Method and system for measuring double-state interference morphology of discontinuous precise surface

Abstract

The invention provides a double-state interference morphology measurement method and system for a discontinuous precision surface, and belongs to the technical field of optical precision measurement. Based on a Fizeau interferometer, interference images in a focusing state and an out-of-focus state are respectively acquired, two-dimensional structure information and height information of a sample with a discontinuous precise surface are respectively extracted, and two-state data fusion is carried out, so that three-dimensional morphology reconstruction is realized. The method breaks through the limitation of the optical diffraction limit on the resolution, avoids the failure problem of a traditional phase unwrapping algorithm at a discontinuous boundary, remarkably enhances the environmental interference resistance, improves the calculation efficiency, is suitable for high-precision surface measurement of a vacuum chuck and the like with a large number of discontinuous characteristics, and has a wide application prospect. And a reliable solution is provided for high-end manufacturing quality control.

Description

Technical Field

[0001] This invention belongs to the field of optical precision measurement technology, specifically relating to a method and system for measuring the dual-state interference morphology of discontinuous precision surfaces. Background Technology

[0002] Currently, the following technical solutions are mainly used for morphology inspection of discontinuous planar array structures (taking vacuum chucks as an example):

[0003] 1. Contact measurement method:

[0004] A profilometer acquires surface profile data by linearly scanning the surface of a sample using a diamond probe. This measurement method is indeed suitable for inspecting continuous planes such as wafers and optical plates. For these samples with relatively flat, smooth surfaces without significant undulations or pores, the probe can stably scan along the surface, thereby accurately measuring surface profile parameters such as flatness and roughness, providing accurate measurement data for high-quality planar machining and manufacturing. However, this type of contact measurement method carries the risk of damaging the sample.

[0005] 2. Traditional laser interferometry:

[0006] An interferometer is used to acquire surface interference images, and height information is extracted using a phase unwrapping algorithm. This technique is primarily designed for continuous optical surfaces, and its phase unwrapping algorithm relies on the assumption of phase continuity. This method is truncated at discontinuous boundaries, enabling phase unwrapping only for locally continuous surfaces and failing to handle suction cup array structures; it may be able to handle a small number of discontinuous surfaces, but computation for a large number of discontinuous surfaces is time-consuming and has limited accuracy.

[0007] 3. Discontinuous surface interferometry techniques based on morphological methods:

[0008] References under existing technology [1] A mathematical morphology-based MBPU algorithm is proposed, which achieves high-precision measurement through phase stacking and 3D connected component analysis, providing a new solution for wafer flatness control. This technique bypasses the traditional boundary marking step by binarizing phase data, performing 3D stacking, and applying morphological operations (dilation and connected component analysis), directly handling discontinuous phase transitions. Experiments use a mask method to generate discontinuous test surfaces, acquire data using a planar laser interferometer, and achieve high-precision reconstruction by filtering out systematic errors.

[0009] However, the above-mentioned existing technical solutions have the following drawbacks when dealing with the inspection of precision surface morphology with discontinuous features:

[0010] 1. Resolution limitations:

[0011] Existing optical measuring instruments are limited by the optical diffraction limit, making it difficult to significantly improve axial resolution and tomography capabilities, thus restricting the improvement of focusing accuracy and parameter measurement accuracy of component surfaces. For example, the objective lens NA (numerical aperture) of a traditional Fizeau interferometer is limited, and in the focused state, the diffraction limit makes it difficult to resolve the edges of circular array units with diameters less than 0.5 mm. When the diameter of the micro-hole and / or boss of the suction cup is reduced to a certain extent, interference fringes overlap at the edge of the hole or boss, enhancing the edge diffraction effect and leading to larger edge positioning deviations.

[0012] 2. Weak anti-interference ability:

[0013] Traditional interferometric measurement methods are difficult to measure samples with surface scattering characteristics, and the measurement accuracy is easily affected by environmental factors such as airflow disturbance and ground vibration.

[0014] 3. Insufficient ability to perform discontinuous surface treatment

[0015] To address the accuracy and efficiency challenges of phase unwrapping on discontinuous surfaces (such as vacuum chucks used for wafer measurement), traditional measurement methods, such as coordinate measuring machines (CMMs) or white light interferometers, are unsuitable due to insufficient accuracy or software limitations. While laser interferometers offer high precision, existing phase unwrapping algorithms cannot handle discontinuous phase transitions. This technological bottleneck restricts the quality control of critical components in precision equipment.

[0016] Traditional phase unwrapping algorithms (such as the least squares method) require the phase field to be continuously differentiable. However, the needle / ring array structure of the vacuum chuck forms a large number of well-defined boundaries on the surface, resulting in an excessively large phase jump region. Existing route-dependent algorithms are forcibly truncated at the boundaries, making it impossible to achieve global phase unwrapping. Although route-independent algorithms can handle a small number of discontinuous surfaces, the computational residuals increase significantly when the number of discontinuous surfaces reaches hundreds to thousands.

[0017] [1]WANG Shuai, DUAN Bosong, JU Bingfeng, et al. Interferometric measurement of discontinuous surfaces based on morphology method [J]. Optics and Lasers in Engineering, 2025, 194: 109131. DOI: 10.1016 / j.optlaseng.2024.109131. Summary of the Invention

[0018] This invention is made to solve the above-mentioned problems. The purpose is to provide a method and system for measuring the dual-state interferometric topography of discontinuous precision surfaces, so as to solve the problems of resolution limitation, phase unwrapping failure and poor environmental robustness of the prior art when measuring discontinuous precision surfaces (such as small-diameter circular array planes).

[0019] This invention provides a two-state interferometric topography measurement method for discontinuous precision surfaces, characterized by using a Fizeau interferometer to measure the surface shape of a sample with a discontinuous precision surface, including the following steps: S10, acquiring an interference image of the sample with a discontinuous precision surface in the focused state of the Fizeau interferometer, thereby extracting two-dimensional structural information of the sample surface; S20, adjusting the defocusing amount Δz of the Fizeau interferometer to a degree where the intensity map corresponding to the interference image is blurred but the interference image can present a smooth surface shape, acquiring an interference image in this defocused state, thereby extracting height information of the sample surface; S30, performing two-state fitting between the two-dimensional structural information and the height information to reconstruct the three-dimensional topography of the sample surface.

[0020] The dual-state interferometric topography measurement method for discontinuous precision surfaces provided by this invention may also have the following feature: step S10 includes the following sub-step: S11, representing the light intensity of the interference image in the focused state at pixel point (x,y) as: In the above formula, A(x,y) is the background light intensity, and B(x,y) is the modulation index. For phases containing information about the transverse structure of the sample surface; S12, using Accurately identify the structural boundaries and geometric features of the sample surface to obtain two-dimensional structural information: In the above formula, λ represents the wavelength of the light source. h represents the initial phase of the system. focus (x,y) represents the height, h focus (x,y) is used only to characterize the horizontal and vertical coordinates in two-dimensional structural information and not to characterize the surface morphology height of the sample.

[0021] The dual-state interference morphology measurement method for discontinuous precision surfaces provided by the present invention may also have the following feature: wherein, in step S10, the two-dimensional structural information includes the position, shape and spatial distribution of holes and / or protrusions on the sample surface.

[0022] The dual-state interferometric topography measurement method for discontinuous precision surfaces provided by this invention may also have the following feature: step S20 includes the following sub-step: S21, defocusing the Fizeau interferometer along the optical axis by Δz to introduce defocused wavefront aberration, the pupil function of which is: In the above formula, u and v represent the horizontal and vertical coordinates of the pupil plane, respectively, P0(u,v) represents the ideal circular pupil function, i represents the imaginary unit, and W... 20This is the defocus coefficient. S22, After determining the pupil function P(u,v) from Δz, the modulation transfer function MTF(f; Δz) of the system is obtained through its autocorrelation; S23, Select the characteristic frequency f corresponding to the period of the measured structure of the sample. c Then, let MTF(f) c ; Δz)≥γ, thus solving for the maximum value of Δz, denoted as Δz max Wherein, the threshold γ is determined by the system noise; S24, the actual defocusing amount of the Fizeau interferometer is controlled to Δz. max The light intensity of the interference image in the defocused state at this time is expressed as: In the above formula, A'(x,y) is the background light intensity, and B'(x,y) is the modulation index. The phase is in the out-of-focus state; S25, solved using the phase unwrapping algorithm. This leads to the acquisition of altitude information h. defocus (x,y):

[0023] This invention also provides a dual-state interferometric topography measurement system for discontinuous precision surfaces, characterized by using any of the aforementioned dual-state interferometric topography measurement methods for discontinuous precision surfaces, comprising: a Fizeau interferometer; a defocus control module for controlling the defocus amount Δz of the Fizeau interferometer according to the MTF threshold; an image processing unit for performing dual-state image acquisition, phase calculation, and feature extraction during the defocusing process of the Fizeau interferometer; and a data fusion module for performing dual-state fitting of two-dimensional structural information and height information to reconstruct the three-dimensional topography of the sample surface.

[0024] The role and effect of invention

[0025] According to the present invention, a two-state interferometric topography measurement method for discontinuous precision surfaces is provided, which uses a Fizeau interferometer to measure the surface shape of a sample with a discontinuous precision surface. The method includes the following steps: S10, acquiring an interference image of the sample with a discontinuous precision surface in the focused state of the Fizeau interferometer, thereby extracting two-dimensional structural information of the sample surface; S20, adjusting the defocusing amount Δz of the Fizeau interferometer to a degree where the intensity map corresponding to the interference image is blurred but the interference image still presents a smooth surface shape, acquiring an interference image in this defocused state, thereby extracting height information of the sample surface; S30, performing two-state fitting between the two-dimensional structural information and the height information to reconstruct the three-dimensional topography of the sample surface. The two-state interferometric topography measurement system for discontinuous precision surfaces of the present invention utilizes this method.

[0026] Therefore, the dual-state interferometric topography measurement method and system for discontinuous precision surfaces of the present invention have the following beneficial effects:

[0027] (1) While ensuring high-precision measurement, it also takes into account efficiency and stability, providing a brand-new solution for quality control and inspection of various non-continuous precision surfaces in the high-end manufacturing field.

[0028] (2) Breaking the Optical Resolution Limit: This invention uses a Fizeau interferometer to acquire interferograms in both focused and defocused states. The focused state retains structural position information, while the defocused state retains surface undulation information. This dual-state complementarity overcomes the optical diffraction limit's limitation on resolution. Through the dual-state measurement strategy employed in this invention, the smoothing effect of the defocused interferogram on edge aliasing is utilized, significantly improving the edge resolution capability of discontinuous surfaces. This method overcomes the diffraction limit problem caused by the numerical aperture (NA) limitation of traditional interferometers and solves the positioning deviation caused by fringe aliasing and diffraction effects at the edges of micro-holes and / or protrusions.

[0029] (3) Completely avoids the risk of phase unwrapping failure: This invention adopts a dual-source data fusion strategy of extracting XY plane coordinates from focused interferograms and extracting Z-axis height from defocused interferograms, completely bypassing the dependence of traditional phase unwrapping algorithms on phase continuity. This innovation enables the method of this invention to handle discontinuous surfaces with a large number of phase jump regions (such as vacuum chuck arrays), solving the technical bottleneck of existing methods being unable to perform interferometric measurements under a large number of discontinuous boundaries.

[0030] (4) Significantly Enhanced Environmental Robustness: Due to the reduced spatial frequency, the defocused interferogram is significantly less sensitive to environmental noise such as airflow disturbances and mechanical vibrations. This characteristic enables the method of this invention to maintain stable measurements in ordinary indoor environments, overcoming the shortcomings of traditional interferometry which is susceptible to data inaccuracies due to micro-vibrations. By utilizing the insensitivity of the defocused state to small displacements, the sensitivity of measurements to airflow disturbances is reduced, improving the applicability to industrial sites.

[0031] (5) Order-of-magnitude improvement in computational efficiency: This invention directly fuses XY coordinates and Z height data, eliminating the iterative calculation process of global phase unwrapping and shortening the processing time for a large number of discontinuous surfaces. This optimization significantly improves detection efficiency and makes online real-time quality control possible. Attached Figure Description

[0032] Fig. 1 This is a schematic diagram of the experimental setup in an embodiment of the present invention;

[0033] Fig. 2 This is a top view of the sample under test in an embodiment of the present invention;

[0034] Fig. 3 This is a flowchart illustrating the DSIP method in an embodiment of the present invention. Detailed Implementation

[0035] To make the technical means, creative features, objectives and effects of this invention easier to understand, the following embodiments, in conjunction with the accompanying drawings, specifically illustrate a method and system for measuring the dual-state interference morphology of a discontinuous precision surface according to this invention.

[0036] <Example>

[0037] This embodiment provides a two-state interferometric topography measurement method for discontinuous precision surfaces, which uses a Fizeau interferometer to measure the surface shape of a sample with a discontinuous precision surface.

[0038] In this embodiment, the "dual-state interferometric profilometry method for measuring the topography of discontinuous precision surfaces" is referred to as the DSIP method (Dual-State Interferometric Profilometry).

[0039] Preliminary preparations must be made before measurement: (Refer to...) Fig. 1 The Fizeau interferometer is configured in measurement mode. A sample with a discontinuous precision surface (specifically, a vacuum chuck is used in this embodiment) is placed on the measurement stage, and its top view is shown below. Fig. 2 As shown.

[0040] Fig. 3 This is a flowchart illustrating the DSIP method in an embodiment of the present invention.

[0041] like Figs. 1-3 As shown, the DSIP method in this embodiment includes the following steps:

[0042] S10, Extract the two-dimensional structural information of the sample surface, specifically including the following sub-steps S11 to S12:

[0043] S11, When the Fizeau interferometer is at its ideal focal plane, the interference fringe image with the highest spatial resolution can be obtained. Therefore, adjust the defocusing amount Δz of the Fizeau interferometer to the point where the intensity map is clearest. This is the focused state, and the interference image at this point is captured. The intensity of the interference image at pixel (x,y) in the focused state is expressed as:

[0044]

[0045] In the above formula, A(x,y) is the background light intensity, and B(x,y) is the modulation index. This is the phase that contains information about the lateral structure of the sample surface.

[0046] In this step, the key role of the focused state lies in utilizing its high-resolution fringe distribution. To accurately identify the structural boundaries and geometric features of discontinuous surfaces (specifically, in this embodiment, the precise location and shape of vacuum suction cup holes and / or bosses).

[0047] S12, utilizing Accurately identify the structural boundaries and geometric features of the sample surface to obtain high-precision two-dimensional structural information (XY information):

[0048]

[0049] In the above formula, λ represents the wavelength of the light source. h represents the initial phase of the system. focus (x,y) represents the height, h focus (x,y) is used only to characterize the horizontal and vertical coordinates in two-dimensional structural information and not to characterize the surface morphology height of the sample.

[0050] S20, Adjust the defocus amount Δz to the degree that corresponds to a blurred light intensity map but a smooth surface shape in the interference image, thereby extracting the height information of the sample surface. This specifically includes the following sub-steps S21 to S23:

[0051] S21, the Fizeau interferometer is defocused along the optical axis by Δz, thus introducing a defocused wavefront aberration. Its pupil function is:

[0052]

[0053] In the above formula, u and v represent the horizontal and vertical coordinates of the pupil plane, respectively, P0(u,v) represents the ideal circular pupil function, i represents the imaginary unit, and W... 20 This is the defocus coefficient.

[0054] S22, after determining the pupil function P(u,v) by Δz, the modulation transfer function MTF(f; Δz) of the system is obtained through its autocorrelation.

[0055] S23, Select the characteristic frequency f corresponding to the period of the measured structure of the sample. c Then, let MTF(f) c ; Δz)≥γ, thus solving for the maximum value of Δz, denoted as Δz max The threshold γ is determined by the system noise.

[0056] S24, controlling the actual defocusing amount of the Fizeau interferometer to Δz max The light intensity of the interference image in the defocused state at this time is expressed as:

[0057]

[0058] In the above formula, A'(x,y) is the background light intensity, and B'(x,y) is the modulation index. This is the phase of the defocused state.

[0059] S25 is solved using the phase unwrapping algorithm. This leads to the acquisition of altitude information h. defocus (x,y):

[0060]

[0061] S30, transfer the two-dimensional structural information h focus (x,y) and height information h defocus The three-dimensional contour of the sample surface is obtained by performing a two-state fitting on (x,y), which is used to reconstruct the three-dimensional morphology of the sample surface.

[0062] This embodiment also provides a dual-state interferometric topography measurement system for discontinuous precision surfaces, which uses the DSIP method in this embodiment, including a Fizeau interferometer, a defocus control module, an image processing unit, and a data fusion module.

[0063] The defocus control module is used to control the defocus amount Δz of the Fizeau interferometer according to the threshold of MTF according to the method of steps S10 to S20.

[0064] The image processing unit is used to perform dual-state image acquisition, phase calculation, and feature extraction according to steps S10 to S20 during the defocusing process of the Fizeau interferometer.

[0065] The data fusion module is used to perform dual-state fitting of two-dimensional structural information and height information according to the method in step S30, and reconstruct the three-dimensional morphology of the sample surface.

[0066] Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for measuring the two-state interferometric topography of a discontinuous precision surface, characterized in that, The surface shape measurement of a sample with a discontinuous precision surface using a Fizeau interferometer includes the following steps: S10, acquire the interference image of the sample with a discontinuous precision surface in the focused state of the Fizeau interferometer, thereby extracting the two-dimensional structural information of the sample surface; S20, adjust the defocus amount Δz of the Fizeau interferometer to the degree that the light intensity map corresponding to the interference image is blurred but the interference image can present a smooth surface shape, obtain the interference image under this defocus state, and thereby extract the height information of the sample surface; S30, the two-dimensional structural information and the height information are fitted in a dual-state manner to reconstruct the three-dimensional morphology of the sample surface.

2. The method for measuring the dual-state interferometric topography of discontinuous precision surfaces according to claim 1, characterized in that: in, Step S10 includes the following sub-steps: S11, the light intensity at pixel (x,y) of the interference image in the focused state is expressed as: In the above formula, A(x,y) is the background light intensity, and B(x,y) is the modulation index. This is a phase that contains information about the lateral structure of the sample surface; S12, utilizing Accurately identify the structural boundaries and geometric features of the sample surface to obtain two-dimensional structural information: In the above formula, λ represents the wavelength of the light source. h represents the initial phase of the system. focus (x,y) represents the height, h focus (x,y) is used only to characterize the horizontal and vertical coordinates in the two-dimensional structural information and not to characterize the surface morphology height of the sample.

3. The method for measuring the two-state interferometric topography of discontinuous precision surfaces according to claim 1 or 2, characterized in that: in, In step S10, the two-dimensional structural information includes the location, shape, and spatial distribution of the holes and / or protrusions on the sample surface.

4. The method for measuring the dual-state interferometric topography of discontinuous precision surfaces according to claim 1, characterized in that: in, Step S20 includes the following sub-steps: S21, the Fizeau interferometer is defocused along the optical axis by Δz, thereby introducing a defocused wavefront aberration, and its pupil function is: In the above formula, u and v represent the horizontal and vertical coordinates of the pupil plane, respectively, P0(u,v) represents the ideal circular pupil function, i represents the imaginary unit, and W... 20 This is the defocus coefficient. S22, after determining the pupil function P(u,v) by Δz, the modulation transfer function MTF(f; Δz) of the system is obtained through its autocorrelation; S23, Select the characteristic frequency f corresponding to the period of the measured structure of the sample. c Then, let MTF(f) c ; Δz)≥γ, thus solving for the maximum value of Δz, denoted as Δz max The threshold γ is determined by the system noise. S24, control the actual defocusing amount of the Fizeau interferometer to Δz max The light intensity of the interference image in the defocused state at this time is expressed as: In the above formula, A'(x,y) is the background light intensity, and B'(x,y) is the modulation index. The phase is in the defocus state; S25 is solved using the phase unwrapping algorithm. This leads to the acquisition of altitude information h. defocus (x,y):

5. A two-state interferometric topography measurement system for discontinuous precision surfaces, characterized in that, The method for measuring the two-state interferometric topography of discontinuous precision surfaces using any one of claims 1 to 4 includes: Fizeau interferometer; The defocus control module is used to control the defocus amount Δz of the Fizeau interferometer according to the MTF threshold. The image processing unit is used for dual-state image acquisition, phase calculation, and feature extraction during the defocusing process of the Fizeau interferometer; and The data fusion module is used to perform dual-state fitting between the two-dimensional structural information and the height information to reconstruct the three-dimensional morphology of the sample surface.

Images