Diffraction-based overlay mark

Abstract

The present invention relates to the field of overlay alignment, and in particular to a diffraction-based overlay mark. The diffraction-based overlay mark comprises, from top to bottom in sequence, a current layer overlay mark arranged on a current layer, a first front layer overlay mark arranged on a first front layer, and a second front layer overlay mark arranged on a second front layer; the current layer overlay mark comprises a first quadrant pattern, a second quadrant pattern, a third quadrant pattern, and a fourth quadrant pattern; each quadrant pattern comprises a plurality of parallel mark lines, and the mark lines are all lines having inclination angles; each front layer overlay mark corresponds to a group of diagonal quadrant patterns and comprises the plurality of mark lines; and both a pattern formed by the first front layer overlay mark and the current layer overlay mark and a pattern formed by the second front layer overlay mark and the current layer overlay mark are central symmetrical patterns. According to the present invention, by providing the central symmetrical overlay marks having inclined mark lines, the measurement time is shortened, and the area occupied by the overlay marks is reduced.

Description

A diffraction-based overlay mark

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on July 27, 2023, with application number 202310934464.9 and application name “A Diffraction-Based Overlay Marking”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present invention relates to the field of overlay alignment, and in particular to an overlay mark based on diffraction. Background Art

[0003] Overlay error is one of the most important parameters in the photolithography process, measuring the offset between the upper and lower patterns on the wafer. Currently, the main methods for measuring overlay error are image-based overlay (IBO) and diffraction-based overlay (DBO). Compared to IBO, DBO offers better performance in terms of equipment-induced measurement errors, repeatability of measurement results, and overall measurement uncertainty, leading to its widespread adoption in advanced nodes.

[0004] The DBO device measures the acceptance light of the gratings stacked on the current layer and the previous layer. The intensity distribution of the first-order diffracted light after diffraction by the two grating layers and the relative position offset of the two grating layers have an approximately sinusoidal variation law, and have an approximately linear relationship within a certain overlay error range. The displacement deviation can be obtained by detecting the intensity of the ±1st-order diffracted light.

[0005] However, in current logic circuits, there are multiple key layers, and sometimes it is necessary to simultaneously monitor the overlay results of the current layer on the two previous layers. However, traditional DBO overlay error measurement can only measure the overlay error of a single layer. If you want to collect and calculate the overlay error of two layers, you can only set a set of overlay marks for each of the two layers, and obtain the two sets of overlay marks for calculation. However, the above method takes up too much space, and the measurement data needs to be obtained separately, which takes a long time.

[0006] Therefore, how to reduce the area occupied by the overlay mark when measuring the two front layers and reduce the measurement time is an urgent problem to be solved by those skilled in the art.

[0007] Summary of the Invention

[0008] The purpose of the present invention is to provide an overlay mark based on diffraction to solve the problems in the prior art that the overlay calibration of two front layers cannot be performed simultaneously, the overlay mark occupies a large space, and the measurement time is long.

[0009] To solve the above technical problems, the present invention provides a diffraction-based overlay mark, which includes, from top to bottom, a current layer overlay mark set on the current layer, a first front layer overlay mark set on the first front layer, and a second front layer overlay mark set on the second front layer;

[0010] The current layer overlay mark includes a first quadrant pattern, a second quadrant pattern, a third quadrant pattern, and a fourth quadrant pattern; each quadrant pattern includes a plurality of mutually parallel marking lines, and the marking lines are all lines at an inclined angle;

[0011] Each front layer overlay mark corresponds to a set of diagonal quadrant patterns and includes a plurality of marking lines; the marking lines of the first front layer overlay mark and the marking lines of the second front layer overlay mark correspond to the marking lines of the current layer overlay mark;

[0012] The pattern formed by the first front layer overlay mark and the current layer overlay mark, and the pattern formed by the second front layer overlay mark and the current layer overlay mark are both centrosymmetric patterns.

[0013] Optionally, in the diffraction-based overlay mark, the product of the slope of the mark line of the first front layer overlay mark and the slope of the mark line of the second front layer overlay mark is a negative number.

[0014] Optionally, in the diffraction-based overlay mark, the product of the slope of the mark line of the first front layer overlay mark and the slope of the mark line of the second front layer overlay mark is -1.

[0015] Optionally, in the diffraction-based overlay mark, the slopes of the mark lines of the two front-layer overlay marks are 1 and -1 respectively.

[0016] Optionally, in the diffraction-based overlay mark, the marking line of the first previous layer overlay mark and the marking line of the second thousandth layer overlay mark are located outside the corresponding marking line of the current layer overlay mark.

[0017] Optionally, in the diffraction-based overlay mark, the first quadrant pattern, the second quadrant pattern, the third quadrant pattern and the fourth quadrant pattern are rectangular patterns.

[0018] Optionally, in the diffraction-based overlay mark, the current layer overlay mark is a square mark.

[0019] Optionally, in the diffraction-based overlay mark, the pattern formed by the first front layer overlay mark and the second front layer overlay mark has the same size as the current layer overlay mark.

[0020] Optionally, in the diffraction-based overlay mark, the number of marking lines in the pattern composed of the first front layer overlay mark and the second front layer overlay mark is the same as the number of marking lines in the current layer overlay mark.

[0021] Optionally, in the diffraction-based overlay mark, the current layer overlay mark and / or the first previous layer overlay mark and / or the second previous layer overlay mark are patterns obtained by photolithography and etching.

[0022] The diffraction-based overlay mark provided by the present invention includes, from top to bottom, a current layer overlay mark set on the current layer, a first front layer overlay mark set on the first front layer, and a second front layer overlay mark set on the second front layer; the current layer overlay mark includes a first quadrant pattern, a second quadrant pattern, a third quadrant pattern, and a fourth quadrant pattern; each quadrant pattern includes a plurality of marking lines parallel to each other, and the marking lines are all lines with inclined angles; each front layer overlay mark corresponds to a group of diagonal quadrant patterns and includes a plurality of marking lines; the marking lines of the first front layer overlay mark and the marking lines of the second front layer overlay mark correspond to the marking lines of the current layer overlay mark; the pattern composed of the first front layer overlay mark and the current layer overlay mark, and the pattern composed of the second front layer overlay mark and the current layer overlay mark are both centrally symmetrical patterns.

[0023] The present invention changes the traditional method of separately measuring the overlay error of the traditional overlay mark in the X direction and the overlay error in the Y direction by providing a centrally symmetrical overlay mark with an inclined marking line. The inclined marking line can simultaneously determine the errors of the two overlapping overlay marks in the X direction and the Y direction, thereby reducing the area occupied by the overlay mark. In addition, while maintaining the central symmetry of the two different front-layer overlay marks, each front-layer overlay mark is distributed in a group of diagonal quadrants, so that the two front-layer overlay marks can be combined into an overall structure including a pattern of four quadrants. The overlapping overlay mark patterns in the four quadrants can be simultaneously obtained through a single shot, without the need to obtain the patterns composed of the current layer overlay mark and the two front-layer overlay marks in batches, thereby greatly shortening the measurement time and further reducing the area occupied by the overlay mark. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. 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 any creative work.

[0025] FIG1 is a schematic diagram of a partial structure of a specific embodiment of a diffraction-based overlay mark provided by the present invention;

[0026] FIG2 is a schematic diagram of a partial structure of a specific embodiment of a diffraction-based overlay mark provided by the present invention;

[0027] FIG3 is a schematic diagram of a partial structure of a specific embodiment of a diffraction-based overlay mark provided by the present invention;

[0028] FIG4 is a schematic diagram of a partial structure of a specific embodiment of a diffraction-based overlay mark provided by the present invention;

[0029] FIG5 is a schematic structural diagram of a specific embodiment of a diffraction-based overlay mark provided by the present invention;

[0030] FIG6 is a schematic diagram of a partial structure of another specific embodiment of the diffraction-based overlay mark provided by the present invention;

[0031] FIG7 is a schematic structural diagram of another specific embodiment of the diffraction-based overlay mark provided by the present invention;

[0032] FIG8 is a partial cross-sectional view of a specific embodiment of the diffraction-based overlay mark provided by the present invention.

[0033] In the figure, it includes: 10 - first front layer overlay mark, 20 - second front layer overlay mark, 30 - current layer overlay mark, 11, 12, 13 - marking lines. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the present invention, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0035] The core of the present invention is to provide a diffraction-based overlay mark. The structural schematic diagram of a specific embodiment thereof is shown in Figures 1 to 5, referred to as specific embodiment 1. From top to bottom, it includes a current layer overlay mark 30 set on the current layer, a first front layer overlay mark 10 set on the first front layer, and a second front layer overlay mark 20 set on the second front layer;

[0036] The current layer overlay mark 30 includes a first quadrant pattern, a second quadrant pattern, a third quadrant pattern, and a fourth quadrant pattern; each quadrant pattern includes a plurality of mutually parallel marking lines, and the marking lines are all inclined angle lines;

[0037] Each front layer overlay mark corresponds to a set of diagonal quadrant patterns and includes a plurality of marking lines; the marking lines of the first front layer overlay mark 10 and the marking lines of the second front layer overlay mark 20 correspond to the marking lines of the current layer overlay mark 30;

[0038] The pattern formed by the first front layer overlay mark 10 and the current layer overlay mark 30 , and the pattern formed by the second front layer overlay mark 20 and the current layer overlay mark 30 are both centrosymmetric patterns.

[0039] Please refer to Figures 1 to 4. Figures 1 and 2 illustrate a front-layer overlay mark, respectively. For ease of illustration, assume that the pattern occupying the second and fourth quadrants in Figure 1 is the first front-layer overlay mark 10, and the pattern occupying the first and third quadrants in Figure 2 is the second front-layer overlay mark 20. Figure 3 shows the pattern formed by the overlapping arrangement of the first and second front layers, resulting from the overlapping of the first and second front layers. Figure 4 illustrates the corresponding current-layer overlay mark 30. To meet the basic requirements for DBO overlay error measurement, the marking lines of the current-layer overlay mark 30 in Figure 4 must be slightly offset from the marking lines of the two front-layer overlay marks in Figures 1 and 2. This allows light to diffract twice when passing through the grating formed by the front and back layers, and this serves as the basis for calculating the overlay error. Furthermore, reference numerals 11, 12, and 13 in the figures represent the marking lines of the first, second, and current-layer overlay marks 10, 20, and 30, respectively.

[0040] As a preferred embodiment, the product of the slope of the marking line of the first front layer overlay mark 10 and the slope of the marking line of the second front layer overlay mark 20 is a negative number.

[0041] That is, the marking lines in the first front layer overlay mark 10 and the second front layer overlay mark 20 have different inclination directions and opposite slopes, thereby avoiding mutual interference between the two front layer overlay marks inclined in the same direction, or manual recognition errors, thereby improving the recognition accuracy and avoiding human operational errors.

[0042] Furthermore, the product of the slope of the marking line of the first front layer overlay mark 10 and the slope of the marking line of the second front layer overlay mark 20 is -1. The product of the slopes of the marking lines of the two front layer overlay marks being -1 means that the two marking lines are perpendicular to each other. These perpendicular marking lines eliminate the possibility of interference at the contact point, thereby improving the accuracy of the data obtained in the overlay error measurement.

[0043] Furthermore, the slopes of the marking lines of the two front-layer overlay marks are 1 and -1, respectively. That is, the inclination angles of the marking lines within the two front-layer overlay marks are 45° and 135°, respectively. The marking lines within the four quadrants can be pieced together to form a square with the top corners on the X and Y axes, greatly improving the efficiency of subsequent alignment of different layer overlays.

[0044] On the other hand, the marking line of the first previous layer overlay mark 10 and the marking line of the second thousandth layer overlay mark are located outside the corresponding marking line of the current layer overlay mark 30 .

[0045] Of course, in addition to the marking lines perpendicular to the diagonal lines shown in Figure 1, the marking lines in the first front layer overlay mark 10 and the second front layer overlay mark 20 can select other angles. As shown in Figure 6, it is a structural schematic diagram of the first front layer overlay mark 10 in another specific embodiment, in which the extension direction of the marking line is the same as the extension direction of the center line connecting the diagonal quadrants. Figure 7 is a structural schematic diagram after the first front layer overlay mark 10 in Figure 6 overlaps with the corresponding current layer overlay mark 30. It can be seen that the second front layer overlay mark 20 in Figure 7 is the same as the first front layer overlay mark 10 in Figure 6, and both are overlay marks in which the extension direction of the marking line is the same as the extension direction of the center line connecting the diagonal quadrants.

[0046] Please see Figure 8, which is a schematic diagram of the positional relationship between the current layer overlay mark 30 and its corresponding previous layer overlay mark (the second previous layer overlay mark 20 is taken as an example in Figure 8). Since the pattern needs to be centrally symmetrical, the marking line of the previous layer overlay mark needs to be uniformly located on the inside or outside of the marking line of the corresponding current layer overlay mark 30. The inside or outside refers to the distance from the marking line of the previous layer overlay mark to the center of symmetry compared with the marking line of the corresponding current layer overlay mark 30. If the distance from the marking line of the previous layer overlay mark to the center of symmetry is longer than the distance from the marking line of the corresponding current layer overlay mark 30 to the center of symmetry, it is considered that the marking line of the previous layer overlay mark is located outside the marking line of the current layer overlay mark 30, otherwise it is considered to be inside. In this preferred embodiment, the marking line of the first previous layer overlay mark 10 and the marking line of the second thousandth layer overlay mark are located outside the marking line of the corresponding current layer overlay mark 30 to reduce the difficulty of calculation and improve the calculation efficiency.

[0047] Taking Figure 5 as an example, Figure 5 is a schematic diagram of the structure after the three overlay marks overlap. The current layer overlay mark 30 includes multiple marking lines that are distributed in sequence with equal intervals and are parallel to each other in the diagonal areas, and the lines in adjacent areas form a 90° angle. The arrangement direction of the marking lines is perpendicular to the extension direction of the marking lines. The marking lines occupy two diagonal areas (i.e., quadrants), and the spacing can be adjusted according to different structures; the first front layer overlay mark 10 includes multiple equally spaced marking lines that are distributed in sequence with equal intervals and are parallel to each other in the diagonal areas. The first front layer overlay mark 10 occupies one group of diagonal areas, and the marking lines are parallel to the marking lines of the current layer overlay mark 30 in the area, and are offset from the current layer by a distance d perpendicular to the line extension direction (as shown in Figure 8 As shown), the first front layer overlay mark 10 in the diagonal area is offset in the opposite direction to the current layer overlay mark 30 in the same area in a distance perpendicular to the line extension direction; the second front layer overlay mark 20 includes a plurality of equally spaced marking lines that are distributed in sequence and parallel to each other. The overlay mark occupies the diagonal area adjacent to the first front layer overlay mark, and the lines are parallel to the lines of the current layer overlay mark 30 in the area, and are offset from the current layer in a distance d' perpendicular to the line extension direction. The second front layer overlay mark 20 in the diagonal area is offset in the opposite direction to the current layer overlay mark 30 in the same area in a distance perpendicular to the line extension direction, so as to satisfy central symmetry.

[0048] In addition, the first quadrant pattern, the second quadrant pattern, the third quadrant pattern, and the fourth quadrant pattern are rectangular patterns. As shown in Figures 3 and 4, all four quadrants are rectangular patterns, which can greatly reduce production difficulty and improve production efficiency.

[0049] Furthermore, the current layer overlay mark 30 is a square mark, which can further reduce the production difficulty of the three overlay marks and improve production efficiency.

[0050] Furthermore, the current layer overlay mark 30 and / or the first front layer overlay mark 10 and / or the second front layer overlay mark 20 are patterns obtained by photolithography and etching. Graphical etching is a method for quickly obtaining overlay marks. The graphical representation of the marking lines in the overlay marks is achieved by etching, which has low requirements for equipment, that is, low production costs. Of course, other graphical methods for obtaining overlay marks can also be selected according to actual conditions, and the present invention does not limit this. Of course, the sizes of the marking lines included in the first front layer overlay mark 10, the second front layer overlay mark 20 and the current layer overlay mark 30 need to be determined according to the photolithography and etching conditions of the corresponding layers.

[0051] The diffraction-based overlay mark provided by the present invention includes, from top to bottom, a current layer overlay mark 30 set on the current layer, a first front layer overlay mark 10 set on the first front layer, and a second front layer overlay mark 20 set on the second front layer; the current layer overlay mark 30 includes a first quadrant pattern, a second quadrant pattern, a third quadrant pattern and a fourth quadrant pattern; each quadrant pattern includes a plurality of marking lines parallel to each other, and the marking lines are all lines with inclined angles; each front layer overlay mark corresponds to a group of diagonal quadrant patterns and includes a plurality of marking lines; the marking lines of the first front layer overlay mark 10 and the marking lines of the second front layer overlay mark 20 correspond to the marking lines of the current layer overlay mark 30; the pattern composed of the first front layer overlay mark 10 and the current layer overlay mark 30, and the pattern composed of the second front layer overlay mark 20 and the current layer overlay mark 30 are both centrally symmetrical patterns. The present invention replaces the traditional method of measuring overlay mark errors in the X and Y directions separately by providing centrally symmetrical overlay marks with tilted marking lines. The tilted marking lines simultaneously determine the errors of two overlapping overlay marks in the X and Y directions, reducing the area occupied by the overlay marks. Furthermore, by maintaining central symmetry between two different previous-layer overlay marks and distributing each of them within a set of diagonal quadrants, the two previous-layer overlay marks can be combined into a four-quadrant pattern. The overlapping overlay mark pattern within the four quadrants can be simultaneously acquired in a single shot, eliminating the need to acquire the pattern composed of the current-layer overlay mark 30 and the two previous-layer overlay marks separately. This significantly shortens measurement time and further reduces the area occupied by the overlay marks. Placing the overlay mark near the device within the exposure area can improve the accuracy of the overlay error results, conforming to the development trend of overlay marks in advanced technology nodes.

[0052] On the basis of the first embodiment, the number of marking lines in the overlay mark is further limited to obtain the second embodiment, the structural diagram of which is shown above, which includes, from top to bottom, a current layer overlay mark 30 set on the current layer, a first front layer overlay mark 10 set on the first front layer, and a second front layer overlay mark 20 set on the second front layer;

[0053] The current layer overlay mark 30 includes a first quadrant pattern, a second quadrant pattern, a third quadrant pattern, and a fourth quadrant pattern; each quadrant pattern includes a plurality of mutually parallel marking lines, and the marking lines are all inclined angle lines;

[0054] Each front layer overlay mark corresponds to a set of diagonal quadrant patterns and includes a plurality of marking lines; the marking lines of the first front layer overlay mark 10 and the marking lines of the second front layer overlay mark 20 correspond to the marking lines of the current layer overlay mark 30;

[0055] The pattern formed by the first front layer overlay mark 10 and the current layer overlay mark 30, and the pattern formed by the second front layer overlay mark 20 and the current layer overlay mark 30 are both centrosymmetric patterns;

[0056] The number of marking lines in the pattern formed by the first front layer overlay mark 10 and the second front layer overlay mark 20 is the same as the number of marking lines in the current layer overlay mark 30 .

[0057] The difference between this specific embodiment and the above specific embodiment is that this specific embodiment limits the quantitative relationship between the current layer overlay mark 30 and the marking lines in the two previous layer overlay marks. Other structures are the same as the above specific embodiment and will not be elaborated here.

[0058] In this specific embodiment, the number of marking lines in the combined pattern of the first front layer mark and the second front layer mark is the same as the number of marking lines in the pattern of the current layer overlay mark 30 and they correspond one to one, that is, the two should have slightly different line positions but the same pattern. The obtained diffraction pattern is uniform and regular, and the calculated overlay error is more precise and accurate.

[0059] On the basis of the first embodiment, the number of marking lines in the overlay mark is further limited to obtain the third embodiment, the structural diagram of which is shown above, and includes, from top to bottom, a current layer overlay mark 30 set on the current layer, a first front layer overlay mark 10 set on the first front layer, and a second front layer overlay mark 20 set on the second front layer;

[0060] The current layer overlay mark 30 includes a first quadrant pattern, a second quadrant pattern, a third quadrant pattern, and a fourth quadrant pattern; each quadrant pattern includes a plurality of mutually parallel marking lines, and the marking lines are all inclined angle lines;

[0061] Each front layer overlay mark corresponds to a set of diagonal quadrant patterns and includes a plurality of marking lines; the marking lines of the first front layer overlay mark 10 and the marking lines of the second front layer overlay mark 20 correspond to the marking lines of the current layer overlay mark 30;

[0062] The pattern formed by the first front layer overlay mark 10 and the current layer overlay mark 30, and the pattern formed by the second front layer overlay mark 20 and the current layer overlay mark 30 are both centrosymmetric patterns;

[0063] The pattern formed by the first front layer overlay mark 10 and the second front layer overlay mark 20 has the same size as the current layer overlay mark 30 .

[0064] The difference between this embodiment and the above embodiment is that this embodiment defines the size relationship between the current layer overlay mark 30 and the two previous layer overlay marks. Other structures are the same as the above embodiment and will not be elaborated here.

[0065] In this specific embodiment, the combined pattern of the first front layer mark and the second front layer mark is set to the same size as the current layer overlay mark 30, avoiding the existence of non-overlapping pattern areas, resulting in space waste, and further reducing space occupancy.

[0066] A method for measuring the overlay error of the diffraction-based overlay mark described above is provided below, comprising the following steps:

[0067] Step 1: Provide a wafer and design a set of overlay marks. The overlay marks include a first front layer overlay mark 10, a second front layer overlay mark 20, and a current layer overlay mark 30. The first front layer overlay mark 10 comprises a plurality of equally spaced lines that are sequentially distributed and parallel to each other, and the marks occupy one set of diagonal regions. The second front layer overlay mark 20 comprises a plurality of equally spaced lines that are sequentially distributed and parallel to each other, and the marks occupy another set of diagonal regions.

[0068] Step 2: Complete the photolithography and etching processes of the first front layer of the wafer to form the first front layer overlay mark 10 .

[0069] Step 3: Complete the photolithography and etching process of the second front layer of the wafer to form the second front layer overlay mark 20. The overlay mark formed by the first front layer overlay mark 10 and the second front layer overlay mark 20 is shown in FIG3 , occupying the second quadrant and the first quadrant respectively.

[0070] Step 4: Complete the photolithography process of the current layer of the wafer to form the current layer overlay mark 30 . The first overlay mark, the second overlay mark, and the current layer mark constitute a final overlay mark.

[0071] Step 5: Use the optical diffraction method to measure. According to the diffraction light intensity distribution formed by the current layer overlay mark 30 and the first previous layer overlay mark 10, the overlay errors of the current layer overlay mark 30 and the first previous layer overlay mark 10 in the X direction and Y direction can be obtained respectively; according to the diffraction light intensity distribution formed by the current layer overlay mark 30 and the second previous layer overlay mark 20, the overlay errors of the current layer overlay mark 30 and the second previous layer overlay mark 20 in the X direction and Y direction can be obtained respectively. Finally, in the same area, the overlay errors of the current layer to the first previous layer and the second previous layer can be obtained at the same time.

[0072] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from the other embodiments. Reference can be made to the descriptions of the identical or similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and the relevant parts can be referred to the descriptions of the methods.

[0073] It should be noted that, in this specification, relational terms such as first and second, etc. are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element.

[0074] The above describes in detail the diffraction-based overlay marking provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is intended only to facilitate understanding of the method and core concepts of the present invention. It should be noted that those skilled in the art may make various improvements and modifications to the present invention without departing from the principles of the present invention, and such improvements and modifications fall within the scope of protection of the claims of the present invention.

Claims

1. A diffraction-based overlay mark, characterized in that: From top to bottom, it includes a current layer overlay mark set on the current layer, a first front layer overlay mark set on the first front layer, and a second front layer overlay mark set on the second front layer; The current layer overlay mark includes a first quadrant pattern, a second quadrant pattern, a third quadrant pattern and a fourth quadrant pattern; each quadrant pattern includes a plurality of mutually parallel marking lines, and the marking lines are all lines with inclined angles; Each front layer overlay mark corresponds to a set of diagonal quadrant patterns and includes a plurality of marking lines; the marking lines of the first front layer overlay mark and the marking lines of the second front layer overlay mark correspond to the marking lines of the current layer overlay mark; The pattern formed by the first front layer overlay mark and the current layer overlay mark, and the pattern formed by the second front layer overlay mark and the current layer overlay mark are both centrally symmetrical patterns.

2. The diffraction-based overlay mark of claim 1, wherein: The product of the slope of the mark line of the first front layer overlay mark and the slope of the mark line of the second front layer overlay mark is a negative number.

3. The diffraction-based overlay mark of claim 2, wherein: The product of the slope of the mark line of the first front layer overlay mark and the slope of the mark line of the second front layer overlay mark is -1.

4. The diffraction-based overlay mark of claim 3, wherein: The slopes of the marking lines of the two front layer overlay marks are 1 and -1 respectively.

5. The diffraction-based overlay mark of claim 4, wherein: The marking line of the first front layer overlay mark and the marking line of the second thousand layer overlay mark are located outside the corresponding marking line of the current layer overlay mark.

6. The diffraction-based overlay mark of claim 1, wherein: The first quadrant pattern, the second quadrant pattern, the third quadrant pattern, and the fourth quadrant pattern are rectangular patterns.

7. The diffraction-based overlay mark of claim 1, wherein: The current layer overlay mark is a square mark.

8. The diffraction-based overlay mark of claim 1, wherein: The pattern formed by the first front layer overlay mark and the second front layer overlay mark has the same size as the current layer overlay mark.

9. The diffraction-based overlay mark of claim 1, wherein: The number of mark lines in the pattern composed of the first front layer overlay mark and the second front layer overlay mark is the same as the number of mark lines of the current layer overlay mark.

10. The diffraction-based overlay mark according to any one of claims 1 to 9, characterized in that The current layer overlay mark and / or the first front layer overlay mark and / or the second front layer overlay mark are patterns obtained by photolithography and etching.

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