An optical detection system with a full-angle oblique-incidence dark-field illumination system
By combining the first and second conical lenses to generate a parallel annular beam, and combining it with an annular reflector and an annular focusing system, the problems of poor detection effect and high installation accuracy caused by the single light source in the existing dark field detection system are solved. This achieves improved sensitivity, stability and functional expandability, and supports simultaneous detection of bright and dark fields.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JIANGSU XINSHI TECHNOLOGY CO LTD
- Filing Date
- 2026-05-21
- Publication Date
- 2026-07-24
AI Technical Summary
In existing dark field defect detection systems, the single light source leads to poor detection results, and the optical components require high installation precision, making it difficult to insert additional optical components and resulting in poor functional expandability.
A parallel ring beam is generated by combining a first conical lens and a second conical lens. Combined with a ring mirror and a ring focusing system, it achieves oblique incidence dark field illumination at all angles. The parallel optical path facilitates the insertion of additional optical elements, enhancing the system's sensitivity and functional expandability.
It improves the sensitivity and comprehensiveness of defect detection, reduces the accuracy requirements of assembly and adjustment, enhances system stability and functional expandability, and supports simultaneous detection in bright and dark fields to obtain richer surface information.
Smart Images
Figure CN122448873A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to an optical inspection system with a full-angle oblique incidence dark field illumination system, belonging to the field of wafer defect detection technology, and particularly to an optical inspection system with a full-angle oblique incidence dark field illumination system. Background Technology
[0002] With the rapid development of semiconductor manufacturing processes, the requirements for detecting the size of defects on the wafer surface are becoming increasingly stringent. Currently, there are two main methods for wafer defect detection: bright-field defect detection and dark-field defect detection. Bright-field defect detection collects reflected or transmitted light from the surface under test to form an image; dark-field defect detection is a non-contact optical inspection technique that detects defects by collecting scattered signals from the surface of the sample. Compared to bright-field illumination detection, dark-field detection offers advantages such as high contrast, high precision, low background noise, and non-destructive testing characteristics, and is widely used in the field of wafer defect detection.
[0003] However, current mainstream dark-field defect detection systems, both domestically and internationally, employ a method where a light source is independently incident on the wafer under test at a specific angle to achieve dark-field illumination. This means that the illumination source is a single light source, which leads to sensitivity to defects only in certain directions, resulting in poor detection performance.
[0004] Currently, patent documents with patent application numbers 2024111832448 and 2018103380443 have proposed using a conical lens to generate a ring beam, and then using a ring focusing element to converge the beam to form full-angle oblique incidence dark field illumination.
[0005] Because the above scheme uses a single conical lens, the resulting ring-shaped light spot is divergent, and the spot diameter changes with the propagation distance. It is sensitive to the installation position of subsequent optical components and requires high installation accuracy of the objective lens distance. Moreover, once the installation is completed, the distance between the conical lens and the objective lens cannot be adjusted. Therefore, it is difficult to conveniently insert additional optical components, such as mirrors, beam splitters, and filters, between the conical lens and the objective lens according to the detection needs. As a result, the above-mentioned functional expandability is poor. Summary of the Invention
[0006] To address the aforementioned issues, this invention provides an optical detection system with an all-angle oblique incidence dark field illumination system, comprising a first conical lens, a second conical lens, and a ring mirror with a central opening arranged sequentially along the incident direction of a first laser beam. The first incident light first passes through the first conical lens to generate a diverging ring beam, and then enters the coaxial second conical lens with the same deflection angle to form a parallel ring beam. The parallel ring beam is reflected by the ring mirror to form a reflected ring beam. An objective lens and a ring focusing system are arranged sequentially along the direction of the reflected ring beam. The reflected ring beam undergoes total internal reflection inside the ring focusing system and forms a converging beam that illuminates the surface of the object under test. The surface of the object under test generates scattered light after being illuminated, and the scattered light is imaged onto the photodetector through the objective lens. In some embodiments, the photodetector can be a point detector, such as a PMT, APD, PD, etc., which characterizes the surface information of the object under test by the intensity of the light signal, or it can be an array detector such as a CCD, CMOS, etc., which can acquire the specific morphology of the surface of the object under test.
[0007] In some embodiments, the annular reflector is configured to form a 45-degree angle with the direction of the first incident light, and the inner diameter of the spot of the parallel annular beam is set to be larger than the diameter of the objective lens.
[0008] In some embodiments, the first conical lens is a circular conical lens, and the second conical lens is an axial conical lens that is coaxial with the first conical lens and has the same deflection angle.
[0009] In some embodiments, the annular focusing system is a quadratic surface lens with a central aperture, in which the reflected annular beam undergoes total internal reflection within the annular focusing system to form a converging beam that converges at a point F on the surface of the object to be measured.
[0010] In some embodiments, the photodetector is positioned in the opposite direction of the reflected ring beam and is capable of receiving scattered light collected by the objective lens; the photodetector is a PMT, which generates an optical signal to detect the surface information of the object under test.
[0011] In some embodiments, the annular focusing system includes a tire mirror and a third conical lens with a central opening arranged sequentially along the direction of the reflected annular beam. The tire mirror focuses the reflected annular beam and then the converging light is reflected onto the surface of the object being measured by total internal reflection through the conical surface of the third conical lens to form a circular light spot.
[0012] In some embodiments, the photodetector is positioned in the opposite direction to the reflected ring beam and is capable of receiving scattered light collected by the objective lens; the photodetector is a CCD element and is capable of acquiring information about the specific morphology of the surface of the object under test by connecting to a computer.
[0013] In some embodiments, a second incident light parallel to the first incident light is provided below it. A light-collecting mirror and a small mirror are sequentially arranged between the ring mirror and the objective lens along the direction of the reflected ring beam. The small mirror is at a 45-degree angle to the direction of the second incident light. After being reflected by the small mirror, the second incident light is converged at point F by the objective lens to form normal incident illumination. The first incident light forms oblique incident illumination.
[0014] In some embodiments, the angle between the light-collecting mirror and the optical axis of the objective lens is set to 45 degrees.
[0015] In some embodiments, the scattered light emitted by the object under test includes large-angle scattered light and small-angle scattered light; the photodetector includes a first photodetector and a second photodetector. The small-angle scattered light is collected by the objective lens and reflected by the light-collecting mirror to the first photodetector. The second photodetector is located in the opposite direction of the reflected ring beam and can receive the large-angle scattered light collected by the objective lens. Therefore, the scattered light can be detected and analyzed separately at different scattering angles to obtain richer surface information.
[0016] Advantages and effects of the present invention: The optical detection system provided by this invention collimates the incident laser beam into a parallel ring beam through a combination of a first conical lens and a second conical lens. Then, through a ring mirror and a ring focusing system, it achieves full-angle oblique incidence dark field illumination. This fundamentally overcomes the problems of high directional sensitivity of existing single light sources and high assembly and adjustment accuracy and poor scalability of divergent ring beams. While ensuring the advantages of high contrast, high accuracy and non-destructive testing in dark fields, it significantly improves the system's detection sensitivity, assembly and adjustment convenience and functional expansion capabilities.
[0017] The specific beneficial effects are as follows: 1. Achieving omnidirectional oblique incidence dark-field illumination, enhancing defect detection sensitivity: Parallel annular beams are converged by an annular focusing system and simultaneously illuminate a single point on the surface of the object under test from all directions at the same incident angle, forming rotationally symmetrical illumination. This method can excite effective scattered signals for defects in all directions, avoiding missed detections caused by the sensitivity of single-direction illumination to defect orientation, and significantly improving the comprehensiveness and sensitivity of defect detection.
[0018] 2. Utilizing a parallel ring beam reduces assembly accuracy requirements and enhances system stability: The first and second conical lenses generate a parallel ring beam whose diameter does not change with the propagation distance. Positional deviations of subsequent optical components only alter the inner and outer diameters of the light spot, without disrupting the ring illumination pattern. Therefore, the accuracy requirements for the installation distances of components such as the conical lenses, ring mirrors, and objectives are significantly reduced, improving the robustness of the optical system and facilitating engineering implementation and maintenance.
[0019] 3. The parallel light path structure facilitates functional expansion and allows for the flexible insertion of additional optical components: Since a parallel light path is formed between the first conical lens and the objective lens, optical components such as mirrors, beam splitters, and filters can be easily inserted into the parallel light segment before or after the ring mirror to increase functions such as bright and dark field multiplexing and multi-wavelength detection without affecting illumination uniformity, thus providing strong expandability.
[0020] 4. The ring focusing system employs total internal reflection convergence, resulting in high light energy utilization and low background noise: The ring focusing system utilizes internal total internal reflection to direct the converged beam towards the surface of the object under test, avoiding stray light scattered by transmission elements. While maintaining the advantage of low background noise in dark fields, it improves illumination efficiency and convergence uniformity. Simultaneously, the central opening of the ring mirror, in conjunction with the objective lens, effectively separates the scattered light collection from the illumination path, further ensuring high-contrast imaging.
[0021] 5. Can be integrated with coaxial bright field illumination to achieve simultaneous detection of bright and dark fields: The system can add a second incident light path, which forms a normal incident bright field illumination through a small reflector and the same objective lens. It shares the objective lens and part of the light path with the oblique incident dark field illumination. Bright field and dark field information can be obtained simultaneously without changing the main body of the system, enriching the means of defect characterization.
[0022] 6. Supports multi-angle scattered light channel detection to obtain richer surface information: By using a light-collecting mirror and multiple detectors, the large-angle and small-angle components of the scattered light from the object under test can be collected and analyzed separately. By comparing the differences in intensity and angle domain information, the defect type and morphological characteristics can be further revealed, enhancing the information dimension of the detection system. Attached Figure Description
[0023] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention.
[0024] Figure 2 This is a schematic diagram of the structure of Embodiment 2 of the present invention.
[0025] Figure 3 This is a schematic diagram of the structure of Embodiment 3 of the present invention.
[0026] Figure 1 In the diagram, 11. First laser beam; 12. First conical lens; 13. Second conical lens; 14. Ring mirror; 15. Ring focusing system; 16. Object under test; 17. Objective lens; 18. Photodetector.
[0027] Figure 2 In the diagram, 21. First laser beam; 22. First conical lens; 23. Second conical lens; 24. Ring mirror; 25a. Tire mirror; 25b. Third conical lens; 26. Object under test; 27. Objective lens; 28. Photodetector.
[0028] Figure 3 In the diagram, 31a is the first laser beam; 31b is the second laser beam; 32 is the first conical lens; 33 is the second conical lens; 34a is the ring mirror; 34b is the small mirror; 35 is the ring focusing system; 36 is the object under test; 37 is the objective lens; 38a is the second photodetector; and 38b is the first photodetector. Detailed Implementation
[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0030] In this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.
[0031] In this invention, the terms "first" and "second" are used only to distinguish similar components / parts in different positions or with different characteristics, and have no other limiting meaning; "upper" refers to the direction in which each component is away from the ground, and "lower" refers to the direction in which each component is away from the ground.
[0032] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.
[0033] Example 1 like Figure 1 As shown, the present invention provides an optical detection system with a full-angle oblique incidence dark field illumination system, including a first conical lens 12, a second conical lens 13 and a ring-shaped reflector 14 with a central opening arranged sequentially along the incident direction of the first laser beam 11. The first conical lens 12 is a conical lens and the second conical lens 13 is an axial conical lens that is coaxial with the first conical lens 12 and has the same deflection angle.
[0034] The first incident light first passes through the first conical lens 12 to generate a diverging ring beam, and then enters the coaxial second conical lens 13 with the same deflection angle to form a parallel ring beam. The parallel ring beam is reflected by the ring mirror 14 to form a reflected ring beam.
[0035] An objective lens 17 and a ring focusing system 15 are arranged sequentially along the direction of the reflected ring beam. The reflected ring beam undergoes total internal reflection inside the ring focusing system 15 and forms a converging beam that illuminates the surface of the object under test 16. After being illuminated, the surface of the object under test 16 generates scattered light, which is imaged onto the photodetector 18 via the objective lens 17.
[0036] The photodetector 18 can be a point detector, such as a PMT, APD, or PD, which characterizes the surface information of the object under test by the intensity of the light signal. Alternatively, it can be an array detector, such as a CCD or CMOS, which can acquire the specific morphology of the object's surface. In this embodiment, the photodetector 18 is positioned in the opposite direction of the reflected ring beam and can receive the scattered light collected by the objective lens 17. In this embodiment, the photodetector 18 is a PMT; the scattered light is imaged onto the photodetector 18 by the objective lens 17 and then generates a light signal through the PMT, thereby detecting the surface information of the object under test 16.
[0037] The annular reflector 14 is set to form a 45-degree angle with the direction of the first incident light, and the inner diameter of the spot of the parallel annular beam is set to be larger than the diameter of the objective lens 17 so that the objective lens will not block the beam.
[0038] The ring focusing system 15 is a quadric surface lens with a central opening. The reflected ring beam undergoes total internal reflection inside the ring focusing system 15 and forms a converging beam that converges at a point F on the surface of the object to be measured. Using a quadric surface lens can improve the energy concentration at the beam focal point.
[0039] Example 2 like Figure 2 As shown, the present invention provides an optical detection system with a full-angle oblique incidence dark field illumination system, including a first conical lens 22, a second conical lens 23 and a ring-shaped reflector 24 with a central opening arranged sequentially along the incident direction of the first laser beam 21. The first conical lens 22 is a conical lens, and the second conical lens 23 is an axial conical lens that is coaxial with the first conical lens 22 and has the same deflection angle.
[0040] The first incident light first passes through the first conical lens 22 to generate a diverging ring beam, and then enters the coaxial second conical lens 23 with the same deflection angle to form a parallel ring beam. The parallel ring beam is reflected by the ring mirror 24 to form a reflected ring beam.
[0041] An objective lens 27 and a ring focusing system are arranged sequentially along the direction of the reflected ring beam. The reflected ring beam undergoes total internal reflection inside the ring focusing system and forms a converging beam that illuminates the surface of the object under test 26. After being illuminated, the surface of the object under test 26 generates scattered light, which is imaged onto the photodetector 28 via the objective lens 27.
[0042] The photodetector 28 can be a point detector, such as a PMT, APD, or PD, which uses light signal intensity to characterize the surface information of the object under test 26. Alternatively, it can be an array detector such as a CCD or CMOS, which can acquire the specific morphology of the surface of the object under test 26. In this embodiment, the photodetector 28 is positioned in the opposite direction to the reflected ring beam and can receive the scattered light collected by the objective lens 27. In this embodiment, the photodetector 28 is a CCD component.
[0043] In this embodiment, the annular reflector 24 is configured the same as in Embodiment 1.
[0044] In this embodiment, the annular focusing system includes a tire mirror 25a and a third conical lens 25b with a central opening, arranged sequentially along the direction of the reflected annular beam. The tire mirror 25a focuses the reflected annular beam, and the concentric light is reflected by total internal reflection from the conical surface of the third conical lens 25b onto the surface of the object under test 26, forming a circular light spot. The illumination area is no longer a focal point, but a circular area. The objective lens 27 images the morphology within this circular light spot onto the photodetector 28. Since the photodetector 28 is a CCD element, the specific morphology information of the surface can be obtained on a computer, which is suitable for occasions where it is necessary to observe the specific morphology of the object under test.
[0045] Example 3 The present invention provides an optical detection system with a full-angle oblique incidence dark field illumination system, including a first conical lens 32, a second conical lens 33 and a ring-shaped reflector 34a with a central opening arranged sequentially along the incident direction of a first laser beam 31a. The first conical lens 32 is a conical lens and the second conical lens 33 is an axial conical lens that is coaxial with the first conical lens 32 and has the same deflection angle.
[0046] The first incident light first passes through the first conical lens 32 to generate a diverging ring beam, and then enters the coaxial second conical lens 33 with the same deflection angle to form a parallel ring beam. The parallel ring beam is reflected by the ring mirror 34a to form a reflected ring beam.
[0047] An objective lens 37 and a ring focusing system 35 are arranged sequentially along the direction of the reflected ring beam. The reflected ring beam undergoes total internal reflection inside the ring focusing system 35 and forms a converging beam that irradiates the surface of the object under test 16. The surface of the object under test 36 is then irradiated and produces scattered light.
[0048] The annular reflector 34 is set to form a 45-degree angle with the direction of the first incident light, and the inner diameter of the spot of the parallel annular beam is set to be larger than the diameter of the objective lens 37 so that the objective lens will not block the beam.
[0049] Because a ring-shaped parallel beam is formed, the beam length can be changed arbitrarily, which is beneficial for adding other components in the optical path and expanding the system's functionality.
[0050] In this embodiment, a second incident light parallel to the first incident light is located below it. A light-collecting mirror and a small mirror 34b are sequentially arranged between the ring mirror 34a and the objective lens 37 along the direction of the reflected ring beam. The small mirror 34b forms a 45-degree angle with the direction of the second incident light. After being reflected by the small mirror 34b, the second incident light is converged at point F by the objective lens 37 to form positive incident illumination. The first incident light forms oblique incident illumination. Therefore, the first incident light is focused to a point at all angles. Regardless of the shape of the object being measured, it will always generate a scattered light signal due to the large difference between it and the background object at one or more angles. The scattered light signal will not be missed or the signal intensity will be different due to a single incident angle.
[0051] The light-collecting mirror and the objective lens 37 are set at an angle of 45 degrees, with the light-collecting mirror tilted to the right and the small mirror 34b tilted to the left; at the same time, the second incident light and the first incident light are set on the same side.
[0052] In some embodiments, the scattered light emitted by the object under test 36 after being irradiated by focused light is divided into large-angle scattered light and small-angle scattered light; the photodetector includes a first photodetector 38b and a second photodetector 38a. The first photodetector 38b is disposed on the opposite side of the second incident light. Since the tilt directions of the small reflector 34b and the light-collecting reflector are opposite, the direction of the large-angle scattered light reflected by the light-collecting reflector is opposite to the direction of the second incident light.
[0053] The small-angle scattered light is collected by the objective lens 37 and reflected by the light-collecting mirror to the first photodetector 38b. The second photodetector 38a is set in the opposite direction of the reflected ring beam and can receive the large-angle scattered light collected by the objective lens 37. Therefore, the scattered light can be detected and analyzed separately at different scattering angles to obtain richer surface information.
[0054] Among them, the first and second photodetectors can be point detectors, such as PMT, APD, PD, etc., to characterize the surface information of the object under test by the intensity of light signal, or they can be array detectors such as CCD, COMS, etc., to obtain the specific morphology of the surface of the object under test.
[0055] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.
Claims
1. An optical inspection system with a full-angle oblique incidence dark field illumination system, characterized in that, The system includes a first conical lens, a second conical lens, and a ring-shaped reflector with a central opening, arranged sequentially along the incident direction of the first laser beam. The first incident light first passes through the first conical lens to generate a diverging ring beam, and then enters the coaxial second conical lens with the same deflection angle to form a parallel ring beam. The parallel ring beam is reflected by the ring-shaped reflector to form a reflected ring beam. An objective lens and a ring focusing system are arranged sequentially along the direction of the reflected ring beam. The reflected ring beam undergoes total internal reflection inside the ring focusing system and forms a converging beam that illuminates the surface of the object under test. The surface of the object under test generates scattered light after being illuminated, and the scattered light is imaged onto a photodetector by the objective lens.
2. The optical detection system according to claim 1, characterized in that, The annular reflector is set at a 45-degree angle to the direction of the first incident light, and the inner diameter of the spot of the parallel annular beam is set to be larger than the diameter of the objective lens.
3. The optical detection system according to claim 2, characterized in that, The first conical lens is a circular conical lens, and the second conical lens is an axial conical lens that is coaxial with the first conical lens and has the same deflection angle.
4. The optical detection system according to claim 3, characterized in that, The ring focusing system is a quadratic surface lens with a central opening. The reflected ring beam undergoes total internal reflection inside the ring focusing system and forms a converging beam that converges at a point F on the surface of the object to be measured.
5. The optical detection system according to claim 4, characterized in that, The photodetector is positioned in the opposite direction of the reflected ring beam and is capable of receiving the scattered light collected by the objective lens; the photodetector is a PMT, which generates an optical signal to detect the surface information of the object under test.
6. The optical detection system according to claim 3, characterized in that, The ring focusing system includes a tire mirror and a third conical lens with a central opening arranged sequentially along the direction of the reflected ring beam. After the tire mirror focuses the reflected ring beam, the converging light is reflected onto the surface of the object being measured by total internal reflection through the conical surface of the third conical lens to form a circular light spot.
7. The optical detection system according to claim 6, characterized in that, The photodetector is positioned in the opposite direction of the reflected ring beam and is capable of receiving the scattered light collected by the objective lens; the photodetector is a CCD element and can acquire information about the specific morphology of the surface of the object under test by connecting to a computer.
8. The optical detection system according to claim 4, characterized in that, Below the first incident light is a second incident light parallel to it. Along the direction of the reflected ring beam, a light-collecting mirror and a small mirror are arranged sequentially between the ring mirror and the objective lens. The small mirror is at a 45-degree angle to the direction of the second incident light. After being reflected by the small mirror, the second incident light is converged at point F by the objective lens to form normal incident illumination. The first incident light forms oblique incident illumination.
9. The optical detection system according to claim 8, characterized in that, The angle between the optical axis of the light-collecting mirror and the objective lens is set to 45 degrees.
10. The optical detection system according to claim 9, characterized in that, The scattered light emitted by the object under test includes large-angle scattered light and small-angle scattered light; the photodetector includes a first photodetector and a second photodetector. The small-angle scattered light is collected by the objective lens and reflected by the light-collecting mirror to the first photodetector. The second photodetector is set in the opposite direction of the reflected ring beam and can receive the large-angle scattered light collected by the objective lens.