Shearing interference zooming three-dimensional shape measuring method and measuring system

Abstract

The invention belongs to the related technical field of optical measurement engineering, and discloses a shearing interference zooming three-dimensional shape measurement method and a measurement system. The method comprises the following steps: acquiring diffraction light interference images of a sample at different sample heights, and acquiring an incident light intensity distribution diagram and an incident light phase distribution diagram at the current sample height; performing focusing evaluation on each sampling point in the incident light intensity distribution diagram under each sample height, and determining an incident light intensity distribution diagram and an incident light phase distribution diagram corresponding to the maximum focusing evaluation value of each sampling point; taking the height of the incident light intensity distribution diagram corresponding to the maximum focusing evaluation value of the sampling point relative to the initial image as the height of the sampling point, thereby obtaining the heights of all the sampling points; and calculating the roughness by using the phase in the incident phase distribution diagram corresponding to the maximum focusing evaluation value of the sampling point, so as to obtain the roughness of all the sampling points. According to the invention, the problem of low measurement of morphology and surface roughness of a large-depth sample is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field related to optical measurement engineering. More specifically, it relates to a shear interference zoom three-dimensional topography measurement method and a measurement system. Background Art

[0002] Currently, microstructure measurement methods are mainly divided into two categories: optical and non-optical. Optical measurement methods are widely used due to their non-destructiveness, high measurement efficiency, and environmental adaptability, such as laser confocal method, white light interference method, and auto-zoom. The laser confocal method has extremely high precision and is suitable for point-by-point measurement of objects, capable of providing detailed surface topography information. However, its measurement efficiency is relatively low because it requires point-by-point scanning, which is cumbersome for large-scale measurements and has high requirements for operating equipment. The white light interference method is based on its short coherence length and can achieve rapid measurement, thus performing well in high-precision measurement tasks. It is particularly suitable for the measurement of planar and smooth surfaces, providing high-resolution and high-precision results. However, its drawback is that it has poor effects on samples with severely changing surface shapes and is difficult to meet the measurement requirements of complex structures. The auto-zoom measurement method combines the small depth of field characteristics of the optical system with vertical scanning, enabling it to focus and obtain images at different heights, and then synthesizing the measurement results. This method is flexible and novel and can adapt to samples of different materials and shapes. However, the auto-zoom method has difficulties in measuring smooth surfaces, and although the precision is high, it is limited by sample characteristics.

[0003] The selection of current optical measurement methods depends on specific application requirements and sample characteristics. In this context, it is of great significance to develop a measurement method with high precision, low cost, and wide adaptability. Summary of the Invention

[0004] Aiming at the above defects or improvement requirements of the prior art, the present invention provides a shear interference zoom three-dimensional topography measurement method and a measurement system, which solve the problem of low measurement of the topography and surface roughness of large-depth samples.

[0005] To achieve the above object, according to one aspect of the present invention, a shear interference zoom three-dimensional topography measurement method is provided. The method includes the following steps:

[0006] Obtain the diffraction light interference images of the sample at different sample heights, and obtain the incident light intensity distribution map and the incident light phase distribution map at the current sample height from each interference image;

[0007] Perform focus evaluation on each sampling point in the incident light intensity distribution maps at each sample height, and determine the incident light intensity distribution map and the incident light phase distribution map corresponding to the maximum focus evaluation value of each sampling point;

[0008] The height of the incident light intensity distribution map corresponding to the maximum focus evaluation value of the sampling point relative to the initial image is used as the height of the sampling point, and the heights of all sampling points are obtained therefrom; the roughness of the sampling point is calculated using the phase in the incident phase distribution map corresponding to the maximum focus evaluation value of the sampling point, and the roughnesses of all sampling points are obtained therefrom; the three-dimensional topography of the sample is reconstructed using the heights and roughnesses of all the sampling points.

[0009] Further preferably, the diffracted light interference image is an interference image generated after a pair of spatially orthogonal lights irradiate the surface of the sample.

[0010] Further preferably, the incident light intensity distribution map is obtained by filtering and extracting the spectrum of the 0th-order light from the interference image, and then performing an inverse Fourier transform on the spectrum of the 0th-order light.

[0011] Further preferably, the steps for obtaining the incident light phase distribution map are as follows:

[0012] Filter and extract the spectrum of the 1st-order light from the interference image;

[0013] Perform an inverse Fourier transform and an unwrapping process on the spectrum of the 1st-order light to obtain the shear wavefront in the orthogonal direction;

[0014] Perform wavefront recovery on the shear wavefront in the orthogonal direction.

[0015] Further preferably, the unwrapping method is the row-column method, the spiral scanning method or the minimum norm method.

[0016] Further preferably, the wavefront recovery method is the least squares method, the finite difference method, the Zernike fitting method or the Fourier basis method.

[0017] Further preferably, the focus evaluation function is the gradient evaluation, the Laplacian operator evaluation or the wavelet transform evaluation function.

[0018] Further preferably, the formula for calculating the roughness using the phase is as follows:

[0019]

[0020] where h(x, y) is the surface roughness of the sample, H(x, y) is the recovered phase of the incident light, and θ is the tilt angle of the incident light.

[0021] According to another aspect of the present invention, there is provided a measurement system for performing measurement using the above-mentioned shear interference zoom three-dimensional topography measurement method. The system includes a light source, a condenser lens, a beam splitter, an objective lens, a tube lens and an image acquisition device, wherein:

[0022] The light source is arranged in front of the condenser lens, and the beam splitter is arranged behind the condenser lens for splitting light. The objective lens and the tube lens are respectively arranged on both sides of the beam splitter. One of the two beams of light split from the beam splitter enters the objective lens, and the other enters the tube lens. The objective lens is arranged above the sample to be measured, and the image acquisition device is arranged behind the tube lens. The light reflected from the surface of the sample to be measured forms diffraction interference fringes in the image acquisition device.

[0023] Further preferably, the image acquisition device adopts a four-wave interferometer.

[0024] Generally speaking, compared with the prior art, the above technical solutions conceived by the present invention have the following beneficial effects:

[0025] 1. The present invention extracts the intensity distribution and phase distribution from the interference pattern. Among them, a set of intensity distribution images obtained by scanning recovery are reconstructed by a zoom algorithm to obtain the three-dimensional morphology of the whole sample. The set of phase distribution images obtained by recovery represents the three-dimensional morphology distribution of each layer during the scanning process. The overall morphology size can reach the millimeter level, and the accuracy can reach the sub-micron level. The three-dimensional morphology distribution size of each layer is at the micron level, and the accuracy can reach the sub-nanometer level. The combination of the two realizes the high-precision morphology and surface roughness measurement of large-depth samples.

[0026] 2. The present invention can directly measure the entire plane. For different scale measurement requirements, the algorithm structure and zoom step distance can be adjusted. When the accuracy requirement is high, the zoom step distance is reduced, multiple layers of images are collected, and the four-wave recovery hierarchy surface roughness is used. When the accuracy requirement is low, the zoom step distance is increased, the number of collected images is reduced, and the zoom reconstruction algorithm is used to recover the three-dimensional morphology of the sample, effectively improving the measurement speed. The combination of the two meets different measurement requirements.

[0027] 3. The zoom measurement system of the present invention uses a four-wave interferometer to replace the camera at the end position of the optical path. The image obtained by the system is an interference image carrying the surface information of the sample. The intensity distribution and phase distribution of the incident wavefront are obtained from the interference pattern through the four-wave recovery algorithm.

[0028] 4. The measurement method of the present invention can not only meet the complex and diverse measurement requirements in the semiconductor industry, but also play a role in other industrial and scientific fields, improving production efficiency and product quality. Through continuous technological innovation and integration of various measurement means, future measurement systems can reach new heights in terms of accuracy, speed and adaptability, providing solid support for scientific and technological progress and industrial development. Description of the Drawings

[0029] Figure 1 is a flowchart of the shear interference zoom three-dimensional morphology measurement method constructed according to the preferred embodiment of the present invention;

[0030] Figure 2 is a schematic structural diagram of a measurement system constructed according to a preferred embodiment of the present invention;

[0031] Figure 3 is a schematic diagram of the process for recovering the intensity distribution and phase distribution of a four-wave interference pattern constructed according to a preferred embodiment of the present invention;

[0032] Figure 4 is the recovered phase distribution diagram constructed according to a preferred embodiment of the present invention;

[0033] Figure 5 is the intensity recovery diagram and the fitting curve of the focus evaluation function for the pixel points within the diagram constructed according to a preferred embodiment of the present invention;

[0034] Figure 6 is the reconstructed topographic model of the sample to be measured constructed according to a preferred embodiment of the present invention.

[0035] In all the drawings, the same reference numerals are used to denote the same elements or structures, where:

[0036] 1 - four-wave interferometer, 2 - reflection measurement optical path, 3 - moving sample platform, 4 - tube lens, 5 - beam splitter, 6 - objective lens, 7 - condenser lens group. Detailed implementation manners

[0037] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0038] As Figure 1 shown, a shear interference zoom three-dimensional topography measurement method specifically includes the following steps:

[0039] S1: Test the positions of the sample to be measured when entering and leaving the depth of focus range, set the two absolute positions where the sample to be measured has not entered and has completely left the focus range as the initial position and the end position of the moving platform respectively, determine the platform step distance based on the depth of field parameter of the objective lens, calculate the number of acquired images, and set the initial parameters of the control system;

[0040] After determining the system parameters, acquire a reference image at the initial position, control the moving platform to step, and acquire an interference image after arrival. Repeat the stepping and image acquisition until the platform reaches the preset end position, and the system stops acquisition;

[0041] Acquire a set of sequential interference images of the sample to be measured, and each image corresponds to different vertical position information, such asFigure 3 The figure shows the algorithm flow chart for restoring the incident light intensity image and the phase image from the four-wave lateral shear interference image. By performing spectral filtering and inverse Fourier transform on each interference image, a set of sequential restored intensity images can be obtained. By performing spectral filtering and inverse Fourier transform on each interference image and then performing gradient integration, a set of sequential restored phase images can be obtained. Among them, the restored intensity image performs spectral filtering on the 0th order of the interference image, and the restored phase image performs spectral filtering on two adjacent 1st orders of the interference image. As Figure 4 shown is one of the sequential phase restoration images, which characterizes the surface roughness of the sample;

[0042] S2 performs Fourier transform on each interference image to obtain the frequency domain distribution of the diffracted light, and simultaneously filters and extracts the 0th order light and the 1st order light in the frequency domain; the filtering window functions used include but are not limited to flat-top window, cylindrical mosaic cosine window, Hanning window function, etc.;

[0043] Perform inverse Fourier transform on the filtered 0th order light to obtain the incident light intensity distribution map corresponding to each interference image; perform inverse Fourier transform and unwrapping on two adjacent filtered 1st order spectra to obtain the shear wavefront in the orthogonal direction, and then perform wavefront restoration to obtain the incident light phase distribution corresponding to each interference image; the unwrapping methods include but are not limited to row-column method, spiral scanning method, minimum norm method, etc.; the wavefront restoration methods include but are not limited to least squares method, finite difference method, Zernike fitting method, Fourier basis method, etc.;

[0044] S3 performs focus evaluation on the restored sequential intensity images (a set of incident light intensity distribution maps with order), determines the maximum focus evaluation value of each point, and the image acquisition height of the image where the maximum focus evaluation value is located relative to the initial image is the relative height of this point, and the actual height (the height of each point on the sample surface relative to the initial position) coordinates of each point in the figure are determined by fitting with the focus evaluation function, realizing the reconstruction of the three-dimensional contour of the model; the focus evaluation functions include but are not limited to gradient evaluation, Laplace operator evaluation, wavelet transform evaluation function, etc.;

[0045] Perform a zoom three-dimensional reconstruction algorithm on the obtained set of sequential restored intensity images, use the focus evaluation function to perform focus evaluation on each pixel point, and then use Gaussian curve fitting to fit the best focus position of each pixel point, as Figure 5 shown is the Gaussian fitting curve of pixel points at different heights in the measurement experiment. It can be seen that the fitting curves of two points at different heights obtain the best focus evaluation values at different image positions respectively.

[0046] S4 The restored sequential phase images correspond to the surface roughness at different heights of the sample. Assigning them to the reconstructed three-dimensional contour model can obtain a high-precision reconstruction of the sample morphology; asFigure 6 As shown, the best focus positions of all pixels are traversed to restore the three-dimensional surface topography of the sample to be measured. The calculation formula for roughness is as follows:

[0047]

[0048] Among them, h(x,y) is the surface roughness of the sample, H(x,y) is the restored phase of the incident light, θ is the tilt angle of the incident light. In this invention, vertical measurement is used, so cosθ = 1.

[0049] As Figure 2 shown, a measurement system for a shear interference zoom three-dimensional topography measurement method of this invention. The measurement system is composed of a four-wave interferometer 1, a reflection measurement optical path 2, and a moving sample platform 3. The four-wave interferometer 1 includes four-wave interferometers with different structures such as those based on an improved Hartmann template and a random coding grating. In the embodiment of this invention, the reflection measurement optical path is composed of a tube lens 4, a beam splitter 5, an objective lens 6, and a condenser lens group 7. The reflection measurement optical paths of other structures can also be applied. The light sources that can be used in this system are white light and green light. In the embodiment of this invention, 533nm green light is used as the incident light source of the system. The measurement optical path of the system is: the light beam emitted by the light source passes through the condenser lens group 7, the beam splitter 5, and the objective lens 6 in sequence and then irradiates the surface of the object to be measured on the moving sample stage 3. After being reflected by the object, the optical path passes through the tube lens 4, and the four-wave interferometer 1 collects the light beam carrying the object information and forms an image, and synchronously collects images with the moving sample platform 3 for longitudinal scanning.

[0050] The moving sample platform is a three-axis displacement stage in this patent. Among them, the longitudinal movement is driven by a motor to achieve high-precision longitudinal platform movement. The XY two axes in the horizontal direction are used to adjust the horizontal position of the sample. Its moving displacement stage can use a manual knob or be driven by a motor, and the XY horizontal displacement device can also be not provided.

[0051] The four-wave interferometer is located at the camera position of the reflection measurement optical path. The acquired image is a four-wave wavefront interference pattern. Its original incident light information is restored by an algorithm. The four-wave interference pattern can restore both the intensity information and the phase information of the incident light. Among them, the restored intensity image carries the focus information and is used for the overall three-dimensional reconstruction of the zoom measurement algorithm.

[0052] Those skilled in the art can easily understand that the above is only a preferred embodiment of this invention and is not used to limit this invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of this invention should be included in the protection scope of this invention.

Claims

1. A shear interference zoom three-dimensional topography measurement method, characterized in that, The method includes the following steps: Obtain the diffraction light interference images of the sample at different sample heights, and obtain the incident light intensity distribution map and the incident light phase distribution map at the current sample height from each interference image; Perform focusing evaluation on each sampling point in the incident light intensity distribution maps at each sample height, and determine the incident light intensity distribution map and the incident light phase distribution map corresponding to the maximum focusing evaluation value of each sampling point; Take the height of the incident light intensity distribution map corresponding to the maximum focusing evaluation value of the sampling point relative to the initial image as the height of this sampling point, and thus obtain the heights of all sampling points; Calculate the roughness of this sampling point using the phase in the incident phase distribution map corresponding to the maximum focusing evaluation value of the sampling point, and thus obtain the roughnesses of all sampling points; Reconstruct the three-dimensional topography of the sample using the heights and roughnesses of all sampling points.

2. The shear interference zoom three-dimensional topography measurement method according to claim 1, characterized in that, The diffraction light interference image is an interference image generated after a pair of spatially orthogonal lights irradiate the sample surface.

3. A shear interference zoom three-dimensional topography measurement method according to claim 1 or 2, characterized in that The incident light intensity distribution map is obtained by filtering and extracting the spectrum of the 0th-order light from the interference image, and then performing an inverse Fourier transform on the spectrum of the 0th-order light.

4. The shear interference zoom three-dimensional topography measurement method according to claim 3, characterized in that, The steps for obtaining the incident light phase distribution map are as follows: Filter and extract the spectrum of the 1st-order light from the interference image; Perform an inverse Fourier transform and unwrapping process on the spectrum of the 1st-order light to obtain the shear wavefront in the orthogonal direction; Perform wavefront recovery on the shear wavefront in the orthogonal direction.

5. A shear interference zoom three-dimensional topography measurement method according to claim 4, characterized in that, The method of unwrapping is the row-column method, the spiral scanning method, or the minimum norm method.

6. A shear interference zoom three-dimensional topography measurement method according to claim 4 or 5, characterized in that The method of wavefront recovery is the least squares method, the finite difference method, the Zernike fitting method, or the Fourier basis method.

7. The method for measuring three-dimensional topography by shear interference zoom according to claim 1, characterized in that, The function for focusing evaluation is the gradient evaluation, the Laplacian operator evaluation, or the wavelet transform evaluation function.

8. A shear interference zoom three-dimensional topography measurement method according to claim 1, characterized in that, The formula for calculating roughness using the phase is as follows: where h(x, y) is the surface roughness of the sample, H(x, y) is the recovered phase of the incident light, and θ is the tilt angle of the incident light.

9. A measurement system that performs measurements using the shear interference zoom three-dimensional topography measurement method according to any one of claims 1-8, characterized in that, The system includes a light source, a condenser lens, a beam splitter, an objective lens, a tube lens, and an image acquisition device, where: The light source is arranged in front of the condenser lens, the beam splitter is arranged behind the condenser lens for splitting light, the objective lens and the tube lens are respectively arranged on both sides of the beam splitter, one of the two beams of light split from the beam splitter enters the objective lens, and the other enters the tube lens. The objective lens is arranged above the sample to be measured, and the image acquisition device is arranged behind the tube lens. The light reflected from the surface of the sample to be measured forms diffraction interference fringes in the image acquisition device.

10. The measurement system according to claim 9, characterized in that, The image acquisition device uses a four-wave interferometer.

Images