Imaging method and device
By combining spectral domain interferometry and white light interferometry for demodulation, the contradiction between detection accuracy and speed in vertical scanning white light interferometry is resolved, achieving high-precision, large-area three-dimensional imaging, reducing costs and improving noise resistance.
Patent Information
- Application Number
- CN202511311679.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-15
- Publication Date
- 2025-11-18
AI Technical Summary
In vertical scanning white light interferometry, existing technologies suffer from problems such as a contradiction between detection accuracy and scanning speed, a small displacement range that is susceptible to mechanical hysteresis, and the susceptibility of phase methods to noise.
A spectral domain interferometry system is used to replace the high-precision displacement stage. High-precision displacement detection is achieved by jointly demodulating the white light interferometry system and the spectral domain interferometry system. Combined with fast Fourier transform and phase compensation, a three-dimensional surface morphology is constructed.
It provides high-precision demodulation over a wide range, improves imaging speed and measurement range, reduces costs, has strong noise resistance, and avoids the effects of mechanical hysteresis.
Smart Images
Figure CN120970531A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of optical detection technology, and in particular to an imaging method and device. BACKGROUND
[0002] Vertical Scanning Interferometry (VSI) is a non-contact optical measurement technology for high-precision three-dimensional surface profile measurement, which combines the characteristics of low coherence and vertical scanning technology. The basic principle is to drive the objective lens or the sample to scan precisely in the vertical direction, and the camera continuously collects the interference pattern sequence during the scanning process. The system extracts the interference signal intensity change curve of each pixel point at different height positions, and uses a certain signal processing algorithm to accurately locate the coherent peak position, i.e. the position of zero optical path difference, which is used as the relative height of the point, and then reconstructs the three-dimensional topography of the sample surface.
[0003] The demodulation algorithm of white light interference can be divided into phase demodulation and intensity demodulation. The phase demodulation algorithm can achieve nanometer or even sub-nanometer vertical resolution, and is suitable for precision topography measurement scenarios. However, this kind of algorithm requires high scanning accuracy of the system, and usually relies on a high-precision displacement stage for closed-loop scanning in the vertical direction to ensure the accuracy of the phase information. Although the commonly used displacement actuator such as piezoelectric ceramic (PZT) has high resolution, its displacement range is small (only a few hundred microns) and the scanning speed is slow. In actual work, it is easily affected by mechanical hysteresis, nonlinearity and system noise, resulting in phase error. At the same time, the current phase shift method only uses a limited number of sampling points for phase calculation, such as the three-step phase shift method, which uses three points, so it is easily affected by signal noise. The white light interference demodulation algorithm based on intensity information determines the equal optical path point by extracting the maximum value position of the interference signal envelope, which requires dense sampling to ensure the demodulation accuracy, which to some extent limits the imaging speed. At present, in the vertical scanning white light interference measurement, how to improve the measurement speed while maintaining high-precision demodulation capability is still a key research problem. SUMMARY
[0004] In view of the above problems existing in the current VSI: (1) the detection accuracy and scanning speed of the intensity demodulation algorithm are contradictory, (2) the use of PZT has high accuracy but small displacement range and is easily affected by mechanical hysteresis and nonlinearity, (3) the phase method is easily affected by noise, etc. To solve the above problems, the present application proposes an imaging method and device, which no longer relies on high-precision displacement devices for measurement accuracy, uses a spectral domain interference system to detect the displacement of VSI, and provides high-precision demodulation in a larger range, effectively breaking the restrictive relationship between step size and accuracy in the traditional scanning strategy, while ensuring the imaging accuracy, significantly improving the imaging speed and imaging range.
[0005] The technical scheme of the present application is as follows: an imaging method, comprising the following steps:
[0006] acquiring an interference signal of a sample in a vertical scanning process by a white light interference system;
[0007] simultaneously acquiring a spectral domain interference spectrum by a spectral domain interference system, and calculating a vertical scanning displacement based on the interference spectrum;
[0008] jointly demodulating the interference signal and the vertical scanning displacement to obtain height information of the sample, and constructing a three-dimensional surface topography;
[0009] wherein the displacement information is provided by the spectral domain interference system, and is used to replace displacement measurement of a high-precision displacement stage.
[0010] performing fast Fourier transform on the spectral domain interference spectrum, calculating a phase and performing phase unwrapping, so as to obtain the vertical scanning displacement.
[0011] The height information of the sample is obtained in the following process:
[0012] demodulation of the spectral domain interference spectrum:
[0013] performing fast Fourier transform on the spectral domain interference spectrum to calculate a phase of the spectral domain interference spectrum , , , wherein the sampling sequence is represented; phase unwrapping operation is performed on to obtain a real phase , and then the vertical scanning displacement of the VSI is obtained , is a center wave number of a second white light source 8 of the spectral domain interference system;
[0014] demodulation of the VSI white light interference signal:
[0015] setting a point on the sample, and imaging a camera point ; the vertical scanning displacement is , , and the interference image light intensity signal collected by the camera point is ; fitting or centroid calculation is performed on the envelope of the white light interference signal to obtain a low-precision solution of the equal optical path point; and high-precision solution of the equal optical path point is obtained by calculating phase compensation.
[0016] obtaining the height of the point on the sample; the height of each point on the sample is calculated in sequence to obtain the three-dimensional profile of the sample 5.
[0017] The low-precision solution is obtained in the following process:
[0018] interferometric image light intensity signal interpolation to obtain displacement equidistant sampling interferometric signal , then calculate the white light interference fringe zero optical path difference position, displacement equidistant sampling interferometric signal Fourier transform to extract positive frequency part and move it back to the center of the amplitude frequency curve, and the envelope of the interferometric image light intensity signal is obtained by inverse Fourier transform, the envelope of the interferometric image light intensity signal is fitted by Gaussian curve or by centroid method, and the coordinates corresponding to the maximum points of the envelope of the interferometric image light intensity signal are calculated , low precision solution of equal optical path position.
[0019] The high precision solution solving process is as follows:
[0020] According to the peak value method, the center wave number of the first white light source 1 of the white light interference system is calculated displacement equidistant sampling interferometric signal Each wave peak is found by peak finding algorithm, and the position of each wave peak is obtained by centroid method for sampling points near the wave peak , the position difference between all adjacent wave peaks is calculated and the average value is obtained ; the phase difference between adjacent wave peaks is , then the center wave number of the first white light source 1 of the white light interference system is ;
[0021] constructing an interference signal , respectively and Fourier transform is performed, and the phase difference between signal and signal is calculated , and it is compensated in the constructed interference signal, and ; since the equal optical path point coordinates of the constructed interference signal and the white light interference signal are equal, the low precision solution determines that the equal optical path position is located in the period of the curve , The calculation formula is , wherein is the rounding function; the horizontal coordinate distance at the maximum value in the period is calculated , , , which is the high precision solution of the height of the point on the sample.
[0022] An imaging device, comprising:
[0023] A white light interference system for collecting interference signals of a sample during a vertical scanning process;
[0024] A spectral domain interference system for collecting interference spectra and calculating scanning displacement during the vertical scanning process;
[0025] A synchronous control and processing unit for triggering data collection of the white light interference system and the spectral domain interference system simultaneously during the vertical scanning, and jointly demodulating the interference image and the interference spectra to obtain height information of the sample.
[0026] The spectral domain interference system is used to realize nanoscale displacement detection in a millimeter-level scanning range.
[0027] The synchronous control and processing unit comprises a computer and a synchronous triggering module for simultaneously controlling the collection processes of the spectrometer and the camera.
[0028] Compared with the prior art, the present application has the following beneficial effects:
[0029] 1. The spectral domain interference technology is added in the white light interference to detect the position of the moving platform, without the need of a high-precision moving platform, thereby reducing the cost. Meanwhile, the influence of the PZT on mechanical hysteresis and nonlinearity is eliminated.
[0030] 2. The high-precision moving platform generates a precise displacement range of only a few hundred microns, while the spectral domain interference technology can position the position of the moving platform in a range of a few millimeters with high precision, thereby greatly increasing the measurement range.
[0031] 3. The traditional white light interference needs a small scanning step to improve the demodulation precision, and the demodulation precision of the present application is not dependent on the scanning step. With the assistance of the spectral domain interference technology, high-precision demodulation can be provided under a large scanning step, and the scanning speed is fast.
[0032] 4. The traditional phase demodulation method is easily affected by noise, and the present application obtains a low-precision solution through the white light interference signal, and a high-precision solution is obtained by constructing the phase information of the interference signal. The specific parameters in the constructed interference signal are solved by Fourier transform, and the anti-noise ability is high, thereby improving the measurement precision. BRIEF DESCRIPTION OF DRAWINGS
[0033] Figure 1 is a schematic diagram of an imaging device;
[0034] Figure 2 is a schematic diagram of a demodulation curve.
[0035] In the figure: 1 - first white light source, 2 - collimating lens, 3 - beam splitter prism, 4 - interference objective, 5 - sample, 6 - lens, 7 - camera, 8 - second white light source, 9 - circulator, 10 - collimating lens, 11 - beam splitter prism, 12 - lens, 13 - mirror, 14 - lens, 15 - reference mirror, 16 - spectrometer, 17 - computer. DETAILED DESCRIPTION
[0036] An imaging method, characterized by comprising the following steps:
[0037] acquiring an interference signal of a sample in a vertical scanning process by a white light interference system;
[0038] simultaneously acquiring a spectral domain interference spectrum by a spectral domain interference system, and calculating a vertical scanning displacement based on the interference spectrum;
[0039] jointly demodulating the interference signal and the vertical scanning displacement to obtain height information of the sample, and constructing a three-dimensional surface topography;
[0040] wherein the displacement information is provided by the spectral domain interference system to replace displacement measurement of a high-precision displacement stage, so as to realize high-precision demodulation under a large-step scanning condition and improve imaging speed and measurement range.
[0041] The height information of the sample 5 is specifically:
[0042] Spectral domain interference signal demodulation:
[0043] In the spectral domain interference system, the interference spectrum collected by the spectrometer 16 is subjected to fast Fourier transform to calculate the phase of the interference signal , , denotes a sampling sequence; the phase unwrapping operation is performed on to obtain the real phase , and then the vertical scanning displacement of the VSI , is the center wave number of the second white light source 8 of the spectral domain interference system;
[0044] White light interference signal demodulation:
[0045] An arbitrary point on the sample 5 is imaged at a point of the camera 7; the vertical scanning displacement of the VSI is , , and the interference image light intensity signal collected by the camera 7 point is ;
[0046] The low-precision solution and the high-precision solution are sequentially solved to obtain the point The height of each point of sample 5 is calculated in turn to obtain the three-dimensional profile of the surface of sample 5.
[0047] The low-precision solution process is as follows:
[0048] The interference signal is interpolated to obtain the displacement equidistant sampled interference signal , and then the white light interference fringe zero optical path difference position is calculated, the signal is Fourier transformed, the positive frequency part in is extracted and moved back to the center of the amplitude frequency curve, and the envelope of the interference signal is obtained by inverse Fourier transform, and the envelope of the interference signal is fitted by a Gaussian curve or by a centroid method to calculate the coordinates corresponding to the maximum value point of the envelope of the interference signal . The low-precision solution of the equal optical path position.
[0049] The high-precision solution process is as follows:
[0050] The center wave number of the first white light source 1 of the white light interference system is calculated according to the peak value method , the interference signal is , each peak is found by a peak finding algorithm, and the position of each peak is obtained by a centroid method on the sampling points near the peak , the position difference between all adjacent peaks is calculated, and the average value is obtained ; the phase difference between adjacent peaks is , and the center wave number of the first white light source 1 of the white light interference system is .
[0051] The interference signal is constructed , the Fourier transform is performed on and respectively, and the phase is calculated to obtain the phase difference between the signal and the signal , and the compensation is made to the constructed interference signal, and there is , as shown by curve 3 in Figure 2 . Since the equal optical path point coordinates of the constructed interference signal and the white light interference signal are equal, the equal optical path position is determined by the low-precision solution to be located at the period of the curve, , and the calculation formula is , wherein is the rounding function; the horizontal coordinate distance at the maximum value in the period is calculated , , i.e. sample upper point high precision solution, As Figure 2 indicated by the middle solid line.
[0052] An imaging device comprises:
[0053] a white light interference system for acquiring an interference image of a sample during a vertical scanning process;
[0054] a spectral domain interference system for acquiring an interference spectrum and calculating a scanning displacement during the vertical scanning process;
[0055] a synchronous control and processing unit for triggering data acquisition of the white light interference system and the spectral domain interference system simultaneously during vertical scanning, and jointly demodulating the interference image and the interference spectrum to obtain height information of the sample.
[0056] The white light interference system comprises a first white light source 1, a collimating lens a2, a beam splitter prism a3, an interference objective 4, a lens a6 and a camera 7;
[0057] The first white light source 1 emits a light beam, which is collimated into a first probe light by the collimating lens a2, and enters the interference objective 4 through the beam splitter prism 3; in the interference objective 4, the first probe light is divided into a first reference light and a first sample light; the first reference light returns through a reference mirror inside the interference objective 4, and the first sample light returns through the sample 5; the returned first reference light and the returned first sample light converge in the interference objective 4, and then pass through the beam splitter prism a3 and the lens a6 to form an interference image on the surface of the camera 7, which is acquired by the camera 7 and transmitted to the computer 17 for processing and display; the VSI vertical scanning of the white light interference system is performed without moving the sample stage, and the white light interference system scans in the vertical direction with the interference objective, so that the distance between the white light interference system and the sample changes, thereby changing the optical path of the sample light;
[0058] The spectral domain interference system comprises a second white light source 8, a circulator 9, a collimating lens b10, a beam splitter prism b11, a lens b12, a mirror 13, a lens c14, a reference mirror 15 and a spectrometer 16;
[0059] The second white light source 8 emits a light beam which, after entering the ring resonator 9, is collimated by the collimating lens b10 into the second probe light; the beamsplitter b11 divides the second probe light into the second reference light and the second sample light; the second reference light is focused by the lens c14 on the reference mirror 15, and after being reflected by the reference mirror 15, returns along the original light path; the second sample light is focused by the lens b12 on the mirror 13, and after being reflected by the mirror 13, returns along the original light path, and the returned second sample light and the second reference light converge at the beamsplitter a11; the light enters the spectrometer 16 through the lens 10 and the ring resonator 9, and the interference spectrum is collected by the spectrometer 16 and transmitted to the computer 17 for demodulation; the VSI vertical scanning drives the mirror 13 to move, changing the optical path of the sample light; the mirror can be placed on the interference objective lens of the white light interference system, and only needs to be ensured to move synchronously with the white light interference system in the vertical direction.
[0060] The mirror 13 moves synchronously with the VSI vertical scanning; while the VSI performs vertical scanning, the computer 17 sends a synchronous signal to the spectrometer 16 and the camera 7, controlling the spectrometer 16 and the camera 7 to collect the interference spectrum and the interference image at the same time; the collected data of the two collection ports are combined for demodulation, and the height information of the sample 5 is obtained.
Claims
1. An imaging method characterized by, The method comprises the following steps: acquiring an interference signal of the sample in a vertical scanning process by a white light interference system; simultaneously acquiring a spectral domain interference spectrum by a spectral domain interference system, and calculating a vertical scanning displacement based on the interference spectrum; jointly demodulating the interference signal and the vertical scanning displacement to obtain height information of the sample, and constructing a three-dimensional surface topography; wherein the displacement information is provided by the spectral domain interference system to replace displacement measurement of a high-precision displacement stage.
2. The imaging method of claim 1, wherein, The spectral domain interference spectrum is subjected to fast Fourier transform to calculate a phase and perform phase unwrapping, thereby obtaining the vertical scanning displacement.
3. The imaging method of claim 1, wherein, The height information of the sample is obtained as follows: demodulation of the spectral domain interference spectrum: Fast Fourier transform is performed on the spectral domain interference spectrum to calculate the phase of the spectral domain interference spectrum , , represents a sampling sequence; a phase unwrapping operation is performed on to obtain a real phase , and then a vertical scanning displacement of the VSI is obtained , is a center wave number of a second white light source (8) of the spectral domain interference system demodulation of the VSI white light interference signal: Set a point on the sample , image on the camera point ; the vertical scanning displacement is , , the interference image light intensity signal collected by the camera point is ; the envelope fitting or centroid calculation is performed on the white light interference signal to obtain a low-precision solution of the equal optical path point; and the high-precision solution of the equal optical path point is obtained by calculating and compensating the phase; Obtaining sample points Height; the height of each point of the sample is calculated in turn to obtain the three-dimensional profile of the surface of the sample (5).
4. The demodulation method according to claim 3, characterized by, The low-precision solving process is as follows: Interferogram intensity signal Interpolation is performed to obtain displacement equidistant sampling interferogram signal , then the white light interference fringe zero optical path difference position is calculated, and the displacement equidistant sampling interferogram signal is subjected to Fourier transform to extract the positive frequency part and move it back to the center of the amplitude frequency curve, and the envelope of the interferogram intensity signal is obtained through inverse Fourier transform, and the envelope of the interferogram intensity signal is subjected to Gaussian curve fitting or centroid method to calculate the coordinates corresponding to the maximum points of the envelope of the interferogram intensity signal , is a low-precision solution of the equal optical path position.
5. The demodulation method according to claim 3, characterized by, The high-precision solving process is as follows: According to the peak value method, the center wave number of the first white light source (1) of the white light interference system is calculated , the interference signals are sampled at equal intervals according to the displacement , each peak is found out through a peak finding algorithm, and the position of each peak is obtained through a centroid method on the sampling points near the peak , the position difference between all adjacent peaks is calculated, and the average value is obtained ; the phase difference between adjacent peaks is , and the center wave number of the first white light source (1) of the white light interference system is ; Constructing interference signals , respectively and Perform a Fourier transform and calculate the phase to obtain the signal. and signal phase difference between And compensate it into the constructed interference signal, with Since the coordinates of the equipathic points of the constructed interference signal and the white light interference signal are equal, the low-precision solution... Determine the position of equal optical path length. The first curve cycle, The calculation formula is: ,in This is a rounding function; it calculates the value within this period. x-coordinate distance at the maximum value , , That is, the spot on the sample Highly accurate solution.
6. An image forming apparatus characterized by comprising: The imaging method according to any one of claims 1-5 comprises: a white light interference system for acquiring an interference signal of the sample in a vertical scanning process; a spectral domain interference system for acquiring an interference spectrum and calculating a scanning displacement in the vertical scanning process; a synchronous control and processing unit for simultaneously triggering data acquisition of the white light interference system and the spectral domain interference system in the vertical scanning, and jointly demodulating the interference image and the interference spectrum to obtain height information of the sample.
7. The imaging apparatus according to claim 6, wherein The spectral domain interference system is used to realize nanoscale displacement detection in a millimeter-level scanning range.
8. The imaging apparatus according to claim 7, wherein The synchronous control and processing unit comprises a computer and a synchronous triggering module for simultaneously controlling acquisition processes of a spectrometer and a camera.