A wafer defect detection system based on digital holographic microstructure

Abstract

This invention discloses a wafer defect detection system based on a digital holographic microstructure, belonging to the field of optical detection technology. The invention employs the concept of fiber optic beam splitting and independent optical path design. First, a 1×2 single-mode fiber is used to replace the traditional diffraction grating, achieving physical separation of the reference and object beams. This eliminates the need for diffraction gratings and spatial filtering, preventing any false phase information caused by grating contamination or defects from entering the reference or object beam channels, thus eliminating the generation mechanism of structured pseudo-defects. Then, independent polarization modulation elements are set on the object and reference beam paths respectively to accurately match and enhance the characteristic polarization components of the defect-scattered / reflected light before interference patterning, while suppressing orthogonal polarization components corresponding to periodic structures. Furthermore, off-axis interference with spatial carrier frequencies is introduced by combining an adjustable beam splitter, forming interference fringes throughout the entire detector field of view, ultimately achieving highly accurate detection of wafer defects.

Description

Technical Field

[0001] This invention relates to the field of optical inspection technology, and in particular to a wafer defect detection system based on digital holographic microstructure. Background Technology

[0002] With the rapid development of information technology, integrated circuits (ICs) have become a core foundational industry supporting the operation of modern information society. Driven by Moore's Law, semiconductor manufacturing processes are constantly evolving towards smaller feature sizes. In this process, device structures are becoming increasingly complex, wafer fabrication processes are significantly increasing, and advanced processes involve thousands of process steps. The impact of tiny defects on device performance during wafer manufacturing is exponentially enhanced. Defects such as particles, scratches, bridging, and wire breaks at the submicron or even nanometer scale can all lead to degradation of device electrical performance or even functional failure. Under the dual effects of increased process complexity and enhanced defect sensitivity, wafer defect detection has become one of the key core links restricting the improvement of advanced semiconductor manufacturing capabilities, after photolithography technology.

[0003] Traditional bright-field and dark-field scattering detection based on intensity information relies on the intensity scattering of incident light by defects. Its sensitivity is limited by the diffraction limit, meaning that the smaller the defect, the weaker the scattered signal. It usually relies on deep ultraviolet (DUV) or even extreme ultraviolet (EUV) light sources to improve detection capabilities. This not only significantly increases the complexity and cost of the system, but also presents engineering bottlenecks such as light source damage to wafers and high requirements for vacuum environments. Against this backdrop, interferometric imaging methods based on phase information have gradually attracted attention. Quantitative phase imaging technology can provide structural responses with higher sensitivity than intensity information and has been widely used in fields such as biological detection.

[0004] Quantitative phase imaging techniques, especially digital holographic microscopy (DHM) and diffraction phase microscopy (DPM), can convert weak optical path differences into phase changes and manifest them as interference fringes, exhibiting intrinsically high sensitivity to nanoscale morphological anomalies. However, typical current DPM systems usually employ a common-path grating beam splitting design and extract low-frequency components from the information light using spatial filtering as reference light for defect detection. However, the characteristic size of the diffraction grating is precisely in the nanometer to submicrometer range, and submicrometer-sized dust inevitably adheres to the grating surface during use. These contaminants and minute defects are susceptible to damage under laser illumination. As a fixed secondary scattering source, it generates abnormal diffraction spots that deviate from the ideal diffraction order. These spots are mixed into the reference light as false "optical path difference information." Each frame of the phase image after interferometric reconstruction is imprinted with a pseudo-defect pattern that corresponds one-to-one with the location of the grating contamination / defect. Furthermore, under this grating contamination, the reference light and the information light are obtained from the same beam through spatial filtering. This inherently leads to the fact that the intensity of the reference light cannot be independently adjusted and is significantly weaker than that of the information light. It is difficult to selectively enhance or suppress the optical response differences between the periodic structure and random defects of the wafer, ultimately making it difficult to detect wafer defects with high accuracy. Summary of the Invention

[0005] This invention provides a wafer defect detection system based on digital holographic microstructures, which can solve the problems existing in the prior art.

[0006] This invention provides a wafer defect detection system based on digital holographic microstructure, including a light source module, a beam splitting module, an object light imaging module, a reference light modulation module, and an interference imaging module; The laser emitted by the light source in the light source module is split by a 1×2 single-mode fiber in the beam splitting module to form two coherent object beams and reference beams. In the object light imaging module, the object light is formed into a detection object light through a linear polarizer. The detection object light passes through a first polarization modulation element to independently adjust the polarization state and light intensity of the detection object light. The adjusted detection object light is incident on the first beam splitter, and after being reflected by the first beam splitter, it illuminates the surface of the wafer sample. The detection object light reflected by the wafer sample, carrying the phase information of the wafer sample, is reflected back and transmitted through the first beam splitter again, and is focused by the tube lens into the object light wavefront to be interfered with and enters the second beam splitter. In the reference light modulation module, the reference light passes through the second polarization modulation element and the third polarization modulation element in sequence to adjust the polarization state and intensity of the reference light independently of the detection object light for the second time. The independently adjusted reference light enters the second beam splitter, so that it preferentially interferes with the polarization component scattered or reflected by the wafer sample defect. The angle between the reference light and the detection object light is changed by adjusting the tilt angle of the second beam splitter to achieve off-axis interference. In the interferometric imaging module, the reference light after off-axis interference from the second beam splitter is superimposed on the object light at the first imaging lens and the second imaging lens to form an interference fringe image at the detector for wafer defect detection.

[0007] Preferably, the object-optical imaging module further includes a lens group and an objective lens; The lens group is disposed between the 1×2 single-mode fiber and the linear polarizer, and is used to expand the object light beam to a preset aperture so as to illuminate the linear polarizer. The objective lens is positioned between the first beam splitter and the wafer sample. The detection object light reflected by the first beam splitter is focused by the objective lens to illuminate the wafer sample. The detection object light reflected by the wafer sample, carrying the phase information of the wafer sample, is collected again by the objective lens and transmitted back through the first beam splitter.

[0008] Preferably, the objective lens focuses the detection beam onto the surface of the wafer sample and collects the detection beam containing wafer sample information by reflection.

[0009] Preferably, the reference light modulation module further includes a collimating lens; The collimating lens is disposed between the third polarization modulation element and the second beam splitter. The collimating lens is used to expand and collimate the reference light into a uniform plane wavefront.

[0010] Preferably, the 1×2 single-mode fiber is a polarization-maintaining fiber, used to maintain the polarization state stability of the output object light and reference light.

[0011] Preferably, the linear polarizer, the first polarization modulation element, the second polarization modulation element, and the third polarization modulation element are all rotatable linear polarizers, half-wave plates, or liquid crystal polarization controllers.

[0012] Preferably, the tilt angle of the second beam splitter is adjustable. By adjusting the tilt angle of the second beam splitter, the spatial angle between the reference light and the object light is changed, thereby adjusting the spatial carrier frequency of the interference fringes to achieve the separation of the 0th and 1st order components in the frequency domain.

[0013] Preferably, it also includes an electromechanical coordination control unit; The electromechanical co-control unit is used to drive the displacement platform to move the wafer sample precisely at a preset step distance through a preset scanning step distance, and trigger the detector at each position to complete image acquisition and obtain an interference fringe image with a fixed spatial interval.

[0014] Preferably, it further includes an image processing unit; The image processing unit performs spatial second-order difference operations on three consecutive frames of interference fringe images acquired along the scanning direction with weights of -1, +2, and -1. This is used to make the non-periodic defects of the wafer sample appear as a positive-negative-positive or negative-positive-negative tripole enhancement structure, so as to locate the defect position of the wafer sample.

[0015] Preferably, the image processing unit is further configured to perform moving average or stitching fusion on the differential images to generate a complete wafer sample defect distribution map.

[0016] This invention provides a wafer defect detection system based on digital holographic microstructures, which has the following advantages compared with the prior art: This invention employs the concept of fiber optic splitting and independent optical path design. First, it replaces the traditional diffraction grating with a 1×2 single-mode fiber, achieving physical separation of the reference and object beams. This completely eliminates the need for diffraction gratings and spatial filtering, preventing any spurious phase information caused by grating contamination or defects from entering the reference or object beam channels, thus fundamentally eliminating the generation mechanism of structured spurious defects. Then, independent polarization modulation elements are placed on the object and reference beam paths respectively to precisely match and enhance the characteristic polarization components of the defect-scattered / reflected light before interference patterning, while simultaneously suppressing orthogonal polarization components corresponding to periodic structures. In this process of independently controlling the intensity and polarization state of the object beam and the reference beam, the independent control of the object beam can enhance the matching of the defect-scattered / reflected light, while the independent control of the reference beam can make the reference beam preferentially interfere with the polarization component of the object beam corresponding to the defect to suppress the background of the wafer periodic structure. Thus, it is possible to selectively enhance or suppress the difference in optical response between the wafer periodic structure and random defects. In addition, by combining the adjustable beam splitter to introduce off-axis interference of the spatial carrier frequency, stable, uniform, and high-contrast interference fringes can be formed throughout the entire detector field of view, ultimately achieving high-accuracy detection of wafer defects. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of conventional bright and dark field defect detection provided in an embodiment of the present invention; Figure 2 A schematic diagram of a commonly used quantitative phase imaging method provided in the embodiments of the present invention; Figure 3 This is a schematic diagram of the conventional DPM optical path principle provided in an embodiment of the present invention; Figure 4 This is a simplified schematic diagram of the traditional DPM optical path principle provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the overall architecture of the wafer defect detection system provided in an embodiment of the present invention; Figure 6 The image is a result of image post-processing defect detection provided in an embodiment of the present invention.

[0018] The components are: 1. Light source, 2. 1×2 single-mode fiber, 3. Lens group, 4. Linear polarizer, 5. First polarization modulation element, 6. First beam splitter, 7. Objective lens, 8. Wafer sample, 9. Tube lens, 10. Second polarization modulation element, 11. Third polarization modulation element, 12. Collimating lens, 13. Second beam splitter, 14. First imaging lens, 15. Second imaging lens, 16. Detector. Detailed Implementation

[0019] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0020] Optical inspection methods have become the mainstream technology for wafer defect detection due to their advantages such as high throughput, non-contact operation, and suitability for online inspection. Based on the different optical information utilized, optical methods mainly include bright-field and dark-field scattering detection based on intensity information, and interferometric detection methods based on phase information. Bright-field and dark-field detection identifies defects by analyzing the intensity changes of reflected or scattered light. Due to its high detection speed and large field of view, it is widely used in practice, such as... Figure 1 As shown; however, traditional optical detection methods face significant physical limitations at the nanoscale. According to the diffraction limit, the intensity of the scattered signal generated by the defect is proportional to the defect size and the wavelength of the light source. As the defect size decreases, the scattered signal attenuates rapidly. To improve detection sensitivity, current mainstream methods typically employ a strategy of shortening the light source wavelength, such as using 193 nm deep ultraviolet (DUV) or even extreme ultraviolet (EUV) light sources for detection. Although this method improves detection capabilities to some extent, it also brings problems such as high system complexity, high cost, and difficult maintenance. In addition, EUV light sources have extremely high requirements for vacuum environment and material performance, and high-energy laser beams can easily damage the wafer surface. Furthermore, its core technology has long been restricted by foreign countries, and it is difficult to achieve a comprehensive breakthrough in the short term.

[0021] Against this backdrop, interferometric imaging methods based on phase information have gradually attracted attention; quantitative phase imaging technology can provide structural responses with higher sensitivity than intensity information and has been widely used in fields such as biological detection; common interferometric imaging configurations include digital holographic microscopy (DHM), diffraction phase microscopy (DPM), and differential phase contrast microscopy (DPC), such as... Figure 2As shown, these methods can achieve efficient, label-free imaging of micrometer-scale structures. Since the interference process can convert the height or optical path difference of the sample into a phase change, which is manifested as the brightness and darkness distribution of interference fringes, it has extremely high sensitivity to minute axial (z-direction) morphological changes and is widely used in surface morphology measurement and microstructure detection.

[0022] However, the application of traditional interferometric methods remains relatively limited for detecting nanoscale defects on wafers. Current research indicates that diffraction phase microscopy (DPM) can detect defects at the approximately 22 nm scale under specific conditions. This is mainly due to its common-path interference structure's excellent suppression of common-mode noise such as environmental vibrations, thus significantly improving the system's signal-to-noise ratio. Nevertheless, as... Figure 3 and Figure 4 As shown, this method still has certain limitations: its reference light needs to be extracted from the information light through spatial filtering, resulting in a weak reference light intensity, which in turn affects the interference contrast; at the same time, the effective interference area is usually limited to the center of the field of view, which limits the imaging range and detection efficiency of the system; the filter aperture size in the system is less than 10 micrometers, which makes mechanical processing difficult and the precision cannot be guaranteed, resulting in obvious speckle and uneven illumination in the image; the system uses grating beam splitting, and the grating will have defects or dust during processing and use. Due to the nanoscale structure of the grating, it cannot be wiped or cleaned by normal means, and finally the phase field has a lot of grating defects and dust, which affects image processing.

[0023] In summary, current defect detection methods mainly suffer from the following problems: ① In patterned wafer defect detection, existing quantitative phase imaging techniques are limited by optical path structure and beam splitting methods. The reference light and information light are usually obtained from the same beam through spatial filtering, resulting in the inability to independently adjust their light intensities and limiting interference contrast, thus making it difficult to achieve high signal-to-noise ratio nanoscale defect detection; ② In existing technologies based on diffraction phase microscopy (DPM), grating beam splitting and pinhole filtering are usually used to obtain the reference light. This process not only introduces additional optical element errors (such as grating processing defects) but also causes severe energy loss of the reference light, resulting in effective interference only in a local area of ​​the field of view, limiting the system's imaging field of view and detection efficiency; ③ In existing interferometric detection methods, the polarization states of the reference light and information light are usually not independently controllable, making it difficult to selectively enhance or suppress the optical response differences between the wafer's periodic structure and random defects, resulting in severe background structure interference and affecting the accuracy of defect detection; ④ For the problem of superposition of complex periodic structure background and nanoscale defect signals in patterned wafers, existing methods often rely on complex post-processing algorithms for separation, which has high computational complexity and limited stability.

[0024] Based on this, the present invention proposes a wafer defect detection system based on digital holographic microstructures, such as... Figure 5As shown, this invention achieves independent tunability of the intensity and polarization state of the reference light and information light without the need for grating beam splitting, obtaining a large field of view, high-contrast interference image, and possessing the ability to suppress wafer periodic structures, thereby meeting the requirements for high-precision and high-efficiency detection of nanoscale defects in advanced processes; its core includes a light source module, a beam splitting module, an object light imaging module, a reference light modulation module, and an interference imaging module; specifically: The laser emitted by light source 1 is split into two coherent beams by a 1×2 single-mode fiber 2, which are used as the object beam and the reference beam, respectively, as input to the system.

[0025] The object beam is expanded by the beam expanding and collimating lens group 3 and the first polarization modulation element 5 to increase the cross-sectional area of ​​the optical field. It then passes through the linear polarizer 4 to form a detection optical path. The beam is focused by the objective lens 7 and then illuminates the wafer sample 8 to be tested. The reflected light from the wafer sample is collected again by the objective lens 7 and returns. It then passes through the first beam splitter 6 and the tube mirror 9 to enter the subsequent imaging optical path.

[0026] A polarization modulation element is set in the object light path to adjust the polarization state and intensity of the object light to adapt to the detection requirements of different defect types.

[0027] Another beam of light serves as a reference beam. After being output through an optical fiber, it passes sequentially through a beam expander and collimator system, namely the second polarization modulation element 10, the third polarization modulation element 11, and the collimator 12, to form a uniform reference wavefront. Subsequently, the reference beam is introduced into the interference path through the second beam splitter 13 and forms a certain angle with the object beam in space, thus achieving off-axis interference.

[0028] Setting a second polarization modulation element 10 in the reference light path can adjust the intensity of the reference light, and setting a third polarization modulation element 11 can adjust the polarization state of the reference light. In the interferometric imaging module, the object light and the reference light are superimposed under the action of the first imaging lens 14 and the second imaging lens 15, and finally form an interference fringe image at the detector 16. By adjusting the tilt angle of the second beam splitter 13, the angle between the reference light and the object light can be changed, thereby controlling the spatial angular frequency and realizing the 0th and 1st order separation in the frequency domain.

[0029] In the above implementation process, this invention replaces the traditional grating beam splitting structure with fiber beam splitting, making the reference beam and object beam completely independent. This allows for the separate adjustment of the light intensity and polarization state of the two beams, improving the system's adjustment freedom and stability. By adjusting the polarization state of the reference beam, it preferentially interferes with the polarization component corresponding to the defect, thereby suppressing the background of the wafer's periodic structure and enhancing the defect signal. Through the off-axis interference structure, stable interference fringes can be formed throughout the entire detector's field of view, breaking through the limitation of only local imaging in traditional methods and significantly expanding the effective detection field of view. After Fourier transform and phase reconstruction, the interference image acquired by the system is post-processed using a second-order difference algorithm to effectively suppress time-invariant noise and enhance the defect signal.

[0030] The present invention also provides a defect image post-processing algorithm and an electromechanical collaborative control system in conjunction with a wafer defect detection system. The electromechanical control system is used to realize the synchronous control of the wafer displacement stage and the CCD camera. The displacement platform is driven to move precisely by a preset scanning step distance, and the camera is triggered to complete image acquisition at each position, thereby obtaining a set of sequential images with a fixed spatial interval. The distance is set according to the periodic structure size of the wafer under test to ensure the periodic correspondence between adjacent images in space.

[0031] In terms of image processing, this invention adopts a defect enhancement method based on second-order difference. It linearly combines three consecutive frames of images acquired along the scanning direction according to the weights "-1, +2, -1" to realize spatial second-order difference operation, thereby effectively suppressing periodic structural background and time-invariant noise that exists stably in the system.

[0032] After differential processing, periodic patterns exhibit similar distributions in adjacent frames, and their differential results approach zero. Aperiodic defects, lacking the spatial characteristic of periodic repetition, are preserved and significantly enhanced in the differential results. Ultimately, in the processed image, the defect region displays a "positive-negative-positive" or "negative-positive-negative" tripolar structure with clear intensity contrast, thus enabling rapid location of defects. The post-processing defect detection results are as follows: Figure 6 As shown.

[0033] The differential images can be further fused with moving average or stitching algorithms to reduce the impact of random noise on the detection results and generate a complete wafer defect distribution map. Compared with existing post-processing algorithms that rely on complex models or deep learning methods, the second-order differential method proposed in this invention has low computational complexity, fast processing speed, and can achieve real-time linkage with electromechanical scanning systems, possessing good engineering feasibility and online detection potential.

[0034] This invention employs a beam-splitting interference structure, introducing different angular frequencies in space by adjusting the beam-splitting mirror angle to achieve effective separation of 0th-order and 1st-order light. This eliminates the need for a diffraction grating, simplifying the optical path structure and avoiding the impact of grating defects on imaging quality, thus improving system stability and engineering feasibility. Furthermore, by constructing independent optical paths for the reference and object beams, the intensity and polarization state of each beam can be controlled separately, enabling stable interference fringes to form across the entire field of view. This overcomes the limitation of traditional methods that only image in localized areas; its effective imaging range is primarily determined by the field of view of the CCD detector. The field determination significantly improves detection efficiency. This invention introduces a polarization modulation mechanism, adjusting the polarization state of the reference light to preferentially interfere with the polarization component corresponding to the defect. This effectively suppresses background signals generated by the periodic structure of the wafer, enhances defect contrast, reduces false detection rate, and improves detection accuracy. In image processing, this invention combines optical modulation characteristics and employs a second-order difference method for post-processing the interference image. This effectively removes time-invariant noise in the system while significantly reducing computational complexity, resulting in higher processing speed and real-time performance compared to methods relying on complex algorithms. The detection system constructed by this invention can stably detect wafer defects at scales of 110 nm, 55 nm, and 22 nm, verifying the effectiveness and reliability of this method in nanoscale defect detection.

[0035] This invention employs a 1×2 polarization-maintaining fiber coupler for direct beam separation, ensuring the purity of the interference phase measurement from the optical path topology level. This ensures that each frame of the phase image reflects only the true optical path difference distribution of the wafer itself, completely eliminating fixed false alarms caused by defects in system components and significantly reducing the false alarm rate. This provides a practical and feasible physical guarantee for high-sensitivity online detection at the production line level. At the same time, this invention replaces the diffraction grating with an optical fiber, eliminating the need for complex modules such as high-precision pinhole filters, grating assembly and adjustment mechanisms, and their precise temperature control compensation. After the reference beam is expanded and collimated, it directly intersects with the object beam in front of the CCD without an additional imaging objective, reducing the number of optical components and the possibility of introducing non-common optical path errors.

[0036] This invention sets independent polarization modulation elements on the object light and reference light paths, respectively. This polarization-selective interference mechanism significantly amplifies the defect signal in terms of interference contrast, while actively suppressing background texture, thereby profoundly improving the intrinsic signal-to-noise ratio of the defect and the background. At the same time, this suppression is completed in the optical imaging stage, directly reducing the background energy entering the detector and post-processing process. This is equivalent to significantly compressing the proportion of invalid information in the dynamic range at the signal source, so that the limited dynamic range and quantization bit depth of the detector can be used more effectively to characterize the subtle phase changes of nanodefects. Ultimately, the detection limit is no longer limited by background photon noise.

[0037] This invention combines an adjustable beam splitter to introduce an off-axis interference structure with a spatial carrier frequency, which can form stable, uniform, and high-contrast interference fringes throughout the entire detector field of view. This operation not only increases the effective detection area per frame by orders of magnitude, but also greatly simplifies the spectral filtering operation in subsequent phase reconstruction: since there is sufficient fringe contrast throughout the entire field of view, the +1 order component in the Fourier spectrum has a complete and uniform amplitude distribution. Phase reconstruction only requires a single filtering and inverse transform to obtain the phase map of the entire field of view, avoiding the computational burden and edge effects brought about by the stitching algorithm, and fundamentally improving detection efficiency and measurement consistency.

[0038] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A wafer defect detection system based on digital holographic microstructure, characterized in that, include: Light source module, beam splitting module, object light imaging module, reference light modulation module, and interferometric imaging module; The laser emitted by the light source (1) in the light source module is split by the 1×2 single-mode fiber (2) in the beam splitting module to form two coherent object beams and reference beams. In the object light imaging module, the object light is formed into a detection object light through a linear polarizer (4). The detection object light passes through a first polarization modulation element (5) to independently adjust the polarization state and light intensity of the detection object light. The adjusted detection object light is incident on the first beam splitter (6), and after being reflected by the first beam splitter (6), it illuminates the surface of the wafer sample (8). The detection object light carrying the phase information of the wafer sample (8) reflected by the wafer sample (8) is again transmitted in reverse through the first beam splitter (6), and is focused by the tube lens (9) into the object light wavefront to be interfered and enters the second beam splitter (13). In the reference light modulation module, the reference light passes through the second polarization modulation element (10) and the third polarization modulation element (11) in sequence to adjust the polarization state and intensity of the reference light independently of the detection object light for the second time. The independently adjusted reference light enters the second beam splitter (13) so that it preferentially interferes with the polarization component scattered or reflected by the defects of the wafer sample (8). The angle between the reference light and the detection object light is changed by adjusting the tilt angle of the second beam splitter (13) to achieve off-axis interference. In the interferometric imaging module, the reference light after off-axis interference from the second beam splitter (13) and the object light are superimposed at the first imaging lens (14) and the second imaging lens (15) to form an interference fringe image at the detector (16) for wafer defect detection.

2. The wafer defect detection system based on digital holographic microstructure according to claim 1, characterized in that, The object-optical imaging module also includes a lens group (3) and an objective lens (7); The lens group (3) is disposed between the 1×2 single-mode fiber (2) and the linear polarizer (4) for expanding the object beam to a preset aperture to illuminate the linear polarizer (4). The objective lens (7) is positioned between the first beam splitter (6) and the wafer sample (8). The detection object light reflected by the first beam splitter (6) is focused by the objective lens (7) to illuminate the wafer sample (8). The detection object light carrying the phase information of the wafer sample (8) reflected by the wafer sample (8) is collected again by the objective lens (7) and transmitted back through the first beam splitter (6).

3. The wafer defect detection system based on digital holographic microstructure according to claim 2, characterized in that, The objective lens (7) focuses the detection object light onto the surface of the wafer sample (8) and collects the detection object light containing information about the wafer sample (8) by reflection.

4. The wafer defect detection system based on digital holographic microstructure according to claim 1, characterized in that, The reference light modulation module also includes a collimating lens (12); The collimating lens (12) is disposed between the third polarization modulation element (11) and the second beam splitter (13). The collimating lens (12) is used to expand and collimate the reference light into a uniform plane wavefront.

5. The wafer defect detection system based on digital holographic microstructure according to claim 1, characterized in that, The 1×2 single-mode fiber (2) is a polarization-maintaining fiber used to maintain the polarization state stability of the output object light and reference light.

6. The wafer defect detection system based on digital holographic microstructure according to claim 1, characterized in that, The linear polarizer (4), the first polarization modulation element (5), the second polarization modulation element (10) and the third polarization modulation element (11) are all rotatable linear polarizers, half-wave plates or liquid crystal polarization controllers.

7. The wafer defect detection system based on digital holographic microstructure according to claim 1, characterized in that, The tilt angle of the second beam splitter (13) is adjustable. By adjusting the tilt angle of the second beam splitter (13), the spatial angle between the reference light and the object light is changed, thereby adjusting the spatial carrier frequency of the interference fringes to achieve the separation of the 0th and 1st order components in the frequency domain.

8. A wafer defect detection system based on digital holographic microstructure according to claim 1, characterized in that, It also includes electromechanical coordination control units; The electromechanical co-control unit is used to drive the displacement platform to move the wafer sample (8) precisely according to the preset step distance through the preset scanning step distance, and trigger the detector (16) at each position to complete image acquisition and obtain an interference fringe image with a fixed spatial interval.

9. A wafer defect detection system based on digital holographic microstructure according to claim 1, characterized in that, It also includes an image processing unit; The image processing unit performs spatial second-order difference operations on the three consecutive frames of interference fringe images acquired along the scanning direction with weights of -1, +2, and -1, in order to make the non-periodic defects of the wafer sample (8) present as a positive-negative-positive or negative-positive-negative tripole enhancement structure, so as to locate the defect position of the wafer sample (8).

10. A wafer defect detection system based on digital holographic microstructure according to claim 9, characterized in that, The image processing unit is also configured to perform moving average or stitching fusion on the differential images to generate a defect distribution map of the complete wafer sample (8).

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