Common-path dual-telecentric dark-field microscope defocus measurement adjustment device and method

Abstract

This invention belongs to the field of optical precision measurement technology, specifically a common-path dual-telecentric dark-field microscope defocus measurement and adjustment device and method. Through a common-path design, this invention enables the microscope objective to simultaneously function as both the dark-field microscopy imaging optical path and the dual-telecentric optical path for defocus measurement. A parallel beam is used to measure the surface of the sample under test via the dual-telecentric structure, utilizing interference phase difference to achieve non-contact measurement of defocus. Rapid adjustment ensures the sample remains within the focus range. The device includes a dark-field microscopy imaging optical path, a displacement platform module, a beam splitting module, a converging mirror, an interferometer, and a host computer; the dark-field microscopy imaging and defocus measurement share the same optical path. This invention eliminates the need for an additional measurement optical path, significantly improving vibration resistance; the working distance adaptability covers various microscope objectives, and it possesses nanometer-level high measurement accuracy; simultaneously achieving compact integration of dark-field imaging and defocus measurement, it is suitable for high-precision scenarios such as online detection of surface defects on semiconductor wafers.

Description

Technical Field

[0001] This invention belongs to the field of optical precision measurement technology, specifically relating to a device and method for real-time measurement and adjustment of defocusing amount in a common-path dual-telecentric dark-field microscope for online detection of surface defects on semiconductor wafers. Background Technology

[0002] Optical precision measurement technology plays a crucial role in semiconductor manufacturing, micro / nano fabrication, and advanced materials characterization, especially in wafer defect detection and critical dimension measurement, where its accuracy and efficiency directly impact product yield and performance. In these applications, accurate, real-time, and non-contact measurement of defocus is a core prerequisite for ensuring microscopic imaging quality and defect identification accuracy. Traditional defocus measurement methods mainly include the following categories:

[0003] Active / passive focusing methods based on image sharpness evaluation functions: These methods assess image sharpness by analyzing features such as the gradient modulus, Laplacian energy, and spectral entropy, and use this as feedback signals to adjust the focus. For example, structured light illumination can enable rapid wafer focusing measurements with errors controlled within 0.06 micrometers. However, these methods typically require multiple samplings, resulting in relatively slow measurement speeds, which are difficult to meet the high-throughput online inspection requirements in semiconductor manufacturing.

[0004] Phase-sensitive measurement methods based on the principle of interference include Thyman-Green interferometers, Michelson interferometers, and digital holographic interferometers. White light interferometry offers advantages such as a large field of view, high precision, and non-contact operation, and is widely used for three-dimensional topography measurement of micro- and nano-sized optoelectronic devices. Grating shearing interferometry is also applied in optical equipment to measure wafer defocusing and tilting, achieving measurement accuracy at the nanometer scale. However, traditional interferometric measurement systems are often bulky, have complex optical path calibration, and are susceptible to mechanical vibration and thermal drift.

[0005] The aforementioned traditional methods have significant limitations when dealing with online detection scenarios requiring high integration, high stability, and high environmental robustness. For example:

[0006] (1) Independent optical path problem: Most solutions rely on a dedicated measurement optical path that is independent of the imaging optical path, resulting in a large system size, complex optical path calibration, and susceptibility to mechanical vibration and thermal drift. In wafer inspection platforms, discrete optical path structures can easily introduce environmental noise on the order of tens of nanometers, which significantly affects the yield of semiconductor processes with nanometer-level precision.

[0007] (2) Poor working distance adaptability: Conventional telecentric or non-telecentric measurement optical paths are highly sensitive to working distance. This makes it difficult for the system to be compatible with industrial objectives of different magnifications and numerical apertures (NA), which seriously restricts the adaptability of the production line during model changeover.

[0008] (3) Difficult to integrate with dark-field microscopy: Dark-field microscopy can effectively enhance the contrast of surface scattering defects (such as scratches, particles, and micro-protrusions). It has important applications in the detection of surface defects on semiconductor wafers. However, dark-field illumination usually requires large-angle ring or oblique incident light, which inherently conflicts with the mainstream defocused measurement optical path (which often requires coaxial or paraxial collimated light), making it difficult to integrate the two in a common optical path. Summary of the Invention

[0009] The purpose of this invention is to provide a common-path dual-telecentric dark-field microscope defocus measurement and adjustment device and method to solve the technical problems of existing defocus measurement systems that require independent optical paths, have high environmental sensitivity, poor working distance adaptability, and are difficult to integrate with dark-field microscopy imaging.

[0010] This invention employs a common-path dual-telecentric architecture, embedding the principle of interference phase difference into the standard dark-field optical path to achieve real-time, non-destructive measurement of nanometer-level defocus. The device, through the collaborative design of the dark-field illumination module, beam splitter module, converging mirror, interferometer, and host computer, allows the measurement and imaging optical paths to be shared, eliminating the need for an additional measurement optical path and significantly improving the system's vibration resistance. Furthermore, the parallel light measurement combined with the dual-telecentric design enables the device to adapt to a wide range of microscope objectives with nanometer-level high measurement accuracy. This compact integrated solution solves the problem of the difficulty in coexisting dark-field imaging and defocus measurement, making it suitable for industrial applications with extremely high precision and efficiency requirements, such as online detection of semiconductor wafer surface defects. In summary, the common-path dual-telecentric dark-field microscope defocus measurement and adjustment device and method proposed in this invention overcomes the limitations of existing defocus measurement systems in terms of integration, robustness, and adaptability, providing core optical enabling technology for closed-loop automatic focusing and high-throughput online detection of semiconductor wafer surface defects.

[0011] The common-path dual-telecentric dark-field microscope defocus measurement and adjustment device provided by this invention includes a dark-field microscopy imaging optical path, a displacement platform module, a beam splitting module, a converging lens, an interferometer, and a host computer; wherein:

[0012] The dark-field microscopy imaging optical path includes a dark-field illumination module, a microscope objective, a tube lens, and a microscope detector;

[0013] The dark field illumination module includes a light source and a collimating lens, used to generate a dark field imaging beam that is obliquely incident on the sample, the wavelength of the dark field imaging beam being a first wavelength; the light emitted by the light source is adjusted by the collimating lens and then illuminates the sample located below the microscope objective at an oblique angle to form dark field illumination;

[0014] The microscope objective has its objective surface facing the sample and is used to collect the scattered light generated by the sample after dark field illumination.

[0015] The tube lens is located between the microscope objective and the microscope detector, and is used to magnify the intermediate image formed by the microscope objective and image it onto the photosensitive surface of the microscope detector.

[0016] The microscope detector is located on the image side of the tube lens and is used to receive the light signal after the tube lens images the image and convert it into an electrical signal.

[0017] The displacement platform module includes a controller, a drive motor, and a displacement platform. The controller is communicatively connected to a host computer and is used to receive defocus data and output control signals. The drive motor is electrically connected to the controller and is used to receive the control signals and output driving force. The displacement platform is drive-connected to the drive motor and is used to carry the sample and, under the drive of the drive motor, move the sample horizontally and adjust its height to adjust the measurement position and achieve automatic focusing.

[0018] The beam splitting module includes a dichroic mirror and a dual filter;

[0019] The dichroic mirror is tilted and positioned in the optical path between the microscope objective and the tube lens. It is used to have high reflectivity for light of the second wavelength and high transmittance for light of the first wavelength, without affecting the polarization state of light of the second wavelength.

[0020] The dual filter includes a first filter and a second filter; the first filter is disposed between the dichroic mirror and the tube mirror, and is used to transmit light of a first wavelength and block light of a second wavelength; the second filter is disposed between the interferometer and the converging mirror, and is used to transmit light of a second wavelength and block light of the first wavelength.

[0021] The converging mirror, located in the optical path between the second filter and the dichroic mirror, is used to converge the parallel measurement beam from the interferometer. After being reflected by the dichroic mirror, the focal point is located exactly at the back focal plane of the microscope objective, so that the measurement beam emitted from the microscope objective to the sample is parallel light.

[0022] The interferometer is used to provide a defocus measurement beam, the wavelength of which is a second wavelength; the interferometer is a laser phase-shifting interferometer, which uses a spatial phase-shifting method to simultaneously acquire interference information of multiple phase-shifting states in a single frame image; the interferometer, together with the converging mirror and the microscope objective, constitutes the defocus measurement optical path;

[0023] In the dark-field microscopy imaging optical path, the imaging light from the sample passes sequentially through the microscope objective, dichroic mirror, first filter, and tube lens before reaching the microscope detector.

[0024] In the defocus measurement optical path, the measurement light from the interferometer passes through the second filter, converging mirror, dichroic mirror, and microscope objective in sequence before reaching the sample. After reflection, it passes through the microscope objective, dichroic mirror, converging mirror, and second filter (returning to the interferometer and reaching the photosensitive surface of the detector inside the interferometer).

[0025] Among them, the optical path from the sample through the microscope objective to the beam splitter is a shared optical path for dark-field microscopy imaging and defocus measurement.

[0026] The host computer is connected to the interferometer and the controller for processing the interference information acquired by the interferometer, calculating the current defocus amount, and sending the defocus amount data to the controller.

[0027] Furthermore, the microscope objective simultaneously undertakes the relevant responsibilities in both the dark-field microscopy imaging optical path and the defocus measurement optical path. In the dark-field microscopy imaging optical path, the microscope objective, as the objective of the microscopy system, together with the tube lens, determines the magnification of the microscopy system, thus constituting the microscopy imaging system. In the defocus measurement optical path, the microscope objective and the converging lens form a double telecentric optical path. The converging lens converges the parallel measurement light from the interferometer to its image-side focal point, which coincides with the back focal plane of the microscope objective, so that the measurement light exits as parallel light after passing through the microscope objective and is emitted to the sample, forming a double telecentric measurement optical path where both the object and image sides are telecentric.

[0028] Furthermore, the laser phase-shifting interferometer specifically includes an interferometric laser, a collimating lens, a polarization beam splitting assembly, a spatial phase-shifting element, and an interferometer detector;

[0029] The interferometric laser is used to output a measurement beam, which is collimated by a collimating lens and then incident on a polarization beam splitter. The polarization beam splitter splits the incident beam into a reference beam and a measurement beam, and modulates the polarization state of the reference beam and the measurement beam so that the reference beam is incident on a reference reflecting surface inside the interferometer, and the measurement beam is output to the converging mirror. The measurement beam returning from the sample is combined with the reference beam by the polarization beam splitter. The combined beam is then introduced into spatial phase modulation by the spatial phase shifting element and received by the interferometer detector to form an interference image.

[0030] The interferometer detector is connected to the host computer for communication, and is used to send the interferometric image to the host computer for defocus calculation.

[0031] The common-path dual-telecentric dark-field microscope defocus measurement and adjustment method provided by the present invention, based on the device described in any one of the above claims, includes the following steps:

[0032] S1: Place the sample on the displacement platform and perform calibration and zeroing operations;

[0033] S2: Drive the displacement platform to move the sample to the next preset measurement position;

[0034] S3: The interferometer emits a measurement beam of the second wavelength. This beam is focused by a converging lens onto the back focal plane of the microscope objective, illuminates the sample, and is reflected back to the interferometer along the original optical path. The returning measurement beam enters a laser phase-shifting interferometer, and a single-frame spatial phase-shifting interferogram is obtained through spatial phase shifting (the spatial phase shifting method used here is a four-step phase shift, with a phase difference of ). );

[0035] S4: The host computer calculates the interference phase based on the single-frame spatial phase-shift interferogram, and calculates the defocus amount at the current measurement position according to the defocus amount calculation formula; the defocus amount calculation formula is:

[0036] ,

[0037] In the formula, To measure the wavelength of the light beam, The characteristic phase of the measurement region of the sample is the phase diagram of the measurement region. The calculation results show that I1, I2, I3, and I4 are the light intensities of the interference light with phase shifts of 0, 0.5π, π, and 1.5π, respectively.

[0038] S5: Determine whether the defocus amount at the current measurement position exceeds the preset threshold: If it does not exceed the threshold, proceed to step 6; if it exceeds the threshold, proceed to step 7.

[0039] S6: Determine whether all preset measurement positions have been detected: If there is a next position to be measured, return to step 2 and move to the next measurement position; if not, end the measurement process.

[0040] S7: The host computer sends a focusing command to the controller, driving the displacement platform to adjust its height and complete the automatic focusing; after focusing is completed, return to step 2 and move to the next measurement position.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) The present invention adopts a common optical path design, which enables the microscope objective to simultaneously serve as the optical path for dark field microscopy imaging and the dual telecentric optical path for defocus measurement, eliminating the need for an additional measurement optical path and significantly improving the system's anti-vibration capability.

[0043] (2) The present invention adopts parallel light measurement combined with dual telecentric design, and the working distance adaptability range can cover various microscope objectives, which solves the problem of poor working distance adaptability of traditional solutions;

[0044] (3) The present invention utilizes a laser phase-shifting interferometer to achieve single-frame spatial phase shifting without the need for time phase shifting, thus avoiding vibration interference caused by mechanically moving the reference mirror, and simultaneously achieving millisecond-level real-time measurement;

[0045] (4) The present invention achieves wavelength separation of dark field imaging and defocus measurement by using a dichroic mirror and a dual filter, while maintaining a common optical path, thus realizing compact integration of dark field imaging and defocus measurement.

[0046] (5) The present invention has high measurement accuracy at the nanometer level and is suitable for high-precision scenarios such as online detection of surface defects of semiconductor wafers. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the overall optical path structure of the common optical path dual telecentric dark field microscope defocus measurement and adjustment device provided in an embodiment of the present invention.

[0048] Figure 2 This is a schematic diagram showing the details of the common optical path in an embodiment of the present invention.

[0049] Figure 3 This is a flowchart of the defocus measurement and adjustment method provided in an embodiment of the present invention.

[0050] In the diagram, the following labels represent different components: 1-Dark-field illumination laser, 2-Object under test and displacement platform module, 3-Microscopic objective, 4-Dichroic mirror, 5-Short-pass filter, 6-Tube mirror, 7-Microscope detector, 8-Long-pass filter, 9-Converging mirror, 10-Quarter-wave plate, 11-Polarizing beam splitter, 12-Polarizer, 13-Beam expander, 14-Laser, 15-Reference mirror, 16-Detector protective glass, 17-Interference detector, 18-Laser phase-shifting interferometer, 19-Host computer, 20-Dark-field microscopic imaging optical path, 21-Defocus measurement focusing optical path. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0052] The specific implementation of the defocus measurement and adjustment device for a common-path dual-telecentric dark-field microscope is as follows: Figure 1 As shown, this embodiment provides a common-path dual-telecentric dark-field microscope defocus measurement and adjustment device, including a dark-field microscopy imaging optical path, a displacement platform module, a beam splitting module, a converging lens, an interferometer, and a host computer.

[0053] The dark-field microscopy imaging optical path includes a dark-field illumination module, a microscope objective, a tube lens, and a microscope detector;

[0054] The dark-field illumination module includes a light source and a collimating lens, used to generate a dark-field imaging beam obliquely incident on the sample. The wavelength of the dark-field imaging beam is a first wavelength, with a wavelength range of 400-550 nm. The light emitted by the light source, after being adjusted by the collimating lens, illuminates the sample located below the microscope objective at an oblique angle, forming dark-field illumination. The oblique incident angle is affected by the numerical aperture (NA) of the microscope objective and the scattering characteristics of the sample surface, and must satisfy the following:

[0055]

[0056] In the formula, n is the working medium of the microscope objective, which is usually air (n=1), and θ is the angle between the oblique incident light and the normal to the surface of the object being measured. Since NA affects the imaging resolution of the microscope objective, the resolution requirements of the object being measured also need to be considered.

[0057] The microscope objective has its objective surface facing the sample and is used to collect the scattered light generated by the sample after dark field illumination. The working distance of the microscope objective is 5mm-50mm. Specifically, it needs to meet the spatial requirements of dark field illumination. In this embodiment, the microscope objective uses an objective with NA=0.3, a working distance of 11mm, and an incident angle of 65 degrees for dark field illumination.

[0058] The tube lens is located between the microscope objective and the microscope detector, and is used to magnify the intermediate image formed by the microscope objective and image it onto the photosensitive surface of the microscope detector.

[0059] The microscope detector is located on the image side of the tube lens and is used to receive the light signal after the tube lens images the image and convert it into an electrical signal.

[0060] The displacement platform module includes a controller, a drive motor, and a displacement platform. The controller is communicatively connected to a host computer and is used to receive defocus data and output control signals. The drive motor is electrically connected to the controller and is used to receive the control signals and output driving force. The displacement platform is drive-connected to the drive motor and is used to carry the sample and, under the drive of the drive motor, move the sample horizontally and adjust its height to adjust the measurement position and achieve automatic focusing.

[0061] The beam splitting module includes a dichroic mirror and a dual filter;

[0062] The dichroic mirror is tilted and positioned in the optical path between the microscope objective and the tube lens. It is used to have high reflectivity for light of the second wavelength and high transmittance for light of the first wavelength, without affecting the polarization state of light of the second wavelength.

[0063] The dual filter includes a first filter and a second filter. The first filter is disposed between the dichroic mirror and the tube mirror to transmit light of the first wavelength and block light of the second wavelength. The second filter is disposed between the interferometer and the converging mirror to transmit light of the second wavelength and block light of the first wavelength.

[0064] The optical path from the sample through the microscope objective to the dichroic mirror is a shared optical path for both dark-field microscopy imaging and defocus measurement adjustment. The dark-field imaging beam (400-550 nm) and the measurement beam (550-650 nm) both pass through the microscope objective and enter the dichroic mirror. The dark-field imaging beam, after passing through the dichroic mirror and the first filter, is imaged onto the imaging detector by the tube lens to form a dark-field image. The measurement beam, reflected from the dichroic mirror, enters the interferometer for phase measurement.

[0065] The converging mirror is located between the dichroic mirror and the interferometer, and is used to converge the parallel measurement beam from the interferometer. After reflection by the dichroic mirror, the focal point is located exactly at the back focal plane of the microscope objective, so that the measurement beam emitted from the microscope objective to the sample is parallel light. The focal length of the converging mirror is adjustable, and the ratio of the focal length of the converging mirror to the focal length of the microscope objective determines the diameter of the measurement beam. In this embodiment, the focal length of the converging mirror is 120mm, and the double telecentric optical path formed by the focal length of the converging mirror and the 20mm focal length of the microscope objective reduces the original beam diameter to 1 / 6.

[0066] The interferometer is used to provide a defocus measurement beam. The wavelength of the measurement beam is a second wavelength, ranging from 550 to 650 nm, and needs to be separated from the first wavelength to facilitate the separation of the two beams by the dichroic mirror and filter. The measurement beam should use a narrow linewidth light source to improve the coherence length and be compatible with microscope objectives with longer working distances. The laser phase-shifting interferometer obtains a single-frame spatial phase-shifting interferogram through spatial phase shifting. The interferometer, converging mirror, and microscope objective together constitute the defocus measurement optical path. The phase shifting method of the interferometer can adopt existing spatial phase-shifting interferometry (such as Phasecam from 4D Technology). Its coupling relationship with the common optical path dual telecentric optical structure (i.e., the shared optical path of the measurement beam path and the dark-field imaging optical path in the section from the microscope objective to the dichroic mirror, such as...) Figure 2 (As shown) constitutes the core innovation of this invention.

[0067] The host computer is connected to the interferometer and the controller for processing the interference information acquired by the interferometer, calculating the current defocus amount, and sending the defocus amount data to the controller.

[0068] The specific implementation of the defocus measurement and adjustment method is as follows: Figure 3 As shown, this embodiment provides a method for measuring and adjusting the defocus amount of a common-path dual-telecentric dark-field microscope, specifically including the following steps:

[0069] S1: Place the sample on the displacement platform and perform calibration and zeroing operations;

[0070] S2: Drive the displacement platform to move the sample to the next preset measurement position;

[0071] S3: The interferometer emits a measurement beam of the second wavelength, which is focused by a converging lens onto the back focal plane of the microscope objective. After illuminating the sample, the beam is reflected and returns to the interferometer along the original optical path. The returning measurement beam enters the laser phase-shifting interferometer, and a single-frame spatial phase-shifting interferogram is obtained through spatial phase shifting.

[0072] S4: The host computer calculates the interference phase based on the single-frame spatial phase-shift interferogram, and calculates the defocus amount at the current measurement position according to the defocus amount calculation formula; the defocus amount calculation formula is:

[0073] ,

[0074] In the formula, To measure the wavelength of the light beam, The characteristic phase of the measurement region of the sample is the phase diagram of the measurement region. The calculation results show that I1, I2, I3, and I4 are the light intensities of the interference light with phase shifts of 0, 0.5π, π, and 1.5π, respectively.

[0075] S5: Determine whether the defocus amount at the current measurement position exceeds the preset threshold: If it does not exceed the threshold, proceed to step 6; if it exceeds the threshold, proceed to step 7.

[0076] S6: Determine whether all preset measurement positions have been detected: If there is a next position to be measured, return to step 2 and move to the next measurement position; if not, end the measurement process.

[0077] S7: The host computer sends a focusing command to the controller, driving the displacement platform to adjust its height and complete the automatic focusing; after focusing is completed, return to step 2 and move to the next measurement position.

[0078] In this embodiment, the measurement system achieves defocus measurement with nanometer-level precision (within ±1nm), a measurement response time of less than 5ms, and a working distance adaptability range of 5-50mm, fully meeting the requirements for online detection of semiconductor wafer surface defects.

[0079] The apparatus and method of this embodiment exhibit the following advantages in practical applications: Through a common optical path design, the microscope objective simultaneously serves as both the dark-field microscopy imaging optical path and the dual telecentric optical path for defocus measurement, eliminating the need for an additional measurement optical path and significantly improving the system's vibration resistance; the use of parallel light measurement combined with the dual telecentric design allows for a working distance adaptability covering various microscope objectives. Within a working distance range from 5mm to 50mm, the measurement error variation is less than ±1nm, superior to traditional solutions in both measurement range and error; single-frame spatial phase shift is achieved using a laser phase-shifting interferometer, eliminating the need for time phase shift and avoiding vibration interference caused by mechanically moving the reference mirror, while simultaneously achieving millisecond-level real-time measurement; wavelength separation for dark-field imaging and defocus measurement is achieved through a dichroic mirror and dual filters, while maintaining a shared optical path, realizing a compact integration of dark-field imaging and defocus measurement.

[0080] In summary, the common-path dual-telecentric dark-field microscope defocus measurement and adjustment device and method provided in this embodiment effectively solves the problems of optical path separation, high environmental sensitivity, and poor working distance adaptability in the prior art through innovative optical design, providing reliable technical support for high-precision online inspection in the semiconductor manufacturing field.

Claims

1. A co-axial dual-telecentric dark-field microscope defocus measurement adjustment device, characterized in that, It includes the dark-field microscopy imaging optical path, displacement platform module, beam splitting module, converging lens, interferometer, and host computer; among which: The dark-field microscopy imaging optical path includes a dark-field illumination module, a microscope objective, a tube lens, and a microscope detector; wherein: The dark field illumination module includes a light source and a collimating lens, used to generate a dark field imaging beam that is obliquely incident on the sample, the wavelength of the dark field imaging beam being a first wavelength; the light emitted by the light source is adjusted by the collimating lens and then illuminates the sample located below the microscope objective at an oblique angle to form dark field illumination; The microscope objective has its objective surface facing the sample and is used to collect the scattered light generated by the sample after dark field illumination. The tube lens is located between the microscope objective and the microscope detector, and is used to magnify the intermediate image formed by the microscope objective and image it onto the photosensitive surface of the microscope detector. The microscope detector is located on the image side of the tube lens and is used to receive the light signal after the tube lens images the image and convert it into an electrical signal. The displacement platform module includes a controller, a drive motor, and a displacement platform; wherein: The controller is connected to the host computer for receiving defocusing data and outputting control signals; The drive motor is electrically connected to the controller and is used to receive the control signal and output driving force; The displacement platform is connected to the drive motor to carry the sample and, driven by the drive motor, moves the sample horizontally and adjusts its height to adjust the measurement position and achieve automatic focusing. The beam-splitting module includes a dichroic mirror and a dual filter; wherein: The dichroic mirror is tilted and positioned in the optical path between the microscope objective and the tube lens. It is used to have high reflectivity for light of the second wavelength and high transmittance for light of the first wavelength, without affecting the polarization state of light of the second wavelength. The dual filter includes a first filter and a second filter; the first filter is disposed between the dichroic mirror and the cylindrical mirror to transmit light of a first wavelength and block light of a second wavelength; the second filter is disposed between the interferometer and the converging mirror to transmit light of a second wavelength and block light of the first wavelength. The converging mirror, located in the optical path between the second filter and the dichroic mirror, is used to converge the parallel measurement beam from the interferometer. After being reflected by the dichroic mirror, the focal point is located exactly at the back focal plane of the microscope objective, so that the measurement beam emitted from the microscope objective to the sample is parallel light. The interferometer is used to provide a defocus measurement beam, the wavelength of which is a second wavelength; the interferometer is a laser phase-shifting interferometer, which uses a spatial phase-shifting method to simultaneously acquire interference information of multiple phase-shifting states in a single frame image; the interferometer, together with the converging mirror and the microscope objective, constitutes the defocus measurement optical path; In the dark-field microscopy imaging optical path, the imaging light from the sample passes sequentially through the microscope objective, dichroic mirror, first filter, and tube lens before reaching the microscope detector. In the defocus measurement optical path, the measurement light from the interferometer passes through the second filter, converging mirror, dichroic mirror, and microscope objective in sequence before reaching the sample. After reflection, it passes through the microscope objective, dichroic mirror, converging mirror, and second filter (returning to the interferometer and reaching the photosensitive surface of the detector inside the interferometer). Among them, the optical path from the sample through the microscope objective to the beam splitter is a shared optical path for dark-field microscopy imaging and defocus measurement. The host computer is connected to the interferometer and the controller for processing the interference information acquired by the interferometer, calculating the current defocus amount, and sending the defocus amount data to the controller.

2. The in-focus measurement adjustment device for a co-linear, double-telecentric dark-field microscope according to claim 1, characterized in that The microscope objective simultaneously performs the relevant functions in the dark-field microscopy imaging optical path and the defocus measurement optical path. In the dark-field microscopy imaging optical path, the microscope objective, as the objective of the microscopy system, together with the tube lens, determines the magnification of the microscopy system and constitutes the microscopy imaging system. In the defocus measurement optical path, the microscope objective and the converging lens form a double telecentric optical path. The converging lens focuses the parallel measurement light from the interferometer to its image-side focal point, which coincides with the back focal plane of the microscope objective. This allows the measurement light to exit as parallel light after passing through the microscope objective and reach the sample, forming a double telecentric measurement optical path where both the object and image sides are telecentric.

3. The defocus measurement and adjustment device for a common-path dual-telecentric dark-field microscope according to claim 1, characterized in that, The laser phase-shifting interferometer specifically includes an interferometric laser, a collimating lens, a polarization beam splitter, a spatial phase-shifting element, and an interferometer detector; The interferometric laser is used to output a measurement beam, which is collimated by a collimating lens and then incident on a polarization beam splitter. The polarization beam splitter splits the incident beam into a reference beam and a measurement beam, and modulates the polarization state of the reference beam and the measurement beam so that the reference beam is incident on a reference reflecting surface inside the interferometer, and the measurement beam is output to the converging mirror. The measurement beam returning from the sample is combined with the reference beam by the polarization beam splitter. The combined beam is then introduced into spatial phase modulation by the spatial phase shifting element and received by the interferometer detector to form an interference image. The interferometer detector is connected to the host computer for communication, and is used to send the interferometric image to the host computer for defocus calculation.

4. A method for measuring and adjusting the defocus amount of a common-path dual-telecentric dark-field microscope based on the device described in any one of claims 1-3, characterized in that, The specific steps are as follows: S1: Place the sample on the displacement platform and perform calibration and zeroing operations; S2: Drive the displacement platform to move the sample to the next preset measurement position; S3: The interferometer emits a measurement beam of the second wavelength, which is focused by a converging lens onto the back focal plane of the microscope objective. After illuminating the sample, the beam is reflected and returns to the interferometer along the original optical path. The returning measurement beam enters the laser phase-shifting interferometer, and a single-frame spatial phase-shifting interferogram is obtained through spatial phase shifting. S4: The host computer calculates the interference phase based on the single-frame spatial phase-shift interferogram, and calculates the defocus amount at the current measurement position according to the defocus amount calculation formula; the defocus amount calculation formula is: ， In the formula, To measure the wavelength of the light beam, The characteristic phase of the measurement region of the sample is the phase diagram of the measurement region. The calculation results show that I1, I2, I3, and I4 are the light intensities of the interference light with phase shifts of 0, 0.5π, π, and 1.5π, respectively. S5: Determine whether the defocus amount at the current measurement position exceeds the preset threshold: If it does not exceed the threshold, proceed to step 6; if it exceeds the threshold, proceed to step 7. S6: Determine whether all preset measurement positions have been detected: If there is a next position to be measured, return to step 2 and move to the next measurement position; if not, end the measurement process. S7: The host computer sends a focusing command to the controller, driving the displacement platform to adjust its height and complete the automatic focusing; after focusing is completed, return to step 2 and move to the next measurement position.

Images