Single focal length depth fusion light field camera

Abstract

This invention provides a single-focal-length depth-of-field fusion light field camera, including an objective lens, a zoom drive module, a tube lens assembly, and a light field image sensor. When the camera begins detection, the zoom drive module first moves the objective lens to a preset near-focal position. The objective lens receives light from the wafer surface and forms an optical image. The light then enters the tube lens assembly, passes through its correction optical path, and is transmitted to the light field image sensor to generate near-focal light field image data. Subsequently, the zoom drive module drives the objective lens to sequentially move to preset mid-focal, telephoto, and other positions, repeating the above process to acquire light field image data at corresponding depth levels. In the images captured at each position, the structure of the corresponding focal plane is clear, allowing the user to fuse the clear areas in each image to generate a full depth-of-field image, completely presenting the structure and defects at each depth of the wafer.

Description

Technical Field

[0001] This utility model relates to the field of high-precision semiconductor detection technology, and in particular to a single-focal-length depth-of-field fusion light field camera. Background Technology

[0002] In the field of high-precision semiconductor inspection, extremely stringent requirements are placed on imaging quality. Semiconductor wafer surfaces contain micron- or even nanometer-scale structures, such as circuit patterns, solder joints, and etching trenches, often distributed at different depths. For example, during wafer manufacturing, the depth difference between the surface photoresist patterns and the internal multilayer metal wiring can range from several micrometers to tens of micrometers. Obtaining clear images with full depth of field is essential for accurately detecting various defects, such as scratches, dents, bumps, and bridging.

[0003] Traditional single-focal-length light field cameras, limited by their depth of field, struggle to meet the demands of high-precision semiconductor inspection. They typically only provide clear images of structures within a specific depth range, while structures at other depths remain blurred, making it impossible to accurately determine the presence of defects. This significantly impacts the accuracy and reliability of the inspection, potentially leading to defective products entering subsequent processes and causing substantial economic losses.

[0004] To achieve panoramic depth imaging to meet the needs of semiconductor inspection, existing technical solutions mainly fall into two categories: one is to use a multifocal light field camera, which acquires light information at different depths in a single shot by setting a multifocal microlens array in front of the image sensor, thereby reconstructing a panoramic depth image. However, this type of multifocal light field camera has significant shortcomings in high-precision semiconductor inspection. Its hardware design is complex and costly, hindering large-scale application; more importantly, because the microlens array divides the sensor pixels, the image resolution is low, making it difficult to clearly present the tiny structures and defects on the semiconductor wafer, thus failing to meet the requirements of high-precision inspection.

[0005] Another approach involves using a single-focal-length camera to capture multiple images at different focal planes by changing the focus position. These images are then fused in post-processing to obtain a full depth-of-field image. However, this existing single-focal-length multiple-shot fusion scheme has several problems in high-precision semiconductor inspection scenarios. Due to the lack of dedicated hardware and software co-design for semiconductor inspection, it is difficult to precisely control the focus position during shooting, resulting in the focal planes not accurately covering structures at different depths on the wafer. Regarding image alignment, the precision of semiconductor wafer structures means that even slight displacements can cause alignment deviations, affecting the fusion effect. In terms of fusion processing, the lack of optimized algorithms for addressing minute semiconductor defects makes it difficult to accurately extract and fuse sharp areas at different focal planes, leading to unstable quality of the final full depth-of-field image and an inability to reliably detect minute defects. Utility Model Content

[0006] The purpose of this invention is to provide a single-focal-length depth-of-field fusion light field camera to solve the problem that existing semiconductor inspection technology cannot detect minute defects.

[0007] This utility model provides a single focal length depth-of-field fusion light field camera, including an objective lens, a zoom drive module, a tube lens assembly, and a light field image sensor;

[0008] The objective lens is used to receive light from the external scene and form an optical image;

[0009] The zoom drive module is connected to the objective lens and is used to drive the objective lens to adjust the focal length;

[0010] The tube lens assembly is disposed between the objective lens and the light field image sensor, and is used to correct the optical path deviation generated by the objective lens during zooming;

[0011] The light field image sensor is located behind the tube lens assembly and is used to convert the optical image passing through the tube lens assembly into an electrical signal to generate light field image data.

[0012] In the aforementioned single-focal-length depth-of-field fusion light field camera, when detection begins, the zoom drive module first moves the objective lens to a preset near-focal position. The objective lens receives light from the wafer surface and forms an optical image. The light then enters the tube lens assembly, passes through its correction optical path, and is transmitted to the light field image sensor to generate near-focal light field image data. Subsequently, the zoom drive module drives the objective lens to move sequentially to preset mid-focal, telephoto, and other positions, repeating the above process to acquire light field image data at the corresponding depth levels. In the images captured at each position, the structure of the corresponding focal plane is clear, allowing users to fuse the clear areas in each image to generate a full depth-of-field image, completely presenting the structure and defects of the wafer at each depth.

[0013] This embodiment achieves full-view, high-definition imaging through the coordinated operation of various components, making it suitable for high-precision inspection scenarios such as semiconductor wafers and meeting the stringent requirements for imaging quality in this field.

[0014] Furthermore, the objective lens includes a lens barrel, a front fixed convex lens group located at the front end of the lens barrel, a zoom lens group, a compensation group located in the middle of the lens barrel, and a rear fixed lens group located at the rear end of the lens barrel. The zoom lens group is connected to the zoom drive module.

[0015] Furthermore, the front-end fixed convex lens group includes 1-2 wide-angle lenses to receive wide-angle light from the external scene.

[0016] Furthermore, the compensation group includes 1-2 plano-convex lenses.

[0017] Furthermore, the rear fixed lens group includes one achromatic cemented doublet lens.

[0018] Furthermore, the zoom drive module includes a drive motor, a transmission mechanism connected to the drive motor, a position feedback unit connected to the transmission mechanism, a control circuit connected to the position feedback unit, and a drive block connected to the transmission structure. The control circuit is also connected to the drive motor. The drive block is disposed between the objective lens and the tube lens assembly and is fixedly connected to the objective lens.

[0019] Furthermore, the light field image sensor includes a microlens array and a sensor. The microlens array is used to record the spatial position and angle information of light rays, and the sensor is used to convert the optical image passing through the tube lens assembly and the microlens array into an electrical signal to generate light field image data.

[0020] Furthermore, the endoscope assembly includes a distortion correction mirror, a chromatic aberration correction mirror, a field curvature correction mirror, and an aperture stop arranged sequentially.

[0021] Furthermore, the distortion correction lens includes a cylindrical lens with different surface curvatures along the horizontal and vertical directions, used to correct pincushion or barrel distortion generated when the objective lens is zoomed.

[0022] Furthermore, the chromatic aberration correction mirror includes a set of cemented doublet lenses, which are composed of a low-dispersion glass convex lens and a high-dispersion glass concave lens; the field curvature correction mirror includes a meniscus lens; and the aperture stop is located in the middle of the tube mirror assembly. Attached Figure Description

[0023] Figure 1 This is a three-dimensional structural diagram of the single-focal-length depth-of-field fusion light field camera in the first embodiment of this utility model.

[0024] Explanation of key component symbols:

[0025] objective lens 10 Endoscope assembly 30 Zoom drive module 20 Light field image sensor 40

[0026] The following detailed description, in conjunction with the accompanying drawings, will further illustrate this utility model. Detailed Implementation

[0027] To facilitate understanding of this utility model, a more comprehensive description will be given below with reference to the accompanying drawings. Several embodiments of this utility model are shown in the drawings. However, this utility model can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this utility model will be more thorough and complete.

[0028] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0030] Please see Figure 1 The present invention provides a single-focal-length depth-of-field fusion light field camera, including an objective lens 10, a zoom drive module 20, a tube lens assembly 30, and a light field image sensor 40.

[0031] The objective lens 10 is used to receive light from the external scene and form an optical image. Its focal length is adjustable to adapt to different shooting scenarios.

[0032] The zoom drive module 20 is connected to the objective lens 10 and is used to drive the objective lens 10 to adjust the focal length, so that the camera can clearly image objects at different distances.

[0033] The tube lens assembly 30 is disposed between the objective lens and the light field image sensor 40, and is used to correct the optical path deviation generated by the objective lens 10 during zooming, so as to ensure that light can be accurately transmitted to the light field image sensor 40.

[0034] The light field image sensor 40 is located behind the tube lens assembly 30 and is used to convert the optical image passing through the tube lens assembly 30 into an electrical signal to generate light field image data, thereby realizing the acquisition of light field information.

[0035] In one embodiment of the present invention, the objective lens 10 includes a lens barrel, a front fixed convex lens group disposed at the front end of the lens barrel, a zoom lens group, a compensation group disposed in the middle of the lens barrel, and a rear fixed lens group disposed at the rear end of the lens barrel. The zoom lens group is connected to the zoom drive module.

[0036] In one embodiment of this invention, the front-end fixed convex lens group includes 1-2 wide-angle lenses that receive wide-angle light from the external scene. Their position remains fixed, providing a basic optical axis reference for the entire optical system. The zoom lens group comprises a combination of 2-3 concave and convex lenses, which can move back and forth along the optical axis and is the core lens group for achieving focal length adjustment.

[0037] In one embodiment of this utility model, the compensation group includes 1-2 plano-convex lenses, which move in conjunction with the zoom lens group to counteract the image plane shift generated during zooming.

[0038] In one embodiment of this utility model, the rear fixed lens group includes an achromatic cemented doublet lens, which is used to correct the residual aberrations of the front lens group and ultimately converge the light into a clear intermediate optical image.

[0039] In one embodiment of the present invention, the zoom drive module 20 includes a drive motor, a transmission mechanism connected to the drive motor, a position feedback unit connected to the transmission mechanism, a control circuit connected to the position feedback unit, and a drive block connected to the transmission mechanism. The control circuit is also connected to the drive motor. The drive block is disposed between the objective lens and the tube lens assembly and is fixedly connected to the objective lens. The drive motor uses a micro stepper motor (such as a 42-type stepper motor) or a voice coil motor. The stepper motor has a step angle of up to 1.8°, supporting micron-level precision displacement control, suitable for scenarios requiring precise positioning. The voice coil motor has a fast response speed (millisecond level), suitable for rapid zoom requirements. The transmission mechanism includes a precision gear set (reduction ratio can be 50:1-100:1) and a lead screw slide. The gear set transmits the rotational motion of the motor to the lead screw, which converts the rotational motion into linear motion (along the optical axis) of the zoom lens group through a threaded structure. The position feedback unit consists of a grating ruler or a magnetic encoder. The grating ruler has a resolution of up to 0.1μm, which detects the position information of the zoom lens group in real time and feeds the data back to the control chip (such as an STM32 microcontroller). The control circuit includes a motor drive chip (such as an A4988 stepper motor drive chip) and a microcontroller, which receives external control signals (such as the user's zoom command) and adjusts the motor rotation angle according to the feedback data to achieve closed-loop control.

[0040] In one embodiment of the present invention, the light field image sensor 40 includes a microlens array and a sensor. The microlens array is used to record the spatial position and angle information of light rays, and the sensor is used to convert the optical image passing through the tube lens assembly and the microlens array into an electrical signal to generate light field image data.

[0041] In one embodiment of the present invention, the endoscope assembly 30 includes a distortion correction mirror, a chromatic aberration correction mirror, a field curvature correction mirror, and an aperture stop arranged sequentially.

[0042] In one embodiment of this utility model, the distortion correction lens includes a cylindrical lens with different surface curvatures along the horizontal and vertical directions, used to correct pincushion or barrel distortion generated when the objective lens is zoomed.

[0043] In one embodiment of this utility model, the chromatic aberration correction mirror includes a set of cemented doublet lenses, which are composed of a low-dispersion glass convex lens and a high-dispersion glass concave lens; the field curvature correction mirror includes a meniscus lens; the aperture stop is located in the middle aperture stop of the tube lens assembly, and is an adjustable circular light shield with a diameter that can vary in the range of 2-10mm, used to control the light flux entering the light field image sensor 40, while reducing stray light interference.

[0044] The aforementioned single-focal-length depth-of-field fusion light field camera achieves panoramic depth imaging by combining a single-focal-length lens with multiple images and post-processing fusion. This eliminates the need for complex multi-focal-length microlens arrays, resulting in a simpler hardware structure, reduced costs, and greater suitability for large-scale applications in the semiconductor inspection field. Utilizing a single-focal-length lens avoids the pixel segmentation of the sensor by the microlens array, resulting in high image resolution. This allows for clear visualization of micron- and even nanometer-scale structures and defects on semiconductor wafers, meeting the demands of high-precision inspection.

[0045] The embodiments described above are merely illustrative of several implementations of this utility model, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of this utility model patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this utility model, and these all fall within the protection scope of this utility model. Therefore, the protection scope of this utility model patent should be determined by the appended claims.

Claims

1. A single focal length depth-fused light field camera, comprising: Includes objective lens, zoom drive module, tube lens assembly and light field image sensor; The objective lens is used to receive light from the external scene and form an optical image; The zoom drive module is connected to the objective lens and is used to drive the objective lens to adjust the focal length; The tube lens assembly is disposed between the objective lens and the light field image sensor, and is used to correct the optical path deviation generated by the objective lens during zooming; The light field image sensor is located behind the tube lens assembly and is used to convert the optical image passing through the tube lens assembly into an electrical signal to generate light field image data.

2. The single focal length depth-fused light field camera of claim 1, wherein, The objective lens includes a lens barrel, a front fixed convex lens group located at the front end of the lens barrel, a zoom lens group, a compensation group located in the middle of the lens barrel, and a rear fixed lens group located at the rear end of the lens barrel. The zoom lens group is connected to the zoom drive module.

3. The single focal length depth-fused light field camera of claim 2, wherein, The front-end fixed convex lens group includes 1-2 wide-angle lenses to receive wide-angle light from the external scene.

4. The single focal length depth-fused light field camera of claim 2, wherein, The compensation group includes 1-2 plano-convex lenses.

5. The single focal length depth-fused light field camera of claim 2, wherein, The rear fixed lens group includes one achromatic cemented doublet lens.

6. The single focal length depth-fused light field camera of claim 1, wherein, The zoom drive module includes a drive motor, a transmission mechanism connected to the drive motor, a position feedback unit connected to the transmission mechanism, a control circuit connected to the position feedback unit, and a drive block connected to the transmission mechanism. The control circuit is also connected to the drive motor. The drive block is located between the objective lens and the tube lens assembly and is fixedly connected to the objective lens.

7. The single focal length depth-fused light field camera of claim 1, wherein, The light field image sensor includes a microlens array and a sensor. The microlens array is used to record the spatial position and angle information of light rays, and the sensor is used to convert the optical image passing through the tube lens assembly and the microlens array into an electrical signal to generate light field image data.

8. The single focal length depth-fused light field camera of claim 1, wherein, The endoscope assembly includes a distortion correction mirror, a chromatic aberration correction mirror, a field curvature correction mirror, and an aperture stop arranged in sequence.

9. The single-focal-length depth-of-field fusion light field camera according to claim 8, characterized in that, The distortion correction lens includes a cylindrical lens with different surface curvatures along the horizontal and vertical directions, used to correct pincushion or barrel distortion generated when the objective lens is zoomed.

10. The single focal length depth-fused light field camera of claim 8, wherein, The chromatic aberration correction mirror includes a set of cemented doublet lenses, which are composed of a low-dispersion glass convex lens and a high-dispersion glass concave lens; the field curvature correction mirror includes a meniscus lens; and the aperture stop is located in the middle of the tube mirror assembly.

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