Reflective mask and method for manufacturing semiconductor device

Abstract

The main purpose of the present invention is to provide a reflective mask capable of suppressing excessive light exposure at a seam between pattern regions in a wafer and achieving highly accurate pattern transfer. The present disclosure provides a reflective mask (1) comprising a substrate (2), a multilayer film (3) disposed on one surface of the substrate (2), and a pattern of an absorption layer (5) disposed on the surface of the multilayer film (3) opposite from the substrate. The reflective mask (1) has: a transfer pattern region (11) having the pattern of the absorption layer (5); and a light-shielding region (12) that is disposed on an outer periphery of the transfer pattern region (11), does not include the multilayer film (3) and the absorption layer (5), and exposes the substrate (2). In a plan view, the shape of the boundary between the transfer pattern region (11) and the light-shielding region (12) has rounded corners.

Description

Reflective Mask and Method for Manufacturing Semiconductor Device

[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.

[0002] In recent years, with the miniaturization of semiconductor devices in the semiconductor industry, EUV lithography, which is an exposure technique using EUV, has been regarded as promising. As a mask used in EUV lithography, a reflective mask has been proposed. A reflective mask is, for example, a mask including a substrate, a multilayer film disposed on one surface of the substrate that reflects EUV light, and an absorption layer disposed in a pattern on a surface of the multilayer film opposite to the substrate that absorbs EUV light. In EUV lithography, EUV light incident on a reflective mask is absorbed by the absorption layer and reflected by the multilayer film, and an optical image formed by reflection from the multilayer film is 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 a step-and-repeat method is used. The step-and-repeat method is a method of sequentially moving (stepping) the wafer and performing repeated (repeat) exposure. Step-and-repeat exposure apparatuses are called steppers.

[0004] When exposure is performed by this step-and-repeat method, in order to take out as many chips as possible from the wafer, transfer pattern regions where absorption layer patterns are arranged on the reflective mask are usually transferred as close to each other as possible. Further, in the case of the step-and-repeat method, an area slightly larger than the transfer pattern area is generally exposed. Therefore, in adjacent exposure regions on the wafer, there occurs a region where the exposure regions overlap. Hereinafter, the region where the exposure regions overlap may be referred to as a "multiple exposure region". For example, in the case of a rectangular exposure region, a corner of one exposure region overlaps with the other three exposure regions, resulting in four times of exposure.

[0005] In areas with multiple exposures, the exposure occurs multiple times, and as a result, most of the exposure light is absorbed by the absorption layer. Even if the exposure amount in a single exposure is not substantial enough to contribute to resolution, the total exposure amount can add up to a level that contributes to resolution. Consequently, unwanted patterns are formed, leading to the problem of not being able to obtain high-precision patterns.

[0006] Furthermore, in reflective masks, exposure light is incident from a direction perpendicular to the mask surface, typically at an angle of several degrees, usually around 6 degrees. Because the absorption layer has thickness, the oblique incidence of exposure light creates a shadow of the absorption layer pattern itself. This effect is called the shadow effect. The degree of the shadow effect varies depending on the orientation of the absorption layer pattern relative to the exposure light and affects the transfer dimensions to the wafer. This shadow effect problem has become particularly pronounced with the miniaturization of patterns in recent years.

[0007] To suppress such shadow effects, a thinner absorption layer is preferable. However, reducing the thickness of the absorption layer reduces the absorption of exposure light by the absorption layer, which exacerbates the pattern defects in the multiple exposure regions mentioned above.

[0008] Therefore, as described in Patent Documents 1 to 2, for example, in a reflective mask, it has been proposed to place a light-shielding region on the outer periphery of the transfer pattern region in order to suppress reflected light from the outer periphery region located on the outer periphery of the transfer pattern region that forms the multiple exposure region. The light-shielding region is also called a light-shielding frame or light-shielding band. As for light-shielding regions, as described in Patent Documents 1 to 4, for example, there are forms in which grooves are formed in which the substrate is exposed without having a multilayer film or an absorption layer, forms in which a light-shielding film is formed on the absorption layer without forming grooves, forms in which a layer that reduces reflected light is formed in the exposed recesses, and forms in which the reflectivity is reduced by destroying the multilayer film structure of the reflective layer with laser irradiation.

[0009] Japanese Patent Publication No. 2012-69859, Japanese Patent Publication No. 2012-190979, Japanese Patent Publication No. 2009-141223, Japanese Patent Publication No. 2011-44520

[0010] Currently, the numerical aperture (NA) of the projection optical system lenses in commercially available EUV lithography equipment is 0.33, resulting in a reduction ratio of 4x in both the x and y directions in the projection optical system. In contrast, EUV lithography equipment with an NA of up to 0.55 has been developed, resulting in a reduction ratio of 4x in the x direction and 8x in the y direction in the projection optical system. When the size of the reflective mask is kept constant, compared to the case with an NA of 0.33, the reduction ratio in the y direction becomes twice that of the reduction ratio in the x direction when the NA is 0.55, thus halving the exposure area on the wafer. In this case, for example, as shown in Figures 18(a) to 18(b), two reflective masks 100A and 100B are used, and exposure is performed twice. At this time, it is necessary to join the pattern transferred by reflective mask 100A and the pattern transferred by reflective mask 100B on the wafer 120. This technique is called stitching exposure. In stitching exposure, exposure is performed on the wafer 120 such that the exposure area 121a corresponding to the reflective mask 100A and the exposure area 121b corresponding to the reflective mask 100B partially overlap. As shown in Figures 19(a) and 19(b), the reflective masks 100A and 100B each have a substrate 102, a multilayer film 103 arranged on one side of the substrate 102 that reflects EUV light, and an absorption layer 105 arranged in a pattern on the side of the multilayer film 103 opposite to the substrate 102 that absorbs EUV light. As shown in Figures 18(a), 19(a), and 19(b), the masks have a transfer pattern area 111 on which the pattern of the absorption layer 105 is arranged, and a light-shielding area 112 arranged on the outer periphery of the transfer pattern area 111.

[0011] Furthermore, as described above, in a reflective mask, exposure light is incident from a direction several degrees, usually about 6 degrees, perpendicular to the mask surface. As shown in Figure 19(a), in a reflective mask, when exposure light L1 is incident from an oblique angle, in the transfer pattern region 111, the EUV light reflected by the multilayer film 103 is absorbed and attenuated by the absorption layer 105. However, as shown in Figure 19(b), at the edges of the transfer pattern region 111, when exposure light L1 is incident from an oblique angle, the EUV light reflected by the multilayer film 103 is not attenuated by the absorption layer 105, and leakage light occurs towards 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 taken as 0, the reflectivity is higher at a distance d from the boundary 113 towards the light-shielding region 112. In other words, the reflectivity is higher near the outer edge of the transfer pattern region 111. Furthermore, when the light-shielding region is formed, the absorption layer recedes due to etching, which can expose the multilayer film 103 at the edges of the transfer pattern region 111, as shown in Figure 19(c). In this case, light leakage is more likely to occur, and the reflectivity becomes even higher near the outer edge of the transfer pattern region 111.

[0012] Therefore, as shown in Figure 21(a), in wafer 120, corresponding to the increased reflectivity near the outer edge of the transfer pattern region 111 of the reflective mask 100A, there is a region 122a on the outer edge of the exposure region 121a where the exposure amount increases. Similarly, in wafer 120, corresponding to the increased reflectivity near the outer edge of the transfer pattern region 111 of the reflective mask 100B, there is a region 122b on the outer edge of the exposure region 121b where the exposure amount increases. Hereinafter, in wafer, the region on the outer edge of the exposure region where the exposure amount increases in response to the increased reflectivity near the outer edge of the transfer pattern region of the reflective mask may be referred to as the "high exposure region." In the region where the high exposure region 122a on the outer edge of exposure region 121a and the high exposure region 122b on the outer edge of exposure region 121b overlap, the exposure amounts may be added together to reach an amount that contributes to resolution. Figure 21(b) is a graph illustrating the exposure amount in the a-a section of Figure 21(a), and Figure 21(c) is a graph illustrating the exposure amount in the b-b section of Figure 21(a). As shown in Figure 21(b), in the high exposure area 122a located on the outer periphery of exposure area 121a, even if the exposure amount increases, the resolution threshold T100 is not reached. However, as shown in Figure 21(c), in the region where the high exposure area 122a located on the outer periphery of exposure area 121a and the high exposure area 122b located on the outer periphery of exposure area 121b overlap, the exposure amounts are added together and the resolution threshold T100 may be reached. As a result, unnecessary patterns are formed at the joints between patterns on the wafer, leading to the problem of not being able to obtain high-precision patterns.

[0013] This disclosure has been made in view of the above circumstances, and its main purpose is to provide a reflective mask that can suppress overexposure at the seams between patterns on a wafer and achieve high-precision pattern transfer.

[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 a pattern of an absorption layer disposed on the side of the multilayer film opposite to the substrate, wherein the reflective mask has a transfer pattern region having the pattern of the absorption layer and a light-shielding region disposed on the outer periphery of the transfer pattern region, which does not have the multilayer film or the absorption layer and exposes the substrate, and in a plan 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, comprising the step of performing stitching exposure using the reflective mask described above to form a pattern on a semiconductor substrate, wherein, in the reflective mask, the shape of the corner at the boundary between the transfer pattern region and the light-shielding region in a plan view 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 formula (1), L represents the overlap width between the transfer pattern region during the first exposure and the transfer pattern region during the second exposure. L is shown as L = 8M. M represents the overlap width between 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 the step of performing stitching exposure using the reflective mask described above to form a pattern on a semiconductor substrate, wherein, in a plan view, the shape of the corners in the boundary between the transfer pattern region and the light-shielding region of the reflective mask 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 formula (2), L represents the overlap width between the transfer pattern region during the first exposure and the transfer pattern region during the second exposure. L is shown as L = 8M. M represents the overlap width between the exposure region during the first exposure and the exposure region during the second exposure on the semiconductor substrate.)

[0017] This disclosure has the effect of suppressing overexposure at the seams between patterns on a wafer, thereby enabling high-precision pattern transfer.

[0018] These are schematic plan views and cross-sectional views illustrating the reflective mask in this disclosure. This is a schematic diagram illustrating an exposure method using the reflective mask in this disclosure. This is a schematic plan view illustrating a wafer exposed using the reflective mask in this disclosure and a graph illustrating the exposure amount. These are schematic plan views and cross-sectional views illustrating the reflective mask in this disclosure. These are schematic plan views and cross-sectional views illustrating the reflective mask in this disclosure. This is a schematic plan view illustrating a wafer exposed using the reflective mask in this disclosure and a graph illustrating the exposure amount. This is a schematic plan view illustrating the shape of the boundary between the transfer pattern area and the light-shielding area in the reflective mask in this disclosure. This is a schematic plan view illustrating the shape of the boundary between the transfer pattern area and the light-shielding area in the reflective mask in this disclosure. This is a schematic plan view illustrating the shape of the boundary between the transfer pattern area and the light-shielding area in the reflective mask in this disclosure. This is a schematic plan view illustrating the shape of the boundary between the transfer pattern area and the light-shielding area in the reflective mask in this disclosure. This is a graph showing the relationship between the coefficient α of the overlap width L and the intersection angle θ1. This is a schematic plan view illustrating the shape of the boundary between the transfer pattern region and the light-shielding region in a reflective mask according to this disclosure, as well as a wafer exposed using the reflective mask according to this disclosure. This is a graph showing the relationship between the coefficient α of the overlap width L and the intersection angle. This is a schematic plan view illustrating the shape of the boundary between the transfer pattern region and the light-shielding region in a reflective mask according to this disclosure. This is a schematic plan view illustrating 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 in a reflective mask according to this disclosure. This is a process diagram illustrating a method for manufacturing a reflective mask according to this disclosure. This is a schematic diagram illustrating a conventional exposure method using a reflective mask. This is a schematic diagram illustrating a conventional exposure method using a reflective mask. This is a graph showing the reflectance near the outer edge of the transfer pattern region in a conventional reflective mask. This is a schematic plan view illustrating a wafer exposed using a conventional reflective mask and a graph illustrating the exposure amount.This is a schematic plan view illustrating the shape of the boundary between the transfer pattern area and the light-shielding area, and the shape of the boundary between the light-shielding area and the non-transfer pattern area in a conventional reflective mask.

[0019] Embodiments of this disclosure will be described below with reference to drawings and other figures. However, this disclosure can be implemented in many different ways and should not be interpreted as being limited to the embodiments described below. In addition, in order to make the explanation clearer, the drawings may schematically represent the width, thickness, shape, etc. of each part compared to the actual form, but these are merely examples and should not limit the interpretation of this disclosure. Furthermore, in this specification and each figure, elements similar to those described above with respect to previously shown figures will be denoted by the same reference numerals, and detailed explanations may be omitted as appropriate.

[0020] In this specification, when describing a configuration in which one member is placed on top of another member, unless otherwise specified, the terms "on top" or "below" include both cases: when the other member is placed directly above or below the other member so as to be in contact with it, and when the other member is placed above or below the other member via yet another member. Similarly, when describing a configuration in this specification in which one member is placed on the surface of another member, unless otherwise specified, the terms "on the surface" or "on the surface" include both cases: when the other member is placed directly above or below the other member so as to be in contact with it, and when the other member is placed above or below the other member via yet another member.

[0021] The following describes in detail the manufacturing method of the reflective mask and semiconductor device described herein.

[0022] A. Reflective Mask The reflective mask in this disclosure comprises a substrate, a multilayer film disposed on one side of the substrate, and a pattern of an absorption layer disposed on the side of the multilayer film opposite to the substrate, wherein the reflective mask has a transfer pattern region having the pattern of the absorption layer and a light-shielding region disposed on the outer 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 plan view, the shape of the boundary between the transfer pattern region and the light-shielding region is rounded.

[0023] Figure 1(a) is a schematic plan view showing an example of a reflective mask in this disclosure, and Figure 1(b) is a cross-sectional view taken along line A-A in Figure 1(a). As illustrated in Figures 1(a) and 1(b), the reflective mask 1 includes a substrate 2, a multilayer film 3 disposed on one side of the substrate 2, a protective layer 4 formed on the side of the multilayer film 3 opposite to the substrate 2, a pattern of an absorption layer 5 disposed on the side of the protective layer 4 opposite to the multilayer film 3, and a conductive film 6 disposed on the side of the substrate 2 opposite to the multilayer film 3. The reflective mask 1 also includes a transfer pattern region 11 having the pattern of the absorption layer 5, and a light-shielding region 12 disposed on the outer periphery of the transfer pattern region 11, which does not have the multilayer film 3, protective layer 4, or absorption layer 5, and exposes the substrate 2. In plan view, the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 is rounded. In Figure 1(a), the shape of the boundary 13 between the transfer pattern area 11 and the light-shielding area 12 is a rounded rectangle, with rounded corners.

[0024] Generally, in stitching exposure, as shown in Figures 18(a) to 18(b), exposure is performed on the wafer 120 such that the exposure area 121a corresponding to the reflective mask 100A and the exposure area 121b corresponding to the reflective mask 100B partially overlap. Furthermore, in the case of a reflective mask, the exposure light is incident from a direction tilted several degrees, usually about 6 degrees, from a direction perpendicular to the mask surface. As shown in Figure 19(b), at the edge of the transfer pattern area 111, the EUV light reflected by the multilayer film 103 is not attenuated by the absorption layer 105, and leakage light occurs towards the light-shielding area 112. For example, as shown in Figure 20, when the position of the boundary 113 between the transfer pattern area 111 and the light-shielding area 112 is taken as 0, the reflectivity is high at a distance d from the boundary 113 towards the light-shielding area 112. In other words, the reflectivity is high near the outer edge of the transfer pattern area 111. Furthermore, when the light-shielding region is formed, the absorption layer recedes due to etching, which can expose the multilayer film 103 at the edges of the transfer pattern region 111, as shown in Figure 19(c). In this case, light leakage is more likely to occur, and the reflectivity becomes even higher near the outer edge of the transfer pattern region 111.

[0025] Therefore, as shown in Figure 21(a), in wafer 120, corresponding to the increased reflectivity near the outer edge of the transfer pattern region 111 of the reflective mask 100A, there is a high exposure region 122a on the outer edge of the exposure region 121a where the exposure amount increases. Similarly, in wafer 120, corresponding to the increased reflectivity near the outer edge of the transfer pattern region 111 of the reflective mask 100B, there is a high exposure region 122b on the outer edge of the exposure region 121b where the exposure amount increases. In the region where the high exposure region 122a on the outer edge of exposure region 121a and the high exposure region 122b on the outer edge of exposure region 121b overlap, the exposure amounts may be added together to reach an amount that contributes to resolution. Figure 21(b) is a graph illustrating the exposure amount in the a-a line portion of Figure 21(a), and Figure 21(c) is a graph illustrating the exposure amount in the b-b line portion of Figure 21(a). As shown in Figure 21(b), in the high exposure region 122a located on the outer periphery of the exposure region 121a, the resolution threshold T100 is not reached even if the exposure amount increases. However, as shown in Figure 21(c), in the region where the high exposure region 122a located on the outer periphery of the exposure region 121a and the high exposure region 122b located on the outer periphery of the exposure region 121b overlap, the exposure amounts are added together and the resolution threshold T100 may be reached. As a result, unnecessary patterns are formed at the joints between patterns on the wafer, leading to the problem of not being able to obtain high-precision patterns.

[0026] Conventionally, as shown in Figure 16(a), for example, in reflective masks 100A and 100B, the shape of the light-shielding region 112 is frame-shaped, and in a plan view, the shape of the boundary 113 between the transfer pattern region 111 and the light-shielding region 112 is rectangular. When the shape of the boundary 113 between the transfer pattern region 111 and the light-shielding region 112 is rectangular, as shown in Figures 19(a) and 19(d), in the wafer 120, the high-exposure region 122a located on the outer periphery of the exposure region 121a and the high-exposure region 122b located on the outer periphery of the exposure region 121b overlap in a straight line. Therefore, the overlap between the high-exposure region 122a located on the outer periphery of the exposure region 121a and the high-exposure region 122b located on the outer periphery of the exposure region 121b becomes large. Note that Figure 19(d) is an enlarged view of the portion along the b-b line in Figure 19(a).

[0027] In contrast, in this disclosure, as illustrated in Figure 1(a), the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 in a plan view is rounded. Therefore, as shown in Figures 2(a) and 2(b), when stitching exposure is performed on the wafer 120 using two reflective masks 1A and 1B such that the exposure region 21a corresponding to the reflective mask 1A and the exposure region 21b corresponding to the reflective mask 1B partially overlap, the overlap between the high exposure region 22a on the outer periphery of the exposure region 21a and the high exposure region 22b on the outer periphery of the exposure region 21b can be reduced on the wafer 20, as illustrated in Figures 3(a) and 3(c). Specifically, the high-exposure region 22a located on the outer periphery of exposure region 21a and the high-exposure region 22b located on the outer periphery of exposure region 21b overlap in a point-like manner, thus reducing the overlap between the high-exposure region 22a located on the outer periphery of exposure region 21a and the high-exposure region 22b located on the outer periphery of exposure region 21b. Figure 3(c) is an enlarged view of the c-c line portion of Figure 3(a).

[0028] Figure 3(b) is a graph illustrating the exposure amount in the c-c line portion of Figure 3(a). Compared to the case where high exposure areas overlap linearly, the resolution threshold T1 is higher when high exposure areas overlap as points. This is because, as shown in Figure 19(d), when high exposure areas 122a and 122b overlap linearly, the resist 131 tends to remain during development, whereas, as shown in Figure 3(c), when high exposure areas 22a and 22b overlap as points, the resist 31 tends to remain during development. As a result, when high exposure areas 22a and 22b overlap as points, the resist 31 is less likely to be resolved, and the resolution threshold T1 is higher. Therefore, it is possible to suppress the resolution of unintended patterns at the seams between patterns on the wafer.

[0029] Therefore, when performing stitching exposure using the reflective mask in this disclosure, overexposure at the seams between patterns on the wafer can be suppressed, enabling high-precision pattern transfer. In particular, when the absorption layer recedes by etching during the formation of the light-shielding region, and the multilayer film is exposed at the edges of the transfer pattern region, the resolution of unintended patterns can be effectively suppressed.

[0030] The following describes the various components of the reflective mask in this disclosure.

[0031] 1. Shape of the boundary between the transfer pattern region and the light-shielding region In the reflective mask of this disclosure, the transfer pattern region is the region having the pattern of the absorption layer. The light-shielding region is located on the outer periphery of the transfer pattern region and is a region that does not have a multilayer film or absorption layer, and in which the substrate is exposed. In this disclosure, in a plan view, the shape of the boundary between the transfer pattern region and the light-shielding region is rounded.

[0032] Conventionally, as shown in Figure 16(a), in reflective masks 100A and 100B, the planar shape of the transfer pattern region 111 is usually rectangular. Therefore, in plan view, the shape of the boundary 113 between the transfer pattern region 111 and the light-shielding region 112 is rectangular, with all corners being right angles.

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

[0034] In this specification, "rounded corners" refers to a shape whose corners are not right angles, that is, a shape in which the corners are cut off by a straight line or a curve. Specifically, examples of rounded corners include shapes in which the corners are cut off by a curve, that is, shapes with rounded corners, as shown in Figures 1(a) and 4(a), and shapes in which the corners are cut off by a straight line, as shown in Figure 5(a). Shapes with rounded corners may have a circular arc shape or an elliptical arc shape in which the corners protrude outward, as shown in Figure 1(a), or a circular arc shape or an elliptical arc shape in which the corners are recessed inward, as shown in Figure 4(a). There may be only one type of rounded corner, or two or more types may be combined.

[0035] For example, in Figure 1(a), in a plan view, the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 is such that the corners are rounded and the corners are arc-shaped with protruding outwards. Therefore, as shown in Figures 2(a) and 2(b), when stitching exposure is performed on the wafer 20 using two reflective masks 1A and 1B such that the exposure region 21a corresponding to the reflective mask 1A and the exposure region 21b corresponding to the reflective mask 1B partially overlap, the overlap between the high exposure region 22a on the outer periphery of the exposure region 21a and the high exposure region 22b on the outer periphery of the exposure region 21b can be reduced, as illustrated in Figures 3(a) and 3(c). Specifically, the high exposure region 22a located on the outer periphery of exposure region 21a and the high exposure region 22b located on the outer periphery of exposure region 21b overlap in a point-like manner, thus reducing the overlap between the high exposure region 22a located on the outer periphery of exposure region 21a and the high exposure region 22b located on the outer periphery of exposure region 21b. Figure 3(c) is an enlarged view of the c-c line portion of Figure 3(a). Figure 3(b) is a graph illustrating the exposure amount in the c-c line portion of Figure 3(a). Compared to the case where the high exposure regions overlap linearly, the resolution threshold T1 is higher when the high exposure regions overlap in a point-like manner. Therefore, it is possible to suppress the resolution of unintended patterns at the seams between patterns on the wafer.

[0036] For example, in Figure 4(a), in a plan view, the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12 is such that the corners are rounded and the corners are curved inward. Therefore, when stitching exposure is performed using two reflective masks, as illustrated in Figures 6(a) and 6(c), the overlap between the high exposure region 22a on the outer periphery of the exposure region 21a and the high exposure region 22b on the outer periphery of the exposure region 21b can be reduced on the wafer 20. Specifically, the high exposure region 22a on the outer periphery of the exposure region 21a and the high exposure region 22b on the outer periphery of the exposure region 21b overlap in a point-like manner, thus reducing the overlap between the high exposure region 22a on the outer periphery of the exposure region 21a and the high exposure region 22b on the outer periphery of the exposure region 21b. Figure 6(c) is an enlarged view of the section along the line c-c in Figure 6(a). Figure 6(b) is a graph illustrating the exposure amount at the c-c line in Figure 6(a). Compared to the case where high exposure areas overlap linearly, the resolution threshold T1 is higher when high exposure areas overlap as points. Therefore, it is possible to suppress the resolution of unintended patterns at the seams between patterns on the wafer.

[0037] For example, in Figure 5(a), in a plan view, the shape of the boundary 13 between the transfer pattern area 11 and the light-shielding area 12 is such that the corners are cut off by straight lines. Therefore, when stitching exposure is performed using two reflective masks, as illustrated in Figures 7(a) and 7(c), the overlap between the high exposure area 22a on the outer periphery of the exposure area 21a and the high exposure area 22b on the outer periphery of the exposure area 21b can be reduced on the wafer 20. Specifically, the high exposure area 22a on the outer periphery of the exposure area 21a and the high exposure area 22b on the outer periphery of the exposure area 21b overlap in a point-like manner, thus reducing the overlap between the high exposure area 22a on the outer periphery of the exposure area 21a and the high exposure area 22b on the outer periphery of the exposure area 21b. Figure 7(c) is an enlarged view of the c-c line portion of Figure 7(a). Figure 7(b) is a graph illustrating the exposure amount at the c-c line portion of Figure 7(a). Compared to cases where high-exposure regions overlap linearly, the resolution threshold T1 is higher when high-exposure regions overlap point-like. Therefore, it is possible to suppress the resolution of unintended patterns at the seams between patterns on a wafer.

[0038] In particular, as illustrated in Figure 1(a), in a plan view, the shape of the boundary 13 between the transfer pattern area 11 and the light-shielding area 12 is preferably a shape with rounded corners, and has an arc shape or elliptical arc shape with corners that protrude outward. This is because such a shape can be easily formed.

[0039] In a plan view, if the shape of the boundary between the transfer pattern area and the light-shielding area has rounded corners and the corners have an outward-projecting arc shape, the radius of curvature of the corners is not particularly limited.

[0040] As described above, in stitching exposure, as shown, for example, in FIGS. 2A and 2B, two reflective masks 1A and 1B are used to perform exposure on a wafer 20 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 each other. The overlap width M between the exposure region 21a and the exposure region 21b on the wafer 20 as exemplified in FIG. 2B can be converted to the overlap width L of the transfer pattern regions 11 in the reflective masks 1A and 1B as exemplified in FIG. 8A, according to the reduction ratio of the projection optical system. When NA is 0.55, the reduction ratio in the x-direction is 4 times and the reduction ratio in the y-direction is 8 times in the projection optical system. For example, when NA is 0.55 and the overlap width M between the exposure region 21a and the exposure region 21b on the wafer 20 is 10 nm, the overlap 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 overlap width M between the exposure region 21a and the exposure region 21b on the wafer 20, that is, the overlap 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 is appropriately selected.

[0041] When the overlap width between the transfer pattern region 11 of the reflective mask 1A and the transfer pattern region 11 of the reflective mask 1B is defined as 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 NA is 0.55 and the overlap width M between the exposure region 21a and the exposure region 21b on the wafer 20 is 10 nm, the overlap 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. In this case, R1 ≧ 0.5 × 80 = 40 is satisfied, 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. In the case of R1 = 0.5 × L in Figure 8(a), 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 overlap at a point. Also, in the case of R1 > 0.5 × L in Figure 8(c), 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 overlap at a point, and overlap at an angle compared to the case of R1 = 0.5 × L in Figure 8(a). In contrast, in the case of R1 < 0.5 × L in Figure 8(b), 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 partially overlap by a line, resulting in a linear overlap. As described above, in the reflective masks 1A and 1B, the reflectivity is high near the outer edge of the transfer pattern region 11. Therefore, by reducing the 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, the overlap between high-exposure regions located on the outer edge of the exposure region on the wafer can be reduced. Thus, by setting R1 ≥ 0.5 × L, the resolution of unintended patterns at the seams between patterns on the wafer can be further suppressed.

[0044] Furthermore, as illustrated in Figures 9 to 11, when the intersection point of the transfer pattern region 11 of the reflective mask 1A and the transfer pattern region 11 of the reflective mask 1B is denoted as p1, and the angle between the tangent line t1 at intersection point p1 of the transfer pattern region 11 of the reflective mask 1A and the tangent line t2 at intersection point p1 of the transfer pattern region 11 of the reflective mask 1B is denoted as the intersection angle θ1, the following equation (4-1) holds true for the radius of curvature R1 of the above angle, the overlap width L, and the intersection angle θ1. That is, the radius of curvature R1 of the above angle is expressed by the following equation (4-2). L / 2 = R1 × [1 - cos(θ1 / 2)] (4-1) R1 = L / {2 × [1 - cos(θ1 / 2)]} (4-2)

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

[0046] FIG. 9 shows a case where the intersection angle θ1 is 90°, FIG. 10 shows a case where the intersection angle θ1 is 60°, and FIG. 11 shows a 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. Although not shown in the drawings, 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(150° / 2)]}=L / {2×[1−cos75°]}≅0.7L. FIG. 12 shows the relationship between the coefficient α of the overlapping width L and the intersection angle θ1.

[0047] For simplicity, the above explanation assumes that the reduction ratio in the x-direction and the reduction ratio in the y-direction are equal. However, as mentioned above, an EUV exposure system with an NA of up to 0.55 has been developed, in which the reduction ratio in the x-direction is 4 times and the reduction ratio in the y-direction is 8 times in the projection optical system, meaning the reduction ratio in the y-direction is twice that of the reduction ratio in the x-direction. Therefore, the circular arc shape with a radius of curvature R1 and an intersection angle (θ1) of 90° on a reflective mask, as exemplified in Figure 13(a), becomes an elliptical arc shape on the wafer, as shown in Figure 13(b), where the width of the y-direction component is halved. As a result, compared to the case where the reduction ratios in the x-direction and y-direction are equal, when the reduction ratio in the y-direction is twice that of the reduction ratio in the x-direction, the slope of the arc is halved, and therefore the intersection angle also changes. In Figure 13(a), when θ2 is the angle of arc A, |tanθ2| represents the absolute value of the slope of arc A. When θ² = 0°, the slope of arc A is the slope along the y-axis and is 0. Also, when θ² = 90°, the slope of arc A is ∞. |tanθ²| also corresponds to the slope of arc B with the x-axis as the axis of symmetry. If the reduction ratio is different on the wafer, and the reduction ratio in the y-direction is twice the reduction ratio in the x-direction, the slope of the arc corresponds to 1 / 2, and is represented by |tanθ²| / 2. The angle of the arc on the wafer at that time can be found by arctan(|tanθ²| / 2). From this, 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 is 45° on the wafer, arctan(|tan63.4°| / 2) = 45°, and the arc angle θ2 on the mask is 63.4°.

[0048] Therefore, it can be seen that, with respect to the overlap width L, the radius of curvature R1 of the above-mentioned angle needs to be smaller compared to the case where the reduction ratio in the x and y directions is equal. The radius of curvature R1 of the above-mentioned angle when the arc angle θ2 on the mask is 63.4°, that is, the radius of curvature R1 of the above-mentioned angle where the intersection angle is 90° on the wafer, is R1 = L / {2 × [1 - cos 63.4°]} ≈ 0.9L with respect to the overlap width L.

[0049] Similarly, calculating, the radius of curvature R1 for the above angle where the intersection angle on the wafer is 60° is R1 ≈ 0.69L. The radius of curvature R1 for the above angle where the intersection angle on the wafer is 120° is R1 ≈ 1.45L. The radius of curvature R1 for the above angle where the intersection angle on the wafer is 30° is R1 ≈ 0.58L. The radius of curvature R1 for the above angle 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] As illustrated in Figures 3(a) and 3(c), in wafer 20, the high exposure region 22a located on the outer periphery of exposure region 21a and the high exposure region 22b located on the outer periphery of exposure region 21b partially overlap. Referring to Figures 13(a) and 13(b), when the intersection angle on the wafer is 90°, the intersection area where the high exposure regions 22a and 22b overlap 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°. This is because it is possible to reduce the intersection area where the high exposure regions 22a and 22b overlap on the wafer 20.

[0052] From the above calculations, the radius of curvature R1 of the above-mentioned angle where the intersection angle on the wafer is 90° is R1 ≈ 0.9L. Furthermore, the range of the radius of curvature R1 of the above-mentioned angle where the intersection angle on the wafer is 90±30° is 0.69L ≤ R1 ≤ 1.45L. Furthermore, the range of the radius of curvature R1 of the above-mentioned angle where the intersection angle on the wafer is 90±60° is 0.58L ≤ R1 ≤ 4.22L. Therefore, from the preferred range of intersection angles on the wafer, the radius of curvature R1 of the above-mentioned angle preferably satisfies the following equation (1), more preferably satisfies the following equation (1-2), and even more preferably satisfies the following equation (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 corners described above varies depending on the overlap width L, which is a value appropriately selected as described above. For example, when the overlap width L is set to 80 nm to 1200 nm, the radius of curvature R1 of the corners may be, for example, 50 nm to 5000 nm, 60 nm to 1700 nm, or 80 nm to 1000 nm. By setting the radius of curvature of the corners to a predetermined value or higher, it is possible to sufficiently suppress the resolution of unintended patterns at the joints between patterns on the wafer as described above. On the other hand, by setting the radius of curvature of the corners to a predetermined value or lower, it is possible to prevent the transfer pattern area from becoming excessively narrow.

[0054] Conversely, taking into account the deformation of the shape due to the difference in magnification, the reflective mask may be designed so that the shape of the corners on the wafer becomes an arc shape.

[0055] In the above case, the shape of the corner at the boundary between the transfer pattern region and the light-shielding region in the reflective mask is an elliptical arc shape where the ratio of the major axis radius a1 to the minor axis radius b1, a1 / b1, is 1. In the projection optical system, the reduction ratio in the x direction is 4 times, and the reduction ratio in the y direction is 8 times. Since the reduction ratio in the y direction is twice that of the reduction ratio in the x direction, the major axis side is the y direction and the minor axis side is the x direction. In the relationship between the overlap width M of the exposure region 21a and the exposure region 21b on the wafer 20 and the overlap width L of the transfer pattern region 11 of the reflective mask 1A and the transfer pattern region 11 of the reflective mask 1B, it is sufficient to set L = 8M on the major axis side and L = 4M on the minor axis side. If the shape of the above-mentioned corner becomes an arc shape when it is reduced in the x and y directions on the wafer, then the radius of curvature R1 of the arc shape described above is replaced with the major axis radius a1 of the elliptical arc shape, and the range of the major axis radius a1 of the elliptical arc shape 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, if the shape of the above-mentioned corner in the reflective mask is an elliptical arc shape, then the shape of the above-mentioned corner becomes an arc shape on the wafer, so the same derivation method as when the shape of the above-mentioned corner is an arc shape can be applied to the specific derivation method. Therefore, from the preferred range of intersection angles on the wafer, the major axis radius a1 of the above-mentioned corner preferably satisfies the following equation (2), more preferably satisfies the following equation (2-2), and even more preferably satisfies the following equation (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 described above varies depending on the overlap width L, which is a value appropriately selected as described above. For example, when the overlap width L is set to 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 setting the major axis radius a1 of the corner to a predetermined value or higher, it is possible to sufficiently suppress the resolution of unintended patterns at the seams between patterns on the wafer as described above. On the other hand, by setting the major axis radius a1 of the corner to a predetermined value or lower, it is possible to prevent the transfer pattern area from becoming excessively narrow.

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

[0058] Furthermore, in a plan view, if the shape of the boundary between the transfer pattern area and the light-shielding area has rounded corners and is an arc shape with the corners recessed inward, the radius of curvature of the corner is not particularly limited. The radius of curvature of the corner can be considered in the same way as the radius of curvature of the corner when the shape of the boundary between the transfer pattern area and the light-shielding area has rounded corners and is an arc shape with the corners protruding outward.

[0059] Furthermore, in a plan view, if the shape of the boundary between the transfer pattern area and the light-shielding area is such that the corners are cut off by straight lines, for example, as shown in Figure 15(a), the corners may be cut off by a single straight line, or as shown in Figures 15(b) and 15(c), the corners may be cut off by multiple straight lines.

[0060] In a plan view, if the shape of the boundary between the transfer pattern area and the light-shielding area is such that the corners are cut off by straight lines, then, for example as shown in Figures 15(a) to 15(c), the angle θ11 between the main side 13a and the hypotenuse 13c of the boundary 13 between the transfer pattern area 11 and the light-shielding area 12 is not particularly limited, and is, for example, 30° or more and 60° or less. Also, the angle θ12 between the main side 13b and the hypotenuse 13d of the boundary 13 between the transfer pattern area 11 and the light-shielding area 12 is not particularly limited, and is, for example, 30° or more and 60° or less.

[0061] In a plan view, if the shape of the boundary between the transfer pattern area and the light-shielding area is such that the corners are cut off by straight lines, then, for example as shown in Figures 15(a) to 15(c), the distance c1 from the intersection of the main side 13a and the hypotenuse 13c of the boundary 13 between the transfer pattern area 11 and the light-shielding area 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 hypotenuse 13c or 13d of the boundary 13 between the transfer pattern area 11 and the light-shielding area 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] In a plan view, if the shape of the boundary 13 between the transfer pattern area 11 and the light-shielding area 12 is a roughly rectangular shape with rounded corners, the four angles θ11 may be the same or different. Similarly, the four angles θ12 may be the same or different. Also, the four distances c1 may be the same or different. Similarly, the four distances c2 may be the same or different.

[0063] Furthermore, in a plan view, if the shape of the boundary 13 between the transfer pattern area 11 and the light-shielding area 12 is a roughly rectangular shape with rounded corners, then of the four corners, at least two corners in the overlapping portions of the transfer pattern areas 11 in the reflective masks 1A and 1B during stitching exposure should have a rounded shape. Therefore, in the above case, of the four corners, the two corners in the non-overlapping portions of the transfer pattern areas 11 in the reflective masks 1A and 1B during stitching exposure may or may not have a rounded shape. In particular, it is preferable that all four corners have a rounded shape.

[0064] Furthermore, as illustrated in Figures 1(a) and 1(b), the reflective mask 1 has a non-transfer pattern region 14 arranged on the outer periphery of the light-shielding region 12. In a 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 it is preferable that it has rounded corners. Even at the edges of the non-transfer pattern region 14, if exposure light is incident from an oblique angle, the EUV light reflected by the multilayer film 3 may not be attenuated by the absorption layer 5, and leakage light may occur on the light-shielding region 12 side. Therefore, similar to the shape of the boundary 13 between the transfer pattern region 11 and the light-shielding region 12, if the shape of the boundary 15 between the light-shielding region 12 and the non-transfer pattern region 14 has rounded corners, it is possible to suppress the resolution of unintended patterns at the joints 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 area and the light-shielding area, and the shape of the boundary between the light-shielding area and the non-transfer pattern area, both have rounded corners, and that the corners have an outward-projecting arc shape or an elliptical arc shape. This is because such shapes can be easily formed.

[0068] As illustrated in Figure 1(a), if both the shape of the boundary 13 between the transfer pattern area 11 and the light-shielding area 12, and the shape of the boundary 15 between the light-shielding area 12 and the non-transfer pattern area 14, have rounded corners and have arc shapes with corners that protrude outward, then the radius of curvature R1 of the corner in the shape of the boundary 13 between the transfer pattern area 11 and the light-shielding area 12, and the radius of curvature R2 of the corner in the shape of the boundary 15 between the light-shielding area 12 and the non-transfer pattern area 14, may be the same or different. In particular, it is preferable that the radius of curvature R1 of the corner is less than or equal to the radius of curvature R2 of the corner, and more preferably less than the radius of curvature R2 of the corner.

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

[0070] Therefore, if 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 furthermore less than the radius of curvature R2 of the above-mentioned corner, it is considered that the resolution of unintended patterns at the joints between patterns on the wafer can be further suppressed.

[0071] Furthermore, if both 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, have rounded corners and have an elliptical arc shape with 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 less than or equal to 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 less 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, if the shape of the corners in the reflective mask is an elliptical arc shape, the shape of the corners on the wafer will be a circular arc shape, and similarly to the above, it is considered that the resolution of unintended patterns at the seams between patterns on the wafer can be further suppressed.

[0072] 2. Light-shielding region In this disclosure, the light-shielding region is the region where the substrate is exposed and there are no multilayer films or absorption layers. In a reflective mask, if a protective layer or buffer layer is placed between the multilayer film and the absorption layer, the light-shielding region will be the region where there are no protective layers or buffer layers.

[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 is set to an amount that does not contribute to resolution when exposure is performed using a step-and-repeat method with the reflective mask of this disclosure. Specifically, the reflectance is preferably 0.5% or less.

[0074] The light-shielding region may be located on the outer periphery of the transfer pattern region. The light-shielding region may be located on a part of the outer periphery of the transfer pattern region, or it may be located 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 located on the entire outer periphery of the transfer pattern region.

[0075] The shape of the light-shielding area can be any shape that allows it to be positioned around the outer edge of the transfer pattern area, but it is usually frame-shaped.

[0076] The dimensions of the light-shielding area are not particularly limited as long as they prevent the occurrence of defective patterns in the multiple exposure area, and can be appropriately adjusted based on the dimensions of the reflective mask, the dimensions of the exposure area when performing step-and-repeat exposure using the reflective mask described herein, etc.

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

[0078] As materials for the multilayer film, those commonly used for multilayer films in reflective masks can be used. Among these, materials with extremely high reflectivity to EUV light are preferred, as they can enhance contrast when using a reflective mask. For example, a Mo / Si periodic multilayer film is typically used as a multilayer film that reflects EUV light. In addition, as multilayer films that can obtain high reflectivity in a specific wavelength range, for example, a Ru / Si periodic multilayer film, a Mo compound / Si compound periodic multilayer film, a Si / Nb periodic multilayer film, a Si / Mo / Ru periodic multilayer film, a Si / Mo / Ru periodic multilayer film, a Si / Ru / Mo / Ru periodic multilayer film can also be used.

[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 as appropriate. For example, as a Mo / Si periodic multilayer film, a multilayer film can be used in which 40 to 60 layers each of Mo and Si films, each with a thickness of a few nanometers, are stacked.

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

[0081] 4. Absorption Layer The absorption layer in this disclosure is arranged in a pattern on the surface of the multilayer film opposite to the substrate and absorbs EUV light in EUV lithography using a reflective mask in this disclosure.

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

[0083] Methods for forming the absorption layer include, for example, magnetron sputtering, ion beam sputtering, CVD, and vapor deposition. Typically, photolithography and electron beam lithography are used to form the absorption layer in a patterned manner. Specifically, an absorption layer is formed on a substrate with a multilayer film, a resist layer is formed on this absorption layer, the resist layer is patterned, the absorption layer is etched using the resist pattern as a mask, and the remaining resist pattern is removed to form the absorption layer in a patterned manner. General methods can be used for photolithography and electron beam lithography.

[0084] 5. Protective Layer In this disclosure, a protective layer may be placed 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 Mo film, the presence of a protective layer can suppress oxidation of the Si film or Mo film. If the Si film or Mo film is oxidized, the reflectivity of the multilayer film may decrease. When the buffer layer described later is placed on the side of the multilayer film opposite to the substrate, the protective layer and the buffer layer are usually placed in that order on the side of the multilayer film opposite to the substrate.

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

[0086] Furthermore, the thickness of the protective layer is, for example, between 2 nm and 15 nm. Methods for depositing the protective layer include sputtering.

[0087] 6. Buffer Layer In this disclosure, a buffer layer may be placed between the multilayer film and the absorption layer. The buffer layer is provided to suppress damage to the underlying multilayer film. The presence of the buffer layer makes it possible to suppress damage to the underlying multilayer film when the absorption layer is pattern-etched by methods such as dry etching.

[0088] The buffer layer material should have high etching resistance, and typically, a material with different etching properties from the absorption layer, i.e., a material with a high etching selectivity ratio with the absorption layer, is used. The etching selectivity ratio of the buffer layer and the absorption layer is preferably 5 or higher, more preferably 10 or higher, and even more preferably 20 or higher. Furthermore, the buffer layer material is preferably low-stress and has excellent smoothness. 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 viewpoint, the buffer layer material is preferably microcrystalline or amorphous. Examples of such buffer layer materials include SiO ２ Al ２ O ３ Examples include Cr and CrN.

[0089] Furthermore, the thickness of the buffer layer is, for example, between 2 nm and 25 nm.

[0090] Examples of methods for depositing the buffer layer include magnetron sputtering and ion beam sputtering. When using Cr, it is preferable to deposit Cr on the multilayer film using RF magnetron sputtering with a Cr target in an Ar gas atmosphere.

[0091] If the buffer layer is located on the side opposite to the substrate of the multilayer film, the exposed buffer layer may be peeled off after patterning the absorption layer. General buffer layer peeling methods can be used, such as dry etching.

[0092] 7. Low-reflection layer In this disclosure, a low-reflection layer may be arranged on the side opposite to the multilayer film of the absorption layer. The low-reflection layer is provided to increase the detection sensitivity during mask pattern inspection.

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

[0094] 8. Substrates The substrates used in this disclosure can be those generally used for reflective masks, and for example, glass substrates are preferably used. Glass substrates are particularly suitable as substrates for reflective masks because they provide good smoothness and flatness. Examples of glass substrate materials include quartz glass and amorphous glass with a low coefficient of thermal expansion (e.g., SiO2). ２ -TiO ２ Examples include crystallized glass with precipitated β-quartz solid solutions (such as glass systems). Metal substrates such as silicon and Fe-Ni Invar alloys can also be used.

[0095] To obtain high reflectivity and transfer accuracy for reflective masks, 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, in order to obtain high reflectivity and transfer accuracy of the reflective mask, the flatness of the substrate is preferably 100 nm or less. Flatness is a value that indicates the surface warp (amount of deformation) as shown by TIR (Total Indicator Reading). This value is the absolute value of the height difference between the highest point on the substrate surface above the focal plane and the lowest point below the focal plane, when the focal plane is defined by the least squares method based on the substrate surface. The flatness is the flatness in a 142 mm square area. Flatness is measured using an oblique incidence interferometer. For example, the "UltraFlat" manufactured by Tropel can be used as an oblique incidence interferometer.

[0097] 9. Conductive Film In this disclosure, the conductive film may be arranged on the side of the substrate opposite to the multilayer film. The conductive film is provided to attract the reflective mask in this disclosure to the electrostatic chuck of the exposure apparatus. Having such a conductive film makes it possible to easily and firmly fix the reflective mask to the exposure apparatus 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 in reflective masks. For example, metals or metal compounds such as Cr and CrN that exhibit conductivity can be used.

[0099] Furthermore, the thickness of the conductive film is, for example, between 30 nm and 150 nm.

[0100] Methods for depositing conductive films include sputtering. Furthermore, when forming conductive films in a patterned manner, methods such as sputtering via a mask, photolithography, and electron beam lithography can be used.

[0101] 10. Applications The reflective masks in this disclosure are preferably used as reflective masks for lithography using EUV as the exposure light.

[0102] 11. Method for Manufacturing a Reflective Mask The method for manufacturing a reflective mask according to this disclosure includes, for example, a preparation step of preparing a mask blank having a substrate, a multilayer film, and an absorption layer in that order; an absorption layer patterning step of patterning the absorption layer; and a light-shielding region formation step of forming a light-shielding region on the outer periphery of a transfer pattern region having the pattern of the absorption layer, in which the multilayer film and the absorption layer are removed and the substrate is exposed.

[0103] Figures 17(a) to 17(c) are process diagrams showing an example of a method for manufacturing a reflective mask according to this disclosure. First, as shown in Figure 17(a), a mask blank 20 is prepared by sequentially laminating a multilayer film 3, a protective layer 4, and an absorption layer 5 on a substrate 2 (mask blank preparation step). Next, as shown in Figure 17(b), the absorption layer 5 is patterned to form a transfer pattern region 11 having the pattern of the absorption layer 5 (absorption layer patterning step). This yields a reflective mask intermediate 30 having a substrate 2, a multilayer film 3 formed on the substrate 2, a protective layer 4 formed on the multilayer film 3, and a pattern of the absorption layer 5 formed on the protective layer 4, and having a transfer pattern region 11 having the pattern of the absorption layer 5. Next, as shown in Figure 17(c), the absorption layer 5, protective layer 4, and multilayer film 3 on the outer periphery of the transfer pattern region 11 are removed to form a light-shielding region 12 where the substrate 2 is exposed (light-shielding region formation step). In this way, a reflective mask 1 having a light-shielding region 12 is obtained.

[0104] Each step in the method for manufacturing a reflective mask as described in this disclosure will be explained.

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

[0106] (2) Absorption layer patterning process The method for patterning the absorption layer has been described in the section on absorption layers above, so the explanation will be omitted here.

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

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

[0109] In the semiconductor device manufacturing method described herein, stitching exposure is performed using the reflective mask described above, which makes it possible to suppress overexposure at the joints between patterns on the semiconductor substrate and to achieve high-precision pattern transfer. In particular, when the absorption layer recedes by etching during the formation of the light-shielding region, and the multilayer film is exposed at the edges of the transfer pattern region, the resolution of unintended patterns can be effectively suppressed.

[0110] Reflective masks are described in detail in section "A. Reflective Masks" above, so we will omit the explanation here.

[0111] In a reflective mask, it is preferable that the shape of the corner at the boundary between the transfer pattern region and the light-shielding region in a plan view is an arc shape, and that the radius of curvature R1 of the arc shape satisfies the following equation (1): 0.58L ≤ R1 ≤ 4.22L (1) (In equation (1) above, L represents the overlap width between the transfer pattern region during the first exposure and the transfer pattern region during the second exposure. L is shown as L = 8M. M represents the overlap width between the exposure region during the first exposure and the exposure region during the second exposure on the semiconductor substrate.)

[0112] Furthermore, it is preferable that the reflective mask, in a plan view, has an elliptical arc shape at the boundary between the transfer pattern area and the light-shielding area, with a ratio a1 / b1 of the major axis radius a1 to the minor axis radius b1 of the elliptical arc shape being 2, and the major axis radius a1 of the elliptical arc shape being designed to satisfy the following equation (2): 0.7L ≤ a1 ≤ 14.7L (2) (In the above equation (2), L represents the overlap width where the transfer pattern area during the first exposure and the transfer pattern area during the second exposure overlap each other. L is shown as L = 8M. M represents the overlap width where the exposure area during the first exposure and the exposure area during the second exposure overlap each other.)

[0113] As the above equations (1) and (2) are described in the section "A. Reflective Mask 1. Shape of the Boundary Between the Transfer Pattern Area and the Light-Shielding Area" above, their explanation is omitted here.

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

[0115] This disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of this disclosure and achieves similar effects is included within the technical scope of this disclosure.

[0116] This disclosure provides the following inventions: [1] A reflective mask having a substrate, a multilayer film disposed on one side of the substrate, and a pattern of an absorption layer disposed on the side of the multilayer film opposite to the substrate, wherein the reflective mask has a transfer pattern region having the pattern of the absorption layer and a light-shielding region disposed on the outer periphery of the transfer pattern region, which does not have the multilayer film or the absorption layer and exposes the substrate, and in a plan view, the shape of the boundary between the transfer pattern region and the light-shielding region is rounded. [2] A reflective mask having a substrate, a multilayer film disposed on one side of the substrate, and a pattern of an absorption layer disposed on the side of the multilayer film opposite to the substrate, wherein the reflective mask has a transfer pattern region having the pattern of the absorption layer and a light-shielding region disposed on the outer periphery of the transfer pattern region to suppress reflected light from the outer periphery of the transfer pattern region, and in a plan view, the shape of the boundary between the transfer pattern region and the light-shielding region is rounded. [3] The reflective mask according to [1] or [2], wherein in a plan view, the shape of the boundary between the transfer pattern area and the light-shielding area has rounded corners. [4] The reflective mask according to any one of [1] to [3], wherein in a plan view, the shape of the boundary between the transfer pattern area and the light-shielding area is a substantially rectangular shape with rounded corners. [5] The reflective mask according to any one of [1] to [4], wherein the substrate has a conductive film on the side opposite to the multilayer film. [6] The reflective mask according to any one of [1] to [5], further comprising a non-transfer pattern area arranged on the outer periphery of the light-shielding area, wherein the radius of curvature R1 of the corners in the shape of the boundary between the transfer pattern area and the light-shielding area is less than or equal to the radius of curvature R2 of the corners in the shape of the boundary between the light-shielding area and the non-transfer pattern area. [7] The reflective mask according to any one of [1] to [6], wherein the shape of the corner in the shape 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 of the major axis radius a1 to the minor axis radius b1 of the elliptical arc shape a1 / b1 is 2.[8] A method for manufacturing a semiconductor device, comprising the step of performing stitching exposure using a reflective mask described in any of [1] to [7] to form a pattern on a semiconductor substrate, wherein in the reflective mask, in a plan view, the shape of the corner at the boundary between the transfer pattern region and the light-shielding region 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 at which the transfer pattern region during the first exposure and the transfer pattern region during the second exposure overlap each other. L is shown as L = 8M. M represents the overlap width at which the exposure region during the first exposure and the exposure region during the second exposure overlap each other.) [9] A method for manufacturing a semiconductor device, comprising the step of performing stitching exposure using a reflective mask described in any of [1] to [7] to form a pattern on a semiconductor substrate, wherein in the reflective mask, in a plan view, the shape of the corner in the shape of the boundary between the transfer pattern region and the light-shielding region 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 equation (2) above, L represents the overlap width between the transfer pattern region during the first exposure and the transfer pattern region during the second exposure. L is given by L = 8M. M represents the overlap width between the exposure region during the first exposure and the exposure region during the second exposure.)

[0117] 1...Reflective mask 2...Substrate 3...Multilayer film 4...Protective layer 5...Absorption layer 6...Conductive film 11...Transfer pattern area 12...Light-shielding area 13...Boundary between transfer pattern area and light-shielding area 14...Non-transfer pattern area 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 side of the substrate, and a pattern of an absorption layer disposed on the side of the multilayer film opposite to the substrate, wherein the reflective mask has a transfer pattern region having the pattern of the absorption layer and a light-shielding region disposed on the outer 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 plan view, the shape of the boundary between the transfer pattern region and the light-shielding region is rounded.

2. A reflective mask having a substrate, a multilayer film disposed on one side of the substrate, and a pattern of an absorption layer disposed on the side of the multilayer film opposite to the substrate, wherein the reflective mask has a transfer pattern region having the pattern of the absorption layer and a light-shielding region disposed on the outer periphery of the transfer pattern region to suppress reflected light from the outer periphery of the transfer pattern region, and in a plan view, the shape of the boundary between the transfer pattern region and the light-shielding region is rounded.

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

4. The reflective mask according to claim 1 or 2, wherein, in a plan view, the shape of the boundary between the transfer pattern area and the light-shielding area is a substantially rectangular shape with rounded corners.

5. The reflective mask according to claim 1 or claim 2, wherein the substrate has a conductive film on the side opposite to the multilayer film.

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

7. The reflective mask according to claim 1 or claim 2, wherein the shape of the corner in 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 of the major axis radius a1 to the minor axis radius b1 of the elliptical arc shape a1 / b1 is 2.

8. A method for manufacturing a semiconductor device, comprising the step of performing stitching exposure using a reflective mask according to any one of claims 1 to 7 to form a pattern on a semiconductor substrate, wherein, in a plan view, the shape of the corner at the boundary between the transfer pattern region and the light-shielding region of the reflective mask 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 between the transfer pattern region during the first exposure and the transfer pattern region during the second exposure. L is shown as L = 8M. M represents the overlap width between the exposure region during the first exposure and the exposure region during the second exposure on the semiconductor substrate.) 9. A method for manufacturing a semiconductor device, comprising the step of performing stitching exposure using a reflective mask according to any one of claims 1 to 7 to form a pattern on a semiconductor substrate, wherein in the reflective mask, in a plan view, the shape of the corner at the boundary between the transfer pattern region and the light-shielding region 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 between the transfer pattern region during the first exposure and the transfer pattern region during the second exposure. L is shown as L = 8M. M represents the overlap width between the exposure region during the first exposure and the exposure region during the second exposure on the semiconductor substrate.

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