Wafer focusing system

Abstract

The application discloses a wafer focusing system, comprising: a focus-pursuing sensor, a focusing controller, a photoelectric acquisition board, a fine adjustment motor and a motor controller; the focusing controller is used for acquiring an out-of-focus height analog signal of a target wafer from the focus-pursuing sensor to generate and output a predicted focusing position analog signal to the motor controller; the motor controller is used for controlling the fine adjustment motor to move to pursue the focus based on the predicted focusing position analog signal, and sending an objective lens position analog signal to the photoelectric acquisition board based on a measured objective lens movement position; the photoelectric acquisition board is used for synchronously acquiring a light beam interference analog signal to generate and output a focusing digital signal to the focusing controller when the objective lens position analog signal is received; and the focusing controller is further used for generating an indication signal indicating a measured objective lens focusing position based on the focusing digital signal and sending the indication signal to the motor controller through a digital signal interface, so that the target wafer alignment error measurement efficiency is high, the signal acquisition time is short, the indication signal accuracy is high, and the applicability is strong.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor technology, and in particular to a wafer focusing system. BACKGROUND

[0002] Semiconductor detection technology plays an important role in the processes of semiconductor production, packaging and testing, and the measurement of alignment error is an important part of the key process in the semiconductor production process. The alignment error is one of the most important errors that need to be controlled in the key process, which refers to the pattern alignment error between the previous layer and the current layer in the key process operation process, and there is a certain distribution rule on the wafer and the exposure field. In order to ensure that the alignment error is within the threshold range, after each batch of wafer exposure, a lot of alignment error measurements of mark points need to be performed on the overlay measurement machine, and the measurement values are processed by mathematics to obtain the distribution model (overlay model terms) of the alignment error, which is fed back to the semiconductor production equipment for alignment error control of the next batch of wafer exposure. In order to obtain the distribution rule of the alignment error on the wafer and the exposure field, the mark points for alignment error measurement need to be distributed as evenly as possible on the whole wafer, and the wafer measurement image containing the information of the previous layer and the current layer (i.e. the wafer scanning image containing the alignment error measurement mark points) is obtained by a camera during the alignment error measurement process, and the alignment error is obtained through the wafer measurement image. Therefore, in order to improve the measurement accuracy of the alignment error, the positioning accuracy of the wafer measurement image acquisition also has very high requirements, and high-precision wafer image scanning positioning technology and auto-focusing technology are needed.

[0003] In the process of improving the positioning accuracy of wafer image scanning, a focusing operation can be performed once before and after the positioning operation of the mark points for alignment error measurement by using white light interference focusing. White light interference focusing is a focusing technology with extremely high precision (about 10 nm), but it needs a large-load and large-stroke Z motor (i.e. precision motor) to perform a scanning motion of about 20 um stroke each time, which leads to the consumption of 70 ms~80 ms of time for each flow of white light interference focusing, and twice white light interference focusing makes the acquisition of wafer measurement image time-consuming and the alignment error measurement efficiency of the wafer low. In addition, the acquisition of the light beam interference signal is not synchronized with the acquisition of the position signal of the measurement objective lens during the white light interference focusing process, which leads to the need to wait for the completion of the acquisition of both types of signals before predicting the focusing position, the signal acquisition time is long, and the asynchronization of signal acquisition will lead to low accuracy of the focusing position predicted by the light beam interference signal and the position signal of the measurement objective lens, and poor applicability. SUMMARY

[0004] This application provides a wafer focusing system that can improve the efficiency of measuring alignment error of the target wafer, reduce the signal acquisition time of beam interference signal and measurement objective lens position signal, improve the accuracy of predicted focusing position, and has strong applicability.

[0005] In a first aspect, embodiments of this application provide a wafer focusing system, including: a focus sensor, a focus controller, a photoelectric acquisition board, a fine-tuning motor, and a motor controller; the focus controller is configured to: acquire a defocus height analog signal of the target wafer from the focus sensor, generate a predicted focus position analog signal of the target wafer based on the defocus height analog signal, and send the predicted focus position analog signal to the motor controller; the motor controller is configured to: control the fine-tuning motor to drive the measurement objective lens to move to focus on the target wafer based on the predicted focus position analog signal, and send an objective lens position analog signal to the photoelectric acquisition board based on the movement position of the measurement objective lens; the photoelectric acquisition board is configured to: simultaneously receive the objective lens position analog signal and... The method involves acquiring a simulated beam interference signal, which is used to: indicate the intensity of the beam obtained by beam interference at the photoelectric acquisition plate during the movement of the measurement objective lens; generate a focusing digital signal based on the simulated beam interference signal and the simulated objective lens position, and send the focusing digital signal to the focusing controller; the focusing controller is further used to: generate an indication signal indicating the focusing position of the measurement objective lens based on the peak intensity of the beam indicated by the focusing digital signal and the movement position of the measurement objective lens, and send the indication signal to the motor controller; the indication signal is used to: trigger the motor controller to control the fine-tuning motor to drive the measurement objective lens to the focusing position to focus the target wafer.

[0006] This implementation method allows for the acquisition of a defocus height analog signal via a focus tracking sensor. The focus controller then generates a predicted focus position analog signal based on this signal to trigger the fine-tuning motor for focus tracking. This eliminates the time required for acquiring beam interference signals and measuring objective lens position signals via white light interferometry, thereby improving the efficiency of target wafer alignment error measurement. Furthermore, a photoelectric acquisition board can simultaneously acquire beam interference analog signals and objective lens position analog signals to generate a focus digital signal. This focus digital signal is used to generate a focus position indication signal, triggering the fine-tuning motor to focus on the target wafer. This improves the accuracy of the predicted focus position and offers broad applicability.

[0007] In one possible implementation of the first aspect, the focus controller includes a first analog-to-digital conversion module, a digital-to-analog conversion module, and a microcontroller; the microcontroller is connected to the first analog-to-digital conversion module and the digital-to-analog conversion module; the first analog-to-digital conversion module is configured to: acquire the defocus height analog signal from the focus tracking sensor, perform analog-to-digital conversion on the defocus height analog signal, and send the defocus height digital signal to the microcontroller; the microcontroller is configured to: generate a predicted focus position digital signal based on the defocus height digital signal and send the predicted focus position digital signal to the digital-to-analog conversion module; the digital-to-analog conversion module is configured to: perform digital-to-analog conversion on the predicted focus position digital signal to generate the predicted focus position analog signal, and output the predicted focus position analog signal to the motor controller. This implementation method allows the analog defocus height signal to be converted into a digital defocus height signal via an analog-to-digital converter for digital signal processing. Since digital signals are more accurate than analog signals, the processing is simpler and has stronger anti-interference capabilities, thus improving the accuracy of the generated predicted focus position digital signal. Furthermore, the predicted focus position digital signal can be converted into a predicted focus position analog signal via digital-to-analog conversion to control devices such as motor controllers. Controlling via analog signals avoids encoding conversion between two digital signal interfaces using different protocols, resulting in faster control speed and further improving the efficiency of alignment error measurement of the target wafer.

[0008] In one possible implementation of the first aspect, the photoelectric acquisition board includes a first isolation circuit, a second isolation circuit, a photodiode, and a second analog-to-digital converter module; the second analog-to-digital converter module is connected to the first isolation circuit and the second isolation circuit, and the second isolation circuit is connected to the photodiode; the first isolation circuit is used to: receive the objective lens position simulation signal from the motor controller, and output a target objective lens position simulation signal to the second analog-to-digital converter module based on the objective lens position simulation signal; the second isolation circuit is used to: acquire the beam interference simulation signal corresponding to the beam intensity obtained by beam interference on the photodiode during the movement of the measurement objective lens, and output a target beam interference simulation signal to the second analog-to-digital converter module based on the beam interference simulation signal; the second analog-to-digital converter module is used to perform analog-to-digital conversion on the target objective lens position simulation signal and the target beam interference simulation signal to generate the focusing digital signal and send the focusing digital signal to the focusing controller. In this implementation, the motor controller and the second digital-to-analog converter module can be isolated by a first isolation circuit, and the photodiode and the second digital-to-analog converter module can be isolated by a second isolation circuit. This reduces signal interference and improves the accuracy of the focus digital signal, thereby further improving the accuracy of the focus position generated based on the focus digital signal.

[0009] In one possible implementation of the first aspect, the first isolation circuit includes a first operational amplifier, a connector, and a first resistor. The first resistor connects a first connection terminal and a second connection terminal of the first operational amplifier. The second connection terminal of the first operational amplifier serves as the output terminal of the first isolation circuit. The first and third connection terminals of the first operational amplifier serve as the input terminals of the first isolation circuit. The third connection terminal of the first operational amplifier is grounded through the connector. The fourth and fifth connection terminals of the first operational amplifier are connected to a power supply. Using this implementation, a first isolation circuit (i.e., a follower circuit) for signal isolation can be formed based on the first operational amplifier, and the motor controller and ground can be connected through the connector. Furthermore, the electronic components in the first isolation circuit are lightweight, flexible in installation, and highly adaptable.

[0010] In one possible implementation of the first aspect, the second isolation circuit includes a second operational amplifier, a second resistor, a third resistor, and a capacitor. The second resistor connects the first and second terminals of the second operational amplifier, which serve as the input terminals of the second isolation circuit. The first terminal of the second operational amplifier is connected to the photodiode, and the third and fourth terminals are connected to a power supply. The first terminal of the third resistor is connected to the second terminal of the second operational amplifier, which serves as the output terminal of the second isolation circuit. The capacitor connects the fifth terminal of the second operational amplifier and the second terminal of the third resistor, and the fifth terminal of the second operational amplifier is grounded. Using this implementation, a second isolation circuit (i.e., a follower circuit) for signal isolation can be formed based on the second operational amplifier. The electronic components in the second isolation circuit are lightweight, flexible in placement, and highly adaptable.

[0011] In one possible implementation of the first aspect, the system further includes a first beam splitter, a second beam splitter, and a third beam splitter. The aforementioned focus sensor is configured to: emit a first beam, which sequentially passes through the first beam splitter, the second beam splitter, the third beam splitter, and the measurement objective lens before converging on the target wafer; after being reflected by the target wafer, it sequentially passes through the measurement objective lens, the third beam splitter, the second beam splitter, and the first beam splitter before returning to the focus sensor; the focus sensor is further configured to: send at least two defocus height analog signals to the focus controller based on the beam data of the returned first beam; one of the defocus height analog signals is obtained from a received beam data of the first beam, and the defocus height analog signal is converted into a defocus height digital signal after analog-to-digital conversion; the beam data includes at least one of spot size, shape, or light intensity signal; the focus controller is further configured to: perform digital signal processing on the at least two defocus height digital signals to generate the focus feedback parameters, and generate the predicted focus position digital signal based on the focus feedback parameters; the digital signal processing includes at least one of signal averaging and signal denoising. Using this implementation method, the focus tracking sensor can achieve focus tracking using light tracking devices such as the first beam splitter, the second beam splitter, and the measurement objective lens in the wafer focusing system. Focus tracking can be completed without long-term beam interference focusing, resulting in fast focus tracking speed. This can further improve the efficiency of measuring the alignment error of the target wafer. In addition, the focus tracking sensor and other newly added devices (such as the third beam splitter) are small in size and flexible in installation position, further improving applicability.

[0012] In one possible implementation of the first aspect, the system further includes a light source, a reference objective lens, and a reference reflector; the light source is used to: emit a second beam, the second beam passing sequentially through the third beam splitter and the measurement objective lens and converging on the target wafer, and after being reflected by the target wafer, passing sequentially through the measurement objective lens, the third beam splitter, the second beam splitter, and the first beam splitter and converging on the photoelectric acquisition tube; the second beam also passes sequentially through the third beam splitter and the reference objective lens and converging on the reference reflector, and after being reflected by the reference reflector, passing sequentially through the reference objective lens, the third beam splitter, the second beam splitter, and the first beam splitter and converging on the photoelectric acquisition tube to perform beam interference. Using this implementation, the second beam can be focused onto the photodiode on the photoelectric acquisition board by light-tracking devices such as the first beam splitter, second beam splitter, third beam splitter, measuring objective lens, and reference objective lens to cause beam interference. This allows the second analog-to-digital converter module on the photoelectric acquisition board to simultaneously acquire the beam interference analog signal and the objective lens position analog signal. The acquisition process does not require complex transmission circuits, thus enabling near-end signal acquisition, reducing interference during signal transmission, and improving the accuracy of the focusing digital signal generated based on the beam interference analog signal and the objective lens position analog signal. This further improves the accuracy of the focusing position generated based on the focusing digital signal.

[0013] In one possible implementation of the first aspect, the system further includes a power supply; the power supply is used to power the focus tracking sensor, the focus controller, the motor controller, the photoelectric acquisition board, and the fine-tuning motor.

[0014] In one possible implementation of the first aspect, the system further includes a memory connected to the microcontroller, wherein the memory is used to store program code so that the microcontroller can call the program code stored in the memory to perform digital signal processing. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the wafer focusing system provided in this application;

[0016] Figure 2 This is a schematic diagram of the optical path of the first beam provided in this application;

[0017] Figure 3 This is a schematic diagram of the optical path of the second beam provided in this application;

[0018] Figure 4 This is another schematic diagram of the wafer focusing system provided in this application;

[0019] Figure 5 This is a schematic diagram of the photoelectric acquisition board provided in this application;

[0020] Figure 6 This is a circuit diagram of the first isolation circuit provided in this application;

[0021] Figure 7 This is a circuit diagram of the second isolation circuit provided in this application. Detailed Implementation

[0022] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.

[0023] To facilitate understanding, the following brief explanations are provided for some of the terms:

[0024] 1. Defocus height, also known as defocus amount, refers to the data indicating the focus offset difference when acquiring an image of the target wafer during the scanning process. It can be used to adjust the distance between the target wafer and the measurement objective lens to ensure that the target wafer image achieves a preset sharpness. The preset sharpness refers to the specified value of the target wafer image sharpness, which can be determined according to the specific form of the product.

[0025] 2. Focusing feedback parameters, also known as proportional-integral-derivative (PID) feedback values, are obtained by comparing the difference (i.e., error) between the expected output and the actual output. These feedback PID values ​​can be used to implement feedback PID control via a PID controller, correcting deviations and compensating for the defocus height of the target wafer, thus ensuring system stability and accuracy.

[0026] 3. Fine-tuning motor, also known as a fine-tuning Z-axis motor or Z-axis fine-tuning motor, is a type of motor that can provide high-precision positioning and control. It is usually used in applications that require precise adjustment or positioning. This type of motor has high precision, high stability and good control performance, and can achieve precise adjustment and movement in the Z-axis direction.

[0027] 4. The first beam refers to the beam used by the focus sensor to measure the defocus height of the target wafer, such as structured light, partially coherent light, or laser beam. Among them, structured light typically has a narrow linewidth, which can achieve high contrast and high definition imaging when captured by the focus sensor; partially coherent light is a beam between fully coherent and incoherent light, and its coherence can be controlled by adjusting the light source or using a scatterer; laser is highly coherent monochromatic light with extremely high directionality and brightness, and the phase and frequency of the laser remain consistent in both space and time.

[0028] This application uses structured light as the first beam as an example. The focus sensor can project a specific optical pattern onto the surface of a target wafer by projecting structured light. Then, the focus sensor calculates information such as the height of the target wafer based on the returned beam data (optical signal), thereby reconstructing the entire three-dimensional space to obtain the defocus height of the target wafer. The optical pattern projected by the focus sensor using structured light can be a plane, a grid, a straight line, or other shapes. The focus sensor calculates the height change of the target wafer surface by observing the distortion of the light rays.

[0029] 5. The second beam refers to the beam used to generate beam interference, which is usually a monochromatic laser beam (the aforementioned monochromatic laser beam can also be called a monochromatic beam). For example, the aforementioned monochromatic beam can be a white beam, a red beam, etc. Monochromatic beams have high precision, strong stability, and specific wavelengths and coherence. Specific interference patterns can be generated by adjusting the phase and amplitude of the beam.

[0030] 6. Beam interference refers to beam interference experiments, which generally use monochromatic light beams, such as white light interference and red light interference. Beam interference experiments rely on the phenomenon of light interference, specifically the generation of interference patterns when two monochromatic light beams meet. In this application, a monochromatic light beam (such as white light) is split into two beams by a beam splitter. One beam is reflected by a reference mirror, and the other is reflected by the target wafer. The beams then converge at a photodiode, producing bright and dark fringes. These fringes are caused by the phase difference between the two monochromatic beams, which depends on the optical path difference. The intensity of the interference fringes depends on the optical path difference between the two beams. Based on the brightness of the white light interference fringes and their location, the height of the target wafer can be determined. Interference occurs only when the optical path difference between the reference arm and the measuring arm is within one coherent length of the light source. The backscattered light (i.e., the reflected light from the target wafer) and the reference light (i.e., the reflected light from the reference mirror) will interfere, and the optical path difference will be equal to 0. That is, when the optical paths of the two beams are completely consistent, the coherence intensity reaches its maximum, producing a peak illumination intensity. This signal is the beam interference simulation signal.

[0031] 7. Analog signals are used to indicate voltage, current, etc., in the form of continuously changing physical quantities. Their amplitude, frequency, or phase changes continuously with time. Analog signals have strong time sensitivity, and control can be performed quickly using them.

[0032] 8. Digital signals are used to represent physical quantities in discrete form. They typically transmit information using binary codes ("0" and "1"), have an infinite number of possible values, and can present a smooth and continuous curve based on multiple values. Digital signals are easy for computers to process and store. Processing digital signals offers high accuracy, strong stability, and strong anti-interference capabilities.

[0033] 9. An analog-to-digital converter (ADC) is a device that converts analog signals into digital signals. Its main function is to convert analog signals with continuous time and continuous amplitude into digital signals with discrete time and discrete amplitude. An ADC typically includes four processes: sampling, holding, quantization, and encoding. The first and second ADC modules in this application can be ADCs.

[0034] 10. A digital-to-analog converter (DAC) is a device that converts digital signals into analog signals. It converts discrete signals in binary digital form into analog signals based on a standard (or reference) quantity. A DAC mainly consists of a resistor network, an operational amplifier, a reference power supply, and analog switches. The DAC module in this application can be a DAC.

[0035] The wafer focusing system provided in this application is applicable to wafer focusing scenarios and can also be extended to other scenarios requiring focusing. For ease of description, this application uses a wafer focusing scenario as an example. See [link to application]. Figure 1 , Figure 1 This is a schematic diagram of the wafer focusing system provided in this application. Figure 1 As shown, the wafer focusing system may include a tracking sensor, a focus controller, a photoelectric acquisition board, a fine-tuning motor, and a motor controller.

[0036] In some feasible implementations, the aforementioned focus sensor is used to receive a light beam reflected from the target wafer and generate a defocus height analog signal indicating the defocus height of the target wafer based on the beam data. The beam data includes at least one of spot size, shape, or light intensity signal. Furthermore, the light beam illuminating the surface of the target wafer can be emitted by the focus sensor or by an external light source; this application is not limited to this. The example given is a focus sensor emitting a light beam illuminating the target wafer. For instance, the aforementioned focus sensor can be used to emit a first light beam and, based on the beam data of the returned first beam, feed back the defocus height analog signal of the target wafer to the focus controller.

[0037] Optionally, in some feasible implementations, the first beam can be a structured light, and the focus sensor can illuminate the target wafer with the structured light and calculate the defocus height based on the optical path data of the light spot returned by the structured light. The structured light can be a point structured light, line structured light, or area structured light beam, etc., used to illuminate the target wafer and generate optical path data by reflection from the target wafer; the beam data includes at least one of the light spot size, shape, or light intensity signal of the light spot.

[0038] Optionally, in some feasible implementations, if the first beam is partially coherent light, the wafer focusing system may further include a photomask aligned with the target wafer. The focus sensor can obtain the defocus height using an eccentric photomask method; this method includes calculating the defocus height based on changes in light intensity signals caused by photomask misalignment. For example, after the photomask is aligned with the target wafer, the focus sensor can illuminate the photomask with partially coherent light to generate beam diffraction. The partially coherent light is projected onto the target wafer through the photomask. The focus sensor receives the optical path data reflected from the target wafer and the photomask, and determines the defocus height by analyzing changes in the light intensity signals within the optical path data.

[0039] Optionally, in some feasible implementations, if the first beam is a laser, the wafer focusing system may further include at least two photodiodes. The focus sensor can obtain the defocus height using a differential confocal method, which includes obtaining the defocus height based on the difference between the light intensity signals detected by the two photodiodes. For example, the focus sensor emits a laser and focuses it onto the target wafer. The laser reflected from the target wafer is received by two photodiodes to obtain two light intensity signals. The difference between the two light intensity signals can then be used to determine the wafer's focus position to generate the defocus height of the target wafer.

[0040] Optionally, in some feasible implementations, the first beam can also be other high-intensity beams, and the wafer focusing system can further include a chopper (such as a knife edge). The focus sensor can generate the defocus height using a knife-edge method, which includes: moving the chopper within the laser beam or other high-intensity beam, measuring the phase change of the light intensity signal of the beam passing through the chopper, and then generating the defocus height based on the phase change. For example, the focus sensor can output a laser beam or other high-intensity beam to converge onto the target wafer. After the beam passes through the chopper knife edge, it generates a light intensity signal, and the focus sensor can generate the defocus height by analyzing the phase change of the light intensity signal.

[0041] It should be noted that this application does not limit the type of beam used in the first beam or the method for generating the defocus height. The following explanation uses structured light as the first beam as an example and will not be repeated here. To facilitate understanding of the process by which the focus sensor tracks the first beam, the optical path of the first beam and the processing of the beam data by the focus sensor are described below. See [link to documentation]. Figure 2 , Figure 2 This is a schematic diagram of the optical path of the first beam provided in this application.

[0042] like Figure 2As shown, the optical path of the first beam includes a first beam splitter, a second beam splitter, a third beam splitter, and a measurement objective lens. A focus sensor can be used to emit the first beam. The first beam passes sequentially through the first beam splitter, the second beam splitter, the third beam splitter, and the measurement objective lens before converging on the target wafer. After being reflected by the target wafer, it passes sequentially through the measurement objective lens, the third beam splitter, the second beam splitter, and the first beam splitter back to the focus sensor.

[0043] In some feasible implementations, the focus tracking sensor can acquire beam data of the first beam at regular intervals (e.g., once every 1 second). When the time interval for the focus tracking sensor to acquire beam data is set to a small value (e.g., 0.1 seconds), it can be approximated as real-time acquisition of beam data. Exemplarily, the beam data includes at least one of the following: spot size, spot shape, and light intensity signal. In this implementation, a controller (e.g., a focus controller) for controlling the focus tracking sensor can generate a focus tracking control command to trigger the focus tracking sensor to emit the first beam, so that the focus tracking sensor acquires at least two defocus height analog signals of the target wafer based on the beam data. One defocus height analog signal can be converted into a defocus height digital signal through analog-to-digital conversion. The defocus height indicated by the aforementioned defocus height analog signal or defocus height digital signal can be distinguished by "+" and "-". For example, if the target wafer is 2mm below the focus position, the defocus height can be recorded as -2mm; if the target wafer is 2mm above the focus position, the defocus height can be recorded as +2mm. The "+" and "-" symbols mentioned above are only used to distinguish directions and do not indicate the magnitude of specific values. The same applies below, and will not be repeated here.

[0044] Optionally, the focus sensor identifies beam data through artificial intelligence algorithms such as image recognition. For example, the size of the light spot can be identified through image recognition algorithms, and then the defocus height of the target wafer can be inferred based on the size of the light spot to generate a defocus height analog signal.

[0045] In some feasible implementations, such as Figure 1The focus controller shown can be a focus control board, which can be a printed circuit board (PCB). The focus control board may include power supply, analog signal interface, digital signal interface, storage interface, network interface, etc., which are not limited in this application. The focus controller acquires an analog signal of the defocus height of the target wafer from the focus tracking sensor, predicts the focus position based on the analog signal, and then generates a predicted focus position analog signal of the target wafer based on the predicted focus position and sends the predicted focus position analog signal to the motor controller. The focus controller performs analog-to-digital conversion on the defocus height analog signal to obtain a defocus height digital signal, and performs digital signal processing based on at least two defocus height digital signals to generate focus feedback parameters. Based on the focus feedback parameters, it generates a predicted focus position digital signal of the target wafer. The predicted focus position digital signal can be used to indicate the predicted focus position. For example, the digital signal processing includes at least one of signal averaging and signal denoising.

[0046] In one example, the focus controller can generate a focus feedback parameter for the defocus height of the target wafer by using the difference between two defocus heights indicated by two defocus height digital signals. Based on this focus feedback parameter, the predicted value of the defocus height is corrected, thereby making the predicted focus position more accurate. Assuming the defocus height is +2mm and the focus feedback parameter is -1mm, the predicted defocus height is corrected to +1mm, and the predicted focus position can be recorded as -1mm. This -1mm indicates that the focus position is 1mm below the current target wafer. Optionally, the focus controller can also acquire the difference between every two adjacent defocus heights in the order they are acquired, and calculate the focus feedback parameter by calculating the average or median, etc. This application does not limit the method of calculating the focus feedback parameter.

[0047] Optionally, in some feasible implementations, the above-mentioned focus controller may integrate a processor ( Figure 1 (Not shown in the image), such as a central processing unit (CPU), microcontroller unit (MCU), or other chip. This application uses a focus controller that includes a microcontroller as an example for illustration. The aforementioned microcontroller can be used to receive data and process the data, such as receiving the digital signal of defocus height and performing signal averaging, signal denoising, and other processing on the digital signal of defocus height.

[0048] Optionally, in some feasible implementations, the focus controller described above may also integrate a memory ( Figure 1(Not shown in the image), the aforementioned memory can be connected to a microcontroller. The memory is used to store data and programs or code that control the operation of the microcontroller, thereby ensuring the normal operation of the microcontroller. The memory may include random access memory (RAM) and non-volatile memory (NVM), such as erasable programmable read-only memory (EPROM). Alternatively, the memory may be at least one storage device located remotely from the aforementioned processor, such as a memory mounted externally to the focus controller; this application does not impose any limitations.

[0049] Optionally, in some feasible implementations, the focus controller described above may include a power supply ( Figure 1 (not shown in the image) The power source mentioned above can be a power supply circuit, an energy storage battery, a DC power supply, etc., and this application does not impose any restrictions.

[0050] In some feasible implementations, the motor controller may also integrate a processor and a memory. The motor controller is used to control the fine-tuning motor to drive the measurement objective lens movement based on the predicted focus position analog signal, thereby achieving focus tracking of the target wafer. For example, the motor controller can generate focus tracking control commands based on the predicted focus position analog signal to control the fine-tuning motor to drive the measurement objective lens movement. The movement direction of the measurement objective lens can be vertical in space. Optionally, the movement direction of the measurement objective lens can also be horizontal in space or other angular directions, which should be determined according to the specific shape of the product. This application does not impose any restrictions; the vertical direction in space is used as an example for illustration.

[0051] It should be noted that the focus feedback parameter can be used to indicate the defocus height prediction error generated during the target wafer's movement. The focus controller can compensate for the defocus height prediction error, making the predicted focus position indicated by the analog signal of the predicted focus position more accurate. This, in turn, triggers the motor controller to drive the fine-tuning motor to move the measurement lens to a more accurate predicted focus position to track the target wafer. Thus, even if the target wafer does not need to undergo white light interferometry focusing,

[0052] It can also meet the focusing requirements for alignment error detection. Furthermore, the aforementioned focus tracking process does not involve digital signal transmission between multiple digital signal interfaces, thus avoiding the complex digital encoding conversion operations caused by different encoding schemes used by different digital signal interfaces. This improves signal transmission speed and consequently, focus tracking speed. In summary, using a focus tracking sensor for focus tracking saves the time spent on white light interferometric focusing before alignment error detection, thereby improving the efficiency of alignment error measurement.

[0053] In some feasible implementations, the motor controller can also detect the movement position of the fine-tuning motor to detect the movement position of the measuring objective lens, and generate an objective lens position simulation signal based on the movement position of the measuring objective lens, so as to transmit the objective lens position simulation signal to the photoelectric acquisition board.

[0054] Optionally, the aforementioned focus controller and motor controller can be integrated into a single controller. The integrated controller can acquire the defocus height analog signal of the target wafer from the focus tracking sensor, and generate a predicted focus position analog signal based on the defocus height analog signal to control the fine-tuning motor for focus tracking. At the same time, the integrated controller can also detect the movement position of the measuring objective lens and send the objective lens position analog signal to the photoelectric acquisition board.

[0055] In some feasible implementations, the aforementioned photoelectric acquisition board is used to simultaneously acquire a beam interference simulation signal upon receiving an objective lens position simulation signal. This beam interference simulation signal is used to indicate the beam intensity of the beam obtained by beam interference occurring at the photoelectric acquisition board during the objective lens's movement. The photoelectric acquisition board is also used to generate a focusing digital signal based on the beam interference simulation signal and the objective lens position simulation signal through analog-to-digital conversion, and to send the focusing digital signal to the focusing controller. In some feasible implementations, the beam used for beam interference at the photoelectric acquisition board can be a second beam (such as a white laser). This second beam can be emitted by a light source such as a laser. After the light source illuminates the target wafer and the reference mirror, the second beam is reflected by the target wafer and the reference mirror, respectively. The two reflected beams converge at the photoelectric acquisition board to cause beam interference, thereby generating the beam interference simulation signal.

[0056] For a better understanding of the optical path of the second beam used for beam interference, see [link to relevant documentation]. Figure 3 , Figure 3 This is a schematic diagram of the optical path of the second beam provided in this application. Figure 3 As shown, the optical path of the second beam includes a reference objective, a measuring objective, a first beam splitter, a second beam splitter, and a third beam splitter. The wafer focusing system also includes a light source and a reference mirror. Figure 3 The multiple arrows shown are used to indicate the direction of illumination of the second beam.

[0057] In some feasible implementations, the aforementioned light source is used to emit a second beam. This second beam passes sequentially through a third beam splitter and a measuring objective lens, converges onto a target wafer, is reflected by the target wafer, and then passes sequentially through a measuring objective lens, a third beam splitter, a second beam splitter, and the aforementioned first beam splitter before converging onto a photodiode on a photoelectric acquisition board. The second beam also passes sequentially through the third beam splitter and the aforementioned reference objective lens, converges onto a reference mirror, is reflected by the reference mirror, and then passes sequentially through a reference objective lens, a third beam splitter, a second beam splitter, and the first beam splitter before converging onto the photodiode. The second beam reflected by the reference mirror and the second beam reflected by the target wafer converge onto the photodiode, causing beam interference on the photodiode to generate a simulated beam interference signal.

[0058] Understandably, this application acquires the objective lens position analog signal and the beam interference analog signal through the same analog-to-digital converter on the same photoelectric acquisition board. The resulting focusing digital signal, generated after analog-to-digital conversion of the objective lens position analog signal and the beam interference analog signal, is sent to the focusing controller for processing. This ensures the synchronization of sampling and signal transmission, avoiding situations where asynchronous signal acquisition results in one objective lens position analog signal or beam interference analog signal requiring additional time to wait for the other signal to complete acquisition, thus reducing signal acquisition time. Furthermore, the focusing digital signal includes both digital signals indicating the objective lens position and digital signals indicating beam intensity. Processing the focusing digital signal by the focusing controller avoids deviations in the calculated focusing position due to differences in digital signal acquisition time, thereby improving the accuracy of the predicted focusing position.

[0059] In some feasible implementations, such as Figure 1 The focusing controller shown can also receive a focusing digital signal via a digital signal interface, process the focusing digital signal, and generate an indication signal indicating the focusing position of the measuring objective lens based on the peak intensity of the beam intensity indicated by the focusing digital signal and the movement position of the measuring objective lens. This indication signal is then sent to the motor controller. The indication signal triggers the motor controller to control the fine-tuning motor to drive the measuring objective lens to the focusing position, thereby focusing the target wafer. For example, the focusing controller can identify the peak intensity of the beam intensity in the focusing digital signal using a focusing algorithm, and identify the position of the measuring objective lens at the moment the peak intensity is generated. This position of the measuring objective lens can then be considered the focusing position.

[0060] In some feasible implementations, after the focusing controller generates an indication signal for the focusing position, it can output the indication signal to the motor controller via a digital signal interface to trigger the motor controller to control the fine-tuning motor to move the measuring objective to the focusing position. For example, the motor controller can generate a motion control command based on the indication signal, and then trigger the fine-tuning motor to drive the measuring objective to move to the aforementioned focusing position based on the motion control command.

[0061] It should be noted that digital signal control offers high precision and strong anti-interference capabilities, and can trigger the measurement objective lens to perform small-range movements for precise focusing. When the aforementioned motor controller controls the measurement objective lens for focusing based on a predicted focus position analog signal, high precision is not required, but timely focusing is crucial; therefore, analog signal control is used to achieve rapid focusing. Conversely, when the measurement objective lens is controlled by a focus position indication signal, high focusing speed is not required, but high focusing accuracy is necessary; therefore, digital signal control is used to achieve precise focusing.

[0062] In some feasible implementations, the aforementioned analog signals such as defocus height analog signal, predicted focus position analog signal, and objective lens position analog signal can be transmitted through an analog signal interface. There can be one or more of these analog signal interfaces, which can be sensor interfaces, etc. The aforementioned digital signals such as focus position digital signal, defocus height digital signal, and indication signal can be transmitted through a digital signal interface. There can also be one or more of these digital signal interfaces, which can be RS232 interfaces, RS485 interfaces, transistor-transistor logic interfaces (TTL), universal asynchronous receiver and transmitter (UART), serial peripheral interfaces (SPI), universal serial bus interfaces (USB), Ethernet interfaces, etc. This application does not impose any limitations.

[0063] Using this application, the focus controller in the wafer focusing system is used to acquire a defocus height analog signal of the target wafer from the focus tracking sensor, generate a predicted focus position analog signal of the target wafer based on the defocus height analog signal, and send the predicted focus position analog signal to the motor controller; the motor controller is used to control the fine-tuning motor to drive the measurement objective lens to move to track the target wafer based on the predicted focus position analog signal, and send the objective lens position analog signal to the photoelectric acquisition board based on the movement position of the measurement objective lens; the photoelectric acquisition board is used to simultaneously acquire a beam interference analog signal when receiving the objective lens position analog signal, generate a focus digital signal through analog-to-digital conversion based on the beam interference analog signal and the objective lens position analog signal, and send the focus digital signal to the focus controller; the focus controller is also used to generate an indication signal indicating the focus position of the measurement objective lens based on the intensity peak value of the beam intensity indicated by the focus digital signal and the movement position of the measurement objective lens, and send the indication signal to the motor controller through a digital signal interface to trigger the motor controller to control the fine-tuning motor to drive the measurement objective lens to the focus position, thereby focusing the target wafer. The wafer focusing system uses a focus sensor to acquire a defocus height analog signal to generate a predicted focus position analog signal, which triggers the fine-tuning motor to perform focus tracking. This eliminates the time required to acquire beam interference signals and measure the objective lens position signals via white light interferometry focusing, thereby improving the efficiency of measuring the alignment error of the target wafer. In addition, the system can simultaneously acquire beam interference analog signals and objective lens position analog signals via an optoelectronic acquisition board and generate a focus digital signal. This allows the focus controller to generate and send a focus position indication signal to the fine-tuning motor via a digital signal interface, triggering the fine-tuning motor to focus on the target wafer. Therefore, it reduces the signal acquisition time for beam interference signals and objective lens position signals, improves the accuracy of the predicted focus position, and has strong applicability.

[0064] For a better understanding of the structure of the focus controller described above, please refer to [link / reference]. Figure 4 , Figure 4 This is another schematic diagram of the wafer focusing system provided in this application. (See diagram below.) Figure 4 As shown, the focus controller may include a first analog-to-digital conversion module, a digital-to-analog conversion module, and a microcontroller. Optionally, the focus controller may also include a memory and a power supply. The microcontroller is connected to the first analog-to-digital conversion module and the digital-to-analog conversion module, the memory is connected to the microcontroller, and the power supply provides power to the focus controller. In some feasible embodiments, the first analog-to-digital conversion module may be an analog-to-digital converter. The first analog-to-digital conversion module receives an analog signal of the defocus height from the focus sensor through an analog signal interface, performs analog-to-digital conversion on the received defocus height analog signal to generate a defocus height digital signal, and sends the defocus height digital signal to the microcontroller.

[0065] In some feasible implementations, the microcontroller is used to perform digital signal processing on the received defocus height digital signal to predict the focusing position of the measurement objective lens through the defocus height digital signal, generate a predicted focusing position digital signal based on the predicted focusing position of the measurement objective lens, and send the predicted focusing position digital signal to the digital-to-analog conversion module.

[0066] In some feasible implementations, the aforementioned digital-to-analog conversion module can be a digital-to-analog converter. The digital-to-analog conversion module is used to perform digital-to-analog conversion on the received predicted focus position digital signal to generate a predicted focus position analog signal, and outputs the predicted focus position analog signal to the aforementioned motor controller through an analog signal interface, so that after receiving the predicted focus position analog signal, the motor controller controls the fine-tuning motor movement to perform focus tracking according to the focus position indicated by the predicted focus position analog signal.

[0067] In some feasible implementations, the aforementioned memory can be used to store data such as defocus height analog signal, defocus height digital signal, predicted focus position, predicted focus position digital signal, predicted focus position analog signal, focus digital signal, and indicator signal, so that the first analog-to-digital conversion module, microcontroller, and digital-to-analog conversion module can retrieve the data and perform operations such as processing and transmission.

[0068] In some feasible implementations, the aforementioned power supply can be used to power the focus controller, or it can output power to external devices through the focus controller, such as powering the motor controller, fine-tuning motor, photoelectric acquisition board, focus controller, etc. through circuit connection. This application does not impose any restrictions.

[0069] Understandably, based on the characteristics of analog and digital signals, analog signals have highly variable waveforms, making them difficult to process directly. Digital signals, on the other hand, only have high and low levels (represented by "0" and "1"). Therefore, digital signals are suitable for more complex signal processing such as signal averaging and denoising. Furthermore, digital signals have strong anti-interference capabilities and can recover disturbed waveforms, ensuring high accuracy and reliability in digital signal processing. In addition, since the signal directly obtained from the focus sensor is an analog signal (such as a voltage signal), and analog signals are generally used to control equipment such as the fine-tuning motor, the focus controller receives the analog signal through an analog signal interface, converts it into a digital signal for digital signal processing, and then converts it back to an analog signal and outputs it through the analog signal interface. The analog signal interface used for input and the analog signal interface used for output can be the same analog signal interface or different analog signal interfaces (such as...). Figure 4 The analog signal interface 1 and analog signal interface 2 shown are not limited in this application.

[0070] In some feasible implementations, the focus controller described above may also include one or more digital signal interfaces (such as...). Figure 4 (Showing digital signal interfaces 1 and 2). The focus controller can receive the focusing digital signal sent by the photoelectric acquisition board through the digital signal interface (such as digital signal interface 1), and the microcontroller in the focus controller determines the motion position of the measuring objective lens when the intensity peak is generated based on the intensity peak of the beam intensity indicated by the focusing digital signal. The motion position can be regarded as the focusing position of the measuring objective lens. The microcontroller can also generate an indication signal indicating the focusing position of the measuring objective lens based on the focusing position, and output the indication signal to the motor controller through the digital signal interface (such as digital signal interface 2).

[0071] For a better understanding of the structure of the aforementioned photoelectric acquisition board, please refer to [link / reference]. Figure 5 , Figure 5 This is a schematic diagram of the photoelectric data acquisition board provided in this application. Figure 5 As shown above, Figure 4 The wafer focusing system shown includes a photoelectric acquisition board that may include a first isolation circuit, a second isolation circuit, a photodiode, and a second analog-to-digital converter (ADC). The second ADC is connected to both the first and second isolation circuits, and the second isolation circuit is connected to the photodiode.

[0072] In some feasible implementations, the first isolation circuit is used to receive the objective lens position analog signal from the motor controller and output the target objective lens position analog signal to the second analog-to-digital converter module based on the objective lens position analog signal. The first isolation circuit is used for signal isolation between the motor controller and the second analog-to-digital converter module to prevent interference between different devices and different functional areas, thereby improving the stability and driveability of the objective lens position analog signal.

[0073] In some feasible implementations, the second isolation circuit is used to acquire the beam interference simulation signal corresponding to the beam intensity obtained by beam interference on the photodiode during the movement of the measuring objective lens, and outputs the target beam interference simulation signal to the second analog-to-digital converter module based on the beam interference simulation signal. The second isolation circuit is used for signal isolation between the photodiode and the second digital-to-analog converter module, thereby improving the stability and driveability of the beam interference simulation signal.

[0074] In some feasible implementations, the second analog-to-digital conversion module is used to perform analog-to-digital conversion on the target objective position analog signal and the target beam interference analog signal to generate a target objective position digital signal and a target beam interference digital signal. Based on the target objective position digital signal and the target beam interference digital signal, the focusing digital signal is generated and sent to the focusing controller. The focusing digital signal is used to indicate the beam intensity of the beam transmitting beam interference and the objective position of the measuring objective. Optionally, the second analog-to-digital conversion module may not generate a focusing digital signal, but instead synchronously send the target objective position digital signal and the target beam interference digital signal as the output of the photoelectric acquisition board to the focusing controller; this application does not impose any limitations.

[0075] In some feasible implementations, the aforementioned photoelectric acquisition board may include a digital signal interface (such as...) Figure 5 As shown in digital signal interface 3, the photoelectric acquisition board outputs the focus digital signal to the focus controller through the digital signal interface. The focus controller can also receive the aforementioned focus digital signal through the digital signal interface, thereby ensuring the accuracy of the focus digital signal through digital signal transmission between the two digital signal interfaces.

[0076] For a better understanding of the first isolation circuit described above, please refer to [link / reference]. Figure 6 , Figure 6 This is a circuit diagram of the first isolation circuit provided in this application. Figure 6 As shown, the first isolation circuit may include a first operational amplifier, a connector, and a first resistor. The first resistor is connected between a first connection terminal and a second connection terminal of the first operational amplifier. The second connection terminal of the first operational amplifier serves as the output terminal of the first isolation circuit. The first connection terminal and the third connection terminal of the first operational amplifier serve as the input terminals of the first isolation circuit. The third connection terminal of the first operational amplifier is grounded through the connector. The fourth connection terminal and the fifth connection terminal of the first operational amplifier are connected to a power supply.

[0077] In some feasible implementations, the first operational amplifier can be connected to the motor controller and ground via a connector, and then receive the objective lens position analog signal transmitted by the motor controller from the connector through the third connection terminal of the first operational amplifier. The connector can be a coaxial RF connector (sub-Miniature version a, SMA), which features wide bandwidth, superior performance, high reliability, and long lifespan. Using an SMA interface supports a wide frequency range, and the shielded interface effectively prevents the influence of external interference signals, thus ensuring high-precision signal transmission between the motor controller and the photoelectric acquisition board.

[0078] In some feasible implementations, the fourth connection terminal of the first operational amplifier can be connected to a negative voltage power supply, for example, a power supply with a voltage of -10V; the fifth connection terminal of the first operational amplifier can be connected to a positive voltage power supply, for example, a power supply with a voltage of +10V. In addition, the specific value of the voltage can be determined according to the actual product form, and this application does not impose any restrictions.

[0079] It is understood that the aforementioned first isolation circuit is a follower circuit based on the first operational amplifier. It can receive the analog signal of the objective lens position through the connector and then isolate the signal. It can output the analog signal of the target objective lens position to the second analog-to-digital converter through the second connection terminal of the first operational amplifier.

[0080] For a better understanding of the second isolation circuit described above, please refer to [link / reference]. Figure 7 , Figure 7 This is a circuit diagram of the second isolation circuit provided in this application. The second isolation circuit includes a second operational amplifier, a second resistor, a third resistor, and a capacitor. The second resistor is connected between the first connection terminal and the second connection terminal of the second operational amplifier. The first connection terminal and the third connection terminal of the second operational amplifier serve as the input terminals of the second isolation circuit. The first connection terminal of the second operational amplifier is connected to the photodiode. The third connection terminal and the fourth connection terminal of the second operational amplifier are connected to a power supply. The first connection terminal of the third resistor is connected to the second connection terminal of the second operational amplifier. The second connection terminal of the third resistor serves as the output terminal of the second isolation circuit. The capacitor is connected between the fifth connection terminal of the second operational amplifier and the second connection terminal of the third resistor. The fifth connection terminal of the second operational amplifier is grounded.

[0081] In some feasible implementations, the first connection terminal of the second operational amplifier can be used to receive a beam interference analog signal from a photodiode. The photodiode can be connected to a bias power supply (vbias), which provides stable voltage and current to ensure normal beam interference. The bias power supply can also adjust the brightness and intensity of the beam, improving the stability and reliability of the beam interference analog signal. Furthermore, the power supply connected to the third connection terminal of the second operational amplifier can also be a bias power supply. The bias power supplies connected to the photodiode and the third connection terminal of the second operational amplifier can be the same or different bias power supplies. The voltage provided by the bias power supply should be determined according to the actual product form, and this application does not impose any limitations. The fourth connection terminal of the second operational amplifier can be connected to a negative voltage power supply, for example, a power supply with a voltage of -10V. The specific voltage value of the power supply should be determined according to the actual product form, and this application also does not impose any limitations.

[0082] It is understood that the aforementioned second isolation circuit is a follower circuit based on the second operational amplifier. It can receive the beam interference analog signal from the photodiode through the first connection terminal of the second operational amplifier, perform signal isolation, and output the target beam interference analog signal to the second analog-to-digital converter through the second connection terminal of the third resistor.

[0083] In some feasible implementations, the wafer focusing system also includes a power supply, which can power the tracking sensor, the focusing controller, the motor controller, the photoelectric acquisition board and the fine-tuning motor. The power supply can be a power supply circuit, an energy storage battery, a DC power supply, an AC power supply, a bias power supply, etc. The type and installation location of the power supply should be determined according to the actual product form. This application does not limit the type, connection method or installation location of the power supply.

[0084] Using this application, the focus controller in the wafer focusing system is used to acquire a defocus height analog signal of the target wafer from the focus tracking sensor, generate a predicted focus position analog signal of the target wafer based on the defocus height analog signal, and send the predicted focus position analog signal to the motor controller; the motor controller is used to control the fine-tuning motor to drive the measurement objective lens to move to track the target wafer based on the predicted focus position analog signal, and send the objective lens position analog signal to the photoelectric acquisition board based on the movement position of the measurement objective lens; the photoelectric acquisition board is used to simultaneously acquire a beam interference analog signal when receiving the objective lens position analog signal, generate a focus digital signal through analog-to-digital conversion based on the beam interference analog signal and the objective lens position analog signal, and send the focus digital signal to the focus controller; the focus controller is also used to generate an indication signal indicating the focus position of the measurement objective lens based on the intensity peak of the beam intensity indicated by the focus digital signal and the movement position of the measurement objective lens, and send the indication signal to the motor controller through a digital signal interface to trigger the motor controller to control the fine-tuning motor to drive the measurement objective lens to the focus position to focus the target wafer. The wafer focusing system uses a focus sensor to acquire a defocus height analog signal to generate a predicted focus position analog signal, which triggers the fine-tuning motor to perform focus tracking. This eliminates the time required to acquire beam interference signals and measure the objective lens position signals via white light interferometry focusing, thereby improving the efficiency of measuring the alignment error of the target wafer. In addition, the system can simultaneously acquire beam interference analog signals and objective lens position analog signals via an optoelectronic acquisition board and generate a focus digital signal. This allows the focus controller to generate and send a focus position indication signal to the fine-tuning motor via a digital signal interface, triggering the fine-tuning motor to focus on the target wafer. Therefore, it reduces the signal acquisition time for beam interference signals and objective lens position signals, improves the accuracy of the predicted focus position, and has strong applicability.

[0085] Those skilled in the art will recognize that the wafer focusing systems and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of each example have been generally described in terms of functionality in the foregoing description. Those skilled in the art can implement the described functions using different methods for each specific application, but such implementations should not be considered beyond the scope of this application.

Claims

1. A wafer focusing system, characterized in that, include: Focusing sensor, focus controller, photoelectric acquisition board, fine-tuning motor and motor controller; The focus controller is used to: acquire a defocus height simulation signal of the target wafer from the focus tracking sensor, generate a predicted focus position simulation signal of the target wafer based on the defocus height simulation signal, and send the predicted focus position simulation signal to the motor controller; The motor controller is used to: control the fine-tuning motor to drive the measurement objective lens to move to track the target wafer based on the predicted focusing position analog signal; and send the objective lens position analog signal to the photoelectric acquisition board based on the movement position of the measurement objective lens. The photoelectric acquisition board is used to: synchronously acquire a beam interference simulation signal when the objective lens position simulation signal is received; the beam interference simulation signal is used to indicate the beam intensity obtained by beam interference on the photoelectric acquisition board during the movement of the measuring objective lens; generate a focus digital signal based on the beam interference simulation signal and the objective lens position simulation signal and send the focus digital signal to the focus controller. The focusing controller is further configured to: generate an indication signal indicating the focusing position of the measuring objective lens based on the peak intensity of the beam intensity indicated by the focusing digital signal and the movement position of the measuring objective lens, and send the indication signal to the motor controller. The indication signal is used to trigger the motor controller to control the fine-tuning motor to drive the measuring objective lens to the focusing position to focus the target wafer.

2. The system according to claim 1, characterized in that, The focusing controller includes a first analog-to-digital conversion module, a digital-to-analog conversion module, and a microcontroller; the microcontroller is connected to the first analog-to-digital conversion module and the digital-to-analog conversion module. The first analog-to-digital conversion module is used to: acquire the defocus height analog signal from the focus tracking sensor, perform analog-to-digital conversion on the defocus height analog signal, and send the defocus height digital signal to the microcontroller; The microcontroller is used to: generate a predicted focus position digital signal based on the defocus height digital signal and send the predicted focus position digital signal to the digital-to-analog converter module; The digital-to-analog conversion module is used to: perform digital-to-analog conversion on the predicted focus position digital signal to generate the predicted focus position analog signal, and output the predicted focus position analog signal to the motor controller.

3. The system according to claim 2, characterized in that, The photoelectric acquisition board includes a first isolation circuit, a second isolation circuit, a photodiode, and a second analog-to-digital converter module; the second analog-to-digital converter module is connected to the first isolation circuit and the second isolation circuit, and the second isolation circuit is connected to the photodiode; The first isolation circuit is used to: receive the objective lens position analog signal from the motor controller, and output the target objective lens position analog signal to the second analog-to-digital conversion module based on the objective lens position analog signal; The second isolation circuit is used to: acquire the beam interference analog signal corresponding to the beam intensity obtained by beam interference on the photodiode during the movement of the measuring objective lens, and output the target beam interference analog signal to the second analog-to-digital conversion module based on the beam interference analog signal; The second analog-to-digital conversion module is used to: perform analog-to-digital conversion on the target objective lens position analog signal and the target beam interference analog signal to generate the focusing digital signal and send the focusing digital signal to the focusing controller.

4. The system according to claim 3, characterized in that, The first isolation circuit includes a first operational amplifier, a connector, and a first resistor; the first resistor connects a first connection terminal and a second connection terminal of the first operational amplifier, the second connection terminal of the first operational amplifier serves as the output terminal of the first isolation circuit, the first connection terminal and the third connection terminal of the first operational amplifier serve as the input terminal of the first isolation circuit, the third connection terminal of the first operational amplifier is grounded through the connector, and the fourth connection terminal and the fifth connection terminal of the first operational amplifier are connected to a power supply.

5. The system according to claim 3, characterized in that, The second isolation circuit includes a second operational amplifier, a second resistor, a third resistor, and a capacitor. The second resistor connects the first and second terminals of the second operational amplifier. The first and third terminals of the second operational amplifier serve as the input terminals of the second isolation circuit. The first terminal of the second operational amplifier is connected to the photodiode. The third and fourth terminals of the second operational amplifier are connected to a power supply. The first terminal of the third resistor is connected to the second terminal of the second operational amplifier. The second terminal of the third resistor serves as the output terminal of the second isolation circuit. The capacitor connects the fifth terminal of the second operational amplifier and the second terminal of the third resistor. The fifth terminal of the second operational amplifier is grounded.

6. The system according to any one of claims 1-5, characterized in that, The system also includes a first beam splitter, a second beam splitter, and a third beam splitter; The focus sensor is used to: emit a first beam of light, which passes sequentially through the first beam splitter, the second beam splitter, the third beam splitter and the measurement objective lens and converges onto the target wafer; after being reflected by the target wafer, it passes sequentially through the measurement objective lens, the third beam splitter, the second beam splitter and the first beam splitter and returns to the focus sensor. The focus sensor is further configured to: send at least two defocus height analog signals to the focus controller based on the beam data of the returned first beam; one of the defocus height analog signals is obtained from a received beam data of the first beam, and the defocus height analog signal is converted into a defocus height digital signal after analog-to-digital conversion, wherein the beam data includes at least one of spot size, shape, or light intensity signal; The focus controller is further configured to: perform digital signal processing on at least two of the defocus height digital signals to generate focus feedback parameters, and generate a predicted focus position digital signal based on the focus feedback parameters, wherein the digital signal processing includes at least one of signal averaging and signal denoising.

7. The system according to claim 6, characterized in that, The system also includes a light source, a reference objective lens, and a reference reflector; The light source is used to: emit a second beam, which passes sequentially through the third beam splitter and the measurement objective lens, converges on the target wafer, is reflected by the target wafer, and then passes sequentially through the measurement objective lens, the third beam splitter, the second beam splitter, and the first beam splitter before converging on the photoelectric acquisition plate. The second beam also passes sequentially through the third beam splitter and the reference objective lens, converges on the reference reflector, is reflected by the reference reflector, and then passes sequentially through the reference objective lens, the third beam splitter, the second beam splitter, and the first beam splitter before converging on the photoelectric acquisition plate to perform beam interference.

8. The system according to any one of claims 1-5, characterized in that, The system also includes a power supply; the power supply is used to power the focus sensor, the focus controller, the motor controller, the photoelectric acquisition board and the fine-tuning motor.

9. The system according to any one of claims 2-5, characterized in that, The system also includes a memory connected to the microcontroller, wherein the memory is used to store program code so that the microcontroller can call the program code stored in the memory to perform digital signal processing.

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