Planar substrate defect detection system and method based on weak measurement differential

Abstract

The invention belongs to the technical field of optical application, and discloses a planar substrate defect detection system and method based on weak measurement differential, the detection system comprises a laser generating device, a beam splitter, an objective lens, a tube lens, a differential assembly and an image receiving unit; parallel light beams generated by the laser generating device are incident on the plane substrate to be measured through the beam splitter and the objective lens; a light beam reflected from the plane substrate to be measured enters the differential assembly through the objective lens, the beam splitter and the barrel lens, the light beam is modulated through the differential assembly, and the modulated light beam is received by the image receiving unit; the differential assembly comprises a first polaroid, a first birefringent crystal, a second birefringent crystal and a second polaroid; the first birefringent crystal and the second birefringent crystal are orthogonal; the first polarizer and the second polarizer are orthogonal to each other. According to the invention, not only can complex, hidden and tiny defects be effectively detected, but also the detection precision is obviously improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical applications, relates to the detection of planar sinking defects, and particularly relates to a planar substrate defect detection system and method based on weak measurement differentiation. Background Art

[0002] Substrate defect detection technology is widely used in the manufacturing processes of semiconductors, optoelectronics, and high-precision optical devices. As a basic material, the surface and internal micro-defects of the substrate have an important impact on subsequent processing and the performance of the final product. Existing substrate defect detection methods mainly include traditional optical imaging methods, confocal microscopy methods, interference methods, etc. These methods can detect some macroscopic defects on the substrate surface to a certain extent, but have corresponding defects and deficiencies in the actual detection process.

[0003] Conventional optical microscopes in optical imaging methods can provide relatively clear images. However, since the resolution of optical imaging methods is limited not only by the diffraction limit but also by the signal-to-noise ratio of the imaging system; it is difficult to detect defect structures with weak signals. Therefore, due to factors such as the refractive index and surface roughness of the substrate material, the effect of optical imaging methods is relatively limited on substrates with high reflectivity, low contrast, or large surface roughness.

[0004] Confocal microscopes can effectively improve the imaging resolution through techniques such as focal length scanning and image stitching. However, its detection speed is slow, and the requirements for samples are relatively high. It is usually suitable for detection in a small range and is not suitable for efficient detection in large-scale production. Patent CN106674321B proposes a substrate defect detection method based on laser scanning and image processing. By laser scanning, a high-precision image of the substrate surface is obtained, and then defect information is analyzed in combination with image processing technology. This method is applicable to substrates of various materials and surface morphologies and has high detection accuracy; the disadvantage is that multiple scans and image processing are required, resulting in a relatively time-consuming detection process and a slow detection speed. Especially in large-scale production, it cannot meet the requirements of rapid detection.

[0005] By detecting the difference in surface morphology through the change of interference fringes, the slight height change of the surface can be measured more accurately. At present, the scheme of realizing differential imaging of substrate defects by coherent light source imaging is more common. However, the detection accuracy of the interference method is easily interfered by the ambient light and its system, and needs to be analyzed with subsequent algorithms. On multi-layer materials or complex structures, the interference image is difficult to accurately analyze. For example, patent US9325820B2, based on the principle of optical interference, uses the interference effect of light source and detector to detect slight deformation and defects on the surface of the substrate. This method can detect defects such as microcracks and undulations on the surface of the substrate with high precision, and is particularly suitable for precision semiconductor substrates. However, the optical interference method is limited by the surface cleanliness, and when the substrate surface is more complex, the resolution and accuracy of the interference image will be significantly reduced, and the type and location of small defects cannot be accurately identified, resulting in false detection or missed detection. In addition, there is currently no mature technology for interference method that can take into account both high efficiency and high precision.

[0006] X-ray imaging has strong penetrating power and can detect internal defects of materials. However, this method is complex and costly, and has high requirements for the use environment and operators, making it unsuitable for widespread application in large-scale production. In addition, X-ray imaging requires high professional technology and maintenance costs, which limits its application in some small and medium-sized manufacturers or research institutions. X-ray imaging equipment itself is technically complex and requires precise control and protection devices. At the same time, its use cost is high, which limits its widespread application. Summary of the invention

[0007] The purpose of the present invention is to address the problems existing in the above-mentioned prior art and to provide a planar substrate defect detection system and method based on weak measurement differential, so as to realize defect imaging detection of planar substrates more efficiently and accurately.

[0008] The present invention is based on the combination of a partially coherent light source and a weak measurement differential component. The object is measured through weak interference, and its detailed information can be obtained without significantly changing the measured object. At the same time, the coupling property of weak measurement can be used to achieve regulation of the light field.

[0009] The present invention provides a planar substrate defect detection system based on weak measurement differentiation, which includes a laser generating device, a beam splitter, an objective lens, a tube lens, a differential component and an image receiving unit;

[0010] The parallel light beam generated by the laser generating device is incident on the plane substrate to be measured through the beam splitter and the objective lens; the light beam reflected from the plane substrate to be measured is incident on the differential component through the objective lens, the beam splitter and the tube lens, the light beam is modulated by the differential component, and the modulated light beam is received by the image receiving unit;

[0011] The differential component includes a first polarizer, a first birefringent crystal, a second birefringent crystal and a second polarizer; the first birefringent crystal is orthogonal to the second birefringent crystal; and the first polarizer and the second polarizer are orthogonal to each other.

[0012] In one possible implementation, the laser generating device includes a laser, an optical fiber, an optical fiber flange, and a collimating lens; the laser, the optical fiber, and the optical fiber flange are connected in sequence; and the collimating lens is located behind the optical fiber flange in the laser emission direction.

[0013] In one achievable manner, the objective lens and the tube lens form a 4f system, the planar substrate to be measured is located at the front focal plane of the objective lens, and the image acquisition window of the image receiving unit is located at the back focal plane of the tube lens; the back focus of the objective lens coincides with the front focus of the tube lens.

[0014] In an implementable manner, the first birefringent crystal and the second birefringent crystal are both at an angle of ±45° to the polarization directions of the first polarizer and the second polarizer.

[0015] The present invention also provides a planar substrate defect detection method based on weak measurement differential, using the above detection system, and following the steps:

[0016] S1 adjusts the position of the substrate to be measured so that the center of the substrate to be measured is aligned with the center of the incident light beam, and the substrate to be measured is located at the front focal plane of the objective lens;

[0017] S2: adjusting the angles of the first polarizer and the second polarizer so that their polarization directions are orthogonal to each other, and adjusting the crystal axis directions of the first birefringent crystal and the second birefringent crystal so that their crystal axis directions are perpendicular to each other and are 45° and -45° to the directions of the first polarizer and the second polarizer respectively;

[0018] S3 transmits the reflected light beam reflected from the plane substrate to be measured to the differential component through the objective lens and the tube lens, and modulates the light beam through the differential component to obtain the differential light field distribution;

[0019] S4 receives the differential light field distribution through an image receiving unit to generate a differential image, and detects defects of the planar substrate to be tested.

[0020] The present invention combines a partially coherent light source with a weak measurement differential component, which significantly improves detection accuracy and efficiency. The partially coherent light source can provide better imaging results during the imaging process, and can improve the spatial resolution higher than coherent light, thereby achieving more detailed substrate imaging. The weak measurement differential component further improves the sensitivity and accuracy of detection by differentially analyzing the slight changes on the substrate surface, increasing the effective signal contrast and filtering out invalid stray light.

[0021] Compared with the prior art, the planar substrate defect detection system and method based on weak measurement differentiation provided by the present invention have the following beneficial effects:

[0022] (1) The present invention constructs a differential component by using a birefringent crystal and a polarizer, combines partial light source interference with weak measurement differential imaging technology, and can accurately capture tiny defects on the substrate surface. Especially in the case of complex surface or uneven reflection, it can still maintain high precision; the present invention can not only effectively detect complex, hidden and tiny defects, but also significantly improve the detection accuracy;

[0023] (2) Through an automated and efficient detection process, the present invention not only reduces the labor cost, but also reduces manual intervention, improves the detection speed and real-time feedback ability;

[0024] (3) The planar substrate defect detection system based on weak measurement differentiation provided by the present invention has a simple structure and convenient operation, reduces the possibility of beam interference, and is especially suitable for the detection of high-precision and complex surface structures;

[0025] (4) It has higher stability, faster speed, wider application range, simple detection process, and is suitable for use in industrial production environments.

[0026] Therefore, the present invention realizes defect detection by using a thin weak measurement differential component composed of conventional optical elements, and uses differential imaging for real-time defect recognition. The core differential component has the characteristics of easy preparation and operation. Only by embedding this component into any existing imaging system can defect detection be realized, and this component can be constructed in a small optical fiber device to realize a portable detection device. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of the principle of the planar substrate defect detection system based on weak measurement differentiation;

[0028] Figure 2 is a schematic diagram of the principle of the differential component;

[0029] Figure 3 is the detection result of silicon substrate sample A obtained by the planar substrate defect detection system based on weak measurement differentiation, where (a) and (b) correspond to different positions on the sample; there are scratch, breakage and pitting defects at the position corresponding to (a); there are scratch and pitting defects at the position corresponding to (b);

[0030] Figure 4 is the detection result of silicon substrate sample B obtained by the planar substrate defect detection system based on weak measurement differentiation, where (a) and (b) correspond to different positions on the sample; there are scratch, breakage and pitting defects at the position corresponding to (a); there is a breakage defect at the position corresponding to (b);

[0031] Figure 5 The detection result obtained by the planar substrate defect detection system based on weak measurement differentiation for the silicon substrate sample C, where (a) and (b) correspond to different positions on the sample; there are pitted defects at the position corresponding to (a); there are breakage and scratch defects at the position corresponding to (b). Detailed implementation manners

[0032] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other implementation manners obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope protected by the present invention.

[0033] Embodiment 1

[0034] The concept of weak measurement was initially proposed by Aharonov, Albert and Vaidman, and is specifically described as follows: when the pre- and post-selection states are close to being orthogonal, the output value of the instrument can be significantly amplified, and the measured value can be much larger than the observable eigenvalue of the instrument. The present invention constructs a weak measurement differentiation component adapted to a partially coherent light source by utilizing the weak coupling effect of weak measurement, which eliminates chromatic aberration by orthogonally coupling the optical axes of two uniaxial quartz crystals (the angle between the optical axis and the incident plane is 45°). The uniaxial quartz crystal can better ensure the optical properties, so this glued birefringent crystal can be stably installed in the device for a long time.

[0035] Based on the above analysis, this embodiment provides a planar substrate defect detection system based on weak measurement differentiation, as Figure 1 and Figure 2 shown, which includes a laser generating device 1, a beam splitter 2, an objective lens 3, a tube lens 5, a differentiation component 6 and an image receiving unit 7. The parallel light beam generated by the laser generating device 1 is incident on the plane substrate 4 to be measured through the beam splitter 2 and the objective lens 3; the light beam reflected from the plane substrate 4 to be measured is incident on the differentiation component 6 through the objective lens 3, the beam splitter 2 and the tube lens 5, and the beam is modulated by the differentiation component 6, and the modulated beam is received by the image receiving unit 7. In this embodiment, a silicon substrate is used as the plane substrate to be measured.

[0036] The above laser generating device 1 includes a laser 11, an optical fiber 12, an optical fiber flange 13 and a collimating lens 14. The laser 11, the optical fiber 12 and the optical fiber flange 13 are connected in sequence; the collimating lens 14 is located in the laser output direction behind the optical fiber flange. The model of the laser 11 used in this embodiment is Anyang SC-PRO, which can generate a partially coherent light source.

[0037] The above objective lens 3 and tube lens 5 form a 4f system. The plane substrate 4 to be measured is located on the front focal plane of the objective lens 3, and the image acquisition window of the image receiving unit 7 is located on the rear focal plane of the tube lens 5; the rear focal point of the objective lens 3 coincides with the front focal point of the tube lens 5. In this embodiment, the objective lens 3 used is an infinite conjugate objective lens, with the model number Mitutoyo, 10X Plan Apo; the model number of the tube lens 5 is Mitutoyo, MT-1.

[0038] The above differential component 6 includes a first polarizer 61, a first birefringent crystal 62, a second birefringent crystal 63, and a second polarizer 64. The first birefringent crystal 62 is orthogonal to the second birefringent crystal 63; the first polarizer 61 and the second polarizer 64 are orthogonal to each other. The first birefringent crystal 62 forms an angle of ±45° with the polarization directions of the first polarizer 61 and the second polarizer 64, and at the same time, the second birefringent crystal 63 forms an angle of ±45° with the polarization directions of the first polarizer 61 and the second polarizer 64.

[0039] The above image receiving unit 7 uses a CCD (Charge Coupled Device).

[0040] In this embodiment, a partially coherent light source after beam expansion and shaping is used as the detection light, and its central wavelength is 633 nm. In this embodiment, the light field is modulated into an approximately parallel light by a collimating lens, so the detection light field can be expressed as:

[0041] φ0(r) = Ee ikr (1);

[0042] where E represents the amplitude of the light field, k represents the wave vector of the light field, and r represents the spatial coordinate. The detection light illuminates the silicon substrate to be measured after passing through the objective lens, and the overall light field reflected from the surface of the silicon substrate can be obtained as:

[0043] φ(r) = φ0(r)φ s (r) = Ee ikr φ s (r) (2);

[0044] where φ s (r) represents the structural information of the silicon substrate. The information of the overall light field is collected by the objective lens and then transmitted into the differential component. After the light field passes through the differential component, the differential operation of the overall light field is realized. The differential operation is realized through weak measurement modulation. First, the polarization state of the light field is modulated as:

[0045]

[0046] Here, different polarization states are represented by left and right vectors, where |H> represents the horizontal polarization state and |V> represents the vertical polarization state. The overall state of the modulated light field is:

[0047]

[0048] where |φ> represents the quantum state corresponding to the detected optical field, with <r|φ> = φ0(r)φ s (r). Subsequently, a weak coupling amount is provided by the first birefringent crystal and the second birefringent crystal, and the weak coupling effect can be expressed as:

[0049]

[0050] where is the Stokes parameter, is the momentum operator, and at the same time, the post-selected state is introduced as:

[0051]

[0052] The post-selected state is completely orthogonal to the pre-selected state, and based on this, an optical differential operation is constructed:

[0053]

[0054] where r represents the spatial coordinate, p represents the momentum space coordinate; |r> represents the eigenstate in the position space; |p> represents the eigenstate in the momentum space; represents the weak value; |φ> represents the quantum state corresponding to the detected optical field; φ(r) represents the spatial distribution of the overall optical field; φ(p) represents the momentum distribution of the overall optical field; g represents the coupling factor.

[0055] In this embodiment, the CCD is placed at the back focal plane of the tube mirror for imaging, and the obtained light intensity distribution is:

[0056]

[0057] Since φ(r) = φ0(r)φ s (r), and φ0(r) = Ee ikr is an approximately plane optical field, the differential optical field received by the CCD is only the optical field that reflects and carries the substrate structure distribution information.

[0058]

[0059] From Equation (8), it can be obtained that when there is a steep change structure on the substrate (which often corresponds to a defect on the substrate), the defect information can be obtained in real time in the CCD.

[0060] Embodiment 2

[0061] This embodiment provides a method for detecting plane substrate defects based on weak measurement differential. Using the detection system provided in Embodiment 1, it is carried out according to the following steps:

[0062] S1 Adjust the position of the silicon substrate to be measured so that the center of the silicon substrate to be measured is aligned with the center of the incident light beam, and place the silicon substrate to be measured at the front focal plane of the objective lens 3;

[0063] S2 Adjust the angles of the first polarizer 61 and the second polarizer 64 so that their polarization directions are orthogonal to each other, and adjust the crystal axis directions of the first birefringent crystal 62 and the second birefringent crystal 63 so that their crystal axis directions are perpendicular to each other, and are 45° and -45° respectively with respect to the directions of the first polarizer 61 and the second polarizer 63;

[0064] S3 The reflected light beam reflected from the silicon substrate to be measured is transmitted through the objective lens 3 and the tube lens 5 to the differential component 6, and the differential component 6 modulates the light beam to obtain a differential light field distribution;

[0065] S4 Receive the differential light field distribution through the image receiving unit 7 to generate a differential image, and detect the defects of the silicon substrate to be measured.

[0066] Figures 3 to 5 The detection results of three different silicon substrate samples A, B, and C obtained by the above-mentioned planar substrate defect detection system based on weak measurement differentiation according to the above steps S1 - S4 are given. It can be seen from the figure that by means of differentiation, the relatively flat illumination light field and the area without steep changes can be filtered out, while the signals of the defects are highlighted to improve the signal-to-noise ratio. At the same time, the prominent display of the defect signals makes it simple to obtain effective signals and can better adapt to the real-time detection of large-area silicon substrates. In the actual detection process, a fully automated real-time detection system can also be realized by pre-collecting various types of defects and combining defect recognition algorithms.

[0067] In summary, the main advantages of the planar substrate defect detection system and method based on weak measurement differentiation provided by the present invention are as follows:

[0068] (1) The combination of a partially coherent light source and a weak measurement differentiation component

[0069] The present invention combines a partially coherent light source and a weak measurement differentiation component and applies them to substrate defect detection. Due to its short coherence length, the partially coherent light source can effectively avoid the interference noise caused by stray light interference and provide a clearer imaging result; the weak measurement differentiation technology can perform high-contrast imaging detection on minute phase and amplitude defects; this combination can effectively improve the detection accuracy and sensitivity, especially for the detection of minute defects.

[0070] The prior art usually relies on a light source of a single wavelength, or only uses traditional optical imaging and electron beam scanning imaging, and cannot fully utilize the advantages of a polychromatic light source and differentiation technology.

[0071] (2) The high-contrast detection ability of differential imaging

[0072] The present invention utilizes differential imaging technology to perform high-contrast imaging on the minute phase changes and amplitude changes on the substrate surface, making even extremely small defects clearly visible, thereby providing more precise defect identification; this technology can identify minute internal or surface defects and is particularly effective for detecting deep defects.

[0073] Traditional optical microscope imaging or single-wavelength laser scanning methods usually cannot simultaneously solve the problems of precision and contrast; most existing solutions are limited by insufficient imaging contrast or low sensitivity when detecting minute defects, and are prone to missed detections or misidentifications.

[0074] (3) Reducing interference noise with a partially coherent light source

[0075] The light source of the present invention uses a partially coherent light source, which effectively reduces the miscellaneous interference noise brought by the coherent light source during the imaging process and improves the image quality; through the combination of multiple wavelengths, some light sources can provide more stable illumination, thus avoiding the interference effect of a single-wavelength light source and enhancing the imaging quality.

[0076] In the prior art, a single laser light source or a completely coherent light source is usually used, which easily causes interference effects. Especially in high-resolution detection, the interference noise may seriously affect the clarity of the imaging.

[0077] (4) High-efficiency detection and real-time feedback capabilities

[0078] The present invention combines some light sources and differential imaging technology, not only providing high-precision defect detection capabilities, but also being able to quickly complete the scanning of the substrate surface and interior, quickly generate detection results and provide real-time feedback; there is no need for subsequent algorithm enhancement or analysis, which can improve the detection efficiency of the production line; this feature is particularly suitable for an efficient production environment and meets the requirements of automated and large-scale detection.

[0079] The prior art usually sacrifices speed during high-precision detection, or sacrifices precision when pursuing speed.

[0080] Those of ordinary skill in the art will realize that the embodiments described herein are for helping the reader understand the principles of the present invention, and it should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other specific deformations and combinations that do not depart from the essence of the present invention based on the technical revelations disclosed in the present invention, and these deformations and combinations are still within the protection scope of the present invention.

Claims

1. A planar substrate defect detection system based on weak measurement differential, characterized in that: It comprises a laser generating device (1), a beam splitter (2), an objective lens (3), a tube lens (5), a differential component (6) and an image receiving unit (7); The parallel light beam generated by the laser generating device (1) is incident on the plane substrate (4) to be measured via the beam splitter (2) and the objective lens (3); the light beam reflected from the plane substrate (4) to be measured is incident on the differential component (6) via the objective lens (3), the beam splitter (2) and the tube lens (5); the light beam is modulated by the differential component (6), and the modulated light beam is received by the image receiving unit (7); The differential component (6) comprises a first polarizer (61), a first birefringent crystal (62), a second birefringent crystal (63) and a second polarizer (64); the first birefringent crystal (62) and the second birefringent crystal (63) are orthogonal to each other; and the first polarizer (61) and the second polarizer (64) are orthogonal to each other.

2. The planar substrate defect detection system based on weak measurement differentiation according to claim 1, characterized in that: The laser generating device (1) comprises a laser (11), an optical fiber (12), an optical fiber flange (13) and a collimating lens (14); the laser (11), the optical fiber (12) and the optical fiber flange (13) are connected in sequence; the collimating lens (14) is located behind the optical fiber flange in the laser emission direction.

3. The planar substrate defect detection system based on weak measurement differentiation according to claim 1, characterized in that: The objective lens (3) and the tube lens (5) form a 4f system, the planar substrate (4) to be measured is located at the front focal plane of the objective lens (3), and the image acquisition window of the image receiving unit (7) is located at the back focal plane of the tube lens (5); The rear focus of the objective lens (3) coincides with the front focus of the tube lens (5).

4. The planar substrate defect detection system based on weak measurement differentiation according to claim 1, characterized in that: The first birefringent crystal (62) and the second birefringent crystal (63) are both at an angle of ±45° to the polarization directions of the first polarizer (61) and the second polarizer (64).

5. A planar substrate defect detection method based on weak measurement differential, characterized in that: Using the detection system according to any one of claims 1 to 4, proceed according to the following steps: S1 adjusts the position of the planar substrate (4) to be measured so that the center of the planar substrate (4) to be measured is aligned with the center of the incident light beam, and the planar substrate to be measured is located at the front focal plane of the objective lens (3); S2 adjusts the angles of the first polarizer (61) and the second polarizer (64) so ​​that their polarization directions are orthogonal to each other, and adjusts the crystal axis directions of the first birefringent crystal (62) and the second birefringent crystal (63) so that their crystal axis directions are perpendicular to each other and are 45° and -45° to the directions of the first polarizer (61) and the second polarizer (64) respectively; S3 transmits the reflected light beam reflected from the plane substrate to be measured to the differential component (6) through the objective lens (3) and the tube lens (5), and modulates the light beam through the differential component to obtain the differential light field distribution; S4 receives the differential light field distribution through an image receiving unit (7) to generate a differential image, and detects defects of the planar substrate (4) to be tested.

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