A zoom microscopic surface reconstruction method based on coherent scanning interferometry system

Abstract

The present invention relates to a zoom microscopic surface reconstruction method based on a coherent scanning interference system, comprising the following steps: 1: obtaining a surface scanning interference three-dimensional signal; 2: performing a three-dimensional Fourier transform on the three-dimensional signal to obtain its three-dimensional spectrum; 3: extracting a zoom microscopic imaging signal spectrum from the three-dimensional spectrum; 4: performing a three-dimensional Fourier inverse transform on the zoom microscopic imaging signal spectrum to obtain a three-dimensional zoom microscopic image; 5: obtaining the surface morphology through a zoom microscopic surface reconstruction algorithm. The present invention utilizes the separability of the interference signal and the zoom microscopic imaging signal in the coherent scanning interference pattern in the three-dimensional spectrum to obtain the three-dimensional zoom microscopic signal in the coherent scanning interference imaging, and finally obtains the surface morphology through a zoom microscopic surface reconstruction algorithm, thereby improving the morphology measurement capability of the coherent scanning interferometer for extremely rough surfaces, large inclination angles and vertical surfaces.

Description

Technical Field

[0001] The present invention relates to the technical field of precision optical measurement engineering, and in particular to a zoom microscopic surface reconstruction method suitable for a coherent scanning interferometer. Background Art

[0002] With the development of high-end manufacturing fields such as optics, integrated circuits, aerospace, new energy vehicles, and medical devices, the requirements for the quality and manufacturing precision of high-end components are constantly increasing, components are constantly miniaturized, and functional surfaces are becoming increasingly complex. This has put higher demands on the detection capability and accuracy of product surface morphology. In order to achieve high-efficiency measurement and avoid surface damage, optical methods are usually used to measure surface morphology, mainly coherent scanning interferometers, confocal microscopes, and zoom microscopes. However, a single measurement method is usually difficult to meet the measurement needs of various functional surfaces, such as surfaces with different material compositions and complex geometric morphologies. When measuring extremely rough surfaces, the interference signal generated by the coherent scanning interferometer has a low signal-to-noise ratio, high fringe density, and poor contrast, which may lead to a significant reduction in measurement accuracy. Zoom microscopes rely on light intensity information (rather than phase information) for measurement, and they have higher robustness when measuring extremely rough surfaces and surfaces with large inclination angles. Therefore, combining these two measurement methods in a system can effectively improve the accuracy and robustness of measuring complex surfaces. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a zoom microscopic surface reconstruction method based on a coherent scanning interferometer. A set of coherent scanning interferometers is used to realize two surface measurement methods, coherent scanning and zoom microscopy, thereby improving the coherent scanning interferometer's ability to measure the topography of extremely rough surfaces, large inclination angles and vertical surfaces.

[0004] The technical solution adopted by the present invention to solve the technical problem is to provide a zoom microscopic surface reconstruction method based on a coherent scanning interferometer, the steps of which are as follows:

[0005] (1): A broad spectrum light source is used as the illumination light source for the coherent scanning interferometric imaging system.

[0006] (2): Use a scanning stage to scan the front focal plane of the objective lens along the optical axis across the surface to be measured. Each time the scanning stage moves, the camera captures an interference pattern and adds it to the image stack. After the scan is completed, the final three-dimensional interference signal is formed.

[0007] (3): Preprocess the three-dimensional interference signal obtained in step (2) to constrain the background light intensity distribution in the longitudinal direction (i.e., the optical axis direction) to avoid frequency aliasing;

[0008] (4): Performing a three-dimensional Fourier transform on the three-dimensional interference signal preprocessed in step (3) to obtain a three-dimensional interference signal spectrum;

[0009] (5) Separating the zoom microscopy imaging signal spectrum from the three-dimensional spectrum using the bandwidth of the three-dimensional transfer function of the zoom microscopy system obtained through simulation or experimental calibration;

[0010] (6) performing a three-dimensional inverse Fourier transform on the zoom microscopy imaging signal spectrum obtained in step (4) to obtain the zoom microscopy imaging signal during the scanning process;

[0011] (7) Obtain the surface morphology through zoom microscopic surface reconstruction algorithm.

[0012] The steps of separating the zoom microscopy imaging signal in step (4) are as follows:

[0013] (a) The three-dimensional transfer function of the zoom microscope system is simulated by the theoretical model, and its expression is:

[0014]

[0015] Where K is the spatial frequency vector, k0 is the wave number (i.e. 2π / λ, λ is the wavelength), S(k0) is the spectral power density,

[0016]

[0017] in is the three-dimensional pupil function of the optical imaging system limited by NA, δ() is the Dirac Delta function, h is the Heaviside step function, is the longitudinal unit vector, A N is the system numerical aperture.

[0018] (b) The bandwidth of the zoom microscopy signal is determined based on the three-dimensional transfer function calculated above. The three-dimensional spectrum of the three-dimensional interference signal is filtered so that only the spectrum components within the bandwidth are related to the zoom microscopy signal. The spectrum of the signal outside the bandwidth is zeroed. It can be expressed as follows:

[0019]

[0020] Wherein, O(K) is the three-dimensional spectrum of the zoom microscopic imaging signal, and I(K) is the three-dimensional spectrum of the obtained three-dimensional interference pattern. The steps of obtaining the surface morphology by the zoom microscopic surface reconstruction algorithm in step (6) are as follows:

[0021] (I) Calculating the focusing degree of the zoom microscopy imaging signal along the Z direction at each pixel point, the focusing degree is calculated by the focusing operator;

[0022] (II) Taking the amplitude calculated by the focusing operator as a function of height, the amplitude is fitted near the peak value to obtain the surface height corresponding to the peak value after fitting.

[0023] (III) Obtain the surface shape through pixel-by-pixel calculation results.

[0024] Compared with the prior art, the present invention has the following beneficial effects: the present invention utilizes the separability of the interference signal and the zoom microscopy imaging signal in the three-dimensional spectrum in the coherent scanning interferometer pattern to obtain the three-dimensional zoom microscopy signal in the coherent scanning interferometer imaging, thereby realizing the use of a set of coherent scanning interferometers to complete the two surface measurement methods of coherent scanning and zoom microscopy, and improving the coherent scanning interferometer's ability to measure the topography of extremely rough surfaces, large inclination angles, and vertical surfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 :Flowchart of the coherent scanning interferometer and zoom microscopy method of the present invention

[0026] Figure 2 : Central XZ cross-section of the collected three-dimensional interference signal

[0027] Figure 3 : Central XZ cross-section of the interference signal three-dimensional spectrum

[0028] Figure 4 : Central XZ cross-section of the separated zoom microscopy signal 3D spectrum

[0029] Figure 5 : Zoom microscopic image separated from coherent scanning interferometer image

[0030] Figure 6 : Surface morphology of the object under test obtained through zoom microscopy signal DETAILED DESCRIPTION

[0031] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0032] Example 1:

[0033] like Figure 1 The device and zoom microscopic surface reconstruction method based on a coherent scanning interferometer are shown. The coherent scanning interferometer device 1 includes an image acquisition CCD 3, a tube lens 4, a piezoelectric ceramic scanning stage 5, an interference objective lens 6, a test piece 7, and an illumination optical path 8. The piezoelectric ceramic scanning stage 5 can move along the optical axis. The zoom microscopic surface reconstruction method 2 includes the following steps:

[0034] (1): A wide spectrum light source 8 is used as the illumination light source of the coherent scanning interferometric imaging system 1 .

[0035] (2): Use the piezoelectric ceramic translation stage 5 to scan the front focal plane of the objective lens 6 along the optical axis across the surface to be measured 7. Each time the piezoelectric ceramic translation stage 5 moves, an interference pattern is collected and added to the image stack. After the scanning is completed, the final three-dimensional interference signal is formed. The central XZ cross-section of the collected three-dimensional interference signal is shown as follows: Figure 2 As shown;

[0036] (3): Preprocess the three-dimensional interference signal obtained in step (2) to constrain the background light intensity distribution in the longitudinal direction (i.e., the optical axis direction) to avoid frequency aliasing;

[0037] (4): Perform a three-dimensional Fourier transform on the three-dimensional interference signal preprocessed in step (3) to obtain a three-dimensional interference signal spectrum. The central XZ cross-section of the three-dimensional interference signal spectrum is as follows: Figure 3 As shown;

[0038] (4) Using the bandwidth of the three-dimensional transfer function of the zoom microscopy system obtained by simulation or experimental calibration, the zoom microscopy imaging signal spectrum is separated from the three-dimensional spectrum. The central XZ cross-section of the separated three-dimensional spectrum of the zoom microscopy signal is as follows: Figure 4 As shown;

[0039] (5) Performing a three-dimensional inverse Fourier transform on the zoom microscopy signal spectrum obtained in step (4) to obtain the zoom microscopy signal during the scanning process. The zoom microscopy image separated from the coherent scanning interference image is as follows: Figure 5 As shown;

[0040] (6) Obtain the surface morphology through zoom microscopic surface reconstruction algorithm. The surface morphology of the object to be tested obtained by zoom microscopic signal is as follows: Figure 6 shown.

[0041] The steps of separating the zoom microscopy imaging signal in step (4) are as follows:

[0042] (a) The three-dimensional transfer function of the zoom microscope system is simulated by the theoretical model, and its expression is:

[0043]

[0044] Where K is the spatial frequency vector, k0 is the wave number (i.e. 2π / λ, λ is the wavelength), S(k0) is the spectral power density,

[0045]

[0046] in is the three-dimensional pupil function of the optical imaging system limited by NA, δ() is the Dirac Delta function, h is the Heaviside step function, is the longitudinal unit vector, A N is the system numerical aperture.

[0047] (b) The bandwidth of the zoom microscopy imaging signal is determined based on the three-dimensional transfer function calculated above. The three-dimensional spectrum of the three-dimensional interference signal is filtered so that only the spectral components within the bandwidth are related to the zoom microscopy imaging signal. The spectrum of the signal outside the bandwidth is zeroed. This can be expressed by the following formula:

[0048]

[0049] Wherein, O(K) is the three-dimensional spectrum of the zoom microscopic imaging signal, and I(K) is the three-dimensional spectrum of the obtained three-dimensional interference pattern. The steps of obtaining the surface morphology by the zoom microscopic surface reconstruction algorithm in step (6) are as follows:

[0050] (I) Calculate the focusing degree of the zoom microscopy imaging signal along the Z direction at each pixel point using the Laplace operator (focusing operator);

[0051] (II) Taking the amplitude calculated by the focusing operator as a function of height, the amplitude is fitted near the peak value to obtain the surface height corresponding to the peak value after fitting.

[0052] (III) Obtain the surface shape through pixel-by-pixel calculation results.

Claims

1. A zoom microscopic surface reconstruction method based on a coherent scanning interferometer system. It is characterized in that A set of coherent scanning interferometers is used to realize two surface measurement methods: coherent scanning interferometry and zoom microscopy. The zoom microscopy surface reconstruction method includes the following steps: (1.1) Use a scanning stage to obtain three-dimensional interferometric signals; (1.2) Preprocessing the three-dimensional interference pattern to constrain the background light intensity distribution in the longitudinal direction, i.e., the optical axis direction, to avoid frequency aliasing; (1.3) Performing a three-dimensional Fourier transform on the preprocessed interference pattern to obtain a three-dimensional spectrum of the three-dimensional interference pattern; (1.4) Separating the zoom microscopy signal spectrum from the three-dimensional spectrum; (1.5) performing a three-dimensional inverse Fourier transform on the zoom microscopy imaging signal spectrum to obtain the zoom microscopy imaging signal during the scanning process; (1.6) Obtain the surface morphology through zoom microscopic surface reconstruction algorithm.

2. According to the zoom microscopic surface reconstruction method based on the coherent scanning interferometer system described in claim 1, It is characterized in that The scanning stage in step (1.1) is a piezoelectric ceramic nano-stage or a mechanical stage.

3. According to the zoom microscopic surface reconstruction method based on the coherent scanning interferometer system described in claim 1, It is characterized in that The steps for separating the zoom microscopy signal spectrum from the three-dimensional spectrum in step (1.4) are as follows: (4.1) The three-dimensional transfer function of the zoom microscope system is simulated by the theoretical model, and its expression is: Where K is the spatial frequency vector, k 0 is the wave number, that is, 2π / λ, λ is the wavelength, S(k 0 ) is the spectral power density, in is the three-dimensional pupil function of the optical imaging system limited by NA, δ() is the Dirac Delta function, h is the Heaviside step function, is the vertical unit vector, A N is the system numerical aperture; (4.2) The bandwidth of the zoom microscopy imaging signal is determined according to the three-dimensional transfer function, and the three-dimensional spectrum of the three-dimensional interference pattern is filtered, so that only the spectrum components within the bandwidth are related to the zoom microscopy imaging signal, and the spectrum of the signal outside the bandwidth is zeroed, which is expressed by the following formula: Wherein, O(K) is the three-dimensional spectrum of the zoom microscopy imaging signal, and I(K) is the three-dimensional spectrum of the acquired original three-dimensional interference pattern.

4. According to the zoom microscopic surface reconstruction method based on the coherent scanning interferometer system described in claim 3, It is characterized in that The three-dimensional transfer function described in step (4.1) is obtained through theoretical model simulation.

5. According to the zoom microscopic surface reconstruction method based on the coherent scanning interferometer system described in claim 3, It is characterized in that The steps for obtaining the surface morphology by zoom microscopic surface reconstruction algorithm in step (1.6) are as follows: (6.1) Calculating the focusing degree of the zoom microscopy imaging signal at each pixel point along the longitudinal direction, the focusing degree is calculated by a focusing operator; (6.2) Taking the amplitude calculated by the focusing operator as a function of height, fitting the amplitude near the peak value, and obtaining the surface height corresponding to the peak value after fitting; (6.3) The surface morphology is obtained through pixel-by-pixel calculation results.

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