Signal synchronous acquisition and processing system and method for white light interference focusing

Abstract

The invention provides a signal synchronous acquisition and processing system and method for white light interference focusing, and is applied to the technical field of semiconductor measurement, the signal acquisition and processing system is used for overlay error measurement in the semiconductor measurement technology, and a CMOS sensor and an avalanche breakdown diode sensor are adopted. High-precision white light interference measurement is realized through components such as a beam splitter, a tube mirror, a halogen light source, a shutter, a microscope objective, a reference mirror and piezoelectric ceramics; a signal conditioning channel is designed and comprises a passive attenuation circuit, an impedance conversion circuit, a gain amplification circuit and an ADC (Analog to Digital Converter) driving circuit, so that accurate acquisition and processing of signals are ensured; the signal acquisition and processing system evaluates acquired interference signals through a template matching method, and realizes rapid determination of a zero optical path difference position and automatic focusing of wafer. The system has the advantages of high stability, high accuracy, high cost effectiveness and compact space structure, and is suitable for high-precision semiconductor measurement equipment.

Description

Technical Field

[0001] The present application relates to the field of semiconductor measurement technology, and in particular to a signal synchronization acquisition and processing system and method for white light interferometric focusing. Background Art

[0002] In the field of semiconductor technology, overlay error measurement plays an important role in large-scale lithography production and ensuring the electrical characteristics of devices and normal signal transmission. It is crucial for large-scale lithography production, and high-precision overlay error measurement is required to ensure the electrical characteristics and signal transmission of devices. However, when focusing the image, a clearer image cannot be obtained. In order to solve this technical problem, an image focusing method needs to be used to solve it.

[0003] The traditional image focusing method uses the method of adjusting the focal length for measurement. Although this focusing adjustment method can solve the problem of unclear measured images, it also has some defects. For example, because the flatness of the chuck (a device for clamping and positioning silicon wafers) exceeds the depth of field of the high-power objective lens, the traditional image focusing method needs to continuously adjust the vertical position of the objective lens during the image-based overlay measurement process to keep the measured surface on a clear focal plane to ensure that a high-contrast image and focal plane are obtained. However, this method of adjusting the objective lens relies on manual adjustment of the objective lens focal length and image contrast analysis, and requires continuous adjustment of the vertical position of the acquisition objective lens. It is easily affected by the operator's skills and changes in ambient light, resulting in limited consistency and reliability of the measurement results. This measurement method is not only inefficient, but also greatly affects the final measurement accuracy.

[0004] Based on this, a high-stability and high-accuracy signal acquisition system is required to support the white light interferometric focusing system.

[0005] Application Contents

[0006] In view of this, the embodiments of this specification provide a signal acquisition and processing system for white light interferometric focusing, which realizes fast and accurate positioning of white light interferometric focusing through high-precision signal acquisition and processing, improves the efficiency of semiconductor measurement, and improves the measurement accuracy of semiconductor images.

[0007] The embodiments of this specification provide the following technical solutions:

[0008] A voltage signal processing system for white light interferometric focusing, comprising a signal transmission channel, an input impedance selection module, an impedance conversion circuit module, a signal conditioning channel, an ADC driving circuit and an ADC acquisition circuit;

[0009] The signal transmission channel includes an avalanche breakdown diode signal acquisition channel and a piezoelectric ceramic signal acquisition channel, which transmits the interference signal from the avalanche breakdown diode sensor and the position signal from the piezoelectric platform;

[0010] The input impedance selection module selects the input impedance of the avalanche breakdown diode sensor and the piezoelectric sensor;

[0011] The signal conditioning channel includes a first signal conditioning channel and a second signal conditioning channel, wherein the first signal conditioning channel is used to process the signal from the avalanche breakdown diode sensor, and the first signal conditioning channel includes a passive attenuation circuit and a gain amplification circuit;

[0012] The second signal conditioning channel is used for conditioning the output signal of the piezoelectric sensor, wherein the second signal conditioning channel is used for processing the signal from the piezoelectric sensor, and the second signal conditioning channel includes a passive attenuation circuit and a gain amplification circuit;

[0013] The ADC driving circuit converts the output signals of the first signal conditioning channel and the second signal conditioning channel into differential signals matching the ADC;

[0014] The ADC acquisition circuit converts the acquired differential signal into a digital signal.

[0015] Preferably, the control unit synchronously collects and processes signals from the avalanche breakdown diode sensor and the piezoelectric position sensor, the processing unit synchronously collects and digitizes the interference signal of the avalanche breakdown diode sensor and the position signal of the piezoelectric position sensor, and generates a template of the interference signal based on the zero optical path difference position, performs template matching on the collected interference signal, calculates the matching coefficient, selects the piezoelectric position with the highest matching coefficient as the zero optical path difference position, and outputs the processed signal data

[0016] The dual signal acquisition channel acquires the avalanche breakdown diode signal acquisition channel and the piezoelectric signal acquisition channel of the avalanche breakdown diode sensor, and each channel is designed with an adjustable input range device to adapt according to the output voltage range of different sensors;

[0017] In addition, the output signals of the avalanche breakdown diode sensor and the piezoelectric device synchronously collect the vertical position information of the objective lens and the corresponding interference signal intensity, and convert the light intensity signal into a voltage signal output, and match the avalanche breakdown diode and the piezoelectric analog output different voltage ranges;

[0018] Preferably, the host computer system is used to analyze and process the data of the signal acquisition circuit and determine the vertical position corresponding to the zero-order interference fringe, and the determined zero-order interference fringe position is combined with the fixed offset value.

[0019] Preferably, the avalanche breakdown diode sensor is used to collect interference signals at different vertical positions of the objective lens, and convert the light intensity signal into a voltage signal for output, and the output signals of the avalanche breakdown diode sensor and the piezoelectric device synchronously collect the vertical position information of the objective lens and the corresponding interference signal intensity;

[0020] Preferably, the piezoelectric device is used to synchronously collect the vertical position signal of the objective lens;

[0021] Preferably, the analog-to-digital converter is used to process the signal collected by the signal collection channel and output a digital value;

[0022] Preferably, the host computer system is used to analyze and process the data of the signal acquisition circuit and determine the vertical position corresponding to the zero-order interference fringe, and the determined zero-order interference fringe position is combined with the fixed offset value to determine the clear focal plane position.

[0023] Among them, the signal acquisition channel includes an avalanche breakdown diode signal acquisition channel and a piezoelectric signal acquisition channel. The avalanche breakdown diode signal acquisition channel is responsible for acquiring the voltage signal output by the avalanche breakdown diode sensor, and the piezoelectric signal acquisition channel is responsible for acquiring the position signal output by the piezoelectric device.

[0024] The embodiment of this specification also provides a method of a signal acquisition and processing system, which is applied to a signal acquisition and processing system for white light interferometric focusing as described in any one of the embodiments of this specification, and the method of the signal acquisition and processing system includes:

[0025] Synchronously collecting the vertical position of the objective lens and the corresponding interference signal intensity, and converting the collected signal into a digital value through a signal collection circuit;

[0026] Preferably, the digital value is read by the STM32 system and transmitted to the host computer system;

[0027] Preferably, a template matching method is used in the host computer system to evaluate and analyze the collected interference signal;

[0028] Preferably, the position of the sharp focus plane is determined by a fixed offset value according to the analysis result.

[0029] Preferably, synchronous acquisition is achieved by a CMOS sensor and an avalanche breakdown diode sensor, wherein the CMOS sensor is used to acquire the focus plane image, and the avalanche breakdown diode sensor is used to acquire the interference signal.

[0030] In addition, the template matching method for evaluating the scanning interference signal includes:

[0031] Generate and select templates Based on the interference signal strength under the current system, generate and select one or more templates for confirming the interference signal strength at the zero optical path difference position;

[0032] Collecting the interference signal strength at different piezoelectric positions; Collecting the interference signal strength at different piezoelectric positions;

[0033] Template matching matches the collected interference signal strengths at different piezoelectric positions with the template selected in the generating and selecting templates to obtain a matching coefficient;

[0034] Compare the matching coefficients, detect whether the optical interference signal intensities at all piezoelectric positions have been compared, and compare the obtained matching coefficients;

[0035] Confirm the zero optical path difference position and confirm the piezoelectric position with the highest matching coefficient as the zero optical path difference position.

[0036] The embodiment of this specification also provides a template matching method for evaluating a scanning interference signal, which is applied to a method of a signal acquisition and processing system as described in any one of the embodiments of this specification. The template matching method for evaluating a scanning interference signal includes:

[0037] Generate and select templates Based on the interference signal strength under the current system, generate and select one or more templates for confirming the interference signal strength at the zero optical path difference position;

[0038] Collecting the interference signal strength at different piezoelectric positions; Collecting the interference signal strength at different piezoelectric positions;

[0039] Template matching matches the collected interference signal strengths at different piezoelectric positions with the template selected in the generating and selecting templates to obtain a matching coefficient;

[0040] Compare the matching coefficients, detect whether the optical interference signal intensities at all piezoelectric positions have been compared, and compare the obtained matching coefficients;

[0041] Confirm the zero optical path difference position and confirm the piezoelectric position with the highest matching coefficient as the zero optical path difference position.

[0042] Preferably, a database comprising a plurality of templates is established, each template corresponding to a different zero optical path difference position;

[0043] Real-time acquisition of interference signal intensity during white light interferometric focusing process;

[0044] Extract key features from the interference signal collected in real time;

[0045] Based on the extracted features, the best matching template is selected from the database;

[0046] The zero optical path difference position corresponding to the selected template is determined as the zero optical path difference position of the current interference signal.

[0047] Compared with the prior art, the at least one technical solution adopted in the embodiments of this specification can achieve the following beneficial effects:

[0048] This application designs a signal acquisition and processing system for the white light self-focusing system of overlay measurement. By synchronously acquiring the signal of the avalanche breakdown diode sensor and the piezoelectric position signal and using the template matching method for comparison and analysis, the optimal focusing position of the mark on the wafer can be quickly determined.

[0049] First of all, compared with other signal acquisition cards with fixed range and impedance input, the designed signal acquisition and processing system can freely define the attenuation ratio and gain amplification ratio according to the sensor signal characteristics to adapt to the selection and signal output of different sensors. It has greater scalability in application and ensures the accuracy of signal acquisition, improves the focusing speed and measurement accuracy of semiconductor measurement equipment, and achieves high integration with a smaller spatial structure, realizing high efficiency and high-precision positioning of white light interferometric focusing, which can be better applied to the focusing system of overlay equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0051] Figure 1 This is a diagram of a self-focusing system based on white light interferometry provided by the present application;

[0052] Figure 2 This is a diagram of a voltage signal acquisition system for white light interferometric focusing provided by the present application;

[0053] Figure 3 It is a flow chart of a template matching method provided by this application;

[0054] Figure 4 It is a passive attenuation circuit diagram provided by the present application;

[0055] Figure 5 It is a gain amplification circuit diagram provided by the present application;

[0056] Figure 6 This is an ADC driving circuit diagram provided by the present application;

[0057] Figure 7It is an AD acquisition circuit diagram provided by this application;

[0058] Figure 8 This is an avalanche breakdown diode and electrical signal diagram provided by the present application;

[0059] exist Figure 1 Middle: CMOS sensor 1, avalanche breakdown diode sensor 2, first beam splitter 3, tube lens 4, illumination halogen light source 5, second beam splitter 6, shutter 7, first microscope objective 8, reference lens 9, second microscope objective 10, vertical motion mechanism 11, wafer 12, voltage system acquisition signal 13. DETAILED DESCRIPTION

[0060] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0061] The following describes the implementation methods of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific implementation methods, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the following embodiments and the features in the embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present application.

[0062] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on the present application, it should be understood by those skilled in the art that an aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number and aspect described herein can be used to implement the device and / or practice the method. In addition, other structures and / or functionalities other than one or more of the aspects described herein can be used to implement this device and / or practice this method.

[0063] It should also be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present application. The drawings only show components related to the present application rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0064] Additionally, in the following description, specific details are provided to facilitate a thorough understanding of the examples. However, it will be understood by those skilled in the art that the examples can be practiced without these specific details.

[0065] In semiconductor processing, overlay error measurement is a key step to ensure the electrical characteristics of devices and normal signal transmission, especially in large-scale lithography process production. However, existing technologies have some obvious shortcomings in achieving precise focusing and measurement.

[0066] First, the traditional image focusing method relies on the depth of field of the high-power objective lens. When faced with chuck flatness that exceeds the depth of field of the high-power objective lens, it is impossible to ensure that the measured surface is always in a clear focal plane, which will lead to insufficient contrast in the acquired image, thus affecting the measurement accuracy. The accurate focal plane can be obtained, which greatly affects the final measurement accuracy.

[0067] In addition, in the image-based overlay measurement process, the traditional method requires the operator to continuously adjust the vertical position of the objective lens during the focusing process to keep the measured surface on a clear focal plane at all times to ensure that high-contrast graphics are obtained. This process is not only time-consuming and labor-intensive to operate, but also difficult to ensure repeatability and consistency. It is also more troublesome to obtain high-contrast graphics.

[0068] Secondly, although traditional signal acquisition system technology can obtain high-contrast graphics, it still has limitations in signal acquisition and processing. For example, traditional image focusing relies on the operator to manually adjust the focal length by observing the clarity of the image. This process is not only time-consuming, but also has limited accuracy because the human eye has difficulty recognizing small changes in clarity and is easily affected by subjective judgment. In addition, traditional methods often have difficulty achieving precise focus when dealing with samples with irregular or reflective surfaces. Existing signal acquisition systems often use fixed-range inputs, which limits their ability to adapt to different sensor selections and signal outputs; in addition, these systems also have deficiencies in integration, cost control, and spatial structure optimization, making it difficult to meet the requirements for high stability and high accuracy in the focusing system of overlay equipment.

[0069] Furthermore, when traditional signal acquisition and processing systems process voltage signals, the acquisition accuracy is limited due to the inconsistent voltage ranges of these signals. The lack of flexible signal conditioning channel design makes it impossible for the system to adjust the attenuation ratio and gain amplification ratio according to specific application requirements, thereby failing to fully utilize the performance of the sensor and making it difficult to achieve accurate analysis and rapid processing of the collected data. This not only limits the system's focusing accuracy and speed, but also affects the final measurement results.

[0070] In summary, the prior art has many deficiencies in overlay error measurement in semiconductor processes, including limitations in focusing accuracy and speed, cumbersome operating steps, limitations in signal acquisition and processing, and deficiencies in data processing and analysis. These shortcomings limit the application and development of the prior art in the field of high-precision measurement, and a new technical solution is needed to overcome these difficulties and achieve more efficient and accurate overlay error measurement. The present invention solves the shortcomings of the prior art through an innovative signal acquisition and processing system, and promotes the advancement of semiconductor process measurement technology.

[0071] Based on this, the embodiments of this specification propose an innovative signal acquisition and processing system for white light interferometric self-focusing, such as Figure 1 As shown, it is specially designed to accurately collect and compare the analog output signals of avalanche breakdown diodes and piezoelectric ceramics to confirm the Z-direction position of the strongest interference peak and achieve fast focusing positioning.

[0072] It should be noted that by synchronously collecting the vertical position of the objective lens and the corresponding interference signal intensity, the signal acquisition and processing system is responsible for collecting the interference signal of the objective lens at different vertical positions through the avalanche breakdown diode sensor, and converting it into a voltage signal output. At the same time, the voltage signal output by the piezoelectric device reflects the vertical position of the objective lens, and is collected through the signal conditioning channel, including input impedance selection, passive attenuation circuit, impedance conversion circuit, gain amplifier circuit and ADC drive circuit, to ensure accurate signal acquisition and processing.

[0073] In addition, the collected signals are converted into digital values ​​by an analog-to-digital converter, read by the STM32 system and transmitted to the host computer system. The host computer system uses the template matching method to evaluate and analyze the collected interference signals. By comparing the interference signal intensity at different piezoelectric positions with the preset template, the matching coefficient is calculated, and finally the piezoelectric position with the highest matching coefficient is determined as the zero optical path difference position, that is, the Z-direction position of the strongest interference peak.

[0074] The present invention designs a signal acquisition and processing system for the white light self-focusing system of overlay measurement, and realizes rapid focusing of the mark on the wafer by synchronously acquiring the signal of the avalanche breakdown diode sensor and the signal of the piezoelectric position.

[0075] Secondly, the designed signal acquisition and processing system has greater scalability and can freely define the attenuation ratio and gain amplification ratio to adapt to the selection and signal output of different sensors. The system has lower cost, smaller spatial structure and higher integration, which makes it better suitable for the focusing system of overlay equipment. It improves the measurement accuracy and efficiency of the white light interferometric self-focusing system and provides an effective solution for the overlay error measurement in semiconductor processes.

[0076] The technical solutions provided by various embodiments of the present application are described below in conjunction with the accompanying drawings.

[0077] like Figure 1 As shown, this embodiment provides a white light interferometric focusing system, comprising: a CMOS sensor 1, an avalanche breakdown diode sensor 2, a first beam splitter 3, a tube lens 4, an illumination halogen light source 5, a second beam splitter 6, a shutter 7, a first microscope objective lens 8, a reference lens 9, a second microscope objective lens 10, a vertical motion mechanism 11 and a voltage system acquisition signal 13, wherein in the white light interferometric focusing system of the present invention, each component works together to achieve high-precision and high-efficiency focusing positioning, and the following is a detailed description of the functions and effects of the key components in the system:

[0078] CMOS sensor 1 is one of the core components of the system and is responsible for collecting focal plane images. CMOS sensor 1 converts optical signals into electrical signals and generates digital image data. These digital image data are crucial for subsequent image processing and analysis because they provide detailed information about the object being measured. CMOS sensor 1 is widely used in various imaging systems due to its high sensitivity, low power consumption and fast response time.

[0079] Avalanche breakdown diode sensor 2 is used to collect interference signals of the objective lens at different vertical positions. Compared with traditional photodiodes, avalanche breakdown diode sensor 2 can provide higher sensitivity and faster response speed. Avalanche breakdown diode sensor converts light intensity signals into voltage signal outputs, providing basic data for subsequent signal processing.

[0080] The first beam splitter 3 is a component in the optical system used to split a light beam into two or more parts. The first beam splitter 3 splits the light beam emitted by the illumination halogen light source into two beams, one for illuminating the sample and the other for reference, allowing the system to perform sample imaging and interference measurement simultaneously, thereby improving the measurement efficiency and accuracy of the system.

[0081] Tube lens 4 is used for optical path connection to ensure the transmission efficiency and accuracy of the light beam in the system. Tube lens 4 is composed of a series of lenses, which can correct the divergence angle of the light beam and ensure the stability and uniformity of the light beam during transmission.

[0082] The illumination halogen light source 5 provides the light source required for white light interference. The halogen light source is widely used due to its high brightness, good color temperature and stable spectral output. The light beam emitted by the illumination halogen light source 5 passes through the beam splitter and is used to illuminate the sample and the reference mirror to produce interference fringes.

[0083] The second beam splitter 6 further splits the light beam into beams for sample imaging and reference, which helps to improve the flexibility and adjustability of the system and allows the user to adjust the distribution of the light beam as needed.

[0084] Shutter 7 is used to control whether the interference signal enters the main optical path. When interference measurement is required, shutter 7 opens to allow the interference signal to enter; when interference measurement is not required, shutter 7 closes to prevent the interference signal from entering. This design helps protect the sensor from unnecessary interference.

[0085] The first microscope objective lens 8 is used to achieve interference. The first microscope objective lens 8 focuses the light beam emitted by the illumination halogen light source 5 onto the sample to generate interference fringes. The first microscope objective lens 8 ensures the quality and stability of the focused light beam, which is crucial to the formation of interference fringes.

[0086] The reference mirror 9 is used to generate a reference beam to interfere with the beam on the sample. The stability and accuracy of the reference beam 9 are crucial to the formation and measurement of interference fringes. The position of the reference mirror 9 needs to be precisely controlled to ensure the accuracy of the interference measurement.

[0087] The second microscope objective lens 10 is used to magnify the measurement mark pattern. The second microscope objective lens 10 magnifies the interference fringes on the sample so that the CMOS sensor 1 can capture these fringes more clearly. The magnification function of the second microscope objective lens 10 can improve the resolution and measurement accuracy of the system.

[0088] The vertical motion mechanism 11 is driven by piezoelectricity and is used to achieve automatic focusing. The vertical motion mechanism 11 can accurately control the vertical position of the objective lens to achieve accurate focusing on the sample. At the same time, the vertical motion mechanism 11 also outputs a piezoelectric position signal to provide the system with real-time information on the objective lens position.

[0089] Wafer12 is the object to be measured by the white light interferometric focusing system. Wafer12 is usually the substrate in the semiconductor manufacturing process. The white light interferometric focusing system performs measurement by precisely focusing on the measured area on wafer12 to ensure high precision and high efficiency in the overlay process. The surface characteristics and structural complexity of the wafer require the system to have extremely high measurement accuracy and stability. Chuck is a wafer carrier on which wafer12 is placed for inspection.

[0090] The voltage system acquisition signal 13 is used to collect and process the voltage signals of the avalanche breakdown diode and the piezoelectric output. These voltage signals pass through the signal conditioning channel, including input impedance selection, passive attenuation circuit, impedance conversion circuit, gain amplifier circuit and ADC drive circuit to ensure accurate signal acquisition and processing. The collected signals are converted into digital values ​​through an analog-to-digital converter, read by the STM32 system and transmitted to the host computer system for further processing and analysis.

[0091] In summary, through the coordinated work of the above components, the white light interferometric focusing system can achieve high-precision and high-efficiency focusing positioning, providing an effective solution for overlay error measurement in semiconductor processes. In addition, by precisely controlling the vertical position of the objective lens and collecting interference signals, the white light interferometric focusing system can quickly locate the Z-position of the strongest interference peak to achieve precise focusing.

[0092] In some examples, white light interferometry technology uses the coherence of the light source to produce interference fringes. The contrast and clarity of these fringes are not limited by the human eye's recognition ability, making the measurement more accurate. Although the coherence of the white light source is relatively small, it can produce interference fringes that can be used for precise measurement. It can produce interference fringes with an extremely small range and can provide extremely high spatial resolution, which significantly improves the measurement accuracy.

[0093] In the white light interferometric focusing system, the position of the zero-order interference fringe provides a clear reference point. This position corresponds to the precise distance between the objective lens and the sample, and can be used as an absolute position reference during the focusing process. By accurately acquiring the vertical position of the objective lens and synchronously acquiring the interference signal intensity corresponding to each vertical position, the position of the zero-order interference fringe can be accurately determined.

[0094] At the same time, the avalanche breakdown diode sensor is responsible for collecting the interference signals of the objective lens at different vertical positions and converting them into voltage signal outputs, while the piezoelectric device is responsible for accurately controlling the vertical position of the objective lens and outputting corresponding position signals.

[0095] Since the voltage signal ranges output by the avalanche breakdown diode and the piezoelectric device are inconsistent, in order to ensure the accuracy of signal acquisition, different signal conditioning channels need to be designed for these two signals. The signal conditioning channel includes input impedance selection, passive attenuation circuit, impedance conversion circuit, gain amplifier circuit and ADC drive circuit. These circuits ensure the stability and accuracy of the signal during the acquisition process, so that the acquired signal can truly reflect the actual state of the sample.

[0096] The input impedance selection ensures the matching of the sensor output signal with the acquisition system. The passive attenuation circuit adjusts the attenuation ratio according to the signal strength to protect the subsequent circuit from damage by excessive voltage. The impedance conversion circuit improves the circuit's driving ability for the subsequent stage. The gain amplifier circuit adjusts the signal to the full-scale value of the ADC to ensure that the dynamic range of the signal is fully utilized. The ADC drive circuit converts the input single-ended signal into a differential signal to match the ADC input requirements.

[0097] The collected digital values ​​are read by the STM32 system and transmitted to the host computer system for further processing and analysis of the two sets of data. The host computer system uses the template matching method to evaluate and analyze the collected interference signals. By comparing the interference signal intensity at different piezoelectric positions with the preset template, the matching coefficient is calculated, and finally the piezoelectric position with the highest matching coefficient is determined as the zero optical path difference position, and the vertical position corresponding to the zero-order interference fringe is obtained.

[0098] Finally, the system can accurately determine the position of the clear focal plane through a fixed offset value. This offset value is based on system design and experimental data, which ensures that in practical applications, the objective lens can quickly and accurately focus on the mark on the wafer to achieve high-precision overlay error measurement.

[0099] Therefore, white light interferometry technology has high-precision and high-efficiency measurement capabilities, as well as a high-stability and high-accuracy signal acquisition system. This high-stability and high-accuracy signal acquisition system is extremely important for the white light interferometry focusing system. The avalanche breakdown diode and piezoelectric device selected for the white light interferometry focusing system have inconsistent output voltage signal ranges. In order to ensure the accuracy of signal acquisition and make the full-scale acquisition match the collected voltage value, different signal conditioning channels need to be designed for the two signals. This provides an effective solution for the measurement of overlay errors in semiconductor processes. This solution not only improves production efficiency, but also significantly improves product quality and reliability.

[0100] like Figure 2 As shown, Figure 2 It is a voltage signal acquisition system. The voltage signal acquisition system first receives analog voltage signals from the avalanche breakdown diode sensor and the piezoelectric sensor. The input voltage signal represents the light intensity change detected by the sensor and the vertical position change of the objective lens.

[0101] Next, in order to match the output impedance of the sensor, the voltage signal acquisition system provides an input impedance selection function, which can select 50Ω or 1MΩ input impedance to ensure that the signal can be transmitted to the subsequent circuit efficiently and without loss. According to the strength of the signal, the system can choose whether to attenuate the input signal or transmit it directly. The attenuation circuit is implemented through a set of resistors and capacitors to reduce excessive signals to the processable range of the ADC.

[0102] Firstly, the voltage signal processing system for white light interferometric focusing includes a signal transmission channel, an input impedance selection module, an impedance transformation circuit module, a signal conditioning channel, an ADC driving circuit and an ADC acquisition circuit. The signal transmission channel includes an avalanche breakdown diode signal acquisition channel and a piezoelectric ceramic signal acquisition channel. These two channels are responsible for transmitting the interference signal from the avalanche breakdown diode sensor and the position signal from the piezoelectric platform, respectively, and transmitting the interference signal from the avalanche breakdown diode sensor and the position signal from the piezoelectric platform.

[0103] In addition, the input impedance selection module is responsible for selecting the input impedance that matches the avalanche breakdown diode sensor and the piezoelectric sensor to ensure that the signal is not lost or distorted during transmission. The signal conditioning channel enhancement system includes two independent channels: a first signal conditioning channel and a second signal conditioning channel.

[0104] Among them, the first signal conditioning channel specifically processes the signal from the avalanche breakdown diode sensor and is used for conditioning the output signal of the piezoelectric sensor. The first signal conditioning channel includes a passive attenuation circuit and a gain amplifier circuit, which can adjust the strength and amplitude of the signal to meet the needs of subsequent processing.

[0105] Similarly, the second signal conditioning channel processes the signal from the piezoelectric sensor. The second signal conditioning channel is used for conditioning the output signal of the piezoelectric sensor. The second signal conditioning channel also includes a passive attenuation circuit and a gain amplifier circuit to ensure the stability and accuracy of the signal during transmission.

[0106] Specifically, the ADC driving circuit converts the output signals of the first signal conditioning channel and the second signal conditioning channel into differential signals compatible with the ADC. The ADC requires a differential input signal to improve the signal's anti-interference capability and ensure the integrity and accuracy of the signal. The differential signal consists of two signals with opposite phases, which can effectively offset common-mode noise, thereby maintaining signal quality in long-distance transmission or high-noise environments. The ADC driving circuit converts a single-ended signal into a differential signal, so that the signal can be correctly identified and processed by the ADC, thereby achieving high-precision analog-to-digital conversion.

[0107] At the same time, the ADC acquisition circuit converts the collected differential signal into a digital signal. In a digital system, processing and analyzing signals requires data in digital form. Although the differential signal can effectively resist common-mode interference, it needs to be converted into a digital signal before entering the digital processing system. The analog-to-digital converter quantifies the amplitude of the analog signal and converts it into a discrete digital value. This process involves sampling, quantizing and encoding the analog signal to ultimately generate a digital signal.

[0108] In one embodiment, the impedance conversion circuit is used to improve the circuit's driving capability for subsequent stages, ensuring the integrity and stability of the signal during transmission. Through impedance matching, the signal can more effectively drive subsequent gain amplifier circuits.

[0109] Gain amplifier circuit such as Figure 5 As shown, the gain amplifier circuit is used to adjust the signal passing through the attenuation path to the full-scale value of the ADC. The maximum gain is set by the external feedback resistor RF and the gain resistor RG, and the formula is G=2*(RF / RG). In addition, the maximum gain is adjusted between -1V and 1V by Vadj to adapt to different signal strengths. The system bandwidth is configured by R1, C1, and RS to ensure that the system can respond to signal changes of different frequencies.

[0110] ADC driver circuit such as Figure 6 As shown, the ADC driving circuit converts the input single-ended signal into a differential signal to match the input requirement of the ADC. The differential signal can effectively suppress common-mode noise and improve the signal-to-noise ratio of the signal.

[0111] ADC acquisition circuit such as Figure 7 As shown, the ADC acquisition circuit is responsible for acquiring the analog signal after gain amplification and ADC drive circuit processing, and converting it into a digital quantity. The conversion of analog signal to digital signal provides the basis for subsequent data processing.

[0112] In addition, the STM32 system is a high-performance microcontroller for reading the digital value output by the ADC acquisition circuit. The STM32 system has high-speed data processing capabilities and rich peripheral interfaces, and can efficiently process the collected data. The STM32 system is used to read the digital value and transmit it to the host computer system. The host computer system is used to process the data read by the STM32 system. The host computer system is usually based on a PC or a workstation, and runs professional data processing and analysis software to determine the vertical position corresponding to the zero-order interference fringe, and calculate the position of the clear focal plane. The host computer processes and compares the avalanche breakdown diode signal and the piezoelectric signal synchronously collected by the acquisition card, and performs matching analysis to obtain them.

[0113] In one embodiment, dual signal acquisition channels are designed in the white light interferometric focusing system, which are used for signal acquisition of avalanche breakdown diode sensors and piezoelectric sensors respectively. Each channel is equipped with an adjustable input range device, allowing the system to accurately adapt according to the output voltage range of different sensors. The avalanche breakdown diode signal acquisition channel is responsible for collecting the analog voltage signals output by the avalanche breakdown diode sensor. These signals reflect the interference signal intensity of the objective lens at different vertical positions. The piezoelectric signal acquisition channel is responsible for collecting the voltage signals output by the piezoelectric sensor. These signals correspond to the vertical position of the objective lens.

[0114] Specifically, in order to adapt to the different output voltage ranges of the two sensors, the input impedance selection module includes an impedance converter, and the impedance converter is used to provide 50Ω or 1MΩ impedance options to match the output impedance of different sensors. The avalanche breakdown diode sensor is responsible for collecting the interference signal of the objective lens at different vertical positions. The avalanche breakdown diode sensor can convert the received light intensity signal into a voltage signal output. The avalanche breakdown diode signal acquisition channel conditions the output signal of the avalanche breakdown diode sensor to a format suitable for ADC acquisition through an input impedance selector, a passive attenuation circuit, an impedance conversion circuit, a gain amplifier circuit and an ADC drive circuit. The input impedance selector allows the system to select an input impedance of 50Ω or 1MΩ according to the output impedance of the avalanche breakdown diode sensor, and the passive attenuation circuit selects an appropriate attenuation ratio according to the strength of the signal to ensure that the signal is within the full scale range of the ADC.

[0115] Among them, when the input impedance of the impedance conversion circuit is 50Ω, the input signal is processed in a straight-through manner. The circuit does not change the impedance characteristics of the signal, allowing the signal to pass directly without any attenuation or amplification. In the straight-through mode, the input and output impedances of the circuit are matched, avoiding signal reflection and distortion, ensuring that the signal is transmitted to the next-level circuit in the best state, such as the ADC acquisition circuit, thereby achieving efficient and accurate signal acquisition and processing.

[0116] In addition, when the input impedance of the impedance conversion circuit is 1MΩ, the impedance conversion circuit attenuates the input signal to adapt to the output impedance and signal strength of different sensors and ensure that the signal does not exceed the tolerance range of the subsequent circuit during transmission. The circuit can appropriately attenuate the signal of the high-impedance sensor to match the input requirements of the ADC, ensure the stability and accuracy of the signal during the conversion process, and the attenuated signal enters the ADC with an appropriate amplitude, thereby achieving effective analog-to-digital conversion.

[0117] Among them, in order to ensure that the collected signal can truly reflect the vertical position of the objective lens and the corresponding interference signal intensity, the signal acquisition channel includes an adjustable input range device. The output voltage signal of the avalanche breakdown diode sensor usually varies within a certain range, while the voltage signal output by the piezoelectric device reflects the actual position of the objective lens.

[0118] In addition, the gain amplifier circuit further amplifies the attenuated signal to an appropriate level, sets the maximum gain through the external feedback resistor RF and the gain resistor RG, and adjusts the gain between -1V and 1V through Vadj to adapt to different signal strengths. The system bandwidth is configured through R1, C1, and RS to ensure that signals of different frequencies can be accurately collected.

[0119] At the same time, the host computer system receives digital values ​​transmitted from the STM32 system. These digital values ​​are converted by the ADC acquisition circuit and represent the voltage signals output by the avalanche breakdown diode sensor and the piezoelectric sensor. The host computer system analyzes the data and determines the vertical position corresponding to the zero-order interference fringes. The host computer system further analyzes the data processed by the STM32 system to determine the vertical position corresponding to the zero-order interference fringes. By accurately analyzing the avalanche breakdown diode signal and the piezoelectric signal, the system can quickly determine the strongest peak position of the interference fringes, that is, the position of the zero-order interference fringes, and determine the position of the clear focal plane in combination with the fixed offset value.

[0120] The analysis and processing flow of the host computer system usually includes steps such as signal filtering, noise suppression, peak detection and pattern recognition. First, the system may apply a digital filter to remove noise and unnecessary frequency components in the signal to improve the signal quality. Then, the system analyzes the processed signal through a peak detection algorithm to find the peak with the highest intensity of the interference fringe, that is, the position of the zero-order interference fringe.

[0121] In one embodiment, an avalanche breakdown diode signal acquisition channel is responsible for collecting voltage signals output by an avalanche breakdown diode sensor. These signals are related to the light intensity received by the objective lens at different vertical positions. The avalanche breakdown diode sensor converts the light signal into a voltage signal. The signal acquisition channel includes input impedance selection, passive attenuation circuit, impedance conversion circuit and gain amplification circuit, which condition these voltage signals into a format suitable for processing by an analog-to-digital converter.

[0122] Among them, the input impedance selection ensures the impedance matching between the sensor and the acquisition system. The passive attenuation circuit performs appropriate attenuation according to the signal strength to protect the subsequent circuits and ensure that the signal is within the full-scale range of the ADC. The gain amplifier circuit further amplifies the attenuated signal to the full-scale value of the ADC to ensure that the dynamic range of the signal is fully utilized.

[0123] The piezoelectric signal acquisition channel acquires the position signal output by the piezoelectric device. The piezoelectric device is responsible for accurately controlling the vertical position of the objective lens and outputting a voltage signal corresponding to the position. The piezoelectric signal acquisition channel also includes input impedance selection, passive attenuation circuit, impedance conversion circuit and gain amplifier circuit to ensure accurate acquisition and conditioning of the position signal.

[0124] The CMOS sensor is responsible for capturing the focal plane image and providing intuitive information about the focus position of the objective lens. The CMOS sensor converts optical signals into electrical signals, generates digital image data, and provides important visual feedback for the system.

[0125] All conditioned signals are converted into digital signals through analog-to-digital converters. The STM32 system is responsible for reading these digital values ​​and performing preliminary data processing, such as filtering, amplification, and format conversion. The design of the STM32 system enables it to efficiently process large amounts of data and provide accurate digital signals for the host computer system.

[0126] This dual-channel signal acquisition design, combined with the image acquisition function of the CMOS sensor, enables the white light interferometric focusing system of the present invention to achieve high-precision synchronous signal acquisition and processing, significantly improving the accuracy and efficiency of measurement.

[0127] In one embodiment, the white light interferometric focusing system includes a series of key signal conditioning circuits for adapting and optimizing the signals collected from the avalanche breakdown diode sensor and the piezoelectric sensor.

[0128] First, the input impedance selector allows the system to select the appropriate input impedance, either 50Ω or 1MΩ, based on the output impedance of the sensor. This selection is critical to ensuring efficient transmission of the signal from the sensor to the acquisition system, helping to prevent signal distortion and power loss, thereby ensuring signal integrity and accuracy.

[0129] The avalanche breakdown diode sensor can output a wide voltage signal range from -10V to 10V when the stroke is 50um. This voltage signal range covers the full stroke of the piezoelectric platform, allowing the APD sensor to provide continuous and accurate voltage signal output throughout the movement of the piezoelectric platform to reflect the change in the platform position, ensuring that the system accurately captures and processes interference signals, thereby achieving precise focusing and measurement.

[0130] Next, the passive attenuation circuit performs necessary attenuation or pass-through processing on the input signal. For piezoelectric sensors, since their output signals may have a high voltage amplitude, the passive attenuation circuit attenuates the signal through a resistor and capacitor network to adapt it to the input voltage range of the subsequent circuit. This attenuation is necessary to avoid overloading the subsequent gain amplifier circuit and analog-to-digital converter, and to ensure that the signal is within the full range of the analog-to-digital converter.

[0131] The impedance conversion circuit is used to improve the circuit's driving ability for the subsequent circuit. Through impedance conversion, the signal can more effectively drive the subsequent gain amplifier circuit, ensuring the strength and quality of the signal during transmission, thereby improving the signal integrity of the entire signal chain.

[0132] The gain amplifier circuit further conditions the signal to the full-scale value of the ADC. This circuit sets the maximum gain through the external feedback resistor RF and the gain resistor RG. By adjusting Vadj between -1V and 1V, the gain can be adjusted to adapt to different signal strengths to ensure that the signal can effectively utilize the entire dynamic range of the ADC. In addition, the system bandwidth is configured through R1, C1, and RS to ensure that the system can accurately collect signals of different frequencies.

[0133] Finally, the ADC driver circuit converts the input single-ended signal into a differential signal to match the ADC input requirements. The differential signal format helps suppress noise and improve the signal-to-noise ratio, thereby improving the signal quality and ADC measurement accuracy.

[0134] In one embodiment, in the white light interferometric focusing system of the present invention, the template matching method is one of the key technologies to achieve precise focusing. Figure 3 As shown, this method is implemented by the following steps:

[0135] First, the system generates and selects templates for the current system in the template matching process. This step involves creating one or more reference templates based on known or pre-measured interference signal patterns. These templates represent the expected interference signal intensity distribution under specific conditions, such as a specific objective lens position or specific sample characteristics. The generation of templates can be based on historical data, experimental measurements, or theoretical calculations.

[0136] Next, the system collects interference signal intensity at different piezoelectric positions of the sliding window. The interference signal intensity at different piezoelectric positions is selected to obtain a series of interference signal data, which reflects the interference effect between the sample and the light source at different vertical positions of the objective lens. This step is to capture the subtle changes in the interference fringes, thereby providing sufficient data support for subsequent template matching.

[0137] Then, the system will match the collected interference signal strength with the pre-set template. Matching the interference signal strength with the template and calculating the matching coefficient is the core step in the template matching method. In this step, the system will compare the similarity between the actual collected interference signal and the reference template, and calculate a matching coefficient, which reflects the degree of matching between the two. The higher the matching coefficient, the better the consistency between the collected interference signal and the template.

[0138] Among them, the template matching method is a scanning interference signal evaluation method, which is widely used in the fields of precision measurement and optical detection. The core of this method is to identify and evaluate the interference signal through template generation and matching, so as to determine the position of zero optical path difference, which is crucial to achieve high-precision interference measurement.

[0139] First of all, the first step of the template matching method is the generation and selection confirmation of the template. At this stage, the system will generate a reference template based on the interference signal intensity at the zero optical path difference position; this position is the point where the phase difference in the interference pattern is zero, corresponding to the constructive interference of the light wave, so the signal intensity is the largest; by accurately measuring and recording the signal intensity at this position, a reference standard can be provided for the subsequent matching process.

[0140] Next, the system will select the interference signal strength at different piezoelectric positions. The displacement capability of piezoelectric ceramics enables the system to collect interference signals at different positions; the signal strength at these positions will vary due to the change in optical path difference, thus forming a series of signal strength data corresponding to the piezoelectric displacement.

[0141] The third step is to match the interference signal intensity at these different piezoelectric positions with the pre-generated template to calculate the matching coefficient. This step involves a complex algorithm. By comparing the similarity between the actual signal and the template, a quantitative matching index, namely the matching coefficient, can be obtained. The higher the matching coefficient, the greater the similarity between the actual signal and the template, and thus the degree of closeness of the optical path difference at this position to the zero optical path difference position can be inferred.

[0142] The fourth step is to check whether the optical interference signal intensity at all piezoelectric positions has been compared. This step ensures the comprehensiveness and accuracy of the system. By checking all data points, it is possible to avoid missing any important information that may affect the final result.

[0143] Finally, the system will confirm the piezoelectric position with the highest matching coefficient as the zero optical path difference position. This conclusion is based on the quantitative analysis of the matching coefficient, which represents the signal that is most similar to the reference template, so that the zero optical path difference position can be accurately determined.

[0144] In summary, the template matching method provides a systematic and automated way to evaluate scanning interferometer signals. Through precise template generation, signal acquisition, matching calculation and result confirmation, high-precision identification of the zero optical path difference position is achieved. This method not only improves the accuracy of interferometric measurement, but also provides a powerful tool for the design and optimization of optical systems.

[0145] Next, the system needs to detect the intensity of the optical interference signal at the piezoelectric position to complete the comparison. This step is to ensure that the system has collected enough data for accurate analysis. The system will check whether all important piezoelectric positions have been collected and compared. If the window has not completed all sliding, the matching coefficient calculation will continue. If the window has completed all sliding, the template matching will be completed to avoid missing any important data that may affect the final result.

[0146] Finally, the system will confirm that the piezoelectric position with the highest matching coefficient is the zero optical path difference position. At the zero optical path difference position, that is, when the distance between the objective lens and the sample is the optimal focus position, the intensity distribution of the interference signal will be closest to the reference template, so the matching coefficient will be the highest. By identifying the piezoelectric position with the highest matching coefficient, the system can determine the optimal focus position, that is, the zero optical path difference position.

[0147] In one embodiment, the host computer system uses an advanced zero-order interference fringe recognition method to achieve high-precision focusing. This method ensures the accuracy and reliability of focusing through a series of refined steps.

[0148] First, the host system generates and selects the template under the current system during the template matching process, which involves creating or selecting a suitable reference template based on the current configuration of the system and the known interference pattern.

[0149] Next, the system selects the interference signal intensity at different piezoelectric positions. This step is to collect the actual interference signal intensity data at different objective lens vertical positions. These data are actually measured and reflect the actual interference fringe pattern.

[0150] Then, the host computer system matches the collected interference signal strength with the pre-set template. Matching the interference signal strength with the template and calculating the matching coefficient is the core of the recognition process. The system obtains a matching coefficient by calculating the similarity between the actual interference signal and the reference template. This coefficient quantifies the degree of match between the two and is an important indicator for evaluating the focus quality.

[0151] Next, the system needs to detect the intensity of the optical interference signal at the piezoelectric position to complete the comparison. This step is to ensure that all important piezoelectric positions have been signal collected and compared, thereby ensuring the comprehensiveness and accuracy of the focusing process.

[0152] Finally, the host computer system will confirm that the piezoelectric position with the highest matching coefficient is the zero optical path difference position. This conclusion is based on the observation that at the zero optical path difference position, that is, when the distance between the objective lens and the sample is the best focus position, the intensity distribution of the interference signal will be closest to the reference template, so the matching coefficient will be the highest. By identifying the piezoelectric position with the highest matching coefficient, the system can accurately determine the zero optical path difference position and achieve the best focus.

[0153] Through this series of precise and efficient steps, the zero-order interference fringe recognition method of the host computer system can quickly and accurately determine the position of the zero-order interference fringe in the white light interferometric focusing process, thereby significantly improving the focusing accuracy and efficiency. This has important practical significance for improving the accuracy of overlay error measurement in semiconductor processes, and helps to improve product quality and production efficiency.

[0154] In one embodiment, the system selects an avalanche breakdown diode sensor, whose output signal range is 0 to 5 V. This signal range is suitable for high-sensitivity light intensity measurement and can accurately reflect the interference signal intensity of the objective lens at different vertical positions.

[0155] At the same time, the system also uses a piezoelectric platform with a stroke of 50μm, and its output signal range is -10V to 10V, which can correspond to the full stroke of 50μm. This design ensures that the piezoelectric platform can accurately control the position of the objective lens within a large vertical range to meet the needs of high-precision focusing. By effectively matching the output signal of the avalanche breakdown diode sensor with the piezoelectric platform, the system can accurately collect and process the interference signal, thereby improving the measurement accuracy and efficiency of the white light interferometric focusing system.

[0156] Specifically, for the avalanche breakdown diode signal acquisition channel, when the output impedance of the avalanche breakdown diode is 50Ω, the impedance selection module selects 50Ω. The passive attenuation circuit includes resistors R1 and R2 and capacitors C1 and C2. The first resistor R1 and the first capacitor C1 are connected in parallel to form a first capacitive resistor circuit, the second resistor R2 and the second capacitor C2 are connected in parallel to form a second capacitive resistor circuit, and the first capacitive resistor circuit and the second capacitive resistor circuit are connected in parallel to each other to form a passive attenuation circuit.

[0157] Among them, the signal acquisition channel is the key to ensure that the white light interferometric focusing system can accurately collect and process the signal from the avalanche breakdown diode sensor. The output impedance of the avalanche breakdown diode sensor in the output impedance matching of the avalanche breakdown diode is 50Ω. In order to ensure the effective transmission of the signal and minimize reflection, when the impedance selection is set to 50Ω, this impedance matching helps to improve the signal transmission quality and reduce signal loss.

[0158] First, the passive attenuation network is Figure 4 As shown, the resistance values ​​of R1 and R2 are 230KΩ and 200KΩ respectively, the capacitance values ​​of C1 and C2 are both 20PF, and the impedance conversion circuit selects direct pass. When the output voltage range is higher than the input range of the circuit, the signal amplitude is reduced by setting the attenuation multiple to 2. The attenuation multiple is set to 2, which means that the input signal will be reduced to half of its original amplitude. In this network, the resistor R1 is 230KΩ, R2 is 200KΩ, and the capacitors C1 and C2 are both 20PF. This configuration allows the system to adjust the amplitude of the signal as needed to adapt to the input requirements of the subsequent circuit.

[0159] In addition, for the piezoelectric ceramic signal acquisition channel, when the output impedance of the piezoelectric ceramic is 50Ω, the impedance of the impedance selection module is selected as 50Ω, wherein the resistance value of R1 is 230KΩ, the resistance value of R2 is 630KΩ, the capacitance values ​​of C1 and C2 are both 20PF, and the impedance conversion circuit selects direct pass. When the amplitude of the input signal is higher than the maximum input voltage of the analog-to-digital converter or other subsequent processing circuits, the signal amplitude is reduced by setting the attenuation multiple to 4. Since the input impedance is 50Ω, the impedance conversion circuit selects direct pass, that is, no impedance conversion is performed. This design simplifies the circuit, while ensuring direct transmission of the signal and reducing signal distortion caused by impedance mismatch.

[0160] At the same time, the gain amplifier circuit is Figure 5 As shown in the figure, the gain amplifier circuit is designed to amplify the attenuated signal to a level suitable for the analog-to-digital converter input. For the selected analog-to-digital conversion chip ADS1256, the acquisition voltage value is 0-5V, so the gain amplification factor is set to 2.5 times. In this gain amplifier circuit, the feedback resistor RG is 150Ω and RF is 180Ω. These values ​​determine the size of the gain. At the same time, the circuit also includes R1=20Ω, C1=3pF, and Rs=50Ω, which are used to further adjust the performance and response characteristics of the circuit.

[0161] ADC driver circuit such as Figure 6 As shown in the figure, its function is to convert the input single-ended signal into a differential signal. However, since the input of the analog-to-digital conversion chip ADS1256 selected this time is a single-ended signal, differential conversion is actually not required.

[0162] ADC acquisition circuit such as Figure 7 As shown in Figure 1, the avalanche breakdown diode signal enters the ADC acquisition card through the AI0 channel. This channel is specially designed for avalanche breakdown diode signals to ensure that the signal can be accurately acquired and converted into digital format.

[0163] Data transmission and processing Through the SPI protocol, the analog-to-digital conversion chip transmits the read signal data to the STM32 system. SPI is a common serial communication protocol that allows high-speed, full-duplex data communication. The STM32 system, as a microcontroller, is responsible for the preliminary processing of the collected data, such as filtering, amplification, and format conversion. The processed data is then transmitted to the host computer system for more in-depth analysis and processing.

[0164] In summary, the design of the avalanche breakdown diode signal acquisition channel takes into account the precise acquisition, conditioning and conversion of signals. Through precise signal conditioning and acquisition, the system can achieve high-precision analysis of interference fringes during white light interferometric focusing, thereby quickly and accurately determining the focusing position and improving the accuracy and efficiency of overlay error measurement in semiconductor processes.

[0165] In one embodiment, the design of the piezoelectric signal acquisition channel is the key to ensure that the white light interferometric focusing system can accurately acquire and process the signal from the piezoelectric sensor. In the piezoelectric output impedance matching, the output impedance of the piezoelectric sensor is 50Ω. In order to ensure the effective transmission of the signal and minimize reflection, Figure 2 The impedance selection in is set to 50Ω. This impedance matching helps to improve the transmission quality of the signal and reduce signal loss.

[0166] Specifically, the output impedance of the APD signal acquisition channel is designed to be 50Ω. Figure 2 The impedance selection shown in Figure 1 is matched to ensure the stability and minimum loss of the signal during transmission. This precise impedance matching is critical to maintaining signal integrity, especially in long-distance transmission or high-frequency applications.

[0167] In addition, the design of the gain amplifier circuit is as follows Figure 5 As shown in the figure, for the selected analog-to-digital conversion chip ADS1256, the acquisition voltage value is 0-5V, so the gain amplification factor is set to 2.5 times. This gain setting is achieved through the precise combination of RG=150Ω, RF=180Ω, R1=20Ω, C1=3pF, and Rs=50Ω. The design of this gain amplifier circuit ensures that the signal is amplified to a level suitable for analog-to-digital conversion without distortion, while maintaining the dynamic range of the signal.

[0168] In addition, the design of the ADC driver circuit is as follows Figure 6 As shown, it converts the input single-ended signal into a differential signal. The selected analog-to-digital conversion chip ADS1256 inputs a single-ended signal and does not require conversion, allowing the system to adapt according to the specific analog-to-digital conversion chip requirements to achieve the best signal transmission efficiency.

[0169] The APD signal enters the ADC acquisition card through the AI0 channel. This process is as follows: Figure 7 As shown. This channel design ensures that the signal can be directly and efficiently transmitted to the acquisition card, reducing signal loss and interference during transmission. The gain ratio determines how the signal is amplified after passing through the attenuation path to match the full-scale input range of the analog-to-digital converter. The attenuated signal may be too weak to be effectively recognized by the ADC. By accurately defining the gain ratio, the system can ensure that the signal is amplified to the optimal level without distortion, thereby making full use of the dynamic range of the ADC.

[0170] The maximum gain is set by the external feedback resistor RF and the gain resistor RG. The ratio of these two resistors determines the maximum gain of the amplifier circuit.

[0171] In addition, a voltage regulator Vadj is included, which allows the maximum gain to be adjusted within the range of -1V to 1V. This adjustment provides additional flexibility, allowing the system to fine-tune the gain to adapt to real-time changing signal conditions or to optimize signal quality. Through the adjustment of Vadj, the system can quickly respond to different measurement requirements without replacing hardware, improving the adaptability and flexibility of the system.

[0172] In general, through the gain amplification ratio and adjustable resistance configuration, combined with Vadj's real-time adjustment capabilities, the signal acquisition system can efficiently process a variety of signals, ensuring that the signal is always kept in the best state before being converted into digital form.

[0173] Finally, through the SPI protocol, the analog-to-digital conversion chip transmits the read signal data to the STM32 system, and then transmits the data to the host for processing. This choice of communication protocol ensures the high speed and reliability of data transmission, while simplifying the overall architecture of the system.

[0174] In one embodiment, the piezoelectric signal acquisition channel processes the signal from the piezoelectric sensor, and the output impedance of the piezoelectric sensor is 50Ω, which matches the impedance selection module in the system, ensuring the stability and minimum loss of the signal during transmission.

[0175] In addition, the passive attenuation network design in the system is as follows Figure 4 As shown in the figure, the attenuation factor is precisely set to 4, which is achieved through a specific combination of resistors and capacitors, specifically R1 = 230KΩ and R2 = 630KΩ, and C1 and C2 are both 20PF. The design of this attenuation network helps to adjust the amplitude of the signal to meet the input requirements of the subsequent circuit while keeping the shape and characteristics of the signal unchanged.

[0176] In addition, the input impedance is also 50Ω, which matches the output impedance of the piezoelectric sensor. A direct connection is achieved through the impedance transformation circuit module, which reduces signal distortion and reflection during transmission, thereby improving signal quality and system reliability.

[0177] The design of the gain amplifier circuit is as follows Figure 5 As shown, for the selected analog-to-digital conversion chip ADS1256, the acquisition voltage value is 0-5V, so the gain amplification factor is set to 2.5 times. This gain setting is achieved through the precise combination of RG=150Ω, RF=180Ω, R1=20Ω, C1=3pF, and Rs=50Ω. The design of this gain amplifier circuit ensures that the signal is amplified to a level suitable for analog-to-digital conversion without distortion, while maintaining the dynamic range of the signal.

[0178] The design of ADC drive circuit is as follows Figure 6As shown in the figure, it converts the input single-ended signal into a differential signal that matches the ADC. Since the selected analog-to-digital conversion chip ADS1256 inputs a single-ended signal, there is actually no need for conversion, allowing the system to adapt according to the specific analog-to-digital conversion chip requirements to achieve the best signal transmission efficiency.

[0179] The impedance conversion circuit includes an ADC driving circuit, which includes a driving amplifier and a differential conversion network. The piezoelectric signal enters the ADC acquisition card through the AI1 channel. This process is as follows Figure 7 This channel design ensures that the signal can be directly and efficiently transmitted to the acquisition card, reducing signal loss and interference during transmission.

[0180] Finally, through the SPI protocol, the analog-to-digital conversion chip transmits the read signal data and the APD signal synchronously to the STM32 system, and then transmits the data to the host for processing. The choice of this communication protocol ensures the high speed and reliability of data transmission, while simplifying the overall architecture of the system.

[0181] Collect data such as Figure 8 As shown, the piezoelectric position corresponding to the zero-order interference fringe is obtained by the template matching method for focusing. This method uses template matching technology to identify and locate interference fringes, thereby achieving precise piezoelectric position control and focusing.

[0182] In one embodiment, the differential conversion network is a key component in the signal acquisition system. The differential conversion network includes a differential amplifier. The function of the differential amplifier is to convert a single-ended signal into a differential signal to improve the signal's anti-interference ability and enhance the signal's stability. In this process, the single-ended input signal Vin is directly connected to the positive input terminal of the differential amplifier, while the negative input terminal is grounded to form a reference point. This configuration enables the differential amplifier to amplify the voltage difference between the input signal and the ground, that is, the amplitude of the single-ended signal.

[0183] The working principle of the differential amplifier is based on amplifying the voltage difference between the two input terminals. In this case, since the negative input terminal is grounded, the differential amplifier is actually amplifying the voltage difference between the single-ended signal and ground. This amplification not only enhances the strength of the signal, but also suppresses common-mode noise, that is, noise that appears at both input terminals at the same time. In this way, the differential amplifier is able to provide a clearer signal output, which is essential for accurate signal measurement and processing.

[0184] In practical applications, the use of differential amplifiers can significantly improve the signal-to-noise ratio of signals, especially in long-distance transmission or in high electromagnetic interference environments. Due to its symmetry, differential signals have better suppression effects on external interference such as electromagnetic radiation and ground loop noise.

[0185] In summary, the differential amplifier in the differential conversion network converts the single-ended signal into a differential signal, thereby enhancing the signal's anti-interference ability and providing high-quality input for subsequent digital signal processing.

[0186] In one embodiment, the impedance conversion circuit includes an ADC acquisition circuit, which is responsible for converting analog signals into digital signals for further processing and analysis. The ADC acquisition circuit is a complex integrated system consisting of multiple sub-modules, each of which has its own specific functions and works together to achieve efficient signal acquisition and conversion.

[0187] Among them, the analog-to-digital converter is the core of the ADC acquisition circuit, which receives the analog signal from the signal conditioning channel and converts it into a digital signal. This conversion process is a key step in the digitization of analog signals, which determines the quality and accuracy of the signals that the system can process.

[0188] The channel selection switch allows the system to select one of multiple different analog signal inputs to the ADC. This flexibility enables the system to adapt to different measurement requirements and process signals from multiple sensors at the same time.

[0189] Multichannel analog switches further expand the system's capabilities by being able to select specific analog signals from multiple input channels. This is especially important in applications where multiple parameters need to be monitored simultaneously, such as in complex industrial control systems or medical monitoring equipment.

[0190] The sample-and-hold circuit plays a vital role in the analog-to-digital conversion process. It stabilizes the analog signal and ensures that the signal does not change during the conversion process, thereby ensuring the accuracy of the conversion.

[0191] Signal buffers are used to buffer analog signals and reduce signal loss during transmission, especially when transmitting over long distances or through complex circuits, which helps maintain signal integrity.

[0192] The signal amplifier is another important component, which amplifies the weak analog signal to the level range that the ADC analog-to-digital converter can receive. This is especially important for detecting weak signals, such as in scientific research or precision measurement.

[0193] The digital filter performs filtering processing on the collected digital signal in the digital domain to remove noise and unnecessary frequency components and improve the signal quality.

[0194] The clock management unit controls the sampling rate of the ADC analog-to-digital converter to ensure that the signal is sampled at an appropriate rate, which is crucial to meeting the real-time requirements of specific applications.

[0195] Finally, the data interface is the bridge between the ADC acquisition circuit and the external system. It transmits the converted digital signal to the STM32 system and then to the host computer system. This interface ensures the smooth transmission of data so that the data can be further processed, stored or displayed.

[0196] In summary, the impedance conversion circuit and the ADC acquisition circuit included therein are a highly integrated and collaborative system, which provides a reliable data acquisition solution for various applications through precise analog signal processing and efficient digital signal conversion.

[0197] In one embodiment, the synchronous acquisition and processing device integrates multiple key components to achieve white light interferometric focusing and signal acquisition. The synchronous acquisition and processing system includes core components such as a halogen light source, a piezoelectric ceramic driver, a first microscope objective, a reference mirror, a shutter, a first beam splitter, a second beam splitter, and a second microscope objective. Each of the above components is connected through an optical path to ensure that the light beam can be transmitted efficiently and accurately in the system.

[0198] The halogen light source is used as the light source of the system to provide stable white light, which is connected to the second beam splitter through the optical path to achieve the initial distribution of the light beam. The function of the second beam splitter is to split the light beam from the halogen light source into two beams, one for the reference optical path and the other for the measurement optical path of the target object.

[0199] In addition, the piezoelectric ceramic drive is the key to achieve precise vertical positioning of the objective lens. It is connected to the objective lens mount through a support frame and can accurately control the vertical movement of the objective lens to achieve automatic focusing. This precise vertical positioning is essential for obtaining accurate interference signals.

[0200] First, the optical path connection between the first microscope objective and the reference mirror ensures the accurate transmission of the reference beam, which is used to reflect the beam so that it interferes with the beam reflected from the target object. The shutter is located between the reference mirror and the first beam splitter to control the on and off of the beam to synchronously collect the interference signal. The optical path connection between the first beam splitter and the second beam splitter is responsible for further distribution of the beam, with part of the beam being directed to the CMOS sensor to collect the focal plane image and the other part being directed to the avalanche breakdown diode sensor to collect the interference signal.

[0201] Secondly, the second microscope objective is responsible for magnifying and measuring specific marks on the target object, which is crucial for accurately measuring and analyzing the surface features of the target object. The optical path connections in the entire system are precisely designed to ensure that the transmission of the light beam between the various components is both efficient and accurate, thereby achieving high-precision white light interferometry.

[0202] In addition, through this precise optical path design and the coordinated work of components, the synchronous acquisition and processing device can achieve accurate measurement of the target object, which is crucial for semiconductor manufacturing, precision engineering and other fields that require high-precision measurement. Each part of the system plays a specific role, which together ensures the accuracy and reliability of the measurement process.

[0203] Specifically, in the impedance conversion circuit, since the input impedance is 50Ω, the impedance conversion circuit selects a direct-through mode, that is, no impedance conversion is performed. This design simplifies the circuit and ensures direct signal transmission, reducing signal distortion caused by impedance mismatch. Data transmission is through the SPI protocol, and the analog-to-digital conversion chip transmits the read signal data and the avalanche breakdown diode signal to the STM32 system synchronously. SPI is a common serial communication protocol that allows high-speed, full-duplex data communication. As a microcontroller, the STM32 system is responsible for the preliminary processing of the collected data, such as filtering, amplification, and format conversion. The processed data is then transmitted to the host computer system for more in-depth analysis and processing.

[0204] The data collected during data collection and processing are as follows: Figure 8 As shown in the figure, through the template matching method, the system matches the collected interference signal with the preset template and calculates the matching coefficient to determine the piezoelectric position corresponding to the zero-order interference fringe. This step is the key to achieving precise focusing, which provides accurate measurement of the optimal distance between the objective lens and the sample.

[0205] In general, the design of the piezoelectric signal acquisition channel takes into account the precise acquisition, conditioning and conversion of the signal, ensuring the quality and integrity of the signal throughout the acquisition process. This design not only improves the flexibility and accuracy of signal acquisition, but also ensures that the system can adapt to sensors of different types and specifications, enhancing the versatility and reliability of the system. Through precise signal conditioning and acquisition, the system can achieve high-precision analysis of interference fringes during white light interferometric focusing, thereby quickly and accurately determining the focus position and improving the accuracy and efficiency of overlay error measurement in semiconductor processes.

[0206] In one embodiment, a synchronous voltage acquisition signal processing method for white light interferometric focusing, the white light interferometric technique uses white light to scan the target object, which can generate interference signals, and these interference signals contain information about the surface characteristics of the object. When white light is irradiated onto the target object, a series of light and dark interference fringes will be generated due to the interference effect of the light waves. The position and spacing of these fringes are directly related to the microstructure and morphology of the surface of the object. Therefore, by analyzing these interference fringes, accurate measurement data of the surface of the object can be obtained.

[0207] Specifically, in the white light interferometric focusing system, the white light generated by the halogen light source is the key to achieve high-precision measurement. The white light of this light source is first focused and then injected into the second beam splitter in the system. The function of the second beam splitter is to split the focused white light into two beams, which are respectively called the first beam and the second beam. After being controlled by the shutter, the first beam is further focused by the first microscope objective lens and finally injected into the reference mirror to prepare for interference with the reflected light from the target object. The shutter here plays the role of controlling the light path to ensure that only the required beam passes at the right time.

[0208] The second light beam is transmitted through the tube lens and enters the first beam splitter, where it is split again into two new light beams, namely the third and fourth beams. The third light beam is directly injected into the CMOS sensor to collect the focal plane image and provide direct visual information about the surface features of the target object. The fourth light beam is injected into the avalanche breakdown diode sensor, whose function is to collect the interference signal of the objective lens at different vertical positions. The avalanche breakdown diode sensor can detect the change in light intensity reflected by the target object and convert it into a voltage signal output. These voltage signals are then used to analyze the intensity changes of the interference fringes to determine the vertical position of the objective lens to achieve precise focusing. By precisely controlling the path and intensity of the light beam, the system can achieve high-precision measurement of the surface features of the target object.

[0209] In order to achieve this measurement process, two key voltage signals need to be collected synchronously: the interference signal output by the avalanche breakdown diode sensor and the position signal output by the piezoelectric ceramic sensor. The avalanche breakdown diode sensor is responsible for collecting the interference signals of the objective lens at different vertical positions. These signals reflect the changes in light intensity and can be converted into voltage signal outputs. The piezoelectric ceramic sensor is responsible for outputting the vertical position signal of the objective lens, which indicates the precise position of the objective lens. The synchronous collection of these two signals is crucial for subsequent data processing and analysis because they provide a direct correspondence between the intensity of the interference signal and the position of the objective lens.

[0210] The collected voltage signals need to be conditioned to ensure that they can meet the input requirements of the analog-to-digital converter. Signal conditioning includes two steps: passive attenuation and gain amplification. Passive attenuation is to reduce the amplitude of the signal through the circuit network to prevent excessive signals from damaging the ADC. Gain amplification is to increase the amplitude of the signal through the amplification circuit to ensure that the signal is within the quantization range of the ADC so that it can be accurately converted into a digital signal. These two steps together ensure the linearity and accuracy of the signal during the conversion process.

[0211] The conditioned voltage signal is then converted to a digital signal via an ADC. This conversion process is a key step in the digitization of analog signals, which allows the signal to be processed and analyzed by a computer system. The processing of digital signals involves algorithmic analysis of the collected data to determine the vertical position corresponding to the zero-order interference fringe. Zero-order interference fringes refer to the interference fringes generated when the optical path difference is zero during the interference process, and their position corresponds to the precise focal plane position of the objective lens. By accurately determining the position of these fringes, the objective lens can be quickly focused and positioned to ensure that the measured surface is always in a clear focal plane.

[0212] Finally, based on the processed data, the system automatically adjusts the vertical position of the objective lens to keep the measured surface in a clear focal plane. This adjustment process is part of a closed-loop control that ensures the accuracy and repeatability of the measurement process. In this way, white light interferometry can provide high-precision overlay error measurement in semiconductor processes, which plays a vital role in ensuring the electrical characteristics of devices and normal signal transmission.

[0213] Specifically, the same or similar parts between the various embodiments in this specification can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the product embodiment described later, since it corresponds to the method, the description is relatively simple, and the relevant parts can be referred to the partial description of the system embodiment.

[0214] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A voltage signal processing system for white light interferometric focusing, characterized in that: It includes a signal transmission channel, an input impedance selection module, an impedance conversion circuit module, a signal conditioning channel, an ADC driving circuit and an ADC acquisition circuit; The signal transmission channel includes an avalanche breakdown diode signal acquisition channel and a piezoelectric ceramic signal acquisition channel, which transmits the interference signal from the avalanche breakdown diode sensor and the position signal from the piezoelectric platform; The input impedance selection module selects the input impedance of the avalanche breakdown diode sensor and the piezoelectric sensor; The signal conditioning channel includes a first signal conditioning channel and a second signal conditioning channel, wherein the first signal conditioning channel is used to process the signal from the avalanche breakdown diode sensor, and the first signal conditioning channel includes a passive attenuation circuit and a gain amplification circuit; The second signal conditioning channel is used for conditioning the output signal of the piezoelectric sensor, wherein the second signal conditioning channel is used for processing the signal from the piezoelectric sensor, and the second signal conditioning channel includes a passive attenuation circuit and a gain amplification circuit; The ADC driving circuit converts the output signals of the first signal conditioning channel and the second signal conditioning channel into differential signals matching the ADC; The ADC acquisition circuit converts the acquired differential signal into a digital signal.

2. A voltage signal processing system for white light interferometric focusing as claimed in claim 1, characterized in that: The input impedance selection module includes an impedance converter, and the impedance converter is used to select an impedance of 50Ω or 1MΩ to match the output impedance of different sensors; The impedance conversion circuit directly passes the input signal when the input impedance is 50Ω; The impedance conversion circuit attenuates the input signal when the input impedance is 1 MΩ.

3. A voltage signal processing system for white light interferometric focusing as claimed in claim 1, characterized in that: When the stroke of the avalanche breakdown diode sensor is 50 um, the output signal range is -10 V to 10 V, and the stroke of the piezoelectric platform is 50 um.

4. A voltage signal processing system for white light interferometric focusing as claimed in claim 1, characterized in that: The signal conditioning path includes passive attenuation circuits: The passive attenuation circuit is for the avalanche breakdown diode signal acquisition channel. When the output impedance of the avalanche breakdown diode is 50Ω, the impedance of the impedance selection module is selected as 50Ω. The passive attenuation circuit includes resistors R1 and R2 and capacitors C1 and C2. The first resistor R1 and the first capacitor C1 are connected in parallel to form a first capacitive resistance circuit. The second resistor R2 and the second capacitor C2 are connected in parallel to form a second capacitive resistance circuit. The first capacitive resistance circuit and the second capacitive resistance circuit are connected in parallel to each other to form a passive attenuation circuit. The resistance values ​​of R1 and R2 are 230KΩ and 200KΩ respectively. The capacitance values ​​of C1 and C2 are both 20PF. The impedance conversion circuit selects direct pass. When the output voltage range is higher than the input range of the circuit, the signal amplitude is reduced by setting the attenuation multiple to 2. For the piezoelectric ceramic signal acquisition channel, the passive attenuation circuit selects 50Ω of the impedance selection module when the output impedance of the piezoelectric ceramic is 50Ω, wherein the resistance value of R1 is 230KΩ, the resistance value of R2 is 630KΩ, the capacitance values ​​of C1 and C2 are both 20PF, and the impedance conversion circuit selects direct pass. When the amplitude of the input signal is higher than the maximum input voltage of the analog-to-digital converter or other subsequent processing circuits, the signal amplitude is reduced by setting the attenuation multiple to 4.

5. A voltage signal processing system for white light interferometric focusing as claimed in claim 1, characterized in that: The signal conditioning channel includes a gain amplifier circuit; The selected analog-to-digital conversion chip has a collection voltage value of 0 to 5V, which defines the gain amplification ratio. The signal passing through the attenuation path is adjusted to the full-scale value of the ADC. The maximum gain is set by the external feedback resistor RF and the gain resistor RG, and the maximum gain is adjusted between -1V and 1V by adjusting the voltage Vadj.

6. A voltage signal processing system for white light interferometric focusing as claimed in claim 1, characterized in that: The impedance conversion circuit includes an ADC driving circuit, and the ADC driving circuit includes a driving amplifier and a differential conversion network: The driving amplifier is used to amplify the single-ended signal passing through the attenuation path; The differential conversion network is used to convert the amplified single-ended signal into a differential signal.

7. A voltage signal processing system for white light interferometric focusing as claimed in claim 6, characterized in that: The differential conversion network includes a differential amplifier: The differential amplifier is used to receive a single-ended signal and generate a corresponding differential output signal, the input Vin is a single-ended signal, the single-ended signal is directly connected to the positive input terminal, and the negative input terminal of the channel is grounded; The differential amplifier amplifies the difference between input signals.

8. The voltage signal processing system for white light interferometric focusing according to claim 1, characterized in that: The impedance conversion circuit includes an ADC acquisition circuit, and the ADC acquisition circuit includes an analog-to-digital converter, a channel selection switch, a multi-channel analog switch, a sample-and-hold circuit, a signal buffer, a signal amplifier, a digital filter, a clock management unit, and a data interface; The analog-to-digital converter receives an analog signal and outputs a corresponding digital signal; The channel selection switch selects different analog signals to be input into the ADC analog-to-digital converter; The multi-channel analog switch selects an analog signal from a plurality of input channels; The sample-and-hold circuit stabilizes the analog signal during analog-to-digital conversion; The signal buffer buffers the analog signal to reduce signal loss during transmission; The signal amplifier amplifies the weak analog signal to a level range that can be received by the ADC analog-to-digital converter; The digital filter performs filtering processing on the collected digital signal in the digital domain; The clock management unit controls the sampling rate of the ADC analog-to-digital converter; The data interface transmits the converted digital signal to the STM32 system and then to the host computer system.

9. A self-focusing signal synchronous acquisition and processing device for white light interferometric focusing, characterized in that: The synchronous acquisition and processing device comprises a halogen light source, a piezoelectric ceramic driver, a first microscope objective lens, a reference mirror, a shutter, a first beam splitter, a second beam splitter and a second microscope objective lens;' The halogen light source is connected to the second beam splitter through an optical path; The piezoelectric ceramic driver is connected to the objective lens mounting seat through a support frame to achieve accurate vertical positioning of the objective lens; The first microscope objective lens is connected to the reference mirror via an optical path, the reference mirror is connected to the shutter via an optical path, the first microscope objective lens is connected to the reference mirror via an optical path, the shutter is connected to the first beam splitter via an optical path, the first beam splitter is connected to the second beam splitter via an optical path, and the second beam splitter is connected to the second microscope objective lens via an optical path.

10. The self-focusing signal synchronous acquisition and processing device of white light interferometric focusing according to claim 9, characterized in that: The white light from the halogen light source is focused and incident on the second beam splitter, and is split into two light beams by the second beam splitter, forming a first light beam and a second light beam; The first light beam passes through the shutter and the first microscope objective lens and is focused into the reference lens, and the second light beam passes through the tube lens and enters the first beam splitter and is then split into two light beams, forming a third light beam and a fourth light beam; The third light beam is injected into the CMOS sensor to collect the focal plane image, and the fourth light beam is injected into the avalanche breakdown diode sensor to collect the interference signal at different vertical positions of the objective lens, and converts the light intensity signal into a voltage signal for output.

11. A synchronous voltage acquisition signal processing method for white light interferometric focusing, characterized in that: include: Use white light to scan the target object to obtain an interference signal; Synchronously collecting voltage signals of an avalanche breakdown diode sensor and a piezoelectric ceramic sensor, wherein the avalanche breakdown diode sensor is used to collect interference signals at different vertical positions of the objective lens, and the piezoelectric ceramic sensor is used to output a vertical position signal of the objective lens; Perform signal conditioning on the collected voltage signal, including passive attenuation and gain amplification, to match the input requirements of the analog-to-digital converter; The conditioned voltage signal is converted into a digital signal through an ADC, and the digital signal is processed to determine the vertical position corresponding to the zero-order interference fringe, thereby achieving rapid focusing positioning; Adjust the vertical position of the objective lens to keep the measured surface in a clear focal plane.

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