Wafer focusing system

Abstract

The invention discloses a wafer focusing system. The wafer focusing system comprises a focus tracking 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 the target wafer from the focus tracking sensor so as to generate and output a predicted focusing position analog signal to the motor controller; the motor controller is used for controlling a fine adjustment motor to move based on the predicted focusing position analog signal so as to follow focus, and sending an objective lens position analog signal to the photoelectric acquisition board based on the measured objective lens motion position; the photoelectric acquisition board is used for synchronously acquiring a light beam interference analog signal when receiving the objective lens position analog signal so as to generate and output a focusing digital signal to the focusing controller; the focusing controller is further used for generating an indication signal indicating the focusing position of the measurement objective lens based on the focusing digital signal and sending the indication signal to the motor controller through the digital signal interface. 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 high.

Description

Technical Field

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

[0002] Semiconductor inspection technology plays an important role in the processes of semiconductor production, packaging and testing. Among them, the measurement of alignment error is an important part of the key process in the semiconductor production process. Alignment error is one of the most important errors that need to be controlled in the above key processes. It refers to the pattern alignment error between the previous layer and the current layer during the key process operation. There is a certain distribution law on the wafer and the exposure field. In order to ensure that the alignment error is within the threshold range, after each batch of wafers is exposed, it is necessary to perform alignment error measurement on the overlay measurement machine for many marking points. After mathematical processing, the measurement value obtains the distribution model of the alignment error (overlay model terms), which is fed back to the semiconductor production equipment for the alignment error control of the next batch of wafer exposure. In order to obtain the distribution law of the alignment error on the wafer and the exposure field, the marking points for alignment error measurement need to be distributed as evenly as possible on the entire wafer. In the process of measuring the alignment error, the camera is mainly used to obtain a wafer measurement image containing information of both the previous layer and the current layer (that is, a wafer scanning image containing alignment error measurement marking points), and the alignment error is obtained through the wafer measurement image. Therefore, in order to improve the measurement accuracy of alignment errors, the positioning accuracy of wafer measurement image acquisition also has extremely high requirements, requiring high-precision wafer image scanning positioning technology and autofocus technology.

[0003] In the process of improving the positioning accuracy of wafer image scanning, the white light interferometric focusing method can be used to perform a focusing operation before and after the positioning operation of the mark point for alignment error measurement. White light interferometric focusing is a focusing technology with extremely high precision (approximately equal to 10nm), but each time it performs focusing, it requires a Z-direction motor (i.e., a precision motor) with a large load and large stroke to perform a scanning movement of about 20um stroke, which results in each process of white light interferometric focusing taking 70ms to 80ms. Two white light interferometric focusing operations make the acquisition of wafer measurement images time-consuming and the wafer alignment error measurement efficiency low. In addition, during the white light interferometric focusing process, the acquisition of the beam interference signal is not synchronized with the acquisition of the position signal of the measurement objective lens, resulting in the need to wait for both types of signals to be acquired before the prediction of the focus position can be performed. The signal acquisition time is long, and the asynchronous signal acquisition will result in the low accuracy and poor applicability of the focus position predicted by the beam interference signal and the position signal of the measurement objective lens. Summary of the invention

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

[0005] In a first aspect, an embodiment of the present application provides a wafer focusing system, including: a focus tracking sensor, a focus controller, a photoelectric collection board, a fine-tuning motor and a motor controller; the focus controller is used to: obtain 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 measuring objective lens to move to focus the target wafer based on the predicted focus position analog signal, and send the objective lens position analog signal to the photoelectric collection board based on the moving position of the measuring objective lens; the photoelectric collection board is used to: upon receiving the objective lens position analog signal The step of acquiring a beam interference analog signal is used to indicate the intensity of the beam obtained by the beam interference occurring on the photoelectric collection board during the movement of the measuring objective lens, and to generate a focusing digital signal based on the beam interference analog signal and the objective lens position analog signal, and to send the focusing digital signal to the focusing controller; the focusing controller is also used to generate an indication signal indicating the focusing position of the measuring objective lens based on the intensity peak value of the beam intensity indicated by the focusing digital signal and the moving position of the measuring objective lens, and to send the indication signal to the motor controller, and the indication signal is used to trigger the motor controller to control the fine-tuning motor to drive the measuring objective lens to move to the focusing position so as to focus on the target wafer.

[0006] By adopting this implementation mode, a defocus height analog signal can be obtained through a focus tracking sensor, and a predicted focus position analog signal can be generated based on the defocus height analog signal through a focus controller to trigger a fine-tuning motor to focus, thereby saving the time for collecting light beam interference signals and measuring the position signal of the objective lens through white light interferometric focusing, thereby improving the efficiency of measuring the alignment error of the target wafer; in addition, the light beam interference analog signal and the objective lens position analog signal can be synchronously collected through a photoelectric collection board to generate a focus digital signal, and a focus position indication signal can be generated through the focus digital signal to trigger the fine-tuning motor to focus on the target wafer, thereby improving the accuracy of the predicted focus position and having strong applicability.

[0007] In a 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 used to: obtain 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 conversion 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. By adopting this implementation mode, the defocus height analog signal can be converted into a defocus height digital signal through the analog-to-digital conversion module for digital signal processing. Since digital signals have higher accuracy than analog signals, the processing process is simpler, and the anti-interference ability is strong, the accuracy of the generated predicted focus position digital signal can be improved. In addition, the predicted focus position digital signal can be converted into a predicted focus position analog signal through digital-to-analog conversion to control devices such as motor controllers. Control through analog signals can avoid code conversion between two digital signal interfaces with different protocols, so the control speed is fast, which can further improve the alignment error measurement efficiency of the target wafer.

[0008] In a possible implementation of the first aspect, the photoelectric collection board includes a first isolation circuit, a second isolation circuit, a photodiode and a second analog-to-digital conversion module; the second analog-to-digital conversion 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: obtain the beam interference analog signal corresponding to the beam intensity obtained by the beam interference occurring on the photodiode during the measurement of the movement of the 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 focus digital signal and send the focus digital signal to the focus controller. By adopting this implementation, signal isolation can be performed between the motor controller and the second digital-to-analog conversion module through a first isolation circuit, and signal isolation can be performed between the photodiode and the second digital-to-analog conversion module through a second isolation circuit, thereby reducing signal interference and improving the accuracy of the focused digital signal, thereby further improving the accuracy of the focused position generated based on the focused digital signal.

[0009] In a possible implementation of the first aspect, the first isolation circuit includes a first operational amplifier, a connector and a first resistor; the first resistor is connected to the first connection terminal and the 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 of the first operational amplifier 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 of the first operational amplifier and the fifth connection terminal of the first operational amplifier are connected to the power supply. With 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 the ground are connected through the connector, and the electronic components in the first isolation circuit are light and simple, flexible to load, and highly applicable.

[0010] In a 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 is connected to the first connection end of the second operational amplifier and the second connection end of the second operational amplifier, the first connection end of the second operational amplifier and the third connection end of the second operational amplifier serve as the input end of the second isolation circuit, the first connection end of the second operational amplifier is connected to the photodiode, the third connection end of the second operational amplifier and the fourth connection end of the second operational amplifier are connected to a power supply, the first connection end of the third resistor is connected to the second connection end of the second operational amplifier, the second connection end of the third resistor serves as the output end of the second isolation circuit, the capacitor is connected between the fifth connection end of the second operational amplifier and the second connection end of the third resistor, and the fifth connection end of the second operational amplifier is grounded. With this implementation, a second isolation circuit (i.e., a follower circuit) for signal isolation can be formed based on the second operational amplifier, and the electronic components in the second isolation circuit are light and simple, flexible to load, and highly applicable.

[0011] In a possible implementation manner of the first aspect, the system further includes a first beam splitter, a second beam splitter, and a third beam splitter. The above-mentioned tracking focus sensor is used to: emit a first light beam, and the above-mentioned first light beam passes through the above-mentioned first beam splitter, the above-mentioned second beam splitter, the above-mentioned third beam splitter and the above-mentioned measuring objective lens in sequence and then converges on the above-mentioned target wafer. After being reflected by the above-mentioned target wafer, it passes through the above-mentioned measuring objective lens, the above-mentioned third beam splitter, the above-mentioned second beam splitter and the above-mentioned first beam splitter in sequence and returns to the above-mentioned tracking focus sensor; the above-mentioned tracking focus sensor is also used to: send at least two of the above-mentioned defocus height analog signals to the above-mentioned focus controller based on the beam data of the above-mentioned first light beam returned; one of the above-mentioned defocus height analog signals is obtained from a received portion of the beam data of the above-mentioned first light beam, and one of the above-mentioned defocus height analog signals is converted into a defocus height digital signal through analog-to-digital conversion, and the above-mentioned beam data includes at least one of the spot size, shape or light intensity signal; the above-mentioned focus controller is also used to: perform digital signal processing on the above-mentioned at least two of the above-mentioned defocus height digital signals to generate the above-mentioned focus feedback parameters, and generate the above-mentioned predicted focus position digital signal based on the above-mentioned focus feedback parameters, and the above-mentioned digital signal processing includes at least one of signal averaging and signal denoising. By adopting this implementation mode, the focus tracking sensor can utilize the first beam splitter, the second beam splitter, the measuring objective lens and other light tracing devices in the wafer focusing system to achieve focus tracking. Focus tracking can be completed without the need for a long period of beam interference focusing. The focus tracking speed is fast, which 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 have flexible installation positions, which further improves applicability.

[0012] In a 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 light beam, the second light beam sequentially passes through the third beam splitter and the measuring objective lens, converges on the target wafer and is reflected by the target wafer, then sequentially passes through the measuring objective lens, the third beam splitter, the second beam splitter and the first beam splitter, then converges on the photodiode, the second light beam also sequentially passes through the third beam splitter and the reference objective lens, converges on the reference reflector and is reflected by the reference reflector, then sequentially passes through the reference objective lens, the third beam splitter, the second beam splitter and the first beam splitter, then converges on the photodiode to perform light beam interference. By adopting this implementation mode, the second light beam can be converged to the photodiode on the photoelectric collection board through the first beam splitter, the second beam splitter, the third beam splitter, the measuring objective lens, the reference objective lens and other light tracing devices to generate beam interference, so that the second analog-to-digital conversion module on the photoelectric collection board can synchronously collect the light beam interference analog signal and the objective lens position analog signal. No complex transmission circuit is required during the collection process, so near-end signal collection can be completed, reducing interference during signal transmission, and improving the accuracy of the focused digital signal generated according to the light beam interference analog signal and the objective lens position analog signal, so as to further improve the accuracy of the focused position generated according to the focused digital signal.

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

[0014] In a possible implementation of the first aspect, the system further includes a memory; the memory is connected to the microcontroller, wherein the memory is used to store program code so that the microcontroller calls the program code stored in the memory to perform digital signal processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a structural schematic diagram of a wafer focusing system provided by the present application;

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

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

[0018] Figure 4 is another structural schematic diagram of the wafer focusing system provided by the present application;

[0019] Figure 5 It is a structural schematic diagram of the photoelectric collection board provided by this application;

[0020] Figure 6 is a circuit diagram of a first isolation circuit provided by the present application;

[0021] Figure 7 It is a circuit diagram of the second isolation circuit provided by the present application. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application.

[0023] To facilitate understanding, some nouns are briefly explained as follows:

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

[0025] 2. Focus feedback parameters, also known as feedback proportional-integral-derivative (PID) values, can be obtained by comparing the difference (i.e., error) between the expected output and the actual output. The above feedback PID value can be used to implement feedback PID control through a PID controller, which can correct deviations and compensate for the defocus height of the target wafer, thereby ensuring the stability and accuracy of the system.

[0026] 3. Fine-tuning motor, also known as precision Z motor or Z-axis fine-tuning motor, is a motor that can provide high-precision positioning and control. It is usually used in applications that require precise adjustment or positioning. This 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 tracking sensor to measure the defocus height of the target wafer, such as structured light, partially coherent light, laser and other beams. Among them, structured light usually has the characteristics of narrow line width, which can obtain high-contrast and high-definition imaging effects when captured by the focus tracking sensor; partially coherent light is a beam between fully coherent light 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 are consistent in space and time.

[0028] This application uses structured light as the first light beam as an example for explanation. The tracking sensor can project a specific optical pattern onto the target wafer surface by projecting structured light, and then the tracking sensor calculates the height of the target wafer and other information based on the returned light beam data (light signal), and then restores the entire three-dimensional space to obtain the defocus height of the target wafer. Among them, the optical pattern projected by the tracking sensor through structured light can be a plane, a grid, a straight line, etc. The tracking sensor calculates the height change of the target wafer surface by observing the distortion of the light.

[0029] 5. The second light beam refers to the light beam used for light beam interference, which is usually a monochromatic laser beam (the monochromatic laser beam may also be referred to as a monochromatic beam). For example, the monochromatic beam may be a white beam, a red beam, etc. The monochromatic beam has high precision, strong stability, a specific wavelength and coherence, and can generate a specific interference pattern by adjusting the phase and amplitude of the beam.

[0030] 6. Beam interference refers to the beam interference experiment, which is generally carried out using a monochromatic beam, such as white light interference, red light interference, etc. The beam interference experiment relies on the interference phenomenon of light, that is, the phenomenon that an interference pattern is generated when two monochromatic light beams meet. In the present application, a monochromatic light beam (such as white light) can be divided into two beams of light through a beam splitter, one of which is reflected by a reference reflector, and the other is reflected by a target wafer, and finally converges at a photodiode to produce light and dark stripes. These stripes are caused by the phase difference between the two monochromatic light beams, and the phase difference depends on the optical path difference of the two monochromatic light beams. The intensity of the interference fringes depends on the optical path difference of the two beams. According to the brightness of the white light interference fringes and the position where the interference fringes appear, the height of the target wafer can be analyzed. Among them, only when the optical path difference between the reference arm and the measuring arm is within a coherence length of the light source, the backscattered light (i.e. the reflected light of the target wafer) and the reference light (i.e. the reflected light of the reference reflector) will interfere, and the optical path difference is equal to 0, that is, when the optical paths of the two beams are completely consistent, the coherence intensity reaches the maximum, generating a peak light intensity. This signal is the beam interference simulation signal.

[0031] 7. Analog signal, used to indicate voltage, current, etc. in the form of continuously changing physical quantities, whose amplitude, frequency or phase changes continuously over time. Analog signals have strong timeliness and can be controlled quickly through analog signals.

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

[0033] 9. Analog to digital converter (ADC) is a device that converts analog signals into digital signals. Its main function is to convert analog signals that are continuous in time and continuous in amplitude into digital signals that are discrete in time and discrete in amplitude. Analog to digital converters usually include four processes: sampling, holding, quantization, and encoding. The first analog to digital conversion module and the second analog to digital conversion module in the present application can be analog to digital converters.

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

[0035] The wafer focusing system provided in this application can be applied to wafer focusing scenarios, and can also be extended to other scenarios that require focusing. For ease of description, this application takes the wafer focusing scenario as an example. Figure 1 , Figure 1 Schematic diagram of the structure of the wafer focusing system provided by this application. Figure 1 As shown, the wafer focusing system may include a focus tracking sensor, a focus controller, a photoelectric collection board, a fine-tuning motor and a motor controller.

[0036] In some feasible embodiments, the above-mentioned tracking focus sensor is used to receive the light beam reflected by the target wafer and generate a defocus height analog signal indicating the defocus height of the target wafer based on the beam data of the light beam, wherein the beam data includes at least one of the spot size, shape or light intensity signal of the spot. In addition, the light beam irradiated to the surface of the target wafer can be emitted by the tracking focus sensor or by an external light source. This application is not limited and is explained by taking the example of the tracking focus sensor emitting a light beam to illuminate the target wafer. For example, the above-mentioned tracking focus sensor can be used to emit a first light beam and feedback the defocus height analog signal of the target wafer to the focus controller based on the beam data of the returned first light beam.

[0037] Optionally, in some feasible implementations, the first light beam may be structured light, and the focus tracking sensor may irradiate the structured light onto the target wafer, and calculate the defocus height based on the light path data of the light spot returned by the structured light. The structured light may be a light beam such as a point structured light, a line structured light, or a surface structured light, which is used to illuminate the target wafer and is reflected by the target wafer to generate light path data; the light beam data includes at least one of the light spot size, shape, or light spot intensity signal.

[0038] Optionally, in some feasible embodiments, if the above-mentioned first light beam is partially coherent light, the wafer focusing system may further include a mask, and the above-mentioned mask is aligned with the above-mentioned target wafer. The tracking focus sensor can obtain the defocus height by an eccentric mask method; the above-mentioned eccentric mask method includes: calculating the defocus height according to the change of the light intensity signal generated by the misalignment of the mask imaging. For example, after the above-mentioned mask is aligned with the target wafer, the tracking focus sensor can irradiate the partially coherent light onto the mask to generate a light beam diffraction through the mask, and the above-mentioned partially coherent light is projected onto the target wafer through the mask. The tracking focus sensor receives the light path data reflected by the target wafer and the mask, and determines the defocus height by analyzing the change of the light intensity signal in the light path data.

[0039] Optionally, in some feasible embodiments, if the first light beam is a laser, the wafer focusing system may further include at least two photodiodes. The focus tracking sensor can obtain the defocus height by a differential confocal method, and the differential confocal method includes: obtaining the defocus height according to the difference in light intensity signals detected by two photodiodes. For example, the focus tracking sensor emits a laser and converges it on the target wafer. The laser reflected by the target wafer is received by two photodiodes respectively to obtain two light intensity signals, and then the wafer focusing position can be determined by the difference between the two light intensity signals to generate the defocus height of the target wafer.

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

[0041] It should be noted that the present application does not limit the type of light beam used for the first light beam and the method for generating the defocus height. The following description will take structured light as the first light beam as an example and will not be repeated. To facilitate understanding of the process of enabling the tracking sensor to track focus through the first light beam, the following description will describe the optical path of the first light beam and the processing of the light beam data by the tracking sensor. Figure 2 , Figure 2 It is a schematic diagram of the optical path of the first light beam provided in this application.

[0042] like Figure 2As shown, the optical path of the first light beam includes a first beam splitter, a second beam splitter, a third beam splitter and a measuring lens. The tracking focus sensor can be used to emit the first light beam, which sequentially passes through the first beam splitter, the second beam splitter, the third beam splitter and the measuring lens and converges on the target wafer. After being reflected by the target wafer, the first light beam sequentially passes through the measuring lens, the third beam splitter, the second beam splitter and the first beam splitter and returns to the tracking focus sensor.

[0043] In some feasible implementations, the tracking focus sensor may collect the beam data of the first light beam once every period of time (for example, once every 1 second). When the time interval for the tracking focus sensor to collect the beam data is set to a smaller value (for example, every 0.1 second), it can be approximately regarded as real-time collection of the beam data. Exemplarily, the beam data includes at least one of the spot size, the spot shape, and the light intensity signal. In this implementation, the controller (such as the focus controller) for controlling the tracking focus sensor may generate a tracking focus control instruction to trigger the tracking focus sensor to emit the first light beam, so that the tracking focus sensor obtains at least two defocus height analog signals of the target wafer based on the beam data, wherein a defocus height analog signal can generate a defocus height digital signal through analog-to-digital conversion. The defocus height indicated by the above defocus height analog signal or the defocus height digital signal can be distinguished by the direction in the form of "+" 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 above “+” and “-” are only used to distinguish directions and do not refer to the size of specific values. The same applies to the following text and will not be repeated here.

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

[0045] In some possible implementations, such as Figure 1The focus controller shown may be a focus control board, and the focus control board may be a printed circuit board (PCB). The focus control board may include a power supply, an analog signal interface, a digital signal interface, a storage interface, a network interface, etc., which is not limited in this application. The focus controller obtains the defocus height analog signal of the target wafer from the focus tracking sensor, predicts the focus position based on the defocus height analog signal, and then generates the 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, and generates a predicted focus position digital signal of the target wafer based on the focus feedback parameters. The above-mentioned predicted focus position digital signal can be used to indicate the predicted focus position. Exemplarily, the above-mentioned 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 of the defocus height of the target wafer by the difference between the two defocus heights indicated by the two defocus height digital signals, and then correct the predicted value of the defocus height based on the focus feedback parameter, so that the focus position predicted based on the defocus height is more accurate. Assuming the defocus height is +2mm and the focus feedback parameter is -1mm, the predicted value of the defocus height is corrected to +1mm, and the predicted focus position can be recorded as -1mm. The above-mentioned -1mm is used to indicate that the focus position is located 1mm below the current target wafer. Optionally, the focus controller can also obtain the difference between each two adjacent defocus heights in the multiple defocus heights sorted in the acquisition order, and calculate the focus feedback parameter by calculating the average or median. The present application does not limit the method of calculating the focus feedback parameter.

[0047] Optionally, in some feasible implementations, the focus controller may be integrated with a processor ( Figure 1 The present application takes the focus controller including the microcontroller as an example for explanation. The above-mentioned microcontroller can be used to receive data and process the data, for example, receive the defocus height digital signal and perform signal averaging, signal denoising and other processing on the defocus height digital signal.

[0048] Optionally, in some feasible implementations, the focus controller may also be integrated with a memory ( Figure 1The memory may be connected to a microcontroller. The memory is used to store data and programs or codes that control the operation of the microcontroller, thereby ensuring the normal operation of the microcontroller. The memory may include a random access memory (RAM) and a non-volatile memory (NVM), such as an erasable programmable read-only memory (EPROM). The memory may optionally be at least one storage device located away from the aforementioned processor, such as a memory loaded outside the focus controller, which is not limited in this application.

[0049] Optionally, in some feasible implementations, the focus controller may include a power supply ( Figure 1 The power source may be a power supply circuit, a storage battery, a DC power supply, etc., and is not limited in this application.

[0050] In some feasible implementations, a processor and a memory may also be integrated in the motor controller, and the motor controller is used to control the fine-tuning motor to drive the measurement lens to move based on the predicted focus position analog signal, thereby achieving the tracking focus of the target wafer. For example, the motor controller may generate a tracking focus control instruction based on the predicted focus position analog signal to control the fine-tuning motor to drive the measurement lens to move. The movement direction of the measurement lens may be the vertical direction in space. Optionally, the movement direction of the measurement lens may also be the horizontal direction or other angle direction in space, which should be determined according to the specific form of the product. This application is not limited thereto, and the vertical direction in space is used as an example for explanation.

[0051] It should be noted that the focus feedback parameter can be used to indicate the defocus height prediction error generated during the movement of the target wafer. The focus controller can compensate for the defocus height prediction error to make the predicted focus position indicated by the predicted focus position simulation signal more accurate, thereby causing the motor controller to trigger the fine-tuning motor to drive the measuring lens to move to a more accurate predicted focus position to track the target wafer. Therefore, even if the target wafer does not need to perform white light interferometric focusing operations,

[0052] It can also meet the focusing requirements of alignment error detection. In addition, the above-mentioned tracking process does not involve the transmission of digital signals between multiple digital signal interfaces, so it can avoid the complex digital coding conversion operation caused by different coding schemes used by different digital signal interfaces, thereby increasing the signal transmission speed, thereby increasing the tracking speed. In short, the method of tracking focus by tracking focus sensor can save the time of white light interferometric focusing before alignment error detection, thereby improving the efficiency of alignment error measurement.

[0053] In some feasible embodiments, the motor controller can also detect the moving position of the fine-tuning motor to detect the moving position of the measuring objective lens, and generate an objective lens position analog signal based on the moving position of the measuring objective lens to transmit the objective lens position analog signal to the photoelectric collection board.

[0054] Optionally, the focus controller and the motor controller can also be integrated into one controller, and the integrated controller can realize the function of obtaining the defocus height analog signal of the target wafer from the focus tracking sensor, and generating 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 and measure the movement position of the objective lens and send the objective lens position analog signal to the photoelectric collection board.

[0055] In some feasible embodiments, the above-mentioned photoelectric collection board is used to synchronously obtain a beam interference analog signal when receiving an objective lens position analog signal, and the above-mentioned beam interference analog signal is used to indicate the beam intensity of the light beam obtained by beam interference occurring on the above-mentioned photoelectric collection board during the measurement of the movement of the objective lens. The photoelectric collection board is also used to 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. In some feasible embodiments, the above-mentioned light beam used for beam interference on the photoelectric collection board may be a second light beam (such as a white laser), and the above-mentioned second light beam may be emitted by a light source such as a laser. After the light source irradiates the second light beam to the target wafer and the reference reflector, it is reflected by the target wafer and the reference reflector respectively. The two reflected light beams converge on the photoelectric collection board to cause beam interference, thereby generating a beam interference analog signal.

[0056] To understand the optical path of the second beam used for beam interference, see Figure 3 , Figure 3 is a schematic diagram of the optical path of the second light beam provided in this application. Figure 3 As shown, the optical path of the second light beam includes a reference objective lens, a measuring objective lens, a first beam splitter, a second beam splitter and a third beam splitter, and the wafer focusing system also includes a light source and a reference reflector. Figure 3 The multiple arrows shown in FIG. 1 are used to indicate the illumination direction of the second light beam.

[0057] In some feasible embodiments, the light source is used to emit a second light beam, which passes through the third beam splitter and the measuring objective lens in sequence and converges on the target wafer. After being reflected by the target wafer, the second light beam passes through the measuring objective lens, the third beam splitter, the second beam splitter and the first beam splitter in sequence and converges on the photodiode on the photoelectric collection board. The second light beam also passes through the third beam splitter and the reference objective lens in sequence and converges on the reference reflector. After being reflected by the reference reflector, the second light beam, the third beam splitter, the second beam splitter and the first beam splitter in sequence and converges on the photodiode. After the second light beam reflected by the reference reflector and the second light beam reflected by the target wafer converge on the photodiode, beam interference occurs on the photodiode to generate a beam interference analog signal.

[0058] It is understandable that the present application collects 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, and sends the focused digital signal generated after analog-to-digital conversion of the objective lens position analog signal and the beam interference analog signal to the focus controller for processing, which can ensure the synchronization of sampling and signal transmission, and avoid the situation where additional time is required to wait for the completion of the acquisition of the other signal after the acquisition of one of the objective lens position analog signal or the beam interference analog signal is completed due to asynchronous signal acquisition, thereby reducing the signal acquisition time. In addition, the focused digital signal includes both a digital signal indicating the objective lens position and a digital signal indicating the beam intensity. The processing of the focused digital signal by the focus controller can avoid the deviation of the calculated focused position due to the difference in the digital signal acquisition time, thereby improving the accuracy of the predicted focused position.

[0059] In some possible implementations, such as Figure 1 The focus controller shown can also be used to receive a focus digital signal through a digital signal interface, process the focus digital signal, generate an indication signal indicating the focus position of the measurement objective lens based on the intensity peak of the light beam intensity indicated by the focus digital signal and the moving position of the measurement objective lens, and send the indication signal to the above-mentioned motor controller. The above-mentioned indication signal is used to trigger the motor controller to control the fine-tuning motor to drive the measurement objective lens to move to the above-mentioned focus position, thereby focusing on the above-mentioned target wafer. For example, the above-mentioned focus controller can identify the intensity peak of the light beam intensity in the focus digital signal through a focus-finding algorithm, and identify the position of the measurement objective lens at the moment when the intensity peak is generated. At this time, the position of the measurement objective lens can be regarded as the focus position.

[0060] In some feasible implementations, after the focus controller generates the indication signal of the focus position, it can output the indication signal to the motor controller through the digital signal interface to trigger the motor controller to control the fine-tuning motor to measure the movement of the objective lens to the focus position. For example, the motor controller can generate a motion control instruction based on the indication signal, and then trigger the fine-tuning motor to drive the measurement objective lens to move to the above-mentioned focus position based on the motion control instruction.

[0061] It should be noted that the control method using digital signals is highly accurate and has strong anti-interference capabilities, and can trigger the measuring lens to move in a small range for precise focusing. When the motor controller controls the measuring lens to follow the focus based on the predicted focus position analog signal, the accuracy requirement is not high, but the timeliness of the follow-up focus is high, so the analog signal control method is used to achieve fast follow-up focus; and when the measuring lens is controlled to move by the focus position indication signal, the focus speed requirement is not high, but a high focus accuracy is required, so the digital signal control method is used to achieve precise focusing.

[0062] In some feasible implementations, the above-mentioned defocus height analog signal, predicted focus position analog signal, objective lens position analog signal and other analog signals can be transmitted through an analog signal interface, and there can be one or more of the above-mentioned analog signal interfaces, and the analog signal interface can be a sensor interface, etc.; the above-mentioned focus position digital signal, defocus height digital signal, indication signal and other digital signals can be transmitted through a digital signal interface, and there can be one or more of the above-mentioned digital signal interfaces, and the digital signal interface can be an RS232 interface, an RS485 interface, a transistor-transistor logic interface (transistor transistor logic, TTL), a universal asynchronous receiver and transmitter (universal asynchronous receiver and transmitter, UART), a serial peripheral interface (serial peripheral interface, SPI), a universal serial bus interface (universal serial bus, USB), an Ethernet interface, etc., and this application does not impose any restrictions.

[0063] According to the present application, a focus controller in a wafer focusing system is used to obtain a defocus height analog signal of a target wafer from a 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 a motor controller; the motor controller is used to control a fine-tuning motor to drive a measuring objective lens to move to focus the target wafer based on the predicted focus position analog signal, and send an objective lens position analog signal to a photoelectric collection board based on the moving position of the measuring objective lens; the photoelectric collection board is used to synchronously obtain a beam interference analog signal upon 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 measuring objective lens based on the intensity peak of the beam intensity indicated by the focus digital signal and the moving position of the measuring objective lens, and send an 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 measuring objective lens to move to the focus position, thereby focusing the target wafer. The wafer focusing system obtains the defocus height analog signal through the focus tracking sensor to generate a predicted focus position analog signal, which can trigger the fine-tuning motor for focus tracking, thereby eliminating the time for collecting the beam interference signal and measuring the position signal of the objective lens through white light interferometry focusing, thereby improving the efficiency of measuring the alignment error of the target wafer; in addition, the beam interference analog signal and the objective lens position analog signal can be synchronously collected through the photoelectric collection board and a focus digital signal can be generated, so that the focus controller generates and sends a focus position indication signal to the fine-tuning motor through the digital signal interface to trigger the fine-tuning motor to focus on the target wafer, thereby reducing the signal acquisition time of the beam interference signal and the measurement objective lens position signal, improving the accuracy of the predicted focus position, and having strong applicability.

[0064] To understand the structure of the focus controller, see Figure 4 , Figure 4 is another structural schematic diagram of the wafer focusing system provided by the present application. 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 supplies power to the focus controller. In some feasible implementations, the first analog-to-digital conversion module may be an analog-to-digital converter, which receives a defocus height analog signal from a focus tracking 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 embodiments, the above-mentioned microcontroller is used to perform digital signal processing on the received defocus height digital signal, so as to predict the focus position of the measurement objective lens through the defocus height digital signal, generate a predicted focus position digital signal based on the predicted focus position of the measurement objective lens, and send the predicted focus position digital signal to the above-mentioned digital-to-analog conversion module.

[0066] In some feasible embodiments, the digital-to-analog conversion module may be a digital-to-analog converter, which 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 output the predicted focus position analog signal to the motor controller through an analog signal interface, so that after receiving the predicted focus position analog signal, the motor controller controls the fine-tuning of the motor movement according to the focus position indicated by the predicted focus position analog signal to perform focus tracking.

[0067] In some feasible embodiments, the above-mentioned memory can be used to store data such as defocus height analog signals, defocus height digital signals, predicted focus positions, predicted focus position digital signals, predicted focus position analog signals, focus digital signals, indication signals, etc., so that the first analog-to-digital conversion module, microcontroller, and digital-to-analog conversion module can retrieve data and perform processing, transmission, and other operations.

[0068] In some feasible implementations, the above-mentioned power supply can be used to power the focus controller, and can also output electrical energy to the outside through the focus controller, for example, through circuit connection to power motor controllers, fine-tuning motors, photoelectric collection boards, focus controllers and other devices, and this application does not impose any restrictions.

[0069] It is understandable that, according to the characteristics of analog signals and digital signals, the waveform of analog signals is changeable, which makes it difficult to process directly, while digital signals 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 signal denoising. Digital signals have strong anti-interference ability and can restore disturbed waveforms, ensuring high accuracy and reliability in the digital signal processing process. In addition, since the signal directly obtained from the focus tracking sensor is an analog signal (such as a voltage signal), and analog signals are generally used to control equipment such as fine-tuning motors, the focus controller receives the analog signal through the analog signal interface, and then converts the analog signal 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. Among them, the analog signal interface for input and the analog signal interface for output can be the same analog signal interface, or they can be different analog signal interfaces (such as Figure 4 The analog signal interface 1 and the analog signal interface 2 are shown, and this application does not impose any limitation on this.

[0070] In some feasible implementations, the focus controller may further include one or more digital signal interfaces (such as Figure 4 The focus controller can receive the focusing digital signal sent by the photoelectric collection board through the digital signal interface (such as the digital signal interface 1), and determine the moving position of the measuring objective lens when the intensity peak is generated based on the intensity peak of the light beam intensity indicated by the focusing digital signal through the microcontroller in the focus controller. The moving 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 the digital signal interface 2).

[0071] To understand the structure of the above-mentioned photoelectric collection board, see Figure 5 , Figure 5 This is a schematic diagram of the structure of the photoelectric collection board provided by this application. Figure 5 As shown above Figure 4 The photoelectric collection board included in the wafer focusing system shown may include a first isolation circuit, a second isolation circuit, a photodiode and a second analog-to-digital conversion module. The second analog-to-digital conversion module is connected to the first isolation circuit and the second isolation circuit, 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 conversion 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 digital-to-analog conversion 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 obtain a beam interference analog signal corresponding to the beam intensity of the beam obtained by beam interference on the photodiode during the measurement of the movement of the objective lens, and output a target beam interference analog signal to the second analog-to-digital conversion module based on the beam interference analog signal. The second isolation circuit is used for signal isolation between the photodiode and the second digital-to-analog conversion module, thereby improving the stability and driveability of the beam interference analog 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 lens position analog signal and the target beam interference analog signal to generate a target objective lens position digital signal and a target beam interference digital signal, generate the above-mentioned in-focus digital signal based on the target objective lens position digital signal and the target beam interference digital signal, and send the above-mentioned in-focus digital signal to the above-mentioned focus controller. The above-mentioned in-focus digital signal is used to indicate the beam intensity of the light beam that transmits the beam interference and the objective lens position of the measuring objective lens. Optionally, the second digital-to-analog conversion module may not generate a in-focus digital signal, but instead send the target objective lens position digital signal and the target beam interference digital signal as the output of the photoelectric acquisition board to the focus controller synchronously, which is not limited in this application.

[0075] In some feasible implementations, the above-mentioned photoelectric collection board may include a digital signal interface (such as Figure 5 The photoelectric acquisition board outputs the focus digital signal to the focus controller through the digital signal interface 3), wherein the focus controller can also receive the above focus digital signal through the digital signal interface, and then ensure the accuracy of the focus digital signal through the digital signal transmission between the two digital signal interfaces.

[0076] For easier understanding of the first isolation circuit, see Figure 6 , Figure 6 is a circuit diagram of the first isolation circuit provided by the present 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 the first connection terminal and the 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 of the first operational amplifier 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, and the fourth connection terminal of the first operational amplifier 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 the ground through a connector, and then receive the objective lens position analog signal transmitted by the motor controller from the connector through the third connection end of the first operational amplifier. The above connector can be a coaxial radio frequency connector (subMiniature version a, SMA), which has the characteristics of wide frequency band, excellent performance, high reliability, long life, etc., and can support a wider frequency range by adopting an SMA interface, and the SMA interface has a shielding interface, which can effectively prevent the influence of external interference signals, thereby ensuring high-precision signal transmission between the motor controller and the photoelectric collection board.

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

[0079] It can be understood that the above-mentioned first isolation circuit is a follower circuit based on the first operational amplifier, which can perform signal isolation after receiving the objective lens position analog signal through the connector, and output the target objective lens position analog signal to the second analog-to-digital conversion module through the second connection end of the first operational amplifier.

[0080] To facilitate understanding of the second isolation circuit, see Figure 7 , Figure 7 It is a circuit diagram of the second isolation circuit provided by the present application. The second isolation circuit includes a second operational amplifier, a second resistor, a third resistor and a capacitor. The above-mentioned second resistor is connected between the first connection terminal of the above-mentioned second operational amplifier and the second connection terminal of the second operational amplifier, the first connection terminal of the second operational amplifier and the third connection terminal of the second operational amplifier serve as the input terminal of the above-mentioned second isolation circuit, the first connection terminal of the second operational amplifier is connected to the above-mentioned photodiode, the third connection terminal of the second operational amplifier and the fourth connection terminal of the above-mentioned second operational amplifier are connected to the power supply, the first connection terminal of the above-mentioned 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 above-mentioned second isolation circuit, the above-mentioned capacitor is connected between the fifth connection terminal of the second operational amplifier and the second connection terminal of the third resistor, and 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, wherein the photodiode can be connected to a bias power supply (vbias), and the bias power supply can provide a stable voltage and current to enable the beam interference to proceed normally. The brightness and intensity of the light beam can also be adjusted by the bias power supply to improve the stability and reliability of the beam interference analog signal. In addition, the power supply connected to the third connection terminal of the second operational amplifier can also be a bias power supply, and the bias power supplies connected to the photodiode and the third connection terminals of the second operational amplifier can be the same or different bias power supplies, and the voltage provided by the bias power supply should be determined according to the actual product form, and this application does not limit it. 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 can be connected, and the specific voltage value of the power supply should be determined according to the actual product form, and this application does not limit it.

[0082] It can be understood that the above-mentioned second isolation circuit is a follower circuit composed of a second operational amplifier. After receiving the light beam interference analog signal from the photodiode through the first connection end of the second operational amplifier, it can perform signal isolation and output the target light beam interference analog signal to the second analog-to-digital conversion module through the second connection end of the third resistor.

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

[0084] According to the present application, a focus controller in a wafer focusing system is used to obtain a defocus height analog signal of a target wafer from a 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 a motor controller; the motor controller is used to control a fine-tuning motor to drive a measuring objective lens to move to focus the target wafer based on the predicted focus position analog signal, and send an objective lens position analog signal to a photoelectric collection board based on the moving position of the measuring objective lens; the photoelectric collection board is used to synchronously obtain a beam interference analog signal upon 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 measuring objective lens based on the intensity peak of the beam intensity indicated by the focus digital signal and the moving position of the measuring 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 measuring objective lens to move to the focus position to focus the target wafer. The wafer focusing system obtains the defocus height analog signal through the focus tracking sensor to generate the predicted focus position analog signal, which can trigger the fine-tuning motor for focus tracking, thereby eliminating the time of collecting the beam interference signal and measuring the position signal of the objective lens through white light interferometry focusing, thereby improving the efficiency of measuring the alignment error of the target wafer; in addition, the beam interference analog signal and the objective lens position analog signal can be synchronously collected through the photoelectric collection board and a focus digital signal can be generated, so that the focus controller generates and sends the focus position indication signal to the fine-tuning motor through the digital signal interface to trigger the fine-tuning motor to focus on the target wafer, thereby reducing the signal collection time of the beam interference signal and the measurement of the objective lens position signal, improving the accuracy of the predicted focus position, and having strong applicability.

[0085] Those skilled in the art will appreciate that the wafer focusing systems and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented with electronic hardware, computer software, or a combination of both. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in terms of function in the above description. Professional and technical personnel may use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

Claims

1. A wafer focusing system, characterized in that: include: Focus tracking sensor, focus controller, photoelectric acquisition board, fine-tuning motor and motor controller; The focus controller is used to: obtain 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 adjustment motor to drive the measuring lens to move based on the predicted focus position analog signal to focus the target wafer, and send the lens position analog signal to the photoelectric collection board based on the moving position of the measuring lens; The photoelectric collection board is used to: synchronously obtain a beam interference analog signal when receiving the objective lens position analog signal, the beam interference analog signal is used to indicate the intensity of the beam obtained by the beam interference occurring on the photoelectric collection board during the measurement of the objective lens movement, generate a focus digital signal 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 focusing position of the measurement objective lens based on the intensity peak of the light beam intensity indicated by the focusing digital signal and the moving position of the measurement objective lens, and send the indication signal to the motor controller, wherein the indication signal is used to trigger the motor controller to control the fine-tuning motor to drive the measurement objective lens to move to the focusing position to focus on the target wafer.

2. The system according to claim 1, characterized in that The focus controller comprises 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: obtain 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 conversion 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 1 or 2, characterized in that: The photoelectric collection board includes a first isolation circuit, a second isolation circuit, a photodiode and a second analog-to-digital conversion module; the second analog-to-digital conversion 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 a 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: obtain the beam interference analog signal corresponding to the beam intensity obtained by the 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 light beam interference analog signal to generate the focus digital signal and send the focus digital signal to the focus 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 is connected to the first connection end and the second connection end of the first operational amplifier, the second connection end of the first operational amplifier serves as the output end of the first isolation circuit, the first connection end of the first operational amplifier and the third connection end of the first operational amplifier serve as input ends of the first isolation circuit, the third connection end of the first operational amplifier is grounded through the connector, and the fourth connection end of the first operational amplifier and the fifth connection end of the first operational amplifier are connected to a power supply.

5. The system according to claim 3 or 4, characterized in that: The second isolation circuit includes a second operational amplifier, a second resistor, a third resistor and a capacitor; the second resistor is connected to the first connection end of the second operational amplifier and the second connection end of the second operational amplifier, the first connection end of the second operational amplifier and the third connection end of the second operational amplifier serve as input ends of the second isolation circuit, the first connection end of the second operational amplifier is connected to the photodiode, the third connection end of the second operational amplifier and the fourth connection end of the second operational amplifier are connected to a power supply, the first connection end of the third resistor is connected to the second connection end of the second operational amplifier, the second connection end of the third resistor serves as an output end of the second isolation circuit, the capacitor is connected between the fifth connection end of the second operational amplifier and the second connection end of the third resistor, and the fifth connection end of the second operational amplifier is grounded.

6. The system according to any one of claims 2 to 5, characterized in that: The system also includes a first beam splitter, a second beam splitter, and a third beam splitter; The tracking focus sensor is used to: emit a first light beam, which sequentially passes through the first beam splitter, the second beam splitter, the third beam splitter and the measuring objective lens and converges on the target wafer, and then is reflected by the target wafer and sequentially passes through the measuring objective lens, the third beam splitter, the second beam splitter and the first beam splitter and returns to the tracking focus sensor; The tracking focus sensor is further used to: send at least two defocus height analog signals to the focus controller based on the beam data of the first light beam returned; one defocus height analog signal is obtained from a portion of the beam data of the first light beam received, and one defocus height analog signal is converted into a defocus height digital signal through analog-to-digital conversion, and the beam data includes at least one of a spot size, a shape or a light intensity signal; The focus controller is also used 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, and 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 light beam, which passes through the third beam splitter and the measuring objective lens in sequence, converges on the target wafer, and is reflected by the target wafer, then passes through the measuring objective lens, the third beam splitter, the second beam splitter and the first beam splitter in sequence, then converges on the photodiode. The second light beam also passes through the third beam splitter and the reference objective lens in sequence, converges on the reference reflector, and is reflected by the reference reflector, then passes through the reference objective lens, the third beam splitter, the second beam splitter and the first beam splitter in sequence, then converges on the photodiode to perform beam interference.

8. The system according to any one of claims 1 to 7, characterized in that: The system also includes a power supply; the power supply is used to supply power to the focus tracking sensor, the focus controller, the motor controller, the photoelectric collection board and the fine-tuning motor.

9. The system according to any one of claims 2 to 7, characterized in that: The system further comprises a memory; the memory is connected to the microcontroller, wherein the memory is used to store program codes so that the microcontroller calls the program codes stored in the memory to perform digital signal processing.

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