A coaxial laser confocal machining and measurement integrated system and an in-situ topography measurement method thereof

Abstract

The application discloses a coaxial laser confocal processing and measuring integrated system and an in-situ shape measuring method thereof, and belongs to the technical field of ultrafast laser precision processing and in-situ measuring. The system comprises a laser confocal shape measuring module, an ultrafast laser scanning processing module, a CCD microscopic imaging module, a beam splitting prism, a low-pass dichroic mirror, a long working distance achromatic laser processing objective and a combined three-axis precision displacement stage. The laser confocal shape measuring module generates a measuring beam to realize shape measurement of a sample. The ultrafast laser scanning processing module generates a processing beam to realize scanning processing on the surface of the sample. The CCD microscopic imaging module generates an illumination beam to realize illumination of a processing position and acquisition of image information of the surface of the sample. The measuring beam, the processing beam and the illumination beam pass through the low-pass dichroic mirror to form coaxial beams, and the coaxial beams are focused on the same position on the surface of the sample through the long working distance achromatic laser processing objective, so that coaxial in-situ measuring conditions are realized.

Description

Technical Field

[0001] This invention belongs to the fields of ultrafast laser precision machining technology and in-situ measurement technology, specifically relating to a coaxial laser confocal machining and measurement integrated system and its in-situ morphology measurement method. Background Technology

[0002] Ultrafast laser processing technology, with its significant advantages such as high processing speed, high precision, strong controllability, easy integration, and high material compatibility, has shown broad application prospects in fields such as biosensing, aerospace, and optoelectronic device manufacturing, and is increasingly becoming an important support and core driving force for precision manufacturing. However, current ultrafast laser processing is mainly an "open-loop" processing mode—non-in-situ measurement methods are required to obtain the morphology of the processed surface. On the one hand, this processing mode inevitably suffers from measurement errors caused by the conversion between the measurement coordinate system and the processing coordinate system. This is especially true when processing large-scale structural splicing or complex structures with high aspect ratios. Frequent workpiece disassembly and assembly due to multiple measurements, focusing, and processing not only accumulates measurement errors but also introduces secondary clamping errors, affecting processing accuracy. On the other hand, in ultrafast laser subtractive manufacturing, due to the complexity of the interaction mechanism between laser and matter, it is usually difficult to accurately calculate or predict the actual amount of material removed. Factors such as laser energy density, pulse width, repetition frequency, material physicochemical properties, surface state, thermal diffusivity, and material inhomogeneity can all significantly affect the processing effect, making it difficult to establish a stable and generalizable mapping relationship between processing parameters and the final morphology, thus restricting the improvement of processing accuracy. Therefore, to further improve processing accuracy, ensure processing quality, and obtain microstructures and structures consistent with the design, it is necessary to conduct real-time in-situ monitoring of the processed surface morphology during ultrafast laser processing to calculate the deviation between the actual and expected morphology, thereby effectively monitoring and timely adjusting the processing process.

[0003] In summary, in-situ measurement technology is indispensable for further improving the accuracy and efficiency of ultrafast laser processing, optimizing laser processing techniques, and enhancing the quality of laser-processed structures. Currently, research on in-situ ultrafast laser topography measurement is limited both domestically and internationally, and a mature, systematic solution has not yet been developed. Research on in-situ topography measurement methods focuses on confocal microscopy, optical coherence tomography (OCT), and interferometry (CN112207425A). Interferometry offers high accuracy but is significantly affected by environmental disturbances and sample surface roughness, and the system is relatively complex and difficult to integrate. Optical coherence tomography has low axial resolution, limited to the micrometer level, and has a limited scanning speed. These shortcomings restrict the adaptability and practicality of current ultrafast laser in-situ topography measurement technology.

[0004] Therefore, there is an urgent need to develop a more accurate and adaptable morphology measurement method based on coaxial optical path to achieve in-situ measurement and morphology monitoring during ultrafast laser processing, transforming the previous "open-loop" processing mode into a closed-loop processing mode based on "processing-measurement". Summary of the Invention

[0005] To address the challenges of in-situ morphology measurement and morphology monitoring during ultrafast laser processing, this invention proposes an integrated coaxial laser confocal processing measurement system and its in-situ morphology measurement method. The aim is to achieve high-precision coaxial in-situ morphology measurement based on laser confocalization, thereby enabling morphology monitoring of the ultrafast laser processing process and transforming the previous "open-loop" processing mode into a closed-loop processing mode based on "processing-measurement".

[0006] This invention first provides a coaxial laser confocal processing and measurement integrated system, which includes a laser confocal topography measurement module, an ultrafast laser scanning processing module, a CCD microscopic imaging module, a beam splitter prism, a low-pass dichroic mirror, a long working distance achromatic laser processing objective lens, and a combined triaxial precision displacement stage; The combined three-axis precision displacement stage is used to fix the sample and realize the three-dimensional motion control of the sample in space; A low-pass dichroic mirror can reflect the processing beam while transmitting the measurement beam and the illumination beam; The laser confocal topography measurement module includes a measurement beam generation unit and a photoelectric detection unit. The measurement beam generation unit generates a measurement beam, which is focused onto the sample surface by a long working distance achromatic laser processing objective lens. The reflected light is detected by the photoelectric detection unit. The ultrafast laser scanning processing module generates a processing beam; the processing beam is reflected by a low-pass dichroic mirror and enters a long working distance achromatic laser processing objective, and is finally focused on the sample surface for scanning processing; The CCD microscopic imaging module includes an illumination beam generation unit and an imaging unit. The illumination beam generation unit generates an illumination beam, which is focused onto the sample surface by a long working distance achromatic laser processing objective lens to illuminate the processing position. The reflected light carries the image information of the sample surface and is received and imaged by the imaging unit. The measuring beam, processing beam, and illumination beam are combined into a coaxial beam by a low-pass dichroic mirror. The beam is then focused onto the same position on the sample surface by a long working distance achromatic laser processing objective, thus achieving coaxial in-situ measurement conditions.

[0007] According to a preferred embodiment of the present invention, the optical paths of both the measuring beam and the illumination beam pass through the first reflector mounting station, and the reflected optical paths of both the measuring beam and the illumination beam pass through the second reflector mounting station. When performing microscopic imaging, a first detachable right-angle mirror is installed at the first mirror mounting station, while a second detachable right-angle mirror is not installed at the second mirror mounting station. At this time, the illumination beam is reflected by the first detachable right-angle mirror to the low-pass dichroic mirror; the reflected light of the illumination beam is transmitted through the beam splitter prism and directly enters the imaging unit. When performing confocal topography measurement, the first detachable right-angle mirror is not installed at the first mirror installation station, and the second detachable right-angle mirror is installed at the second mirror installation station. At this time, the measurement beam output by the measurement beam generation unit is directly incident on the low-pass dichroic mirror. The reflected light of the measurement beam is transmitted through the beam splitter prism and then reflected by the second detachable right-angle mirror into the photoelectric detection unit.

[0008] This invention enables rapid and repeatable adjustment of the optical path structure by assembling and disassembling a first detachable right-angle reflector and a second detachable right-angle reflector.

[0009] According to a preferred embodiment of the present invention, the sample is mounted and fixed on a combined triaxial precision displacement stage, which includes a piezoelectric displacement stage, a leveling device, and a triaxial electric displacement stage. The piezoelectric displacement stage is fixed to the leveling device, which is mounted on the triaxial electric displacement stage. The piezoelectric displacement stage is used for nanometer-level positioning along the Z-axis, the leveling device is used to ensure the sample surface is level, and the triaxial electric displacement stage is used for micrometer-level positioning of the sample along the X, Y, and Z axes in space.

[0010] According to a preferred embodiment of the present invention, the system further includes a host computer, which controls a combined three-axis precision displacement stage to perform sample positioning and morphology measurement. The host computer acquires signals from the photoelectric detection unit, processes them to obtain in-situ morphology measurement results, acquires image data from the imaging unit, and performs microscopic imaging of the sample surface. During the processing, an illumination beam is used to illuminate the processing area for microscopic imaging, while a processing beam is used for scanning processing. After the scanning processing is completed, a measurement beam is used for in-situ morphology measurement. The scanning processing and in-situ measurement process are repeated until the expected morphology requirements are met, thus completing the processing.

[0011] The present invention also provides an in-situ topography measurement method based on the aforementioned system, wherein the method is a single-point height measurement method based on piezoelectric scanning, specifically including the following steps: Step 1: Use a leveling device to level the piezoelectric displacement stage to eliminate height measurement errors caused by tilting; Step 2: Coarse adjustment is achieved using the Z-axis of the three-axis electric displacement stage, and fine axial adjustment is achieved using the piezoelectric displacement stage to make the focal plane coincide with the measurement position reference. Step 3: Move the sample to the point to be measured in the horizontal plane, and the piezoelectric displacement stage starts high-speed scanning along the Z-axis. The movement trajectory of the piezoelectric displacement stage is an axisymmetric waveform trajectory; for example, it can be a triangular wave, a sine wave, or other common axisymmetric waveform trajectories. The data processing and filtering methods used can be low-pass filtering, smoothing filtering, etc., in order to reduce the data size and reduce the signal interference on peak extraction caused by light intensity fluctuations. Step 4: During the scanning process, the light intensity signal of the photodetector is recorded synchronously. After the scanning is completed, the light intensity change curve is processed and filtered. The two light intensity peaks of the light intensity change curve are extracted and the time corresponding to the peak points is obtained. The height difference between the current measurement point and the position reference is calculated using the time interval corresponding to the two peak points. Step 5: Use a three-axis electric displacement stage to move the sample to different measurement points in the horizontal plane and repeat the single-point height measurement described above.

[0012] The present invention also provides an in-situ topography measurement method based on the aforementioned system. This method is a focal tomography-based measurement method, specifically including the following steps: Step 1: Use a leveling device to level the piezoelectric displacement stage to eliminate height measurement errors caused by tilting; Step 2: Coarse adjustment is achieved using the Z-axis of the electric displacement stage, and fine adjustment is achieved using the piezoelectric displacement stage, so that the focal plane coincides with the starting point of the axial measurement. Step 3: Determine the axial measurement range and measurement step interval based on the maximum height difference of the sample morphology, and set the measurement range for the transverse scan; Step 4: Change the axial position of the piezoelectric displacement stage, scan layer by layer according to the set step interval, perform a transverse scan measurement at each axial position, and record the corresponding light intensity signal; the transverse scan is a one-dimensional line scan or a two-dimensional surface scan. Step 5: Store the light intensity signal data obtained from each layer of scanning to form a light intensity dataset matrix. Each column in the matrix corresponds to the light intensity variation data of a certain horizontal scanning measurement point at different axial positions. Step 6: Perform "light intensity-axial position" data fitting and peak extraction column by column on the light intensity dataset matrix to determine the axial position corresponding to the light intensity peak at each measurement point. The difference between this position and the axial position of the measurement starting point is the relative height data of that measurement point. The data fitting method can be polynomial fitting, Gaussian fitting, etc. Step 7: Traverse all transverse scanning measurement points, acquire height data respectively, and reconstruct the three-dimensional morphology information of the sample surface.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: (i) Enables rapid switching between processing, measurement, and imaging functions, significantly improving the integration and operational efficiency of the ultrafast laser processing system. This invention proposes an integrated coaxial laser confocal processing and measurement system, mainly comprising a laser confocal topography measurement module, an ultrafast laser scanning processing module, and a CCD microscopic imaging module, which respectively realize functions such as confocal in-situ topography measurement, ultrafast laser scanning processing, and microscopic image monitoring of the processing area. Through the efficient integration and reasonable layout of the three modules, stable and rapid function switching can be achieved by using plug-and-play reflectors.

[0014] (ii) Achieve high-precision in-situ topography measurement, avoiding measurement errors caused by the conversion between the measurement coordinate system and the machining coordinate system, as well as workpiece secondary clamping errors. By constructing a coaxial optical path structure for the machining beam and the measurement beam, spatial consistency between the measurement coordinate system and the machining coordinate system is ensured. This design allows topographic measurement and laser processing to be completed under the same coordinate reference, eliminating the need for workpiece disassembly or repositioning, and significantly reducing cumulative errors caused by secondary clamping and coordinate system transformation. Single-point height measurement and scanning measurement based on the laser confocal principle are suitable for various measurement needs, exhibiting strong flexibility and adaptability. They can be used for topographic measurement of curved structures, rough surfaces, etc., with measurement accuracy and resolution reaching sub-micron levels. Both of the aforementioned measurement methods can be directly performed without prior calibration, further simplifying the in-situ measurement process.

[0015] (iii) Enables morphological monitoring during laser processing, facilitating timely adjustments to processing strategies and improving processing precision and accuracy. The confocal in-situ scanning morphology measurement method can intuitively monitor the material removal during the processing and the morphological changes of the material surface before and after laser processing, thereby improving the processing position accuracy and structural consistency, and providing an important guarantee for improving the accuracy and quality of ultrafast laser processing. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall optical path of the coaxial laser confocal processing and measurement integrated system provided in this embodiment of the invention.

[0017] Figure 2 This is a schematic diagram of the optical path of the laser confocal topography measurement module provided in an embodiment of the present invention.

[0018] Figure 3 This is a schematic diagram of the optical path of the CCD microscopic imaging module provided in an embodiment of the present invention.

[0019] Figure 4 This is a schematic diagram of the optical path of the ultrafast laser scanning processing module provided in an embodiment of the present invention.

[0020] Figure 5 This is a physical assembly drawing of the coaxial laser confocal machining and measurement integrated system provided in the embodiments of the present invention.

[0021] Figure 6 This is a schematic diagram illustrating the working principle of the single-point height measurement method based on piezoelectric scanning provided in this embodiment of the invention.

[0022] Figure 7 This is a schematic diagram illustrating the working principle of the measurement method based on focal tomography provided in this embodiment of the invention.

[0023] Figure 8 This is a flowchart illustrating the workflow of the single-point height measurement method based on piezoelectric scanning provided in this embodiment of the invention.

[0024] Figure 9 This is a flowchart illustrating the workflow of the measurement method based on focal tomography provided in this embodiment of the invention.

[0025] Figure 10 This is the confocal axial response curve provided in the embodiments of the present invention.

[0026] Figure 11 The following are light intensity variation curves provided in the embodiments of the present invention: (a) light intensity variation curves at different locations in single-point height measurement; (b) single-point light intensity distribution curves and their Gaussian fitting results in the measurement method based on focal tomography.

[0027] Figure 12 The following are the in-situ morphological measurement results provided by the embodiments of the present invention: (a) single-point height measurement results of the stepped structure; (b) morphological measurement results of a single sinusoidal surface structure based on the measurement method of focal tomography.

[0028] In the diagram: 001A - First detachable right-angle mirror, 001B - Second detachable right-angle mirror, 002 - Beam splitter prism, 003 - Beam scatterer, 004 - Low-pass dichroic mirror, 005 - Long working distance achromatic laser processing objective lens, 006 - Combined three-axis precision stage, 006A - Piezoelectric stage, 006B - Leveling device, 006C - Three-axis motorized stage, 101 - Continuous laser source, 102 - Beam collimation module, 102A - Five-dimensional fiber coupler, 103 - Spatial filtering module, 103A - First lens, 103B - Spatial filter aperture, 103C-Second lens, 104-Low-pass filter, 105-Infinity correction objective, 106-Aperture stop, 107-Photodetector, 201-LED white light source, 202-Reflector, 203-Bow lens, 204-CCD camera, 301-Ultrafast laser source, 302-Beam expander, 303-Laser reflector, 304-XY two-dimensional galvanometer system, 305-4f system, 305A-First lens of 4f system, 305B-Second lens of 4f system, 401-Breadboard, 402-Mounting support, 501-Piezoelectric displacement stage motion trajectory, 502A-Intensity change curve of the sample surface below the position reference, 502B-Intensity change curve of the sample surface above the position reference, 601A-Confocal axial response curve of the measurement starting point, 601B-Single-point light intensity distribution curve, 601C-Single-point light intensity signal. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0030] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components.

[0031] Example: like Figure 1 The diagram shows the coaxial laser confocal processing and measurement integrated system of the present invention. This system mainly includes a laser confocal topography measurement module, an ultrafast laser scanning processing module, a CCD microscopic imaging module, a beam splitter prism 002, a low-pass dichroic mirror 004, a long working distance achromatic laser processing objective lens 005, and a combined triaxial precision displacement stage 006. The combined triaxial precision displacement stage is used to fix the sample and realize the spatial three-dimensional motion control of the sample; the low-pass dichroic mirror reflects the processing beam while transmitting the measurement beam and illumination beam.

[0032] The laser confocal topography measurement module of this embodiment includes a measurement beam generation unit and a photoelectric detection unit. The measurement beam generation unit generates a measurement beam, which is focused onto the sample surface by a long working distance achromatic laser processing objective lens 005, and the reflected light is detected by the photoelectric detection unit. The ultrafast laser scanning processing module generates a processing beam; the processing beam is reflected by the low-pass dichroic mirror 004 and enters the long working distance achromatic laser processing objective lens 005, and is finally focused on the sample surface for scanning processing; The CCD microscopic imaging module includes an illumination beam generation unit and an imaging unit. The illumination beam generation unit generates an illumination beam, which is focused onto the sample surface by the long working distance achromatic laser processing objective lens 005 to illuminate the processing position. The reflected light carries the image information of the sample surface and is received and imaged by the imaging unit. The measuring beam, processing beam, and illumination beam are combined into a coaxial beam by a low-pass dichroic mirror. The beam is then focused onto the same position on the sample surface by a long working distance achromatic laser processing objective, thus achieving coaxial in-situ measurement conditions.

[0033] like Figure 1 As shown, the optical paths of both the measurement beam and the illumination beam pass through the first reflector mounting station, and the reflected optical paths of both the measurement beam and the illumination beam pass through the second reflector mounting station. When performing microscopic imaging, a first detachable right-angle reflector 001A is installed on the first reflector mounting station, while a second detachable right-angle reflector 001B is not installed on the second reflector mounting station. In this case, the illumination beam is reflected by the first detachable right-angle reflector 001A to the low-pass dichroic mirror 004; the reflected light from the illumination beam is transmitted through the beam splitter prism 002 and directly enters the imaging unit. When performing confocal topography measurement, the first detachable right-angle mirror 001A is not installed on the first mirror mounting station, and the second detachable right-angle mirror 001B is installed on the second mirror mounting station. At this time, the measurement beam output by the measurement beam generation unit is directly incident on the low-pass dichroic mirror 004. The reflected light of the measurement beam is transmitted through the beam splitter prism 002 and then reflected by the second detachable right-angle mirror 001B before entering the photoelectric detection unit.

[0034] This invention enables rapid and repeatable adjustment of the optical path structure by assembling and disassembling a first detachable right-angle reflector and a second detachable right-angle reflector.

[0035] In an embodiment of the present invention, the sample is fixed on the piezoelectric displacement stage 006A in the combined triaxial precision displacement stage 006.

[0036] like Figure 2The diagram shows the optical path structure of the laser confocal topography measurement module in the aforementioned coaxial laser confocal processing and measurement integrated system. During confocal topography measurement, the first detachable right-angle mirror 001A is removed; the second detachable right-angle mirror 001B is installed. In this example, the measurement beam is generated by a continuous laser source 101 with a wavelength of 532nm. The measurement beam is transmitted to the beam collimation module 102 via a single-mode fiber, collimated by a five-dimensional fiber coupler 102A, and then output to free space. Further, the measurement beam passes through a spatial filtering module 103, which consists of a first lens 103A with focal lengths of f1 and a second lens 103C with focal lengths of f2, and a spatial filter aperture 103B. The lens group consisting of the first lens 103A and the second lens 103C has a beam-expanding function for the measurement beam, with a beam expansion ratio of f2 / f1. The spatial filter aperture 103B acts as a low-pass filter, eliminating high-frequency noise in the measurement beam and improving beam quality. Furthermore, the measurement beam is partially reflected by the beam splitter prism 002 and transmitted through the low-pass dichroic mirror 004. Finally, it is focused onto the sample surface by the long working distance achromatic laser processing objective lens 005. The measurement beam transmitted at the beam splitter prism 002 is absorbed by the beam scatterer 003.

[0037] Furthermore, the measurement beam reflected from the sample surface is transmitted through the long working distance achromatic laser processing objective 005, the low-pass dichroic mirror 004, and the beam splitter prism 002, and then reflected by the second detachable right-angle mirror 001B. After passing through the low-pass filter 104, only the wavelength range corresponding to the measurement beam is retained. Subsequently, the reflected light is focused by the infinity correction objective 105, and the beam passing through the aperture 106 is collected by the photodetector 107. The aperture 106 in front of the photodetector 107 is used to filter out stray light signals from the reflection, thereby improving the resolution of the system in detecting axial displacement. The confocal axial response curve of the aforementioned laser confocal topography measurement module is shown below. Figure 10 As shown, in this example, a long working distance achromatic laser processing objective 005 with a numerical aperture of 0.42 and an aperture stop 106 with an aperture of 10 μm is used, and the full peak half width (FWHM) of the confocal axial response curve is approximately 7 μm.

[0038] like Figure 3The diagram shows the optical path structure of the CCD microscopic imaging module in the aforementioned coaxial laser confocal processing and measurement integrated system. During CCD microscopic imaging monitoring, the first detachable right-angle mirror 001A is in the installed state; the second detachable right-angle mirror 001B is in the removed state. The illumination beam is emitted by an LED white light source 201, which contains a collimating lens to collimate the illumination beam into parallel light. Further, the illumination beam is continuously reflected by the reflector 202, the first detachable right-angle mirror 001A, and the beam-splitting prism 002, then transmitted through a low-pass dichroic mirror 004, and finally focused onto the sample surface by the long working distance achromatic laser processing objective lens 005, achieving white light illumination of the processing position. The coaxiality of the illumination beam and the processing beam can be ensured by adjusting the position and pitch of the reflector 202.

[0039] Furthermore, the aforementioned illumination beam reflected from the sample surface carries image information of the laser processing location. After passing through the long working distance achromatic laser processing objective 005, the low-pass dichroic mirror 004, and the beam splitter prism 002, it is focused by the lens 203 and finally imaged onto the CCD camera 204, realizing the acquisition of a microscopic image of the processing location. In this example, the long working distance achromatic laser processing objective 005 used has a magnification of 50x, thus it can acquire a microscopic image of the processing area magnified 50x, which can be used to monitor the accumulation of debris, ablation, etc. at the processing location.

[0040] like Figure 4The diagram shows the optical path structure of the ultrafast laser scanning processing module in the aforementioned coaxial laser confocal processing and measurement integrated system. The processing beam is generated by the ultrafast laser source 301. In this example, the ultrafast laser source 301 has a femtosecond pulse width of 400 fs, a wavelength of 1040 nm, and a maximum average laser power of 8 W. The low-pass dichroic mirror 004 used in this example has a transmission cutoff wavelength of 685 nm, thus reflecting the processing beam while transmitting the measurement beam and illumination beam. The aforementioned processing beam is expanded by the beam expander 302 to obtain a suitable diameter. On the one hand, this ensures that the beam energy can be fully utilized and uniformly cover the entrance pupil of the processing objective, thereby achieving high focusing energy density under high numerical aperture conditions. On the other hand, the collimated beam after beam expansion can effectively reduce the divergence angle, improve the focusing spot quality and processing stability, and provide a good beam quality foundation for subsequent high-precision microstructure processing. Furthermore, the processing beam, after being reflected by the laser reflector 303, enters the XY two-dimensional galvanometer system 304. The XY two-dimensional galvanometer system 304 consists of an X-mirror and a Y-mirror arranged in mutually perpendicular directions. By controlling the deflection angle of the galvanometers, rapid and high-precision scanning of the processing beam on the sample surface is achieved, thereby completing the processing trajectory control of arbitrary two-dimensional graphics or paths. The high response speed and angular resolution of the galvanometer system ensure the accuracy of the spot position during scanning, providing flexible path control capabilities for the precision processing of complex micro / nano structures.

[0041] Furthermore, the processing beam emitted from the aforementioned XY two-dimensional galvanometer system 304 is reflected by the low-pass dichroic mirror 004 after passing through the 4f system 305 and then enters the long working distance achromatic laser processing objective lens 005, where it is focused on the sample surface to achieve precise scanning processing. The 4f system 305 is composed of a first 4f system lens 305A and a second 4f system lens 305B with the same focal length, realizing the conjugate relationship between the reflecting surface of the XY two-dimensional galvanometer system 304 and the entrance pupil surface of the long working distance achromatic laser processing objective lens 005.

[0042] The physical assembly drawing (front view) of the aforementioned coaxial laser confocal machining and measurement integrated system is as follows: Figure 5 As shown. The measurement beam of the aforementioned laser confocal topography measurement module is input via single-mode fiber through Port1. Figure 5 The continuous laser source 101 is not shown; the processing beam of the aforementioned ultrafast laser scanning processing module is input through Port2, and the XY two-dimensional galvanometer system 304 and its forward optical path structure and optical components are not shown.

[0043] Furthermore, the optical components of the aforementioned coaxial laser confocal processing and measurement integrated system are mounted on a breadboard 401. The breadboard 401 is fixed to the air-bearing optical platform by a mounting bracket 402, thereby achieving vertical mounting of the aforementioned coaxial laser confocal processing and measurement integrated system. Compared with horizontal mounting, this method makes sample leveling and fixing more convenient.

[0044] Furthermore, the sample is mounted on the piezoelectric displacement stage 006A within the combined triaxial precision displacement stage 006. The piezoelectric displacement stage 006A can achieve single-axis nanometer-level axial positioning and scanning in the Z direction. In this example, the repeatability of the piezoelectric displacement stage 006A is 1 nm, and the closed-loop travel is 100 μm. The piezoelectric displacement stage 006A is mounted on the leveling device 006B, which can achieve pitch adjustment in both the X and Y directions to ensure that the sample surface is in a horizontal state, i.e., perpendicular to the optical axis. The leveling device 006B is mounted on the Z-axis of the triaxial electric displacement stage 006C. The triaxial electric displacement stage 006C can achieve micrometer-level precision positioning of the sample in three-dimensional space. In this example, the repeatability of each axis of the triaxial electric displacement stage 006C is 0.2 μm, and the closed-loop travel is 20 mm.

[0045] It should be noted that in this example, the Z direction is parallel to the optical axis and is therefore also called "axial"; the X and Y directions are parallel to the horizontal plane and are therefore also called "lateral". Within the scope of this invention, to avoid ambiguity, the two expressions specifically described above can be regarded as equivalent expressions.

[0046] Figure 8 The flowchart illustrates the workflow of the single-point height measurement method provided by this invention. The single-point height measurement method based on piezoelectric scanning specifically includes the following steps: Step 1: First, use the leveling device 006B to level the piezoelectric displacement stage 006A. Adjust the axial position, using a combination of coarse adjustment with the triaxial electric displacement stage 006C and fine adjustment with the piezoelectric displacement stage 006A, to move the surface of the sample to be tested to the position reference. And adjust the focal plane of the measuring beam to the position reference. The light intensity signal of the photodetector is strongest when the light coincides with the photodetector.

[0047] Step 2: The triaxial electric displacement stage 006C moves the sample to the desired measurement position in the horizontal plane, and the piezoelectric displacement stage 006A begins high-speed scanning along the Z-axis. The motion trajectory of the piezoelectric displacement stage is a triangular wave, as shown below. Figure 6 As shown in (a), the position reference for the triangular wave motion is The maximum displacement is The minimum value is One scan is one cycle of the triangular wave. In this example, the position reference for the triangular wave motion is... The maximum displacement is The minimum value is Therefore, the axial height measurement range is 60μm.

[0048] Step 3: During the scanning process, the light intensity signal of the photodetector 107 is recorded synchronously using the acquisition card. If the surface of the sample being measured is lower than the position reference... The light intensity change curve obtained during the scanning process is as follows: Figure 6 (b) shows the light intensity variation curve 502A when the surface of the tested sample is below the position reference; if the surface of the tested sample is above the position reference... The light intensity change curve obtained during the scanning process is as follows: Figure 6 The light intensity variation curve of the sample surface above the position reference in (b) is shown in Figure 502B.

[0049] Specifically, during the scanning process, the acquisition card simultaneously records the light intensity signal from the photodetector. If the surface of the sample being measured is lower than the position reference... The light intensity change curve obtained during the scanning process is as follows: Figure 6 As shown by the dashed line in (b), the piezoelectric displacement stage starts from... arrive Then During the scanning process, the light intensity will show two peaks, corresponding to the following times: , Furthermore, the two light intensity peaks are symmetrical about the maximum displacement of the triangular wave; if the surface of the sample being measured is higher than the position reference... The light intensity change curve obtained during the scanning process is as follows: Figure 6 As shown by the solid line in (b), the piezoelectric displacement stage starts from... arrive Then During the scanning process, the light intensity will show two peaks, corresponding to the following times: , Furthermore, the two light intensity peaks are symmetrical about the minimum displacement of the triangular wave. Since the piezoelectric scanning speed is constant... By obtaining the time difference between the occurrence of two light intensity peaks, the position of the piezoelectric displacement stage corresponding to the occurrence of the light intensity peak can be calculated, thereby obtaining the sample surface relative to the position reference. The relative height. For example Figure 6 As shown by the dashed line in (b), assuming a light intensity peak occurs. The corresponding time is , Time difference Then the sample surface and the position reference The relative height is .

[0050] Step 4: After the axial scan is completed, the acquisition card transmits the photodetector light intensity signal to the host computer. The host computer processes the light intensity variation curve. First, mean filtering is performed to eliminate some periodic noise and reduce the data volume, thus accelerating the calculation speed. Then, Gaussian filtering is used to smooth the data, eliminating some false peak data caused by environmental disturbances and light intensity drift, thereby improving the accuracy and stability of subsequent peak extraction. Finally, the peak extraction algorithm is used to extract the two light intensity peak points and obtain the time corresponding to the peak points. The time relative to the position reference is calculated using the method described in Step 3. The height value; when the data is abnormal and two valid peaks cannot be extracted, steps 2 to 4 above will be repeated. In this example, the movement speed of the piezoelectric displacement stage 006A is set to 100 μm / s, the sampling frequency of the acquisition card is set to 20 kHz, and the position reference is as described above. Under these conditions, the light intensity variation curves at axial positions of 55-75 μm are shown below. Figure 11 As shown in (a) of the diagram.

[0051] Furthermore, the sample was moved to different measurement points in the horizontal plane using a triaxial electric displacement stage 006C, and the aforementioned single-point height measurement was repeated. In this example, the X-axis of the electric displacement stage 006C was moved to different measurement points to perform the aforementioned single-point height measurement, with an X-direction spacing of 100 μm between adjacent measurement points. The morphology of the stepped structure sample was measured in situ using the aforementioned method, and the single-point height measurement results of the stepped structure are as follows. Figure 12 As shown in (a) in the figure; the test results show that the axial resolution of single-point height measurement can reach 0.1 μm, and the measurement repeatability accuracy is close to 0.1 μm, which can be applied to application scenarios that require high-precision positioning, such as autofocus.

[0052] Figure 9 A flowchart illustrating the workflow of the focal tomography-based measurement method provided by this invention. The aforementioned focal tomography-based measurement method specifically includes the following steps: Step 1: First, use the leveling device 006B to level the piezoelectric displacement stage 006A, ensuring that the upper surface of the piezoelectric displacement stage 006A is parallel to the X and Y axes of the triaxial electric displacement stage 006C, thus avoiding height measurement errors caused by tilting. Perform coarse adjustment of the Z-axis of the triaxial electric displacement stage 006C, followed by fine adjustment using the piezoelectric displacement stage 006A. Finally, adjust the focal plane of the measurement beam to align with the axial measurement starting point. The light intensity signal of the photodetector is strongest when the light coincides with the photodetector.

[0053] Step 2: Determine the axial measurement range and measurement step interval. Based on the maximum height difference of the actual measured topography, initially estimate the axial measurement range and determine the aforementioned axial measurement starting point. With the measurement endpoint To ensure the measurement range completely covers the topography to be measured, the axial measurement step interval is set according to the required level of precision. Generally speaking, step interval The smaller the value, the more precise the topographic measurement, but the longer the measurement time. Further, the lateral measurement range needs to be determined, that is, the scanning range of the three-axis electric displacement stage in the X and Y directions.

[0054] Step 3: Begin layer-by-layer scanning. For example... Figure 7 As shown in (a), firstly, based on the axial measurement range (axial measurement starting point) in step 2 above. Measurement endpoint and step interval The parameter settings can establish a scale of axial position vector As shown in equation (1): (1) Then, scanning and measurement began for the axial position matrix. Each height value Set the Z-axis position of the piezoelectric displacement stage to A transverse scan measurement is performed, therefore a total of repeated transverse scans are required. Next. Assume a horizontal scan yielded... Data points, the measured light intensity signals are stored in a scale of Light intensity data vector In the middle, as shown in equation (2): (2) The size of the light intensity data vector is the number of transverse scan data points, which is determined by the transverse scan speed and the sampling interval of the light intensity signal. It can be freely adjusted according to the transverse accuracy requirements of the topography measurement.

[0055] Step 4: After each layer of scanning is completed, the acquisition card will transmit the light intensity data vector corresponding to the current axial position. Transmit and store to the host computer.

[0056] Step 5: Complete different axial positions The following total After the second transverse scan, it is necessary to base the axial position vector on... With the light intensity data vector acquired in each horizontal scan Merge data and establish a scale of Light intensity dataset matrix As shown in equation (3): (3) Each row of the light intensity dataset matrix is ​​the axial position. Discrete data of light intensity signal changes obtained during each transverse scan process; each column corresponds to the position of each measurement point on the transverse scan path at different axial directions. Discrete data of single-point light intensity signal changes.

[0057] Step 6: Calculate the horizontal scan path height information point by point. For example... Figure 7 As shown in (b), based on each column of the aforementioned light intensity dataset matrix, with axial position as the horizontal axis and light intensity as the vertical axis, and based on the single-point light intensity signal 601C, the single-point light intensity distribution curve 601B and its peak value for each measurement point on the transverse scanning path can be obtained through data fitting and peak signal extraction methods. Based on the confocal theory model, the aforementioned single-point light intensity distribution curve 601B can be obtained by translating the confocal axial response curve 601A at the topography measurement starting point along its axial position. Finally, the peak value of the fitted single-point light intensity distribution curve 601B is extracted, and the axial position corresponding to the light intensity peak value is determined. Location of the starting point for topographic measurement The axial position difference is the position of this measurement point relative to the starting point of the topography measurement. The relative height.

[0058] Furthermore, by traversing the aforementioned lateral scanning path to obtain each measurement point, and calculating the height data using the aforementioned method, the surface morphology information of the sample along the lateral scanning path can be reconstructed. In this example, as... Figure 12 (b) shows the morphology measurement results of a single sinusoidal surface structure in situ using the aforementioned focal tomography-based measurement method. The test results show that the aforementioned focal tomography-based measurement method can meet the measurement requirements of large-scale structures and curved surfaces. At the same time, the axial resolution of the morphology measurement reaches 0.2 μm, the repeatability accuracy is better than 0.3 μm, the axial morphology measurement range can be extended to 100 μm, and the transverse scanning measurement range can reach 20 × 20 mm. It can be applied to the in-situ morphology measurement of large-scale structures and curved surfaces.

[0059] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. Those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A coaxial laser confocal machining and measurement integrated system, characterized in that, It includes a laser confocal topography measurement module, an ultrafast laser scanning processing module, a CCD microscopic imaging module, a beam splitter prism, a low-pass dichroic mirror, a long working distance achromatic laser processing objective lens, and a combined triaxial precision displacement stage; The combined three-axis precision displacement stage is used to fix the sample and realize the three-dimensional motion control of the sample in space; A low-pass dichroic mirror can reflect the processing beam while transmitting the measurement beam and the illumination beam; The laser confocal topography measurement module includes a measurement beam generation unit and a photoelectric detection unit. The measurement beam generation unit generates a measurement beam, which is focused onto the sample surface by a long working distance achromatic laser processing objective lens. The reflected light is detected by the photoelectric detection unit. The ultrafast laser scanning processing module generates a processing beam; the processing beam is reflected by a low-pass dichroic mirror and enters a long working distance achromatic laser processing objective, and is finally focused on the sample surface for scanning processing; The CCD microscopic imaging module includes an illumination beam generation unit and an imaging unit. The illumination beam generation unit generates an illumination beam, which is focused onto the sample surface by a long working distance achromatic laser processing objective lens to illuminate the processing position. The reflected light carries the image information of the sample surface and is received and imaged by the imaging unit. The measuring beam, processing beam, and illumination beam are combined into a coaxial beam by a low-pass dichroic mirror. The beam is then focused onto the same position on the sample surface by a long working distance achromatic laser processing objective, thus achieving coaxial in-situ measurement conditions.

2. The coaxial laser confocal machining and measurement integrated system according to claim 1, characterized in that, The optical paths of both the measuring beam and the illumination beam pass through the first reflector mounting station, and the reflected optical paths of both the measuring beam and the illumination beam pass through the second reflector mounting station. When performing microscopic imaging, a first detachable right-angle mirror is installed at the first mirror mounting station, while a second detachable right-angle mirror is not installed at the second mirror mounting station. At this time, the illumination beam is reflected by the first detachable right-angle mirror to the low-pass dichroic mirror; the reflected light of the illumination beam is transmitted through the beam splitter prism and directly enters the imaging unit. When performing confocal topography measurement, the first detachable right-angle mirror is not installed on the first mirror mounting station, and the second detachable right-angle mirror is installed on the second mirror mounting station. At this time, the measurement beam output by the measurement beam generation unit is directly incident on the low-pass dichroic mirror. The reflected light of the measurement beam is transmitted through the beam splitter prism and then reflected by the second detachable right-angle mirror into the photoelectric detection unit. The optical path structure can be quickly and repeatedly adjusted by assembling and disassembling the first and second detachable right-angle mirrors.

3. The coaxial laser confocal machining and measurement integrated system according to claim 1, characterized in that, The measurement beam generation unit includes a continuous laser source, a beam collimation module, and a spatial filtering module; the photoelectric detection unit includes a low-pass filter, an infinity correction objective lens, an aperture stop, and a photoelectric detector. A continuous laser source generates an initial measurement beam, which is transmitted through a single-mode fiber to a beam collimation module for collimation. The beam is then filtered by a spatial filtering module, which outputs the measurement beam. The measurement beam reflected from the sample surface is filtered by a low-pass filter to eliminate stray light, and then focused by an infinity-corrected objective lens. The reflected beam passing through the aperture stop is detected and collected by a photodetector. The aperture stop in front of the detector is used to filter the stray light signal reflected, thereby improving the resolution of the system in detecting axial displacement.

4. The coaxial laser confocal machining and measurement integrated system according to claim 1, characterized in that, The ultrafast laser scanning processing module includes an ultrafast laser source, a beam expander, a laser reflector, an XY two-dimensional galvanometer system, and a 4f system. The ultrafast laser source generates an initial processing beam, which is expanded by the beam expander and reflected by the laser reflector. Then, the beam is deflected by the XY two-dimensional galvanometer system. Subsequently, the processing beam passes through the 4f system and is reflected by a low-pass dichroic mirror into the long working distance achromatic laser processing objective, where it is finally focused on the sample surface. The 4f system is used to optically conjugate the reflecting surface of the XY two-dimensional galvanometer system to the entrance pupil of the long working distance achromatic laser processing objective.

5. The coaxial laser confocal machining and measurement integrated system according to claim 1, characterized in that, The illumination beam generating unit includes an LED white light source and a reflector; the imaging unit includes a lens barrel and a CCD camera; the LED white light source emits an initial illumination beam, which is collimated by the lens and then reflected by the reflector and the first detachable right-angle reflector to the beam splitter prism; the reflected light of the illumination beam transmitted through the beam splitter prism carries the image of the sample surface and is focused by the lens barrel, and finally imaged on the CCD camera.

6. The coaxial laser confocal machining and measurement integrated system according to claim 1, characterized in that, The sample is mounted and fixed on a combined triaxial precision displacement stage, which includes a piezoelectric displacement stage, a leveling device, and a triaxial electric displacement stage. The piezoelectric displacement stage is fixed on the leveling device, which is mounted on the triaxial electric displacement stage. The piezoelectric displacement stage is used for nanometer-level positioning along the Z-axis, the leveling device is used to ensure that the sample surface is level, and the triaxial electric displacement stage is used for micrometer-level positioning of the sample along the X, Y, and Z axes in space.

7. The coaxial laser confocal machining and measurement integrated system according to claim 6, characterized in that, The system also includes a host computer that controls a combined three-axis precision displacement stage to position and measure the sample's morphology. The host computer acquires signals from the photoelectric detection unit, processes them to obtain in-situ morphology measurement results, acquires image data from the imaging unit, and performs microscopic imaging of the sample surface. During processing, an illumination beam is used to illuminate the processing area for microscopic imaging, while a processing beam is used for scanning. After scanning and processing, a measurement beam is used for in-situ morphology measurement. The scanning and processing and in-situ measurement processes are repeated until the desired morphology is achieved, thus completing the processing.

8. A method for measuring in-situ topography based on the system of claim 7, characterized in that, The method is a single-point height measurement method based on piezoelectric scanning, which specifically includes the following steps: Step 1: Use a leveling device to level the piezoelectric displacement stage to eliminate height measurement errors caused by tilting; Step 2: Coarse adjustment is achieved using the Z-axis of the three-axis electric displacement stage, and fine axial adjustment is achieved using the piezoelectric displacement stage to make the focal plane coincide with the measurement position reference. Step 3: Move the sample to the point to be measured in the horizontal plane, and the piezoelectric displacement stage starts high-speed scanning along the Z-axis. The motion trajectory of the piezoelectric displacement stage is an axisymmetric waveform trajectory. Step 4: During the scanning process, the light intensity signal of the photoelectric detection unit is recorded synchronously. After the scanning is completed, the light intensity change curve is processed and filtered. The two light intensity peaks of the light intensity change curve are extracted and the time corresponding to the peak points is obtained. The height difference between the current measurement point and the position reference is calculated using the time interval corresponding to the two peak points. Step 5: Use a three-axis electric displacement stage to move the sample to different measurement points in the horizontal plane and repeat the single-point height measurement described above.

9. A method for measuring in-situ topography based on the system of claim 7, characterized in that, The method is a measurement method based on focal tomography, and specifically includes the following steps: Step 1: Use a leveling device to level the piezoelectric displacement stage to eliminate height measurement errors caused by tilting; Step 2: Coarse adjustment is achieved using the Z-axis of the electric displacement stage, and fine adjustment is achieved using the piezoelectric displacement stage, so that the focal plane coincides with the starting point of the axial measurement. Step 3: Determine the axial measurement range and measurement step interval based on the maximum height difference of the sample morphology, and set the measurement range for the transverse scan; Step 4: Change the axial position of the piezoelectric displacement stage, scan layer by layer according to the set step interval, perform a transverse scan measurement at each axial position, and record the corresponding light intensity signal; the transverse scan is a one-dimensional line scan or a two-dimensional surface scan. Step 5: Store the light intensity signal data obtained from each layer of scanning to form a light intensity dataset matrix. Each column in the matrix corresponds to the light intensity variation data of a certain horizontal scanning measurement point at different axial positions. Step 6: Perform "light intensity-axial position" data fitting and peak extraction on each column of the light intensity dataset matrix to determine the axial position corresponding to the light intensity peak at each measurement point. The difference between this position and the axial position of the measurement starting point is the relative height data of that measurement point. Step 7: Traverse all transverse scanning measurement points, acquire height data respectively, and reconstruct the three-dimensional morphology information of the sample surface.

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