A confocal micro-raman spectroscopy optical defect detection system

Abstract

The application discloses a confocal microscopic Raman spectrum optical defect detection system and relates to the technical field of Raman spectrum analysis. Two filtering methods are used. One is to control the micro area scanning position of the system by using the microscopic confocal technology and filter out the scattered light signals of non-focal areas. The other is to filter out the strong reflected light and background stray light by using the property of Raman scattering light frequency change. Finally, the Raman spectrum change conditions of different positions of the sample are analyzed, and the surface defects are indirectly characterized. The scanning galvanometer is used to control the light beam, the speed is high, the control precision is high, and the problem of rapid detection of large-aperture optical elements is solved.

Description

Technical Field

[0001] This invention belongs to the field of optical components and relates to Raman spectroscopy analysis technology, specifically a confocal micro Raman spectroscopy optical defect detection system. Background Technology

[0002] In optical fields such as space optics, inertial confinement fusion, micro-optics, extreme ultraviolet lithography, and very large-scale integrated circuits, there is a widespread demand for ultra-smooth optical components with high surface quality. Defects such as morphological errors, roughness, scratches, and pitting in optical components can cause scattering, energy absorption, harmful flares, diffraction patterns, film damage, and laser damage, directly affecting the performance and normal operation of the entire optical system.

[0003] Research on defect detection technology for precision optical components such as optical crystals in the field of optical inspection started relatively early. For high-precision detection of optical components with localized micro-defects, researchers have successively developed a series of physical detection and evaluation methods: light scattering-based detection techniques, including dark-field microscopy and scanning imaging based on sample scattering characteristics. Currently, the most commonly used method for scanning surface defects of optical components in industry is dark-field scattering microscopy. This method uses the scattering image generated by the scattering of incident light by the defect under dark-field conditions to invert the defect contour. However, dark-field imaging under white light sources is difficult to perform quantitative analysis of defect morphology types, and this method is greatly affected by environmental illumination and imaging system settings, resulting in limited accuracy in defect contour inversion.

[0004] Therefore, a confocal micro Raman spectroscopy optical defect detection system is proposed. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a method for detecting defects in optical components based on micro-Raman spectroscopy. This confocal micro-Raman spectroscopy optical defect detection system innovatively employs confocal micro-Raman spectroscopy analysis combined with a scanning galvanometer to rapidly and accurately detect and identify micro-defects on the surface and inside of lasers and nonlinear optical crystals, thereby extending to precision optical components and large-aperture optical devices. This solves the problem of how to systematically analyze the types, distribution, and formation mechanisms of defects in optical components.

[0006] To achieve the above objectives, according to an embodiment of the first aspect of the present invention, a confocal micro-Raman spectroscopy optical defect detection system is provided, comprising a light source 1, a filter 2, a scanning galvanometer module 3, a scanning galvanometer mirror group 4, a first beam splitter 5, a second beam splitter 6, a microscope objective lens group 7, an optical element under test 8, a three-dimensional motion control platform 9, a lens group 10, a slit 11, a Raman spectrometer 12, a two-dimensional photoelectric sensor 13, a data processing and analysis module 14, and a controller module 15;

[0007] The Raman spectrometer 12 and the two-dimensional photoelectric sensor 13 acquire data, and the data processing and analysis module processes the acquired data, including the following steps:

[0008] Step S1: Turn on the light source to allow incident light to enter the two-dimensional photoelectric sensor 13;

[0009] Step S2: Establish the mapping relationship between the measured optical element 8 and the rectangular plane coordinates of the two-dimensional photoelectric sensor 13;

[0010] Step S3: The optical element 8 under test is moved into the image plane position of the microscope objective lens group 7;

[0011] Step S4: Control the two-dimensional photoelectric sensor 13 to acquire image data of the optical element under test 8 in real time; divide the optical element under test (8) into different fields of view;

[0012] Step S5: Move the optical element under test to the focal plane of the microscope lens group (7) for each field of view; the two-dimensional photoelectric sensor (13) collects dark field scattering image data under each field of view and sends it to the data processing and analysis module (14).

[0013] Step S6: The Raman spectrometer (12) collects Raman spectral data for each field of view and sends it to the data processing and analysis module (14).

[0014] Step S7: Obtain the dark field scattering image data and Raman spectrum data of the optical element under test 8 collected by the two-dimensional photoelectric sensor 13 under all fields of view, and send them all to the data processing and analysis module 14.

[0015] Step S8: The data processing and analysis module 14 analyzes the changes of each characteristic peak in the Raman spectral data under each field of view, and selects the wavenumber with the largest change for characteristic analysis;

[0016] Step S9: The data processing and analysis module 14 analyzes the Raman spectral data under each field of view based on the spatial coordinate position fed back by the three-dimensional motion control platform.

[0017] Step S10: The data processing and analysis module 14 analyzes the image data of several dark field scattering acquired by the two-dimensional photoelectric sensor 13 to achieve accurate two-dimensional stitching imaging;

[0018] Step S11: The data processing and analysis module 14 evaluates the surface defects of the optical element 8 under test by combining the results of dark field scattering data analysis and Raman spectroscopy data analysis.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] This invention is based on dual filtering: firstly, it utilizes microscopic confocal technology to control the micro-area scanning position of the system and filter out scattered light signals from out-of-focus areas; secondly, it utilizes the property of Raman scattering light frequency change to filter out strongly reflected light and background stray light. Finally, by analyzing the Raman spectral changes at different locations of the sample, surface defects can be indirectly characterized. This enables rapid detection of large-aperture optical components. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the present invention;

[0022] Figure 2 This is a schematic diagram of the motion trajectory of the controller module in this embodiment;

[0023] Figure 3 This is a schematic diagram of the Raman spectral data of this embodiment;

[0024] Figure 4 This is a flowchart of the optical component defect detection method of this embodiment. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] like Figure 1 As shown, a confocal micro-Raman spectroscopy optical defect detection system includes an optical defect detector and a data processing and analysis module 14;

[0027] The optical defect monitoring instrument includes a light source 1, a filter 2, a scanning galvanometer module 3, a scanning galvanometer mirror group 4, a first beam splitter 5, a second beam splitter 6, a microscope objective lens group 7, an optical element under test 8, a three-dimensional motion control platform 9, a lens group 10, a slit 11, a Raman spectrometer 12, a two-dimensional photoelectric sensor 13, and a controller module 15.

[0028] The scanning galvanometer assembly 4 consists of two rotating mirrors and is connected to the controller module 15. The rotation angle of the two rotating mirrors can be controlled by the controller module 15, thereby controlling the propagation angle of the laser beam.

[0029] The microscope objective lens group 7 can achieve detection of different micro-area scales by changing the magnification of the microscope objective lens;

[0030] The microscope objective lens group 7 can analyze the photoelectric image data collected by the two-dimensional photoelectric sensor 13 in the data processing and analysis module 14 to determine whether the optical element under test 8 is located at the optimal focal plane position of the microscope objective lens group 7. If it is in a defocused state, the three-dimensional motion control platform 9 can be controlled to move up and down to ensure that the optical element under test 8 is located at the optimal focal plane of the microscope objective lens group 7.

[0031] The three-dimensional motion control platform 9 is a three-dimensional displacement stage used to place the optical element under test 8, move the optical element under test into the detection point position, and drive the optical element under test 8 to move stepwise along the x, y and z directions.

[0032] The lens group 10 is used to adjust the beam that will enter the Raman spectrometer 12 after being split by the second beam splitter 6, and to adjust the position and width of the slit 11 in conjunction with the adjustment of the position and width of the slit 11, so as to achieve a confocal effect with the laser source.

[0033] The slit 11 can be positioned and its width set to enable the acquisition of confocal micro Raman spectroscopy data.

[0034] The two-dimensional photoelectric sensor 13 is a camera, CCD, CMOS image sensor, or two-dimensional photoelectric detector array. Its detection surface receives two-dimensional optical image data of the optical element 8 under test and is connected to the data processing and analysis module 14.

[0035] The data processing and analysis module 14 is used to process, analyze and store the data collected by the Raman spectrometer 12 and the two-dimensional photoelectric sensor 13. The data processing and analysis module 14 can analyze the Raman spectral data collected by the Raman spectrometer 12 and use the optical data of characteristic peaks combined with the spatial position information fed back by the three-dimensional motion control platform 9 to perform stitching imaging.

[0036] The data processing and analysis module 14 is connected to the controller module 15, and the controller module 15 can adjust the working status parameters of the three-dimensional motion control platform 9, the microscope objective lens group 7 and the scanning galvanometer lens group 4 by setting parameters on the data processing and analysis module 14.

[0037] like Figure 4 As shown, a confocal micro-Raman spectroscopy optical defect detection system is disclosed for the detection process of the optical element 8 under test, including the following steps:

[0038] Step S1: Turn on the light source 1 to form an incident beam 101. After the incident beam 101 is incident on the scanning galvanometer assembly 4, the beam position can be adjusted by controlling the angle of the two rotating mirrors of the scanning galvanometer assembly 4. The incident beam 101 is incident on the optical element under test 8 after passing through the first beam splitter 5, the second beam splitter 6 and the microscope objective assembly 7. The microscope objective assembly is controlled by the controller module 15 to focus on the upper surface of the optical element under test 8. When the focused spot is located in the defect area of ​​the optical element under test 8, due to the light scattering phenomenon caused by the defect morphology, part of the scattered light enters the microscope objective assembly 7, and is split by the second beam splitter 6 and enters the Raman spectrometer 12 through the lens assembly 10 and the slit 11. The other part of the scattered light from the optical element under test 8 enters the two-dimensional photoelectric sensor 13 after passing through the first beam splitter 5.

[0039] Step S2: Calibrate the coordinates of the two-dimensional photoelectric sensor 13 and the optical element 8 under test, and establish the mapping relationship between the coordinates of the optical element 8 under test and the rectangular plane coordinates of the two-dimensional photoelectric sensor 13.

[0040] Step S3: Place the optical element under test 8 on the three-dimensional motion control platform 9. The controller module 15 controls the three-dimensional motion control platform 9 to drive the optical element under test 8 to move in steps along the x, y and z directions, so as to move the optical element under test 8 into the image plane position of the microscope objective lens group 7.

[0041] Step S4: The controller module 15 controls the three-dimensional motion control platform 9 to move along the path with a large step size. Figure 1 The Z-direction moves upward or downward as shown, and simultaneously controls the two-dimensional photoelectric sensor 13 to acquire image data of the optical element 8 under test in real time; the larger step size is determined based on actual experience and can be 10µm.

[0042] The data processing and analysis module 14 reads the image data of the optical element 8 under test collected by the two-dimensional photoelectric sensor 13, and determines whether the optical element 8 under test is at the optimal focal plane of the microscope objective lens group 7 by analyzing the image contrast change information. When it is determined that the optical element 8 under test is in a defocused state, the controller module 15 controls the three-dimensional motion control platform 9 to move up and down with a small step, and simultaneously controls the two-dimensional photoelectric sensor 13 to collect the image data of the optical element 8 under test in real time. The small step is determined based on actual experience and can be 2.2 μm.

[0043] When the data processing and analysis module 14 analyzes the image and determines that the measured optical element 8 is at the optimal focal plane of the microscope objective lens group 7, the three-dimensional motion control platform 9 stops moving up and down; the optimal contrast and the optimal focal plane are determined based on actual experience.

[0044] The optical element under test (8) is divided into different fields of view; such as Figure 2 As shown in A11, A12…;

[0045] Step S5: Controller module 15 controls the three-dimensional motion control platform 9 to translate along the x or y direction, as shown below. Figure 2 The A11 position of the optical element under test 8 shown is moved to the focal plane position of the microscope objective lens group 7; the two-dimensional photoelectric sensor 13 collects the dark field scattering image data Image_11 of the optical element under test 8 and sends it to the data processing and analysis module 14;

[0046] Step S6: Keeping the sample stage stationary, the controller module 15 controls the system to perform micro-area scanning. By adjusting the rotation of the two rotating mirrors of the scanning galvanometer group 4, the position of the laser spot on the optical element under test 8 is adjusted, so that the laser spot moves rapidly on the optical element under test 8 in an array of P×Q points. By synchronously triggering the Raman spectrometer 12 to collect data, rapid Raman spectral scanning in the micro-area is achieved, thereby obtaining P×Q Raman spectral data at A11. The data at each point are named Raman_A11_pq and sent to the data processing and analysis module 14; where p and q correspond to the spatial position information fed back by the three-dimensional motion control platform 9.

[0047] Step S7: After completing the micro-area scan at position A11, the controller module 15 controls the three-dimensional motion control platform 9 to move position A21 along the x-direction to the focal plane position of the microscope objective lens group 7, requiring that the field of view at position A21 and the field of view at position A11 maintain a 10% overlap in the x-direction; repeat steps S5 to S6, thereby achieving the desired effect. Figure 2 The motion trajectory shown obtains the dark field scattering image data Image_nm and the Raman spectrum data Raman_Anm_pq of the optical element under test 8 under n×m fields of view of the two-dimensional photoelectric sensor 13, and sends them all to the data processing and analysis module 14; it is required that the fields of view in the x and y directions retain 10% overlap area respectively;

[0048] Step S8: The data processing and analysis module 14 analyzes the Raman spectral data under any field of view (taking the A11 field of view as an example), and finds that when the detection point is located at the defective and defect-free points of the optical element 8 under test, the acquired Raman spectral data are different, such as... Figure 3As shown, when defects are present, light scattering occurs at the defect location, weakening the peak value of characteristic peaks at the same wavenumber position. (When the system's focused spot is located in the sample defect region, random scattering caused by the defect morphology alters the Raman scattered light signal received by the detection system within the same time frame, thus affecting the relative intensity of the Raman spectrum, especially the relative intensity of characteristic spectral peaks, such as...) Figure 3 In the diagram, 'a' represents the Raman intensity peak of the defect-free sample, and 'b' represents the Raman intensity peak of the defective sample. By analyzing the changes in each characteristic peak, such as... Figure 3 W_1, W_2, and W_3 in the equation represent different wavenumbers. The wavenumber W_i with the largest peak value variation is selected for feature analysis.

[0049] Step S9: The data processing and analysis module 14 uses the spatial coordinate position fed back by the three-dimensional motion control platform 9 as a reference to analyze the Raman spectrum data under the A11 field of view. The peak data of W_i wavenumber are spliced ​​together to obtain a P×Q distributed two-dimensional array. Each point on the two-dimensional array represents the light intensity value at the W_i wavenumber of the Raman spectrum.

[0050] Step S10: The data processing and analysis module 14 analyzes the n×m dark field scattering image data collected by the two-dimensional photoelectric sensor 13, and uses feature matching to perform sub-aperture stitching based on the edge changes of the dark field scattering image data, thereby reducing the stitching misalignment caused by the error of the three-dimensional motion control platform.

[0051] Step S11: The data processing and analysis module 14 evaluates the quality information such as surface defects of the tested optical element 8 by combining the results of dark field scattering data analysis and Raman spectroscopy data analysis, thereby determining the morphology, size and contour information of the defects.

[0052] The above embodiments are only used to illustrate the technical methods of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical methods of the present invention without departing from the spirit and scope of the technical methods of the present invention.

Claims

1. A confocal micro-Raman spectroscopic optical defect detection system, characterized by, The optical defect detector comprises: an optical defect detector and a data processing and analysis module (14); the optical defect detector is used to collect dark field scattering image data of the measured optical element (8) and Raman spectrum data of the measured optical element (8); the data processing and analysis module (14) selects the largest wave number with the largest change for feature analysis by analyzing the change of each characteristic peak in the Raman spectrum data; the data processing and analysis module (14) analyzes the Raman spectrum data under each field of view based on the spatial coordinate position feedback by the three-dimensional motion control platform; the data processing and analysis module (14) analyzes the collected dark field scattering image data to realize accurate two-dimensional splicing imaging; the data processing and analysis module (14) evaluates the surface defects of the measured optical element (8) by combining the analysis results of the dark field scattering data and the analysis results of the Raman spectrum data; the optical defect detector comprises a scanning galvanometer lens group (4), a second beam splitter (6), a lens group (10), a clamping gap (11), a Raman spectrometer (12) and a controller module (15); the scanning galvanometer lens group (4) is composed of two rotating lenses and is connected with the controller module (15), the rotation angle of the two rotating lenses is controlled by the controller module (15), and the propagation angle of the laser beam is controlled; the lens group (10) is used to adjust the light beam entering the Raman spectrometer (12) after being split by the second beam splitter (6), and cooperates with the adjustment of the position and width of the clamping gap (11); the data processing and analysis module (14) analyzes the photoelectric image data collected by the two-dimensional photoelectric sensor (13); judges whether the measured optical element (8) is located at the best focal plane position of the microscopic objective lens group (7); if it is out of focus, the three-dimensional motion control platform (9) is controlled to move up and down; the data processing and analysis module (14) is used for processing, analyzing and data storage of the data collected by the Raman spectrometer (12) and the two-dimensional photoelectric sensor (13); the data processing and analysis module (14) analyzes the Raman spectrum data collected by the Raman spectrometer (12), and splices imaging by using the photoelectric data of the characteristic peak and the spatial position information feedback by the three-dimensional motion control platform (9); wherein, the data processing and analysis module (14) is connected with the controller module (15), and the working state parameters of the three-dimensional motion control platform (9), the microscopic objective lens group (7) and the scanning galvanometer lens group (4) are adjusted by setting parameters on the data processing and analysis module (14) and through the controller module (15).

2. A confocal micro-Raman spectroscopy optical defect detection system according to claim 1, wherein The optical defect detector further comprises a light source (1), a filter (2), a scanning galvanometer module (3), a first beam splitter (5), a microscopic objective lens group (7), a measured optical element (8), a three-dimensional motion control platform (9) and a two-dimensional photoelectric sensor (13).

3. A confocal micro-Raman spectroscopy optical defect detection system according to claim 2, wherein The three-dimensional motion control platform (9) is used for placing the measured optical element (8) and moving the measured optical element into a detection point position, and is a three-dimensional displacement table for driving the measured optical element (8) to step along the x direction, the y direction and the z direction.

4. A confocal micro-Raman spectroscopy optical defect detection system according to claim 2, wherein The two-dimensional photoelectric sensor (13) is a camera, a CCD, a CMOS image sensor or a two-dimensional photoelectric detector array, receives two-dimensional optical image data of the measured optical element (8) on a detection surface, and is connected with the data processing and analysis module (14).

5. A confocal micro-Raman spectroscopic optical defect detection system according to claim 2, wherein The data processing and analysis module (14) evaluates the surface defects of the measured optical element (8) by the following steps: Step S1: turn on a light source to make incident light enter the two-dimensional photoelectric sensor (13); Step S2: establish a mapping relationship between the measured optical element (8) and a two-dimensional orthogonal plane coordinate of the two-dimensional photoelectric sensor (13); Step S3: move the measured optical element (8) into a position of an image plane of the microscopic objective lens group (7); Step S4: control the two-dimensional photoelectric sensor (13) to collect image data of the measured optical element (8) in real time, and divide the measured optical element (8) into different fields of view; Step S5: move the measured optical element to move each field of view to a focal plane position of the microscopic objective lens group (7), and the two-dimensional photoelectric sensor (13) collects dark field scattering image data under each field of view and sends the data to the data processing and analysis module (14); Step S6: the Raman spectrometer (12) collects Raman spectrum data of each field of view and sends the data to the data processing and analysis module (14); Step S7: the two-dimensional photoelectric sensor (13) collects dark field scattering image data of the measured optical element (8) under several fields of view and Raman spectrum data of the measured optical element (8), and sends the data to the data processing and analysis module (14); Step S8: the data processing and analysis module (14) selects a largest wave number for characteristic analysis by analyzing changes of each characteristic peak in the Raman spectrum data; Step S9: the data processing and analysis module (14) analyzes the Raman spectrum data under each field of view based on a space coordinate position fed back by the three-dimensional motion control platform; Step S10: the data processing and analysis module (14) analyzes several dark field scattering image data collected by the two-dimensional photoelectric sensor (13) to realize accurate two-dimensional splicing imaging; Step S11: the data processing and analysis module (14) evaluates the surface defects of the measured optical element (8) by combining results of dark field scattering data analysis and results of Raman spectrum data analysis.

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