Double-grating alignment mark and alignment method

Abstract

The invention relates to the technical field of photoetching, in particular to a double-grating alignment mark and an alignment method. The double-grating alignment mark comprises a first mark group and a second mark group. The first mark group is arranged on the wafer and comprises a circular grating A1 and two long gratings B1, B2. And the second mark group is arranged on the mask and comprises a circular grating A2 and two long gratings B3-B4. According to the double-grating alignment mark, on one hand, coarse alignment is achieved through a circular grating, fine alignment in the X direction and fine alignment in the Y direction are conducted through a vertically-arranged long grating, and on the other hand, the deviation angle delta theta is calculated based on inclined strip-shaped moire fringes formed when the long grating is not aligned. Therefore, the wafer is adjusted to be completely aligned with the mask, and the alignment precision of the wafer and the mask is effectively improved. The problem that errors caused by angular displacement cannot be eliminated when only a circular grating is adopted as an alignment mark in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the field of photolithography technology, and more specifically to: 1. a double grating alignment mark; 2. a double grating alignment method. Background Art

[0002] Optical alignment is one of the key technologies of lithography system and an important factor affecting lithography resolution.

[0003] The most important part of optical alignment is the high-precision alignment between the wafer and the mask. Usually, there will be translation, rotation, and runout errors between the wafer and the mask. Among them, rotation and translation misalignment are mainly determined by the relative state between the two planes of the wafer and the mask, which greatly affects the alignment accuracy. As long as the misalignment is controlled within the accuracy requirement range, the lithography accuracy can be guaranteed.

[0004] In order to achieve alignment, alignment marks are usually designed on the wafer and mask, for example, the alignment marks are designed as circular gratings - circular moiré fringes are generated during circular grating alignment to determine whether alignment is achieved. However, the inventors have found through research that the circular moiré fringes generated by circular grating alignment are symmetrical and isotropic, such as Figure 1 As shown: Figure 1 The middle (a) area shows the moiré fringes that appear when the center of the circular grating is not aligned. The fringes near the center are not isotropic. Figure 1 The middle area (b) shows the moiré fringes that appear when the circular grating is aligned in the center, which are symmetrical and isotropic.

[0005] However, if the wafer and the mask rotate relative to each other with the center of the circular grating as the origin, the circular grating will still produce circular moiré fringes, but in fact the wafer and the mask are not aligned, and there is an angular displacement between the two, which will cause alignment errors and affect the lithography accuracy. Therefore, how to correct the angular displacement becomes a difficult problem that needs to be solved. Summary of the invention

[0006] Based on this, it is necessary to provide a dual grating alignment mark and alignment method to address the problem that the error caused by angular displacement cannot be eliminated when only a circular grating is used as an alignment mark.

[0007] The present invention is implemented by the following technical solutions:

[0008] In a first aspect, the present invention discloses a double grating alignment mark, comprising: a first mark group and a second mark group.

[0009] The first marking group is set on the wafer; the first marking group includes: 1 circular grating A1, 2 long gratings B1~B2; B1 and B2 are located on the periphery of A1; the side of B1 closest to A1 is b1; the midline of b1 passes through the center of A1, and the distance between the center of A1 and b1 is L1; the side of B2 closest to A1 is b2; the midline of b2 passes through the center of A1, and the distance between the center of A1 and b2 is L2; ​​the midline of b1 is perpendicular to the midline of b2.

[0010] The second marking group is set on the mask; the second marking group includes: 1 circular grating A2, 2 long gratings B3~B4; B3 and B4 are located on the periphery of A2; the side of B3 closest to A2 is b3; the midline of b3 passes through the center of A2, and the distance between the center of A2 and b3 is L3; the side of B4 closest to A2 is b4; the midline of b4 passes through the center of A2, and the distance between the center of A2 and b4 is L4; the midline of b3 is perpendicular to the midline of b4.

[0011] Among them, A1 and A2 are used to achieve coarse alignment;

[0012] L1 = L3; B1 and B3 are used to achieve precise alignment in the X direction and eliminate rotational misalignment;

[0013] L2=L4; B2 and B4 are used to achieve precise alignment in the Y direction and eliminate rotational misalignment;

[0014] The period of A1 is Q1; the period of A2 is Q2;

[0015] The interval of A1 is q1; the period of A2 is q2;

[0016] The periods of B1 and B2 are both P1; the periods of B3 and B4 are both P2;

[0017] The gaps of B1 and B2 are both p1; the gaps of B3 and B4 are both p2;

[0018] Q1, Q2, q1, q2, P1, P2, p2, p3 satisfy:

[0019] 1.05≤Q1 / Q2≤1.15, 1.05≤P1 / P2≤1.15, q1 / Q1=q2 / Q2, p1 / P1=p2 / P2;

[0020] Or, 1.05≤Q2 / Q1≤1.15, 1.05≤P2 / P1≤1.15, q1 / Q1=q2 / Q2, p1 / P1=p2 / P2.

[0021] Such a dual grating alignment mark implements a method or process according to an embodiment of the present disclosure.

[0022] In a second aspect, the present invention discloses a dual grating alignment method, which is applied to the dual grating alignment mark disclosed in the first aspect.

[0023] Dual grating alignment methods include:

[0024] The dual grating alignment method comprises:

[0025] S1, stack the wafer and the mask up and down, keep the mask still and move the wafer until A1 and A2 are roughly aligned;

[0026] S2, rotating the wafer in a single direction while keeping the center of circle A1 stationary, until two strip-shaped moiré fringes appear when observing the mask in the up and down directions;

[0027] S3, comparing the strip moiré fringes at any location with the long grating where it is located, to determine whether the strip moiré fringes at that location are tilted;

[0028] If yes, proceed to S4;

[0029] If not, proceed to S7;

[0030] S4, obtaining the image of the strip moiré fringes in S3, and performing image processing on the image to obtain the period P of the strip moiré fringes at that location m ;

[0031] S5, based on P m , P1, P2 calculate the deviation angle Δθ;

[0032] in,

[0033] S6, rotating the wafer according to Δθ while keeping the center of circle A1 stationary, thus eliminating the rotational misalignment;

[0034] S7, moving the wafer along the X direction and the Y direction until B1 and B3 complete the fine alignment in the X direction, and B2 and B4 complete the fine alignment in the Y direction.

[0035] This dual grating alignment method implements the method or process according to an embodiment of the present disclosure.

[0036] In a third aspect, the present invention discloses a computer program product, comprising a computer program. When the computer program is executed by a processor, the steps of the double grating alignment method disclosed in the second aspect are implemented.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The present invention provides a dual-grating alignment mark. On the one hand, a circular grating is used to achieve coarse alignment, and a vertically arranged long grating is used to perform fine alignment in the X direction and the Y direction respectively. On the other hand, a deviation angle Δθ is calculated based on the inclined strip moiré fringes formed when the long grating is not aligned, so that the wafer is adjusted so that it can be fully aligned with the mask and the alignment accuracy of the two is effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0040] Figure 1 This is an optical diagram of the moiré fringes that may appear when a circular grating is used for coarse alignment;

[0041] Figure 2 A structural diagram of a double grating alignment mark provided in Example 1 of the present invention;

[0042] Figure 3 for Figure 2 Schematic diagram of structural parameters of A1 and A2;

[0043] Figure 4 for Figure 2 Schematic diagram of structural parameters of B1 and B3;

[0044] Figure 5 For use Figure 2 Schematic diagram of the deviation angle Δθ when aligning the double grating alignment marks;

[0045] Figure 6 An optical image of moiré fringes formed by a long grating when a rotational misalignment occurs provided in Example 1 of the present invention;

[0046] Figure 7 This is an optical image of the moiré fringes formed by the long grating after the rotational misalignment is eliminated, as provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0047] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] It should be noted that when a component is referred to as being "mounted on" another component, it may be directly on the other component or there may be a central component. When a component is considered to be "set on" another component, it may be directly set on the other component or there may be a central component at the same time. When a component is considered to be "fixed to" another component, it may be directly fixed on the other component or there may be a central component at the same time.

[0049] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "or / and" used herein includes any and all combinations of one or more of the related listed items.

[0050] Example 1

[0051] See also Figure 2 , Figure 2 FIG. 1 shows a structural diagram of a dual grating alignment mark provided in this embodiment 1. Figure 2 As shown, the double grating alignment mark includes: a first mark group and a second mark group.

[0052] 1. See Figure 2 In the left area, a first marking group is set on the wafer.

[0053] The first marking group includes: 1 circular grating A1 and 2 long gratings B1-B2.

[0054] B1 and B2 are located outside A1; the side of B1 closest to A1 is b1; the midline of b1 passes through the center of A1, and the distance between the center of A1 and b1 is L1; the side of B2 closest to A1 is b2; the midline of b2 passes through the center of A1, and the distance between the center of A1 and b2 is L2; ​​the midline of b1 is perpendicular to the midline of b2.

[0055] 2. See Figure 2 In the right area, a second marking group is set on the mask.

[0056] The second marking group includes: 1 circular grating A2 and 2 long gratings B3-B4.

[0057] B3 and B4 are located outside A2; the side of B3 closest to A2 is b3; the midline of b3 passes through the center of A2, and the distance between the center of A2 and b3 is L3; the side of B4 closest to A2 is b4; the midline of b4 passes through the center of A2, and the distance between the center of A2 and b4 is L4; the midline of b3 is perpendicular to the midline of b4.

[0058] in:

[0059] (i) A1 and A2 are used to achieve coarse alignment.

[0060] See also Figure 3 , A1 includes: a plurality of concentric circular slits arranged at varying intervals;

[0061] A2 includes: a plurality of concentric circular slits arranged at varying intervals.

[0062] In other words, the structures of A1 and A2 are similar.

[0063] like Figure 3 As shown, the period of A1 is Q1; the period of A2 is Q2;

[0064] The interval of A1 is q1; the period of A2 is q2;

[0065] The maximum outer diameter of A1 is D1; ​​the maximum outer diameter of A2 is D2.

[0066] It should be noted that although there is no strict limit on D1 and D2, due to processing considerations, the difference between the two should not be too large.

[0067] (ii) L1 = L3; B1 and B3 are used to achieve precise alignment in the X direction;

[0068] L2=L4; B2 and B4 are used to achieve precise alignment in the Y direction.

[0069] See also Figure 4 , B1 includes: a plurality of strip slits with the same height, the same width and equidistant intervals;

[0070] B2 includes: a plurality of strip-shaped slits of the same height, width and equidistant intervals;

[0071] B3 includes: a plurality of strip slits of the same height, width and equidistant intervals;

[0072] B4 includes: a plurality of strip-shaped slits with the same height, width and equidistant intervals.

[0073] In other words, the structures of B1 to B4 are similar:

[0074] The midline of B1 is perpendicular to the strip slits within it, and the same is true for B2 to B4.

[0075] like Figure 3 As shown, the periods of B1 and B2 are both P1; the periods of B3 and B4 are both P2;

[0076] The gaps of B1 and B2 are both p1; the gaps of B3 and B4 are both p2;

[0077] The height of the strip slits in B1 and B3 is h1; the height of the strip slits in B2 and B4 is h2;

[0078] The total width of B1 and B2 is l1, and the total width of B3 and B4 is l2.

[0079] It should be noted that

[0080] Although there is no strict limit on h1 and h2, for processing considerations, the difference between the two should not be too large. It is recommended that h1=h2.

[0081] Similarly, although there are no strict restrictions on l1 and l2, for processing considerations, the difference between the two should not be too large, and it is recommended that l1=l2.

[0082] In summary, Q1, Q2, q1, q2, P1, P2, p2, and p3 satisfy any of the following conditions:

[0083] ①1.05≤Q1 / Q2≤1.15, 1.05≤P1 / P2≤1.15, q1 / Q1=q2 / Q2, p1 / P1=p2 / P2;

[0084] ②1.05≤Q2 / Q1≤1.15, 1.05≤P2 / P1≤1.15, q1 / Q1=q2 / Q2, p1 / P1=p2 / P2.

[0085] In this embodiment 1, considering the convenience of processing, q1 / Q1 and p1 / P1 are both set to 0.5, Q2 / Q1 is set to 1.1, and P2 / P1 is set to 1.1; in addition, L1=L2, D1=D2, l1=l2, and h1=h2 are set to reduce the difficulty of processing.

[0086] In addition, considering the requirements of the process technology, Q1, Q2, P1, and P2 should all be less than 10μm.

[0087] Based on the double grating alignment mark of the above structure, this embodiment 1 also simultaneously discloses a double grating alignment method, which is applied to the double grating alignment mark of the above structure.

[0088] Dual grating alignment methods include:

[0089] S1, stack the wafer and the mask up and down, keep the mask still and move the wafer until A1 and A2 are roughly aligned.

[0090] As for how to complete the rough alignment, the existing technology can already achieve it, which will not be described here in detail:

[0091] Since the processing has reached the nanometer level, a CCD camera is usually set in the direction of looking down at the mask to identify whether the rough calibration has been completed: if the CCD camera captures the circular moiré fringes formed by the interference of A1 and A2 (such as Figure 1 As shown in area b of FIG, the rough alignment has been completed.

[0092] However, it should be noted that there may still be nanometer-level errors in coarse alignment.

[0093] S2, rotate the wafer in a single direction while keeping the center of circle A1 stationary until two strip-shaped moiré fringes appear when observing the mask in the up and down directions.

[0094] This step aims to obtain two strip moiré fringes: one is formed by the interference of B1 and B3, and the other is formed by the interference of B2 and B4.

[0095] S3, comparing the stripe moiré fringes at any location with the long grating where it is located, to determine whether the stripe moiré fringes at that location are tilted;

[0096] If yes, proceed to S4;

[0097] If no, proceed to S7.

[0098] It should be noted that if the strip moiré fringes are tilted compared to the long grating, it means that a rotational misalignment has occurred. Since the deviation angles corresponding to the strip moiré fringes at the two locations are the same, it is only necessary to judge the strip moiré fringes at any location and the long grating where it is located.

[0099] See also Figure 5 , showing a schematic diagram of the inclined strip moiré fringes formed by B1 and B3. It can be seen that the direction of the moiré fringes here is not perpendicular to the midline of B1 or B3, and the deviation angle is Figure 5 For ease of understanding, see Figure 6 , showing the optical image of the moiré fringes formed by a long grating when a rotational misalignment occurs.

[0100] S4, obtaining the image of the strip moiré fringes in S3, and performing image processing on the image to obtain the period P of the strip moiré fringes at that location m .

[0101] In S4, it is recommended to firstly take a picture of the stripe moiré fringe with a CCD camera to obtain a stripe moiré fringe image; and then process the captured stripe moiré fringe image with a relevant image processing algorithm (such as image optimization, edge profile detection and edge profile extraction, etc.) to obtain its period P. m .

[0102] S5, based on P m , P1, P2 calculate the deviation angle Δθ;

[0103] in,

[0104] In order to explain the origin of Δθ, we can use Figure 5 For example:

[0105] Δθ is the angle formed by the midline of B3 and the midline of B1, which satisfies:

[0106] In the formula, Δr represents the rotational misalignment offset of B1 and B3; Δx is the decomposition of Δr in the X direction, and Δy is the decomposition of Δr in the Y direction.

[0107] Obviously, when the rotational angular displacement is in the nanometer range, direct measurement is difficult to solve, so other geometric relationships are needed to solve it.

[0108] Depend on Figure 5 It can be seen that the angle between the line d3 where the edge of B3 (i.e. the end of the strip slit in B3) is located and the line d1 where the edge of B1 (i.e. the end of the strip slit in B1) is located is Δδ;

[0109] 1. Δδ satisfies:

[0110] Specifically, according to existing literature: By transforming it, we can get

[0111] 2. Δδ and Δθ are of the same magnitude.

[0112] See also Figure 5 , the midline of B3 is parallel to d3, and the midline of B1 is parallel to d1, so: Δδ=Δθ.

[0113] therefore, That is, we only need to obtain the period P of the strip moiré fringes. m , we can calculate Δθ.

[0114] S6, rotating the wafer according to Δθ while keeping the center of circle A1 stationary, thereby eliminating the rotational misalignment.

[0115] Specifically, if the wafer is rotated clockwise in S2, then in S6, the wafer is continued to be rotated counterclockwise by Δθ, or the wafer is rotated clockwise by 360°-Δθ;

[0116] If the wafer is rotated counterclockwise in S2 , the wafer is further rotated clockwise by Δθ in S6 , or the wafer is rotated counterclockwise by 360°-Δθ.

[0117] For easier understanding, see Figure 7, showing the optical image of the moiré fringes formed by the long grating after eliminating the rotational misalignment. Figure 7 The middle a area shows the moiré fringes formed by the interference of B1 and B3 after eliminating the rotational misalignment, and its direction is consistent with the strip slits of B1 and B3; Figure 7 The middle b area shows the moiré fringes formed by the interference of B2 and B4 after the rotational misalignment is eliminated, and its direction is consistent with the strip slits of B2 and B4.

[0118] S7, moving the wafer along the X direction and the Y direction until B1 and B3 complete the fine alignment in the X direction, and B2 and B4 complete the fine alignment in the Y direction.

[0119] After the operations of S1 to S6, the rough alignment has been achieved and the rotational misalignment has been eliminated, but the error of the rough alignment will still cause errors in the X and Y directions. Therefore, the fine alignment of the X and Y directions is required.

[0120] As for how to complete the X-direction and Y-direction precise alignment, the existing technology can already achieve it, and will not be repeated here:

[0121] Considering that the processing process has reached the nanometer level, a photoelectric sensor is generally set in the direction of looking down at the mask to identify whether the precise alignment in the X direction and the precise alignment in the Y direction has been completed.

[0122] If the photoelectric sensor detects that the peak of the moiré fringe formed by the interference of B1 and B3 is at the target position in the X direction, the X-direction precise alignment has been completed;

[0123] If the photoelectric sensor detects that the peak of the strip moiré fringe formed by the interference of B2 and B4 is at the target position in the Y direction, the precise alignment in the Y direction has been completed.

[0124] At this point, the first marking group and the second marking group are fully aligned.

[0125] It should be noted that the calculation accuracy of Δθ directly affects the full alignment accuracy of the wafer and the mask, that is, the full alignment accuracy of the present invention is affected by the manufacturing accuracy of the alignment mark, the resolution of the CCD camera, the image processing accuracy, etc. In the specific experimental operation, it is possible to: 1. Adapt the parameter size of the double grating alignment mark to meet different occasions; 2. Ensure the high manufacturing accuracy of the double grating alignment mark; 3. Use a high-resolution CCD camera to obtain the image of the strip moiré fringe, and use a high-precision image processing algorithm to calculate P m .

[0126] Example 2

[0127] This embodiment 2 discloses a computer device, including a memory and a processor, wherein a computer program is stored in the memory, and when the processor executes the computer program, the steps of the dual grating alignment method disclosed in embodiment 1 are implemented.

[0128] This embodiment 2 also discloses a readable storage medium, in which computer program instructions are stored. When the computer program instructions are read and executed by a processor, the steps of the dual grating alignment method disclosed in embodiment 1 are executed.

[0129] This embodiment 2 also discloses a computer program product, including a computer program. When the computer program is executed by a processor, the steps of the double grating alignment method disclosed in embodiment 1 are implemented.

[0130] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A double grating alignment mark, characterized in that: include: A first marking group is disposed on the wafer; The first marking group includes: a circular grating A1, and two long gratings B1-B2; B1 and B2 are located on the periphery of A1; the side of B1 closest to A1 is b1; the midline of b1 passes through the center of A1, and the distance between the center of A1 and b1 is L1; the side of B2 closest to A1 is b2; the midline of b2 passes through the center of A1, and the distance between the center of A1 and b2 is L2; ​​the midline of b1 is perpendicular to the midline of b2; A second marking group is arranged on the mask; the second marking group includes: 1 circular grating A2, 2 long gratings B3-B4; B3 and B4 are located at the periphery of A2; the side of B3 closest to A2 is b3; the midline of b3 passes through the center of A2, and the distance between the center of A2 and b3 is L3; the side of B4 closest to A2 is b4; the midline of b4 passes through the center of A2, and the distance between the center of A2 and b4 is L4; the midline of b3 is perpendicular to the midline of b4; Among them, A1 and A2 are used to achieve coarse alignment; L1 = L3; B1 and B3 are used to achieve precise alignment in the X direction and eliminate rotational misalignment; L2=L4; B2 and B4 are used to achieve precise alignment in the Y direction and eliminate rotational misalignment; The period of A1 is Q1; the period of A2 is Q2; The interval of A1 is q1; the period of A2 is q2; The periods of B1 and B2 are both P1; the periods of B3 and B4 are both P2; The gaps of B1 and B2 are both p1; the gaps of B3 and B4 are both p2; Q1, Q2, q1, q2, P1, P2, p2, p3 satisfy: 1.05≤Q1 / Q2≤1.15, 1.05≤P1 / P2≤1.15, q1 / Q1=q2 / Q2, p1 / P1=p2 / P2; Or, 1.05≤Q2 / Q1≤1.15, 1.05≤P2 / P1≤1.15, q1 / Q1=q2 / Q2, p1 / P1=p2 / P2.

2. The double grating alignment mark according to claim 1, characterized in that: Q1, Q2, P1, and P2 are all less than 10 μm.

3. The double grating alignment mark according to claim 1 or 2, characterized in that: A1 includes: A plurality of concentric circular slits arranged at varying intervals; A2 includes: a plurality of concentric circular slits arranged at varying intervals.

4. The double grating alignment mark according to claim 1 or 2, characterized in that: B1 includes: A plurality of strip-shaped slits having the same height, the same width and being arranged at equal intervals; B2 includes: a plurality of strip-shaped slits of the same height, width and equidistant intervals; B3 includes: a plurality of strip slits of the same height, width and equidistant intervals; B4 includes: a plurality of strip-shaped slits with the same height, width and equidistant intervals.

5. The double grating alignment mark according to claim 4, characterized in that: The heights of the strip slits in B1 and B3 are both h1; the heights of the strip slits in B2 and B4 are both h2.

6. The double grating alignment mark according to claim 4, characterized in that: The total width of B1 and B2 is l1, and the total width of B3 and B4 is l2.

7. The dual grating alignment mark according to claim 1, characterized in that: L1=L2; Or / and, p1 / P1=0.

5.

8. A dual grating alignment method, characterized in that: It is applied to the double grating alignment mark as described in any one of claims 1 to 7; The dual grating alignment method comprises: S1, stack the wafer and the mask up and down, keep the mask still and move the wafer until A1 and A2 are roughly aligned; S2, rotating the wafer in a single direction while keeping the center of circle A1 stationary, until two strip-shaped moiré fringes appear when observing the mask in the up and down directions; S3, comparing the strip moiré fringes at any location with the long grating where it is located, to determine whether the strip moiré fringes at that location are tilted; If yes, proceed to S4; If not, proceed to S7; S4, obtaining the image of the strip moiré fringes in S3, and performing image processing on the image to obtain the period P of the strip moiré fringes at that location m ; S5, based on P m , P1, P2 calculate the deviation angle Δθ; in, S6, rotating the wafer according to Δθ while keeping the center of circle A1 stationary, thus eliminating the rotational misalignment; S7, moving the wafer along the X direction and the Y direction until B1 and B3 complete the fine alignment in the X direction, and B2 and B4 complete the fine alignment in the Y direction.

9. The dual grating alignment method according to claim 8, characterized in that: If the wafer is rotated clockwise in S2, then in S6, the wafer is continued to be rotated counterclockwise by Δθ, or the wafer is rotated clockwise by 360°-Δθ; If the wafer is rotated counterclockwise in S2 , the wafer is further rotated clockwise by Δθ in S6 , or the wafer is rotated counterclockwise by 360°-Δθ.

10. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the dual grating alignment method according to any one of claims 1 to 9 are implemented.

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