Micro-area scanning imaging device and measuring method

Abstract

The invention discloses a micro-area scanning imaging device and a measuring method. The micro-area scanning imaging device comprises a laser, a double-axis scanning galvanometer SM, a cubic beam splitter CB and a microscope objective OB, wherein the double-axis scanning galvanometer SM gathers laser on a sample S. The cubic beam splitter CB splits signal light reflected after the laser irradiates the sample S to a sample signal detector SD; a plate-shaped beam splitter PB is also arranged between the cubic beam splitter CB and the sample signal detector SD, so that the signal light is further split to the laser detector PD; in the measurement process, a two-dimensional characteristic optical signal graph of the surface of a sample S is obtained based on a sample signal detector SD, then a blank substrate is placed in a to-be-measured area, a two-dimensional reflected light signal graph in the same area as the sample S on the substrate is obtained based on a laser detector PD, the two-dimensional characteristic optical signal graph is subjected to normalization processing based on the two-dimensional reflected light signal graph, and the normalized two-dimensional characteristic optical signal graph is obtained. And obtaining a normalized two-dimensional characteristic optical signal graph, and further drawing a two-dimensional space scanning graph of the physical properties of the sample S. The device and the method are suitable for signal acquisition of fluorescence spectrum, Raman spectrum, second harmonic and the like, and high-resolution imaging of various material microcells is realized by performing two-dimensional laser scanning on the surface of a sample.

Description

Technical Field

[0001] The invention relates to the field of optical measurement, and in particular to a micro-area scanning imaging device and a measuring method. Background Art

[0002] Microscopic optical technology can perform non-contact and non-destructive analysis of materials at the micrometer scale, and obtain multi-dimensional information such as material microstructure, physical properties and chemical composition through optical detection. Compared with traditional large-scale characterization methods, microscopic optics is particularly good at analyzing the spatial heterogeneity of tiny samples. For example, based on the scanning imaging function, the optical characteristic signals of two-dimensional materials (such as Raman spectroscopy, fluorescence and frequency-doubled light, etc.) are collected to obtain the spatial distribution information of the surface of two-dimensional materials, which is particularly critical in the characterization of inhomogeneous materials, local stress distribution analysis and nano-device performance research.

[0003] However, building a scanning imaging device and measurement solution with high stability, fast sampling capability and high data accuracy faces certain technical challenges. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a micro-area scanning imaging device and a measuring method for realizing high-resolution imaging of material micro-areas.

[0005] Technical solution: To achieve the above-mentioned purpose, a micro-area scanning imaging device described in the present invention includes a laser Laser, and a dual-axis scanning galvanometer SM and a microscope objective lens OB are sequentially arranged on the laser light path where the laser Laser emits the laser, and a cubic beam splitter CB is arranged between the dual-axis scanning galvanometer SM and the microscope objective lens OB, which is used to split the signal light reflected after the laser is irradiated to the sample S to the sample signal detector SD for signal collection, and a plate beam splitter PB is arranged on the signal light light path between the cubic beam splitter CB and the sample signal detector SD, which is used to further split the signal light to the laser detector PD for signal collection.

[0006] A reflector M1 is provided on the laser light path between the dual-axis scanning galvanometer mirror SM and the cubic beam splitter CB, for reflecting the laser light deflected by the dual-axis scanning galvanometer mirror SM to the cubic beam splitter CB.

[0007] Among them, a scanning lens SL and a sleeve lens TL are provided on the laser light path between the dual-axis scanning galvanometer SM and the cubic beam splitter CB, or on the laser light path between the dual-axis scanning galvanometer SM and the reflector M1, so as to collimate the laser beam deflected by the dual-axis scanning galvanometer SM, and ensure that the laser beam is vertically incident on the sample within the entire scanning range, providing uniform focusing.

[0008] The cubic beam splitter CB and the plate beam splitter PB are non-polarizing beam splitters, and the transmission and reflection splitting ratio is 10:90.

[0009] The sample signal detector SD is a spectrometer, a photomultiplier tube, etc., and the laser detector PD is a photoelectric detector.

[0010] A reflector I is added in the upstream optical path of the cubic beam splitter CB to introduce LED light into the laser optical path, and a reflector II is added in the downstream optical path of the cubic beam splitter CB to introduce signal light into the camera CM to capture the image of the sample S.

[0011] The dual-axis scanning galvanometer SM includes two reflection mirrors SM1 and SM2, and SM1 and SM2 are respectively driven by a driving device to deflect and are used to perform two-dimensional scanning on the surface of the sample S in the X-axis and Y-axis directions.

[0012] The present invention provides a measurement method based on the above-mentioned micro-area scanning imaging device, comprising the following steps:

[0013] S1. Place the substrate carrying the sample S in the area to be tested;

[0014] S2, start the laser Laser and adjust the microscope objective lens OB to focus the laser on the surface of the sample S, set the scanning angle range and angle step of the dual-axis scanning galvanometer SM on the X-axis and Y-axis, so that the laser beam scans the surface of the sample S point by point, and obtains a two-dimensional characteristic light signal diagram of the surface of the sample S based on the sample signal detector SD;

[0015] S3, placing a blank substrate in the area to be tested, repeating the laser scanning process in S2, and obtaining a two-dimensional reflected light signal map in the same area on the substrate as the surface of the sample S in S2 based on the laser detector PD;

[0016] S4, performing normalization processing on the two-dimensional characteristic light signal graph based on the two-dimensional reflected light signal graph to obtain a two-dimensional characteristic light signal graph after normalization processing;

[0017] S5. Based on the two-dimensional characteristic light signal image after normalization, analyze the sample physical property parameters corresponding to each pixel point, and draw a two-dimensional spatial scanning image of the physical properties of sample S.

[0018] The method for obtaining the normalized two-dimensional characteristic light signal image in S4 is:

[0019] First, the two-dimensional reflected light signal graph is normalized, that is, the maximum intensity value in the two-dimensional reflected light signal graph is found, and the intensity values ​​of all pixels in the two-dimensional reflected light signal graph are divided by the maximum intensity value to obtain the two-dimensional reflected light signal graph after normalization;

[0020] If the characteristic light signal is linearly related to the intensity of the incident light, such as fluorescence and Raman scattering, the intensity value of each pixel in the two-dimensional characteristic light signal map is divided by the intensity value at the corresponding position in the two-dimensional reflected light signal map after normalization to obtain the two-dimensional characteristic light signal map after normalization; if the characteristic light signal is squarely related to the intensity of the incident light, such as the second harmonic signal, the intensity value of each pixel in the two-dimensional characteristic light signal map is divided by the square value of the intensity at the corresponding position in the two-dimensional reflected light signal map after normalization to obtain the two-dimensional characteristic light signal map after normalization.

[0021] Among them, the method of drawing a two-dimensional spatial scanning diagram of the physical properties of sample S based on the two-dimensional characteristic light signal diagram after normalization in S5 is: analyzing the physical property information of sample S based on the two-dimensional characteristic light signal diagram after normalization, including molecular vibration, structure, symmetry, fluorescence properties, etc., to obtain the spatial distribution information of the physical property parameters of sample S.

[0022] Beneficial effects: The present invention has the following advantages: 1. The present invention can perform two-dimensional laser scanning on the sample surface to achieve high-resolution imaging of material micro-areas; 2. The present invention is suitable for signal acquisition such as fluorescence spectroscopy, Raman spectroscopy and second harmonics; 3. The present invention introduces a laser detector PD to normalize the signal light collected by the sample signal detector SD, thereby reducing the sample signal error caused by the change in incident light intensity brought by the scanning laser, so that the collected signal light more accurately reflects the actual optical properties of the sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the optical path structure of the device;

[0024] Figure 2 Based on Figure 1 Schematic diagram of the optical path structure in which a reflector is added to the device to realize image acquisition of sample S;

[0025] Figure 3 It is the imaging data after signal acquisition of reflected light intensity of MoS2 on silicon oxide / silicon substrate and normalization processing;

[0026] Figure 4 Collect imaging data for second harmonic signal intensity, fluorescence spectrum, and Raman spectrum of MoS2 on SiO2 / Si substrate. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is described in detail below in conjunction with the embodiments and drawings.

[0028] like Figure 1As shown, a micro-area scanning imaging device described in the present invention includes a laser Laser, a biaxial scanning galvanometer SM, a cubic beam splitter CB, a microscope objective lens OB, a plate-shaped beam splitter PB, a sample S, a laser detector PD, and a sample signal detector SD. The biaxial scanning galvanometer SM is located on the laser optical path where the laser beam emitted by the laser Laser is located, and performs angle deflection on the laser beam in the XY axis direction. The deflected laser beam is adjusted by the microscope objective lens OB and converges on the sample S. In order to further obtain the signal light (or scattered light, fluorescence, and frequency-doubled light, etc.) reflected after the laser beam is irradiated on the sample S, a cubic beam splitter CB is added on the optical path between the biaxial scanning galvanometer SM and the microscope objective lens OB, and a plate-shaped beam splitter PB is provided on the optical path of the signal light reflected by the cubic beam splitter CB, so as to further split the signal light to the laser detector PD and the sample signal detector SD for signal collection.

[0029] A reflector M1 can be further provided on the laser optical path between the dual-axis scanning galvanometer SM and the cubic beam splitter CB. The reflector M1 reflects the laser beam deflected by the dual-axis scanning galvanometer SM to the cubic beam splitter CB to ensure that the sample S is located on a horizontal plane while facilitating the installation of other components, thereby making the overall structure of the device more compact and improving the space utilization of the device.

[0030] A scanning lens SL and a sleeve lens TL can be further provided on the laser optical path between the dual-axis scanning galvanometer SM and the cubic beam splitter CB, or on the laser optical path between the dual-axis scanning galvanometer SM and the reflector M1, so as to collimate the laser beam deflected by the dual-axis scanning galvanometer SM, ensure that the laser beam is incident on the sample vertically within the entire scanning range, provide uniform focusing, and thus ensure high-quality scanning imaging on the sample.

[0031] In this embodiment, the laser is polarized light, and a 532-nanometer low-noise single longitudinal mode laser can be further used to achieve highly stable output, reduce changes in beam energy and power caused by laser mode drift and mode jump, and ensure the stability of the optical scanning imaging process. At the same time, it can also be switched to other different types of light sources, such as pulsed lasers to meet the optical test requirements of detecting second harmonic generation (i.e., doubled frequency light).

[0032] The cubic beam splitter CB and the plate beam splitter PB are non-polarizing beam splitters. In this embodiment, the cubic beam splitter CB can adopt a splitting ratio of 10:90 for transmitted light and reflected light. After the laser beam on the laser light path passes through the cubic beam splitter CB, 10% of the laser light converges to the sample S. After the signal light formed by the reflection of the surface of the sample S passes through the cubic beam splitter CB, 90% of the signal light is used for subsequent detector collection. The cubic beam splitter CB is composed of two prisms, which can reduce the deviation of the passing light beam, and the single reflecting surface can also avoid ghosting. The plate beam splitter PB can also adopt a splitting ratio of 10:90, wherein 10% of the signal light after splitting is captured by the laser detector PD, and the remaining 90% of the signal light is captured by the sample signal detector SD.

[0033] The sample signal detector SD can select spectrometers, photomultiplier tubes and other equipment based on the characteristics of the optical signal to be collected, so as to obtain the fine spatial distribution information of the surface of a specific sample material. The spectrometer has the characteristics of high sensitivity, high resolution and versatility, and can collect optical signals including Raman spectra, fluorescence spectra, and frequency-doubled light spectra, thereby realizing high-resolution scanning imaging of different optical signal spectra. The photomultiplier tube is used to collect the optical signal generated by the second harmonic. Unlike the frequency-doubled light spectrum collected by the spectrometer, the photomultiplier tube has extremely high sensitivity, high signal-to-noise ratio and ultra-fast time response, which can realize fast and high-quality frequency-doubled light signal scanning imaging.

[0034] In this embodiment, the laser detector PD is a photoelectric detector, which has the advantages of high sensitivity, low noise and low power consumption, and is used to efficiently capture the intensity change of the signal light. Its function is to normalize the signal collected by the sample signal detector SD to eliminate the influence of the change of the incident laser intensity caused by the angle deviation of the light beam entering the entrance pupil of the microscope objective OB, thereby reducing the error caused by the change of light intensity, so that the collected light signal more accurately reflects the actual optical properties of the sample.

[0035] like Figure 2 As shown, in this embodiment, a reflector I can be further provided in the upstream optical path of the cubic beam splitter CB to introduce LED light into the laser optical path, and a reflector II can be provided in the downstream optical path to introduce signal light into the camera CM, so as to realize image acquisition of the sample S, facilitate observation of the sample surface, and facilitate subsequent selection of a suitable optical scanning imaging area. When the laser detector PD and the sample signal detector SD are used to collect signal light in the future, the reflector I and the reflector II can be removed.

[0036] The microscope objective lens OB can be focused to converge the laser beam on a certain detection position on the surface of the sample S, so as to further detect the sample S, especially the detection of unevenness or microstructure. In this embodiment, the microscope objective lens OB can adopt a resolution of 40 times, and a high numerical aperture can ensure a high spot resolution. Therefore, a numerical aperture of 0.6 is adopted to achieve a high-resolution scanning of 1 micron, so as to obtain the physical property distribution information of the sample surface at the micron scale.

[0037] The dual-axis scanning galvanometer SM includes two reflectors SM1 and SM2, which are driven by the driving device to deflect respectively, so as to realize the scanning of the X-axis and Y-axis of the sample S. Among them, the driving device adopts a dynamic magnetic actuator as the rotor, and the dynamic magnetic actuator uses the torque generated by the energized coil in the magnetic field to drive the deflection of the rotor. Unlike ordinary rotating motors, a reset torque is applied to the rotor of the galvanometer, and the magnitude of this reset torque is proportional to the angle of the rotor's deviation from the equilibrium position. When a certain current is passed through the coil, the rotor will deflect until the electromagnetic torque is equal to the reset torque, at which time the rotor stops deflecting. This design enables the scanning galvanometer SM to achieve high-speed and high-precision scanning action, and detect the optical properties of the sample S surface at the micrometer scale. By setting the scanning angle range and angle step of the dual-axis scanning galvanometer SM in the X-axis and Y-axis and combining the focusing function of the microscope objective OB, two-dimensional scanning of the sample S surface can be achieved.

[0038] This embodiment provides a method for measuring reflected light intensity based on the above device, specifically:

[0039] (1) placing a substrate carrying a sample S in the test area;

[0040] (2) Start the laser Laser, set the scanning angle range and angle step of the dual-axis scanning galvanometer SM on the X-axis and Y-axis, adjust the microscope objective OB so that the laser beam converges on the surface of the sample S, move the laser beam to scan the surface of the sample S point by point, and use the sample signal detector SD to collect signal light to obtain a two-dimensional characteristic light signal map of the surface of the sample S;

[0041] (3) placing a blank substrate in the area to be tested, repeating the laser scanning process in step (2), and collecting reflected light using a laser detector PD, thereby obtaining a two-dimensional reflected light signal map in the same area on the substrate as the surface of the sample S in step (2);

[0042] (4) Based on the two-dimensional reflected light signal graph, the two-dimensional characteristic light signal graph is normalized, specifically:

[0043] First, the two-dimensional reflected light signal graph is normalized, that is, the maximum intensity value in the two-dimensional reflected light signal graph is found, and the intensity values ​​of all pixels in the two-dimensional reflected light signal graph are divided by the maximum intensity value to obtain the two-dimensional reflected light signal graph after normalization;

[0044] If the characteristic light signal is linearly related to the incident light intensity, such as fluorescence and Raman scattering, the intensity value of each pixel in the two-dimensional characteristic light signal map is divided by the intensity value at the corresponding position in the normalized two-dimensional reflected light signal map to obtain the normalized two-dimensional characteristic light signal map; if the characteristic light signal is squarely related to the incident light intensity, such as the second harmonic signal, the intensity value of each pixel in the two-dimensional characteristic light signal map is divided by the square value of the intensity at the corresponding position in the normalized two-dimensional reflected light signal map to obtain the normalized two-dimensional characteristic light signal map.

[0045] (5) Based on the normalized two-dimensional characteristic light signal image and the physical property information of sample S (such as molecular vibration, structure, symmetry, fluorescence, etc.) it carries, a two-dimensional spatial scan of the physical property parameters of sample S is drawn.

[0046] This device can achieve optical high-resolution imaging of micro-areas, and is compatible with various optical detection technologies including fluorescence spectroscopy, Raman spectroscopy, and second harmonic generation. For example, when the device is used to collect fluorescence spectra, Raman spectra, etc. in the above embodiment, the sample signal detector SD is a spectrometer, and a 532-nanometer excitation light source is used to obtain the luminescence properties and phonon vibration information of the sample. When the device is used to collect second harmonic generation signals, the sample signal detector SD can use a photomultiplier tube, and by using an 810-nanometer femtosecond pulse excitation light source, the symmetry and other information of the sample can be obtained. In the above optical detection technologies, the laser detectors PD are all photodetectors, which can provide normalized processing data.

[0047] Taking 300 nanometers of molybdenum disulfide on silicon oxide / silicon substrate as an example, the device and measurement method are used to realize spatial scanning imaging of the sample, wherein the laser wavelength of the laser is 532 nanometers or 810 nanometers. Figure 3 As shown, Figure 3 (a) is a white light image of the sample; Figure 3 (b) is a two-dimensional diagram of the intensity distribution of the reflected light signal directly collected by the laser detector PD in the sample area, in which there is an obvious distribution of reflected background intensity; Figure 3 (c) is a two-dimensional graph of the sample light signal intensity after normalization processing of the reflected light signal on a blank substrate. The results show that the reflected background intensity distribution is eliminated, and high-quality scanning imaging of the sample reflected light signal intensity is successfully achieved, demonstrating the reliability of the normalization processing.

[0048] The scanning imaging results of the characteristic light signal of MoS2 are as follows Figure 4As shown, Figure 4 (a) is a white light image of the sample, with the area with 1-4 layers of thickness marked; Figure 4 (b) is a two-dimensional graph of the normalized second harmonic generation signal intensity distribution collected by the photomultiplier tube. Second harmonic is a second-order nonlinear optical effect. An 810 nanometer femtosecond pulse laser light source is used here. For MoS2, odd-numbered layer samples have significant second harmonic signals due to the broken spatial inversion symmetry, while even-numbered layer samples almost do not generate second harmonic signals due to the spatial inversion symmetry. Thus, spatial resolution information such as the number of layers and symmetry of the sample can be obtained.

[0049] Figure 4 (c) is the normalized two-dimensional distribution diagram of fluorescence spectrum intensity collected by the spectrometer. Figure 4 (d) is the fluorescence spectrum of a specific position selected in the corresponding two-dimensional graph. Based on the fluorescence spectrum characteristics of MoS2, the more layers there are, the weaker the fluorescence signal is, so the number of sample layers can be further determined, and the spatial distribution of the number of sample layers and fluorescence properties can be obtained.

[0050] Figure 4 (e) is the normalized two-dimensional distribution diagram of Raman spectrum intensity collected by the spectrometer. Figure 4 (f) is a two-dimensional diagram showing the energy difference distribution of the two characteristic peaks of MoS2 Raman spectrum at 370-430 wavenumbers. Figure 4 (g) is the Raman spectrum of a specific position selected in the corresponding two-dimensional graph. It is known that MoS2 has two Raman active phonon characteristic peaks between 370-430 wavenumbers, and the integrated intensity and energy difference of these two characteristic peaks are layer-dependent. For each pixel position of the laser scan, the Raman signal intensity is integrated within the wavenumber range of 370-430, and the energy difference between the two characteristic peaks within this wavenumber range is analyzed, thereby obtaining the spatial distribution information of the sample Raman signal intensity and the Raman characteristic peak energy difference.

Claims

1. A micro-area scanning imaging device, comprising a laser, characterized in that: A dual-axis scanning galvanometer SM and a microscope objective lens OB are arranged in sequence on the laser optical path where the laser light is emitted from the laser. A cubic beam splitter CB is arranged between the dual-axis scanning galvanometer SM and the microscope objective lens OB, which is used to split the signal light reflected after the laser is irradiated to the sample S to the sample signal detector SD for signal collection. A plate beam splitter PB is arranged on the optical path where the signal light is located between the cubic beam splitter CB and the sample signal detector SD, which is used to further split the signal light to the laser detector PD for signal collection.

2. The micro-area scanning imaging device according to claim 1, characterized in that: A reflector M1 is provided on the laser light path between the biaxial scanning galvanometer SM and the cubic beam splitter CB, for reflecting the laser light deflected by the biaxial scanning galvanometer SM to the cubic beam splitter CB.

3. The micro-area scanning imaging device according to claim 1 or 2, characterized in that: A scanning lens SL and a sleeve lens TL are provided on the laser light path between the dual-axis scanning galvanometer SM and the cubic beam splitter CB, or on the laser light path between the dual-axis scanning galvanometer SM and the reflector M1, so as to collimate the laser beam deflected by the dual-axis scanning galvanometer SM and ensure that the laser beam is incident vertically on the sample within the entire scanning range, thereby providing uniform focusing.

4. The micro-area scanning imaging device according to claim 1, characterized in that: The cubic beam splitter CB and the plate beam splitter PB are non-polarizing beam splitters, and the transmission and reflection splitting ratio is 10:

90.

5. The micro-area scanning imaging device according to claim 1, characterized in that: The sample signal detector SD is a spectrometer and a photomultiplier tube, and the laser detector PD is a photodetector.

6. The micro-area scanning imaging device according to claim 1, characterized in that: A reflector I is added in the upstream optical path of the cubic beam splitter CB to introduce LED light into the laser optical path, and a reflector II is added in the downstream optical path of the cubic beam splitter CB to introduce signal light into the camera CM to capture the image of the sample S.

7. The micro-area scanning imaging device according to claim 1, characterized in that: The dual-axis scanning galvanometer SM includes two reflection mirrors SM1 and SM2. SM1 and SM2 are driven by a driving device to deflect and are used to perform two-dimensional scanning on the surface of the sample S in the X-axis and Y-axis directions.

8. A measurement method based on the micro-area scanning imaging device according to claim 1, characterized in that: The following steps are involved: S1. Place the substrate carrying the sample S in the area to be tested; S2, start the laser Laser and adjust the microscope objective lens OB to focus the laser on the surface of the sample S, set the scanning angle range and angle step of the dual-axis scanning galvanometer SM on the X-axis and Y-axis, so that the laser beam scans the surface of the sample S point by point, and obtains a two-dimensional characteristic light signal diagram of the surface of the sample S based on the sample signal detector SD; S3, placing a blank substrate in the area to be tested, repeating the laser scanning process in S2, and obtaining a two-dimensional reflected light signal map in the same area on the substrate as the surface of the sample S in S2 based on the laser detector PD; S4, performing normalization processing on the two-dimensional characteristic light signal graph based on the two-dimensional reflected light signal graph to obtain a two-dimensional characteristic light signal graph after normalization processing; S5. Based on the two-dimensional characteristic light signal image after normalization, analyze the sample physical property parameters corresponding to each pixel point, and draw a two-dimensional spatial scanning image of the physical properties of sample S.

9. The measuring method according to claim 8, characterized in that: The method for obtaining the normalized two-dimensional characteristic light signal image in S4 is: First, the two-dimensional reflected light signal graph is normalized, that is, the maximum intensity value in the two-dimensional reflected light signal graph is found, and the intensity values ​​of all pixels in the two-dimensional reflected light signal graph are divided by the maximum intensity value to obtain the two-dimensional reflected light signal graph after normalization; If the characteristic light signal is linearly related to the incident light intensity, such as fluorescence and Raman scattering, the intensity value of each pixel in the two-dimensional characteristic light signal image is divided by the intensity value at the corresponding position in the normalized two-dimensional reflected light signal image to obtain the normalized two-dimensional characteristic light signal image; If the characteristic light signal is in a square relationship with the incident light intensity, such as a second harmonic signal, the intensity value of each pixel in the two-dimensional characteristic light signal image is divided by the square value of the intensity at the corresponding position in the normalized two-dimensional reflected light signal image to obtain the normalized two-dimensional characteristic light signal image.

10. The measuring method according to claim 8, characterized in that: The method for drawing a two-dimensional spatial scanning diagram of the physical properties of sample S based on the two-dimensional characteristic light signal diagram after normalization in S5 is: analyzing the physical property information of sample S based on the two-dimensional characteristic light signal diagram after normalization, including molecular vibration, structure, symmetry, and fluorescence properties, to obtain the spatial distribution information of the physical property parameters of sample S.

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