Offset Monitoring Method for Patterns on Both Sides of a Wafer

Abstract

The present invention provides a method for monitoring the offset of patterns on the front and back sides of a wafer. A CD test pattern including a plurality of CD test units arranged in equal-spacing repetition is formed in a reticle, and the CD test pattern is placed in the scribing lane of the wafer. One CD test unit is selected such that its center coincides with the layout center of the wafer to serve as a reference CD test unit. Then, lithography is performed on the front and back sides of the wafer respectively, and a CD lithography pattern with a plurality of CD lithography units is formed in the scribing lane of the wafer. By measuring the center distance between the smallest CD lithography unit and the reference CD lithography unit, the offsets L1 and L2 corresponding to the patterns on the front and back sides of the wafer can be obtained respectively. After taking the difference between L1 and L2, the offset ΔL of the patterns on the front and back sides of the wafer can be obtained. Therefore, the offset monitoring method of the present invention does not require special double-sided monitoring equipment, resulting in a relatively low monitoring cost.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing, and particularly to a method for monitoring the offset of patterns on the front and back sides of a wafer. Background Art

[0002] In semiconductor manufacturing technology, when patterning the front and back sides of a wafer, such as when performing double-sided patterning on a wafer meta-surface product, usually after the pattern on the front side of the wafer is prepared, the wafer is flipped, and then the pattern on the back side of the wafer is prepared. Among them, it is crucial to monitor the offset of the patterns on the front and back sides (that is, to monitor the deviation between the center position of the pattern on the back side of the wafer and the center position of the pattern on the front side of the wafer). Currently, since a single exposure mode is used in the lithography preparation of the front and back side patterns, that is, lithography only performs rough alignment through the notch on the wafer and does not perform fine alignment, and the rough alignment accuracy is often less than 44 μm, which is difficult to meet the process requirements. Therefore, it is necessary to monitor the offset of the patterns on the front and back sides of the wafer.

[0003] Currently, the monitoring of the offset of the patterns on the front and back sides of the wafer is usually carried out by purchasing special double-sided overlay monitoring equipment to measure and monitor the offset of the patterns on the front and back sides of the wafer through the double-sided overlay monitoring equipment, but the price of this double-sided overlay monitoring equipment is relatively expensive.

[0004] Therefore, it is necessary to provide a method for monitoring the offset of the patterns on the front and back sides of the wafer. Summary of the Invention

[0005] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a method for monitoring the offset of the patterns on the front and back sides of the wafer, which is used to solve the high cost problem in the prior art when using double-sided overlay monitoring equipment for offset monitoring.

[0006] To achieve the above purpose and other related purposes, the present invention provides a method for monitoring the offset of the patterns on the front and back sides of the wafer, including the following steps:

[0007] Provide a first mask, the first mask includes a first CD test pattern, and the first CD test pattern includes a plurality of first CD test units arranged in equal-spacing and repeated manner;

[0008] Adjust the exposure layout, place the first CD test pattern in the scribing lane of the wafer, select 1 first CD test unit as the first reference CD test unit, and the center of the first reference CD test unit coincides with the wafer layout center;

[0009] Perform lithography on the front side of the wafer to form a first CD lithography pattern corresponding to the first CD test pattern, and the first CD lithography pattern includes a plurality of first CD lithography units;

[0010] Measure the CD value corresponding to the first CD lithography pattern, select the first CD lithography cell with the smallest CD value formed by overdevelopment as the first minimum CD lithography cell, measure the center distance between the first minimum CD lithography cell and the first reference CD lithography cell corresponding to the first reference CD test cell, and obtain the offset L1 of the front-side pattern of the wafer;

[0011] Provide a second mask, the second mask includes a second CD test pattern, and the second CD test pattern includes a plurality of second CD test cells arranged in equal-spacing repetition;

[0012] Adjust the exposure layout, place the second CD test pattern in the dicing channel of the wafer, select 1 second CD test cell as the second reference CD test cell, and the center of the second reference CD test cell coincides with the layout center of the wafer;

[0013] Flip the wafer, perform lithography on the back side of the wafer to form a second CD lithography pattern corresponding to the second CD test pattern, and the second CD lithography pattern includes a plurality of second CD lithography cells;

[0014] Measure the CD value corresponding to the second CD lithography pattern, select the second CD lithography cell with the smallest CD value formed by overdevelopment as the second minimum CD lithography cell, measure the center distance between the second minimum CD lithography cell and the second reference CD lithography cell corresponding to the second reference CD test cell, and obtain the offset L2 of the back-side pattern of the wafer;

[0015] Take the difference between the offset L1 and the offset L2 to obtain the offset ΔL of the front and back side patterns of the wafer.

[0016] Optionally, it includes 2n + 1 of the first CD test cells, where n ranges from 1 ≤ n ≤ 20; it includes 2m + 1 of the second CD test cells, where m ranges from 1 ≤ m ≤ 20.

[0017] Optionally, the (n + 1)-th CD test cell is used as the first reference CD test cell; the (m + 1)-th CD test cell is used as the second reference CD test cell.

[0018] Optionally, the morphology of the CD test cell is strip-shaped, the width of the CD test cell is 0.1 μm to 0.25 μm, the length of the CD test cell is 1 μm to 3 μm, and the distance between adjacent CD test cells is more than 5 times the width of the CD test cell.

[0019] Optionally, the CD test pattern is a centrosymmetric pattern, and the symmetry center of the CD test pattern coincides with the symmetry center of the reference CD test cell.

[0020] Optionally, the measuring device for the center pitch includes a CD-SEM.

[0021] Optionally, the first CD test pattern and the second CD test pattern have the same morphology.

[0022] Optionally, the first mask has a first etching pattern, the second mask has a second etching pattern, and the first etching pattern and the second etching pattern have different morphologies.

[0023] Optionally, when the offset ΔL is greater than the threshold, the method further includes removing the photoresist on the back side of the wafer and repeating the step of monitoring the offset. The range of the threshold is above 30 μm.

[0024] Optionally, the offset monitoring method is applied to the preparation of wafer metasurface products.

[0025] As described above, in the method for monitoring the offset between the front and back side patterns of a wafer according to the present invention, a CD test pattern including a plurality of CD test units arranged in equal pitch and repeated is formed in a mask, and the CD test pattern is placed in the scribing lane of the wafer. One CD test unit is selected such that its center coincides with the layout center of the wafer as a reference CD test unit. Then, photolithography is performed on the front and back sides of the wafer respectively, and a CD lithography pattern with a plurality of CD lithography units is formed in the scribing lane of the wafer. By measuring the center pitch between the smallest CD lithography unit and the reference CD lithography unit, the offsets L1 and L2 corresponding to the front and back side patterns of the wafer can be obtained respectively. After taking the difference between L1 and L2, the offset ΔL between the front and back side patterns of the wafer can be obtained. Therefore, the offset monitoring method of the present invention does not require a special double-sided monitoring device, so the monitoring cost is relatively low. Description of the Drawings

[0026] Figure 1 It shows a schematic operation flow diagram for monitoring the offset between the front and back side patterns of a wafer in an embodiment of the present invention.

[0027] Figure 2 It shows a schematic structural diagram of the first CD test pattern in an embodiment of the present invention.

[0028] Figure 3 It shows a numerical distribution diagram of the CD values corresponding to the first CD lithography pattern obtained in an embodiment of the present invention.

[0029] Figure 4 It shows a numerical distribution diagram of the CD values corresponding to the second CD lithography pattern obtained in an embodiment of the present invention.

[0030] Description of Reference Numerals

[0031] 100 First CD test pattern

[0032] 101 CD test unit

[0033] 102 Gap

[0034] Steps S1 - S9 Detailed implementation manner

[0035] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0036] When detailing the embodiments of the present invention, for ease of explanation, the cross-sectional views showing the device structure will be enlarged locally in a non-general proportion, and the schematic diagrams are only examples, which should not limit the scope of protection of the present invention here. In addition, in actual production, three-dimensional spatial dimensions including length, width, and depth should be included.

[0037] For convenience of description, spatial relationship terms such as "under", "below", "lower than", "beneath", "above", "on", etc. may be used herein to describe the relationship between one element or feature shown in the drawings and other elements or features. It will be understood that these spatial relationship terms are intended to encompass other directions of the device in use or operation in addition to the directions depicted in the drawings. In addition, when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or there can also be one or more intervening layers. As used herein, "between... and..." means including the endpoint values.

[0038] In the context of the present application, the structure in which the first feature is "above" the second feature described may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0039] It should be noted that the illustrations provided in this embodiment only schematically illustrate the basic concept of the present invention. Therefore, only the components related to the present invention are shown in the illustrations, rather than being drawn according to the number, shape, and size of the components in actual implementation. The type, quantity, and ratio of each component in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0040] In the process of the development of electromagnetic wave theory and technology, metamaterials and metasurfaces have received much attention in the academic community. With the continuous development of semiconductor technology, the long-popular metamaterial and metasurface technologies in the academic community have found some important applications in combination with semiconductor technology, becoming a new opportunity in the semiconductor industry. This application provides a method for monitoring the offset of the patterns on the front and back sides of a wafer during the preparation of a wafer metasurface product, but the offset monitoring method is not limited to wafer metasurface products only.

[0041] It should be noted that during the lithography of the wafer in the present invention, the development process will form an overdevelopment phenomenon at the center position of the wafer (such as using the TEL ACT-8 in the TEL machine tool for the development process of the wafer), resulting in a situation where the CD is smaller at the center position of the wafer. In response to this overdevelopment problem, the present invention proposes the following technical solutions, which specifically include:

[0042] Refer to Figure 1 , a method for monitoring the offset of the patterns on the front and back sides of a wafer is provided, including the following steps:

[0043] S1: Provide a first mask, the first mask includes a first CD test pattern, and the first CD test pattern includes a plurality of first CD test units arranged in equal-spacing repetition;

[0044] S2: Adjust the exposure layout, place the first CD test pattern in the scribe lane of the wafer, select 1 first CD test unit as the first reference CD test unit, and the center of the first reference CD test unit coincides with the wafer layout center;

[0045] S3: Perform lithography on the front side of the wafer to form a first CD lithography pattern corresponding to the first CD test pattern, and the first CD lithography pattern includes a plurality of first CD lithography units;

[0046] S4: Measure the CD value corresponding to the first CD lithography pattern, select the first CD lithography unit with the smallest CD value formed by overdevelopment as the first minimum CD lithography unit, measure the center distance between the first minimum CD lithography unit and the first reference CD lithography unit corresponding to the first reference CD test unit, and obtain the offset L1 of the pattern on the front side of the wafer;

[0047] S5: Provide a second mask, the second mask includes a second CD test pattern, and the second CD test pattern includes a plurality of second CD test units arranged in equal-spacing repetition;

[0048] S6: Adjust the exposure layout, place the second CD test pattern in the scribe lane of the wafer, select 1 second CD test unit as the second reference CD test unit, and the center of the second reference CD test unit coincides with the wafer layout center;

[0049] S7: Flip the wafer, perform photolithography on the back side of the wafer to form a second CD photolithography pattern corresponding to the second CD test pattern, where the second CD photolithography pattern includes a plurality of second CD photolithography units;

[0050] S8: Measure the CD value corresponding to the second CD photolithography pattern, select the second CD photolithography unit with the smallest CD value formed by overdevelopment as the second smallest CD photolithography unit, measure the center distance between the second smallest CD photolithography unit and the second reference CD photolithography unit corresponding to the second reference CD test unit, and obtain the offset L2 of the pattern on the back side of the wafer;

[0051] S9: Take the difference between the offset L1 and the offset L2 to obtain the offset ΔL of the patterns on the front and back sides of the wafer.

[0052] In this embodiment, a CD test pattern including a plurality of CD test units arranged in equal-spacing repetition is formed in a mask, and the CD test pattern is placed in the scribing lane of the wafer. One CD test unit is selected such that its center coincides with the layout center of the wafer as the reference CD test unit. Then, photolithography is performed on the front and back sides of the wafer respectively to form a CD photolithography pattern with a plurality of CD photolithography units in the scribing lane of the wafer. By measuring the center distance between the smallest CD photolithography unit and the reference CD photolithography unit, the offsets L1 and L2 corresponding to the patterns on the front and back sides of the wafer can be obtained respectively. After taking the difference between L1 and L2, the offset ΔL of the patterns on the front and back sides of the wafer can be obtained. Therefore, the offset monitoring method of the present invention does not require a special double-sided monitoring device, so the monitoring cost is relatively low.

[0053] The following introduces the offset monitoring method for the patterns on the front and back sides of the wafer in this embodiment with reference to the accompanying drawings, which specifically may include:

[0054] First, perform step S1 to provide a first mask, where the first mask includes a first CD test pattern, and the first CD test pattern includes a plurality of first CD test units arranged in equal-spacing repetition.

[0055] As an example, preferably, the first CD test pattern may include 2n + 1 first CD test units, where the value of n can be 1 ≤ n ≤ 20, and preferably the (n + 1)-th CD test unit is used as the first reference CD test unit, that is, after subsequent adjustment of the exposure layout, the center of the first reference CD test unit coincides with the layout center of the wafer.

[0056] Specifically, when preferably including an odd number of the first CD test units arranged at equal intervals and repeating, the (n + 1)-th CD test unit can be directly selected as the first reference CD test unit, so that the same number of CD values can be obtained on both sides of the first reference CD lithography unit corresponding to the first reference CD test unit subsequently.

[0057] For example Figure 2 , in this embodiment, the first CD test pattern 100 formed in the first mask plate includes 33 of the first CD test units 101 and 33 gaps 102 arranged in a repeating pattern. Among them, the corresponding first CD test units 101 are respectively denoted as L1, L2... L32, L33. That is, the value of n is 16, and the 17th first CD test unit L17 is selected as the first reference CD test unit. However, the value of n is not limited thereto. For example, the value of n can also be 3, 5, 8, 10, 15, 18, 20, etc. The value of n and the selection of the first reference CD test unit 101 are not limited thereto, and can be specifically set according to needs.

[0058] As an example, the morphology of the first CD test unit can be strip-shaped. Among them, the width of the first CD test unit can be 0.1 μm to 0.25 μm, the length of the first CD test unit can be 1 μm to 3 μm, and the spacing between adjacent first CD test units can be more than 5 times the width of the first CD test unit.

[0059] Specifically, as Figure 2 shown, in this embodiment, the morphology of the first CD test unit 101 adopts a relatively simple strip shape, and preferably the width of the first CD test unit 100 is 0.2 μm. However, it is not limited thereto, and can also be 0.1 μm, 0.15 μm, 0.25 μm, etc. The length D of the first CD test unit 101 is 1 μm. However, it is not limited thereto, and can also be 1.5 μm, 2 μm, 3 μm, etc. The spacing between adjacent first CD test units 101, that is, the width of the gap 102, is 1.3 μm. However, it is not limited thereto. Preferably, the width of the gap 102 is more than 5 times the width of the first CD test unit 101, such as 1.0 μm, 2 μm, 3 μm, etc. The values of the length, width of the first CD test unit 101 and the gap 102 can be set according to process needs and are not overly limited here.

[0060] As an example, the first CD test pattern is a centrosymmetric figure, and the center of symmetry of the first CD test pattern coincides with the center of symmetry of the first reference CD test unit.

[0061] Specifically, in this embodiment, it is preferred that the first CD test pattern 100 is a centrosymmetric pattern, and the center of symmetry of the first CD test pattern 100 coincides with the center of symmetry of the first reference CD test unit L17, so as to reduce the process difficulty of fabricating the first mask and reduce the complexity of monitoring. Of course, the morphology of the first CD test pattern is not limited to this.

[0062] Next, step S2 is performed to adjust the exposure layout, place the first CD test pattern in the dicing channel of the wafer, select 1 first CD test unit as the first reference CD test unit, and the center of the first reference CD test unit coincides with the center of the wafer layout.

[0063] Specifically, since step-by-step exposure is used for exposure, it is necessary to establish an exposure working layout. By adjusting the exposure layout, the center of the selected first reference CD test unit is made to coincide with the center of the wafer layout to meet subsequent measurement requirements. In this embodiment, by adjusting the exposure layout, the center of the first CD test unit L17 and the center of the wafer are arranged on the same vertical line.

[0064] Next, step S3 is performed to perform photolithography on the front side of the wafer to form a first CD photolithography pattern corresponding to the first CD test pattern. The first CD photolithography pattern includes a plurality of first CD photolithography units.

[0065] Specifically, photoresist is coated on the front side of the wafer in sequence, exposure is performed using the first mask, and development is carried out to form a first CD photolithography pattern corresponding to the first CD test pattern on the front side of the wafer. Among them, due to the characteristics of the equipment hardware, the development process will result in overdevelopment at the center position of the wafer (such as using TEL ACT-8 in the TEL machine tool to perform the development process on the wafer), so the CD value at the center position of the wafer will be smaller. Utilizing this characteristic, by designing isolated CD test units, this defect can be amplified to monitor the difference between the CD photolithography pattern and the center position of the wafer and obtain the offset of the pattern. In this embodiment, since the first CD test pattern includes 33 first CD test units, the first CD photolithography pattern formed on the front side of the wafer has 33 first CD photolithography units, and the first CD photolithography unit corresponding to the first reference CD test unit located at the 17th position is used as the first reference CD photolithography unit.

[0066] Next, perform step S4 to measure the CD value corresponding to the first CD lithography pattern, select the first CD lithography cell with the smallest CD value formed by overdevelopment as the first minimum CD lithography cell, measure the center distance between the first minimum CD lithography cell and the first reference CD lithography cell corresponding to the first reference CD test cell, and obtain the offset L1 of the front-side pattern of the wafer.

[0067] As an example, the measuring device for the center distance may include a CD-SEM, but is not limited thereto. In this embodiment, the CD-SEM, which is relatively commonly used, is directly used to measure the CD of 33 first CD lithography cells in the first CD lithography pattern. Among them, to reduce errors, the measurement can be performed from the 2nd to the 32nd position to remove the CD values with larger errors at both ends, and then the first CD lithography cell with the smallest CD value is selected as the first minimum CD lithography cell, and the center distance between the first minimum CD lithography cell and the first reference CD lithography cell is measured, so as to obtain the offset L1 of the front-side pattern of the wafer. As Figure 3 shown, it shows the numerical distribution diagram of the CD values corresponding to the first CD lithography pattern obtained in this embodiment. Finally, the offset L1 of the front-side pattern of the wafer can be obtained as L1 = 3.75 μm.

[0068] Next, perform steps S5 to S8 to obtain the offset L2 of the back-side pattern of the wafer. As Figure 4 shown, it shows the numerical distribution diagram of the CD values corresponding to the second CD lithography pattern obtained in this embodiment. Finally, the offset L2 of the front-side pattern of the wafer can be obtained as L2 = 11.25 μm. For the specific operations, refer to steps S1 to S4, which will not be elaborated here.

[0069] As an example, preferably, the second CD test pattern may include 2m + 1 second CD test cells, where the value of m is 1 ≤ m ≤ 20, and preferably the CD test cell at the (m + 1)-th position is used as the second reference CD test cell.

[0070] Specifically, when preferably including an odd number of repeatedly arranged second CD test cells, the CD test cell at the (m + 1)-th position can be directly used as the second reference CD test cell, so that the same number of CD values can be obtained on both sides of the second reference CD lithography cell corresponding to the second reference CD test cell subsequently.

[0071] As an example, the morphology of the second CD test cell may be strip-shaped. Among them, the width of the second CD test cell may be 0.1 μm to 0.25 μm, the length of the second CD test cell may be 1 μm to 3 μm, and the distance between adjacent second CD test cells may be more than 5 times the width of the second CD test cell.

[0072] Specifically, in this embodiment, the morphology of the second CD test unit is in a relatively simple long strip shape. Preferably, the width of the second CD test unit is 0.2 μm, but it is not limited thereto, and it can also be 0.1 μm, 0.15 μm, 0.25 μm, etc. The length D of the second CD test unit is 1 μm, but it is not limited thereto, and it can also be 1.5 μm, 2 μm, 3 μm, etc. The width of the spacing between adjacent second CD test units is 1.3 μm, but it is not limited thereto. Preferably, the width of the spacing is more than 5 times the width of the second CD test unit, such as 1.0 μm, 2 μm, 3 μm, etc. The values of the length, width, and spacing of the second CD test unit can be set according to process requirements and are not overly limited here.

[0073] As an example, the second CD test pattern is a centrosymmetric pattern, and the center of symmetry of the second CD test pattern coincides with the center of symmetry of the second reference CD test unit.

[0074] Specifically, in this embodiment, preferably, the second CD test pattern is a centrosymmetric pattern, and the center of symmetry of the second CD test pattern coincides with the center of symmetry of the second reference CD test unit, so as to reduce the process difficulty of processing and preparing the second mask and reduce the complexity of monitoring. Of course, the morphology of the second CD test pattern is not limited thereto.

[0075] As an example, preferably, the first CD test pattern and the second CD test pattern have the same morphology for the convenience of process operation, but it is not limited thereto.

[0076] In this embodiment, the second CD test pattern formed in the second mask includes 33 second CD test units and 33 gaps arranged in a repeated manner, that is, the value of m is 16, and the 17th second CD test unit is selected as the second reference CD test unit. However, the value of m is not limited thereto. For example, the value of m can also be 3, 5, 8, 10, 15, 18, 20, etc. The value of m and the selection of the second reference CD test unit are not limited thereto and can be specifically set according to needs.

[0077] As an example, the first mask further has a first etching pattern, and the second mask further has a second etching pattern, and the first etching pattern and the second etching pattern have different morphologies, so that the offset monitoring and the patterning of the wafer product can be carried out simultaneously to reduce the process steps. The morphologies of the first etching pattern and the second etching pattern can be set according to specific product requirements and are not overly limited here.

[0078] Next, step S9 is performed. The difference between the offset L1 and the offset L2 is taken to obtain the offset ΔL of the patterns on the front and back sides of the wafer. In this embodiment, the offset ΔL = offset L2 - offset L1 = 7.5 μm.

[0079] As an example, when the offset ΔL is greater than the threshold, the steps of removing the photoresist on the back side of the wafer and repeating the offset monitoring may further be included. The range of the threshold is above 30 μm.

[0080] Specifically, when the obtained offset ΔL is 30 μm or more, that is, when it exceeds the process limit, the photoresist on the back side of the wafer can be removed, and then steps S5 to S8 are repeated to re-obtain the offset L2 until an offset ΔL that meets the process requirements is obtained, so as to obtain a product that meets the process through rework operations. The selection of the threshold is not limited to 30 μm and can also be 40 μm, etc., and can be selected according to specific requirements.

[0081] In summary, for the method for monitoring the offset of the patterns on the front and back sides of the wafer according to the present invention, a CD test pattern including a plurality of CD test units arranged in equal-spacing repetitions is formed in a mask, and the CD test pattern is placed in the scribing lane of the wafer. One CD test unit is selected such that its center coincides with the layout center of the wafer as a reference CD test unit. Then, photolithography is performed on the front and back sides of the wafer respectively, and a CD lithography pattern with a plurality of CD lithography units is formed in the scribing lane of the wafer. By measuring the center distance between the smallest CD lithography unit and the reference CD lithography unit, the offsets L1 and L2 corresponding to the patterns on the front and back sides of the wafer can be obtained respectively. After taking the difference between L1 and L2, the offset ΔL of the patterns on the front and back sides of the wafer can be obtained. Therefore, the offset monitoring method of the present invention does not require a special double-sided monitoring device, so the monitoring cost is relatively low.

[0082] The above embodiments merely illustrate the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A method for monitoring the offset of patterns on the front and back sides of a wafer, characterized in that, It includes the following steps: Provide a first mask, the first mask includes a first CD test pattern, and the first CD test pattern includes a plurality of first CD test units arranged in equal-spacing repetition; Adjust the exposure layout, place the first CD test pattern in the dicing channel of the wafer, select 1 first CD test unit as the first reference CD test unit, and the center of the first reference CD test unit coincides with the layout center of the wafer; Perform photolithography on the front side of the wafer to form a first CD photolithography pattern corresponding to the first CD test pattern, and the first CD photolithography pattern includes a plurality of first CD photolithography units; Measure the CD value corresponding to the first CD photolithography pattern, select the first CD photolithography unit with the smallest CD value formed by overdevelopment as the first minimum CD photolithography unit, measure the center distance between the first minimum CD photolithography unit and the first reference CD photolithography unit corresponding to the first reference CD test unit, and obtain the offset L1 of the front-side pattern of the wafer; Provide a second mask, the second mask includes a second CD test pattern, and the second CD test pattern includes a plurality of second CD test units arranged in equal-spacing repetition; Adjust the exposure layout, place the second CD test pattern in the dicing channel of the wafer, select 1 second CD test unit as the second reference CD test unit, and the center of the second reference CD test unit coincides with the layout center of the wafer; Flip the wafer, perform photolithography on the back side of the wafer to form a second CD photolithography pattern corresponding to the second CD test pattern, and the second CD photolithography pattern includes a plurality of second CD photolithography units; Measure the CD value corresponding to the second CD photolithography pattern, select the second CD photolithography unit with the smallest CD value formed by overdevelopment as the second minimum CD photolithography unit, measure the center distance between the second minimum CD photolithography unit and the second reference CD photolithography unit corresponding to the second reference CD test unit, and obtain the offset L2 of the back-side pattern of the wafer; Take the difference between the offset L1 and the offset L2 to obtain the offset ΔL of the front and back patterns of the wafer.

2. The offset monitoring method according to claim 1, characterized in that: It includes 2n + 1 of the first CD test units, where n ranges from 1 to 20; it includes 2m + 1 of the second CD test units, where m ranges from 1 to 20.

3. The offset monitoring method according to claim 2, wherein: The (n + 1)-th CD test unit is used as the first reference CD test unit; the (m + 1)-th CD test unit is used as the second reference CD test unit.

4. The offset monitoring method according to claim 1, characterized in that: The morphology of the CD test unit is strip-shaped, the width of the CD test unit is 0.1μm to 0.25μm, the length of the CD test unit is 1μm to 3μm, and the distance between adjacent CD test units is more than 5 times the width of the CD test unit.

5. The offset monitoring method according to claim 1, characterized in that: The CD test pattern is a centrosymmetric pattern, and the symmetry center of the CD test pattern coincides with the symmetry center of the reference CD test unit.

6. The offset monitoring method according to claim 1, wherein: The measuring device for the center distance includes a CD-SEM.

7. The offset monitoring method according to claim 1, characterized in that: The first CD test pattern and the second CD test pattern have the same morphology.

8. The offset monitoring method according to claim 1, wherein: The first mask has a first etching pattern, the second mask has a second etching pattern, and the first etching pattern and the second etching pattern have different morphologies.

9. The offset monitoring method according to claim 1, wherein: When the offset ΔL is greater than the threshold, the method further includes removing the photoresist on the back side of the wafer and repeating the step of monitoring the offset, and the range of the threshold is above 30 μm.

10. The offset monitoring method according to claim 1, wherein: The offset monitoring method is applied to the preparation of wafer metasurface products.

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