Coaxial laser confocal processing and measuring integrated system and in-situ morphology measuring method thereof

Abstract

The invention discloses a coaxial laser confocal processing and measurement integrated system and an in-situ morphology measurement method thereof, and belongs to the technical field of ultrafast laser precision processing and in-situ measurement. The system comprises a laser confocal morphology measurement module, an ultrafast laser scanning processing module, a CCD (Charge Coupled Device) microscopic imaging module, a beam splitter prism, a low-pass dichroscope, a long-working-distance achromatic laser processing objective lens and a combined three-axis precision displacement table, the laser confocal morphology measurement module generates a measurement light beam to realize morphology measurement of a sample; the ultrafast laser scanning processing module generates a processing light beam to scan and process the surface of the sample; the CCD microscopic imaging module generates an illumination light beam to realize illumination of a processing position and acquisition of image information of a sample surface; a measurement light beam, a processing light beam and an illumination light beam form coaxial light beams through a low-pass dichroscope, the coaxial light beams are focused at the same position of the surface of a sample through a long-working-distance achromatic laser processing objective lens, and the coaxial in-situ measurement condition is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ultrafast laser precision machining and in-situ measurement, and particularly relates to a coaxial laser confocal machining and measurement integrated system and an in-situ topography measurement method thereof. BACKGROUND

[0002] Ultrafast laser machining technology has broad application prospects in the fields of biosensing, aerospace, and optoelectronic device manufacturing due to its advantages of fast processing speed, high precision, strong controllability, easy integration, and high material compatibility, and is becoming an important support and core driving force for precision manufacturing. However, current ultrafast laser machining is mainly in an open-loop mode, which requires non-in-situ measurement to obtain the topography of the machined surface. On the one hand, this processing mode cannot avoid measurement errors caused by the conversion between the measurement coordinate system and the processing coordinate system, especially when processing large-scale structures or complex structures with high aspect ratios. Frequent disassembly of the workpiece caused by multiple measurements, focusing, and processing not only leads to the accumulation of measurement errors, but also introduces secondary clamping errors, affecting the processing precision. On the other hand, in ultrafast laser subtractive manufacturing, it is usually difficult to accurately calculate or predict the actual material removal due to the complexity of the interaction mechanism between laser and material. Factors such as laser energy density, pulse width, repetition frequency, material physical and chemical properties, surface state, thermal diffusion coefficient, and material non-uniformity can significantly affect the processing effect, making it difficult to establish a stable and generalizable mapping relationship between processing parameters and the final topography, which restricts the improvement of processing precision. Therefore, to further improve the processing precision, ensure the processing quality, and obtain consistent micro-topography and structure with the design, it is necessary to monitor the processing surface topography in real time during ultrafast laser processing to calculate the deviation between the actual topography and the expected topography, so as to effectively monitor and timely adjust the processing process.

[0003] In summary, in order to further improve the precision and efficiency of ultrafast laser machining, optimize the laser machining process, and improve the quality of laser-processed structures, in-situ measurement technology for laser machining is indispensable. Currently, there is little research on in-situ topography measurement of ultrafast laser at home and abroad, and no mature systematic solution has been formed. The research on in-situ topography measurement methods focuses on confocal, optical coherence tomography (OCT), and interferometric measurement (CN112207425A). Interferometric measurement has high precision, but is significantly affected by environmental disturbances and sample surface roughness, and the system is complex and difficult to integrate. The axial resolution of optical coherence tomography is low, limited to the micron level, and the scanning speed is limited. These shortcomings limit the adaptability and practicality of current ultrafast laser in-situ topography measurement technology.

[0004] Therefore, it is urgent to develop a more accurate and adaptive topography measurement method based on coaxial light path to realize in-situ measurement and topography monitoring in the ultrafast laser processing process, and to change the previous open-loop processing mode into a closed-loop processing mode based on processing-measuring. SUMMARY

[0005] In order to solve the problems of in-situ topography measurement and topography monitoring in the ultrafast laser processing, the application provides a coaxial laser confocal processing and measurement integrated system and an in-situ topography measurement method thereof, aiming to realize in-situ high-precision topography measurement based on laser confocal, and further realize topography monitoring of the ultrafast laser processing process, and change the previous open-loop processing mode into a closed-loop processing mode based on processing-measuring.

[0006] The application first provides a coaxial laser confocal processing and measurement integrated system, which comprises 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 and a combined three-axis precision displacement stage. The combined three-axis precision displacement stage is used for fixing the sample and realizing spatial three-dimensional motion control of the sample. The low-pass dichroic mirror can reflect the processing light beam and transmit the measurement light beam and the illumination light beam. The laser confocal topography measurement module comprises a measurement light beam generating unit and a photoelectric detection unit, wherein the measurement light beam generating unit generates the measurement light beam, the measurement light beam is focused on the sample surface through the long working distance achromatic laser processing objective, and the reflected light is detected by the photoelectric detection unit. The ultrafast laser scanning processing module generates the processing light beam; the processing light beam is reflected by the low-pass dichroic mirror into the long working distance achromatic laser processing objective, and is finally focused on the sample surface for scanning processing. The CCD microscopic imaging module comprises an illumination light beam generating unit and an imaging unit, the illumination light beam generating unit generates the illumination light beam, the illumination light beam is focused on the sample surface through the long working distance achromatic laser processing objective to realize illumination of the processing position; the reflected light carrying the image information of the sample surface is received by the imaging unit and imaged. The measurement light beam, the processing light beam and the illumination light beam form a coaxial light beam through the low-pass dichroic mirror, and are focused on the same position on the sample surface through the long working distance achromatic laser processing objective, so as to realize coaxial in-situ measurement.

[0007] According to the preferred scheme of the application, the light paths of the measurement light beam and the illumination light beam both pass through the first mirror mounting station, and the reflected light paths of the measurement light beam and the reflected light paths of the illumination light beam both pass through the second mirror mounting station. When the microscopic imaging is performed, the first removable right-angle mirror is installed on the first mirror installation station, and the second removable right-angle mirror is not installed on the second mirror installation station, at this time, the illumination light beam is reflected to the low-pass dichroic mirror through the first removable right-angle mirror, and the reflected light of the illumination light beam is directly transmitted to the imaging unit after the beam-splitting prism; When the confocal topography measurement is performed, the first removable right-angle mirror is not installed on the first mirror installation station, and the second removable right-angle mirror is installed on the second mirror installation station, at this time, the measurement light beam output by the measurement light beam generating unit is directly incident to the low-pass dichroic mirror, and the reflected light of the measurement light beam is reflected to the photoelectric detection unit through the second removable right-angle mirror after being transmitted through the beam-splitting prism.

[0008] The first removable right-angle mirror and the second removable right-angle mirror are used to realize the rapid and repeatable adjustment of the optical path structure.

[0009] According to the preferred scheme of the present application, the sample is installed and fixed on the combined three-axis precision displacement table, and the combined three-axis precision displacement table comprises a piezoelectric displacement table, a leveling device and a three-axis electric displacement table. The piezoelectric displacement table is fixed on the leveling device, and the leveling device is installed on the three-axis electric displacement table. The piezoelectric displacement table is used for Z-axis nanometer positioning, the leveling device is used for ensuring the horizontal surface of the sample, and the three-axis electric displacement table is used for micron-level positioning of the sample in the space X, Y and Z axes.

[0010] According to the preferred scheme of the present application, the system further comprises a host computer, the host computer controls the combined three-axis precision displacement table to perform sample positioning and topography measurement, the host computer acquires the signal of the photoelectric detection unit, and the in-situ topography measurement result is obtained after processing; the image data of the imaging unit is acquired, and the microscopic imaging of the sample surface is performed; during the processing, the illumination light beam is used for illuminating the processing area for microscopic imaging, and the processing light beam is used for scanning processing; after the scanning processing is completed, the in-situ topography measurement is performed by using the measurement light beam; the scanning processing and in-situ measurement process are repeated, and finally the expected topography requirement is achieved, and the processing is completed.

[0011] The present application also provides an in-situ topography measurement method based on the foregoing system, which is a single-point height measurement method based on piezoelectric scanning, and specifically comprises the following steps: Step 1: the piezoelectric displacement table is leveled by using the leveling device to eliminate the height measurement error caused by inclination; Step 2: coarse adjustment is realized through the Z-axis of the three-axis electric displacement table, and axial fine adjustment is realized through the piezoelectric displacement table, so that the focal plane and the measurement position reference are coincided; Step 3: move the sample to the point to be measured in the horizontal plane, and the piezoelectric displacement table starts high-speed scanning in the Z axis, the motion track of the piezoelectric displacement table is an axisymmetric wave track; for example, it can be a common axisymmetric wave track such as a triangular wave, a sine wave, etc.; the data processing and filtering method used can be low-pass filtering, smoothing filtering, etc., the purpose is to reduce the data size, and at the same time reduce the signal interference on peak extraction caused by light intensity fluctuation; Step 4: record the photodetector light intensity signal synchronously during the scanning process, and after the scanning is completed, perform data processing and filtering operation on the light intensity change curve, extract two light intensity peaks of the light intensity change curve and obtain the time corresponding to the peak points, and calculate the height difference of the current measurement point relative to the position reference by using the time interval corresponding to the two peak points; Step 5: use the three-axis electric displacement table to move the sample to different measurement points in the horizontal plane to repeat the foregoing single-point height measurement.

[0012] The application also provides an in-situ topography measurement method based on the foregoing system, which is a focus tomography-based measurement method, and specifically includes the following steps: Step 1: use the leveling device to level the piezoelectric displacement table to eliminate the height measurement error caused by inclination; Step 2: realize coarse adjustment through the Z axis of the electric displacement table, and realize fine adjustment through the piezoelectric displacement table, 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 according to the maximum height difference of the sample topography to be measured, and set the measurement range of the lateral scanning; Step 4: change the axial position of the piezoelectric displacement table, and scan layer by layer at the set step interval, perform lateral scanning measurement at each axial position once, and record the corresponding light intensity signal; the lateral scanning is one-dimensional line scanning or two-dimensional surface scanning; Step 5: store the light intensity signal data obtained by each layer scanning to form a light intensity data set matrix, and each column in the matrix corresponds to the light intensity change data of a certain lateral 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 data set matrix to determine the axial position corresponding to the light intensity peak of each measurement point, and the difference between the axial position and the starting position of the measurement is the relative height data of the measurement point; the data fitting method can adopt a polynomial fitting, a Gaussian fitting, etc.; Step 7: traverse all the lateral scanning measurement points to obtain the height data respectively, and reconstruct the three-dimensional topography information of the sample surface.

[0013] Compared with the prior art, the application has the beneficial effects that: (I) Realize the rapid switching of processing, measurement, imaging and other functions, and significantly improve the integration and operation efficiency of the ultrafast laser processing system The application provides a coaxial laser confocal processing and measurement integrated system, which mainly comprises a laser confocal topography measurement module, an ultrafast laser scanning processing module and a CCD microscopic imaging module, and realizes confocal in-situ topography measurement, ultrafast laser scanning processing and processing area microscopic image monitoring.

[0014] (II) Realize high-precision in-situ topography measurement, and avoid measurement errors caused by conversion of measurement coordinate system and processing coordinate system and secondary clamping errors of the workpiece By constructing the coaxial light path structure of the processing beam and the measurement beam, the spatial consistency of the measurement coordinate system and the processing coordinate system is ensured. The design enables the topography measurement and the laser processing to be completed under the same coordinate reference, without the need for disassembly or repositioning of the workpiece, thereby significantly reducing the cumulative error caused by secondary clamping, coordinate system conversion and the like. The single-point height measurement and scanning measurement based on the laser confocal principle are suitable for different measurement requirements, have strong flexibility and adaptability, can be used for topography measurement of curved surface structures and rough surfaces, and the measurement accuracy and resolution can reach submicrons; both the foregoing two measurement methods can directly measure without prior calibration, further simplifying the in-situ measurement process.

[0015] (III) Realize topography monitoring of the laser processing process, facilitate timely adjustment of the processing strategy, and be beneficial to improving the processing precision and accuracy The confocal in-situ scanning topography measurement method can intuitively monitor the material removal during the processing process and the topography change of the material surface before and after the laser processing, thereby improving the processing position precision and the structure consistency, and providing an important guarantee for improving the ultrafast laser processing precision and quality. DETAILED DESCRIPTION

[0016] Figure 1 is a general light path schematic diagram of the coaxial laser confocal processing and measurement integrated system provided by the embodiment of the application.

[0017] Figure 2 is a light path schematic diagram of the laser confocal topography measurement module.

[0018] Figure 3 is a light path schematic diagram of the CCD microscopic imaging module.

[0019] Figure 4 is a light path schematic diagram of the ultrafast laser scanning processing module.

[0020] Figure 5 is a physical assembly diagram of a coaxial laser confocal machining and measurement integrated system provided by an embodiment of the present application.

[0021] Figure 6 is a working principle schematic diagram of a single-point height measurement method based on piezoelectric scanning provided by an embodiment of the present application.

[0022] Figure 7 is a working principle schematic diagram of a measurement method based on focus tomography provided by an embodiment of the present application.

[0023] Figure 8 is a working flowchart of a single-point height measurement method based on piezoelectric scanning provided by an embodiment of the present application.

[0024] Figure 9 is a working flowchart of a measurement method based on focus tomography provided by an embodiment of the present application.

[0025] Figure 10 is a confocal axial response curve provided by an embodiment of the present application.

[0026] Figure 11 is a light intensity variation curve diagram provided by an embodiment of the present application: (a) a light intensity variation curve at different positions in single-point height measurement; (b) a single-point light intensity distribution curve and a Gaussian fitting result thereof in the measurement method based on focus tomography.

[0027] Figure 12 is an in-situ topography measurement result provided by an embodiment of the present application: (a) a single-point height measurement result of a step structure; (b) a single-sinusoidal surface structure topography measurement result based on the measurement method of focus tomography.

[0028] In the figure: 001A-first detachable right-angle reflector, 001B-second detachable right-angle reflector, 002-beam splitter prism, 003-beam expander, 004-low-pass dichroic mirror, 005-long working distance achromatic laser processing objective, 006-combined three-axis precision displacement stage, 006A-piezoelectric displacement stage, 006B-leveling device, 006C-three-axis electric displacement stage, 101-continuous laser light source, 102-beam collimation module, 102A-five-dimensional fiber coupler, 103-space filtering module, 103A-first lens, 103B-space filtering aperture, 103C-second lens, 104-low-pass filter, 105-infinite correction objective, 106-aperture, 107-photoelectric detector, 201-LED white light source, 202-reflector, 203-lens barrel, 204-CCD camera, 301-ultrafast laser light source, 302-beam expander, 303-laser reflector, 304-X-Y two-dimensional galvanometer system, 305-4f system, 305A-4f system first lens, 305B-4f system second lens, 401-breadboard, 402-mounting support, 501-piezoelectric displacement stage motion trajectory, 502A-light intensity change curve when the surface of the measured sample is lower than the position reference, 502B-light intensity change curve when the surface of the measured sample is higher than the position reference, 601A-measurement starting point confocal axial response curve, 601B-single-point light intensity distribution curve, 601C-single-point light intensity signal. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with specific examples.

[0030] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present application should be understood as the common meanings understood by those skilled in the art to which the present application belongs. The terms "first", "second" and similar terms used in the present application do not represent any order, number or importance, but are only used to distinguish different components.

[0031] Embodiment: As Figure 1 shown is a coaxial laser confocal processing and measuring integrated system of the present application, which mainly comprises a laser confocal topography measuring 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 005 and a combined three-axis precision displacement stage 006. Among them, the combined three-axis 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 can reflect the processing light beam and transmit the measuring light beam and the illumination light beam.

[0032] The laser confocal topography measurement module of the embodiment comprises a measurement beam generating unit and a photoelectric detection unit, wherein the measurement beam generating unit generates a measurement beam, the measurement beam is focused on the sample surface through a long working distance achromatic laser processing objective 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 a low-pass dichroic mirror 004 into a long working distance achromatic laser processing objective 005 and is finally focused on the sample surface for scanning processing. The CCD microscopic imaging module comprises an illumination beam generating unit and an imaging unit, the illumination beam generating unit generates an illumination beam, the illumination beam is focused on the sample surface through a long working distance achromatic laser processing objective 005 to realize illumination of the processing position; and the reflected light carrying the image information of the sample surface is received by the imaging unit and imaged. The measurement beam, the processing beam and the illumination beam pass through the low-pass dichroic mirror to form coaxial beams, and are focused on the same position on the sample surface through the long working distance achromatic laser processing objective, so that coaxial in-situ measurement is realized.

[0033] As shown in Figure 1 the light paths of the measurement beam and the illumination beam both pass through the first mirror mounting station, and the reflected light path of the measurement beam and the reflected light path of the illumination beam both pass through the second mirror mounting station; when microscopic imaging is performed, the first detachable right-angle mirror 001A is mounted on the first mirror mounting station, and the second detachable right-angle mirror 001B is not mounted on the second mirror mounting station; at this time, the illumination beam is reflected to the low-pass dichroic mirror 004 through the first detachable right-angle mirror 001A; the reflected light of the illumination beam is transmitted through the beam splitting prism 002 and directly enters the imaging unit; When confocal topography measurement is performed, the first detachable right-angle mirror 001A is not mounted on the first mirror mounting station, and the second detachable right-angle mirror 001B is mounted on the second mirror mounting station; at this time, the measurement beam output by the measurement beam generating unit is directly incident to the low-pass dichroic mirror 004, and the reflected light of the measurement beam is transmitted through the beam splitting prism 002 and reflected through the second detachable right-angle mirror 001B to enter the photoelectric detection unit.

[0034] The first detachable right-angle mirror and the second detachable right-angle mirror are used to realize rapid and repeatable adjustment of the light path structure.

[0035] In the embodiment of the application, the sample is fixed on the piezoelectric displacement table 006A in the combined three-axis precision displacement table 006.

[0036] As shown in Figure 2The optical path structure of the laser confocal topography measurement module in the aforementioned coaxial laser confocal machining and measurement integrated system is shown. When the confocal topography measurement is carried out, the first detachable right-angle mirror 001A is in the detached state, and the second detachable right-angle mirror 001B is in the mounted state. In this example, the measurement beam is generated by a continuous laser light source 101, and the wavelength is 532 nm. The measurement beam is transmitted to the beam collimation module 102 through a single-mode optical fiber, and is output to the free space after collimation through a five-dimensional optical fiber coupler 102A. Further, the aforementioned measurement beam passes through the spatial filtering module 103, which is composed of a first lens 103A with a focal length of f1, a second lens 103C with a focal length of f2, and a spatial filtering aperture 103B. The lens group composed of the first lens 103A and the second lens 103C has a beam expanding function for the measurement beam, and the beam expanding ratio is f2 / f1; the spatial filtering aperture 103B is equivalent to a low-pass filter, which can eliminate high-frequency noise in the measurement beam and improve the beam quality. Further, the measurement beam is transmitted through the low-pass dichroic mirror 004 after being partially reflected by the beam splitting prism 002, and is finally focused on the sample surface by the long working distance achromatic laser machining objective 005. The measurement beam transmitted at the beam splitting prism 002 is absorbed by the beam scatterer 003.

[0037] Further, the measurement beam reflected by the sample surface is reflected by the second detachable right-angle mirror 001B after being transmitted by the long working distance achromatic laser machining objective 005, the low-pass dichroic mirror 004, and the beam splitting prism 002, passes through the low-pass filter 104, only the wavelength range corresponding to the measurement beam is reserved, and then the reflected light is focused by the infinite correction objective 105. The light 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 the reflected stray light signal, thereby improving the resolution of the system for detecting axial displacement. The confocal axial response curve of the aforementioned laser confocal topography measurement module is shown in Figure 10 In this example, the long working distance achromatic laser machining objective 005 with a numerical aperture of 0.42 and the aperture 106 with an aperture of 10 μm are used, and the full peak half width (FWHM) of the confocal axial response curve is about 7 μm.

[0038] As Figure 3The light path structure of the CCD microscopic imaging module in the aforementioned coaxial laser confocal machining and measurement integrated system is shown. When the CCD microscopic imaging monitoring is carried out, the first detachable right-angle mirror 001A is in the installed state; and the second detachable right-angle mirror 001B is in the removed state. The illumination light beam is emitted by the LED white light source 201, and there is a collimating lens in the LED white light source 201 for collimating the aforementioned illumination light beam into parallel light. Further, the aforementioned illumination light beam is reflected and then transmitted through the low-pass dichroic mirror 004 after being continuously reflected by the mirror 202, the first detachable right-angle mirror 001A and the beam splitter prism 002, and finally focused on the sample surface by the long working distance achromatic laser machining objective 005, so as to realize the white light illumination of the machining position; the coaxiality of the illumination light beam and the machining light beam can be ensured by adjusting the position and pitch of the mirror 202.

[0039] Further, the aforementioned illumination light beam reflected by the sample surface carries the image information of the laser machining position, is focused by the lens barrel 203 after being transmitted through the long working distance achromatic laser machining objective 005, the low-pass dichroic mirror 004 and the beam splitter prism 002, and finally imaged on the CCD camera 204, so as to realize the collection of the microscopic image of the machining position. In the present example, the long working distance achromatic laser machining objective 005 used has a magnification of 50 times, so that the microscopic image of the machining area with a magnification of 50 times can be obtained, which can be used for monitoring the accumulation of debris, the ablation and the like of the machining position.

[0040] As shown in FIG. 6, the laser machining system is composed of a laser machining device 100, a coaxial laser confocal machining and measurement integrated system 200 and a computer 300. The coaxial laser confocal machining and measurement integrated system 200 is connected to the laser machining device 100 and the computer 300. Figure 4The optical path structure of the ultrafast laser scanning machining module in the aforementioned coaxial laser confocal machining and measuring integrated system is shown. The machining beam is generated by an ultrafast laser source 301. In this example, the femtosecond pulse width of the ultrafast laser source 301 used is 400 fs, the wavelength is 1040 nm, and the maximum laser average power is 8 w. The low-pass dichroic mirror 004 used in this example has a transmission cutoff wavelength of 685 nm, so it can reflect the machining beam and transmit the measuring beam and the illumination beam. The aforementioned machining beam is expanded by an expansion mirror 302 to obtain a suitable diameter, which on the one hand ensures that the beam energy can be fully utilized and uniformly covers the entrance pupil of the machining objective lens, thereby realizing high focusing energy density under high numerical aperture conditions; on the other hand, the collimated beam after expansion can effectively reduce the divergence angle, improve the focusing spot quality and machining stability, and provide a good beam quality basis for subsequent high-precision microstructure machining. Further, the machining beam is reflected by a laser reflecting mirror 303 and enters an X-Y two-dimensional galvanometer system 304. The X-Y two-dimensional galvanometer system 304 is composed of an X galvanometer and a Y galvanometer arranged along perpendicular directions. By controlling the deflection angle of the galvanometer, rapid and high-precision scanning of the machining beam on the sample surface is realized, thereby completing the machining trajectory control of any two-dimensional pattern or path. The high response speed and angle resolution of the galvanometer system ensure the accuracy of the position of the spot in the scanning process, and provide flexible path control capability for precise machining of complex micro-nano structures.

[0041] Further, the machining beam emitted by the aforementioned X-Y two-dimensional galvanometer system 304 is reflected by the low-pass dichroic mirror 004 after passing through the 4f system 305 and enters the long working distance achromatic laser machining objective lens 005, which is focused on the sample surface to realize precise scanning machining; wherein the 4f system 305 is composed of a 4f system first lens 305A and a 4f system second lens 305B with the same focal length, realizing the conjugate relationship between the reflecting surface of the X-Y two-dimensional galvanometer system 304 and the entrance pupil surface of the long working distance achromatic laser machining objective lens 005.

[0042] The physical assembly diagram (front view) of the aforementioned coaxial laser confocal machining and measuring integrated system is shown. Figure 5 The measuring beam of the aforementioned laser confocal topography measuring module is input through Port1 using a single-mode optical fiber, and the continuous laser source 101 is not drawn. Figure 5 The machining beam of the aforementioned ultrafast laser scanning machining module is input through Port2, and the X-Y two-dimensional galvanometer system 304 and its forward optical path structure and optical elements are not drawn.

[0043] Further, the aforementioned coaxial laser confocal machining and measurement integrated system is installed on the breadboard 401, and the breadboard 401 is fixed on the air floating optical platform through the mounting support 402, so that the coaxial laser confocal machining and measurement integrated system is vertically installed, and compared with horizontal installation, the sample leveling and fixing are more convenient in this method.

[0044] Further, the sample is installed on the piezoelectric displacement table 006A in the combined three-axis precision displacement table 006, the piezoelectric displacement table 006A can realize single-axis nanometer level axial positioning and scanning in the Z direction, in this example, the repeatability of the piezoelectric displacement table 006A is 1 nm, and the closed loop stroke is 100 μm; the piezoelectric displacement table 006A is installed on the leveling device 006B, the leveling device 006B can realize pitch adjustment in the X and Y directions, so that the sample surface is in a horizontal state, that is, perpendicular to the optical axis; the leveling device 006B is installed on the Z axis of the three-axis electric displacement table 006C, and the three-axis electric displacement table 006C can realize micron level precision positioning of the sample in three-dimensional space, in this example, the repeatability of each axis of the three-axis electric displacement table 006C is 0.2 μm, and the closed loop stroke is 20 mm.

[0045] It should be pointed out that in this example, the Z direction is parallel to the optical axis direction, so it is also called “axial direction”; the X and Y directions are parallel to the horizontal plane, so they are also called “lateral directions”; in the scope of the present application, in order to avoid ambiguity, the above two expressions are equivalent.

[0046] Figure 8 The working flow chart of the single-point height measurement method provided by the present application. 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 table 006A. Adjust the axial position, and use the three-axis electric displacement table 006C to combine coarse adjustment with fine adjustment of the piezoelectric displacement table 006A to move the surface of the sample to be measured to the position reference , and adjust the focal plane of the measurement beam to the position reference , that is, the light intensity signal of the photodetector is the strongest at this time.

[0047] Step 2: the three-axis electric displacement table 006C moves the sample in the horizontal plane to the position to be measured, and the piezoelectric displacement table 006A starts high-speed scanning in the Z axis. The motion track of the piezoelectric displacement table is a triangular wave, as shown in Figure 6 (a) of the figure, the position reference of the triangular wave motion is , the maximum displacement is , and the minimum displacement is , and one scan is one period of the triangular wave. In this example, the position reference of the triangular wave motion is , the maximum displacement is The minimum value is Therefore, the axial height measurement range is 60 μm.

[0048] Step 3: The light intensity signal of the photodetector 107 is recorded synchronously by the acquisition card during the scanning process. If the surface of the measured sample is lower than the position reference , the light intensity change curve obtained during the scanning process is shown by the dashed line in (b) of FIG. 5A, and the light intensity will have two peak values during the scanning process of the piezoelectric displacement stage from Figure 6 to to Figure 6 , and the corresponding times are ,

[0049] If the surface of the measured sample is higher than the position reference , the light intensity change curve obtained during the scanning process is shown by the solid line in (b) of FIG. 5A, and the light intensity will have two peak values during the scanning process of the piezoelectric displacement stage from Figure 6 to to , and the corresponding times are , Since the piezoelectric scanning speed is constant , by obtaining the time difference of the two light intensity peak values, the position of the piezoelectric displacement stage corresponding to the light intensity peak values can be calculated, and thus the relative height of the surface of the measured sample relative to the position reference can be obtained. For example, as shown by the dashed line in (b) of FIG. 5A, assuming that the corresponding times of the light intensity peak values Figure 6 are , , the time difference is , and the relative height of the surface of the sample to the position reference is . Figure 6

[0050] ​​​​​​​​Step 4: After the axial scanning is completed, the photoelectric detector light intensity signal is transmitted to the upper computer by the acquisition card, and the upper computer processes the light intensity change curve. First, mean filtering is performed to eliminate part of the periodic noise and reduce the data volume, so as to accelerate the operation speed; then, Gaussian filtering is used to smooth the data, so as to eliminate part of the false peak data caused by environmental disturbance and light intensity drift and the like, so as to improve the accuracy and stability of the subsequent peak extraction; finally, a peak extraction algorithm is used to extract two light intensity peak points, and the time corresponding to the peak points is obtained. The height value relative to the position reference is calculated by using the method as described in step 3; when two effective peaks cannot be extracted due to abnormal data, steps 2 to 4 are performed again. In this example, the movement speed of the piezoelectric displacement table 006A is set to 100 μm / s, the sampling frequency of the acquisition card is set to 20 kHz, and under the condition that the position reference is as described above, the light intensity change curve at the axial position of 55-75 μm is as shown in (a) of Figure 11 .

[0051] Further, the sample is moved to different measurement points in the horizontal plane by using the three-axis electric displacement table 006C to repeat the foregoing single-point height measurement. In this example, the X-axis of the electric displacement table 006C is moved to different measurement points to perform the foregoing single-point height measurement, and the interval between adjacent measurement points in the X direction is 100 μm. The morphology of the step structure sample is measured by using the foregoing method, and the single-point height measurement result of the step structure is as shown in (a) of Figure 12 . The test result shows that the axial resolution of the 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 automatic focusing and other application scenarios requiring high-precision positioning.

[0052] Figure 9 A workflow diagram of the measurement method based on focus tomography provided by the application. The foregoing measurement method based on focus tomography specifically includes the following steps: Step 1: First, use the leveling device 006B to level the piezoelectric displacement table 006A, so that the upper surface of the piezoelectric displacement table 006A is parallel to the X and Y axes of the three-axis electric displacement table 006C, to avoid introducing height measurement errors due to inclination. The Z-axis of the three-axis electric displacement table 006C is controlled for coarse adjustment, and then the piezoelectric displacement table 006A is used for fine adjustment, so that the focal plane of the measurement light beam is coincided with the axial measurement starting point , that is, the light intensity signal of the photoelectric detector is the strongest at this time.

[0053] Step 2: Determine the axial measurement range and measurement step interval. The axial measurement range is preliminarily estimated according to the maximum height difference of the actual measurement morphology, and the axial measurement starting point and 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 transfer 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... 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, The laser confocal topography measurement module, the ultrafast laser scanning processing module, the CCD microscopic imaging module, the beam splitting prism, the low-pass dichroic mirror, the long working distance achromatic laser processing objective and the combined three-axis precision displacement stage are arranged in the laser processing system. The combined three-axis precision displacement stage is used for fixing the sample and realizing the spatial three-dimensional motion control of the sample. The low-pass dichroic mirror can reflect the processing light beam and transmit the measurement light beam and the illumination light beam. The laser confocal topography measurement module comprises a measurement light beam generating unit and a photoelectric detection unit. The ultrafast laser scanning processing module generates a processing light beam. The CCD microscopic imaging module comprises an illumination light beam generating unit and an imaging unit. The measurement light beam, the processing light beam and the illumination light beam form coaxial light beams through the low-pass dichroic mirror, and are focused on the same position on the sample surface through the long working distance achromatic laser processing objective, so that coaxial in-situ measurement is realized.

2. The coaxial laser confocal machining and metrology integrated system of claim 1, wherein, The light paths of the measurement light beam and the illumination light beam pass through the first mirror mounting station, and the reflected light paths of the measurement light beam and the illumination light beam pass through the second mirror mounting station. When microscopic imaging is performed, the first detachable right-angle mirror is mounted on the first mirror mounting station, and the second detachable right-angle mirror is not mounted on the second mirror mounting station. When confocal topography measurement is performed, the first detachable right-angle mirror is not mounted on the first mirror mounting station, and the second detachable right-angle mirror is mounted on the second mirror mounting station. The first detachable right-angle mirror and the second detachable right-angle mirror are used to realize rapid and repeatable adjustment of the light path structure.

3. The coaxial laser confocal machining and metrology integrated system of claim 1, wherein, The measurement light beam generating unit comprises a continuous laser light source, a beam collimation module and a spatial filtering module. The continuous laser light source generates an initial measurement light beam, which is transmitted to the beam collimation module through a single-mode optical fiber for collimation, and then filtered through the spatial filtering module. The spatial filtering module outputs the measurement light beam. The reflected measuring beam of the sample surface passes through a low-pass filter to eliminate stray light, and is then focused by an infinite correction objective, and the reflected beam passing through the aperture is detected by a photodetector; the aperture in front of the detector is used to filter the reflected stray light signal, thereby improving the resolution of the system in detecting axial displacement.

4. The coaxial laser confocal machining and metrology integrated system of claim 1, wherein, The ultrafast laser scanning processing module comprises an ultrafast laser source, a beam expander, a laser reflector, an X-Y two-dimensional galvanometer system and a 4f system; the ultrafast laser source generates an initial processing beam, the initial processing beam is expanded by the beam expander and reflected by the laser reflector, then the deflection of the beam is controlled by the X-Y two-dimensional galvanometer system, and then the processing beam is reflected by the low-pass dichroic mirror into the long working distance achromatic laser processing objective after passing through the 4f system, and finally focused on the sample surface; the 4f system is used to optically conjugate the reflecting surface of the X-Y two-dimensional galvanometer system to the entrance pupil surface of the long working distance achromatic laser processing objective.

5. The coaxial laser confocal machining and metrology integrated system of claim 1, wherein, The illumination beam generating unit comprises an LED white light source and a reflector; the imaging unit comprises a lens barrel and a CCD camera; the LED white light source emits an initial illumination beam, which is reflected by the reflector and the first detachable right-angle reflector to the beam splitter prism after collimation by the lens; the reflected light of the illumination beam transmitted by 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 metrology integrated system of claim 1, wherein, The sample is installed and fixed on the combined three-axis precision displacement stage, which comprises a piezoelectric displacement stage, a leveling device and a three-axis electric displacement stage, wherein the piezoelectric displacement stage is fixed on the leveling device, and the leveling device is installed on the three-axis electric displacement stage; the piezoelectric displacement stage is used for Z-axis nanometer positioning, the leveling device is used to ensure the horizontal surface of the sample, and the three-axis electric displacement stage is used for micron-level positioning of the sample in the space X, Y and Z axes.

7. The coaxial laser confocal machining and metrology integrated system of claim 6, wherein, The system further comprises a host computer, which controls the combined three-axis precision displacement stage to perform sample positioning and topography measurement, acquires the photodetection unit signal, and obtains the in-situ topography measurement result after processing; acquires the image data of the imaging unit to perform microscopic imaging of the sample surface; during the processing, the illumination beam is used to illuminate the processing area for microscopic imaging, and the processing beam is used for scanning processing at the same time; after the scanning processing is completed, the in-situ topography measurement is performed using the measuring beam; the scanning processing and in-situ measurement process are repeated until the desired topography requirement is met, and the processing is completed.

8. A method for measuring the topography of a site based on the system of claim 7, characterized by The method is a single-point height measurement method based on piezoelectric scanning, which specifically comprises the following steps: Step 1: use the leveling device to level the piezoelectric displacement stage to eliminate the height measurement error caused by inclination; Step 2: realize coarse adjustment through the Z-axis of the three-axis electric displacement stage, and realize fine adjustment through 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 start high-speed scanning of the Z-axis of the piezoelectric displacement stage, and the motion trajectory of the piezoelectric displacement stage is an axisymmetric wave trajectory; Step 4: Synchronize the recording of the photodetector light intensity signal during the scanning process, and after the scanning is completed, perform data processing and filtering operations on the light intensity change curve, extract the two light intensity peaks of the light intensity change curve and obtain the time corresponding to the peak points, and calculate the height difference of the current measurement point relative to the position reference 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 to repeat the single-point height measurement described above.

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

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