Overlay measurement method

Abstract

The application provides a method for measuring overlay accuracy, which integrates a first front layer overlay mark pattern, a second front layer overlay mark pattern and a current layer overlay mark pattern on one mark plate; obtains measurement values of the current layer overlay mark pattern in X and Y directions according to the first front layer overlay mark pattern, the second front layer overlay mark pattern and the current layer overlay mark pattern on the mark plate, wherein the X direction is perpendicular to the Y direction; and calculates the etching overlay accuracy of the current layer overlay mark pattern in the X and Y directions according to the measurement values. Compared with the separate placement of the mark plates in the X and Y directions, the area of the mark plate is reduced by half and the measurement efficiency is doubled.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing processes and testing technology, and in particular to a method for measuring overlay accuracy. Background Technology

[0002] In the semiconductor manufacturing field, as process nodes shrink, overlay accuracy has become one of the core indicators determining device performance and yield. Especially when using three-dimensional structures and multiple exposure techniques, overlay accuracy must be controlled within a few nanometers; otherwise, fatal defects such as transistor leakage and interconnect short circuits will occur. However, factors such as residual morphology changes after etching, differences in material selectivity, and process stress release pose significant challenges to the practical characterization of overlay accuracy.

[0003] Overlay measurement techniques based on optical diffraction (DBO) and image principle (IBO) rely on periodic gratings or special graphic markings for non-destructive measurement. However, after etching, optical diffraction measurements are essentially impossible due to edge roughness and material compatibility issues, while image principle measurements have large errors and cannot reflect the true overlay accuracy.

[0004] Therefore, to obtain accurate overlay results, a scanning electron microscope is needed to measure specialized patterns. Some layers require alignment with different preceding layers in the X and Y directions, resulting in separate marking layers for the X and Y directions. This separate marking not only increases the area occupied by the marking plate but also significantly increases measurement time. Therefore, how to simultaneously measure the overlay accuracy in both the X and Y directions is a pressing technical challenge that needs to be addressed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for measuring overlay accuracy, so as to solve the problems of excessive measurement time and excessive area occupied by the ground marking plate due to separate setting of measurement values ​​in the X and Y directions.

[0006] To solve the above technical problems, the present invention provides a method for measuring overlay accuracy, comprising the following steps:

[0007] Provide a first front-layer overprinted logo graphic, a second front-layer overprinted logo graphic, and a current-layer overprinted logo graphic, and integrate the first front-layer overprinted logo graphic, the second front-layer overprinted logo graphic, and the current-layer overprinted logo graphic onto a single logo plate;

[0008] The measurement values ​​of the current layer overprinted logo pattern in the X and Y directions are obtained based on the first front layer overprinted logo pattern, the second front layer overprinted logo pattern, and the current layer overprinted logo pattern on the logo plate, wherein the X direction is perpendicular to the Y direction;

[0009] The etching accuracy of the overlay marking pattern in the X and Y directions is calculated based on the measured values.

[0010] Optionally, the number of the first front layer overprinted markings is greater than or equal to 7, and all the first front layer overprinted markings are arranged sequentially at intervals along the X direction.

[0011] Optionally, the number of the second front layer overprinted markings is greater than or equal to 7, and all the second front layer overprinted markings are arranged sequentially at intervals along the Y direction.

[0012] Optionally, the in-layer overprinted logo includes a first logo and a second logo, wherein the first logo is located at the center of the in-layer overprinted logo, and the second logo is symmetrically distributed around the first logo.

[0013] Optionally, the number of the second figure is greater than or equal to 2 and is an even number.

[0014] Optionally, the horizontal axis of symmetry of the first figure is taken as the dividing line, and the entire second figure is divided into a first sub-figure corresponding to the upper region and a second sub-figure corresponding to the lower region based on the dividing line. The first sub-figure and the second sub-figure are symmetrical about the horizontal axis of symmetry.

[0015] Optionally, the arrangement direction of the second front layer overprinted logo is perpendicular to the arrangement direction of the first front layer overprinted logo, and the second front layer overprinted logo divides each of the first front layer overprinted logos into multiple graphic units with the same spacing, and the first front layer overprinted logo and the second front layer overprinted logo form a grid pattern.

[0016] Optionally, the upper and lower boundaries of the second graphic coincide with the center line of the second front layer overprinted identification graphic, and the graphic units are spaced apart within the second graphic along the Y direction.

[0017] Optionally, the measurement value in the X direction includes the measurement value X1 in the X direction between the left boundary of the first graphic in the current layer overprinted logo pattern and the right boundary of any first front layer overprinted logo pattern to the left of the first graphic, and the measurement value X2 in the X direction between the right boundary of the first graphic in the current layer overprinted logo pattern and the left boundary of any first front layer overprinted logo pattern to the right of the first graphic.

[0018] Optionally, the measured value in the Y direction includes measured value Y1 and measured value Y2, specifically using either of the following two methods:

[0019] The first method: Y1 is the measured value in the Y direction of the upper boundary of any first sub-graphic in the overlay logo pattern and the upper side boundary of the graphic unit located at the top of the first sub-graphic in the Y direction; Y2 is the measured value in the Y direction of the lower boundary of any second sub-graphic in the overlay logo pattern and the lower side boundary of the graphic unit located at the bottom of the second sub-graphic in the Y direction.

[0020] The second method: Y1 is the measured value in the Y direction of the upper boundary of any second sub-graphic in the overlay logo pattern and the upper side boundary of the graphic unit located at the top of the Y direction within the second sub-graphic; Y2 is the measured value in the Y direction of the lower boundary of any first sub-graphic in the overlay logo pattern and the lower side boundary of the graphic unit located at the bottom of the Y direction within the first sub-graphic.

[0021] Optionally, the calculation formula for the overprinting accuracy includes OVL(X)=(X1-X2) / 2 and OVL(Y)=(Y1-Y2) / 2, where OVL(X) is the overprinting accuracy of the overprinted mark in the X direction and OVL(Y) is the overprinting accuracy of the overprinted mark in the Y direction.

[0022] Optionally, the first front-layer overprinted logo and / or the second front-layer overprinted logo are enclosed in a virtual graphic.

[0023] Optionally, before the step of integrating the first front-layer overprinted logo graphic, the second front-layer overprinted logo graphic, and the current layer overprinted logo graphic onto a single logo plate, the overprinting accuracy measurement method further includes the following steps:

[0024] The first wafer is subjected to a first exposure and development process and a first etching process to form the first front layer overlay marking pattern on the first wafer;

[0025] The first wafer is subjected to a second exposure and development process and a second etching process to form the second front layer overlay marking pattern on the first wafer;

[0026] The first wafer is subjected to a third exposure and development process and a third etching process to form the overlay marking pattern on the first wafer.

[0027] Optionally, before the third etching process on the first wafer and after the third exposure and development process on the first wafer, the overlay accuracy measurement method further includes: using a laser interferometer and a grating ruler to obtain the overlay accuracy of the first wafer after development.

[0028] Optionally, after performing the third exposure and development process and the third etching process sequentially on the first wafer, the overlay accuracy measurement method further includes:

[0029] The third exposure and development process is then performed on the second wafer.

[0030] Optionally, before performing the third exposure and development process on the second wafer, the overlay accuracy measurement method further includes: calculating the difference between the overlay accuracy after development and the overlay accuracy after etching of the first wafer and feeding it back to the lithography machine, wherein the lithography machine adjusts the parameters of the third exposure and development based on the difference.

[0031] In the overlay accuracy measurement method provided by the present invention, the first pre-layer overlay marking pattern, the second pre-layer overlay marking pattern, and the current layer overlay marking pattern are integrated on a marking plate. At the same time, the measurement values ​​of the current layer overlay marking pattern in the X and Y directions are obtained, and the overlay accuracy of the current layer overlay marking pattern in the X and Y directions after etching is calculated based on the measurement values. This shortens the measurement time and reduces the area occupied by the marking plate, thereby improving the measurement efficiency.

[0032] In addition, before the third exposure and development process on the second wafer, the difference between the overlay accuracy after development and the overlay accuracy after etching of the first wafer is calculated and fed back to the lithography machine. The lithography machine adjusts the parameters of the third exposure and development based on the difference to make the overlay accuracy of the second wafer more precise. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the first front layer overprinted marking pattern in one embodiment of the present invention;

[0034] Figure 2 This is a schematic diagram of a second front-layer overprinted marking pattern placed horizontally on a first front-layer overprinted marking pattern according to an embodiment of the present invention;

[0035] Figure 3 This is a schematic diagram of the first front-layer overprinted marking pattern being divided by the second front-layer overprinted marking pattern in one embodiment of the present invention;

[0036] Figure 4 This is a schematic diagram illustrating the simultaneous measurement of values ​​in the X and Y directions in one embodiment of the present invention;

[0037] Figure 5 This is a measurement diagram of simultaneous measurement in the X and Y directions under an electron beam microscope according to an embodiment of the present invention;

[0038] Figure 6 This is a flowchart illustrating the feedback process of overlay accuracy in practical applications according to one embodiment of the present invention.

[0039] Figure 7 This is a scanning image of overlay accuracy without feedback in one embodiment of the present invention;

[0040] Figure 8 This is a scanning image of the overlay accuracy after feedback in one embodiment of the present invention;

[0041] In the picture,

[0042] 10 - First front layer overprinted logo graphic; 20 - Second front layer overprinted logo graphic; 30 - Current layer overprinted logo graphic; 101 - Graphic unit; 301 - First graphic; 302 - Second graphic; 302a - First sub-graphic; 302b - Second sub-graphic. Detailed Implementation

[0043] The method for measuring overlay accuracy proposed in this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of this invention will become clearer from the following description and claims. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of this invention.

[0044] With the continuous advancement of semiconductor manufacturing processes, overlay accuracy has become one of the core indicators determining device performance and yield. Especially in processes employing three-dimensional structures and multiple exposure techniques, overlay accuracy (OVL) needs to be controlled within a few nanometers; otherwise, fatal defects such as transistor leakage and interconnect short circuits will occur. Among these, post-etch overlay accuracy (AEIOVL) determines the final device performance. A common practice in semiconductor manufacturing is to compensate for the difference between post-development overlay accuracy (ADIOVL) and post-etch overlay accuracy in the exposure and development parameters of the next wafer, thereby ensuring more precise post-etch overlay accuracy for the next wafer.

[0045] The current post-etching overlay marking pattern requires alignment with different front layers in the X and Y directions, resulting in separate overlay markings in the X and Y directions. This not only occupies more area but also increases design complexity. Separate overlay markings in the X and Y directions not only increase area usage but also significantly increase measurement time, reducing production efficiency.

[0046] Based on this, the present invention provides a method for measuring overlay accuracy, which may specifically include the following steps, please refer to... Figures 1-4 :

[0047] Provide a first front-layer overprinted logo graphic 10, a second front-layer overprinted logo graphic 20, and a current-layer overprinted logo graphic 30, and integrate the first front-layer overprinted logo graphic 10, the second front-layer overprinted logo graphic 20, and the current-layer overprinted logo graphic 30 onto a single logo plate;

[0048] The measurement values ​​of the current layer overprinted mark 30 in the X and Y directions are obtained based on the first front layer overprinted mark 10, the second front layer overprinted mark 20 and the current layer overprinted mark 30 on the mark plate, wherein the X direction is perpendicular to the Y direction;

[0049] The etching accuracy of the overlay marking pattern 30 in the X and Y directions is calculated based on the measured values.

[0050] Prior to the step of integrating the first front-layer overprinted logo graphic 10, the second front-layer overprinted logo graphic 20, and the current-layer overprinted logo graphic 30 onto a single logo plate, the overprinting accuracy measurement method may further include the following steps:

[0051] The first wafer is subjected to a first exposure and development process and a first etching process to form the first front layer overlay marking pattern 10 on the first wafer, and to obtain the marking layer of the first front layer overlay marking pattern 10 after the first etching process.

[0052] The first wafer is subjected to a second exposure and development process and a second etching process to form the second front layer overlay marking pattern 20 on the first wafer, and to obtain the marking layer of the second front layer overlay marking pattern 20 after the second etching process.

[0053] The first wafer is subjected to a third exposure and development process and a third etching process to form the overlay marking pattern 30 on the first wafer, and to obtain the marking layer of the overlay marking pattern 30 after the third etching process.

[0054] In this embodiment, the identifier layer of the first front-layer overprinted identifier 10 includes all the first front-layer overprinted identifiers 10, the identifier layer of the second front-layer overprinted identifier 20 includes all the second front-layer overprinted identifiers 20, and the identifier layer of the current-layer overprinted identifier 30 includes all the current-layer overprinted identifiers 30. This embodiment integrates all the first front-layer overprinted identifiers 10, the second front-layer overprinted identifiers 20, and the current-layer overprinted identifiers 30 onto a single identifier plate, that is, integrates the identifier layers of the first front-layer overprinted identifiers 10, the second front-layer overprinted identifiers 20, and the current-layer overprinted identifiers 30 onto a single identifier plate.

[0055] Please see Figure 1 All the first front-layer overprinted marking graphics 10 are arranged sequentially at intervals along the X direction, with an interval of D. x The number of the first front-layer overprinted marking patterns 10 is greater than or equal to 7. In this embodiment, the size, shape, and D-type conformance of the first front-layer overprinted marking patterns 10 can be set according to actual needs.x For example, the first front-layer overprinted marking pattern 10 can have a width of 45nm and a D... x The lines are 57nm in size. In this embodiment, at least three of the first front-layer overprinted marking patterns 10 need to be set on each side of the first front-layer overprinted marking pattern 10 at the center to ensure the accuracy of the measurement.

[0056] Please see Figure 2 All the second front-layer overprinted marking graphics 20 are arranged sequentially at intervals along the Y direction, with an interval of D. y The number of the second front-layer overprinted marking patterns 20 is greater than or equal to 7. In this embodiment, the size, shape, and D-factor conforming to semiconductor chip design rules of the second front-layer overprinted marking patterns 20 can be set according to actual needs. y For example, the second front-layer overprinted marking pattern 20 can have a width of 40nm and a D... y The lines are 96nm in size. In this embodiment, at least three second front-layer overprinted marking patterns 20 need to be set on each of the upper and lower sides of the center of the second front-layer overprinted marking pattern 20 to ensure the accuracy of the measurement.

[0057] Please see Figure 2 and Figure 3 The arrangement direction of the second front layer overprinted logo pattern 20 is perpendicular to the arrangement direction of the first front layer overprinted logo pattern 10, and each of the first front layer overprinted logo patterns 10 is divided into multiple graphic units 101 with the same spacing. The first front layer overprinted logo pattern 10 and the second front layer overprinted logo pattern 20 form a grid pattern.

[0058] Please see Figure 4 The in-layer overlay marking pattern 30 may include a first pattern 301 and a second pattern 302. The first pattern 301 is located at the center of the in-layer overlay marking pattern 30, and the number of second patterns 302 is greater than or equal to two and is an even number. The second patterns 302 are symmetrically distributed around the first pattern 301. In this embodiment, the size and shape of the in-layer overlay marking pattern 30, as well as the minimum spacing between the first pattern 301 and the second pattern 302 conforming to semiconductor chip design rules, can be set according to actual needs. For example, the first pattern 301 can be a line with a width of 42nm, and the minimum distance between the center of the first pattern 301 and the center of the second pattern 302 can be 264nm.

[0059] The semiconductor chip design rules may include any one or more of the following:

[0060] First: the layout design rules specified in the process design kit (PDK) provided by the wafer foundry;

[0061] Second: Spacing constraints determined by semiconductor manufacturing process capabilities, including but not limited to photolithography resolution, etching accuracy, electromigration reliability, or thermal management requirements;

[0062] Third: Spacing standards verified by the semiconductor industry's recognized Design Rule Check (DRC) tool.

[0063] Furthermore, taking the horizontal axis of symmetry of the first graphic 301 as the dividing line, the entire second graphic 302 is divided into a first sub-graphic 302a corresponding to the upper region and a second sub-graphic 302b corresponding to the lower region, based on this dividing line. The first sub-graphic 302a and the second sub-graphic 302b are symmetrical about the horizontal axis of symmetry. The upper and lower boundaries of the second graphic 302 coincide with the center line of the second front-layer overprinted identification graphic 20, and the graphic units 101 are spaced apart along the Y direction within the second graphic 302.

[0064] Please see Figure 4 and Figure 5 In this embodiment, the first front-layer overprinted logo graphic 10, the second front-layer overprinted logo graphic 20, and the current-layer overprinted logo graphic 30 are integrated onto a single logo plate. Specifically, the logo layers of the first front-layer overprinted logo graphic 10, the second front-layer overprinted logo graphic 20, and the current-layer overprinted logo graphic 30 are integrated onto a single logo plate. Then, the measurement values ​​of the current-layer overprinted logo graphic 30 in the X and Y directions are simultaneously acquired. The measurement value in the X direction may include X1, the measurement value X1 of the left boundary of the first graphic 301 in the current-layer overprinted logo graphic 30 and the measurement value X2 of the right boundary of the first graphic 301 in the current-layer overprinted logo graphic 30 and the measurement value X2 of the left boundary of the first graphic 301 in the current-layer overprinted logo graphic 30 and the measurement value X2 of the right boundary of the first graphic 301 in the current-layer overprinted logo graphic 30 and the measurement value X2 of the left boundary of the first front-layer overprinted logo graphic 10 in the current-layer overprinted logo graphic 30 and the measurement value X2 of the right boundary of the first graphic 301 in the current-layer overprinted logo graphic 30 and the measurement value X2 of the left boundary of the first front-layer overprinted logo graphic 10 in the current-layer overprinted logo graphic 30 and the right boundary of the first graphic 301.

[0065] The measured value in the Y direction includes measured value Y1 and measured value Y2, and can be obtained by any one of the following two methods:

[0066] The first method: Y1 is the measured value in the Y direction between the upper boundary of any first sub-graphic 302a in the overlay identification graphic 30 and the upper side boundary of the graphic unit 101 located at the top of the first sub-graphic 302a in the Y direction; Y2 is the measured value in the Y direction between the lower boundary of any second sub-graphic 302b in the overlay identification graphic 30 and the lower side boundary of the graphic unit 101 located at the bottom of the second sub-graphic 302b in the Y direction.

[0067] The second method: Y1 is the measured value in the Y direction between the upper boundary of any second sub-graphic 302b in the overlay identification graphic 30 and the upper side boundary of the graphic unit 101 located at the top of the Y direction within the second sub-graphic 302b; Y2 is the measured value in the Y direction between the lower boundary of any first sub-graphic 302a in the overlay identification graphic 30 and the lower side boundary of the graphic unit 101 located at the bottom of the Y direction within the first sub-graphic 302a.

[0068] The calculation formulas for the overprinting accuracy include OVL(X) = (X1 - X2) / 2 and OVL(Y) = (Y1 - Y2) / 2, where OVL(X) is the overprinting accuracy of the overprinted marking pattern in the X direction, and OVL(Y) is the overprinting accuracy of the overprinted marking pattern in the Y direction. Furthermore, this embodiment can perform a single measurement or multiple measurements. In this embodiment, performing a single measurement preferably uses the graphic unit 101 and the second graphic 302, which are closest to the first graphic 301, as the measurement objects to ensure better measurement results and smaller errors. Performing multiple measurements in this embodiment can obtain multiple measurement values, calculate corresponding multiple OVL(X) and OVL(Y), and then average the multiple OVL(X) and OVL(Y). Performing multiple measurements in this embodiment further ensures that the values ​​of OVL(X) and OVL(Y) are more accurate. This embodiment can choose to perform a single measurement or multiple measurements according to actual needs. Furthermore, in this embodiment, the calculated OVL(X) and OVL(Y) can be positive or negative. A positive value indicates that the direction is to the right along the X direction or upward along the Y direction, while a negative value indicates that the direction is to the left along the X direction or downward along the Y direction.

[0069] Because etching has different effects on the edges and centers of dense patterns, the first and second front-layer overprinted marking patterns 10 and 20 can be enclosed using dummy graphics to accurately identify the measured values. For example, using dummy graphics to enclose the first and second front-layer overprinted marking patterns 10 and 20 makes the surrounding environment for acquiring the measured values ​​consistent, thereby improving the accuracy of the overprinting precision.

[0070] Furthermore, before the third etching process on the first wafer and after the third exposure and development process on the first wafer, the overlay accuracy measurement method may further include: using a laser interferometer and a grating ruler to obtain the overlay accuracy of the first wafer after development. Please refer to [link to relevant documentation]. Figure 6After sequentially performing the third exposure and development process and the third etching process on the first wafer, the overlay accuracy measurement method further includes performing the third exposure and development process on the second wafer. Before performing the third exposure and development process on the second wafer, the overlay accuracy measurement method may further include calculating the difference between the overlay accuracy after development and the overlay accuracy after etching of the first wafer and feeding it back to the lithography machine, wherein the lithography machine adjusts the parameters of the third exposure and development process based on the difference. Preferably, this embodiment can employ a batch-to-batch (R2R) control system to feed back the difference between the overlay accuracy after development and the overlay accuracy after etching to the lithography machine, wherein the lithography machine adjusts the exposure and development parameters based on the difference to improve the overlay accuracy of the second wafer. Please refer to [link to documentation]. Figure 7 and Figure 8 This embodiment can also use an algorithmic model (preferably a high-order overlay accuracy model, but not limited to this) to calibrate the standard deviation of the entire wafer and observe the degree of dispersion. For example, this embodiment measures multiple marker points on the wafer using an alignment system to fit the deformation model of the entire wafer before and after feedback. The overlay accuracy of the second wafer after feedback is significantly improved compared to the overlay accuracy without feedback.

[0071] In summary, the overlay accuracy measurement method provided in this invention integrates the first pre-layer overlay marking pattern, the second pre-layer overlay marking pattern, and the current layer overlay marking pattern onto a single marking plate. This allows for the simultaneous acquisition of measurements of the current layer overlay marking pattern in both the X and Y directions on a single marking plate, and the calculation of the post-etching overlay accuracy in both directions. This not only shortens the measurement time but also reduces the area occupied by the marking plate, thus improving measurement efficiency. For example, the area of ​​the marking plate can be reduced from 2μm... 2 Shrink to 1μm 2 The measurement time has been reduced from 3 hours to 1.5 hours, a reduction of half, and the area of ​​the label has also been halved.

[0072] In addition, before performing the third exposure and development process on the subsequent wafers, the difference between the overlay accuracy after development and the overlay accuracy after etching of the previous wafers is fed back to the lithography machine. The lithography machine adjusts the parameters of the third exposure and development based on the difference to make the overlay accuracy of the subsequent wafers more accurate, and the overlay accuracy of the subsequent wafers after etching is also improved.

[0073] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A method for measuring overlay accuracy, characterized in that, Includes the following steps: Provide a first front-layer overprinted logo graphic, a second front-layer overprinted logo graphic, and a current-layer overprinted logo graphic, and integrate the first front-layer overprinted logo graphic, the second front-layer overprinted logo graphic, and the current-layer overprinted logo graphic onto a single logo plate; The measurement values ​​of the current layer overprinted logo pattern in the X and Y directions are obtained based on the first front layer overprinted logo pattern, the second front layer overprinted logo pattern, and the current layer overprinted logo pattern on the logo plate, wherein the X direction is perpendicular to the Y direction; The etching accuracy of the overlay marking pattern in the X and Y directions is calculated based on the measured values.

2. The overlay accuracy measurement method as described in claim 1, characterized in that, The number of the first front layer overprinted markings is greater than or equal to 7, and all the first front layer overprinted markings are arranged sequentially at intervals along the X direction.

3. The overlay accuracy measurement method as described in claim 1, characterized in that, The number of the second front layer overprinted markings is greater than or equal to 7, and all the second front layer overprinted markings are arranged sequentially at intervals along the Y direction.

4. The overlay accuracy measurement method as described in claim 1, characterized in that, The in-layer overprinted logo includes a first logo and a second logo. The first logo is located at the center of the in-layer overprinted logo, and the second logo is symmetrically distributed around the first logo.

5. The overlay accuracy measurement method as described in claim 4, characterized in that, The number of the second figure is greater than or equal to 2 and is even.

6. The overlay accuracy measurement method as described in claim 5, characterized in that, The horizontal axis of symmetry of the first figure is taken as the dividing line. Based on the dividing line, the entire second figure is divided into a first sub-figure corresponding to the upper region and a second sub-figure corresponding to the lower region. The first sub-figure and the second sub-figure are symmetrical about the horizontal axis of symmetry.

7. The overlay accuracy measurement method as described in claim 6, characterized in that, The arrangement direction of the second front layer overprinted logo is perpendicular to the arrangement direction of the first front layer overprinted logo, and the second front layer overprinted logo divides each of the first front layer overprinted logos into multiple graphic units with the same spacing, and the first front layer overprinted logo and the second front layer overprinted logo form a grid pattern.

8. The overlay accuracy measurement method as described in claim 7, characterized in that, The upper and lower boundaries of the second graphic coincide with the center line of the second front layer overlaid logo graphic, and the graphic units are spaced apart within the second graphic along the Y direction.

9. The overlay accuracy measurement method as described in claim 8, characterized in that, The measured values ​​in the X direction include X1, which is the measured value in the X direction between the left boundary of the first graphic in the current layer overprinted logo graphic and the right boundary of any first front layer overprinted logo graphic to the left of the first graphic, and X2, which is the measured value in the X direction between the right boundary of the first graphic in the current layer overprinted logo graphic and the left boundary of any first front layer overprinted logo graphic to the right of the first graphic.

10. The overlay accuracy measurement method as described in claim 9, characterized in that, The measured value in the Y direction includes measured value Y1 and measured value Y2, and can be obtained by any one of the following two methods: The first method: Y1 is the measured value in the Y direction of the upper boundary of any first sub-graphic in the overlay logo pattern and the upper side boundary of the graphic unit located at the top of the first sub-graphic in the Y direction; Y2 is the measured value in the Y direction of the lower boundary of any second sub-graphic in the overlay logo pattern and the lower side boundary of the graphic unit located at the bottom of the second sub-graphic in the Y direction. The second method: Y1 is the measured value in the Y direction of the upper boundary of any second sub-graphic in the overlay logo pattern and the upper side boundary of the graphic unit located at the top of the Y direction within the second sub-graphic; Y2 is the measured value in the Y direction of the lower boundary of any first sub-graphic in the overlay logo pattern and the lower side boundary of the graphic unit located at the bottom of the Y direction within the first sub-graphic.

11. The overlay accuracy measurement method as described in claim 10, characterized in that, The calculation formula for the overprinting accuracy includes OVL(X)=(X1-X2) / 2 and OVL(Y)=(Y1-Y2) / 2, where OVL(X) is the overprinting accuracy of the overprinted mark in the X direction and OVL(Y) is the overprinting accuracy of the overprinted mark in the Y direction.

12. The overlay accuracy measurement method as described in claim 1, characterized in that, The first and / or second front-layer overprinted logo graphics are enclosed in a virtual graphic.

13. The overlay accuracy measurement method as described in claim 1, characterized in that, Before the step of integrating the first front-layer overprinted logo graphic, the second front-layer overprinted logo graphic, and the current layer overprinted logo graphic onto a single logo plate, the overprinting accuracy measurement method further includes the following steps: The first wafer is subjected to a first exposure and development process and a first etching process to form the first front layer overlay marking pattern on the first wafer; The first wafer is subjected to a second exposure and development process and a second etching process to form the second front layer overlay marking pattern on the first wafer; The first wafer is subjected to a third exposure and development process and a third etching process to form the overlay marking pattern on the first wafer.

14. The overlay accuracy measurement method as described in claim 13, characterized in that, Before the third etching process on the first wafer and after the third exposure and development process on the first wafer, the overlay accuracy measurement method further includes: using a laser interferometer and a grating ruler to obtain the overlay accuracy of the first wafer after development.

15. The overlay accuracy measurement method as described in claim 13, characterized in that, After performing the third exposure and development process and the third etching process sequentially on the first wafer, the overlay accuracy measurement method further includes: The third exposure and development process is then performed on the second wafer.

16. The overlay accuracy measurement method as described in claim 15, characterized in that, Before performing the third exposure and development process on the second wafer, the overlay accuracy measurement method further includes: calculating the difference between the overlay accuracy after development and the overlay accuracy after etching of the first wafer and feeding it back to the lithography machine, wherein the lithography machine adjusts the parameters of the third exposure and development based on the difference.

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