A photolithography system and a photolithography method for double-sided lithography

Abstract

A double-sided photolithography system and method, the photolithography system comprises a first carrier, a second carrier, a photolithography mechanism and a controller, a substrate is placed on the first carrier with the front side upward, a substrate is placed on the second carrier with the back side upward, the photolithography mechanism performs a photolithography operation on the substrate, the controller controls the first carrier, the second carrier and the photolithography mechanism, the first carrier is provided with a first image acquisition device, when the substrate is placed on the first carrier, a first image of the back side of the substrate is acquired, a second image acquisition device is arranged above the second carrier, the second image acquisition device acquires a second image according to the position of the first image on the back side of the substrate. The alignment of the front side and the back side of the substrate is realized based on the first image and the second image, and the image information is used as the mark point information, so that the alignment accuracy is higher.

Description

Technical Field

[0001] This invention relates to a photolithography system, and more particularly to a method for double-sided photolithography on the front and back sides of a substrate. Background Technology

[0002] Photolithography is widely used in semiconductor and PCB manufacturing, and is one of the process steps in producing semiconductor devices, chips, and PCB boards. It is used to print feature patterns on a substrate surface to ultimately obtain the pattern structure required by the circuit design. Traditional photolithography requires the creation of a master mask or film for exposure, resulting in a long production cycle, and each mask corresponds to a single pattern, limiting its widespread application. To address these issues of traditional photolithography, direct-write lithography has emerged. It utilizes digital light processing technology and a programmable digital mirror device to edit different desired pattern structures, enabling rapid pattern switching. This not only reduces costs but also shortens the production cycle, and is now widely used in the field of photolithography. The principle of direct-write lithography is to transfer the design pattern to the substrate surface coated with a photosensitive material by modulating a light beam, and then obtain the desired pattern structure through processes such as development and etching.

[0003] For printed circuit boards (PCBs), multilayer boards are commonly used. These multilayer boards often include inner layers that can be connected on both sides. These inner layers require exposure not just on one side, but on both sides. During exposure, both the front and back sides of the inner layer must be exposed separately, ensuring the graphics on both sides correspond. In existing technology, when exposing the first side of the inner layer's graphics, a marking device forms a alignment mark on the back side. After the front side exposure is complete, the inner layer is placed back-side up, and a positioning camera captures the alignment mark formed by the marking device to calculate the precise printing position of the graphics to be drawn on the second side. The marking device uses a laser to form the mark on the back of the inner layer. However, the laser energy is difficult to control, the mark boundary shape is prone to change, and it is difficult to accurately identify the boundary, leading to reduced accuracy. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a photolithography system and photolithography method with improved alignment accuracy.

[0005] To address the aforementioned problems, this invention provides a double-sided lithography system. The lithography system includes a first stage, a second stage, a lithography mechanism, and a controller. A substrate is placed face-up on the first stage and back-up on the second stage. The lithography mechanism performs lithography operations on the substrate. The controller controls the first stage, the second stage, and the lithography mechanism. The first stage is equipped with a first image acquisition device. When the substrate is placed on the first stage, a first image of the back side of the substrate is acquired. The first image acquisition device includes at least two first image acquisition units. A second image acquisition device is positioned above the second stage. The second image acquisition device acquires a second image based on the position of the first image on the back side of the substrate. The controller includes an analysis module. The analysis module acquires a template image based on the first image and matches the template image in the second image according to the pixel information of the template image to obtain the position information of the template image in the second image.

[0006] Furthermore, the magnification of the first image acquisition device and the second image acquisition device is the same.

[0007] Furthermore, the first image acquisition device includes at least three first image acquisition units, wherein two first image acquisition units are located on one side of the first stage, and at least one first image acquisition unit is located on an adjacent side.

[0008] Furthermore, the analysis module uses normalized cross-correlation or shape matching algorithms to find the region of the matching template image in the second image and obtains the center point position of the matching template image region.

[0009] Furthermore, the lithography mechanism is located between the first stage and the second stage, and the first stage and the second stage are respectively moved to the lithography mechanism to perform lithography operations.

[0010] Furthermore, the first stage and the second stage share a photolithography mechanism or a second image acquisition device, the first stage and the second stage are arranged in parallel, or the first stage and the second stage are at different plane heights and can move between different plane heights.

[0011] A photolithography method for double-sided lithography includes placing a substrate on a first stage, acquiring a first image of the back side of the substrate using a first image acquisition device, acquiring a template image based on the first image, and performing photolithography on the front side of the substrate. The substrate is then flipped over and placed back-side up on a second stage. A second image acquisition device obtains the reference position of the corresponding area of ​​the template image based on the position information of the first image, acquires a second image on the back side of the substrate, and an analysis module obtains the position of the matching template image in the second image, thereby aligning the photolithographic patterns on the front and back sides of the substrate.

[0012] Furthermore, the first image acquisition device includes a plurality of first image acquisition units, each of which is numbered, and the template image acquired by the first image acquisition unit is identified according to the number.

[0013] Furthermore, the analysis module uses normalized cross-correlation or shape matching algorithms to find the region of the matching template image in the second image and obtains the center point position of the matching template image region.

[0014] Furthermore, the template image is all or part of the first image.

[0015] Compared with existing technologies, the first image acquisition device acquires a template image as a marker point on the back of the substrate. After the substrate is flipped, the second image acquisition device acquires the marker points of the template image, thereby achieving alignment of the front and back graphics of the substrate. Moreover, instead of simply determining the position of the marker point through the boundary, the template image is used for regional matching to confirm the position of the marker point, resulting in higher alignment accuracy. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a double-sided lithography system.

[0017] Figure 2 This is a schematic diagram of an embodiment of the first platform.

[0018] Figure 3 This is a schematic diagram of another embodiment of the first platform.

[0019] Figure 4 This is a schematic diagram of the first embodiment of the photolithography system.

[0020] Figure 5 This is a schematic diagram of the second embodiment of the photolithography system.

[0021] Figure 6 This is a schematic diagram of the third embodiment of the photolithography system.

[0022] Figure 7 This is a schematic diagram of the fourth embodiment of the photolithography system. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be described below with reference to specific embodiments shown in the accompanying drawings.

[0024] Figure 1-3A photolithography system for double-sided photolithography of a substrate is shown. The system includes a first stage 1, a second stage 2, and a controller. The first stage 1 and the second stage 2 support the substrate. The first stage 1 is equipped with a first image acquisition device 10, which acquires an image of the back side of the substrate placed face up on the first stage 1. The second stage 2 is correspondingly equipped with a second image acquisition device 20, which acquires an image of the back side of the substrate placed face down. The controller controls the movement of the first stage 1 and the second stage 2. The controller includes an analysis module that receives image information acquired by the first image acquisition device 10 and the second image acquisition device 20, and analyzes the images to obtain the relative position information of the substrate on the first stage and the second stage. Preferably, the first image acquisition device 10 and the second image acquisition device 20 have the same magnification, which can be a single magnification, a magnification ratio, or a reduction ratio. Images obtained from different locations on the substrate material have different details. A first image of a location on the back of the substrate is obtained through the first image. After the substrate is moved to the second stage 2, the position of the substrate changes. The position of the first image is found in the second image to determine the relative position of the substrate after it has been moved to different stages.

[0025] The front side of the substrate is the side that will undergo photolithography first. During the stage when the substrate is placed on the first stage 1, including the alignment and exposure operations on the substrate, or the stages before and after the above operations, the first image acquisition device 10 acquires a first image of the back side of the substrate and transmits it to the analysis module for storage. The substrate is then flipped and moved to the second stage 2, at which point the front side of the substrate faces the second stage 2 and the back side of the substrate faces upward. Based on the position of the first image acquired by the first image acquisition device 10, the second image acquisition device 20 acquires a second image of the back side of the substrate at the same or similar positions on the back side of the substrate. The control module compares the information of the first image acquired by the first image acquisition device 10 and the second image acquired by the second image acquisition device 20 to obtain the position information of the substrate placed on the second stage 2. Based on the position information, the substrate is subjected to photolithography to align the front and back patterns of the substrate.

[0026] After the substrate is flipped, during the alignment process, the analysis module uses the first image acquired by the first image acquisition unit as a template image and finds the matching position of the template image in the second image acquired by the second image acquisition unit. The template image can be the entire first image, or a portion of the first image cropped out as the template image. Preferably, a portion with prominent features in the first image is selected as the template image. Cropping an image from the first image reduces the amount of data processing and avoids problems caused by light diffraction at the edges when the entire first image is used as the template image. Furthermore, cropping an image from the first image allows for greater flexibility in the shape of the template image, enabling the selection of a suitable region shape.

[0027] The analysis module uses information from the template image and the second image to locate the template image in the second image using methods such as image correlation or shape matching. This allows it to obtain the center point location information of the region on the substrate placed on the second stage that corresponds to the template image. This method of obtaining center point location information through regional matching of the template image and the second image is unaffected by edge shapes and offers higher accuracy.

[0028] The following example uses image correlation matching. The analysis module creates a data group template containing each pixel from the template image. Based on the data group template, the algorithm of normalized cross-correlation is used to find the center point of the region corresponding to the template image in the second image.

[0029] Normalized cross correlation (NCC) is a mathematical method for determining whether there is a relationship between two sets of data. The calculation formula is as follows: in: Representing the window size, the computational complexity is O(n log n). As can be seen from the formula above, the mean and sum of squares can be pre-calculated using the integral image. For application scenarios where the template and target image are of the same size, the NCC calculation formula can be expressed as follows: The size and sum of squares of any window can be calculated in advance based on the integral image. in These represent the window mean values ​​of the image to be detected and the reference template image, respectively. The final NCC result is between 0 and 1, making it easy to quantify and compare the results.

[0030] After establishing five integral image indices—the mean, sum of squares, and cross product of the image to be detected and the template image below the window—the entire pre-computation generation is completed. By relying on the index table to look up the calculation results, NCC can achieve linear-time computation with approximately constant time consumption, independent of the effective region size.

[0031] The first and second images are compared by calculating the cross-correlation of normalized data. The position of the template image in the second image is obtained, and then the center point of the corresponding region of the template image in the second image is obtained.

[0032] The first stage has at least two openings 11, which are covered by light-transmitting baffles 12 to prevent dust from affecting the image quality acquired by the first image acquisition unit 10. The openings can be regular or irregular shapes, such as circles, squares, scalene polygons, or curved shapes. Preferably, the openings are regular shapes, making it easy to calculate the center point. The first image acquisition device 10 acquires at least two images through the openings 11. The first image acquisition device 10 has corresponding first image acquisition units 13 for each opening 11. Each first image acquisition unit 13 includes a light source, such as a coaxial light source or a ring light source, to facilitate image acquisition and position calibration. A second image acquisition device 20 is positioned above the second stage 2. The second image acquisition device 20 includes at least one image acquisition unit 21 and a driving unit. The second image acquisition unit 21 is used to acquire images, and the driving unit is used to drive the second image acquisition unit 21 to move to the corresponding position on the substrate. Figure 3 As shown, preferably, the first stage 1 has three openings 11, two of which are located on one side of the first stage 1, and the third opening 11 is located on the adjacent side of the first stage 1. Preferably, the light-transmitting baffle has marking points 15 on the parts that do not cover the openings. The marking points are close to the edge of the first stage 1, and when the substrate is placed on the first stage 1, the marking points are exposed. The alignment camera corresponding to the first stage 1 obtains the relative position of the front of the substrate based on the position of the marking points.

[0033] Before placing the substrate on the first stage 1, the first image acquisition unit 13 is first calibrated. The coaxial light source used on the first image acquisition unit 13 is turned on, and the light source passes through the opening 11 and the light-transmitting baffle 12 to form a beam of light with the same shape as the opening. The alignment camera corresponding to the first stage 1 captures the pattern formed by the beam of light and records the coordinates of the first image acquisition unit 13 on the first stage 1 at this time, thus completing the calibration work.

[0034] The substrate is placed face up on the first stage 1, and alignment exposure is performed on the front side of the substrate. After the front alignment exposure is completed, the first image acquisition unit 13 begins to acquire a first image through the light-transmitting baffle 12. The first image is used as a template image or a template image is selected from the first image, and the template image is saved locally. Each first image acquisition unit 13 has a corresponding number, and the template image is saved according to the number of the first image acquisition unit 13. The template image can be a regular or irregular shape, such as a circle, square, or a scalene polygon. Preferably, the template image is a regular shape, which is easy to calculate the center point position of the shape. After the front exposure is completed, the plates are flipped left and right to begin the back alignment exposure.

[0035] The analysis module calculates the reference position of the region corresponding to the template image on the second platform based on the position of the first image acquisition unit. The second image acquisition unit 21 moves to the reference position of the template sample and acquires the second image of that region. Based on the number of the first image acquisition unit 13, it retrieves the previously saved template image, creates an NCC template, and then finds the corresponding position of the template image in the second image based on the template image to obtain the center point position of the region corresponding to the current template image, i.e., the coordinate value of the center point. In addition to the center point position information, the rotation angle of the region corresponding to the current template image relative to the template image and the similarity between the two can also be obtained simultaneously to control the alignment accuracy.

[0036] The first stage 1 and the second stage 2 can use the same photolithography mechanism and the same alignment mechanism to expose the substrate for patterning, or they can use different photolithography mechanisms and different alignment mechanisms to expose the substrate for patterning, or they can use different alignment mechanisms and the same photolithography mechanism to expose the substrate for patterning. A first image acquisition unit is provided on the first stage 1 to acquire a first image when the back of the substrate is facing the first stage, thereby obtaining a template image. Alternatively, a first image acquisition unit can be provided on the second stage as needed.

[0037] Specifically, such as Figure 4As shown, the photolithography system includes a first stage 100, a first photolithography mechanism 300, a first alignment mechanism 400, a second stage 200, a second photolithography mechanism 500, a second alignment mechanism 600, and a flipping mechanism. The second alignment mechanism 600 is a second image acquisition device used to acquire an image of the back side of the substrate. The first stage is equipped with a first image acquisition device 101. The substrate is placed face up on the first stage 100. The first stage 100 moves to the first alignment mechanism 400 for alignment, and then moves to the first photolithography mechanism 300 for exposure. During this process, the first image acquisition mechanism 101 acquires an image of the back side of the substrate through an opening on the first stage 100. After the substrate completes the exposure operation, it moves to the flipping mechanism, and after being flipped, the substrate is placed face up on the second stage 200. The second alignment mechanism 600 acquires the position of the image from the first image acquisition device 101, captures the corresponding area of ​​the test image on the back of the substrate, finds the corresponding position of the template in the test image based on the template image acquired by the first image acquisition device 101, and obtains position information, including the position of the template, similarity, etc.

[0038] like Figure 5 As shown, the photolithography system includes a first stage 100, a photolithography mechanism 300, an alignment mechanism 400, a second stage 200, and a flipping mechanism. The alignment mechanism 400 is a second image acquisition device. The first stage 100 and the second stage 200 are arranged in parallel. The photolithography mechanism 300 and the alignment mechanism 400 are slidably arranged, corresponding to the positions of the first stage 100 and the second stage 200. The photolithography mechanism 300 and the alignment mechanism 400 move above the first stage 100 or the second stage 200 to perform alignment or exposure operations on the first stage 100 or the second stage 200. The first stage 100 is equipped with a first image acquisition device 101. The substrate is placed face up on the first stage 100. The first stage 100 moves to the alignment mechanism 400 for alignment operations, and then moves to the photolithography mechanism 300 for exposure operations. During this process, the first image acquisition device 101 acquires an image of the back side of the substrate through an opening on the first stage 100. After the substrate completes the exposure operation, it is moved to the flipping mechanism, and after being flipped by the flipping mechanism, the substrate is placed on the second stage 200 with the back side facing up. The alignment mechanism 400, based on the position of the image obtained by the first image acquisition device 101, grabs the corresponding area of ​​the image to be tested on the back side of the substrate. Based on the template image obtained by the first image acquisition device 101, it finds the corresponding position of the template in the image to be tested and obtains position information, including the center position of the template image, similarity, etc.

[0039] like Figure 6As shown, the photolithography system includes a first stage 100, a photolithography mechanism 300, an alignment mechanism 400, a second stage 200, and a flipping mechanism. The first stage 100 and the second stage 200 can be vertically adjusted in height, and at least when the first stage 100 and the second stage 200 move relative to each other, they are at different stage heights. The photolithography mechanism 300 and the alignment mechanism 400 are fixedly arranged. The alignment mechanism 400 is also a second image acquisition device, wherein the second image acquisition unit 401 is slidably arranged. The first stage 100 and the second stage 200 move to the alignment mechanism 400 and the photolithography mechanism 300 respectively for alignment or exposure operations. The first stage 100 is equipped with a first image acquisition device. The substrate is placed face up on the first stage 100. The first stage 100 moves to the alignment mechanism 400 for alignment operations, and then moves to the photolithography mechanism 300 for exposure operations. During this process, the first image acquisition device acquires an image of the back side of the substrate through an opening on the first stage 100. After the substrate completes the exposure operation, it is moved to the flipping mechanism, which flips it so that the substrate is placed on the second stage 200 with the back side facing up. The alignment mechanism 400, based on the position of the image obtained by the first image acquisition device, captures the corresponding area of ​​the image to be tested on the back side of the substrate. Based on the template image obtained by the first image acquisition device, it finds the corresponding position of the template image in the image to be tested and obtains position information, including the position of the template, similarity, etc.

[0040] like Figure 7As shown, the lithography system includes a first stage 100, a lithography mechanism 300, a first alignment mechanism 400, a second stage 200, a second alignment mechanism 500, and a flipping mechanism. The second alignment mechanism 500 is a second image acquisition device. The first alignment mechanism 400 and the second alignment mechanism 500 are located on both sides of the lithography mechanism 300. The first stage 100 performs alignment and exposure operations with the lithography mechanism 300 via the first alignment mechanism 400, and the second stage 200 performs alignment and exposure operations with the lithography mechanism 300 via the second alignment mechanism 500. The lithography mechanism 300, the first alignment mechanism 400, and the second alignment mechanism 500 are fixedly arranged, while the image acquisition units 600 of the first alignment mechanism 400 and the second alignment mechanism 500 are slidably arranged. The first stage 100 and the second stage 200 respectively perform alignment and exposure operations. The first stage 100 is equipped with a first image acquisition device 101. The substrate is placed face up on the first stage 100. The first stage 100 moves to the first alignment mechanism 400 for alignment, and then moves to the photolithography mechanism 300 for exposure. During this process, the first image acquisition device 101 acquires an image of the back side of the substrate through an opening on the first stage 100. After the substrate completes the exposure, it moves to the flipping mechanism, and after being flipped, the substrate is placed face up on the second stage 200. The second alignment mechanism 500, based on the position of the image acquired by the first image acquisition device, captures a test image of the corresponding area on the back side of the substrate. Based on the template image acquired by the first image acquisition device, it finds the corresponding position of the template image in the test image and obtains position information, including the position of the template, similarity, etc.

[0041] The aforementioned photolithography system is not only suitable for printed circuit boards, but also for other substrates that are not convenient to mark with lasers, such as silicon wafers.

Claims

1. A double-sided photolithography system, the photolithography system comprising a first stage, a second stage, a photolithography mechanism, and a controller, wherein a substrate is placed on the first stage with its front side facing upwards, and the substrate is placed on the second stage with its back side facing upwards; the photolithography mechanism performs photolithography operations on the substrate; and the controller controls the first stage, the second stage, and the photolithography mechanism, characterized in that: The first platform is equipped with a first image acquisition device. When the substrate is placed on the first platform, a first image of the back side of the substrate is acquired. The first image acquisition device includes at least three first image acquisition units, of which two first image acquisition units are located on one side of the first platform and at least one first image acquisition unit is located on an adjacent side. A second image acquisition device is arranged above the second platform. The second image acquisition device acquires a second image based on the position of the first image on the back side of the substrate. The controller includes an analysis module. The analysis module acquires a template image based on the first image. It matches the template image in the second image according to the pixel information of the template image to obtain the position information of the template image in the second image. The analysis module finds the region matching the template image in the second image through normalized cross-correlation or shape matching algorithms to obtain the center point position of the matching template image region.

2. The photolithography system according to claim 1, characterized in that: The magnification of the first image acquisition device and the second image acquisition device is the same.

3. The photolithography system according to claim 1, characterized in that: The lithography mechanism is located between the first stage and the second stage, and the first stage and the second stage are respectively moved to the lithography mechanism to perform lithography operations.

4. The photolithography system according to claim 1, characterized in that: The first stage and the second stage share a photolithography mechanism or a second image acquisition device. The first stage and the second stage are arranged in parallel, or the first stage and the second stage are at different plane heights and can move between different plane heights.

5. A photolithography method for double-sided photolithography, characterized in that: The substrate is placed on the first stage, the first image acquisition device acquires the first image on the back side of the substrate, and acquires the template image based on the first pattern. The photolithography mechanism performs photolithography on the front side of the substrate. The first image acquisition device includes at least three first image acquisition units, of which two first image acquisition units are located on one side of the first stage and at least one first image acquisition unit is located on an adjacent side. Each first image acquisition unit is numbered, and the template image acquired by the first image acquisition unit is identified according to the number. The substrate is flipped over and placed on the second stage with the back side facing up. The second image acquisition device obtains the reference position of the corresponding area of ​​the template image based on the position information of the first image. The second image is acquired on the back side of the substrate. The analysis module finds the area matching the template image in the second image through normalized cross-correlation or shape matching algorithms and obtains the center point position of the matching template image area, so that the photolithographic pattern on the front side and the photolithographic pattern on the back side of the substrate are aligned.

6. The photolithography method according to claim 5, characterized in that: The template image is all or part of the first image.

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