Wafer surface defect detection optical system capable of repeatedly utilizing light energy

Abstract

The invention relates to a wafer surface defect detection optical system capable of repeatedly utilizing light energy, belongs to the technical field of laser detection, and particularly relates to the detection of pattern-free wafer surface defect laser. The invention provides a wafer surface defect detection optical system capable of repeatedly utilizing light energy. The wafer surface defect detection optical system comprises a first objective lens and a second objective lens which are symmetrically arranged on two sides above a wafer; and the reflecting mirror group is arranged on the outer side, relative to the circle center of the wafer, of the first objective lens and / or the second objective lens, and the reflecting mirror group comprises at least one reflecting element arranged on the outer side of the second objective lens. According to the invention, the light energy is efficiently and repeatedly utilized, and the reflector group is matched with the symmetrically arranged double objective lenses, so that multiple circulating focusing irradiation of the laser beams on the wafer surface detection points is realized.

Description

Technical Field

[0001] This invention relates to an optical system for detecting wafer surface defects with reusable optical energy, belonging to the field of laser detection technology, and particularly to the detection of surface defects on patternless wafers using lasers. Background Technology

[0002] The current main technical solution for wafer surface defect detection is to irradiate the wafer surface with a laser while the wafer moves in a straight line at a uniform speed in a certain direction and rotates at high speed simultaneously. The laser scans from the center of the wafer to the edge, and the straight-line movement distance is the wafer radius R. Therefore, the trajectory of the laser on the wafer surface is a spiral. When the laser irradiates a defect, it generates a scattered light signal, which is collected by a scattered light collection system placed directly above the laser spot. By recording the time of this signal and the speed of the wafer's straight-line and rotational movements, the location of the defect on the wafer surface can be determined.

[0003] The industry uses the aforementioned basic principles for defect detection, as exemplified by patents CN119438221A, CN119901753A, CN120213941A, and CN120820548A. High laser power is crucial for obtaining a strong light scattering signal. According to the principle of light scattering, for particles of a certain size, the light scattering intensity is directly proportional to the laser beam energy and inversely proportional to the fourth power of the wavelength. As the size of the particles being detected decreases, the industry has gradually increased the power of lasers, from tens of milliwatts to hundreds of milliwatts, and currently even down to the watt level. The required wavelengths have also expanded from visible light to ultraviolet and even deep ultraviolet, placing extremely high technical demands on laser manufacturers and creating significant cost burdens and reliability risks for wafer surface defect detection equipment suppliers.

[0004] Furthermore, considering the detection speed, the scanning speed of the laser spot during detection is related to the laser spot focused on the wafer surface; the larger the spot, the faster the scanning speed, therefore the spot cannot be minimized. However, the larger the spot, the lower the light energy density within it, leading to a decrease in the intensity of scattered light.

[0005] Currently, all methods of laser irradiation of particles in the industry are as described in the aforementioned patent: a laser emits a beam of light to irradiate the area to be tested. Since the object to be tested is a smooth wafer, the beam of light will be reflected after irradiating the area to be tested and will not be recycled. That is, the amount of light energy emitted by the laser itself is the same as the amount of light energy used during testing. Moreover, the particles are generally nanoscale, so the actual light utilization rate is extremely low. Summary of the Invention

[0006] To address the aforementioned problems, the present invention provides an optical system for detecting wafer surface defects with reusable optical energy, comprising: a first objective lens and a second objective lens symmetrically disposed on both sides above the wafer; and a mirror group disposed on the outer side of the first objective lens and / or the second objective lens relative to the center of the wafer, wherein the mirror group includes at least one reflective element disposed on the outer side of the second objective lens. After the laser beam (i.e., the incident light) is focused by the first objective lens, it forms a converging beam at a certain tilt angle and is focused on point F on the wafer surface, with point F as the focal point. Then, it is reflected on the wafer surface to form a primary reflected beam and a primary diverging beam. The primary reflected beam is collimated by the second objective lens, which coincides with the focal point of the first objective lens. The collimated primary reflected beam is reflected by a group of mirrors to form a primary retroreflected beam that is parallel to the collimated primary reflected beam, opposite in direction, and separated by a certain distance. The primary retroreflected beam is again incident on the second objective lens and focused at point F. It is then reflected again by the wafer to form a secondary reflected beam and a secondary diverging beam. The secondary reflected beam is collimated by the first objective lens. Alternatively, the primary retroreflected beam is processed by the mirror group and then refocused at point F by the first objective lens. If other reflective elements of the mirror group are provided on the outside of the first objective lens, a secondary retroreflected beam parallel to the laser beam, in the same direction and separated by a certain distance can be formed and focused again on point F after being collimated by the first objective lens. Then the above steps are repeated to achieve multiple focusing on point F. In this way, at least two cycles of irradiation of point F can be achieved, which increases the energy focused on the wafer surface. A light-collecting component is set above point F. If there are particles or defects on the wafer surface, they will generate scattered light after being irradiated by the laser beam. This scattered light will be collected by the light-collecting component, and the energy of the scattered light will be significantly higher than that of a single irradiation, thereby improving the detection sensitivity.

[0007] In some embodiments of the present invention, the light-collecting assembly includes at least one light-collecting objective located in the region above point F.

[0008] In some embodiments of the present invention, the reflector group includes a first reflector disposed outside the second objective lens. The first reflector is an isosceles right-angled triangle structure with its base facing the second objective lens. It can generate a 180° back reflection effect on the first reflected beam to form a first back reflection beam and generate a deflection. The first back reflection beam does not coincide with the first reflected beam. After the first back reflection beam re-enters the second objective lens, it converges at point F. Point F is illuminated a second time, and then is reflected again by the wafer surface to form a second reflected beam that enters the first objective lens. After collimation, it exits. Point F is illuminated a total of twice.

[0009] In some embodiments of the present invention, a vertical light-collecting objective lens is disposed directly above point F, perpendicular to point F.

[0010] In some embodiments of the present invention, the reflector group includes a first reflecting device and a second reflecting device respectively disposed outside the first objective lens and the second objective lens. The first reflecting device and the second reflecting device are each composed of two small reflectors that are perpendicular to each other and arranged opposite each other. After the primary reflected beam passes through the two small reflectors of the second reflecting device in sequence, it can generate a 180° back reflection effect and form a primary back reflection beam, which is deflected. The primary back reflection beam does not coincide with the primary reflected beam. After the primary back reflection beam re-enters the second objective lens, it converges at point F. Point F is irradiated for the second time, and then is reflected again by the wafer surface to form a secondary reflected beam that enters the first objective lens. After collimation, it passes through the two small reflectors of the first reflecting device in sequence and forms a secondary back reflection beam. The secondary back reflection beam is re-focused at point F after passing through the first objective lens. Point F is irradiated a total of three times.

[0011] In some embodiments of the present invention, a first light-collecting objective lens perpendicularly facing point F and a second light-collecting objective lens tilted towards point F are disposed above point F. The first light-collecting objective lens collects scattered light in the direction perpendicular to the wafer, and the second light-collecting objective lens collects scattered light at a larger angle relative to the wafer normal.

[0012] In some embodiments of the present invention, the reflector group includes a first reflector and a second reflector respectively disposed outside the first objective lens and the second objective lens. Both the first reflector and the second reflector are planar reflectors. After the primary reflected beam passes through the second objective lens and reaches the second reflector, it can generate a primary retroreflected beam that is horizontal and directed towards the first objective lens. The primary retroreflected beam reaches the second reflector, which reflects the primary retroreflected beam to form a primary retroreflected deflected beam that reaches the first reflector. The secondary retroreflected beam generated by the first reflector passes through the first objective lens and converges again at point F. Point F is illuminated for the second time, and then is reflected again by the wafer surface to form a secondary reflected beam that enters the second objective lens. The above beam movement can then be repeated cyclically to generate any number of subsequent retroreflected beams, enabling any number of irradiations of point F. The secondary retroreflected beam and any subsequent retroreflected beams are parallel to and do not coincide with the laser beam and the primary retroreflected beam.

[0013] In some embodiments of the present invention, an inclined light-collecting objective lens is provided above point F, which is tilted towards point F to collect scattered light at a large angle relative to the wafer normal.

[0014] In some embodiments of the present invention, the reflector group includes a first reflector and a second reflector respectively disposed outside the first objective lens and the second objective lens. A third reflector and a fourth reflector are respectively disposed beside the first reflector and the second reflector. The first reflector, the second reflector, the third reflector and the fourth reflector are all planar reflectors. After the primary reflected beam passes through the second objective lens and reaches the second reflector, it can generate a horizontally forward primary back-reflection beam. The primary back-reflection beam can reach the fourth reflector and be reflected by the fourth reflector to generate an intermediate beam that reaches the third reflector. The third reflector can reflect a secondary back-reflection beam that reaches the first reflector. The primary back-reflection beam generated by the first reflector passes through the first objective lens and converges again at point F. Point F is illuminated for the second time, and then is reflected again by the wafer surface to form a secondary reflected beam that enters the second objective lens. Subsequently, the above beam movement can be repeated to generate a secondary back-reflection beam and any subsequent back-reflection beams, which can achieve at least four irradiations of point F. The secondary back-reflection beam and any subsequent back-reflection beams are parallel to the laser beam and do not coincide with the primary back-reflection beam.

[0015] In some embodiments of the present invention, a vertical beam-collecting objective lens is disposed directly above point F; and multiple beam expanders are disposed between the third and fourth reflecting mirrors, each located in the optical path of any intermediate beam.

[0016] Advantages and effects of the present invention: 1. This invention achieves efficient and reusable light energy utilization. By using a combination of reflector groups (isosceles right-angle reflectors, double vertical small reflectors, plane reflector combinations, etc.) and symmetrically arranged dual objective lenses, the laser beam can be repeatedly focused on the detection point (F point) on the wafer surface. This can be achieved by using a single reflector to achieve a 180° back reflection deflection of the beam, allowing the light energy to act on the F point a second time; or by using a multi-reflector collaborative or cyclic reflection design, the beam can be repeatedly focused on the F point by the dual objective lenses, achieving up to any number of cycles of irradiation. This completely changes the problem of energy waste in traditional single irradiation, allowing the laser beam energy to be fully recovered and repeatedly applied to the detection area, significantly improving the light energy utilization rate compared to traditional systems. 2. This invention utilizes the superposition of scattered light energy to significantly improve detection sensitivity. Multiple cyclic irradiation results in a significantly higher cumulative light energy at point F compared to a single irradiation: when particles or defects are present on the wafer surface, the superimposed light energy excites stronger scattered light, with the scattered light energy increasing exponentially compared to a single irradiation. The light-collecting components (vertical light-collecting objective, tilting light-collecting objective, etc.) can efficiently capture this enhanced scattered light, effectively reducing the false negative rate of tiny defects / ultrafine particles, significantly improving detection sensitivity, and meeting the requirements of high-precision detection. 3. This invention can adapt to different detection scenarios, and optimizes light utilization and detection coverage in a coordinated manner. Dedicated light-collecting components can be designed for different irradiation cycles: a vertical light-collecting objective captures vertically scattered light, a tilted light-collecting objective covers large-angle scattered light, and multiple light-collecting objectives are combined to achieve all-angle scattered light collection. Combined with the reuse of light energy, this ensures both energy intensity and expands the detection coverage. Furthermore, it can further optimize beam propagation stability, maintaining light energy concentration during multiple irradiation cycles, thus balancing light utilization and irradiation accuracy. Attached Figure Description Figure 1 This is a layout diagram of the optical system for detecting wafer surface defects according to Embodiment 1 of the present invention.

[0017] Figure 2 This is a layout diagram of the optical system for detecting wafer surface defects according to Embodiment 2 of the present invention.

[0018] Figure 3 This is a layout diagram of the optical system for detecting wafer surface defects according to Embodiment 3 of the present invention.

[0019] Figure 4 This is a layout diagram of the optical system for detecting wafer surface defects according to Embodiment 4 of the present invention.

[0020] Figure 1 In the image, 11. Wafer; 12. Laser beam; 13. First objective lens; 14. Second objective lens; 15. First reflecting mirror; 16. Vertical beam-collecting objective lens.

[0021] Figure 2 In the diagram, 21 is a wafer; 22 is a laser beam; 23 is a first objective lens; 24 is a second objective lens; 25a is a second reflecting device; 25b is a first reflecting device; 26a is a first light-collecting objective lens; and 26b is a second light-collecting objective lens.

[0022] Figure 3 In the diagram, 31 is a wafer; 32 is a laser beam; 33 is the first objective lens; 34 is the second objective lens; 35a is the second reflecting mirror; 35b is the first reflecting mirror; and 36 is the tilting beam-collecting objective lens.

[0023] Figure 4 In the diagram, 41 is a wafer; 42 is a laser beam; 43 is the first objective lens; 44 is the second objective lens; 45a is the second reflecting mirror; 45b is the fourth reflecting mirror; 45c is the third reflecting mirror; 45d is the first reflecting mirror; and 46 is the vertical beam-collecting objective lens. Detailed Implementation

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] The present invention provides an optical system for detecting wafer surface defects with reusable light energy, comprising: a first objective lens and a second objective lens symmetrically disposed on both sides above the wafer; and a mirror group disposed on the outer side of the first objective lens and / or the second objective lens relative to the center of the wafer, wherein the mirror group includes at least one reflective element disposed on the outer side of the second objective lens.

[0029] After the laser beam (i.e., the incident light) is focused by the first objective lens, it forms a convergent beam at a certain tilt angle and is focused on point F on the wafer surface. Point F is the focal point. Then, it is reflected on the wafer surface to form a primary reflected beam and a primary divergent beam. The primary reflected beam is collimated by the second objective lens, which coincides with the focal point of the first objective lens. The collimated primary reflected beam is reflected by a group of mirrors to form a primary retroreflected beam that is parallel to the collimated primary reflected beam, opposite in direction, and separated by a certain distance. The primary retroreflected beam is again incident on the second objective lens and focused at point F. It is reflected again by the wafer to form a secondary reflected beam and a secondary divergent beam. The secondary reflected beam is collimated by the first objective lens. Alternatively, the primary retroreflected beam is processed by the group of mirrors and then refocused at point F by the first objective lens.

[0030] If other reflective elements of the mirror group are provided on the outside of the first objective lens, a secondary retroreflected beam parallel to the laser beam, in the same direction and separated by a certain distance can be formed and then focused on point F again after being collimated by the first objective lens. The above steps are then repeated to achieve multiple focusing on point F. In this way, at least two cycles of irradiation of point F can be achieved, which increases the energy focused on the wafer surface.

[0031] A light-collecting component is set above point F. If there are particles or defects on the wafer surface, they will generate scattered light after being irradiated by the laser beam. This scattered light will be collected by the light-collecting component, and the energy of the scattered light will be significantly higher than that of a single irradiation, thereby improving the detection sensitivity.

[0032] In some embodiments of the present invention, the light-collecting assembly includes at least one light-collecting objective located in the region above point F.

[0033] Let the reflectivity of the wafer surface to the laser be R, and the reflected light power of the laser be P. Then, after n irradiations, the actual light power obtained at the focal position is: Taking a laser wavelength of 266nm and a wafer material of silicon (Si) as an example, its reflectivity R to 266nm light is about 0.7. If it is recycled once, the light power will be increased to about 170% of that of a single irradiation. If it is recycled four times, the light power will be increased to about 250% of that of a single irradiation.

[0034] Furthermore, since there are unavoidable processing, installation, and adjustment errors in actual optical components such as lenses and reflectors, the collimation of the light after it is recovered and reflected is difficult to guarantee. Therefore, an adjustable beam expander can be set between the collimated beams in the recovery optical path. Since adjusting the beam expander can change the divergence angle of the outgoing beam, it can correct the deterioration of collimation caused by installation and adjustment errors and maintain the consistency of the focusing point.

[0035] If particles are present at point F after the above multiple irradiations, scattered light will be generated. At this time, a light-collecting objective lens can be set to focus on point F to collect the scattered light, which can then be imported into a subsequent scattered light collection system for scattered light signal processing and analysis.

[0036] Example 1 like Figure 1 As shown, the reflector group includes a first reflector 15 disposed outside the second objective lens 14. The first reflector 15 is an isosceles right-angled triangle structure with its base facing the second objective lens 14. It can generate a 180° back reflection effect on the primary reflected beam to form a primary back reflection beam and generate a deflection. The primary back reflection beam does not coincide with the primary reflected beam. After the primary back reflection beam re-enters the second objective lens 14, it converges at point F. Point F is illuminated for the second time, and then is reflected again by the surface of the wafer 11 to form a secondary reflected beam that enters the first objective lens 13. After collimation, it exits. Point F is illuminated a total of twice.

[0037] In addition, a vertical collecting objective 16 is positioned directly above point F. If there are particles or defects on the surface of the wafer 11, they will generate scattered light after being irradiated by the laser beam 12. This scattered light will be collected by the vertical collecting objective 16, and the energy of the scattered light will be significantly higher than that of a single irradiation, thereby improving the detection sensitivity.

[0038] Example 2 like Figure 2 As shown, the reflector group includes a first reflecting device 25b and a second reflecting device 25a respectively disposed outside the first objective lens 23 and the second objective lens 24. Both the first reflecting device 25b and the second reflecting device 25a are composed of two small reflecting mirrors that are perpendicular to each other and arranged opposite each other. After the primary reflected beam passes through the two small reflecting mirrors of the second reflecting device 25a in sequence, it can produce a 180° back reflection effect and form a primary back reflection beam, which is deflected and does not coincide with the primary reflected beam. After the primary back reflection beam re-enters the second objective lens 24, it converges at point F. Point F is illuminated for the second time, and then it is reflected again by the surface of the wafer 21 to form a secondary reflected beam that enters the first objective lens 23. After collimation, it passes through the two small reflecting mirrors of the first reflecting device 25b in sequence to form a secondary back reflection beam. The secondary back reflection beam is re-focused at point F after passing through the first objective lens 23. Point F is illuminated a total of three times.

[0039] Above point F, there is a first light-collecting objective lens 26a perpendicularly facing point F and a second light-collecting objective lens 26b tilted towards point F. The first light-collecting objective lens 26a collects scattered light in the direction perpendicular to the wafer 21, and the second light-collecting objective lens 26b collects scattered light at a larger angle relative to the normal of the wafer 21.

[0040] Example 3 like Figure 3As shown, the reflector group includes a first reflector 35b and a second reflector 35a respectively disposed outside the first objective lens 33 and the second objective lens 34. Both the first reflector 35b and the second reflector 35a are planar reflectors. After the primary reflected beam passes through the second objective lens 34 and reaches the second reflector 35a, it can generate a primary reflected beam that is horizontal and directed towards the first objective lens 33. The primary reflected beam reaches the second reflector 35a, which can reflect the primary reflected beam to form a primary reflected deflected beam that reaches the first reflector 35b. The secondary reflected beam generated by the first reflector 35b passes through the first objective lens 33 and converges again at point F. Point F is illuminated for the second time, and then reflected again by the surface of the wafer 31 to form a secondary reflected beam that enters the second objective lens 34. The above beam movement can then be repeated cyclically to generate any number of subsequent reflected beams, achieving at least five irradiations of point F. The secondary reflected beam and any subsequent reflected beams are parallel to and do not coincide with the laser beam 32 and the primary reflected beam.

[0041] An inclined light-collecting objective lens 36 is set above point F, which is tilted towards point F to collect scattered light at a large angle relative to the normal of the wafer 31.

[0042] Example 4 like Figure 4 As shown, the reflector assembly includes a first reflector 45d and a second reflector 45a respectively disposed outside the first objective lens 43 and the second objective lens 44. A third reflector 45c and a fourth reflector 45b are respectively disposed beside the first reflector 45d and the second reflector 45a. The first reflector 45d, the second reflector 45a, the third reflector 45c, and the fourth reflector 45b are all plane reflectors. After the primary reflected beam passes through the second objective lens 44 and reaches the second reflector 45a, it generates a horizontally forward primary retroreflected beam. This primary retroreflected beam reaches the fourth reflector 45b and is reflected by it. An intermediate beam is emitted once and reaches the third reflecting mirror 45c. The third reflecting mirror 45c can reflect a back-reflected beam and it reaches the first reflecting mirror 45d. The back-reflected beam generated by the first reflecting mirror 45d passes through the first objective lens 43 and converges again at point F. Point F is illuminated for the second time, and then it is reflected again by the surface of the wafer 41 to form a secondary reflected beam that enters the second objective lens 44. The above beam movement can then be repeated to generate secondary back-reflected beams and any subsequent back-reflected beams, which can achieve at least four irradiations of point F. The secondary back-reflected beams and any subsequent back-reflected beams are all parallel to the laser beam 42 and the primary back-reflected beam and do not coincide.

[0043] In some embodiments of the present invention, a vertical light-collecting objective lens 46 is disposed directly above point F; and a plurality of beam expanders are disposed between the third reflecting mirror 45c and the fourth reflecting mirror 45b, each located in the optical path of any intermediate beam.

[0044] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone 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 system for detecting wafer surface defects with reusable optical energy, characterized in that, include: A first objective lens and a second objective lens are symmetrically arranged on both sides above the wafer; a mirror group is arranged on the outer side of the first objective lens and / or the second objective lens relative to the center of the wafer, the mirror group including at least one reflecting element arranged on the outer side of the second objective lens; after the laser beam is focused by the first objective lens, it forms a primary converging beam focused at point F on the wafer surface at a certain tilt angle, with point F as the focal point, and then reflects on the wafer surface to form a primary reflected beam and a primary diverging beam. The primary reflected beam is collimated by the second objective lens that coincides with the focal point of the first objective lens. The collimated primary reflected beam is reflected by the mirror group to form a primary retroreflected beam that is parallel to the collimated primary reflected beam, opposite in direction, and separated by a certain distance. The primary retroreflected beam is again incident on the second objective lens and focused at point F, and is reflected again by the wafer to form a secondary beam. The system consists of a reflected beam and a secondary diverging beam. The secondary reflected beam is collimated by the first objective lens. Alternatively, the primary reflected beam is processed by a mirror group and then refocused at point F by the first objective lens. If other reflective elements of the mirror group are provided outside the first objective lens, a secondary reflected beam parallel to the laser beam, in the same direction, and spaced at a certain distance can be formed and refocused at point F after being collimated by the first objective lens. The above steps are then repeated to achieve multiple focusing of point F. This enables at least two cyclic irradiations of point F, increasing the energy focused on the wafer surface. A light-collecting component is provided above point F. If there are particles or defects on the wafer surface, they will generate scattered light after being irradiated by the laser beam. This scattered light will be collected by the light-collecting component, and its energy will be significantly higher than that of a single irradiation, thereby improving the detection sensitivity.

2. The wafer surface defect detection optical system according to claim 1, characterized in that, The light-collecting assembly includes at least one light-collecting objective located in the region above point F.

3. The wafer surface defect detection optical system according to claim 2, characterized in that, The mirror assembly includes a first mirror disposed outside the second objective lens. The first mirror is an isosceles right-angled triangle with its base facing the second objective lens. It can generate a 180° back reflection effect on the first reflected beam to form a first back reflection beam and cause a shift. The first back reflection beam does not coincide with the first reflected beam. After the first back reflection beam re-enters the second objective lens, it converges at point F. Point F is illuminated a second time, and then is reflected again by the wafer surface to form a second reflected beam that enters the first objective lens. After collimation, it exits. Point F is illuminated a total of twice.

4. The wafer surface defect detection optical system according to claim 3, characterized in that, A vertical light-collecting objective lens is positioned directly above point F, facing point F.

5. The optical system for detecting wafer surface defects according to claim 2, characterized in that, The mirror assembly includes a first reflecting device and a second reflecting device respectively disposed outside the first objective lens and the second objective lens. Both the first reflecting device and the second reflecting device are composed of two small reflecting mirrors that are perpendicular to each other and arranged opposite each other. After the primary reflected beam passes through the two small reflecting mirrors of the second reflecting device in sequence, it can produce a 180° back reflection effect and form a primary back reflection beam, which is deflected and does not coincide with the primary reflected beam. After the primary back reflection beam re-enters the second objective lens, it converges at point F. Point F is illuminated for the second time, and then it is reflected again by the wafer surface to form a secondary reflected beam that enters the first objective lens. After collimation, it passes through the two small reflecting mirrors of the first reflecting device in sequence and forms a secondary back reflection beam. The secondary back reflection beam is re-focused at point F after passing through the first objective lens. Point F is illuminated a total of three times.

6. The wafer surface defect detection optical system according to claim 5, characterized in that, Above point F, there is a first light-collecting objective lens that is perpendicular to point F and a second light-collecting objective lens that is tilted towards point F. The first light-collecting objective lens collects scattered light in the direction perpendicular to the wafer, and the second light-collecting objective lens collects scattered light at a larger angle relative to the wafer normal.

7. The wafer surface defect detection optical system according to claim 2, characterized in that, The mirror assembly includes a first mirror and a second mirror respectively disposed outside the first objective lens and the second objective lens. Both the first mirror and the second mirror are planar mirrors. The primary reflected beam passes through the second objective lens and reaches the second mirror, generating a horizontal primary retroreflected beam that is directed towards the first objective lens. The primary retroreflected beam reaches the second mirror, which reflects it to form a primary retroreflected deflected beam that reaches the first mirror. The primary retroreflected beam generated by the first mirror passes through the first objective lens and converges again at point F. Point F is illuminated a second time and then reflected again by the wafer surface to form a secondary reflected beam that enters the second objective lens. This beam movement can then be repeated cyclically to generate any number of subsequent retroreflected beams, achieving at least five irradiations of point F. The secondary retroreflected beam and any subsequent retroreflected beams are parallel to and do not coincide with the laser beam and the primary retroreflected beam.

8. The optical system for detecting wafer surface defects according to claim 7, characterized in that, An inclined light-collecting objective lens is positioned above point F, tilted towards point F, to collect scattered light at a large angle relative to the wafer normal.

9. The optical system for detecting wafer surface defects according to claim 2, characterized in that, The reflector group includes a first reflector and a second reflector respectively disposed outside the first objective lens and the second objective lens. A third reflector and a fourth reflector are respectively disposed beside the first reflector and the second reflector. The first reflector, the second reflector, the third reflector and the fourth reflector are all planar reflectors. The first reflected beam passes through the second objective lens and reaches the second reflector, which generates a horizontally forward first back-reflection beam. The first back-reflection beam reaches the fourth reflector and is reflected by the fourth reflector to generate an intermediate beam that reaches the third reflector. The third reflector reflects a back-reflection beam that reaches the first reflector. The first back-reflection beam generated by the first reflector passes through the first objective lens and converges again at point F. Point F is illuminated a second time, and then is reflected again by the wafer surface to form a secondary reflected beam that enters the second objective lens. The above beam movement can then be repeated to generate a secondary back-reflection beam and any subsequent back-reflection beams, enabling at least four irradiations of point F. The secondary back-reflection beam and any subsequent back-reflection beams are parallel to and do not coincide with the laser beam and the primary back-reflection beam.

10. The wafer surface defect detection optical system according to claim 9, characterized in that, A vertical beam-collecting objective lens is positioned directly above point F; multiple beam expanders are positioned between the third and fourth reflecting mirrors, each located in the optical path of any intermediate beam.

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