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CN-121994164-A - Automatic refocusing large measurement range nanotopography measurement method

CN121994164ACN 121994164 ACN121994164 ACN 121994164ACN-121994164-A

Abstract

The invention belongs to the technical field of high-precision morphology measurement and discloses an automatic refocusing large-measurement-range nanotopography measurement method which comprises the following steps of 1, collecting a spectrum interference signal of a sample by an OCT system, carrying out one-dimensional inverse Fourier transform on the signal in a wave number domain to obtain a space domain complex amplitude signal, 2, selecting a surface complex amplitude signal according to maximum signal intensity based on the space domain complex amplitude signal, 3, calculating average low-frequency intensity based on the surface complex amplitude signal to obtain an actual defocusing distance, 4, carrying out refocusing calculation based on the surface complex amplitude signal and the actual defocusing distance to obtain a refocusing surface signal, and 5, calculating and outputting a morphology height difference based on the refocusing surface signal. The invention can improve the effective measurement range of OCT nanotopography detection, optimize the capability of detecting the topography of the uneven surface, inhibit sidelobe artifact caused by defocusing, realize based on numerical calculation and reduce the complexity and cost of the system.

Inventors

  • YANG QIUNAN
  • ZHOU PENGYU
  • SUN LIANG
  • ZHANG BO
  • ZHANG YULIN

Assignees

  • 核工业理化工程研究院

Dates

Publication Date
20260508
Application Date
20251222

Claims (10)

  1. 1. An auto-refocusing large measurement range nanotopography measurement method, comprising the steps of: step 1, collecting spectral interference signals of a sample using an OCT system Performing one-dimensional inverse Fourier transform on the signal in the wave number domain to obtain a spatial complex amplitude signal ; Step 2, based on the spatial complex amplitude signal of step 1 Selecting surface complex amplitude signal according to maximum signal intensity ; Step 3, based on the surface complex amplitude signal of step 2 Calculating the average low frequency intensity Obtaining the actual defocus distance ; Step 4, based on the surface complex amplitude signal of step 2 And the actual defocus distance in step 3 Refocusing calculation is carried out to obtain refocusing surface signals ; Step 5, based on the refocusing surface signal of step 4 Calculating and outputting the shape height difference 。
  2. 2. The auto-refocusing large measurement range nanotopography measurement method of claim 1, wherein in step 1, the OCT system is a time domain OCT system, a spectral domain OCT system, or a swept source OCT system.
  3. 3. The method for measuring the nanotopography of the large measurement range by automatic refocusing according to claim 1, wherein in the step 2, the surface complex amplitude signal is selected by a manual selection and automatic identification method based on intensity 。
  4. 4. The auto-refocusing large measurement range nanotopography measurement method according to claim 1, wherein in step 3, the actual defocus distance is The acquisition method of (1) comprises the following steps: Step 301, initializing a reference defocus distance ; Step 302, based on the surface complex amplitude signal obtained in step 2 Calculating a reference complex amplitude signal ; Step 303, based on the reference complex amplitude signal of step 302 Calculating a reference height difference signal ; Step 304, based on the reference level difference signal of step 303 Calculating a reference spectrum signal ; Step 305, based on the reference spectrum signal of step 304 Calculating the average low frequency intensity ; Step 306, determining a reference defocus distance Whether or not it is greater than the axial field of view of the OCT system, if not, the reference defocus distance Increasing the step length by one and repeating steps 302 through 306, if so, traversing different reference defocus distances The obtained average low frequency intensity Selecting the smallest average low frequency intensity Corresponding reference defocus distance As the actual defocus distance 。
  5. 5. The auto-refocusing large measurement range nanotopography measurement method of claim 4, wherein, in step 302, The calculation formula of (2) is as follows: ; Wherein, the Representing a one-dimensional fourier transform in the transverse spatial domain, Representing a one-dimensional inverse fourier transform in the transverse spatial domain, Representing the coordinates of the wavenumber domain, Representing the spatial frequency coordinates of the lateral airspace, Represents the coordinates of the transverse airspace, Indicating the axial position of the sample surface, Representing imaginary units; in the step 303 of the process described above, The calculation formula of (2) is as follows: ; Wherein, the Representing the center wavelength of the OCT system light source, The phase of the complex number is represented, The representation takes the conjugate of a plurality of numbers, Representation and coordinate position Coordinate positions of laterally adjacent sampling intervals; in the step 304 of the process described above, The calculation formula of (2) is as follows: ; Wherein, the Representing a one-dimensional fourier transform in the transverse spatial domain, Representing the frequency coordinates of the reference level difference signal, The representation takes absolute value; In the step 305 of the process described above, The calculation formula of (2) is as follows: ; Wherein, the Representing the corresponding maximum frequency of the reference spectrum signal, Which represents the low-frequency factor of the signal, Representing the boundary value of the low frequency range.
  6. 6. The auto-refocusing large measurement range nanotopography measurement method of claim 1, wherein in step 4, The calculation formula of (2) is as follows: ; Wherein, the Representing a one-dimensional fourier transform in the transverse spatial domain, Representing a one-dimensional inverse fourier transform in the transverse spatial domain, Representing the coordinates of the wavenumber domain, Representing the spatial frequency coordinates of the lateral airspace, Representing the complex amplitude signal of the surface, Indicating the actual defocus distance of the lens, Representing imaginary units.
  7. 7. The auto-refocusing large measurement range nanotopography measurement method of claim 1, wherein in step 5, The calculation formula of (2) is as follows: ; Wherein, the Representing the center wavelength of the OCT system light source, The phase of the complex number is represented, The representation takes the conjugate of a plurality of numbers, Representing coordinate positions Is used for refocusing the surface signal, Representing coordinate positions Is used for refocusing the surface signal, Representation and coordinate position Coordinate positions laterally adjacent to one sampling interval.
  8. 8. An electronic device comprising one or more processors and a memory, the memory configured to store one or more programs, wherein the one or more programs, when executed by the one or more processors, cause the one or more processors to implement the auto-refocusing large measurement range nanotopography measurement method of claim 1.
  9. 9. A computer readable storage medium having stored thereon computer executable instructions which when executed are adapted to implement the auto-refocusing large measurement range nanotopography measurement method according to claim 1.
  10. 10. A computer program product, characterized in that the computer program product comprises computer executable instructions for implementing the auto-refocusing large measurement range nanotopography measurement method according to claim 1 when executed.

Description

Automatic refocusing large measurement range nanotopography measurement method Technical Field The invention relates to the technical field of high-precision morphology measurement, in particular to an automatic refocusing large-measurement-range nanomorphology measurement method. Background The surface morphology is a key factor for determining various functional characteristics of a material interface, such as optics, mechanics, biology and the like. The high-precision topography measurement not only can reveal the surface microstructure characteristics, but also can provide important basis for material design and process optimization. In the fields of precision manufacturing, material performance evaluation, defect detection and the like, a nano surface morphology measurement technology has become a key means for guaranteeing the performance and reliability of products. The existing nanotopography measurement technology is mainly divided into a non-optical method and an optical method. Non-optical methods such as atomic force microscopy (Atomic force microscopy, AFM) and scanning electron microscopy (Scanning electron microscopy, SEM) have sub-nanometer resolution, but the former imaging speed is slow and environmentally sensitive, and the latter require operation under vacuum conditions and may cause electron beam damage to the sample. Furthermore, the axial field of view range of these two types of methods is small and is only applicable to measuring planar samples. Optical methods such as white light interferometry (WHITE LIGHT interferometry, WLI), confocal microscopy (Confocal microscopy, CM), optical coherence tomography (Optical coherence tomography, OCT) and the like can achieve sub-micron resolution topographical imaging. Among them, WLI and CM typically rely on mechanical axial scanning to obtain a large measurement range, which places stringent requirements on the axial alignment of the sample with the detection system, with limited measurement efficiency. In contrast, frequency domain OCT can extract depth information from interference signals without mechanical scanning, and nanotopography detection can be achieved through phase information. However, the axial field of view range of an effective nanotopography measurement of OCT is limited by a shallow depth of focus (typically tens of microns), and once the sample is out of focus, the measurement accuracy and resolution will drop significantly, with side lobe artifacts being prone to occur. To overcome the limitation of focal depth on OCT imaging quality, researchers have proposed a variety of digital refocusing techniques based on diffraction models to achieve imaging optimization by reconstructing out-of-focus interference signals in the wavenumber domain. These methods achieve certain effects in OCT intensity imaging （J. de Wit, G.-O. Glentis, and J. Kalkman, "Computational 3D resolution enhancement for optical coherence tomography with a narrowband visible light source," Biomed. Opt. Express 14(7), 3532-3554 (2023)） and polarization imaging （S. Ruiz-Lopera, R. Restrepo, T. M. Cannon, M. Villiger, B. E. Bouma, and N. Uribe-Patarroyo, "Computational refocusing in phase-unstable polarization-sensitive optical coherence tomography," Opt. Lett. 48(18), 4765-4768 (2023)）, but the phase information is more sensitive to axial displacement, and if defocus amount estimation is inaccurate, refocusing effects will be greatly reduced. Therefore, how to accurately and rapidly estimate the defocus distance and realize automatic refocusing without additional hardware is a key technical difficulty in realizing nanotopography measurement in a large measurement range. Disclosure of Invention The invention aims to provide an automatic refocusing nanotopography measuring method with a large measuring range, which aims at the technical defects of limited focal depth, reduced measuring resolution after defocusing, sidelobe artifact and the like in nanotopography measuring technology in the prior art, and can realize high-accuracy nanotopography measuring results in a large axial view field range. The method can automatically and accurately estimate the defocusing distance and refocus the numerical value on the premise of no need of additional hardware, thereby expanding the axial range of nanotopography measurement, maintaining high transverse resolution and effectively inhibiting sidelobe interference caused by defocusing. The technical scheme adopted for realizing the purpose of the invention is as follows: an auto-refocusing large measurement range nanotopography measurement method comprising the steps of: step 1, collecting spectral interference signals of a sample using an OCT system Performing one-dimensional inverse Fourier transform on the signal in the wave number domain to obtain a spatial complex amplitude signal; Step 2, based on the spatial complex amplitude signal of step 1Selecting surface complex amplitude signal according to maximum signal in