A semiconductor patternless wafer dark field defect detection system and method

Abstract

This invention discloses a semiconductor wafer dark-field defect detection system and method, relating to the field of semiconductor technology. The invention includes: an illumination source assembly for providing a laser beam; a beam expander and shaper assembly for expanding and shaping the laser beam provided by the illumination source assembly to obtain a square strip-shaped light spot that illuminates the wafer surface; and a spiral motion control assembly, positioned below the wafer, for controlling the wafer's movement to achieve spiral line scanning of the wafer. This invention optimizes the inner-circle scanning process of a wafer inspection system based on spiral scanning lines, adjusting the light intensity and size of the strip-shaped scanning spot in real time, and synchronously adjusting the line frequency of the time-delay integration camera in real time. This achieves continuity throughout the scanning process, and ensures that the illumination laser energy obtained per unit pixel per unit time on the wafer remains consistent during imaging, facilitating subsequent image processing and recognition.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, specifically to a system and method for detecting dark field defects in patternless semiconductor wafers. Background Technology

[0002] The semiconductor patternless wafer dark-field defect detection system utilizes probed scattered light to detect defects on the wafer surface. During the entire wafer inspection process, the entire wafer surface needs to be scanned to obtain defect information. Currently, there are two main scanning schemes: one is an S-shaped scanning scheme in the XY coordinate system, and the other is a spiral scanning scheme in the R, θ coordinate system. This invention focuses on the second type, the spiral scanning scheme.

[0003] In helical scanning, a time-delay integration camera (TDI) is often used for imaging. After capturing the image, further analysis is performed to identify the corresponding defects. However, during helical scanning, if a fixed scanning speed is maintained, the linear velocity decreases as the scanning radius decreases. This can lead to a mismatch between the TDI sampling frequency and the speed if the sampling frequency remains constant, causing problems in image acquisition. Therefore, this invention proposes a dark-field defect detection system and method for patternless semiconductor wafers. Summary of the Invention

[0004] The purpose of this invention is to provide a system and method for detecting dark field defects in patternless semiconductor wafers, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a semiconductor patternless wafer dark field defect detection system, comprising:

[0006] The lighting source assembly includes a light source body, an attenuator mechanism set along the light propagation path, and a controllable aperture, wherein the attenuator is used to control the light intensity attenuation during wafer scanning, and the controllable aperture is used to control the spot size according to the scanning process;

[0007] The beam expanding and shaping component is used to expand and shape the laser beam provided by the illumination source component to obtain a square strip-shaped light spot that illuminates the wafer surface.

[0008] The spiral motion control component is located below the wafer and is used to control the movement of the wafer to achieve spiral scanning of the wafer;

[0009] The spiral motion control component includes a rotary table, a linear table, and a controller. The rotary table, linear table, and controller are electrically connected. The rotary table and linear table can realize spiral scanning of the wafer. The spiral scanning is divided into two segments along the outer side of the wafer inward. The first segment scans at a uniform linear velocity with a uniformly increasing angular velocity. The second segment scans at a uniform angular velocity with a uniformly decreasing linear velocity. The light intensity attenuation and the change in spot size are matched with the linear velocity and angular velocity during the scanning process.

[0010] The reflected light collection component is used to collect the light reflected from the wafer surface. The reflected light collection component is connected to a central control unit for analyzing and processing the reflected light information.

[0011] A scattered light collection component is used to collect scattered light emitted from the wafer and transmit it to an image processor for processing.

[0012] Furthermore, the light source body is configured as a UV light source, a DUV light source, or an EUV light source.

[0013] Furthermore, a half-wave plate is provided between the beam expanding and shaping component and the illumination source component. The beam expanding and shaping component includes, in sequence along the beam propagation direction, a beam expander, a collimating lens, a microlens array, and a focusing lens. The parallel beam emitted by the illumination source is diffused by the beam expander and then collimated again by the collimating lens into a parallel light source with a larger diameter. The parallel light is then incident on the microlens array to form a square strip-shaped light spot. Finally, the light spot is focused by the focusing lens group and incident on the wafer surface.

[0014] Furthermore, the reflected light collection component is configured as a collector, which includes an attenuation OD sheet and an energy detector PD, for collecting and analyzing the reflected light energy to ensure that the illumination laser energy obtained per unit pixel per unit time on the wafer remains consistent during the imaging process.

[0015] Furthermore, the scattered light collection assembly includes an objective lens disposed above the wafer, and a first relay mirror, a first beam splitter, a second beam splitter, and a reflector are coaxially arranged along the light transmission direction.

[0016] Furthermore, the collection channels are set to three, namely the first channel, the second channel and the third channel. The light source from the first relay mirror is split into two beams after passing through the first beam splitter. One beam is transmitted to the first channel and the other beam is transmitted to the position of the second beam splitter. The beam transmitted to the second beam splitter is split into two beams again and transmitted to the second channel and the third channel respectively.

[0017] Furthermore, a second relay mirror, a focusing lens, and a detector are sequentially arranged along the beam propagation direction in the first, second, and third channels, and the detector is connected to the image processor, which is connected to the central control unit.

[0018] Furthermore, the illumination source assembly also includes an attenuator and a controllable aperture. The attenuator is configured as a linear polarizer controlled by a rotating motor. A motor controller is electrically connected to the rotating motor. Starting the rotating motor drives the linear polarizer to rotate and controls the light transmission power to achieve controlled attenuation of light intensity, so as to keep the illumination laser energy obtained per unit pixel per unit time on the wafer consistent during the imaging process.

[0019] Furthermore, the controllable aperture includes a left baffle, a right baffle, a coupling, a servo motor, a positive threaded rod, and a negative threaded rod. Guide rails are provided below the left and right baffles, and are threadedly connected to the positive and negative threaded rods above, respectively. The positive and negative threaded rods are coaxially fixed and fixed to the output shaft of the servo motor through the coupling. When the servo motor is started, it drives the positive and negative threaded rods to rotate through the coupling. The left and right baffles can be opened or closed by utilizing the threaded engagement relationship, thereby controlling the size of the light spot.

[0020] According to a second aspect of the present invention, the present invention provides a method for detecting dark field defects in patternless semiconductor wafers, employing a dark field defect detection system for patternless semiconductor wafers described in the first aspect, and the specific steps are as follows:

[0021] S1. Starting from the outer edge of the wafer, the wafer is driven by a linear motion stage and a rotary motion stage to begin scanning at a uniform linear velocity. At this time, the scanning spot size, TDI line frequency, and spot laser power remain unchanged, while the rotation axis angular velocity of the rotary motion stage begins to gradually increase.

[0022] S2. When it enters a position with a radius of R1 from the center of rotation, the rotating axis moves at a constant angular velocity. At this time, the size of the scanning spot remains unchanged, the linear velocity begins to decrease, the TDI line frequency begins to gradually decrease, and the spot laser power also begins to decrease synchronously.

[0023] S3. When the distance from the rotation center radius is R2, the radius of the scanning area from the wafer center is further reduced, and the difference in linear velocity between the center of the spot and the edge of the spot is greater than 5%. At this time, the rotation axis still moves at a uniform angular velocity at the fixed angular velocity in step S2, and while reducing the TDI line frequency and the spot laser power, the spot size is gradually reduced using a variable aperture until the scanning ends.

[0024] This invention has at least the following beneficial effects:

[0025] This invention optimizes the inner-circle scanning process of a wafer inspection system based on spiral scan lines. It adjusts the light intensity and size of the bar scanning spot in real time and adjusts the line frequency of the time-delay integration camera in real time, thereby achieving continuity of the entire scanning process. Furthermore, the inner-circle scanning image is consistent with the outer-circle scanning image, which facilitates subsequent image processing and recognition.

[0026] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall structure of the detection system described in this invention;

[0028] Figure 2 This is a schematic diagram of the beam expanding and shaping component in this invention;

[0029] Figure 3 This is a schematic diagram illustrating the principle of wafer spiral scanning in this invention;

[0030] Figure 4 This is a schematic representation of the relationship between wafer spiral scan time and line frequency in this invention;

[0031] Figure 5 This is a schematic diagram of the external triggering of the time-delay integration camera in this invention;

[0032] Figure 6 This is a schematic representation of the relationship between wafer spiral scanning time and light intensity in this invention;

[0033] Figure 7 This is a schematic diagram of the controllable aperture structure in this invention;

[0034] Figure 8 This is a schematic diagram of a light spot scanning at a radius of R3 in an embodiment of the present invention;

[0035] Figure 9 This is a curve showing the change in spot width with scanning time in an embodiment of the present invention;

[0036] Figure 10 This is a schematic representation of the relationship between wafer spiral scan time and line frequency after modification in an embodiment of the present invention;

[0037] Figure 11 This is a schematic representation of the relationship between wafer spiral scanning time and light intensity after the modification in Embodiment 1 of the present invention;

[0038] Figure 12 This is a schematic diagram of the collector in Embodiment 1 of the present invention;

[0039] Figure 13 This is a schematic diagram illustrating the principle of collecting scattered light through each channel in Embodiment 1 of the present invention;

[0040] Figure 14 This is a schematic diagram of the controllable aperture in Embodiment 2 of the present invention;

[0041] Figure 15 This is a flowchart illustrating the detection method in Embodiment 3 of the present invention. Detailed Implementation

[0042] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this disclosure.

[0043] Example 1:

[0044] Please see Figure 1 This invention provides a technical solution: a semiconductor patternless wafer dark field defect detection system, applied to wafer defect detection, comprising:

[0045] The lighting source assembly includes a light source body 101, an attenuator mechanism 501 arranged along the light propagation path, and a controllable aperture 503. The attenuator mechanism 501 is used to control the light intensity attenuation during wafer scanning, and the controllable aperture 503 is used to control the spot size according to the scanning process.

[0046] The beam expanding and shaping component is used to expand and shape the laser beam provided by the illumination source component to obtain a square strip-shaped light spot that illuminates the wafer surface.

[0047] The spiral motion control component is located below the wafer and is used to control the movement of the wafer to achieve spiral scanning of the wafer;

[0048] The spiral motion control component includes a rotary stage 108, a linear stage 107, and a controller 106. The rotary stage 108, the linear stage 107, and the controller 106 are electrically connected. The rotary stage 108 and the linear stage 107 can realize spiral scanning of the wafer. The spiral scanning is divided into two segments along the outer side of the wafer inward. The first segment scans at a uniform linear velocity with a uniformly increasing angular velocity. The second segment scans at a uniform angular velocity with a uniformly decreasing linear velocity. The light intensity attenuation and the change in the spot size are matched with the linear velocity and angular velocity during the scanning process.

[0049] The reflected light collection component is used to collect the light reflected from the wafer surface. The reflected light collection component is connected to the central control unit 124, which is used to analyze and process the reflected light information to ensure that the illumination laser energy obtained per unit pixel per unit time on the wafer remains consistent during the imaging process.

[0050] A scattered light collection component is used to collect scattered light emitted from the wafer and transmit it to an image processor for processing.

[0051] The light source body 101 (not shown in the figure) is used to provide the illumination beam required for detection. The light source body 101 (not shown in the figure) can be of various types, such as LED light sources, laser light sources, or plasma light sources. Correspondingly, the wavelength range of the light source can also be selected according to specific application requirements, including broadband, ultraviolet (UV), deep ultraviolet (DUV), or extreme ultraviolet (EUV) bands commonly used in semiconductor detection equipment. This embodiment does not impose specific limitations and can be selected according to actual conditions. For ease of explanation, the light source body 101 in this embodiment preferably adopts a single-wavelength continuous output DUV light source, specifically configured as linearly polarized. The linearly polarized light emitted by the DUV light source is first incident on the half-wave plate 102. By precisely rotating the angle of the half-wave plate 102, the polarization direction of the transmitted beam can be controlled, thereby obtaining the specific polarization angle required to irradiate the wafer surface. The polarization-modulated beam then enters the beam expander and shaper assembly 200, which performs optical processing on the beam, including beam expansion, collimation, focusing, and light field distribution shaping. In this embodiment, the output beam processed by the beam expander and shaper assembly 200 forms a specific spot shape on the wafer surface, preferably a square strip-shaped focused spot with uniform energy distribution. The wafer inspection process is completed by scanning the focused spot on the wafer.

[0052] Regarding the technical solution of this embodiment, such as Figure 2 As shown, the beam expanding and shaping component 200 includes, in sequence along the beam propagation direction: beam expander 201, collimator 202, microlens array 203 and focusing lens group 204. Its function is to shape and focus the incident beam into a focused beam with a specific shape (such as a square strip-shaped light spot) and uniform energy distribution, and finally project it onto the wafer surface for illumination scanning.

[0053] Specifically, the parallel beam emitted after modulation by the upstream optical element half-wave plate 102 first enters the beam expander 201. After being processed by the beam expander 201, the beam becomes divergent. This divergent beam then enters the collimator 202, and after being re-collimated by the collimator 202, it is output as a parallel beam with an increased diameter. This parallel beam with an increased diameter then enters the microlens array 203. The microlens array 203 has a key structural feature: its central region is composed of densely arranged microlens units, forming an effective light-transmitting area (or microlens working area), the shape of which is designed to match the morphology of the target light spot, preferably square in this embodiment; while the peripheral region surrounding the central effective light-transmitting area... This area is constructed as a light-blocking region (or non-transparent region). Through this structural design, the microlens array 203 selectively transmits and splits the incident parallel beam, allowing only the sub-beams passing through the central square region to continue propagating. This initially forms a square light spot prototype (or central light spot) corresponding to the shape of the effective transparent area on or near the output surface of the microlens array 203. Subsequently, the beam emitted from the microlens array 203 (i.e., the beam with a square outline) is incident on the focusing lens group 204. Then, the focusing lens group 204 performs final focusing on the square beam, precisely adjusting its size to the specifications required for detection, and then accurately projects the square strip focused light spot onto the wafer surface to be inspected.

[0054] Compared to beam shaping techniques using diffractive optical elements (DOEs), the beam expanding and shaping component 200 used in this embodiment has significant advantages: the segmentation-superposition principle of the microlens array facilitates the homogenization of the light field, enabling the formation of square strip-shaped focused light spots with higher energy distribution uniformity. The highly uniform illumination spot directly acts on the wafer surface, significantly reducing image grayscale fluctuations or artifacts caused by uneven illumination. The highly uniform illumination spot is beneficial for the subsequent time delay integration (TDI) camera to acquire reflected or scattered light signals. Uniform illumination ensures that the signal intensity received by different pixels is more consistent during the line-by-line scanning integration process of the TDI camera, thereby effectively improving the contrast, sharpness, and signal-to-noise ratio of the final acquired image.

[0055] Furthermore, the reflected light collection component is configured as collector 104. After the incident light is reflected from the wafer surface, it is collected by collector 104. Collector 104 transmits the information to the central control unit 124 for further information analysis and processing, such as... Figure 12As shown, the collector 104 includes an attenuation OD sheet 1041 and an energy detector PD 1042, which are used to collect and analyze the reflected light energy to ensure that the illumination laser energy obtained per unit pixel per unit time on the wafer remains consistent during the imaging process. On the one hand, the collector 104 can prevent the reflected light from affecting the detection results after multiple reflections in the system. On the other hand, it can further analyze the collected light, such as the shape of the light spot and energy, so that the system can monitor the incident light system in real time.

[0056] Regarding the technical solution of this embodiment, the spiral motion control component is used to drive the stage (not shown in the figure) carrying the wafer to move in order to execute a specific scanning motion trajectory. In this embodiment, the spiral motion control component mainly includes: a linear motion stage 107, a rotary motion stage 108, and a controller 106. The controller 106 is electrically connected to the linear motion stage 107 and the rotary motion stage 108 respectively (e.g., through a cable or bus) and performs coordinated control on them.

[0057] Specifically, the controller 106 is configured to output a control signal to the linear motion table 107 to drive it to perform reciprocating or unidirectional linear motion along a preset linear direction (e.g., the Z-axis direction).

[0058] The control signal is output to the rotary motion stage 108 to drive it to rotate around a preset rotation axis (e.g., an axis parallel to the direction of linear motion); the motion relationship between the displacement (velocity) of the linear motion stage 107 and the angular displacement (angular velocity) of the rotary motion stage 108 is coordinated in real time so that the composite motion trajectory synthesized by the two motion stages forms a precise spiral scanning curve.

[0059] Regarding the technical solution of this embodiment, the scattered light collection component includes an objective lens 109 disposed above the wafer, and a first relay mirror 110, a first beam splitter 111, a second beam splitter 112, and a reflector 119 are coaxially disposed along the light transmission direction. The objective lens 109 must have the ability to capture scattered signals of a wide range of angles (including high angles) generated by the wafer surface. This is crucial for detecting minute defects (such as nanoscale particles, scratches, or pattern defects), because such defects often generate scattered signals with weak intensity and wide angular distribution. In the solution of this embodiment, the objective lens 109 with an NA of 0.9 or higher ensures that as many scattered photons as possible can be collected, thereby significantly improving the signal intensity and signal-to-noise ratio (SNR), providing a basis for subsequent high-sensitivity detection. It should be noted that the objective lens can include various forms of objective lens design, such as a high NA refractive objective lens or a catadioptric objective lens with reflective lenses. This embodiment does not make specific limitations here.

[0060] Furthermore, the collection channels are configured with three channels: a first channel, a second channel, and a third channel. The light source from the first relay mirror 110 is split into two beams after passing through the first beam splitter 111. One beam is transmitted to the first channel, and the other beam is transmitted to the second beam splitter 112. The beam transmitted to the second beam splitter 112 is split into two beams again and transmitted to the second channel and the third channel, respectively. The first channel, the second channel, and the third channel are respectively arranged with a second relay mirror 113, a focusing lens 114, and a detector 115 along the beam propagation direction. The second relay mirror 113 relays and optimizes the aberrations of the received scattered beam to ensure beam quality and adapt to subsequent optical components. The focusing lens 114 accurately focuses the relayed beam onto the photosensitive surface of the corresponding detector. The detector 115 converts the focused scattered light signal into an electrical signal. The detector can be a high-sensitivity photomultiplier tube (PMT), an avalanche photodiode (APD) array, a scientific-grade CCD / CMOS, or a sensor specifically designed for a particular wavelength (such as DUV).

[0061] Detector 115 is connected to image processor 123, and image processor 123 is connected to central control unit 124, facilitating further analysis after detecting each beam, such as... Figure 13 As shown, the three channels collect scattered light from three different regions. The collected light forms a large circular area across the entire field of view. This area can be blocked using masks, allowing region one to enter the first channel, region two to enter the second channel, and region three to enter the third channel. Specifically:

[0062] Scattered light from Region 1 (the central circular region) enters the first channel, mainly corresponding to near-mirror reflection or small-angle scattering;

[0063] The scattered light from region two (the middle annular region) enters the second channel, mainly corresponding to medium-angle scattering;

[0064] The scattered light from region three (the outer ring region) enters the third channel, mainly corresponding to large-angle scattering.

[0065] This spatial angle partitioning collection strategy enables different channels to specifically capture scattered light with angular distribution characteristics generated by different types of defects (such as microparticles, shallow scratches, deep grooves, and graphic defects), greatly enhancing the system's defect discrimination ability and classification accuracy.

[0066] It should be noted that the purpose of the repeater mirror is to lengthen the optical path of the entire collection channel, thereby creating space for the placement of various optical components in the optical path system, and also facilitating subsequent engineering design. Figure 1The relay lens shown here consists of only two lenses and is for illustrative purposes only. In actual practice, the design of a relay lens needs to consider minimizing aberrations during the optical path propagation process in order to improve image quality and enable better defect detection in the future.

[0067] It should be further explained that after the detector 115 collects the signal, it transmits it to the corresponding image processor 123, which processes the signal. Figure 1 The above is just an example. In practice, the number of image processors can be matched according to the amount of data from the detector. For example, one image processor can be equipped with the amount of data from one detector, or multiple image processors 123 can be equipped with the amount of data from one detector. Finally, the central control unit 124 controls the entire system. The central control unit 124 is the carrier of the entire system software and also the carrier of the human-machine interface with the system user. The final defect detection results can be obtained through the central control unit 124 and further processed.

[0068] Regarding the technical solution of this embodiment, Figure 3 The diagram illustrates the specific principle of spiral scanning of a wafer. During the spiral scanning inspection process, a scanning spiral is formed, and the illumination spot is a long, rectangular spot. The figures show 301 and 302, representing different positions of the same spot on the wafer, corresponding to radii R1 and R2 from the wafer center, respectively. The relationship between angular velocity and linear velocity follows the following formula:

[0069] (1)

[0070] Therefore, if the angular velocity (ω, i.e., rotational speed) is kept constant during the scanning process, the linear velocity at different radii (such as R1 and R2) will have significant differences (V1 / V2 = R1 / R2). However, the key sensors used in this system, such as the time-delay integration camera (TDI), usually require the target's linear velocity (V) to remain constant when acquiring data along its scanning direction. This is because the charge transfer rate (line frequency) of the TDI camera is fixed, and the linear velocity (V) must be precisely matched with the line frequency (i.e., V = pixel size × line frequency) in order to achieve blur-free cumulative integration imaging. Changes in linear velocity will cause image blurring, stretching, or compression.

[0071] Therefore, in order to obtain accurate and usable detection data, it is ideal to ensure that the linear velocity (V) of the target relative to the detector remains constant throughout the entire scan path (uniform linear velocity scan).

[0072] Achieving uniform linear velocity scanning theoretically requires that, during the helical scanning process, the angular velocity (ω) must continuously increase as the scanning radius (R) decreases (because ω = V / R). However, this requirement presents significant challenges in practical engineering implementation.

[0073] Rotary mechanism limit: When the scan approaches the center of the circle (R approaches 0), the required angular velocity (ω) theoretically approaches infinity, which far exceeds the maximum speed capability of physical rotating mechanisms (such as motors and bearings).

[0074] Dynamic performance and stability: Extremely high and continuously changing acceleration requirements will place a huge burden on the motion control system, making it difficult to guarantee motion smoothness and positioning accuracy, and may also cause vibration, which will reduce image quality.

[0075] System complexity and cost: Designing a rotating shaft and drive system capable of withstanding extreme speeds and accelerations significantly increases engineering difficulty, complexity, and cost;

[0076] To effectively resolve the contradiction between the sensor data acquisition requirements and the physical limitations of the rotating mechanism, this embodiment innovatively proposes a segmented variable-speed spiral scanning control strategy. This strategy divides the entire spiral scanning trajectory into two segments with different motion characteristics. The first segment extends from the outer edge of the wafer to a radius R1. Within this segment, the controller 106 dynamically adjusts the angular velocity ω of the rotating stage 108, such that the angle... The linear velocity gradually increases while remaining constant. Within a fixed scanning time interval, the arc length (linear velocity integral) of the scan point movement is equal, but the rotation angle (angular displacement) gradually increases. The second segment extends from the radius R2 to the center of the circle. In this area, the controller 106 fixes the angular velocity ω of the rotating motion stage 108, causing the linear velocity V to gradually decrease. Within a fixed scanning time interval, the rotation angle (angular displacement) of the scan point movement is equal, but the arc length (linear velocity integral) gradually decreases.

[0077] The following discussion uses a time-delay integration camera as an example to further design the detector, focusing on the second scan segment. Within the second scan curve, the wafer rotates at a uniform angular velocity. The relationship between the speed limit, the line frequency f, and the pixel size PixelSize in the scan direction is shown in the following formula:

[0078] (2)

[0079] Substituting equation (2) into equation (1), we can obtain the relationship between the travel frequency, angular velocity, and radius:

[0080] (3)

[0081] The second stage begins at a radius of 25mm, with the line frequency changing linearly until the radius reaches 0.

[0082] As attached Figure 5 As shown, a time-delay integration camera can use an external triggering method to input changes in line frequency. Each time a trigger signal (lookup table input frequency) is received, an electron moves downwards by one pixel. The external signal is based on... Figure 4 A lookup table (LUT) is established to establish the relationship between the scan time and the line frequency, namely the TDI line frequency change table over time. Specifically, the line frequency relationship is linearly related to the scan time. The TDI line frequency is input through the lookup table, enabling the TDI to achieve variable line frequency acquisition, thereby ensuring that the line frequency matches the linear speed.

[0083] In dark-field wafer inspection, the presence and size of defects are determined by acquiring the energy of scattered photons. Therefore, it is crucial to maintain a consistent incident energy per unit time throughout the entire inspection process to ensure that the scattered energy accurately reflects the defect size. However, in the second stage of the inspection process described above, uniform angular velocity motion is used, and the linear velocity gradually decreases, resulting in a longer scanning time per pixel. If the incident laser energy remains constant during this process, the light intensity received by each pixel per unit time will increase. This makes it impossible to accurately determine the size of the scanned particles based on the intensity of the scattered signal. Figure 6 This graph shows the relationship between light intensity and scanning time during the second-stage scanning process. It also shows that the light intensity and scanning time have a linear relationship. The light intensity is in a normalized unit, with the unit set to 1 for the first-stage scanning.

[0084] like Figure 7 As shown, since the light intensity also needs to change constantly, an attenuator mechanism 501 needs to be placed in the optical path system to ensure that the illumination laser energy obtained per unit pixel per unit time on the wafer remains consistent during the imaging process. The attenuator mechanism 501 is a linear polarizer controlled by a rotary motor. The linear polarizer is installed at the output end of the rotary motor, and the controller 502 is used to control the rotary motor. The incident light is linearly polarized light. By starting the rotary motor to drive the polarizer to rotate, the optical axis direction of the polarizer can be controlled to be parallel to the polarization direction of the incident light. In the first scanning stage, the optical axis direction of the polarizer is made parallel to the polarization direction of the incident light. In the second scanning stage, the linear polarizer is controlled to rotate, thereby controlling the light transmission power to be aligned with the attached... Figure 6 The resulting lookup table of scanning time and light intensity is used to attenuate and control the light intensity.

[0085] During wafer inspection, the incident light spot 301 has a certain width, such as 3mm. This is to ensure the overall system yield; a larger spot would shorten the scanning time per wafer. However, a larger spot would bring additional problems, as shown in the attached figure. Figure 8 The diagram shows the scanning behavior of a light spot at a radius of R3. As analyzed earlier, in the inner circle, the system scans at a uniform angular velocity, assuming the angular velocity is... As attached Figure 8 As shown, assuming the linear velocities of the light spot at the far end and near end of the rotation center are V3 and V4 respectively, and the radii of the far end and near end are R3+1.5mm and R3-1.5mm respectively, the linear velocities V3 and V4 are respectively calculated according to equation (1):

[0086] (4)

[0087] (5)

[0088] When R3=5mm, the difference in linear velocity between V3 and V4 is 1.85 times according to the above formula. As described above, when scanning with variable line frequency, the line frequency of the TDI camera is determined by the center position of the spot. This will result in a difference in linear velocity between the two ends relative to the center of more than 40%. Under these circumstances, the image scanned by TDI will show a clear center and a blurry end.

[0089] To address the aforementioned issues, the spot width needs to be adjusted within the inner ring. For example, a condition can be set for the spot width: the difference in linear velocity between the two ends of the spot can be less than 5%. This will yield a curve showing the change in spot width over scanning time, as shown in the attached figure. Figure 9 As shown.

[0090] Therefore, in the entire optical path system, the spot size needs to be controlled according to the scanning process, as shown in the attached figure. Figure 7 and Figure 14As shown, the lighting source assembly also includes a controllable aperture 503. This controllable aperture 503 is driven by a servo motor 5031 to simultaneously move two baffles. 504 is the controller for the controllable aperture 503. Specifically, the controllable aperture 503 includes two baffles (left baffle 5037 and right baffle 5035), a coupling 5032, a servo motor 5031, a positive threaded rod 5033, and a negative threaded rod 5034. Below the left and right baffles is a... A guide rail 5036 is provided, with a positive threaded rod 5033 and a negative threaded rod 5034 threaded to its upper part respectively. The positive threaded rod 5033 and the negative threaded rod 5034 are coaxially fixed and fixed to the output shaft of the servo motor 5031 through a coupling 5032. When the servo motor 5031 is started, it drives the positive threaded rod 5033 and the negative threaded rod 5034 to rotate through the coupling 5032. The threaded engagement relationship allows the left and right baffles to open or close, thereby enabling operation according to the attached... Figure 9 The change curve in the image is used to form a lookup table. During the wafer inspection process, the size of the spot width is controlled to achieve the function of scanning the change in spot width.

[0091] Because of the added variable of light spot variation, if scanning the entire wafer area is still required, the scanning curve needs to be changed from an equidistant spiral to a non-equidistant spiral during the uniform angular velocity stage. In this case, it is necessary to adjust the attached... Figure 4 With appendix Figure 6 The relationship between TDI line frequency and light intensity as a function of scanning time has been corrected from a linear relationship to a non-linear relationship to ensure matching. The corrected curves of TDI line frequency and light intensity as a function of scanning time are shown in the attached figure. Figure 10 and Figure 11 As shown.

[0092] In summary, this embodiment optimizes the inner-circle scanning process of the wafer inspection system based on spiral scan lines, adjusts the light intensity and size of the bar scanning spot in real time, and synchronously adjusts the line frequency of the time-delay integration camera in real time, thereby achieving the continuity of the entire scanning process and ensuring that the inner-circle scanning image is consistent with the outer-circle scanning image, which facilitates subsequent image processing and recognition.

[0093] Example 2:

[0094] The fundamental difference between Embodiment 2 and Embodiment 1 is that: the attenuator mechanism 501 is an acousto-optic deflector (AOD), using its first-order light to coincide with the optical axis, while the 0th-order light is attenuated using an optical stop. 502 is the controller for the acousto-optic deflector, emitting the required waveform signal to control the attenuator mechanism 501 according to the attached... Figure 6 A lookup table of scanning time and light intensity is generated and controlled in real time until the scanning is completed.

[0095] Example 3:

[0096] like Figure 15 As shown, this embodiment provides a method for detecting dark field defects in patternless semiconductor wafers, using a dark field defect detection system for patternless semiconductor wafers described in Embodiment 1. The specific steps are as follows:

[0097] S1. First stage of spiral scanning, outer ring uniform linear velocity scanning:

[0098] Starting from the outer edge of the wafer, the wafer begins to be scanned at a uniform linear velocity by a linear motion stage and a rotary motion stage. At this time, the scanning spot size, TDI line frequency, and spot laser power remain unchanged, while the rotation axis angular velocity of the rotary motion stage gradually increases.

[0099] S2. Second stage of spiral scanning: uniform angular velocity scanning in the inner circle, with the difference in linear velocity between the center and edge of the light spot being less than 5%.

[0100] When it enters a position with a radius of R1 from the center of rotation, the rotating axis moves at a constant angular velocity. At this time, the size of the scanning spot remains unchanged, the linear velocity begins to gradually decrease, the TDI line frequency begins to gradually decrease, and the spot laser power also begins to gradually decrease in sync.

[0101] S3. Second stage of spiral scanning: uniform angular velocity scanning in the inner circle, with a linear velocity difference of more than 5% between the center and edge of the light spot.

[0102] When the laser reaches a position with a radius of R2 from the center of rotation, the radius of the scanning area from the center of the wafer decreases further, and the difference in linear velocity between the center of the spot and the edge of the spot is greater than 5%. At this time, the rotating axis still moves at a uniform angular velocity with a fixed angular velocity as in step S2, and gradually reduces the TDI line frequency and the laser power of the spot while using a variable aperture to gradually reduce the spot size until the scanning ends.

[0103] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0104] For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances. When an element is referred to as being "assembled on," "mounted on," "fixed to," or "set on" another element, it may be directly on the other element or there may be an intermediate element present. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element present. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible embodiments.

[0105] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0106] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

Claims

1. A semiconductor patternless wafer dark field defect detection system, applied to wafer defect detection, characterized in that, include: The illumination source assembly includes a light source body, an attenuator set along the optical propagation path, and a controllable aperture. The attenuator is used to control the attenuation of light intensity during wafer scanning to ensure that the illumination laser energy obtained per unit pixel per unit time on the wafer remains consistent during imaging. The controllable aperture is used to control the spot size according to the scanning process. The beam expanding and shaping component is used to expand and shape the laser beam provided by the illumination source component to obtain a square strip-shaped light spot that illuminates the wafer surface. The spiral motion control component is located below the wafer and is used to control the movement of the wafer to achieve spiral scanning of the wafer; The spiral motion control component includes a rotary table, a linear table, and a controller. The rotary table, linear table, and controller are electrically connected. The rotary table and linear table move in coordination to achieve spiral scanning of the wafer. The spiral scanning is divided into two segments from the outer side of the wafer inward. The first segment scans at a uniform linear velocity with a uniformly increasing angular velocity. The second segment scans at a uniform angular velocity with a uniformly decreasing linear velocity. The light intensity attenuation and spot size change are matched with the linear velocity and angular velocity during the scanning process. The line frequency of the delay integration camera is adjusted synchronously in real time to achieve the continuity of the entire scanning process. The inner circle scanning image is consistent with the outer circle scanning image. The reflected light collection component is used to collect the light reflected from the wafer surface. The reflected light collection component is connected to a central control unit for analyzing and processing the reflected light information. A scattered light collection component is used to collect scattered light emitted from the wafer and transmit it to an image processor for processing. The reflected light collection component is configured as a collector, which includes an attenuation OD sheet and an energy detector PD, used to collect and analyze the reflected light energy to ensure that the illumination laser energy obtained per unit pixel per unit time on the wafer remains consistent during the imaging process; During the spiral scanning process, the light intensity and size of the square strip light spot are adjusted in real time, and the line frequency of the time-delay integration camera is adjusted synchronously in real time, thereby achieving the continuity of the entire scanning process and ensuring that the inner circle scanning image is consistent with the outer circle scanning image.

2. The semiconductor patternless wafer dark field defect detection system according to claim 1, characterized in that: The light source body is configured as a UV light source, a DUV light source, or an EUV light source.

3. The semiconductor patternless wafer dark field defect detection system according to claim 2, characterized in that: A half-wave plate is provided between the beam expanding and shaping component and the illumination source component. The beam expanding and shaping component includes a beam expander, a collimating lens, a microlens array, and a focusing lens in sequence along the beam propagation direction. The parallel beam emitted by the illumination source is diverged by the beam expander and then collimated again by the collimating lens into a parallel light source with a larger diameter. The parallel light is then incident on the microlens array to form a square strip-shaped light spot. Finally, the light spot is focused by the focusing lens group and incident on the wafer surface.

4. The semiconductor patternless wafer dark field defect detection system according to claim 3, characterized in that: The scattered light collection assembly includes an objective lens positioned above the wafer, and a first relay mirror, a first beam splitter, a second beam splitter, and a reflector are coaxially arranged along the light transmission direction.

5. The semiconductor patternless wafer dark field defect detection system according to claim 4, characterized in that: The collection channels are set to three, namely the first channel, the second channel and the third channel. The light source from the first relay mirror is split into two beams after passing through the first beam splitter. One beam is transmitted to the first channel and the other beam is transmitted to the position of the second beam splitter. The beam transmitted to the second beam splitter is split into two beams again and transmitted to the second channel and the third channel respectively.

6. The semiconductor patternless wafer dark field defect detection system according to claim 5, characterized in that: A second relay mirror, a focusing lens, and a detector are sequentially arranged along the beam propagation direction in the first, second, and third channels. The detector is connected to the image processor, and the image processor is connected to the central control unit.

7. The semiconductor patternless wafer dark field defect detection system according to claim 6, characterized in that: The lighting source assembly also includes an attenuator and a controllable aperture. The attenuator is configured as a linear polarizer controlled by a rotating motor. The rotating motor is electrically connected to a motor controller. Starting the rotating motor drives the linear polarizer to rotate, thereby controlling the light transmission power and achieving controlled attenuation of light intensity.

8. The semiconductor patternless wafer dark field defect detection system according to claim 7, characterized in that: The controllable aperture includes a left baffle, a right baffle, a coupling, a servo motor, a positive threaded rod, and a negative threaded rod. Guide rails are provided below the left and right baffles, and are threadedly connected to the positive and negative threaded rods above, respectively. The positive and negative threaded rods are coaxially fixed and fixed to the output shaft of the servo motor through the coupling. When the servo motor is started, it drives the positive and negative threaded rods to rotate through the coupling. The left and right baffles can be opened or closed by utilizing the threaded engagement relationship, thereby controlling the size of the light spot.

9. A method for detecting dark field defects in patternless semiconductor wafers, employing the dark field defect detection system for patternless semiconductor wafers according to any one of claims 1 to 8, characterized in that, The specific steps are as follows: S1. Starting from the outer edge of the wafer, the wafer is driven by a linear motion stage and a rotary motion stage to begin scanning at a uniform linear velocity. At this time, the scanning spot size, TDI line frequency, and spot laser power remain unchanged, while the rotation axis angular velocity of the rotary motion stage begins to gradually increase. S2. When it enters a position with a radius of R1 from the center of rotation, the rotating axis moves at a constant angular velocity. At this time, the size of the scanning spot remains unchanged, the linear velocity begins to decrease, the TDI line frequency begins to gradually decrease, and the spot laser power also begins to decrease synchronously. S3. When the distance from the rotation center radius is R2, the radius of the scanning area from the wafer center is further reduced, and the difference in linear velocity between the center of the spot and the edge of the spot is greater than 5%. At this time, the rotation axis still moves at a uniform angular velocity at the fixed angular velocity in step S2, and while reducing the TDI line frequency and the spot laser power, the spot size is gradually reduced using a variable aperture until the scanning ends.

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