Back overlay method of irregular wafer
By cutting positioning edges on irregular wafers and combining them with a vision alignment system of optical imaging and photolithography equipment, precise positioning and alignment of irregular wafers are achieved, solving the problems of low overlay accuracy and poor process stability, and improving the stability and consistency of production.
Patent Information
- Application Number
- CN202511176743.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-21
- Publication Date
- 2025-10-21
AI Technical Summary
Irregular wafers suffer from low overlay accuracy, poor process stability and repeatability during back-side overlay. Traditional photolithography technology struggles to accurately identify their position and angle, and lacks effective positioning and alignment methods.
Positioning edges with specific shapes are cut out on irregular wafers. Key feature points and contour information are extracted through an optical imaging system. Combined with the vision alignment system of the photolithography equipment, the front pattern of the irregular wafer is accurately positioned and aligned with the photomask. Photoresist is applied manually by rotating the die and then exposed and developed.
It significantly improves the alignment accuracy and process stability of irregular wafers, ensures batch repeatability, reduces production costs and cycle time, and solves the problems of low overlay accuracy and poor process stability.
Smart Images
Figure CN120821162A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the field of semiconductor manufacturing technology, and in particular to a backside overlay method for irregular wafers. Background Art
[0002] Currently, photolithography is crucial in semiconductor manufacturing, especially for wafers requiring backside overlay. Conventional processing for these wafers involves thinning and polishing, followed by backside overlay. Indium Phosphate (InP) is inherently fragile, and when formed into thin wafers, it is highly susceptible to breakage, creating a significant risk of fragmentation. This makes the importance of photolithography particularly crucial in ensuring wafer integrity.
[0003] Among related technologies, current mainstream photolithography techniques are mostly designed based on the characteristics of regularly shaped wafers. With the continuous advancement of semiconductor technology, industry production capacity has steadily increased. However, due to the fragile nature of InP materials, both manual and automated processes carry a high risk of fragmentation. Once fragmentation occurs, irregular wafers are likely to be produced, creating numerous challenges in subsequent manufacturing processes.
[0004] Due to their unique shapes, irregular wafers present numerous challenges during backside overlay. Traditional alignment methods struggle to accurately identify the position and angle of irregular wafers, resulting in reduced overlay accuracy. Furthermore, the backside overlay process for irregular wafers lacks effective positioning and alignment methods, resulting in poor process stability and repeatability, increasing production costs and cycle time.
[0005] Therefore, it is necessary to design a backside overlay method specifically for irregular wafers to solve the above problems. Summary of the Invention
[0006] The present application provides a back-side overlay method for irregular wafers, which can solve the technical problems of low overlay accuracy, poor process stability and repeatability of irregular wafers in related technologies.
[0007] In a first aspect, an embodiment of the present application provides a backside overlay method for an irregular wafer, comprising the following steps: Use a dicing machine to cut a positioning edge with a specific shape on the irregular wafer after the front side process is completed and the back side is thinned; Image the positioning edge of irregular wafers and extract key feature points and contour information; Applying photoresist to the back side of the irregular wafer; Place the irregular wafer on the workbench of the lithography equipment, and locate and align the front pattern of the irregular wafer with the pattern of the photoresist based on the key feature points and contour information of the positioning edge; Expose and develop the photoresist on the back of the irregular wafer.
[0008] In combination with the first aspect, in one embodiment, the positioning edge is an L-shaped right-angle edge.
[0009] In combination with the first aspect, in one embodiment, the short side length of the positioning edge ranges from 1 to 3 mm, the long side length ranges from 3 to 8 mm, and the error of the angle between the long side and the short side and 90° is controlled within ±1°.
[0010] In conjunction with the first aspect, in one embodiment, the step of using a dicing machine to cut a positioning edge having a specific shape on an irregular wafer after the front side process is completed and the back side is thinned comprises: The irregular wafer is fixed on the workbench of the dicing machine. The visual recognition system of the dicing machine accurately identifies the position to be cut on the edge of the irregular wafer, and cuts the front of the irregular wafer according to a specific shape to form a positioning edge.
[0011] In combination with the first aspect, in one embodiment, the cutting speed of the dicing machine is set to 5-12 mm / s, and the cutting depth is 1 / 4-1 / 2 of the thickness of the irregular wafer.
[0012] In conjunction with the first aspect, in one embodiment, imaging the positioning edge of the irregular wafer and extracting key feature points and contour information includes: An optical microscope imaging system is used to clearly image the front pattern corresponding to the positioning edge, and then imaging processing software is used to extract key feature points and contour information from the imaged image, and the key feature points and contour information are classified, marked and saved.
[0013] In combination with the first aspect, in one embodiment, coating the photoresist on the back side of the irregular wafer includes: The irregular wafer after cleaning and drying is placed on a pre-cut white film, wherein the size of the white film is larger than the size of the vacuum adsorption plate of the coating machine; Place the irregular wafer with white film on the vacuum adsorption plate of the coater, and then spin-coat the back of the irregular wafer with photoresist. At the same time, for the edges and special areas on the back of the irregular wafer, use a manual drip device to add an appropriate amount of photoresist to cover the entire surface so that the photoresist on the back is evenly distributed.
[0014] In conjunction with the first aspect, in one embodiment, placing the irregular wafer on a workbench of a lithography apparatus and positioning and aligning the front surface pattern of the irregular wafer with the pattern of the photoresist plate based on key feature points and contour information of the positioning edge includes: Place the irregular wafer on the workbench of the lithography equipment, adjust the X and Y position and rotation angle of the workbench, and use the visual alignment system of the lithography equipment to preliminarily align the positioning edge with the pattern on the reticle; Then, the key feature points and contour information of the positioning edge are precisely aligned with the pattern on the current photomask. By fine-tuning the position and angle of the workbench, the front pattern of the irregular wafer is precisely aligned with the pattern on the photomask.
[0015] In conjunction with the first aspect, in one embodiment, the exposing and developing the photoresist on the back side of the irregular wafer includes: The exposure parameters of the photolithography equipment are set according to the line width of the front pattern, the overlay accuracy requirements and the photosensitivity characteristics of the photoresist used. After the exposure is completed, a wet development process is used for development.
[0016] In combination with the first aspect, in one embodiment, after the exposure and development of the photoresist on the back side of the irregular wafer, the method further includes: Set the microscope magnification to 500-1000x to measure the overlay deviation between the backside and frontside patterns of irregular wafers at key locations, while also checking the quality of the lithographic patterns. If the overlay deviation is found to exceed the allowable range, the NMP degumming method is used for rework and correction.
[0017] The beneficial effects of the technical solutions provided in the embodiments of the present application include: By cutting a positioning edge with a specific shape on the irregular wafer, the positioning and alignment of the front pattern of the irregular wafer and the pattern on the photoresist can be achieved based on the key feature points and contour information of the positioning edge, which greatly improves the alignment accuracy of the irregular wafer and avoids overlay deviation. At the same time, this process does not rely on the operator's superb skills and rich experience. Different personnel can obtain stable and consistent process results by operating in this way, which greatly ensures the stability and repeatability between batches, and solves the technical problems of low overlay accuracy, poor process stability and repeatability of irregular wafers in related technologies. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.
[0019] Figure 1 A flowchart of a backside overlay method for an irregular wafer provided in an embodiment of the present application; Figure 2A schematic diagram of the front alignment mark for preparing an irregular wafer provided in an embodiment of the present application; Figure 3 A schematic diagram of the X-direction positioning and alignment process for the back side of an irregular wafer provided in an embodiment of the present application; Figure 4 A schematic diagram of the Y-direction positioning and alignment process for the back side of an irregular wafer provided in an embodiment of the present application; Figure 5 Schematic diagram of X-direction inspection of irregular wafer backside photolithography patterns provided in an embodiment of the present application; Figure 6 Schematic diagram of the Y-direction inspection of irregular wafer backside photolithography patterns provided in an embodiment of the present application. DETAILED DESCRIPTION
[0020] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.
[0021] The embodiment of the present application provides a back-side overlay method for irregular wafers, which can solve the technical problems of low overlay accuracy, poor process stability and repeatability of irregular wafers in related technologies.
[0022] See also Figure 1 As shown, an embodiment of the present application provides a backside overlay method for an irregular wafer, which may include the following steps: S1: Use a dicing machine to cut a positioning edge with a specific shape on the irregular wafer after the front side process is completed and the back side is thinned.
[0023] S2: Image the positioning edge of the irregular wafer and extract key feature points and contour information.
[0024] S3: Coating photoresist on the back side of the irregular wafer.
[0025] S4: Place the irregular wafer on the workbench of the lithography equipment, and position and align the front pattern of the irregular wafer with the pattern of the photolithography plate based on the key feature points and contour information of the positioning edge.
[0026] S5: Expose and develop the photoresist on the back side of the irregular wafer.
[0027] Before the above-mentioned step S1, an irregular wafer is provided after the front-side process is completed and the back side is thinned. In step S1, a dicing machine can be used to cut at any position of the irregular wafer to form a positioning edge. The size and angle of the positioning edge are determined according to the specific shape of the irregular wafer and the subsequent positioning requirements; the shape of the positioning edge is pre-designed with a specific shape. In actual operation, a simple or complex shape can be designed according to actual needs, and there is no restriction here. In step S2, an optical imaging system can be used to image and store the front pattern of the irregular wafer, and an image processing algorithm is used to extract the key feature points and contour information of the positioning edge. In step S3, when applying the photoresist, it can be applied manually or automatically. In this embodiment, a manual coating machine is preferably used. In step S4, the photolithography equipment can adopt a manual photolithography machine MA6, for example.
[0028] This embodiment cuts a positioning edge with a specific shape on the irregular wafer, and based on the key feature points and contour information of the positioning edge, it can achieve positioning and alignment of the front pattern of the irregular wafer and the pattern on the photoresist. The positioning method of this embodiment breaks through the limitation of irregular wafers without standard edges and positioning features, abandons conventional alignment algorithms and mark recognition methods that are not suitable for such wafers, greatly improves the alignment accuracy of irregular wafers, and avoids overlay deviation; and solves the problem of the visual system being interfered with by the edges and surfaces of irregular wafers, and the operator can accurately adjust the position of the wafer; at the same time, the process does not rely on the operator's superb skills and rich experience. Different personnel can obtain stable and consistent process results by operating in this way, greatly ensuring the stability and repeatability between batches, and can effectively cope with the shape and characteristic differences of irregular wafers. Each photolithography overlay can accurately replicate the process conditions and operation process, significantly improving process stability and product consistency, avoiding the impact of irregular factors on production, and solving the technical problems of low overlay accuracy, poor process stability and repeatability of irregular wafers in related technologies.
[0029] Preferably, in the present embodiment, the positioning edge is an L-shaped right-angled edge. In other embodiments, the positioning edge may also adopt other shapes, such as a "cross" shape, a "earth" shape, or an acute angle "∠" shape, etc., which are not limited here, and other structural shapes may also be selected according to actual needs. The present embodiment adopts an L-shaped right-angled edge, which is not only simple in structure, but also can quickly realize the alignment of the front pattern of the irregular wafer and the pattern of the photoresist in the X and Y directions through the two mutually perpendicular edges of the L-shaped right-angled edge. Step S4 positions and aligns the back side of the irregular wafer, places the irregular wafer on the workbench of the lithography equipment, and performs positioning and alignment in combination with the front pattern features of the cleavage L-shaped right-angled edge.
[0030] Furthermore, in one embodiment, the length of the short side of the positioning edge is in the range of 1 to 3 mm, the length of the long side is in the range of 3 to 8 mm, and the error of the angle between the long side and the short side and 90° is controlled within ±1°. In this embodiment, an L-shaped right-angled edge is cut out at a suitable position on any edge of the irregular wafer. The length of the short side of the L-shaped right-angled edge is determined in the range of 1 to 3 mm according to the size of the irregular wafer, and the length of the long side is determined in the range of 3 to 8 mm. The angle (that is, the angle between the long side and the short side) error is controlled within ±1°. The L-shaped right-angled edge serves as a key reference feature for subsequent positioning. Its precise size and the angle between the two sides can effectively improve the accuracy of positioning and provide a reliable reference for back-side overlay.
[0031] Furthermore, in some optional embodiments, the use of a dicing machine to cut a positioning edge with a specific shape on an irregular wafer after the front side process is completed and the back side is thinned may include: fixing the irregular wafer on a workbench of the dicing machine, accurately identifying the position to be cut on the edge of the irregular wafer through the visual recognition system of the dicing machine, and cutting the front side of the irregular wafer according to the specific shape to form a positioning edge.
[0032] In this embodiment, a dicing machine with a high-precision visual recognition system is selected. The irregular wafer is fixed on the workbench of the dicing machine, and the edge of the irregular wafer is accurately identified by the visual recognition system. Due to the irregular shape of the irregular wafer, conventional positioning methods are difficult to apply, and the visual recognition system can accurately find the appropriate cutting position according to the actual shape of the wafer. According to the shape characteristics of the wafer and the subsequent positioning requirements, a diamond dicing knife is selected. It has high hardness and strong wear resistance, which can minimize damage to the wafer while ensuring cutting accuracy.
[0033] Preferably, in this embodiment, the cutting speed of the dicing machine is set to 5-12 mm / s, and the cutting depth is 1 / 4-1 / 2 of the thickness of the irregular wafer. This parameter combination in this embodiment can ensure that high-quality L-shaped right-angle edges are cut on irregular wafers of different thicknesses.
[0034] In one embodiment, in step S2, imaging the positioning edge of the irregular wafer and extracting key feature points and contour information may include: using an optical microscope imaging system to clearly image the front pattern corresponding to the positioning edge, and then using imaging processing software to extract key feature points and contour information from the imaged image, and classifying, marking and saving the key feature points and contour information.
[0035] In this embodiment, a high-resolution optical microscope imaging system, such as an OLYMPUS BX53M system microscope, is used in conjunction with a CCD camera with at least 5 million pixels. The microscope magnification is set at 200-500 times to clearly image the front pattern corresponding to the L-shaped right-angle edge. After extracting key feature points and contour information, the imaging processing software classifies and marks the key feature points and contours. For example, feature points located at the edge of the pattern are marked as edge feature points, and feature points located at the intersection of the pattern are marked as intersection feature points. The spacing between the edge feature points and the intersection feature points is measured and stored to facilitate faster and more accurate matching during subsequent positioning and alignment, thereby improving positioning efficiency and accuracy.
[0036] In one embodiment, in step S3, coating the back of the irregular wafer with photoresist may include: placing the cleaned and dried irregular wafer on a pre-cut white film, wherein the size of the white film is larger than the size of the vacuum adsorption disk of the coater; then placing the irregular wafer with the white film on the vacuum adsorption disk of the coater, and then spin-coating the back of the irregular wafer with photoresist. At the same time, for the edges and special areas on the back of the irregular wafer, a manual dripping device is used to supplement an appropriate amount of photoresist to cover the entire surface so that the photoresist on the back is evenly distributed.
[0037] In the related art, when coating an irregular wafer, the irregular edges and surface morphology will affect the coating uniformity of the photoresist and the distribution of the exposure dose, thereby affecting the quality of the photolithographic pattern and the performance of the final device. This embodiment adopts a manual spin coater to evenly coat the photoresist on the back of the irregular wafer by spin coating, and the rotation speed and coating time are adjusted according to the size and shape of the irregular wafer. Specifically, a white film that is larger than the vacuum adsorption plate of the coater is cut in advance, and the irregular wafer after cleaning and drying is first placed on the white film to ensure that the photoresist of the irregular wafer will not overflow to the front of the irregular wafer and contaminate the appearance or the vacuum adsorption plate during the coating process. Then, the irregular wafer with the white film is placed on the vacuum adsorption plate of the spin coater to ensure that no displacement occurs. For the edges and special areas of the irregular wafer thinning surface, a manual dosing device is used to add an appropriate amount of photoresist to cover the entire surface, ensuring uniform distribution of the photoresist. After coating, the white film is gently removed. This coating method ensures uniformity of the photoresist on the irregular wafer surface, providing good conditions for subsequent exposure processes. Preferably, the coating speed is 2000-4000 rpm, and the thickness is 0.2-0.5 μm.
[0038] Furthermore, in some embodiments, in step S4, the step of placing the irregular wafer on the workbench of the lithography equipment and positioning and aligning the front pattern of the irregular wafer with the pattern of the photoresist plate based on the key feature points and contour information of the positioning edge may include: placing the irregular wafer on the workbench of the lithography equipment, adjusting the X-direction and Y-direction position and rotation angle of the workbench, and using the visual alignment system of the lithography equipment to preliminarily align the positioning edge with the pattern on the photoresist plate; then performing a fine alignment operation on the key feature points and contour information of the positioning edge with the pattern on the current photoresist plate, and precisely aligning the front pattern of the irregular wafer with the pattern of the photoresist plate by fine-tuning the position and angle of the workbench.
[0039] In this embodiment, an irregular wafer is placed on the worktable of a lithography machine, such as the MA6 manual lithography machine. Using the lithography machine's vision alignment system, manual coarse alignment is first performed. The X and Y positions and rotation angles of the worktable are adjusted to achieve initial alignment of the L-shaped right-angled edge with the pattern on the reticle. The coarse alignment error is controlled within ±10μm. This coarse alignment provides a rough positioning basis for subsequent fine alignment. Fine alignment is then performed on the front-side pattern key features and contour information extracted in step S2 with the pattern on the current reticle. By fine-tuning the position and angle of the worktable, precise alignment of the front-side pattern features with the reticle is achieved, with a final alignment error of less than ±0.2μm. During the alignment process, a combination of vision alignment and mechanical adjustment is used for back-side positioning and alignment. No fewer than three iterative adjustments are performed, and the vision alignment system is used to monitor alignment errors in real time and provide feedback for adjustments. For example, if the alignment error in the X direction is found to be excessive, the worktable is fine-tuned in the X direction using a mechanical adjustment device, while the visual alignment system simultaneously monitors the results of the adjustments in real time until the alignment error meets the required level, thereby improving alignment accuracy and stability. In terms of mechanical adjustment, this embodiment overcomes the precision limitations of manual adjustment mechanisms, achieving more precise and flexible multi-directional and multi-angle adjustment, and reducing adjustment errors. Preferably, the backside lithography in step S4 is performed by making L-shaped right-angle edges as alignment marks and using the front side exposure method to complete the backside overlay process.
[0040] Furthermore, in one embodiment, in step S5, the exposure and development of the photoresist on the back of the irregular wafer may include: setting the exposure parameters of the photolithography equipment according to the line width of the front pattern, the overlay accuracy requirements and the photosensitivity characteristics of the photoresist used, and after the exposure is completed, using a wet development process for development.
[0041] In this embodiment, the exposure parameters include exposure time and light source intensity, which are optimized according to the photosensitivity characteristics of the photoresist, the front pattern information and the overlay requirements; the exposure time is adjusted within the range of 2 to 10 seconds, and the light source intensity is set within the range of 5 to 20 seconds. range. Preferably, in step S5, the exposure time is 2S. After the exposure is completed, a wet development process is adopted, and the irregular wafer is placed in a developer. The amount of developer is controlled to be 150~300ml, and the development time is controlled to be 2~4 minutes. The developer is stirred clockwise at a uniform speed and then counterclockwise at the same speed to ensure uniform development. After the development is completed, the irregular wafer is rinsed with deionized water 3~5 times, each rinsing time is 1~2 minutes, to remove the residual developer and complete the preliminary formation of the back photolithography pattern. The wet development process can effectively remove the unexposed photoresist and make the exposed pattern clearly appear.
[0042] In some optional embodiments, after the exposure and development of the photoresist on the back of the irregular wafer, the following steps may be performed: setting the magnification of the microscope to 500-1000 times, measuring the overlay deviation between the photolithographic pattern on the back of the irregular wafer and the front pattern at key positions, and simultaneously checking the quality of the photolithographic pattern; if the overlay deviation is found to exceed the allowable range, rework and correction are performed using the NMP stripping method. In this embodiment, after step S5, the overlay accuracy and quality of the back photolithographic pattern may be checked, and rework and correction may be performed if there are errors; the overlay accuracy and quality of the back photolithographic pattern may be checked using a microscope or other inspection equipment, and the rework and correction may be performed using flood exposure or wet etching methods to process the areas with errors.
[0043] During the inspection of this embodiment, a high-resolution microscope imaging system, such as the OLYMPUS BX53M system microscope, is used, and the microscope magnification is set at 500~1000 times to inspect the back-side photolithography pattern. The overlay deviation between the photolithography pattern and the front-side pattern at key positions is measured, and the allowable range of overlay deviation is set within ± 0.1μm according to the process requirements. At the same time, the quality of the photolithography pattern is checked, including the integrity of the lines, the roughness of the edges, etc. If it is found that the overlay error exceeds the allowable range, the NMP degumming method is used for rework and correction. For cases where the overlay deviation is small, the alignment parameters of the back-side photolithography pattern are adjusted to ensure that the overlay accuracy and quality meet the process requirements.
[0044] In semiconductor manufacturing, the photolithography process is crucial for back-side overlaying of wafers. However, wafers made of InP material are fragile and prone to irregular shapes, making them difficult to handle with traditional photolithography technology. Irregular wafers face problems such as difficult positioning during back-side overlaying, interference from the visual system, mechanical adjustment limitations, uneven photoresist coating and exposure, and poor process stability. This application solves the problems of traditional alignment methods having difficulty identifying the position and angle of irregular wafers, the impact of irregular shapes on photoresist coating and exposure dose, and the lack of effective positioning and alignment methods. It achieves the goals of improving overlay accuracy, ensuring the quality of photolithography patterns, and enhancing process stability, thereby reducing production costs, shortening production cycles, and promoting technological progress in the semiconductor manufacturing industry in processing irregular wafers.
[0045] In the description of this application, it should be noted that the terms "upper" and "lower" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application. Unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be internal communication between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to the specific circumstances.
[0046] It should be noted that, in this application, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" 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.
[0047] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.
Claims
1. A backside overlay method for irregular wafers, characterized in that: It includes the following steps: Use a dicing machine to cut a positioning edge with a specific shape on the irregular wafer after the front side process is completed and the back side is thinned; Image the positioning edge of irregular wafers and extract key feature points and contour information; Applying photoresist to the back side of the irregular wafer; Place the irregular wafer on the workbench of the lithography equipment, and locate and align the front pattern of the irregular wafer with the pattern of the photoresist based on the key feature points and contour information of the positioning edge; Expose and develop the photoresist on the back of the irregular wafer.
2. The backside overlay method of an irregular wafer according to claim 1, wherein: The positioning edge is an L-shaped right-angle edge.
3. The backside overlay method of an irregular wafer according to claim 2, wherein: The short side length of the positioning edge is in the range of 1 to 3 mm, the long side length is in the range of 3 to 8 mm, and the error of the angle between the long side and the short side and 90° is controlled within ±1°.
4. The backside overlay method of an irregular wafer according to claim 1, wherein: The method of using a dicing machine to cut a positioning edge having a specific shape on an irregular wafer after the front side process is completed and the back side is thinned includes: The irregular wafer is fixed on the workbench of the dicing machine. The visual recognition system of the dicing machine accurately identifies the position to be cut on the edge of the irregular wafer, and cuts the front of the irregular wafer according to a specific shape to form a positioning edge.
5. The backside overlay method of an irregular wafer according to claim 4, wherein: The cutting speed of the dicing machine is set to 5-12 mm / s, and the cutting depth is 1 / 4-1 / 2 of the thickness of the irregular wafer.
6. The backside overlay method for irregular wafers according to claim 1, wherein: The imaging of the positioning edge of the irregular wafer and the extraction of key feature points and contour information include: An optical microscope imaging system is used to clearly image the front pattern corresponding to the positioning edge, and then imaging processing software is used to extract key feature points and contour information from the imaged image, and the key feature points and contour information are classified, marked and saved.
7. The backside overlay method for irregular wafers according to claim 1, wherein: The method of coating photoresist on the back side of the irregular wafer comprises: The irregular wafer after cleaning and drying is placed on a pre-cut white film, wherein the size of the white film is larger than the size of the vacuum adsorption plate of the coating machine; Place the irregular wafer with white film on the vacuum adsorption plate of the coater, and then spin-coat the back of the irregular wafer with photoresist. At the same time, for the edges and special areas on the back of the irregular wafer, use a manual drip device to add an appropriate amount of photoresist to cover the entire surface so that the photoresist on the back is evenly distributed.
8. The backside overlay method for irregular wafers according to claim 1, wherein: Placing the irregular wafer on a workbench of a photolithography device and positioning and aligning the front pattern of the irregular wafer with the pattern of the photoresist plate based on key feature points and contour information of the positioning edge include: Place the irregular wafer on the workbench of the lithography equipment, adjust the X and Y position and rotation angle of the workbench, and use the visual alignment system of the lithography equipment to preliminarily align the positioning edge with the pattern on the reticle; Then, the key feature points and contour information of the positioning edge are precisely aligned with the pattern on the current photomask. By fine-tuning the position and angle of the workbench, the front pattern of the irregular wafer is precisely aligned with the pattern on the photomask.
9. The backside overlay method for irregular wafers according to claim 1, wherein: The exposure and development process of the photoresist on the back side of the irregular wafer includes: The exposure parameters of the photolithography equipment are set according to the line width of the front pattern, the overlay accuracy requirements and the photosensitivity characteristics of the photoresist used. After the exposure is completed, a wet development process is used for development.
10. The backside overlay method of an irregular wafer according to claim 1, wherein: After the exposure and development of the photoresist on the back side of the irregular wafer, the method further includes: Set the microscope magnification to 500-1000x to measure the overlay deviation between the backside and frontside patterns of irregular wafers at key locations, while also checking the quality of the lithographic patterns. If the overlay deviation is found to exceed the allowable range, the NMP degumming method is used for rework and correction.