Annular light enhanced wide field three-dimensional chromatic topography measurement system and method

Abstract

This invention discloses a wide-field three-dimensional color topography measurement system and method enhanced with ring light, belonging to the field of optical three-dimensional topography measurement technology. The disclosed system includes a wide-field imaging module, a coaxial illumination module, a ring light illumination module, and a Z-axis displacement stage. It employs an iterative focusing topography recovery algorithm to reconstruct the full-color three-dimensional topography. Coaxial incident illumination is used for flat areas, while the ring light illuminates steep slopes from a near-horizontal direction. High-precision three-dimensional reconstruction of large-angle surfaces that cannot be measured by traditional coaxial illumination is achieved through the scattered light signal. Experiments show that the system of this invention can achieve sub-micron resolution, rapid scanning, and full-color imaging, making it suitable for high-precision industrial inspection of electronic devices such as chips and printed circuit boards.

Description

Technical Field

[0001] This invention belongs to the field of optical three-dimensional topography measurement technology, specifically relating to a system and method for measuring the color three-dimensional topography of large-angle surfaces, which is particularly suitable for high-throughput industrial inspection of electronic chip pins, microelectromechanical system structures and printed circuit board solder joints. Background Technology

[0002] Three-dimensional topography measurement technology has evolved from contact coordinate measuring machines to non-contact optical methods. Existing non-contact technologies are mainly divided into three levels based on the trade-off between resolution and speed: nanometer-level high precision, submicron-level medium precision, and micron-level rapid imaging.

[0003] While white-light interferometry can achieve sub-nanometer axial resolution and improves imaging speed and measurable slope range through techniques such as lateral scanning and vertical off-axis compensation, it remains fundamentally constrained by the numerical aperture of the objective lens, making it difficult to effectively measure near-horizontal surfaces. Furthermore, its reliance on grayscale point / line scanning results in low 3D acquisition efficiency. White-light color interferometry, while capable of simultaneously acquiring thickness and morphology, suffers from a small field of view and slow scanning, still lacking true color imaging capabilities. Confocal microscopy achieves sub-micron resolution through optical layer cutting and has seen speed improvements in recent years through galvanometer scanning and fiber optic synchronization, but still lacks color information. Its ability to measure steep slopes is limited by the numerical aperture, and its 3D data acquisition speed is insufficient to support high-throughput online inspection. Structured light projection can achieve video-level large-field 3D acquisition, but its lateral resolution is only at the micrometer level and it outputs grayscale images. Large-angle measurements are limited by the relative angle between the projection and the camera. While ring structured light has been used for defect detection on the inner surfaces of deep holes and pipes, as well as the outer surfaces of rotating metal parts, its complex hardware, high cost, and insufficient imaging speed limit it to offline sampling inspections. Wide-field three-dimensional optical slice structured light illumination microscope breaks through the limitations of traditional wide-field microscopy and achieves fast, submicron resolution color three-dimensional imaging. However, it is still constrained by numerical aperture. Reflected light from steep slopes cannot be effectively collected by the objective lens. Although multi-angle illumination can partially alleviate this problem, it will significantly increase the amount of data acquisition and reduce the imaging speed.

[0004] It is evident that existing technologies generally share a common bottleneck: it is difficult to simultaneously achieve full-color imaging, high-speed 3D topography reconstruction, and large-angle (exceeding numerical aperture angle) surface measurement. Summary of the Invention

[0005] In view of the defects or deficiencies of the prior art, the present invention provides a wide-field three-dimensional color topography measurement system with ring light enhancement.

[0006] Therefore, the ring light-enhanced wide-field three-dimensional color morphology measurement system provided by the present invention includes a coaxial illumination module, a ring light illumination source, a wide-field imaging module, and a displacement stage.

[0007] The displacement stage is equipped with a sample stage; the displacement stage can move along the X, Y, and Z axes; The wide-field imaging module includes an objective lens, a tube lens, a reflecting mirror, and an imaging device arranged along the optical path, wherein the objective lens is located above the Z-axis of the sample stage; The coaxial illumination module includes a white light source. The light emitted by the white light source is reflected by a beam splitter and then shines perpendicularly onto the sample stage along the optical axis through the objective lens. The optical axis is set along the Z-axis. The ring light source is set on the sample stage or between the objective lens and the sample stage, and the illumination area of ​​the ring light source surrounds the sample. The light from both the white light source and the ring light source simultaneously illuminates the sample. After being reflected by the sample, the light passes sequentially along the optical axis through the objective lens, beam splitter, and tube lens, and is then reflected by the mirror before entering the imaging device. By moving the stage along the Z-axis, the imaging device acquires a slice of the original color image of the sample.

[0008] An optional solution is that the wide-field imaging module includes an objective lens, a tube lens, a first reflecting mirror, a second reflecting mirror, a third reflecting mirror, and an imaging device arranged along the optical path; the light from the white light source and the ring light source simultaneously irradiating the sample is reflected by the sample, and then passes through the objective lens, the beam splitter, and the tube lens in sequence along the optical axis, and is then reflected multiple times by the first reflecting mirror, the second reflecting mirror, and the third reflecting mirror before being transmitted to the imaging device.

[0009] An alternative is that the emission angle of the ring-shaped illumination source is 0° to 30° relative to the XY plane.

[0010] A further embodiment of the system includes an image processing unit for executing an iterative focused shape restoration algorithm, which includes performing the following steps on all original color image slices: (1) For any original color image slice, calculate the initial focus measure of each pixel on the original color image slice, and the initial focus measure of any pixel (x,y,z) FL(x,y,z) for: FL(x,y,z)=( _xI)^2+( _yI)^2 in: _xI represents the gradient value of pixel (x,y,z) in the x-direction. _yI is the gradient value of pixel (x,y,z) in the y direction; (2) Apply Gaussian filtering to the initial focus measure of each pixel in the original color image slice to obtain the filtered focus measure of each pixel. FL filt (x,y,z)The Z-axis coordinate of the point (x,y) with the largest filtering and focusing measure on the Z-axis is taken as the height of the pixel (x,y,z);

[0011] FL filt (x,y,z) The filtering focus measure for pixel (x,y,z); The standard deviation of the Gaussian filter. ; The initial value is a natural number greater than or equal to 5; (3) Among any point (x,y) on the Z-axis, the pixel whose filter focus measure is greater than twice the average of the filter focus measures of all points (x,y) on the Z-axis is a valid pixel, and the rest are invalid pixels; (4) For any invalid pixel determined in step (3), the invalid pixel is filled by interpolation based on the current height of the current valid pixels in its vicinity. (5) Iteratively execute steps (2) to (4) until... Furthermore, when executing step (3), for a pixel that was determined to be an invalid pixel in the previous iteration, it is a valid pixel if it meets both conditions ① and ②. Condition ① is that the current filter focus measure of a point (x,y) on the Z-axis is greater than twice the average value of the current filter focus measure of all points (x,y) on the Z-axis. Condition ② is that the difference between the current height and the fill height obtained in the previous execution of step (3) is less than a threshold value, where the threshold value is the depth of field of the objective lens. For any pixel, if the pixel is determined to be a valid pixel during the last execution of steps (2) to (4), then the height of the pixel during the last execution of steps (2) to (4) is taken as the final height of the pixel. If any pixel is determined to be an invalid pixel during the last execution of steps (2) to (4), then the fill height of the pixel is taken as the final height of the pixel. The final heights of all pixels constitute the final three-dimensional height map. (6) Map the color information of the corresponding positions of the original color image slices to the final three-dimensional height map to obtain a color three-dimensional image.

[0012] The alternative is, The initial value is greater than or equal to 5, 6, 7 or 8.

[0013] Alternatively, the image processing unit may perform the following steps: (1) The displacement stage moves to the target XY region, the Z-axis displacement stage drives the sample to move along the Z direction, and the imaging device acquires the original color image slice of the target XY region along the Z axis; (2) Step (1) Perform the iterative focusing morphology restoration algorithm on the original color image slices to obtain a color three-dimensional image of the target XY region; (3) The original color image slices of the remaining target XY region are acquired by moving the displacement stage in XY and the corresponding color three-dimensional images are obtained. Then, the color three-dimensional images of all target XY regions are stitched together to obtain the three-dimensional reconstructed morphology of the sample.

[0014] Furthermore, the image processing unit is also used to perform the following: measuring the sample structure dimensions based on the obtained color 3D image or 3D reconstructed topography; and generating a height red-blue map of the sample based on the obtained color 3D image or 3D reconstructed topography.

[0015] This invention also relates to a method for measuring the structural dimensions of a sample, the method comprising: Step 1: Acquire raw color image slices of the sample using the system described above; Step 2: Reconstruct the original color image slices using steps (1) to (6) above to obtain a color three-dimensional image; Step 3: Measure the dimensions of the sample structure based on the obtained color 3D image.

[0016] Furthermore, the sample is an electronic device.

[0017] The present invention also relates to a related storage medium and a computer program / instruction, wherein the related computer program / instruction is stored in the storage medium, and the computer program / instruction, when executed by a processor, implements the above-described method steps.

[0018] This invention combines ring light oblique illumination from a near-horizontal direction with traditional coaxial illumination. Leveraging the scattering effect of surface microstructures, it effectively captures information about steep slopes that are difficult to obtain under traditional coaxial illumination, thus overcoming the limitation of objective lens numerical aperture on measurable angles. By introducing ring light illumination, the fundamental problem of wide-field 3D imaging systems being unable to measure large-angle surfaces due to numerical aperture limitations is solved. Experiments show that the measurable surface tilt angle is as high as 78.1° (nearly vertical), far exceeding that of traditional coaxial illumination systems.

[0019] This invention can measure samples at large angles, improve imaging speed and data efficiency, and is suitable for rapid detection of various electronic samples. It fills the technical gap in the dimensions of "large angle - full color - high speed" and provides a new path for industrial testing.

[0020] This invention combines ring light with color 3D wide-field imaging to achieve rapid full-color 3D topography measurement. It provides color information while preserving geometric information, facilitating material differentiation and defect identification. Employing an iterative focusing topography recovery algorithm, it achieves high-resolution 3D reconstruction while maintaining denoising performance, resolving the trade-off between resolution and denoising in traditional SFF algorithms. Furthermore, only one image needs to be acquired per layer, compared to 3D-OS-SIM which requires two images, doubling the imaging speed and halving the data volume, making it suitable for high-throughput industrial inspection.

[0021] This invention can automatically stitch together large field-of-view samples to obtain a wide range of high-resolution three-dimensional morphology, and is suitable for morphology detection and structural dimension measurement of electronic devices such as semiconductors, chip pins, and printed circuit boards. Attached Figure Description

[0022] Figure 1 The optical path of the wide-field three-dimensional color topography measurement system with ring light enhancement according to the present invention Figure 1 - White light source, 2- Beam splitter BS, 3- Objective lens, 4- Tube lens, 5- First reflecting mirror, 6- Second reflecting mirror, 7- Third reflecting mirror, 8- Ring light source, 9- Imaging device.

[0023] Figure 2 shows the imaging and measurement results of an electronic chip obtained using the system of the embodiment of the present invention; (a), (b), (c) and (d) are all imaging and measurement results obtained using the system of the embodiment; where (a) is a three-dimensional color image of the electronic chip and the measurement of the spacing between the pillars, (b) is a height pseudo-color image, (c) is a top view (top left), a height red-blue map (top right) of a single pillar, and a front view (bottom left) and three-dimensional outline (bottom right) of a single pillar, and (d) is a magnified three-dimensional structure and the measurement of the pillar height (the table data in the figure is the height of the four pillars 1-4 relative to the chip substrate).

[0024] Figure 3 shows the imaging and measurement results of another electronic chip obtained using the system of the embodiment of the present invention; (a)-(f) are all imaging and measurement results obtained using the system of the embodiment; where (a) is the front three-dimensional image of the chip and the measurement results of the pin spacing, (b) is the front three-dimensional reconstruction of the chip and the height of pins 1-6 relative to the chip substrate (table in the lower right corner), the angle measurement results of pins 7-9 (table in the upper right corner), (c) is the top view of a partial area of ​​the front of the chip (upper left) and the corresponding height red-blue map (upper right), and the height measurement results of the structure crossed by the white line in the upper right height red-blue map (bottom), (d) is the three-dimensional orthogonal view of the back of the chip, (e) is the top view of a partial area of ​​the back of the chip and the height red-blue map and three-dimensional outline, (f) is the top view of a partial area of ​​the back of the chip (upper left) and the corresponding height red-blue map (upper right), and the height measurement results of the structure crossed by the white line in the upper right height red-blue map (bottom); in the height red-blue map shown in the figure, red represents high and blue represents low.

[0025] Figure 4 The images show the imaging and measurement results of a printed circuit board (PCB) using the system of this embodiment; (a), (b), (c), and (d) are all imaging and measurement results obtained using the system of this embodiment; where (a) is an overall top view and measurements of solder joint distance and capacitor spacing, (b) is a red-blue diagram of solder joint height and corresponding three-dimensional structure, (c) is a red-blue diagram of chip height on the circuit board and corresponding three-dimensional structure, (d) is a red-blue diagram of large capacitor height on the circuit board and corresponding three-dimensional structure, and (e) is a red-blue diagram of small capacitor height on the circuit board and corresponding three-dimensional structure. Detailed Implementation

[0026] Unless otherwise specified, the scientific and technical terms used in this article are intended for understanding by those skilled in the art in the relevant fields.

[0027] The technical solution of the present invention will be further explained and described below with reference to the accompanying drawings and embodiments. The specific parameters in this embodiment are merely examples and do not constitute a limitation on the scope of protection.

[0028] Example 1: See Figure 1 The ring-light enhanced wide-field three-dimensional color topography measurement system of this embodiment includes a wide-field imaging module, a coaxial illumination module, a ring-light illumination source, and a displacement stage; wherein, the displacement stage is a PDV precision displacement stage, which can move along the XYZ directions, with a Y travel of 50 cm, a Z travel of 30 cm, and an X positioning accuracy of 1 μm; the ring-light illumination source is fixedly set above the sample stage, and the area surrounded by the ring-light illumination source is the sample placement area; The coaxial illumination module includes a collimated white light source 1; the wide field imaging module includes a tube lens 4, mirrors M1~M3 (5, 6, 7), objective lens 3, and imaging device color camera 9.

[0029] When the system is working, the collimated white light is reflected by the beam splitter BS2 and then directed perpendicularly to the sample, providing coaxial incident illumination; at the same time, the ring light illumination source 8 illuminates the sample from a 30° tilt angle (downward relative to the horizontal plane); The reflected light (including scattered light) from the sample is collected by objective lens 3, beam splitter BS2, tube lens 4 (used to adjust the image plane position), and mirrors (5, 6, 7) imaged onto a color camera to acquire the original image. A Z-axis displacement stage moves the sample along a direction perpendicular to the horizontal plane, acquiring one image per step to form an image slice. For samples with a large field of view, multi-field scanning and stitching are performed via XY movement.

[0030] The system also includes an image processing unit to run an iterative focusing shape restoration algorithm. The initial value of i used in Examples 2-4 below is 7.

[0031] Example 2: This embodiment uses the system shown in Embodiment 1 to measure the electronic chip. Specifically, the system uses 2× objectives (NA 0.10, depth of field 20μm).

[0032] Eight × five fields of view were acquired, each with 5360 × 5360 pixels, resulting in a total field of view of 36 mm × 23 mm after stitching. The Z-step was 10 μm, and the number of layers was 160. The reconstruction results based on the iterative focusing topography recovery algorithm are shown in Figure 2, clearly displaying the three-dimensional structure of the micropillars on the chip, including the sidewall topography. The measurement results of the pillar height uniformity are consistent with the packaging reliability requirements.

[0033] Example 3: This embodiment uses the system shown in Embodiment 1 to measure chip pins. Specifically, the system uses a 4× objective lens (NA 0.20, depth of field 10μm), acquiring a 5×5 field of view, a total field of view of 14 mm × 14 mm, a Z-step of 5 μm, and 250 layers. Based on an iterative focusing topography recovery algorithm, the pin length, spacing, relative height, and bending angle were successfully measured, as shown in Figure 3. The pin side tilt angle reached as high as 78.1°, far exceeding the measurable range of traditional coaxial illumination. Ring light captured these near-horizontal surfaces through scattered signals, achieving 3D reconstruction without mechanical probes.

[0034] Example 4: This embodiment uses the system shown in Embodiment 1 to measure printed circuit boards. Specifically, the system uses a 2× objective lens (NA 0.10, depth of field 20μm), acquiring a 9×3 field of view, for a total field of view of 41 mm × 14 mm. The Z-step is 10 μm, and the number of layers is 240. Based on an iterative focusing topography recovery algorithm, the three-dimensional contours and surface defects of the solder joints are clearly presented, while preserving the true color information of the pads, solder mask, and components, facilitating material differentiation and defect identification. See [link to documentation]. Figure 4 As shown.

Claims

1. A ring light enhanced wide-field three-dimensional chromatic topography measurement system, characterized in that, Includes a coaxial illumination module, a ring light illumination source, a wide-field imaging module, and a displacement stage; The displacement stage is equipped with a sample stage; the displacement stage can move along the X, Y, and Z axes; The wide-field imaging module includes an objective lens, a tube lens, a reflecting mirror, and an imaging device arranged along the optical path, wherein the objective lens is located above the Z-axis of the sample stage; The coaxial illumination module includes a white light source. The light emitted by the white light source is reflected by a beam splitter and then shines perpendicularly onto the sample stage along the optical axis through the objective lens. The optical axis is set along the Z-axis. The ring light source is set on the sample stage or between the objective lens and the sample stage, and the illumination area of ​​the ring light source surrounds the sample. The light from both the white light source and the ring light source simultaneously illuminates the sample. After being reflected by the sample, the light passes sequentially along the optical axis through the objective lens, beam splitter, and tube lens, and is then reflected by the mirror before entering the imaging device. By moving the stage along the Z-axis, the imaging device acquires a slice of the original color image of the sample.

2. The wide-field three-dimensional color topography measurement system with ring light enhancement as described in claim 1, characterized in that, The wide-field imaging module includes an objective lens, a tube lens, a first reflecting mirror, a second reflecting mirror, a third reflecting mirror, and an imaging device arranged along the optical path. The light from the white light source and the ring light source simultaneously irradiates the sample. After being reflected by the sample, the light passes sequentially along the optical axis through the objective lens, the beam splitter, and the tube lens, and then is reflected multiple times by the first reflecting mirror, the second reflecting mirror, and the third reflecting mirror before being transmitted to the imaging device.

3. The shape-enhanced wide-field three-dimensional color topography measurement system according to claim 1, characterized in that, The emission angle of the ring-shaped illumination source is 0° to 30° relative to the XY plane.

4. The wide-field three-dimensional color topography measurement system with ring light enhancement according to claim 1, characterized in that, The system also includes an image processing unit for executing an iterative focused topography restoration algorithm, which includes performing the following steps on all original color image slices: (1) For any original color image slice, calculate the initial focus measure of each pixel on the original color image slice, and the initial focus measure of any pixel (x,y,z) FL(x,y,z) for: FL(x,y,z)=( _xI)^2+( _yI)^2 in: _xI represents the gradient value of pixel (x,y,z) in the x-direction. _yI is the gradient value of pixel (x,y,z) in the y direction; (2) Apply Gaussian filtering to the initial focus measure of each pixel in the original color image slice to obtain the filtered focus measure of each pixel. FL filt (x,y,z) The Z-axis coordinate of the point (x,y) with the largest filtering and focusing measure on the Z-axis is taken as the height of the pixel (x,y,z); FL filt (x,y,z) The filtering focus measure for pixel (x,y,z); The standard deviation of the Gaussian filter. ; The initial value is a natural number greater than or equal to 5; (3) Among any point (x,y) on the Z-axis, the pixel whose filter focus measure is greater than twice the average of the filter focus measures of all points (x,y) on the Z-axis is a valid pixel, and the rest are invalid pixels; (4) For any invalid pixel determined in step (3), the invalid pixel is filled by interpolation based on the current height of the current valid pixels in its vicinity. (5) Iteratively execute steps (2) to (4) until... Furthermore, when executing step (3), for a pixel that was determined to be an invalid pixel in the previous iteration, it is a valid pixel if it meets both conditions ① and ②. Condition ① is that the current filter focus measure of a point (x,y) on the Z-axis is greater than twice the average value of the current filter focus measure of all points (x,y) on the Z-axis. Condition ② is that the difference between the current height and the fill height obtained in the previous execution of step (3) is less than a threshold value, where the threshold value is the depth of field of the objective lens. For any pixel, if the pixel is determined to be a valid pixel during the last execution of steps (2) to (4), then the height of the pixel during the last execution of steps (2) to (4) is taken as the final height of the pixel. If any pixel is determined to be an invalid pixel during the last execution of steps (2) to (4), then the fill height of the pixel is taken as the final height of the pixel. The final heights of all pixels constitute the final three-dimensional height map. (6) Map the color information of the corresponding positions of the original color image slices to the final three-dimensional height map to obtain a color three-dimensional image.

5. The wide-field three-dimensional color topography measurement system with ring light enhancement according to claim 4, characterized in that, The initial value is greater than or equal to 5, 6, 7 or 8.

6. The wide-field three-dimensional color topography measurement system with ring light enhancement according to claim 4, characterized in that, The image processing unit is used to perform the following steps: (1) The displacement stage moves to the target XY region, the Z-axis displacement stage drives the sample to move along the Z direction, and the imaging device acquires the original color image slice of the target XY region along the Z axis; (2) Step (1) Perform the iterative focusing morphology restoration algorithm on the original color image slices to obtain a color three-dimensional image of the target XY region; (3) The original color image slices of the remaining target XY region are acquired by moving the displacement stage in XY and the corresponding color three-dimensional images are obtained. Then, the color three-dimensional images of all target XY regions are stitched together to obtain the three-dimensional reconstructed morphology of the sample.

7. The ring-light-enhanced wide-field three-dimensional color topography measurement system according to claim 4 or 6, characterized in that, The image processing unit is also used to perform: measuring the sample structure dimensions based on the obtained color 3D image or 3D reconstructed morphology.

8. The ring-light-enhanced wide-field three-dimensional color topography measurement system according to claim 4 or 6, characterized in that, The image processing unit is also used to perform the following: generating a height red-blue map of the sample based on the obtained color 3D image or 3D reconstructed morphology.

9. A method for measuring the structural dimensions of a sample, characterized in that, The methods include: Step 1: Acquire raw color image slices of the sample using the system described in claim 1; Step 2: Reconstruct the original color image slices using steps (1) to (6) as described in claim 4 to obtain a color three-dimensional image; Step 3: Measure the dimensions of the sample structure based on the obtained color 3D image.

10. The sample structure dimension measurement method according to claim 9, characterized in that, The sample is an electronic device.

11. A storage medium, characterized in that, It stores a computer program / instruction thereon, characterized in that when the computer program / instruction is executed by a processor, it implements the method steps described in any one of claims 4 to 6.

12. A software product comprising a computer program / instructions, characterized in that, When the computer program / instruction is executed by the processor, it implements the method steps of any one of claims 4 to 6.

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