Overlay precision measuring mark and using method and device thereof

Abstract

The invention belongs to the technical field of semiconductor devices, and particularly discloses an overlay precision measuring mark and a using method and device thereof. According to the overlay precision measurement mark, a DBO marking mode and an IBO marking mode are adopted in the edge area of the chip, the area of a Scribe Line used in the overlay precision measurement mark can be reduced, and the accuracy of overlay precision measurement in the Scribe Line area is improved.

Description

Technical Field

[0001] The present application belongs to the field of semiconductor technology, and specifically relates to an overlay accuracy measurement mark and a method and device for using the same. Background Art

[0002] With the development of semiconductor technology, the requirements for silicon wafer overlay accuracy are getting higher and higher. The traditional overlay accuracy measurement method based on image processing has the problems of poor accuracy and large space occupation. Summary of the invention

[0003] The technical purpose of the present application is to at least solve the problem of low accuracy when measuring overlay accuracy within the Scribe Line (located in the chip edge area).

[0004] The above objectives are achieved through the following technical solutions: In the first aspect, the present application provides an overlay accuracy measurement mark, comprising:

[0005] A substrate, a first layer image mark and a second layer image mark;

[0006] The first layer of image marks is located on the surface of either side of the substrate; the first layer of image marks includes a first central image and a first outer image surrounding the periphery of the first central image;

[0007] The second layer of image marks is located on a surface of the first layer of image marks that is away from the substrate, and the second layer of image marks includes a second central image and a second outer image surrounding the second central image;

[0008] The orthographic projection of the first central image on the substrate overlaps with the orthographic projection of the second central image on the substrate;

[0009] The orthographic projection of the first outer image on the substrate does not overlap with the orthographic projection of the second outer image on the substrate;

[0010] The orthographic projection of the first outer image on the substrate is far away from the orthographic projection of the first central image on the substrate; the orthographic projection of the second outer image on the substrate is close to the orthographic projection of the first central image on the substrate;

[0011] The first central image and / or the second central image are images obtained using the optical diffraction principle;

[0012] The first outer image and / or the second outer image are images obtained based on image overlay measurement.

[0013] In some embodiments, the first central image and / or the second central image comprises a first grating unit and a second grating unit;

[0014] The first grating unit comprises a first grating, which extends along the second direction and is arranged at intervals in the first direction;

[0015] The second grating unit comprises a second grating extending along the first direction and arranged at intervals in the second direction;

[0016] The first direction is different from the second direction.

[0017] In some embodiments, the first central image and the second central image each include N first grating units and N second grating units; N is an even number.

[0018] In some embodiments, the first grating units and the second grating units are alternately arranged in the first direction and / or the second direction.

[0019] In some embodiments, the first outer image includes a third grating unit and a fourth grating unit;

[0020] The third grating unit comprises a third grating, which extends along the second direction and is arranged at intervals in the first direction;

[0021] The fourth grating unit includes a fourth grating, which extends along the first direction and is arranged at intervals in the second direction;

[0022] and / or;

[0023] The second outer image includes a fifth grating unit and a sixth grating unit;

[0024] The fifth grating unit includes a fifth grating, the fifth grating extending along the second direction and arranged at intervals in the first direction;

[0025] The sixth grating unit includes a sixth grating extending along the first direction and arranged at intervals in the second direction.

[0026] In some embodiments, the third grating and the fourth grating surround the periphery of the first central image, and the third grating and the fourth grating are alternately distributed around the periphery of the first central image;

[0027] and / or;

[0028] The fifth grating and the sixth grating surround the periphery of the second central image, and the fifth grating and the sixth grating are alternately distributed on the periphery of the second central image.

[0029] In some embodiments, the first grating and / or the second grating has a line width W1;

[0030] The third grating and / or the fourth grating and / or the fifth grating and / or the sixth grating have a line width W2;

[0031] W1 is smaller than W2.

[0032] In some embodiments, the third grating and / or the fourth grating and / or the fifth grating and / or the sixth grating has a line width W2;

[0033] There is a spacing D between each adjacent third grating and / or between each adjacent fourth grating and / or between each adjacent fifth grating and / or between each adjacent sixth grating;

[0034] W2 / D is 0.9:1.1.

[0035] The second aspect of the present application is to provide a method for using the overlay accuracy measurement mark described in the first aspect, comprising:

[0036] providing a substrate;

[0037] Placing a first layer of image marks and a second layer of image marks of required sizes on the substrate;

[0038] After the photolithography exposure, the overlay accuracy of the second layer image mark is confirmed by using the first center image in the first layer image mark and the second center image in the second layer image mark;

[0039] After etching, overlay accuracy measurement is performed based on the first outer image in the first layer of image marks and the second outer image in the second layer of image marks.

[0040] The third aspect of the present application is to provide a semiconductor device, including a semiconductor device prepared after confirmation using the overlay accuracy measurement mark described in the first aspect.

[0041] Beneficial technical effects of this application:

[0042] The overlay accuracy measurement mark provided in the present application is conducive to reducing the Scribe Line area used in the overlay accuracy measurement mark and improving the accuracy of overlay accuracy measurement in the Scribe Line area. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0044] Figure 1 The schematic diagram of the structure of the overlay accuracy measurement mark of some embodiments of the present application is schematically shown;

[0045] Figure 2A The schematic diagram of the structure of the first part of the overlay accuracy measurement mark of some embodiments of the present application is schematically shown;

[0046] Figure 2B The schematic diagram of the structure of the second part of the overlay accuracy measurement mark of some embodiments of the present application is schematically shown;

[0047] Figure 3 The schematic diagram of the structure of the overlay accuracy measurement mark of some embodiments of the present application is schematically shown;

[0048] Figure 4 A process flow chart of a method for using an overlay accuracy measurement mark in some embodiments of the present application is schematically shown.

[0049] Among them, the numbers in the accompanying drawings are as follows:

[0050] 10. Overlay precision measurement mark;

[0051] 100, base;

[0052] 200, first layer image mark; 210, first central image; 220, first outer image; 221, third grating unit; 222, fourth grating unit; 221a, third grating; 222a, fourth grating;

[0053] 300, second layer image mark; 310, second central image; 320, second outer image; 321, fifth grating unit; 322, sixth grating unit; 321a, fifth grating; 322a, sixth grating;

[0054] 211 or 311, a first grating unit; 212 or 312, a second grating unit;

[0055] 211a or 311a, a first grating; 212a or 312a, a second grating;

[0056] First direction: coordinate axis x direction;

[0057] Second direction: coordinate axis y direction. DETAILED DESCRIPTION

[0058] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application.

[0059] Various structural schematic diagrams according to embodiments of the present disclosure are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may further design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0060] In the context of the present application, when a layer / element is referred to as being "on" another layer / element, the layer / element may be directly on the other layer / element or an intervening layer / element may exist between them. In addition, if a layer / element is "on" another layer / element in one orientation, the layer / element may be "under" the other layer / element when the orientation is reversed.

[0061] The application may use the term "coupled with," along with its derivatives. "Coupled" may mean one or more of the following. "Coupled" may mean that two or more elements are in direct physical or electrical contact. However, "coupled" may also mean that two or more elements are in indirect contact with each other, but still cooperate or interact with each other, and may mean that one or more other elements are coupled or connected between the elements said to be coupled to each other. The term "directly coupled" may mean that two or more elements are in direct contact.

[0062] The development of semiconductor technology is often limited to the development of photolithography technology. The reduction of feature size has put forward more stringent requirements on the overlay accuracy of silicon wafers. If the overlay accuracy between photolithography layers does not meet the requirements of the design criteria, it will lead to the failure of the front-end device function and the back-end connection function, directly causing the loss of product yield. The overlay accuracy requirements of the photolithography process are proportional to the technical node of the semiconductor process, that is, higher technical nodes require more precise overlay accuracy.

[0063] The traditional overlay accuracy measurement method based on image processing mainly adopts a standard optical microscope system under bright field, uses a white light source and performs automatic focusing through an interferometer during the measurement process. IBO (Image-Based Overlay Mark) consists of two layers, inner and outer, representing the front layer or the current layer respectively. Its graphic feature is a grating structure with periodic lines and spaces. By acquiring the image and obtaining the center position of the front layer and the current layer through calculation, the corresponding displacement deviation is obtained and decomposed into the X and Y directions. The advantage of IBO is that it can provide intuitive image information, which is easy to analyze and process. However, the disadvantage of IBO is that the measurement accuracy of small-size features is limited and the requirements for the imaging system are high.

[0064] Compared with the traditional IBO measurement mark, DBO (Diffraction-Based Overlay Mark) uses the principle of optical diffraction to obtain better measurement accuracy and precision of the graphics, and can more accurately characterize the performance of the current layer and the overlay accuracy of the previous and next layers of the product. The advantages of DBO are high measurement accuracy and little environmental impact. However, its disadvantages are high cost and sensitivity to the underlying structure, and may not provide accurate measurement results after etching.

[0065] In the manufacture of critical layers, IBO and DBO are usually used to ensure that enough marks are inserted into the Scribe Line in the exposure area for accurate Overlay measurement. Scribe Line is an area on the wafer used to separate different chips. These areas are usually located at the edge of the chip and are not used to form the active area of ​​the final product, but are used as cutting channels. Usually these areas are used to place various measurement and test marks: These test marks are used to monitor and control parameters in the manufacturing process, such as film thickness, etching depth, lithography alignment, etc. Lithography alignment marks are used to ensure precise alignment between different layers during the lithography process.

[0066] With the popularity of high-density chips (HOC, High Overlay Critical), the requirements for Overlay accuracy are further improved, resulting in the need for more Overlay Marks in the exposure area, which makes the space of Scribe Line tight and reduces the accuracy.

[0067] In order to solve the above technical problems, the present application provides an overlay accuracy measurement mark, such as Figure 1As shown, the overlay accuracy measurement mark 10 includes a substrate 100, a first layer image mark 200 and a second layer image mark 300, wherein the first layer image mark 200 is located on any side surface of the substrate 100; the first layer image mark 200 includes a first central image 210 and a first outer image 220 surrounding the periphery of the first central image 210; the second layer image mark 300 is located on the side surface of the first layer image mark 200 away from the substrate 100, and the second layer image mark 300 includes a second central image 310 and a second outer image 320 surrounding the periphery of the second central image 310; the orthographic projection of the first central image 210 on the substrate overlaps with the orthographic projection of the second central image 310 on the substrate; the overlap here includes complete overlap, and the figure also illustrates the way of complete overlap, in addition, the orthographic projection of the image on the substrate in the figure is consistent with the number used by the image itself, and this application does not make additional distinction. The orthographic projection of the first outer image 220 on the substrate 100 does not overlap with the orthographic projection of the second outer image 320 on the substrate 100; the overlap here includes complete non-overlap. And the orthographic projection of the first outer image 220 on the substrate 100 is far away from the orthographic projection of the first central image 210 on the substrate 100; the orthographic projection of the second outer image 320 on the substrate 100 is close to the orthographic projection of the first central image 310 on the substrate 100; the first central image 210 and / or the second central image 310 are images obtained using the optical diffraction principle (DBO); the first outer image 220 and / or the second outer image 320 are images obtained based on image overlay measurement (IBO).

[0068] The overlay accuracy measurement mark provided in the present application adopts a reasonable matching method of DBO and IBO, wherein the DBO and IBO marks are located in the same coordinate axis, which is conducive to establishing reasonable measurement parameters. At the same time, the Scribe Line area used by the overlay accuracy measurement mark is reduced and the accuracy is improved; in addition, even when the measurement of the DBO mark in the center image fails, the mark damage can be indirectly predicted through the IBO mark in the outer image. Therefore, the present application has good application prospects in the field of semiconductor devices.

[0069] In some embodiments, in combination Figure 1As shown in FIG. 2 , the first central image 210 and / or the second central image 310 include a first grating unit 211 or 311 and a second grating unit 212 or 312; the present application provides that the grating units included in the first central image 210 and the second central image 310 are the same, so a design method of the same name but different numbers is adopted. The present application adopts any of the numbers in the following, specifically, the first grating unit 211 includes a first grating 211a, which extends along the second direction and is arranged at intervals in the first direction; the second grating unit 212 includes a second grating 212a, which extends along the first direction and is arranged at intervals in the second direction; the first direction is different from the second direction, and the present application provides in a specific embodiment that the first direction is perpendicular to the second direction.

[0070] The first grating unit 211 and the second grating unit 212 of the present application are located in the central area, which is beneficial to reducing the area of ​​the Scribe Line used. At the same time, the first grating unit 211 and the second grating unit 212 include the same or different numbers of first gratings 211a and second gratings 212a. For any of the first grating units 211, the spacing between adjacent first gratings 211a is equal. Similarly, for any of the second grating units 212, the spacing between adjacent second gratings 212a is equal. The present application adopts this design method to further reduce the area of ​​the Scribe Line used.

[0071] In some embodiments, in combination Figure 1 As shown in FIG. 2 , the first central image 210 and the second central image 310 each include N first grating units 211 and N second grating units 212; N is an even number. In the present application, the number of the first grating units 211 and the second grating units 212 is affected by the actual arrangement of the grating units. For example, the present application illustrates that N is 2 in the accompanying drawings.

[0072] In some embodiments, the first grating units 211 and the second grating units 212 are arranged alternately in the first direction and / or the second direction. In FIG. 2 , the present application illustrates that the first grating units 211 are located at the upper left and lower right of the first central image 210. Similarly, the second grating units 212 are located at the upper right and lower left of the first central image 210. This design method is conducive to reducing the area of ​​the Scribe Line used.

[0073] In some embodiments, the first outer image 220 includes a third grating unit 221 and a fourth grating unit 222; the third grating unit 221 includes a third grating 221a, which extends along the second direction and is arranged at intervals in the first direction; the fourth grating unit 222 includes a fourth grating 222a, which extends along the first direction and is arranged at intervals in the second direction.

[0074] This design method adopted by the present application is beneficial to reducing the area of ​​the Scribe Line used.

[0075] In some embodiments, the second outer image 320 includes a fifth grating unit 321 and a sixth grating unit 322; the fifth grating unit 321 includes a fifth grating 321a, which extends along the second direction and is arranged at intervals in the first direction; the sixth grating unit 322 includes a sixth grating 322a, which extends along the first direction and is arranged at intervals in the second direction. The present application adopts this design method, which is also conducive to reducing the area of ​​the Scribe Line used.

[0076] In some embodiments, the third grating 221 a and the fourth grating 222 a surround the periphery of the first central image 210 , and the third grating 221 a and the fourth grating 222 a are alternately distributed around the periphery of the first central image 210 .

[0077] In some embodiments, the fifth grating 321 a and the sixth grating 322 a surround the periphery of the second central image 310 , and the fifth grating 321 a and the sixth grating 322 a are alternately distributed around the periphery of the second central image 310 .

[0078] In some embodiments, the first grating 211a and / or the second grating 212a has a line width W1;

[0079] The third grating 221a and / or the fourth grating 222a and / or the fifth grating 321a and / or the sixth grating 322a have a line width W2; W1 is smaller than W2.

[0080] In these embodiments, the present application provides that the first grating 211a and the second grating 212a have the same line width, where the line width refers to the relatively smaller distance value between the two opposite end faces on the grating along the first direction or the second direction, and the relatively larger distance value can be called the line length. The present application will have a description of the relevant specific values ​​in subsequent specific embodiments. Similarly, the third grating 221a and / or the fourth grating 222a and / or the fifth grating 321a and / or the sixth grating 322a also have the same line width.

[0081] The present application selects a smaller grating line width for the center image than for the outer images. This design is beneficial for both overlay precision measurement marks and improved measurement accuracy.

[0082] In some embodiments, the third grating 221a and / or the fourth grating 222a and / or the fifth grating 321a and / or the sixth grating 322a have a line width W2; there is a spacing D between each adjacent third grating 221a and / or each adjacent fourth grating 222a and / or each adjacent fifth grating 321a and / or each adjacent sixth grating 322a; W2 / D is 0.9:1.1.

[0083] In a specific embodiment of the present application, W2 / D can be adjusted to an appropriate specific value to achieve relatively good overlay accuracy measurement while meeting product design requirements and process conditions.

[0084] The second aspect of the present application is to provide a method for using the overlay accuracy measurement mark described in the first aspect, such as Figure 4 The schematic includes the following steps:

[0085] S100, providing a substrate;

[0086] S200, placing a first layer of image marks and a second layer of image marks of required sizes on the substrate;

[0087] S300, after photolithography exposure, using a first central image in the first layer image mark and a second central image in the second layer image mark to confirm the overlay accuracy of the second layer image mark;

[0088] S400 , after etching, performing overlay accuracy measurement based on a first outer image in the first layer of image marks and a second outer image in the second layer of image marks.

[0089] Example 1

[0090] Provided is an overlay accuracy measurement mark 10, which includes a substrate 100, a first layer image mark 200 and a second layer image mark 300, wherein the first layer image mark 200 is located on any side surface of the substrate 100; the first layer image mark 200 includes a first central image 210 and a first outer image 220 surrounding the periphery of the first central image 210; the second layer image mark 300 is located on a side surface of the first layer image mark 200 away from the substrate 100, and the second layer image mark 300 includes a second central image 310 and a second outer image 320 surrounding the periphery of the second central image 310; the orthographic projection of the first central image 210 on the substrate overlaps with the orthographic projection of the second central image 310 on the substrate; the overlap here includes complete overlap, and the accompanying drawings also illustrate the manner of complete overlap. In addition, the orthographic projection of the image on the substrate in the accompanying drawings is consistent with the numbering used by the image itself, and the present application does not make additional distinctions. The orthographic projection of the first outer image 220 on the substrate 100 does not overlap with the orthographic projection of the second outer image 320 on the substrate 100; the overlap here includes no overlap at all. The orthographic projection of the first outer image 220 on the substrate 100 is far away from the orthographic projection of the first central image 210 on the substrate 100; the orthographic projection of the second outer image 320 on the substrate 100 is close to the orthographic projection of the first central image 310 on the substrate 100; the first central image 210 and / or the second central image 310 are images obtained using the optical diffraction principle (DBO); the first outer image 220 and / or the second outer image 320 are images obtained based on image overlay measurement (IBO).

[0091] Meanwhile, the first central image 210 includes two first grating units 211 and two second grating units 212, and the second central image 310 includes two first grating units 311 and two second grating units 312. The two first grating units 311 or 211 are respectively located at the upper left and lower right of the image, and similarly, the two second grating units 312 or 212 are respectively located at the upper right and lower left of the image. The first grating unit 211 includes 13 first gratings 211a, and the first grating unit 311 includes 13 first gratings 311a. The area occupied by the first central image 210 in the region formed by the first direction and the second direction is 16μm×16μm.

[0092] In addition, the first outer image 220 includes two third grating units 221 and two fourth grating units 222. The two third grating units 221 are respectively located at the upper left and lower right of the image, and the two fourth grating units 222 are respectively located at the upper right and lower left of the image. The third grating unit 221 includes 11 third gratings 221a, and the fourth grating unit 222 includes 11 fourth gratings 222a. The second outer image 320 includes two fifth grating units 321 and two sixth grating units 322. The two fifth grating units 321 are respectively located at the upper left and lower right of the image, and the two sixth grating units 322 are respectively located at the upper right and lower left of the image. The fifth grating unit 321 includes 11 fifth gratings 321a, and the sixth grating unit 322 includes 11 sixth gratings 322a.

[0093] In this embodiment, the present application also provides that the third grating 221a and / or the fourth grating 222a and / or the fifth grating 321a and / or the sixth grating 322a have a line width W2 of 2 μm and a line length of 1 μm.

[0094] The present application also provides in this embodiment that the area occupied by the substrate 100 in the region formed by the first direction and the second direction is 30 μm×30 μm, wherein the distance between the third grating unit 221 and the end edge of the substrate 100 extending in the first direction and / or the second direction is 1.25 μm, and similarly, the distance between the fourth grating unit 222 and the end edge of the substrate 100 extending in the first direction and / or the second direction is 1.25 μm.

[0095] In this embodiment, the present application also provides that the distance between the first central image 210 and / or the second central image 310 and the fifth grating element 321 and / or the sixth grating element 322 of the second layer image mark 300 is 1.25 μm.

[0096] In this embodiment, the present application also provides that the distance between the third grating unit 221 and the fifth grating unit 321 is 0.5 μm, and the distance between the fourth grating unit 222 and the sixth grating unit 322 is 0.5 μm.

[0097] And / or the distance between the fourth grating unit 222 and the fifth grating unit 321 and / or the sixth grating unit 322 is 0.5 μm.

[0098] In summary, the overlay accuracy measurement mark provided in the present application is conducive to reducing the Scribe Line area used in the overlay accuracy measurement mark and improving the accuracy of overlay accuracy measurement in the Scribe Line area.

[0099] It should be understood that the terms used herein are only for the purpose of describing specific example embodiments and are not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms "one", "an" and "said" as used herein may also be meant to include plural forms. The terms "include", "comprise", "contain", and "have" are inclusive and therefore indicate the presence of the stated features, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, steps, operations, elements, parts, and / or combinations thereof. The method steps, processes, and operations described herein are not interpreted as requiring them to be performed in the specific order described or illustrated, unless the execution order is clearly indicated. It should also be understood that additional or alternative steps may be used. The above is only a preferred specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or replacements that can be easily thought of by a technician familiar with the technical field within the technical scope disclosed in the present application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application shall be subject to the scope of protection of the claims.

Claims

1. An overlay precision measurement mark, characterized in that: include: A substrate, a first layer image mark and a second layer image mark; The first layer of image marks is located on the surface of either side of the substrate; The first layer of image marks includes a first central image and a first outer image surrounding the periphery of the first central image; The second layer of image marks is located on a side surface of the first layer of image marks away from the substrate, and the second layer of image marks includes a second central image and a second outer image surrounding the periphery of the second central image; The orthographic projection of the first central image on the substrate overlaps with the orthographic projection of the second central image on the substrate; The orthographic projection of the first outer image on the substrate does not overlap with the orthographic projection of the second outer image on the substrate; and an orthographic projection of the first outer image on the substrate is away from an orthographic projection of the first central image on the substrate; The orthographic projection of the second outer image on the substrate is close to the orthographic projection of the first central image on the substrate; The first central image and / or the second central image are images obtained using the optical diffraction principle; The first outer side image and / or the second outer side image are images obtained based on image overlay measurement.

2. The overlay accuracy measurement mark according to claim 1, characterized in that: The first central image and / or the second central image comprises a first grating unit and a second grating unit; The first grating unit includes a first grating, the first grating extending along the second direction and arranged at intervals in the first direction; The second grating unit includes a second grating, the second grating extending along the first direction and arranged at intervals in the second direction; The first direction is different from the second direction.

3. The overlay accuracy measurement mark according to claim 2, characterized in that: The first central image and the second central image each include N first grating units and N second grating units; N is an even number.

4. The overlay accuracy measurement mark according to any one of claims 2 to 3, characterized in that: The first grating units and the second grating units are arranged alternately in a first direction and / or a second direction.

5. The overlay accuracy measurement mark according to any one of claims 2 to 3, characterized in that: The first outer image includes a third grating unit and a fourth grating unit; The third grating unit includes a third grating, and the third grating extends along the second direction and is arranged at intervals in the first direction; The fourth grating unit includes a fourth grating, and the fourth grating extends along the first direction and is arranged at intervals in the second direction; and / or; The second outer image includes a fifth grating unit and a sixth grating unit; The fifth grating unit includes a fifth grating, and the fifth grating extends along the second direction and is arranged at intervals in the first direction; The sixth grating unit includes a sixth grating, and the sixth grating extends along the first direction and is arranged at intervals in the second direction.

6. The overlay accuracy measurement mark according to claim 5, characterized in that: The third grating and the fourth grating surround the periphery of the first central image, and the third grating and the fourth grating are alternately distributed around the periphery of the first central image; and / or; The fifth grating and the sixth grating surround the periphery of the second central image, and the fifth grating and the sixth grating are alternately distributed in the periphery of the second central image.

7. The overlay accuracy measurement mark according to any one of claims 5 to 6, characterized in that: The first grating and / or the second grating has a line width W1; The third grating and / or the fourth grating and / or the fifth grating and / or the sixth grating have a line width W2; W1 is smaller than W2.

8. The overlay accuracy measurement mark according to any one of claims 5 to 6, characterized in that: The third grating and / or the fourth grating and / or the fifth grating and / or the sixth grating have a line width W2; There is a spacing D between each adjacent third grating and / or between each adjacent fourth grating and / or between each adjacent fifth grating and / or between each adjacent sixth grating; W2 / D is 0.9:1.

1.

9. A method for using the overlay accuracy measurement mark according to claim 1, characterized in that: include: providing a substrate; Placing a first layer of image marks and a second layer of image marks of required sizes on the substrate; After the photolithography exposure, the overlay accuracy of the second layer image mark is confirmed by using the first center image in the first layer image mark and the second center image in the second layer image mark; After etching, overlay accuracy measurement is performed based on the first outer image in the first layer of image marks and the second outer image in the second layer of image marks.

10. A semiconductor device, characterized in that: The method is prepared by confirming the overlay accuracy measurement mark according to any one of claims 1 to 8.

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