite to the substrate, a transfer pattern region having a pattern of the absorption layer; and a light-shielding region that is disposed on the outer periphery of the transfer pattern region, does not have the multilayer film and the absorption layer, and in which the substrate is exposed; A reflective mask, wherein the shape of the boundary between the transfer pattern area and the light-shielding area is rounded in plan view.

2. 2. The reflective mask according to claim 1, wherein the shape of the boundary between the transfer pattern region and the light-shielding region has rounded corners in plan view.

3. 2. The reflective mask according to claim 1, wherein the shape of the boundary between said transfer pattern region and said light-shielding region is a generally rectangular shape with rounded corners in plan view.

4. 2. The reflective mask according to claim 1, further comprising a conductive film on the surface of said substrate opposite to said multilayer film.

5. Further, a non-transfer pattern area is arranged on the outer periphery of the light-shielding area, 2. The reflective mask according to claim 1, wherein a radius of curvature R1 of a corner in the shape of the boundary between the transfer pattern region and the light-shielding region is equal to or less than a radius of curvature R2 of a corner in the shape of the boundary between the light-shielding region and the non-transfer pattern region.

6. 2. The reflective mask according to claim 1, wherein the shape of a corner of the boundary between the transfer pattern region and the light-shielding region is an elliptical arc shape or a circular arc shape, and the ratio a1 / b1 of the major axis radius a1 to the minor axis radius b1 of the elliptical arc shape is 2.

7. 10. A method for manufacturing a semiconductor device, comprising a step of performing stitching exposure using a reflective mask according to claim 1 to form a pattern on a semiconductor substrate, In the reflective mask, in a planar view, a corner shape of the boundary between the transfer pattern area and the light-shielding area is an arc shape, and a radius of curvature R1 of the arc shape satisfies the following formula (1): 0.58L≦R1≦4.22L (1) (In the above formula (1), L represents the overlap width of the transfer pattern area at the time of the first exposure and the transfer pattern area at the time of the second exposure. L is expressed as L=8M. M represents the overlap width between the exposed area during the first exposure and the exposed area during the second exposure on the semiconductor substrate.

8. 10. A method for manufacturing a semiconductor device, comprising a step of performing stitching exposure using a reflective mask according to claim 1 to form a pattern on a semiconductor substrate, a ratio a1 / b1 of a major axis radius a1 to a minor axis radius b1 of the elliptical arc shape is 2, and the major axis radius a1 of the elliptical arc shape satisfies the following formula (2): 0.7L≦a1≦14.7L (2) (In the above formula (2), L represents the overlap width of the transfer pattern area at the time of the first exposure and the transfer pattern area at the time of the second exposure. L is expressed as L=8M. M represents the overlap width between the exposed area during the first exposure and the exposed area during the second exposure on the semiconductor substrate.

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