A vision-based wafer pre-alignment device and method

Abstract

The application discloses a kind of based on vision wafer pre-alignment device and method, it is related to photolithography process field, including wafer bearing and rotating unit, vision acquisition unit, camera position adjusting unit and control and processing unit, wafer bearing and rotating unit includes fixed mounting on the top surface of equipment base and places the rack, the top end middle part of rack is rotatably installed with wafer bearing platform, the inside of rack is provided with rotary drive part, rotary drive part is transmission connection between the coupling and wafer bearing platform, the upper surface of wafer bearing platform is fixedly installed with several vacuum chuck;Through the synergistic effect of vision acquisition unit and pre-alignment core algorithm, backlight source highlights wafer gap profile, monocular industrial camera collects high-quality image, cooperates SIFT feature extraction algorithm, circle fitting algorithm accurately extracts feature point and calculates circle center deviation and rotation angle offset, effectively compensates rotation cumulative error and mechanical deviation, compared with prior art, improve alignment accuracy.

Description

Technical Field

[0001] This invention relates to photolithography technology, specifically to a vision-based wafer pre-alignment device and method. Background Technology

[0002] In modern semiconductor manufacturing processes, photolithography is a core component of chip manufacturing, and its precision directly determines the performance and reliability of integrated circuits. As semiconductor manufacturing process nodes continue to advance to 7nm, 5nm, and even smaller sizes, the precision requirements for wafer processing have reached the nanometer level. Against this backdrop, the importance of wafer alignment technology has become increasingly prominent.

[0003] Wafer alignment is a critical step in photolithography, mainly divided into two types: global alignment and inter-layer alignment. Inter-layer alignment is particularly important, as it ensures the precise superposition of multi-layer circuit structures by accurately matching the positional relationship between the mask pattern and the existing pattern on the silicon wafer. A typical chip manufacturing process requires dozens of photolithography processes, and some complex structural layers even require multiple exposures and etchings to complete. This makes the accuracy of inter-layer alignment directly affect the yield of the final product.

[0004] In the photolithography process of semiconductor manufacturing, the accuracy of the wafer alignment system directly affects the yield of the final product. The current mainstream alignment system uses a suction cup to drive the wafer to rotate, and uses edge linear array sensors to collect wafer contour data in real time. Specifically, when the wafer completes a certain rotation, the system can obtain the coordinates of the intersection point between the wafer edge and the sensor array at each corner position. However, this solution has two main sources of error: first, the angle encoder of the rotary motor has cumulative error, which causes the actual rotation angle to deviate from the theoretical value; second, the mechanical deviation generated during wafer loading causes the wafer geometric center to not coincide with the rotation center. These systematic errors will significantly reduce the alignment accuracy and may cause critical dimensions to exceed specifications in advanced processes. Summary of the Invention

[0005] The purpose of this invention is to provide a vision-based wafer pre-alignment device and method to solve the problems of poor adaptability of existing wafer pre-alignment devices, inaccurate notch identification, and cumbersome and inefficient pre-alignment methods.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a vision-based wafer pre-alignment device, comprising a wafer carrying and rotating unit, a vision acquisition unit, a camera position adjustment unit, and a control and processing unit;

[0007] The wafer carrier and rotation unit includes a placement frame fixedly installed on the upper surface of the equipment base. A wafer carrier stage is rotatably installed at the top center of the placement frame. A rotation drive unit is provided inside the placement frame. The rotation drive unit is connected to the wafer carrier stage through a coupling. Several vacuum chucks are fixedly installed on the upper surface of the wafer carrier stage. A wafer body is placed on the upper surface of the vacuum chucks.

[0008] The visual acquisition unit includes a monocular industrial camera and a backlight source. The monocular industrial camera is located directly below the wafer body. An adjustable-focus industrial lens is provided at the lens interface at the bottom of the monocular industrial camera. The monocular industrial camera adopts an eye-out-of-hand layout. The backlight source is located at the edge of the upper surface of the placement rack and is a surface light source.

[0009] The camera position adjustment unit includes a camera XY axis fine-tuning platform, and the monocular industrial camera and the camera XY axis fine-tuning platform are fixedly connected.

[0010] The control and processing unit includes a motor controller, an image acquisition card, and a host computer. The motor controller is electrically connected to the rotary drive unit. The image acquisition card is communicatively connected to both the monocular industrial camera and the host computer. The host computer is electrically connected to the motor controller.

[0011] Furthermore, the adjustable-focus industrial lens is equipped with a manual focus ring, and the acquisition range of the monocular industrial camera can be adjusted by the camera's XY axis fine-tuning platform to cover more than 1 / 4 of the wafer area.

[0012] Furthermore, the host computer runs exposure machine software to perform camera parameter calibration, image acquisition and storage, and pre-alignment algorithm calculation.

[0013] A vision-based wafer pre-alignment method includes the following steps:

[0014] S1. Device initialization: The host computer detects the operating status of each unit and establishes a communication connection.

[0015] S2. Place the chopped wafer body on the vacuum suction cup wafer carrier and start vacuum adsorption fixation;

[0016] S3. Adjust the position of the monocular industrial camera using the camera's XY axis fine-tuning platform, and rotate the focus ring to make the image clear;

[0017] S4. The host computer completes the camera parameter calibration;

[0018] S5. The monocular industrial camera acquires the initial position image of the wafer body and transmits it to the host computer for storage.

[0019] S6. The rotary drive unit drives the wafer carrier stage to rotate at a set angle, and the monocular industrial camera acquires the image of the current position.

[0020] S7. The host computer compares the two images and calculates the offset of the notch position.

[0021] S8. The rotation drive unit drives the wafer body to rotate in the opposite direction by a corresponding angle to achieve notch alignment;

[0022] S9. Collect images to verify alignment accuracy. If the accuracy is not met, repeat steps 6-8.

[0023] Compared with the prior art, the vision-based wafer pre-alignment device and method provided by the present invention have the following beneficial effects:

[0024] 1. This invention utilizes the synergistic effect of a visual acquisition unit and a pre-alignment core algorithm. The backlight source highlights the wafer notch outline, and a monocular industrial camera acquires high-quality images. Combined with the SIFT feature extraction algorithm and the circle fitting algorithm, feature points are accurately extracted and the center deviation and rotation angle offset are calculated, effectively compensating for cumulative rotation errors and mechanical deviations. Compared with existing technologies, this invention improves alignment accuracy.

[0025] 2. This invention, through the cooperation of the camera's XY axis fine-tuning platform and the adjustable-focus industrial lens, can flexibly adjust the camera's acquisition range and imaging clarity, adapt to wafers of different sizes, and the vacuum chuck can quickly fix the wafer, with each unit working in an automated manner without the need for complex manual operation. Compared with the prior art, it improves the device's adaptability and ease of operation.

[0026] 3. This invention enhances feature recognition through image preprocessing, accurately solves the rotation angle by combining the slope calculation of the midpoint of the tangent edge with the angle judgment rules, and sets up an alignment verification step and a dynamic deviation compensation mechanism to ensure stable and reliable alignment results, reduce repetitive operations, and improve the efficiency and reliability of the pre-alignment process compared with the prior art. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0028] Figure 1 This is a schematic diagram of the overall structure provided for an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram of the cross-sectional structure of the placement rack provided in an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of the wafer carrier stage structure provided in an embodiment of the present invention;

[0031] Figure 4 This is a schematic diagram of the overall process provided for an embodiment of the present invention;

[0032] Figure 5 This is a schematic diagram of the initial wafer acquisition provided in an embodiment of the present invention;

[0033] Figure 6 This is a schematic diagram of the midpoint of the wafer dicing edge provided in an embodiment of the present invention.

[0034] Explanation of reference numerals in the attached figures:

[0035] 1. Equipment base; 2. Camera XY axis fine-tuning platform; 3. Monocular industrial camera; 4. Placement rack; 5. Rotary drive unit; 6. Wafer carrier stage; 7. Vacuum chuck; 8. Wafer body; 9. Backlight source. Detailed Implementation

[0036] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0037] As attached Figure 1 To be continued Figure 3 As shown:

[0038] Example 1:

[0039] The present invention provides a vision-based wafer pre-alignment device, comprising a wafer carrying and rotating unit, a vision acquisition unit, a camera position adjustment unit, and a control and processing unit;

[0040] The wafer carrier and rotation unit includes a placement frame 4 fixedly installed on the upper surface of the equipment base 1. A wafer carrier stage 6 is rotatably installed at the top center of the placement frame 4. A rotation drive unit 5 is provided inside the placement frame 4. The rotation drive unit 5 is a servo motor. The rotation drive unit 5 is connected to the wafer carrier stage 6 through a coupling. Several vacuum chucks 7 are fixedly installed on the upper surface of the wafer carrier stage 6. A wafer body 8 is placed on the upper surface of the vacuum chucks 7.

[0041] The visual acquisition unit includes a monocular industrial camera 3 and a backlight source 9. The monocular industrial camera 3 is located directly below the wafer body 8. An adjustable-focus industrial lens is provided at the lens interface at the bottom of the monocular industrial camera 3. The monocular industrial camera 3 adopts an eye-out layout. The backlight source 9 is located at the edge of the upper surface of the placement rack 4 and is a surface light source.

[0042] The camera position adjustment unit includes a camera XY axis fine-tuning platform 2, a monocular industrial camera 3, and the camera XY axis fine-tuning platform 2 fixedly connected;

[0043] The control and processing unit includes a motor controller, an image acquisition card, and a host computer. The motor controller is electrically connected to the rotary drive unit 5. The image acquisition card is communicatively connected to the monocular industrial camera 3 and the host computer. The host computer is electrically connected to the motor controller.

[0044] The adjustable-focus industrial lens comes with a manual focus ring, and the acquisition range of the monocular industrial camera 3 can be adjusted by the camera's XY axis fine-tuning platform 2 to cover more than 1 / 4 of the wafer area of ​​the wafer body 8.

[0045] The host computer runs the exposure machine software, which is used to perform camera parameter calibration, image acquisition and storage, and pre-alignment algorithm calculation.

[0046] Working principle: First, the control and processing unit serves as the core control hub. After startup, the host computer automatically loads the pre-alignment core algorithm (including SIFT feature extraction algorithm and circle fitting algorithm), while simultaneously detecting the operating status of the wafer support and rotation unit and the vision acquisition unit. Once all units are in normal condition, the host computer establishes stable communication with the motor controller and image acquisition card, laying the foundation for the collaboration of each structure.

[0047] Next, the wafer carrier and rotation unit starts working. The staff places the diced wafer body 8 on the vacuum chuck 7 of the wafer carrier stage 6. The host computer sends an adsorption command, and the vacuum chuck 7 generates negative pressure to firmly fix the wafer, preventing displacement during subsequent rotation and alignment, and providing a stable wafer posture for accurate acquisition and adjustment.

[0048] Subsequently, the camera position adjustment unit and the vision acquisition unit work together. The host computer controls the movement of the camera XY axis fine-tuning platform 2, which drives the monocular industrial camera 3 to translate along the X and Y axes, adjusting it to cover more than 1 / 4 of the wafer body 8 in the acquisition range, ensuring that the edge notch features are completely included in the acquisition field of view. The operator manually rotates the focus ring of the adjustable industrial lens, and in combination with the imaging screen displayed in real time by the host computer, fine-tunes it until the wafer edge and notch outline are clear. At the same time, the backlight source 9 (surface light source) on the edge of the upper surface of the placement rack 4 is activated, which enhances the contrast between the notch and the background through backlighting, making the feature points easier to identify and providing high-quality image data for subsequent image processing.

[0049] During the image acquisition stage, the monocular industrial camera 3 acquires wafer images according to the instructions of the host computer, and transmits the image data to the host computer through the image acquisition card. The host computer runs the exposure machine software to complete image preprocessing (denoising, contrast enhancement), feature point extraction, circle fitting and deviation calculation, and obtains the position offset of the wafer notch and the center deviation value.

[0050] Finally, the control and processing unit and the wafer carrier and rotation unit work together to perform the alignment action. The host computer converts the deviation data into control commands and sends them to the motor controller. The motor controller drives the rotation drive unit 5 (servo motor) to operate. The servo motor smoothly transmits the torque to the wafer carrier stage 6 through the coupling, causing the wafer to rotate in the opposite direction according to the calculated offset, correcting the center position, and finally making the wafer notch aligned with the preset reference position, and the wafer geometric center coincide with the rotation center.

[0051] Throughout the process, each unit achieves precise pre-alignment of the wafer through the collaborative logic of "central control coordination - fixed support unit - visual unit acquisition - adjustment unit adaptation - drive unit execution", effectively reducing the impact of rotational cumulative error and mechanical deviation, and improving alignment accuracy and efficiency.

[0052] Example 2:

[0053] As attached Figure 4 To be continued Figure 6 As shown:

[0054] A vision-based wafer pre-alignment method includes the following steps:

[0055] S1. Device initialization: The host computer detects the operating status of each unit and establishes communication connections.

[0056] The staff starts the pre-alignment device, and the host computer automatically loads the pre-alignment core algorithm (including SIFT feature extraction algorithm and circle fitting algorithm). At the same time, it detects the operating status of the wafer carrier and rotation unit, vision acquisition unit, and control and processing unit, including the responsiveness of the rotation drive unit 5 (servo motor), the imaging integrity of the monocular industrial camera 3, the brightness stability of the backlight source 9, and the communication smoothness of the image acquisition card. After the detection is passed, the host computer establishes a stable communication connection with the motor controller and the image acquisition card, and outputs a "device ready" signal.

[0057] S2. Place the diced wafer body 8 on the vacuum chuck 7 and activate vacuum adsorption for fixation:

[0058] The staff places the diced wafer body 8 stably on the vacuum chuck 7 and in the center of the wafer carrier stage 6, ensuring that the surface of the wafer body 8 is unobstructed and tilted. Then, the host computer sends a "adsorption fixation" command, the vacuum chuck 7 is activated and generates negative pressure, firmly adsorbing the diced wafer body 8 onto the upper surface of the wafer carrier stage 6. The host computer monitors the adsorption pressure value in real time, and sends a "fixation complete" feedback after the pressure reaches the target, to prevent the wafer body 8 from shifting during subsequent rotation.

[0059] S3. Adjust the position of the monocular industrial camera 3 using the camera's XY axis fine-tuning platform 2, and rotate the focus ring to make the image clear:

[0060] The staff controlled the camera XY axis fine-tuning platform 2 through the host computer, which moved the monocular industrial camera 3 along the X and Y axes to adjust it so that the acquisition range of the monocular industrial camera 3 covered more than 1 / 4 of the wafer area (ensuring that the notch feature was fully captured); then the staff manually rotated the focus ring of the adjustable focus industrial lens, and the host computer displayed the image of the monocular industrial camera 3 in real time. The staff observed the clarity of the edge and notch outline of the wafer body 8, and repeatedly fine-tuned until the outline was sharp and there was no blur or ghosting, thus completing the focus;

[0061] S4. The host computer completes the calibration of three parameters of the monocular industrial camera:

[0062] The host computer acquires real-time preview images from the monocular industrial camera 3 via an image acquisition card. The operator starts the calibration process in the exposure machine software, inputting the known size parameters of the wafer body 8 as a reference. The system automatically completes the calibration of the intrinsic parameters (focal length, principal point coordinates, distortion coefficient) and extrinsic parameters (relative position and orientation of the monocular industrial camera 3 and the wafer body 8) of the monocular industrial camera 3. The calibration data is stored in the host computer, providing a basis for subsequent pixel coordinate and world coordinate conversion.

[0063] S5, the monocular industrial camera 3 acquires the initial position image of the wafer body 8 and transmits it to the host computer for storage:

[0064] The host computer sends an "initial acquisition" command, and the monocular industrial camera 3 captures an image of the current position of the wafer body 8. The image is transmitted to the host computer via the image acquisition card. The system preprocesses the initial image, removes environmental noise through a median filtering algorithm, and enhances image contrast by multiplying pixels one by one, making feature points (such as edge inflection points) at the cut edge clearer. The preprocessed image is stored as the "initial reference image".

[0065] S6, the rotary drive unit 5 drives the wafer carrier stage 6 to rotate at a set angle, and the monocular industrial camera 3 acquires the image of the current position:

[0066] The operator sets the rotation angle (selectable from 30° to 90° to adapt to different notch recognition requirements) through the host computer. The host computer sends a rotation command to the motor controller. The rotation drive unit 5 (servo motor) drives the wafer carrier stage 6 to rotate smoothly to the set angle through the coupling. After the rotation is in place, the rotation drive unit 5 (servo motor) locks itself in place. Then, the monocular industrial camera 3 takes an image of the current position of the wafer body 8, and performs noise reduction and contrast enhancement preprocessing, and stores it as the "current comparison image".

[0067] S7. The host computer compares the two images and calculates the offset of the notch position:

[0068] The host computer uses a pre-alignment algorithm to process the two images:

[0069] ① Extract the edge contour of the wafer from the two images using the Canny operator:

[0070] Because the SIFT feature point detection algorithm is rotation-invariant, the SIFT algorithm is used for feature point extraction, such as... Figure 6 As shown, two feature points, A and B, can be extracted to obtain their pixel coordinates. Based on the camera calibration results, their world coordinates can then be derived. Specifically, the rotated feature points are represented as follows: , ;

[0071] ② Use the SIFT algorithm to extract feature points at the gap (points A and B in the initial image, and points A' and B' in the current image). Combine the calibration data from step 4 to convert the feature points from the pixel coordinate system to the world coordinate system.

[0072] ③ Perform circle fitting on the feature points, solve for the center coordinates (O, O') and radius of the wafer body 8 in the two images, and calculate the center deviation value:

[0073] Let L be the sum of the arc lengths between all adjacent points, where point ( , The sum of the arc lengths between the two points is When calculating the coordinates of the center and the radius, the weight of the distance from the point to the center is... Then the coordinates of the center of the circle ( )for:

[0074]

[0075] The radius is: ;

[0076] ④ Extract the endpoints of the cut edges in the two images (such as points C and D and C' and D'), solve for the midpoints (M and M') of each cut edge, and calculate the rotation angle offset by the slope of the line connecting the midpoints:

[0077] The principle of solving rotation angles using the midpoint is as follows: Figure 6 As shown, and They are straight lines and The midpoint, which is the solution here. That is, the rotation angle, the value of which is... Equal, straight line , Therefore, the slope can be solved. Convert to specific angle values ​​and obtain horn;

[0078] Known and It can be obtained The point coordinates are , and the corresponding number of sampling points is min. The angle value calculation formula is as follows:

[0079]

[0080]

[0081] Similarly, due to the contingency of the trimming position, the angle value also needs to be judged according to some conditions. The slope k takes a positive value in the first and third quadrants and a negative value in the second and fourth quadrants. The total number of sampling points n is determined, and the judgment conditions are as follows:

[0082] (1) When the angle is positive, and the rotation angle is within , when min < 3n / 8, , when min > 3n / 8, +180°;

[0083] (2) When or , at this time, when min < n / 4, , when min > n / 4, ;

[0084] (3) When the angle is negative, and its range is , when min < 5n / 8, +180°, when min > 5n / 4, +360°;

[0085] S8. The servo motor drives the wafer to rotate in the reverse direction by the corresponding angle to achieve notch alignment:

[0086] The host computer generates a composite adjustment instruction according to the rotation angle offset and the center deviation value calculated in step 7; after receiving the instruction, the motor controller controls the rotation drive unit 5 (servo motor) to drive the wafer carrier 6 to rotate in the reverse direction by the corresponding angle, and at the same time corrects the center position through the fine adjustment mechanism of the wafer carrier 6 (adapting to the correction of the center deviation), ensuring that the notch of the wafer body 8 is aligned with the preset reference position and the geometric center of the wafer body 8 coincides with the rotation center;

[0087] S9. Collect images to verify the alignment accuracy. If the standard is not met, repeat steps 6-8:

[0088] After adjustment, the monocular industrial camera 3 acquires an "alignment verification image". The system preprocesses the image and extracts feature points, calculating the deviation between the current notch position and the preset reference position, and the deviation between the current center and the preset rotation center. If both deviations are within the allowable range (±0.01mm, meeting nanoscale processing requirements), the host computer outputs an "alignment complete" signal. If the standard is not met, steps 6-8 are automatically repeated (up to three times). If the standard is still not met, an alarm is triggered to notify staff to check for equipment or wafer problems.

[0089] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A vision-based wafer pre-alignment device, characterized in that, It includes a wafer carrier and rotation unit, a vision acquisition unit, a camera position adjustment unit, and a control and processing unit; The wafer carrier and rotation unit includes a placement frame (4) fixedly installed on the upper surface of the equipment base (1). A wafer carrier stage (6) is rotatably installed at the top center of the placement frame (4). A rotation drive unit (5) is provided inside the placement frame (4). The rotation drive unit (5) is connected to the wafer carrier stage (6) through a coupling. Several vacuum chucks (7) are fixedly installed on the upper surface of the wafer carrier stage (6). A wafer body (8) is placed on the upper surface of the vacuum chucks (7). The visual acquisition unit includes a monocular industrial camera (3) and a backlight source (9). The monocular industrial camera (3) is located directly below the wafer body (8). An adjustable-focus industrial lens is provided at the lens interface at the bottom of the monocular industrial camera (3). The monocular industrial camera (3) adopts an eye-out-of-hand layout. The backlight source (9) is located at the edge of the upper surface of the placement rack (4), and the backlight source (9) is a surface light source. The camera position adjustment unit includes a camera XY axis fine-tuning platform (2), and the monocular industrial camera (3) and the camera XY axis fine-tuning platform (2) are fixedly connected; The control and processing unit includes a motor controller, an image acquisition card and a host computer. The motor controller is electrically connected to the rotary drive unit (5). The image acquisition card is communicatively connected to the monocular industrial camera (3) and the host computer. The host computer is electrically connected to the motor controller.

2. The vision-based wafer pre-alignment device according to claim 1, characterized in that, The adjustable-focus industrial lens has a built-in manual focus ring, and the acquisition range of the monocular industrial camera (3) can be adjusted by the camera XY axis fine-tuning platform (2) to cover more than 1 / 4 of the wafer area of ​​the wafer body (8).

3. The vision-based wafer pre-alignment device according to claim 1, characterized in that, The host computer runs exposure machine software to perform camera parameter calibration, image acquisition and storage, and pre-alignment algorithm calculation.

4. A vision-based wafer pre-alignment method, comprising a vision-based wafer pre-alignment apparatus as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Device initialization: The host computer detects the operating status of each unit and establishes a communication connection. S2. Place the diced wafer body (8) on the vacuum suction cup wafer carrier stage (6) and start vacuum adsorption fixation; S3. Adjust the position of the monocular industrial camera (3) through the camera XY axis fine adjustment platform (2) and rotate the focus ring to make the image clear; S4. The host computer completes the camera parameter calibration; S5. The monocular industrial camera (3) acquires the initial position image of the wafer body (8) and transmits it to the host computer for storage. S6, Rotary drive unit (5) drives wafer carrier stage (6) to rotate at a set angle, and monocular industrial camera (3) acquires image of the current position; S7. The host computer compares the two images and calculates the offset of the notch position. S8. The rotation drive unit (5) drives the wafer body (8) to rotate in the opposite direction by the corresponding angle to achieve notch alignment. S9. Collect images to verify alignment accuracy. If the accuracy is not met, repeat steps 6-8.

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