Method of overlay measurement

Abstract

A method for measuring the stacking of a semiconductor structure includes several steps. A semiconductor structure having a front layer and a current layer is provided, wherein the front layer includes a first stacking mark having a first grating group and a second grating group, and the current layer includes a second stacking mark. A semiconductor fabrication process is performed on the semiconductor structure. A detection beam is emitted toward the first stacking mark. A first light intensity distribution of the first grating group and a second light intensity distribution of the second grating group relative to a reference point of the second stacking mark are received.

Description

Technical Field

[0001] This disclosure relates to semiconductor structures and methods for measuring the stacking of semiconductor structures. Prior Technology

[0002] Determining the stacking relationship between multiple semiconductor layers forming a structure is an important issue. For example, two stacking marks can be formed on two different semiconductor layers, and the alignment between the two semiconductor layers can be determined by the alignment relationship of the two stacking marks. However, if either of the two stacking marks is damaged, the stacking alignment measurement of the two semiconductor layers will fail, and it is difficult to determine whether either of the two stacking marks has been damaged after the semiconductor structure is formed. Summary of the Invention

[0003] This disclosure relates to a method for superimposed measurement.

[0004] According to one or more embodiments of this disclosure, the overlay measurement method includes several steps. A detection beam is emitted toward a first overlay mark on a preceding layer, wherein the first overlay mark includes a first grating group and a second grating group on the surface of the preceding layer. A reference point is determined for a second overlay mark on a current layer above the preceding layer. A first light intensity distribution of the first grating group relative to the reference point of the second overlay mark is received, and a second light intensity distribution of the second grating group relative to the reference point is received. A first offset of the first grating group relative to the reference point is obtained based on the first light intensity distribution. A second offset of the second grating group relative to the reference point is obtained based on the second light intensity distribution. A positional offset between the first and second overlay marks is determined based on the first and second offsets.

[0005] In one or more embodiments disclosed herein, the position offset is a first weight multiplied by a first offset plus a second weight multiplied by a second offset.

[0006] In one or more embodiments disclosed herein, obtaining the first offset includes selecting a first central region of a first light intensity distribution and determining a first center point, wherein the first center point is determined based on the average light intensity of the first central region, and the first offset is the distance between a reference point and the first center point.

[0007] In some implementations, the first center point is the location where the first light intensity distribution reaches an extreme value.

[0008] In one or more embodiments disclosed herein, each of the first grating group and the second grating group includes a plurality of gratings extending in a first direction and arranged in a second direction perpendicular to the first direction, and the number of gratings in the first grating group is different from the number of gratings in the second grating group.

[0009] In some embodiments, the first grating group and the second grating group are arranged in a first direction, and in a second direction, the first density of the gratings in the first grating group is less than the second density of the gratings in the second grating group, and the first average light intensity of the first light intensity distribution is greater than the second average light intensity of the second light intensity distribution.

[0010] In one or more embodiments disclosed herein, the first stacking mark further includes a third grating group. The stacking measurement method further includes receiving a third light intensity distribution of the third grating group relative to a reference point of the second stacking mark.

[0011] In some embodiments, each of the first grating group, the second grating group, and the third grating group includes a plurality of gratings extending in a first direction and arranged in a second direction perpendicular to the first direction, wherein the number of gratings in the first grating group, the number of gratings in the second grating group, and the number of gratings in the third grating group are different from each other.

[0012] In some embodiments, the first density of the gratings in the first grating group is less than the second density of the gratings in the second grating group in the second direction, the first density is less than the third density of the gratings in the third grating group in the second direction, and the first grating group, the second grating group and the third grating group are arranged sequentially in the first direction.

[0013] In one or more embodiments disclosed herein, each of the first light intensity distribution and the second light intensity distribution is a diffraction light intensity distribution.

[0014] In summary, for a semiconductor structure with a front layer and a current layer, multiple sets of grating groups can be formed in the front layer to prevent damage to these grating groups, which could lead to measurement failure. Different grating groups can be considered as different sub-grating groups in the front layer. By receiving multiple light intensity distributions from different grating groups in the front layer, it is possible to determine whether the front layer and the current layer are aligned.

[0015] It should be understood that the above general description and the following detailed description are merely examples intended to provide further explanation of the disclosed content for which protection is claimed. Simple Explanation of the Diagram

[0016] The advantages and illustrations disclosed herein should be better understood through the embodiments listed below and with reference to the accompanying drawings. These illustrations are merely illustrative of embodiments and should not be construed as limiting the scope of any particular embodiment or the invention as being limited to the scope of the patent application. Figure 1 illustrates a schematic top view of a semiconductor structure according to one or more embodiments of the present disclosure; Figure 2 illustrates a schematic perspective view of stacked overlapping markers according to one or more embodiments of this disclosure; Figures 3 through 5 show multiple cross-sectional views along multiple line segments in Figure 2; Figure 6 illustrates a schematic top view of stacked overlapping markers according to one or more embodiments of this disclosure; Figures 7 and 8 illustrate the different grating groups in Figure 6 and their corresponding light intensity distributions; Figure 9 illustrates a schematic top view of stacked overlapping markers according to one or more embodiments of this disclosure; Figures 10 and 11 illustrate the different grating groups in Figure 9 and their corresponding light intensity distributions; Figure 12 illustrates a schematic flowchart of a method for measuring the stacking of semiconductor structures according to one or more embodiments of this disclosure; Figure 13 illustrates a schematic top view of stacked overlapping markers according to one or more embodiments of this disclosure; and Figure 14 illustrates a schematic top view of a stack of overlapping markers according to one or more embodiments of this disclosure. Implementation

[0017] The following detailed description provides examples with reference to the accompanying drawings. However, the provided examples are not intended to limit the scope of this disclosure, and the description of the structural operation is not intended to limit the order of execution. Any structure resulting from the recombination of elements and producing a device with equivalent functionality is within the scope of this disclosure. Furthermore, the drawings are for illustrative purposes only and are not drawn to their original dimensions. For ease of understanding, the same or similar elements will be designated with the same symbols in the following description.

[0018] Furthermore, unless otherwise specified, the terms used throughout this specification and the claims generally have their ordinary meaning in the context of the art, the content of this disclosure, and specific content. Certain terms used to describe this disclosure will be discussed below or elsewhere in this specification to provide additional guidance to those skilled in the art in describing this disclosure.

[0019] In this document, terms such as "first," "second," etc., are used only to distinguish elements or methods of operation that have the same technical terminology, and are not intended to indicate order or limit this disclosure.

[0020] In addition, terms such as "contains," "includes," and "provides" are all open-ended restrictions in this article, meaning that they include but are not limited to.

[0021] Furthermore, in this document, unless otherwise specified in the text, "a" and "the" may refer to one or more. It will be further understood that the terms "comprising," "including," "having," and similar terms as used herein specify the features, regions, integers, steps, operations, elements, and / or components described herein, but do not exclude one or more other features, regions, integers, steps, operations, elements, components, and / or groups thereof described or additionally described herein.

[0022] Please refer to Figures 1 and 2. Figure 1 illustrates a schematic top view of a semiconductor structure 100 according to one or more embodiments of the present disclosure, wherein the semiconductor structure 100 includes a stack of superimposed markers MS on a local region LR. Figure 2 illustrates a schematic perspective view of a stack of superimposed markers MS1 according to one or more embodiments of the present disclosure, wherein the stack of superimposed markers MS1 is an embodiment of the superimposed marker stack of the present disclosure.

[0023] As shown in Figure 1, in this embodiment, a semiconductor structure 100 is formed on a semiconductor wafer. In this embodiment, a stack of superimposed markers MS is formed in a local region LR of the semiconductor structure 100. Figure 2 schematically illustrates the local region LR of the semiconductor structure 100, wherein the superimposed markers MS in Figure 1 corresponds to the superimposed markers MS1 shown in Figure 2. Other integrated circuits, components, or conductive structures may be formed in other regions outside the local region LR where the superimposed markers MS are located.

[0024] As shown in Figure 2, the semiconductor structure 100 includes a front layer 110 and a current layer 120. In one or more embodiments disclosed herein, the current layer 120 is located directly above the front layer 110.

[0025] In one or more embodiments, the front layer 110 and the current layer 120 may be semiconductor layers stacked on a wafer. For example, but not to limit this disclosure, the front layer 110 and the current layer 120 may include a dielectric layer, an intermediate layer, or a photoresist layer.

[0026] In this embodiment, the front layer 110 includes an overlay marker M1. As shown in Figure 2, in this embodiment, the overlay marker M1 includes a plurality of gratings 111 and gratings 112. The gratings 111 and gratings 112 extend along the y-direction. The gratings 111 are arranged along the x-direction to form a grating group 111g, as shown in Figure 3 below. The gratings 112 are arranged along the x-direction to form another grating group 112g, as shown in Figure 4 below.

[0027] As shown in Figure 2, in this embodiment, the number of gratings 111 is less than the number of gratings 112. In other words, the density of gratings 111 in the x-direction is less than the density of gratings 112 in the x-direction, where the densities of gratings 111 and gratings 112 can be regarded as the number of gratings 111 and the number of gratings 112 per unit length in the x-direction, respectively.

[0028] In this embodiment, the current layer 120 includes a stacking mark M2. As shown in Figure 2, the stacking mark M2 is separate from the stacking mark M1 in the direction z, which is perpendicular to both directions x and y. The stacking mark M2 includes a plurality of gratings 121 extending along the y direction and arranged along the x direction.

[0029] Please refer to Figures 3 through 5 for further explanation of the overlap marker M1 in the previous layer 110 and the overlap marker M2 in the current layer. Figures 3 through 5 are multiple cross-sectional views along multiple different line segments 3-3, 4-4, and 5-5 in Figure 2.

[0030] Please refer to Figures 2 and 3 (corresponding line segment 3-3). In this embodiment, multiple gratings 111 are located on the top surface 110T of the front layer 110 to form a grating group 111g. As shown in Figure 3, each grating 111 has the same width W1. The gratings 111 are arranged in the x-direction and separated from each other by a gap g11. In this embodiment, the multiple gratings 111 are arranged at equal intervals with a gap g11 between them.

[0031] Please refer to Figures 2 and 4 (corresponding line segment 4-4). In this embodiment, multiple gratings 112 are located on the top surface 110T of the front layer 110 to form a grating group 112g. As shown in Figure 4, each grating 112 has the same width W1. The gratings 112 are arranged in the x-direction and separated from each other by a gap g12. In this embodiment, the multiple gratings 112 are arranged at equal intervals with a gap g12.

[0032] As shown in Figures 3 and 4, in this embodiment, the length occupied by the arrangement of gratings 111 and gratings 112 in the x-direction is the same. Furthermore, in Figures 3 and 4, gratings 111 and gratings 112 have the same width W1, and the number of gratings 111 in grating group 111g is less than the number of gratings 112 in grating group 112g.

[0033] In this embodiment, the number of gratings 112 in grating group 112g is twice the number of gratings 111 in grating group 111g, and the gap g11 is twice the gap g12. In other words, the density of gratings 112 in grating group 112g is twice the density of gratings 111 in grating group 111g. Grating groups 111g and grating group 112g with different grating densities can produce different light intensity distributions.

[0034] Please refer to Figures 2 and 5 (corresponding line segment 5-5). In this embodiment, multiple gratings 121 are located on the top surface 120T of the current layer 120 to form a grating group 121g. As shown in Figure 5, each grating 121 has the same width W2 in the x-direction. In this embodiment, the width W2 is greater than the width W1. The gratings 121 are arranged in the x-direction, spaced apart from each other by a gap g2. In this embodiment, the gratings 121 are also equidistantly arranged.

[0035] In one or more embodiments disclosed herein, grating groups 111g, 112g, and 121g can be used to generate a diffracted light intensity distribution. For example, a detection beam can be emitted onto a stack of superimposed markers MS1 having superimposed markers M1 and / or M2. The grating groups 111g and 112g of superimposed markers M1 can diffract the detection beam to produce two different diffracted light intensity distributions in the x-direction. In some embodiments, the grating group 121g of superimposed markers M2 can diffract the detection beam to produce a diffracted light intensity distribution in the x-direction, and a reference point / reference line can be determined based on the diffracted light intensity distribution generated by the grating group 121g. By comparing the reference point / reference line of grating group 121g with the intensity distributions of two diffracted lights from grating groups 111g and 112g, the overlap alignment measurement of overlap markers M1 and M2 can be performed, thereby obtaining the positional offset between overlap markers M1 and M2. Please refer to the subsequent discussion for details.

[0036] Figure 6 illustrates a schematic top view of a stack of overlapping markers MS1 according to one or more embodiments of this disclosure, wherein the stack of overlapping markers MS1 shows an overlapping marker M1 in the front layer 110 and an overlapping marker M2 in the current layer 120 located above the front layer 110. It should be noted that the overlapping markers M1 and M2 have different heights in the z-direction.

[0037] As shown in Figure 6, the overlay mark M1 includes two grating groups, namely grating group 111g and grating group 112g, wherein the density of grating 112 in grating group 112g is twice the density of grating 111 in grating group 111g. In other words, grating group 111g and grating group 112g can be regarded as two sub-overlay marks of overlay mark M1. Grating group 111g can be regarded as the pre-iso mark in the previous layer 110. Grating group 112g can be regarded as the pre-dense mark in the previous layer 110. Through grating group 111g and grating group 112g, two independent overlay alignment relationships can be provided to reflect whether overlay mark M1 and overlay mark M2 are aligned.

[0038] As shown in Figure 6, a reference line OX is set. The reference line OX is set based on the overlay mark M2 in the current layer 120. Since the current layer 120 is formed on the previous layer 110, the reference line OX can be determined by capturing an image of the overlay mark M2 or by receiving the corresponding light intensity distribution signal diffracted from the overlay mark M2.

[0039] Figure 6 illustrates the standard overlap of overlap markers M1 and M2. Please refer to Figures 7 and 8 for the overlap alignment measurements between overlap markers M1 and M2. Figures 7 and 8 illustrate the different grating groups in Figure 6 and their corresponding light intensity distributions.

[0040] Figure 7 illustrates the grating assembly 111g and the corresponding light intensity distribution D1. In one or more embodiments, after the current layer 120 and the overlay mark M2 are formed, a measurement beam can be irradiated onto the overlay mark M1. The grating 111 in the grating assembly 111g can diffract the measurement beam to generate a diffracted light signal. The diffracted light signal generated by the grating assembly 111g can be received by a photosensor (not shown) to provide the light intensity distribution D1. The horizontal axis of the light intensity distribution D1 corresponds to the position X along the direction x. The vertical axis of the light intensity distribution D1 corresponds to the diffracted light intensity I(X) relative to the position X.

[0041] In Figure 7, the light intensity distribution D1 is a wave-like distribution, where the peak value of light intensity I(X) corresponds to the gap position between gratings 111 in the grating group 111g. Light intensity I(X) decreases at the positions corresponding to gratings 111. The reference line OX corresponds to the bottom point BP1 of light intensity I(X) in light intensity distribution D1, where BP1 is the extreme point of light intensity I(X) in light intensity distribution D1.

[0042] Similarly, Figure 8 illustrates the grating assembly 112g and the corresponding light intensity distribution D2. In one or more embodiments, after the current layer 120 and the overlay mark M2 are formed, a measurement beam can be irradiated toward the overlay mark M1, and the grating 112 in the grating assembly 112g can diffract the measurement beam to generate a diffracted light signal. The diffracted light signal generated by the grating assembly 112g can be received by a photosensor to provide the light intensity distribution D2. The horizontal axis of the light intensity distribution D2 corresponds to the position X along the direction x. The vertical axis of the light intensity distribution D2 corresponds to the diffracted light intensity I(X) at position X.

[0043] In Figure 8, the light intensity distribution D2 also resembles a fluctuating distribution, where the peak value of light intensity I(X) corresponds to the gap position between gratings 112 in the grating group 112g. Light intensity I(X) decreases at the position corresponding to grating 112. The reference line OX corresponds to the vertex TP1 of light intensity I(X) in light intensity distribution D2, where vertex TP1 is the extreme point of light intensity I(X) in light intensity distribution D2.

[0044] It should be noted that the reference line OX is determined by the reference point of the overlapping mark M2.

[0045] Please refer to Figures 7 and 8 simultaneously. The average light intensity of light intensity I(X) in light intensity distribution D1 is greater than the average light intensity I(X) in light intensity distribution D2. The average light intensities of light intensity distributions D1 and D2 are shown by the horizontal dashed lines in Figures 7 and 8; that is, the greater the density of gratings in the grating group, the smaller the average light intensity. By observing the average intensity, the light intensity distribution D1 generated by grating group 111g and the light intensity distribution D2 generated by grating group 112g can be easily identified.

[0046] Please refer to Figure 9. Figure 9 illustrates a schematic top view of the stacked pair markers MS1 according to one or more embodiments of this disclosure. In Figure 9, the semiconductor structure 100 undergoes further semiconductor processing. During the semiconductor processing, the stacked pair markers M1 are damaged.

[0047] As shown in Figure 9, grating 111 in grating group 111g is damaged. Some gratings 111 are shortened, and some are lengthened. It can be seen that the damage to gratings 111 near the edge of grating group 111g is most severe. Similarly, some gratings 112 in grating group 112g are damaged. However, on the left edge of grating group 112g, only a small number of gratings 112 are damaged and shortened.

[0048] In some embodiments, the semiconductor process performed on the front layer 110 or the current layer 120 of the semiconductor structure 100 may be a planarization process, a polishing process, or an etching process performed on the front layer 110 and / or the current layer 120. In some embodiments, semiconductor processes may be performed during the formation of the semiconductor structure 100. For example, a chemical mechanical planarization / polishing process may be performed on the current layer 120.

[0049] It should be noted that since the current layer 120 is directly located on the overlay mark M1, it is difficult to directly determine whether the overlay mark M1 is damaged. However, once the grating 111 of the grating group 111g or the grating 112 of the grating group 112g is damaged, the light intensity distribution corresponding to the grating group 111g and the grating group 112g will reflect the damage of the grating 111 and the grating 112.

[0050] Figures 10 and 11 illustrate the different grating groups in Figure 9 and the corresponding light intensity distributions.

[0051] Please refer to Figures 9 and 10. The light intensity distribution D1' represents the effect of the damaged grating group 111g on the diffracted light. Since grating 111 is located at the two edges of grating group 111g, when grating group 111g becomes shorter, the light intensity I(X) at the corresponding position on the edge of grating group 111g decreases.

[0052] As shown in Figure 10, a reference line OX can be provided based on the overlapping mark M2.

[0053] The selection region SR1 is the area selected near the reference line OX, where the selection region SR1 includes the waveform near the central extreme point. The central bottom point BP2 can be the extreme point of the light intensity I(X) in the light intensity distribution D1 immediately adjacent to the reference line OX. In Figure 10, the bottom point BP2 of the light intensity I(X) is determined by selecting the selection region SR1 in the light intensity distribution D1'. From another perspective, the selection region SR1 is determined based on the average light intensity near the bottom point BP2. By selecting the selection region SR1, the peak values ​​of the light intensity I(X) in the selection region SR1 have similar magnitudes, and the reduced light intensity corresponding to the damaged grating 111 can be ignored. Thus, the offset d1 can be obtained based on the positional difference between the reference line OX and the bottom point BP2.

[0054] Please refer to Figures 9 and 11. The light intensity distribution D2' represents the effect of the damaged grating group 112g on the diffracted light. Since the grating 112 located at the left edge of the grating group 112g is shortened, the light intensity I(X) at the position corresponding to the left edge of the grating group 112g decreases.

[0055] As shown in Figure 11, the reference line OX can be provided based on the overlapping marker M2. Vertex TP2 is the extreme point of light intensity I(X) immediately adjacent to the reference line OX. The selected region SR2 is the region selected near the reference line OX and vertex TP2 based on the average light intensity near the central vertex TP2. Light intensity I(X) is the waveform in the selected region SR2. By selecting the selected region SR2 from the light intensity I(X) of the light intensity distribution D2', the offset d2 can be obtained based on the positional difference between the reference line OX and the central vertex TP2 of the selected region SR2. Vertex TP2 is the extreme point of light intensity I(X) in the selected region SR2 of the light intensity distribution D2'.

[0056] Based on the offset d1 provided by light intensity distribution D1' and the offset d2 provided by light intensity distribution D2', the alignment relationship between overlapping marker M1 and overlapping marker M2 in direction x can be determined. In some embodiments, the offset between overlapping marker M1 and overlapping marker M2 can be defined by a combination of offset d1 and offset d2, wherein offset d1 and offset d2 are obtained from the selected region SR2 of light intensity distribution D2' within the selected region SR1 of light intensity distribution D1'.

[0057] Please refer to Figure 12 to illustrate the overlay alignment measurement using overlay mark M1 and overlay mark M2 as a whole, which have two grating groups 111g and 112g, respectively, where grating group 111g and grating group 112g can be considered as the sparse mark and dense mark of the front layer 110 separated by overlay mark M1.

[0058] Figure 12 illustrates a schematic flowchart of a semiconductor structure stacking measurement method 300 according to one or more embodiments of the present disclosure.

[0059] Please refer to Figures 1 and 2. In process 301, a semiconductor structure 100 including a front layer 110 and a current layer 120 is formed, wherein the front layer 110 has a first stacking mark M1 and the current layer 120 has a second stacking mark M2. The first stacking mark M1 and the second stacking mark M2 form a stacking mark stack MS1 as shown in Figure 6.

[0060] In process 302, a semiconductor process is performed on the semiconductor structure 100. In some embodiments, the semiconductor process performed on the front layer 110 or the current layer 120 of the semiconductor structure 100 may be a planarization process, a polishing process, or an etching process on the front layer 110 or the current layer 120. As shown in Figure 9, this may cause damage to portions of the gratings 111 and 112 in the overlay mark M1.

[0061] In some implementations, process 302 can be performed during process 301. For example, semiconductor processing can be performed on the front layer 110 before the current layer 120 is formed on the front layer 110.

[0062] In process 303, a reference point for the second stack pair marker M2 is set. As shown in Figures 10 and 11, a reference line OX corresponding to the reference point for the second stack pair marker M2 is provided.

[0063] In process 304, a detection beam is emitted to the first stacked pair marker M1. Subsequently, as shown in Figures 10 and 11, in process 305, a first light intensity distribution D1' and a second light intensity distribution D2' relative to a reference point in the first direction x are received, wherein the first light intensity distribution D1' corresponds to the first grating group 111g damaged by the first stacked pair marker M1, and the second light intensity distribution D2' corresponds to the second grating group 112g damaged by the first stacked pair marker M1.

[0064] In some implementations, processes 303 and 304 can be performed simultaneously. For example, after the measurement beam illuminates the stack of stacked markers MS1, the diffraction intensity distribution of the stacked markers M2 can also be obtained. Subsequently, the reference point corresponding to the position of the reference line OX in the x-direction can be obtained through the diffraction intensity distribution of the stacked markers M2.

[0065] As shown in Figures 10 and 11, in process 306, a first offset d1 relative to the reference point in the first direction x is obtained based on the first light intensity distribution D1', and a second offset d2 relative to the reference point in the first direction x is obtained based on the second light intensity distribution D2'. In Figure 10, the offset d1 is the distance between the reference line OX and the bottom point BP2, where BP2 is an extreme point in the selected region SR1 of the first light intensity distribution D1'. In Figure 11, the offset d2 is the distance between the reference line OX and the vertex TP2, where TP2 is an extreme point in the selected region SR2 of the second light intensity distribution D2'.

[0066] Following step 306, in step 307, the offset of the first stacked pair marker M1 relative to the second stacked pair marker M2 in the first direction x is obtained based on the first offset d1 and the second offset d2. The offset is the positional difference between the first stacked pair marker M1 and the second stacked pair marker M2 in the first direction x. For example, but not excessively limiting this disclosure, in step 307, the offset of the first stacked pair marker M1 relative to the second stacked pair marker M2 can be a first weight value multiplied by the first offset d1 plus a second weight value multiplied by the second offset d2.

[0067] Figure 13 illustrates a schematic top view of a stack of overlapping markers MS2 according to one or more embodiments of this disclosure. The difference between the stack of overlapping markers MS1 in Figure 6 and the stack of overlapping markers MS2 in Figure 13 is that the stack of overlapping markers MS2 further includes additional stacks of overlapping markers, which additionally include two sets of stacks of overlapping markers MS1 as shown in Figure 6. In Figure 13, some stacks of overlapping markers MS2 include gratings extending in the x-direction and arranged in the y-direction. That is, the additional overlapping markers in the front layer 110 and the additional overlapping markers in the current layer 120 have multiple gratings extending in the x-direction and arranged in the y-direction. Thus, the positional difference in the y-direction between the front layer 110 and the current layer 120 can be determined through multiple processes similar to method 300.

[0068] Figure 14 illustrates a schematic top view of the stacked markers MS3 according to one or more embodiments of this disclosure. The difference between the stacked markers MS1 in Figure 6 and the stacked markers MS3 in Figure 14 is that the stacked markers MS1 in Figure 14 further include a grating group 113g. The grating group 113g includes a plurality of gratings 113 extending in the y-direction and arranged in the x-direction. Therefore, by illuminating the stacked markers MS1 in the stacked markers MS3 with a measurement beam, three different light intensity distributions can be obtained.

[0069] It should be noted that in a grating group, the higher the grating density, the lower the average light intensity. As shown in Figure 13, in direction x, the density of grating 113 in grating group 113g is greater than the density of grating 111 in grating group 111g or the density of grating 112 in grating group 112g. This makes it easy to identify the light intensity distributions generated by grating groups 111g, 112g, and 113g respectively, so as to obtain the offsets of grating groups 111g, 112g, and 113g relative to the reference line of the overlay mark M2. Thus, the positional deviation between overlay marks M1 and overlay marks M2 can be obtained by combining the offsets obtained from the light intensity distributions generated by grating groups 111g, 112g, and 113g.

[0070] In this embodiment, as shown in Figure 14, grating groups 111g, 112g, and 113g are arranged sequentially in the y-direction. This makes it easier to identify the light intensity distribution generated by grating groups 111g, 112g, and 113g respectively.

[0071] In summary, for a semiconductor structure with a front layer and a current layer, multiple sets of grating groups can be formed in the front layer to prevent damage to these grating groups and subsequent measurement failure. Different sets of gratings can be considered as different sub-grating groups in the front layer. By receiving multiple light intensity distributions from different grating groups in the front layer, it is possible to determine whether the front layer and the current layer are aligned.

[0072] Although the present disclosure has been described above with reference to embodiments, it is not intended to limit the present disclosure. Any person with ordinary knowledge in the art may make various modifications and refinements without departing from the spirit and scope of the present disclosure. Therefore, the scope of protection of the present disclosure shall be determined by the claims attached.

[0073] It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the embodiments disclosed herein without departing from the scope or spirit of this disclosure. In view of the foregoing, this disclosure is intended to cover modifications and variations of the invention, provided they fall within the appended scope of protection.

[0074] 3-3, 4-4, 5-5: Line segments 100: Semiconductor Structure 110: Front layer 110T: Top surface 111: Raster 111g: Grating assembly 112: Raster 112g: grating assembly 113: Raster 113g: grating assembly 120: Current layer 120T: Top surface 121: Raster 121g: Grating assembly 300: Method 301~307: Process BP1, BP2: Bottom points D1, D1': Light intensity distribution D2, D2': Light intensity distribution g11, g12, g2: gaps LR: Local region M1: Overlapping marker M2: Overlap mark MS, MS1, MS2, MS3: Stacked pair markers OX: Reference line SR1, SR2: Select area TP1, TP2: Vertex W1, W2: Width x, y, z: Direction

[0075] Domestic storage information (please note in order of storage institution, date, and number) none Overseas storage information (please note in the order of storage country, institution, date, and number) none

Claims

1. A method for superimposed measurement, comprising: A detection beam is emitted toward a first stacked marker on a front layer, wherein the first stacked marker includes a first grating group and a second grating group on a surface of the front layer; a reference point is determined for a second stacked marker in a current layer above the front layer; a first light intensity distribution of the first grating group relative to the reference point of the second stacked marker is received, and a second light intensity distribution of the second grating group relative to the reference point is received; a first offset of the first grating group relative to the reference point is obtained based on the first light intensity distribution; a second offset of the second grating group relative to the reference point is obtained based on the second light intensity distribution; and a positional offset between the first stacked marker and the second stacked marker is determined based on the first offset and the second offset, wherein the positional offset is a first weight multiplied by the first offset plus a second weight multiplied by the second offset.

2. The method as described in claim 1, wherein obtaining the first offset includes selecting a first central region of the first light intensity distribution and determining a first center point, the first center point being determined based on an average light intensity of the first central region, and the first offset being a distance between the reference point and the first center point.

3. The method as described in claim 2, wherein the first center point corresponds to a location where an extreme value occurs in the first light intensity distribution.

4. The method as claimed in claim 1, wherein each of the first grating group and the second grating group includes a plurality of gratings extending in a first direction and arranged in a second direction perpendicular to the first direction, and the number of gratings in the first grating group is different from the number of gratings in the second grating group.

5. The method as described in claim 4, wherein the first grating group and the second grating group are arranged in the first direction, a first density of the gratings in the first grating group is less than a second density of the gratings in the second grating group in the second direction, and a first average light intensity of the first light intensity distribution is greater than a second average light intensity of the second light intensity distribution.

6. The method as described in claim 1, wherein the first stacked markers further include a third grating group, the method further comprising: Receive a third light intensity distribution of the third grating group relative to the reference point of the second stacked pair mark.

7. The method as described in claim 6, wherein each of the first grating group, the second grating group, and the third grating group comprises a plurality of gratings extending in a first direction and arranged in a second direction perpendicular to the first direction, wherein the number of gratings in the first grating group, the number of gratings in the second grating group, and the number of gratings in the third grating group are different from each other.

8. The method as described in claim 7, wherein a first density of the gratings of the first grating group is less than a second density of the gratings of the second grating group in the second direction, the second density is less than a third density of the gratings of the third grating group in the second direction, and the first grating group, the second grating group and the third grating group are arranged sequentially in the first direction.

9. The method as described in claim 1, wherein each of the first light intensity distribution and the second light intensity distribution is a diffracted light intensity distribution.

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