A spatial filtering system
By setting a converging lens group and a collimating lens group in the optical system and adding an aperture stop, the problems of limited field of view and low resolution of the traditional 4f system are solved, achieving high resolution, low distortion and large field of view, which is suitable for semiconductor inspection and other scenarios.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- MATRIXTIME ROBOTICS (SHANGHAI) CO LTD
- Filing Date
- 2025-07-30
- Publication Date
- 2026-07-17
AI Technical Summary
Traditional 4F systems suffer from problems such as limited field of view, insufficient telecentricity, and low resolution in aberration correction, noise suppression, and extraction of specific frequency components, making it difficult to meet the needs of complex scenes.
By setting a front lens group with a converging effect and a rear lens group with a collimating effect, and placing an aperture between the front and rear lens groups, the focal length of reflected and/or scattered light can be adjusted and the beam collimated, thereby expanding the field of view and suppressing edge astigmatism and field curvature.
It achieves high resolution, low distortion, and a wide field of view, effectively suppresses noise, improves the measurement accuracy of the inspection lens, and expands the application scenarios of the lens.
Smart Images
Figure CN224519050U_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of semiconductor detection technology, specifically an optical system for detection, and more particularly a spatial filtering system. Background Technology
[0002] Spatial filtering is a crucial component of optical systems, widely used in aberration correction, noise suppression, and extraction of specific frequency components. Traditional 4f systems consist of two lenses with focal lengths of f1 and f2, spaced approximately f1 + f2 apart. While this system can perform Fourier transform and spatial filtering, it suffers from limitations in field of view, insufficient telecentricity, and low resolution in practical applications, making it unsuitable for complex scenarios. Furthermore, existing systems still have room for improvement in performance metrics such as MTF and distortion. Summary of the Invention
[0003] To address the aforementioned technical problems, this application provides a spatial filtering system that, by improving existing optical filtering systems, achieves high resolution, low distortion, and a large field of view.
[0004] To achieve the above objectives, the technical solutions adopted in the embodiments of this application are as follows:
[0005] A spatial filtering system is provided, comprising: a front objective lens group, an aperture stop, and a rear objective lens group coaxially arranged from the object side to the image side, wherein: the front objective lens group has positive optical power and is used to adjust the focal length of the reflected light and / or scattered light from the object under test and direct it to the aperture stop; the aperture stop is located at the focal point of the reflected light and / or scattered light and is used to modulate the size of the exit pupil of the front objective lens group; the rear objective lens group has positive optical power and is used to collimate the reflected light and / or scattered light.
[0006] In another possible implementation, the front objective lens group is provided with at least a first negative power lens group and a second positive power lens group along the beam propagation direction; the first negative power lens group is provided with at least one negative power lens, and the second positive power lens group is provided with multiple positive power lenses.
[0007] In another possible implementation, the first negative power lens group diffuses the reflected and / or scattered light to expand the field of view, and the second positive power lens group converges the reflected and / or scattered light.
[0008] In another possible implementation, the first negative power lens group includes at least one biconcave lens along the beam propagation direction.
[0009] In another possible implementation, the second positive power lens group includes a first meniscus lens and at least one biconvex lens along the beam propagation direction.
[0010] In another possible implementation, the second positive power lens group includes a first meniscus lens, a first biconvex lens, and a second biconvex lens along the beam propagation direction.
[0011] In another possible implementation, the convex surface of the meniscus lens is positioned facing the image side.
[0012] In another possible implementation, the rear objective lens group is provided with at least a first rear objective lens group and a second rear objective lens group along the beam propagation direction; the first rear objective lens group is used to collimate the reflected light and / or scattered light, and the second rear objective lens group is used to correct the residual chromatic aberration of the collimated reflected light and / or scattered light.
[0013] In another possible implementation, the first rear objective lens group is provided with a second meniscus lens with positive optical power, a plano-convex lens with positive optical power, a third biconvex lens with positive optical power, a third meniscus lens with positive optical power, and a fourth meniscus lens with negative optical power along the beam propagation direction; the second rear objective lens group includes a second biconcave lens with positive optical power.
[0014] In another possible implementation, the convex surface of the second meniscus lens is arranged facing the image side, the convex surface of the plano-convex lens is arranged facing the image side, the convex surface of the third meniscus lens is arranged facing the object side, and the convex surface of the fourth meniscus lens is arranged facing the object side.
[0015] In another feasible approach, one or more devices, including diffractive optical elements and spatial light modulators, are also provided at the image plane.
[0016] The embodiments of the present invention bring the following beneficial effects:
[0017] The technical solution provided in this application embodiment achieves adjustment of the focal length of reflected and / or scattered light and collimation of the beam by setting a front lens group with converging effect and a rear lens group with collimation effect, and setting an aperture stop between the front and rear lens groups. This spatial filtering system features a large field of view and achieves high telecentricity and low distortion, effectively suppressing edge astigmatism and field curvature. Furthermore, applying this spatial filtering system to detection scenarios can effectively suppress noise, improve the measurement accuracy of the detection lens, and thus expand the lens's application scenarios.
[0018] Other features and advantages of this disclosure will be set forth in the following description, or some features and advantages may be inferred from the description or determined without doubt, or may be learned by practicing the techniques described above.
[0019] To make the above-mentioned objects, features and advantages of this disclosure more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description
[0020] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0021] The system shown in the accompanying drawings will be further described according to exemplary embodiments. These exemplary embodiments will be described in detail with reference to the drawings. These exemplary embodiments are non-limiting exemplary embodiments, wherein example figures represent similar mechanisms in the various views of the drawings.
[0022] Figure 1 This is a schematic diagram of the spatial filtering system structure provided in an embodiment of this application;
[0023] Figure 2 This is a schematic diagram of the field curvature and distortion results of the spatial filtering system provided in the embodiments of this application;
[0024] Figure 3 A full-field transfer function curve of the spatial filtering system provided in the embodiments of this application;
[0025] Figure 4 A full-field-of-view, full-wavelength dot plot of the spatial filtering system provided in the embodiments of this application. Detailed Implementation
[0026] To better understand the above technical solutions, the technical solutions of this application will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments of this application and the specific features in the embodiments are detailed descriptions of the technical solutions of this application, rather than limitations on the technical solutions of this application. In the absence of conflict, the embodiments of this application and the technical features in the embodiments can be combined with each other.
[0027] In the detailed description below, numerous specific details are illustrated with examples to provide a comprehensive understanding of the relevant guidance. However, it will be apparent to those skilled in the art that this application can be practiced without these details. In other instances, well-known methods, procedures, systems, components, and / or circuits have been described at a relatively high level without detail to avoid unnecessarily obscuring aspects of this application.
[0028] This application provides a spatial filtering system for high-precision imaging, beam shaping, and optical signal processing. It is particularly suitable for use in lenses, expanding their applications, such as semiconductor wafer defect detection.
[0029] In this embodiment, "wafer" generally refers to a substrate formed of semiconductor or non-semiconductor materials. Examples include (but are not limited to) single-crystal silicon, gallium arsenide, gallium nitride, and indium phosphide. Such substrates are typically found and / or processed in semiconductor manufacturing facilities. In some cases, a wafer may contain only a substrate (i.e., a bare die). Alternatively, a wafer may contain one or more layers of different materials formed on the substrate. The one or more layers formed on the wafer may be "patterned" or "unpatterned." For example, a wafer may contain multiple dies with repeatable pattern features.
[0030] For ease of understanding, the microscopic imaging system in the embodiments of this application is described below. Please refer to [link / reference]. Figure 1 One embodiment of the spatial filtering system in this application includes:
[0031] The front objective lens group 10, the aperture 20, and the rear objective lens group 30 are coaxially arranged from the object side to the image side, respectively, wherein:
[0032] The front objective lens group is of positive optical power and is used to adjust the focal length of the reflected and / or scattered light from the object under test and project it to the aperture.
[0033] An aperture stop, located at the focal point of reflected and / or scattered light, is used to adjust the exit pupil size of the front objective lens group.
[0034] The rear objective lens group is of positive optical power and is used to collimate reflected and / or scattered light.
[0035] In this embodiment, the object to be tested refers to the wafer to be tested. Of course, in other possible implementations, it can be other physical objects.
[0036] As an optional embodiment, the optical power of the front objective lens group in this embodiment... Optical power of the rear objective group
[0037] Specifically, in this embodiment, the front objective lens group is provided with a first negative power lens group and a second positive power lens group along the beam propagation direction. The first negative power lens group contains one negative power lens, and the second positive power lens group contains multiple positive power lenses.
[0038] Among them, for negative power lenses, biconcave lenses 11 are preferred. Biconcave lenses can be used to diffuse reflected and / or scattered light to expand the field of view, reduce the edge incident angle, and pre-correct distortion, thereby reducing the off-axis load of subsequent lenses.
[0039] The second positive power lens group includes a first meniscus lens 12 and at least one biconvex lens along the beam propagation direction. In this embodiment, two biconvex lenses are preferably selected for the second positive power lens group. That is, the second positive power lens group is provided with a first meniscus lens 12, a first biconvex lens 13, and a second biconvex lens 14 sequentially along the beam propagation direction.
[0040] In this configuration, the concave surface of the first meniscus lens faces the object side, and the convex surface faces the image side. A first convex lens and a second convex lens are used in combination, with their convex surfaces facing different directions. This can be understood as the convex surface of the first convex lens facing the image side, and the convex surface of the second convex lens facing the object side. In another possible implementation, the convex surface of the first convex lens faces the object side, and the convex surface of the second convex lens faces the image side.
[0041] Specifically, the first and second convex lenses constitute the main converging unit to improve center resolution. The convex surface of the meniscus lens can correct spherical aberration, while the concave surface can suppress initial field curvature and cancel out the edge spherical aberration of the first and second convex lenses, significantly reducing Petzwald field curvature.
[0042] The reflected and / or scattered light is focused after passing through the aforementioned front objective lens group. An aperture stop 20 is provided at the optical focal point to suppress stray light and modulate the size of the exit pupil of the front objective lens group. In this embodiment, a motorized aperture stop is preferably selected, which can be selectively configured and moved.
[0043] In this embodiment, there is a first distance L1 between the front objective lens group and the object side, and a second distance L2 between the front objective lens group and the aperture, and the first distance and the second distance are the same.
[0044] Furthermore, the rear objective lens group is provided with at least a first rear objective lens group and a second rear objective lens group along the beam propagation direction. The first rear objective lens group is used to collimate the reflected light and / or scattered light, and the second rear objective lens group is used to correct the residual chromatic aberration of the collimated reflected light and / or reflected light.
[0045] Specifically, in this embodiment, the first rear objective lens group is provided with a second meniscus lens 31, a plano-convex lens 32, a third biconvex lens 33, a third meniscus lens 34, and a fourth meniscus lens 35 along the beam propagation direction.
[0046] The second meniscus lens has positive optical power, with its convex surface facing the image side for secondary correction of field curvature and optimization of astigmatism, while its concave surface facing the object side allows for fine-tuning of the light path. The plano-convex lens also has positive optical power, with its convex surface facing the image side, for optimizing on-axis point imaging. The third biconvex lens has positive optical power, which, in conjunction with the converging optical path, shortens the overall focal length and, combined with the plano-convex lens, reduces reflection loss, thereby increasing transmittance. The third and fourth meniscus lenses have positive and negative optical powers respectively; when used together, they synergistically expand the field of view. Furthermore, the convex surface of the third and fourth meniscus lenses faces the object side while their concave surface faces the image side. The third meniscus lens flattens the field curvature, and the fourth meniscus lens diverges edge rays to balance the positive optical power of the front objective lens group, thus offsetting chromatic aberration and improving color uniformity.
[0047] The second rear objective lens group includes a second biconcave lens 36 with positive optical power, which, in conjunction with a fourth meniscus lens 35 with negative optical power, can specifically correct chromatic aberration in the blue-violet band and control dispersion tolerance.
[0048] In this embodiment, for the aforementioned spatial filtering system, all lenses are spherical glass lenses with a refractive index of 1.47±0.1, an Abbe number of 67.8±0.1, and an operating wavelength of 355nm. The overall system telecentricity is σ≤0.001°, the object-side field of view is ±15mm, the magnification is -0.33×, the distortion is <0.45%, the meridional field curvature is <|0.50mm|, and the sagittal field curvature is <|0.25mm|.
[0049] For simulation test results of the spatial filtering system in this embodiment, please refer to [link / reference]. Figures 2-4 The corresponding result.
[0050] See Figure 2 The simulation results of the field curvature and distortion of the spatial filtering system in this embodiment are shown in the figure. It can be seen from this figure that the meridional field curvature is <|0.50mm|, the sagittal field curvature is <|0.25mm|, and the distortion is <0.45%.
[0051] See Figure 3 The transfer function curve of the spatial filtering system in this embodiment shows that the spatial filtering system almost reaches the diffraction limit within the application field of view.
[0052] See Figure 4 Regarding the full-field-of-view, full-wavelength dot plot of the spatial filtering system in this embodiment, it can be seen from this figure that the size of the full-field-of-view dot plot is within the Airy disk.
[0053] The spatial filtering system in this embodiment can be used in the inspection lens. The MTF of the inspection lens through this spatial filtering system can meet the requirement of >0.3@40lp / mm.
[0054] In another possible implementation, the spatial filtering system provided in this embodiment may also include a variety of optical devices, including but not limited to diffractive optical elements and spatial light modulators on the plane where the image plane is located, to achieve dynamic control of amplitude and phase and filter out specific frequency components.
[0055] The spatial filtering system provided in this application embodiment achieves adjustment of the focal length of reflected and / or scattered light and collimation by setting a front lens group with converging effect and a rear lens group with collimating effect, and placing an aperture between the front and rear lens groups. This spatial filtering system features a large field of view and achieves high telecentricity and low distortion, effectively suppressing edge astigmatism and field curvature. Furthermore, applying this spatial filtering system to inspection scenarios can effectively suppress noise, improve the measurement accuracy of the inspection lens, and thus expand the lens's application scenarios.
[0056] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.
[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A spatial filtering system, characterized in that, The system includes: The front objective lens group, aperture, and rear objective lens group are coaxially arranged from the object side to the image side, respectively, wherein: The front objective lens group is of positive optical power and is used to adjust the focal length of the reflected and / or scattered light from the object under test and project it to the aperture. The aperture is used to modulate the size of the exit pupil of the front objective lens group; and the first distance of the front objective lens group relative to the object side is the same as the second distance of the aperture relative to the front objective lens group; The rear objective lens group is of positive optical power and is used to collimate the reflected light and / or scattered light.
2. The spatial filtering system according to claim 1, characterized in that, The front objective lens group is provided with at least a first negative power lens group and a second positive power lens group along the beam propagation direction; the first negative power lens group is provided with at least one negative power lens, and the second positive power lens group is provided with multiple positive power lenses.
3. The spatial filtering system according to claim 2, characterized in that, The first negative power lens group diffuses the reflected light and / or scattered light to expand the field of view, and the second positive power lens group converges the reflected light and / or scattered light.
4. The spatial filtering system according to claim 3, characterized in that, The first negative power lens group includes at least one biconcave lens along the beam propagation direction.
5. The spatial filtering system according to claim 3, characterized in that, The second positive power lens group includes a first meniscus lens along the beam propagation direction and at least one biconvex lens.
6. The spatial filtering system according to claim 3, characterized in that, The second positive power lens group includes a first meniscus lens, a first biconvex lens, and a second biconvex lens along the beam propagation direction.
7. The spatial filtering system according to claim 5 or 6, characterized in that, The convex surface of the first meniscus lens is oriented towards the image side.
8. The spatial filtering system according to claim 1, characterized in that, The rear objective lens group is provided with at least a first rear objective lens group and a second rear objective lens group along the beam propagation direction; the first rear objective lens group is used to collimate the reflected light and / or scattered light, and the second rear objective lens group is used to correct the residual chromatic aberration of the collimated reflected light and / or scattered light.
9. The spatial filtering system according to claim 8, characterized in that, The first rear objective lens group is provided with a second meniscus lens with positive optical power, a plano-convex lens with positive optical power, a third biconvex lens with positive optical power, a third meniscus lens with positive optical power, and a fourth meniscus lens with negative optical power along the beam propagation direction; the second rear objective lens group includes a second biconcave lens with positive optical power.
10. The spatial filtering system according to claim 9, characterized in that, The convex surface of the second meniscus lens faces the image side, the convex surface of the plano-convex lens faces the image side, the convex surface of the third meniscus lens faces the object side, and the convex surface of the fourth meniscus lens faces the object side.
11. The spatial filtering system according to claim 1, characterized in that, The image plane is also equipped with one or more devices, including diffractive optical elements and spatial light modulators.