Alignment mark structure applied to wafer optical measurement and measurement method

Abstract

The invention provides an alignment mark structure applied to wafer optical measurement and a measurement method, in the alignment mark structure, the alignment mark structure is arranged in a cutting channel of a wafer and is positioned near an optical measurement target, and the alignment mark structure comprises at least two alignment marks: a first mark and a second mark, the patterns of the first mark and the second mark are non-centrosymmetric patterns and are different, all the alignment marks are embedded among the plurality of measuring pads at intervals, and the patterns of the first mark and the second mark are manufactured by overlay of non-centrosymmetric patterns with the same upper and lower layers of dielectric layers of at least two or more layers of wafers; a plurality of measuring pads are arranged between the first mark and the second mark at intervals, the optical measuring target is located between the first mark and the second mark, or the optical measuring target is located on one side of the first mark or the second mark, and frequent reconstruction or modification of measuring programs of measuring equipment for different products is not needed. And standardization and automation of a measurement program can be realized conveniently.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated circuits, and in particular to an alignment mark structure and a measurement method used in wafer optical measurement. Background Art

[0002] Currently, optical metrology is commonly used in semiconductor manufacturing to measure physical parameters such as film thickness, line width, depth, height, and angle on wafers. To ensure measurement accuracy, the metrology equipment's probe light spot must precisely land on an optical measurement target. The optical measurement target typically refers to one or more measurement pads. Typically, the metrology equipment first locates a specific pattern (also known as a dedicated alignment pattern) on the wafer. The pattern's appearance and relative coordinates to the optical measurement target are predefined in the measurement program. Based on the image information provided in the measurement program, the metrology equipment identifies and locks onto the dedicated alignment pattern on the wafer, using it as a reference. During the measurement process, alignment is often required to align the measurement spot with the optical measurement target. However, because the dedicated alignment pattern is often located far from the optical measurement target, significant errors can accumulate during the long movement of the workstage from the dedicated alignment pattern to the optical measurement target, causing the light spot to deviate from the measurement target. In addition, when there is a lack of unique patterns near the optical measurement target, the difficulty of identifying the measurement target will be greatly increased, and it is easy to measure the wrong position, resulting in measurement failure. Summary of the Invention

[0003] The object of the present invention is to provide an alignment mark structure and a measurement method for wafer optical measurement, so as to improve the alignment accuracy of the optical measurement.

[0004] To achieve the above objectives, the present invention provides an alignment mark structure for wafer optical measurement, which is used to assist in the alignment of optical measurement equipment. The alignment mark structure is disposed within a dicing street of a wafer and is located near an optical measurement target. The alignment mark structure includes at least two alignment marks: a first mark and a second mark. The patterns of the first mark and the second mark are both non-center-symmetrical and different. These alignment marks are intermittently embedded between a plurality of measurement pads and, together with all of the measurement pads, form an integrated measurement structure. The patterns of the first mark and the second mark are produced by overlaying the same non-center-symmetrical patterns on at least two or more dielectric layers of the wafer, such that the patterns of the alignment marks on the upper and lower layers completely overlap. The first mark and the second mark are separated by a number of the measurement pads. The optical measurement target is located between the first mark and the second mark, or the optical measurement target is located on one side of the first mark or the second mark.

[0005] Optionally, in the alignment mark structure, the pattern of the first mark is identical to the pattern of the second mark after being rotated by several angles.

[0006] Optionally, in the alignment mark structure, the alignment mark structure further includes: a third mark, and the optical measurement target is located between the second mark and the third mark or on a side of the third mark away from the second mark.

[0007] Optionally, in the alignment mark structure, the alignment mark structure further includes a fourth mark, and the first mark, the second mark, the third mark and the fourth mark are formed by rotating the same non-centrally symmetrical figure at different angles.

[0008] Optionally, in the alignment mark structure, the third mark and the fourth mark are composed of a combination of regular patterns of preset small size.

[0009] Optionally, in the alignment mark structure, the distance between the first mark and the second mark is approximately the size of the field of view of the alignment magnification of the measurement equipment, and the distance between the first mark and the second mark is in the range of 0.2 mm to 2 mm.

[0010] Optionally, in the alignment mark structure, the first mark and the second mark are composed of a combination of regular patterns of preset small sizes.

[0011] Optionally, the width of the pattern lines inside the first mark and the second mark is in the range of 1 μm to 20 μm, and there is no other pattern within the range of 5 μm to 10 μm around the first mark and the second mark.

[0012] Based on the same inventive concept, the present invention also provides a measurement method for wafer optical measurement, including: providing a wafer, wherein the wafer is provided with a cutting path, a dedicated alignment pattern and an alignment mark structure are formed in the cutting path, the dedicated alignment pattern, the alignment mark structure and the optical measurement target are all in the same exposure unit, and the optical measurement target includes one or more measurement pads; performing coarse alignment on the wafer using the dedicated alignment pattern so that the dedicated alignment pattern is located within the field of view of the alignment magnification of the measurement equipment; performing fine alignment on the wafer using the first mark or the second mark so that the first mark or the second mark is located within the field of view of the alignment magnification of the measurement equipment, and the light spot of the measurement equipment is completely aligned with the optical measurement target to perform film thickness or size measurement on the optical measurement target.

[0013] Optionally, in the measurement method, the exposure unit includes a plurality of positive chip areas arranged in an array and the cutting lanes located between adjacent positive chip areas; and the dedicated alignment pattern is located at a top corner of each exposure unit.

[0014] In the alignment mark structure for wafer optical measurement provided by the present invention, the alignment mark structure is arranged in the cutting path of the wafer and is located near the optical measurement target. The alignment mark structure includes: at least two alignment marks: a first mark and a second mark. The patterns of the first mark and the second mark are non-center-symmetrical and different. All alignment marks are intermittently embedded between multiple measurement pads and together with all the measurement pads form an integral measurement structure. The patterns of the first mark and the second mark are made by overlaying the same non-center-symmetrical patterns on the dielectric layers of at least two or more wafer layers, so that the patterns of the alignment marks on the upper and lower layers are as completely overlapped as possible. Several measurement pads are spaced between the first mark and the second mark, and the optical measurement target is located between the first mark and the second mark, or the optical measurement target is located on one side of the first mark or the second mark. In this way, during the process of wafer optical measurement, the optical measurement target can be accurately aligned through the first mark or the second mark, so that the light spot is completely aligned with the optical measurement target, thereby improving the measurement alignment accuracy. In addition, the alignment mark structure can be placed on different products for use, eliminating the need to frequently rebuild or modify the measurement program for different products, thereby facilitating the standardization and automation of the measurement program. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 1 is a top view of a wafer of an alignment mark structure provided by an embodiment of the present invention.

[0016] Figure 2 FIG. 1 is a top view of an alignment mark structure provided by an embodiment of the present invention.

[0017] Figure 3 FIG. 4 is a top view of an alignment mark structure provided by another embodiment of the present invention.

[0018] Figure 4 4 is a top view of a first mark of an alignment mark structure provided by an embodiment of the present invention.

[0019] Figure 5 FIG. 4 is a top view of a first mark of an alignment mark structure provided by another embodiment of the present invention.

[0020] Figure 6 FIG. 4 is a top view of a first mark of an alignment mark structure provided in another embodiment of the present invention.

[0021] Figure 7 It is a flow chart of a measurement method for wafer optical measurement provided by an embodiment of the present invention.

[0022] Figure 8 It is a top view of a wafer in the wafer optical measurement method provided by an embodiment of the present invention.

[0023] The reference numerals are as follows: 100 - wafer; 110 - cutting lane; 120 - positive chip area; 200 - alignment mark structure; 210 - first mark; 211 - regular pattern; 220 - second mark; 230 - third mark; 240 - fourth mark; 250 - measurement pad; 260 - optical measurement target; 300 - dedicated alignment pattern. DETAILED DESCRIPTION

[0024] The following, in conjunction with the accompanying drawings and specific embodiments, further details the alignment mark structure and measurement method for wafer optical metrology proposed by the present invention. The advantages and features of the present invention will become more apparent from the following description. It should be noted that the drawings are highly simplified and not to exact scale, and are intended solely to facilitate and clarify the purpose of illustrating the embodiments of the present invention.

[0025] Figure 1 1 is a top view of a wafer of an alignment mark structure provided by an embodiment of the present invention. Figure 2 FIG. 1 is a top view of an alignment mark structure provided by an embodiment of the present invention. Figure 1 and combined Figure 2 As shown, this embodiment provides an alignment mark structure 200 for optical measurement of a wafer 100, which is used to assist in the alignment of an optical measurement target 260 of a measurement device. The alignment mark structure 200 is arranged in the cutting street 110 of the wafer 100 and is located near the optical measurement target 260. The alignment mark structure 200 includes: at least two alignment marks.

[0026] like Figure 2 As shown, in some embodiments, the alignment mark structure 200 includes two alignment marks, namely a first mark 210 and a second mark 220. The patterns of the first mark 210 and the second mark 220 are non-center-symmetrical and different. All alignment marks are embedded between the measurement pads 250 in a staggered manner and together with all the measurement pads 250 form an integrated measurement structure. In this way, when alignment is performed using the alignment mark structure 200, the light spot can be reliably aligned with the optical measurement target 260, thereby improving alignment accuracy and avoiding measurement at the wrong position.

[0027] In this embodiment, the patterns of the first mark 210 and the second mark 220 are produced by overlaying the same non-center-symmetrical patterns on the upper and lower dielectric layers of at least two or more dielectric layers of the wafer 100, so that the patterns of the alignment marks of the upper and lower layers are as completely overlapped as possible, that is, the projections of the first mark 210 in each dielectric layer are completely overlapped, and the projections of the second mark 220 in each dielectric layer are completely overlapped.

[0028] It should be noted that, because the dielectric layer is light-transmissive, if the alignment mark patterns on the upper layer and the alignment mark patterns on the lower layer do not overlap as much as possible and are offset from each other, a cluttered pattern will appear in the field of view of the measurement equipment, resulting in an inability to accurately identify the first mark 210 or the second mark 220, and further causing inaccurate alignment. In this embodiment, however, the patterns of the first mark 210 and the second mark 220 are both produced by overlaying identical non-centrosymmetric patterns. The outlines of the first mark 210 or the second mark 220 on each layer completely overlap, thus avoiding the appearance of a cluttered pattern in the field of view of the measurement equipment that could lead to inaccurate identification, and improving the clarity of the first mark 210 and the second mark 220.

[0029] For example, Figure 2 As shown, a plurality of similar measurement pads 250 are spaced between the first mark 210 and the second mark 220. The first mark 210 and the second mark 220 are located within the field of view of the alignment magnification of the measurement device, and the optical measurement target 260 is located between the first mark 210 and the second mark 220. During optical measurement, the field of view of the alignment magnification of the measurement device captures the first mark 210 or the second mark 220 with a unique appearance. The relative positional relationship between the first mark 210 and the second mark 220 and the optical measurement target 260 can effectively identify the optical measurement target 260, thereby accurately positioning the optical measurement target 260, effectively reducing or avoiding alignment deviation problems during the optical measurement process.

[0030] The distance between the first mark 210 and the second mark 220 is approximately the size of the field of view of the alignment magnification of the measuring device, and the distance between the first mark 210 and the second mark 220 is in the range of 0.2 mm to 2 mm.

[0031] For example, Figure 3As shown, a number of similar measuring pads 250 are spaced between the first mark 210 and the second mark 220. The first mark 210 or the second mark 220 is identified within the field of view of the alignment magnification of the measurement device, and the optical measurement target 260 is accurately positioned according to the relative positional relationship between the first mark 210, the second mark 220 and the optical measurement target 260. The optical measurement target 260 is located between the first mark 210 and the second mark 220, or the optical measurement target 260 is located on one side of the first mark 210 or the second mark 220, that is, the optical measurement target 260 is located on the side of the second mark 220 away from the first mark 210 or on the side of the first mark 210 away from the second mark 220.

[0032] The number of measuring pads 250 spaced between the first mark 210 and the second mark 220 may be, for example, three measuring pads 250 , four measuring pads 250 , five measuring pads 250 or six measuring pads 250 . Figure 2 and Figure 3 In the description, an example is given in which two measuring pads 250 or four measuring pads 250 are provided between the first mark 210 and the second mark 220 .

[0033] In this embodiment, the graphic of the first mark 210 is the same as the graphic of the second mark 220 after being rotated by several angles. For example, the graphic of the first mark 210 is the same as the graphic of the second mark 220 after being rotated by 90°. This is conducive to simplifying the manufacturing process of the alignment mark structure 200, while ensuring that the first mark 210 and the second mark 220 can be clearly distinguished and will not be confused with each other.

[0034] In this embodiment, the spacing between the first mark 210 and the second mark 220 is within a range of 0.2 mm to 2 mm, such as 0.3 mm, 0.5 mm, 1 mm, or 1.5 mm. If the spacing is too small, the pattern density of the first mark 210 and the second mark 220 will be too high, wasting the surface area of ​​the wafer 100. If the spacing is too large, there may be a lack of suitable marks near the optical measurement target 260. Therefore, in this embodiment, the spacing between the first mark 210 and the second mark 220 is within a range of 0.2 mm to avoid wasting the surface area of ​​the wafer 100 and ensure that there are suitable marks near the optical measurement target 260.

[0035] In some embodiments, as Figure 3As shown, the alignment mark structure 200 further includes a third mark 230, that is, the alignment mark structure 200 includes three alignment marks, and the optical measurement target 260 can be located on the right side of the second mark 220. The optical measurement target 260 can be located on the right side of the second mark 220 means that the optical measurement target 260 is located between the second mark 220 and the third mark 230.

[0036] In other embodiments, the optical measurement target 260 may be located on a side of the third mark 230 away from the second mark 220 , that is, the optical measurement target 260 may be located on the right side of the third mark 230 .

[0037] In this embodiment, the distance between the first mark 210 and the second mark 220 is approximately the field of view of the alignment magnification of the measurement device, so that the first mark 210 and the second mark 220 are located in the field of view of the alignment magnification of the measurement device.

[0038] In some embodiments, as Figure 3 As shown, the alignment mark structure 200 also includes a fourth mark 240. Specifically, the alignment mark structure 200 includes four alignment marks. The first mark 210, the second mark 220, the third mark 230, and the fourth mark 240 are formed by rotating the same non-centrosymmetric pattern at different angles. For example, the first mark 210 is shaped like an inverted T, the second mark 220 is formed by rotating the first mark 210 by 90°, the third mark 230 is formed by rotating the first mark 210 by 180°, and the fourth mark 240 is formed by rotating the first mark 210 by 270°. This ensures that marks of the same shape do not appear within the larger field of view of the measurement equipment, improving the contrast of the marks, facilitating recognition by the measurement equipment and preventing the measurement equipment from capturing the wrong mark.

[0039] It should be noted that Figure 2 and Figure 3 The graphics of the first mark 210, the second mark 220, the third mark 230 and the fourth mark 240 are described using a T-shape as an example, but the graphics are not limited to the above examples. Other graphics that can be recognized by the measuring equipment, such as an F-shape or a mountain shape, can also be used.

[0040] In this embodiment, the overall size of the first mark 210 , the second mark 220 , the third mark 230 , and the fourth mark 240 may be equal to or greater than 50 um×50 um.

[0041] like Figure 4As shown, the internal line width of the first mark 210, the second mark 220, the third mark 230 and the fourth mark 240, that is, the line width W, is 1μm~20μm, to ensure that the internal lines of the first mark 210, the second mark 220, the third mark 230 and the fourth mark 240 are wider, and there are no other patterns within the range of 5μm~10μm around the first mark and the second mark, so that they can have better clarity and recognition in the optical field of view of the measuring equipment.

[0042] like Figure 5 As shown, due to the limitations of wafer product design rules, when internal lines with larger widths are not allowed, the graphics of the first mark 210, the second mark 220, the third mark 230 and the fourth mark 240 can be spliced ​​and combined by preset small-sized regular graphics 211 to meet the product design rule requirements.

[0043] In some embodiments, as Figure 5 As shown, the shape of the preset small-sized regular pattern 211 can be circular, and the spacing between adjacent regular patterns 211 can be the same so that all regular patterns 211 in the first mark 210, the second mark 220, the third mark 230 and the fourth mark 240 are evenly distributed.

[0044] In some embodiments, as Figure 6 As shown, the shape of the preset small-sized regular pattern 211 can be a rectangle, and the spacing between adjacent regular patterns 211 can be the same so that all regular patterns 211 in the first mark 210, the second mark 220, the third mark 230 and the fourth mark 240 are evenly distributed.

[0045] It should be noted that the shape of the preset small-sized regular pattern 211 is not limited to a rectangle or a circle, and may also be other regular patterns known to those skilled in the art.

[0046] In addition, the alignment mark structure 200 of this embodiment can be placed on wafers 100 of different specifications or used on different products, without the need to frequently rebuild or modify the measurement program of the measurement equipment for different products, thereby facilitating the standardization and automation of the measurement equipment program.

[0047] Figure 7 FIG. 1 is a flow chart of a wafer optical measurement method according to an embodiment of the present invention. Figure 7As shown, this embodiment provides a measurement method for wafer optical measurement, including: step S1: providing a wafer, wherein the wafer is provided with a cutting street, and a dedicated alignment pattern and an alignment mark structure are formed in the cutting street, the dedicated alignment pattern, the alignment mark structure and the optical measurement target are all in the same exposure unit, and the optical measurement target includes one or more measurement pads; step S2: performing coarse alignment on the wafer using the dedicated alignment pattern so that the dedicated alignment pattern is located within the field of view of the alignment magnification of the measurement equipment; step S3: performing fine alignment on the wafer using the first mark or the second mark so that the first mark or the second mark is located within the field of view of the alignment magnification of the measurement equipment, and the light spot of the measurement equipment is completely aligned with the optical measurement target, so as to perform film thickness or size measurement on the optical measurement target.

[0048] The wafer optical measurement method provided in this embodiment will be described in more detail below.

[0049] First, execute step S1, as Figure 8 As shown, a wafer 100 is provided, wherein the wafer 100 is provided with a cutting street 110, wherein a dedicated alignment pattern 300 and an alignment mark structure 200 are formed in the cutting street 110, and the dedicated alignment pattern 300, the alignment mark structure 200 and the optical measurement target 260 are located in the same exposure unit, and the alignment mark structure is located near the optical measurement target 260.

[0050] Specifically, the exposure unit includes a plurality of arrayed prime die areas 120 and dicing lanes 110 located between adjacent prime die areas 120 ; the dedicated alignment pattern 300 is located at a top corner of each exposure unit.

[0051] In this embodiment, the dedicated alignment pattern 300 is a coarse alignment mark, which is used to perform coarse alignment on the wafer 100. Figure 2 As shown, the first mark 210 and the second mark 220 in the alignment mark structure 200 are fine alignment marks for fine alignment of the wafer 100 .

[0052] In some embodiments, the first mark 210 of the alignment mark structure 200 is disposed between the dedicated alignment pattern and the optical measurement target 260. Specifically, when the optical measurement target 260 is located between the first mark 210 and the second mark 220, the first mark 210 is disposed between the dedicated alignment pattern and the optical measurement target 260.

[0053] In some embodiments, the first mark 210 and the second mark 220 of the alignment mark structure 200 are both disposed between the dedicated alignment pattern 300 and the optical measurement target 260. Specifically, when the optical measurement target 260 is located to the right of the second mark 220, the first mark 210 and the second mark 220 are both disposed between the dedicated alignment pattern and the optical measurement target 260.

[0054] Next, step S2 is performed to perform a coarse alignment operation on the wafer 100 using the dedicated alignment pattern, so that the dedicated alignment pattern 300 is located within the field of view of the alignment magnification of the metrology equipment. Specifically, during the coarse alignment operation, the metrology equipment adjusts the position of the wafer 100 by recognizing the dedicated alignment pattern 300, so that the dedicated alignment pattern 300 is completely within the field of view of the alignment magnification of the metrology equipment.

[0055] Next, step S3 is executed, in which a fine alignment operation is performed on the wafer 100 by using the first mark 210 or the second mark 220 so that the first mark 210 or the second mark 220 is located within the field of view of the alignment magnification of the measurement equipment, and the light spot of the measurement equipment is completely aligned with the optical measurement target 260 to perform film thickness or size measurement on the optical measurement target 260.

[0056] Specifically, when performing the fine alignment operation, the measurement device identifies the first mark 210 or the second mark 220 and determines the position of the optical measurement target 260 based on the relative positional relationship between the first mark 210 or the second mark 220 and the optical measurement target 260, so that the measurement device's light spot is completely aligned with the optical measurement target 260, and then performs film thickness or size measurement on the optical measurement target 260. Because the patterns of the first mark 210 and the second mark 220 are non-centrally symmetrical and different, the first mark 210 and the second mark 220 are unique within the field of view of the measurement device's alignment magnification, which can clearly help identify peripheral measurement positions, achieve precise alignment of optical measurement, and ensure that the light spot is completely aligned with the optical measurement target 260, thereby improving measurement alignment accuracy.

[0057] In summary, in the alignment mark structure and measurement method for wafer optical measurement provided by the present invention, the alignment mark structure is arranged in the cutting path of the wafer and is located near the optical measurement target. The alignment mark structure includes: at least two alignment marks: a first mark and a second mark. The patterns of the first mark and the second mark are non-center-symmetrical patterns and are different. All alignment marks are intermittently embedded between measurement pads and together with all measurement pads form an integral measurement structure. The patterns of the first mark and the second mark are made by overlaying the same non-center-symmetrical patterns on the dielectric layers of at least two or more wafer layers, and the patterns of the upper and lower layers are made to completely overlap as much as possible. Several similar measurement pads are spaced between the first mark and the second mark. The optical measurement target is located between the first mark and the second mark, or the optical measurement target is located on one side of the first mark or the second mark. In this way, during the process of wafer optical measurement, precise alignment of optical measurement can be achieved, so that the light spot is completely aligned with the optical measurement target, thereby improving the measurement alignment accuracy. In addition, the alignment mark structure can be placed on different products for use, eliminating the need to frequently rebuild or modify the measurement program of the measurement equipment for different products, thereby facilitating program standardization and automation of the measurement equipment.

[0058] The above description is only a description of the preferred embodiments of the present invention and does not limit the scope of the present invention. Any changes and modifications made by ordinary technicians in the field of the present invention based on the above disclosure shall fall within the scope of protection of the claims.

[0059] Furthermore, it should be recognized that although the present invention has been disclosed above with reference to preferred embodiments, the above embodiments are not intended to limit the present invention. Any person skilled in the art can utilize the above disclosed technical content to make many possible changes and modifications to the technical solution of the present invention, or modify it into equivalent embodiments with equivalent variations, without departing from the scope of the technical solution of the present invention. Therefore, any simple modifications, equivalent variations, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the technical solution of the present invention, shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. An alignment mark structure used in wafer optical measurement, used to assist in the alignment of an optical measurement target of a measurement device, characterized in that: The alignment mark structure is disposed within a dicing line of the wafer and is located near an optical measurement target. The alignment mark structure includes: At least two alignment marks: a first mark and a second mark, wherein the patterns of the first mark and the second mark are non-centrosymmetric and different, all of the alignment marks are intermittently embedded between a plurality of measurement pads, and together with all of the measurement pads form an integral measurement structure, and the patterns of the first mark and the second mark are produced by overlaying the same non-centrosymmetric patterns on at least two or more dielectric layers of the wafer, so that the patterns of the alignment marks on the upper and lower layers completely overlap; A plurality of the measuring pads are spaced between the first mark and the second mark, and the optical measurement target is located between the first mark and the second mark, or the optical measurement target is located on one side of the first mark or the second mark.

2. The alignment mark structure according to claim 1, wherein: The graphic of the first mark is the same as the graphic of the second mark after being rotated by several angles.

3. The alignment mark structure according to claim 1, wherein: The alignment mark structure further includes a third mark, and the optical measurement target is located between the second mark and the third mark or on a side of the third mark away from the second mark.

4. The alignment mark structure according to claim 3, wherein: The alignment mark structure further includes a fourth mark, and the first mark, the second mark, the third mark and the fourth mark are formed by rotating the same non-centrally symmetrical figure at different angles.

5. The alignment mark structure according to claim 4, wherein: The third mark and the fourth mark are composed of a combination of regular patterns of preset small size.

6. The alignment mark structure according to claim 1, wherein: The distance between the first mark and the second mark is approximately the size of the field of view of the alignment magnification of the measuring device, and the distance between the first mark and the second mark is in the range of 0.2mm to 2mm.

7. The alignment mark structure according to claim 1, wherein: The graphics of the first mark and the second mark are composed of regular graphics of preset small size.

8. The alignment mark structure according to claim 1, wherein: The width of the pattern lines inside the first mark and the second mark is within a range of 1 μm to 20 μm, and there is no other pattern within a range of 5 μm to 10 μm around the first mark and the second mark.

9. A wafer optical measurement method, characterized in that: include: Providing a wafer, wherein the wafer is provided with a dicing street, wherein a dedicated alignment pattern and the alignment mark structure according to claim 1 are formed in the dicing street, wherein the dedicated alignment pattern, the alignment mark structure, and an optical measurement target are all located in the same exposure unit, and the optical measurement target includes one or more measurement pads; Performing coarse alignment on the wafer using the dedicated alignment pattern so that the dedicated alignment pattern is located within the field of view of the alignment magnification of the measurement equipment; The wafer is finely aligned using the first mark or the second mark so that the first mark or the second mark is located within the field of view of the alignment magnification of the measurement device, and the light spot of the measurement device is completely aligned with the optical measurement target to perform film thickness or size measurement on the optical measurement target.

10. The measuring method according to claim 9, wherein: The exposure unit includes a plurality of positive chip areas arranged in an array and the cutting lanes located between adjacent positive chip areas; the dedicated alignment pattern is located at a top corner of each exposure unit.

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