Height difference determination method for shadow moire single-step phase shift amount

Abstract

The invention relates to the field of optical detection, and relates to a height difference determination method for shadow moire single-step phase shift amount. Adopting a detected sample, placing the sample at a first position, and obtaining a first shadow moire image of the sample; moving the sample or the grating for any distance, and acquiring a second shadow moire image of the sample; performing self-convolution or mutual convolution processing on the first shadow moire image and / or the second shadow moire image to obtain a self-convolution value or a mutual convolution value; according to two adjacent maximum or minimum values of the self-convolution value and the mutual convolution value, the pixel number of the shadow moire pattern phase shift for one period is obtained; and according to the position difference of the maximum value or the minimum value, the phase shift amount of the moving distance is obtained, and then the height difference of the moving grating or the objective table required by single-step phase shift is calculated. According to the method, the single-step phase shift amount of four-step phase shift or three-step phase shift and the like of the shadow moire pattern image can be accurately obtained, and the phase and height distribution of the sample can be obtained.

Description

Technical Field

[0001] The present disclosure relates to the field of optical detection, and more particularly to a method for detecting the three-dimensional shape of materials such as semiconductor materials, chips, PCBs, and three-dimensional models. Specifically, the method relates to a method for determining the height difference of a single-step phase shift of a shadow moiré pattern. Background Art

[0002] Shadow moiré is a 3D topography detection method that can be applied to large-scale objects, such as meter-scale figures, aircraft, or car models, as well as small-scale objects (mm-cm scale) such as PCBs, panels, stacked chips, fan-out wafers, and other semiconductor materials. Shadow moiré features a simple structure and can be easily integrated into ovens, making it suitable for detecting chip warpage during reflow soldering. A shadow moiré system primarily consists of a light source, a grating, and a camera. Light from the light source passes through the grating and illuminates the sample, casting a shadow. The shadow of the sample and the grating fringe period are similar, but not identical. The superposition of these shadow moiré patterns creates shadow moiré. Mathematically, this is equivalent to multiplying two sine functions with similar frequencies to produce a modulated signal. The low-frequency component of this modulated signal is the shadow moiré pattern, because the camera's resolution cannot distinguish high-frequency signals. Even if the camera can capture the high-frequency signal, only the low-frequency modulated signal is required, requiring the camera-captured image to be low-frequency filtered. By shifting the sample (or grating) height z and / or the light source-camera distance b, we can obtain a four-step phase-shifted image of the shadow moiré pattern. Each phase shift is π / 2 (other phase shifts, such as 2π / 3, are also possible). This four-step phase shift method allows us to calculate the phase of the sample under test. De-phasing this phase yields the sample's phase distribution, and thus its height distribution.

[0003] To accurately calculate the phase distribution using the four-step phase shift method, the phase shift in each step must be precisely controlled to π / 2. The phase shift is dependent on the light source height, camera height, light source-camera distance, sample-to-grating height, and the sample's horizontal position. Based on these parameters, the phase shift can be approximately estimated using a formula. However, most of these parameters, such as the sample-to-grating height, light source, and camera height, cannot be accurately determined. Therefore, only rough estimates are possible, resulting in inaccurate results. Summary of the Invention

[0004] The present invention claims protection for a method for determining the height difference of a single-step phase shift of a shadow moiré pattern, characterized by comprising:

[0005] Using a verified sample, placing the sample at a first position, and acquiring a first shadow moiré image of the sample;

[0006] Moving the sample or the grating by an arbitrary distance less than a phase shift of one period, and acquiring a second shadow moiré image of the sample;

[0007] Performing a self-convolution process on the first shadow moiré image to obtain a self-convolution value, and performing a cross-convolution or cross-correlation process on the first shadow moiré image and the second shadow moiré image to obtain a cross-convolution value;

[0008] Obtaining the number of pixels of the shadow moiré phase shifted by one period according to two adjacent maximum or minimum values ​​of the self-convolution value and the cross-convolution value;

[0009] Obtaining a phase shift of the moving distance dz according to a position difference between a maximum value or a minimum value of the self-convolution value and the cross-convolution value, wherein the unit of the position difference is the number of pixels;

[0010] Based on the given phase shift amount, the height difference of the grating or stage required to be moved is calculated.

[0011] Furthermore, it is preferred that: before performing the self-convolution processing on the first shadow moiré image and the inter-convolution processing on the first shadow moiré image and the second shadow moiré image, performing smoothing and noise reduction processing on the first shadow moiré image and the second shadow moiré image;

[0012] The smoothing and noise reduction processing is one or more of mean filtering, Gaussian filtering, median filtering or filtering with a custom kernel.

[0013] Furthermore, the performing of self-convolution processing on the first shadow moiré image to obtain a self-convolution value, and performing cross-convolution or cross-correlation processing on the first shadow moiré image and the second shadow moiré image to obtain a cross-convolution value may preferably include:

[0014] Selecting cross-sectional data in the x-direction of the first shadow moiré image to perform autoconvolution or autocorrelation processing, and selecting cross-sectional data at the same position as that of the first shadow moiré image to perform cross-convolution or cross-correlation processing on the second shadow moiré image;

[0015] The two-dimensional data of the first shadow moiré image is subjected to autoconvolution or autocorrelation processing, and the two-dimensional image data of the second shadow moiré image at the same position as that of the first shadow moiré image is subjected to cross-convolution or cross-correlation processing, and then the cross-line data at the same position is selected.

[0016] Furthermore, obtaining the number of pixels of the shadow moiré phase shifted by one period based on two adjacent maximum or minimum values ​​of the self-convolution value and the cross-convolution value may preferably include:

[0017] Determine the distance dx(π) of x corresponding to half a period based on the positions of two adjacent maxima and minima of the self-convolution and cross-convolution values; calculate the distance dx(2π)=2dx(π) of x corresponding to one period, where dx(π) and dx(2π) represent the distances of x corresponding to half a period and one period of the shadow moiré image;

[0018] The phase shift amount of the moving distance dz is obtained according to the position difference between the maximum value or the minimum value of the self-convolution value and the cross-convolution value, specifically including:

[0019] The phase shift dp0 corresponding to the stage or grating movement dz0 can be obtained from the position difference dx0 between the maximum value of the self-convolution value and the maximum value of the cross-convolution value in the x direction:

[0020] dp0=2π*dx0 / dx(2π)(1);

[0021] The step of calculating the height difference of the required moving grating or stage based on the given phase shift amount specifically includes:

[0022] The height of the sample (or) grating that needs to be moved for a given phase shift is:

[0023] dz(π / 2)=(π / 2)*dz0 / dp0(2);

[0024] dz(2π / 3)=(2π / 3)*dz0 / dp0(3);

[0025] dz(2π)=2π*dz0 / dp0(4).

[0026] Furthermore, it is preferred that: the range of the cross-section data in the x-direction is selected to be data of one period or multiple periods;

[0027] When determining the maximum and / or minimum position of the self-convolution value or the cross-convolution value, first interpolate the convolution result;

[0028] The interpolation method is linear interpolation, spline interpolation or high-order function interpolation;

[0029] When determining the maximum and / or minimum positions of the self-convolution value or the cross-convolution value, directly select the x-coordinate of the point where the convolution value is maximum or minimum, in pixels, or perform sinusoidal function fitting on the convolution and calculate the maximum and minimum positions from the fitting parameters;

[0030] The calculation of the shadow moiré phase shift dp0 corresponding to the stage or grating moving height dz0 is calculated from the original shadow moiré image;

[0031] The phase shift corresponding to the moving height dz0 is obtained according to the ratio of the x distance that the original shadow moiré moves due to the moving height dz0 to the x distance of one period.

[0032] The present invention relates to the field of optical detection, and relates to a method for determining the height difference of a single-step phase shift of a shadow moiré pattern. A calibrated sample is placed at a first position to obtain a first shadow moiré image of the sample; the sample or grating is moved an arbitrary distance to acquire a second shadow moiré image of the sample; the first shadow moiré image and / or the second shadow moiré image are subjected to self-convolution or inter-convolution processing to obtain a self-convolution value or inter-convolution value; the number of pixels per cycle of the shadow moiré phase shift is obtained based on two adjacent maximum or minimum values ​​of the self-convolution value or inter-convolution value; the phase shift amount of the moving distance dz is obtained based on the positional difference of the maximum or minimum value, and the height difference of the required moving grating or stage is calculated. The present invention can accurately obtain the single-step phase shift amount of a shadow moiré pattern image, such as a four-step phase shift or a three-step phase shift, and obtain the phase and height distribution of the sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a flowchart of a method for determining the height difference of a single-step phase shift of a shadow moiré pattern as claimed in the present invention;

[0034] Figure 2 A schematic diagram of the structure of a shadow moiré optical system for a method for determining the height difference of a single-step phase shift of a shadow moiré as claimed in the present invention;

[0035] Figure 3 Schematic diagrams of shadow moiré images p1 and p2 taken at positions z1 and z2 of a stage / sample in a method for determining height difference of a single-step phase shift of shadow moiré as claimed in the present invention;

[0036] Figure 4 Multiple periodic cross-sectional diagrams of p1 and p2 in the horizontal direction (x direction) of a method for determining the height difference of a single-step phase shift of a shadow moiré claimed in the present invention; wherein the abscissa is x length (unit: pixel), and the ordinate is intensity (unit: grayscale value).

[0037] Figure 5 Schematic diagram of the results of self-convolution of horizontal section data of p1 and mutual convolution of horizontal section data of p1 and p2 in a method for determining the height difference of single-step phase shift of shadow moiré claimed in the present invention; wherein the horizontal coordinate is x-length (unit: pixel); the vertical coordinate is convolution value (arbitrary unit).

[0038] Figure 6Schematic diagram of sample height measurement results for a method for determining the height difference of a single-step phase shift of shadow moiré patterns claimed in the present invention; wherein the x, y coordinates (horizontal direction): length (unit: pixel); the vertical coordinate: height value (unit: mm)

[0039] Figure 7 This is a horizontal x-direction cross-section of the sample height measurement results of the method for determining the height difference of the single-step phase shift of the shadow moiré pattern claimed in the present invention; the abscissa is the x-direction length (unit: mm); the ordinate is the height value (unit: mm)

[0040] Figure 8 This is a module structure diagram of a height difference device for single-step phase shift of shadow moiré that is claimed for protection by the present invention. DETAILED DESCRIPTION

[0041] According to the first embodiment of the present invention, referring to the attached Figure 1 The present invention claims a method for determining the height difference of a single-step phase shift of a shadow moiré pattern, comprising:

[0042] Using a verified sample, placing the sample at a first position, and acquiring a first shadow moiré image of the sample;

[0043] Moving the sample or the grating by an arbitrary distance less than a phase shift of one period, and acquiring a second shadow moiré image of the sample;

[0044] Performing a self-convolution process on the first shadow moiré image to obtain a self-convolution value, and performing a cross-convolution or cross-correlation process on the first shadow moiré image and the second shadow moiré image to obtain a cross-convolution value;

[0045] According to the two adjacent maximum or minimum values ​​of the self-convolution value and the cross-convolution value, the number of pixels of the shadow moiré phase shifted by one period is obtained;

[0046] The phase shift of the moving distance dz is obtained based on the position difference of the maximum or minimum values ​​of the self-convolution value and the cross-convolution value. The unit of the position difference here is the number of pixels.

[0047] Calculate the height difference required to move the grating or stage based on the given phase shift.

[0048] Figure 2It is a structural schematic diagram of the shadow moiré optical system for the method for determining the height difference of the single-step phase shift of the shadow moiré claimed for protection in the present invention, which includes a light source 1, a camera 2, a grating 3 located below the camera 2, and a sample 5 placed on a stage 4. The light source height is h1, the camera height is h2, the distance between the light source and the camera is b, z1 and z2 are different heights of the stage (i.e., the sample), dz0 is the height of the stage movement, α is the light source angle, and β is the camera angle.

[0049] In this embodiment, for qualitative analysis, the light source can be regarded as parallel light, so Figure 2 The angle α shown is the same at any position on the grating 3 and is a constant. The camera angle β can be considered as 0 degrees. However, the actual measurement range of the shadow moiré method can reach about 500mm*500mm. The production of parallel light of such a large size is extremely expensive in terms of engineering technology. Therefore, a point light source (or line light source) can be used in practical applications. Figure 2 The angle α shown varies at different locations on grating 3. Similarly, the camera angle β also varies along grating 3. Furthermore, the height dz of the sample (or grating) phase shift varies with the sample height z from the grating. When appropriate parameters are selected, such as the light source height h1, camera height h2, the distance b between the light source and camera, the sample height z from the grating, and the grating pitch p, the sample (or grating) phase shift height dz is virtually independent of the sample height z from the grating.

[0050] Therefore, the present invention first rationally selects the shadow moiré system's light source height h1, camera height h2, light source-camera distance b, sample-grating distance z, and grating pitch p, ensuring that the shadow moiré phase shift is proportional to the distance the sample (or grating) moves. In other words, the shadow moiré phase shift remains the same when the sample moves the same height dz at any distance z.

[0051] Furthermore, it is preferable to include performing smoothing and noise reduction processing on the first shadow moiré image and the second shadow moiré image before performing the self-convolution processing on the first shadow moiré image and the inter-convolution processing on the first shadow moiré image and the second shadow moiré image;

[0052] The smoothing noise reduction process is one or more of mean filtering, Gaussian filtering, median filtering, or filtering with a custom kernel.

[0053] Further, performing self-convolution processing on the first shadow moiré image to obtain a self-convolution value, and performing cross-convolution or cross-correlation processing on the first shadow moiré image and the second shadow moiré image to obtain a cross-convolution value, preferably may include:

[0054] The cross-section data in the x-direction of the first shadow moiré image is selected for autoconvolution or autocorrelation processing, the cross-section data at the same position as the selected first shadow moiré image is selected for cross-convolution or cross-correlation processing, the two-dimensional data of the first shadow moiré image is self-convolution or autocorrelation processed, the two-dimensional image data at the same position as the selected first shadow moiré image is selected for cross-convolution or cross-correlation processing, and then the cross-section data at the same position is selected.

[0055] In this embodiment, after the optical system parameters are determined, the sample is first placed on the stage at a height of z1, and a shadow moiré image p1 is captured. The stage is then moved to an arbitrary height dz0, so that the stage moves to a height of z2, and another shadow moiré image p2 is captured. The stage movement height dz0 should cause the phase period of the shadow moiré image to shift by less than one cycle. Preferably, the height dz(2π) to which the phase shift should be shifted by one cycle can be visually estimated first, and then the height difference dz(π / 2), dz(π / 3), or dz(2π / 3) corresponding to a phase shift (e.g., π / 2, π / 3, or 2π / 3) can be arbitrarily selected. dz(2π), dz(π / 2), dz(π / 3), and dz(2π / 3) represent the heights dz to which the shadow moiré should shift by one cycle, a quarter cycle, one-sixth cycle, and one-third cycle, respectively. Afterwards, the cross-section data in the x direction of the shadow moiré image piece p1 is selected for self-convolution (or autocorrelation) processing, and the cross-section data at the same position as that of p1 is selected for shadow moiré image p2 for cross-convolution (or cross-correlation) processing of p1 and p2.

[0056] Furthermore, the number of pixels of the shadow moiré phase shifted by one period is obtained based on two adjacent maximum or minimum values ​​of the self-convolution value and the cross-convolution value, which may preferably include:

[0057] The distance dx(π) of x corresponding to half a period is determined by the positions of two adjacent maxima and minima of the self-convolution and cross-convolution values. The distance dx(2π) of x corresponding to one period is calculated to be 2dx(π). dx(π) and dx(2π) represent the distances of x corresponding to half a period and one period of the shadow moiré image.

[0058] The phase shift of the moving distance dz is obtained based on the position difference of the maximum or minimum values ​​of the self-convolution value and the cross-convolution value, which specifically includes:

[0059] The phase shift dp0 corresponding to the stage or grating movement dz0 can be obtained from the position difference dx0 between the maximum value of the self-convolution value and the maximum value of the cross-convolution value in the x direction:

[0060] dp0=2π*dx0 / dx(2π)(1);

[0061] Calculate the required height difference of the grating or stage based on the given phase shift, including:

[0062] The height of the sample (or) grating that needs to be moved for a given phase shift is:

[0063] dz(π / 2)=(π / 2)*dz0 / dp0(2);

[0064] dz(2π / 3)=(2π / 3)*dz0 / dp0(3);

[0065] dz(2π)=2π*dz0 / dp0(4).

[0066] Furthermore, it is preferred that the range of the cross-section data in the x-direction be selected to include data of one period or multiple periods;

[0067] Preferably, in order to avoid selecting multiple maxima (or minima) while ensuring that the convolution of p1 and p2 has at least one maximum and one minimum, the cross-sectional data in the x direction can be selected to be slightly less than one cycle but greater than half a cycle.

[0068] When determining the maximum and / or minimum positions of the self-convolution value or the cross-convolution value, the convolution result is first interpolated;

[0069] The interpolation method is linear interpolation, spline interpolation or high-order function interpolation;

[0070] When determining the maximum and / or minimum positions of the self-convolution value or the cross-convolution value, the x-coordinate of the point where the convolution value is maximum or minimum is directly selected in pixels, or a sine function is fitted to the convolution and the maximum and minimum positions are calculated from the fitting parameters;

[0071] The calculation of the shadow moiré phase shift dp0 corresponding to the stage or grating moving height dz0 is calculated from the original shadow moiré image;

[0072] The phase shift corresponding to the moving height dz0 is obtained according to the ratio of the x distance that the original shadow moiré moves due to the moving height dz0 to the x distance of one period.

[0073] In the specific embodiment, according to the attached Figure 2Build a shadow moiré optical system. Select appropriate parameters. Place the sample on the stage, move the height of the sample, and visually observe that the shadow moiré image needs to be moved by the sample (or grating) height dz (2π visually). Therefore, the sample single-step phase shift is dz (π / 2 visually). Move the stage (sample) to the height z1 and take a shadow moiré image p1. Then move the stage (sample) to the height dz0 = dz (π / 2 visually), move the stage to the height z2, and take another shadow moiré image p2 (see attached). Figure 3 ). Select the cross-section data in the x direction for the shadow moiré image piece p1 (see Appendix Figure 4 ) to perform self-convolution (or autocorrelation) processing (see Appendix Figure 5 ), select the cross-section data at the same position as that selected by p1 for the shadow moiré image p2 (see Appendix Figure 4 ) to perform cross-convolution (or cross-correlation) of p1 and p2 (see Appendix Figure 5 ). From the positions of the maximum and minimum values ​​of the mutual convolution, it can be obtained that the horizontal distance of half a cycle is dx(π) pixels, and the position deviation of the maximum values ​​of self-convolution and mutual convolution is dx0 pixels, so dp0=π*dx0 / dx(π)=0.4927*π. dz(π / 2convolution)=(π / 2)*dz(π / 2visual observation) / dp0=1.0148*dz(π / 2visual observation). Therefore, the sample movement height corresponding to a quarter of a single-step phase shift under this parameter is dz(π / 2convolution). In this embodiment, the aberration between the visual inspection result and the convolution measurement result is less than 0.1um. It can be seen that for cases where the accuracy requirements are not too high, the visual inspection result is also accurate enough. However, for cases where the measurement accuracy requirements are relatively high, the convolution measurement method should be used.

[0074] For different optical system parameters, the comparison between the visual inspection results and the convolution measurement results of the sample movement height dz corresponding to the quarter-cycle single-step phase shift shows that in most cases, the difference between the visual inspection results and the convolution measurement results is about 1-2um (in fact, the repeatability accuracy of most reasonably priced motors is also around ±1um), and the maximum does not exceed 5um. Therefore, when the measurement accuracy requirements are not particularly high, the visual inspection results are accurate enough. However, for situations where the measurement accuracy requirements are relatively high, the convolution measurement method should be used.

[0075] After determining the sample movement height dz corresponding to the single-step phase shift of the four-step phase shift method, a tilted sample with a length of 100mm and a height of 5mm was measured. The results are shown in the attached Figure 6 and attached Figure 7 . It can be seen that the height measurement result is accurate.

[0076] According to the second embodiment of the present invention, referring to the attached Figure 8The present invention claims protection for a height difference determination device for a single-step phase shift of a shadow moiré pattern, comprising:

[0077] An image acquisition module uses a calibrated sample, places the sample at a first position, acquires a first shadow moiré image of the sample, moves the sample or the grating an arbitrary distance less than a phase shift of one period, and acquires a second shadow moiré image of the sample;

[0078] a convolution processing module, performing self-convolution processing on the first shadow moiré image to obtain a self-convolution value, and performing cross-convolution or cross-correlation processing on the first shadow moiré image and the second shadow moiré image to obtain a cross-convolution value;

[0079] A phase shift determination module calculates the number of pixels in a shadow moiré phase shift cycle based on two adjacent maxima or minima of the self-convolution and inter-convolution values, and calculates the phase shift over the moving distance dz based on the positional difference between the maxima or minima of the self-convolution and inter-convolution values.

[0080] The height difference calculation module calculates the height difference of the required moving grating or stage based on the given phase shift amount.

[0081] Furthermore, it is preferred that the method includes performing a smoothing noise reduction process on the first shadow moiré image and the second shadow moiré image before performing the self-convolution process on the first shadow moiré image and the inter-convolution process on the first shadow moiré image and the second shadow moiré image;

[0082] The smoothing noise reduction process is one or more of mean filtering, Gaussian filtering, median filtering, or filtering with a custom kernel.

[0083] Furthermore, the convolution processing module may preferably include:

[0084] The cross-section data in the x-direction of the first shadow moiré image is selected for autoconvolution or autocorrelation processing, and the cross-section data at the same position as that selected by the first shadow moiré image is selected for cross-convolution or cross-correlation processing. The two-dimensional data of the first shadow moiré image is self-convolved or autocorrelated, and the two-dimensional image data at the same position as that selected by the first shadow moiré image is selected for cross-convolution or cross-correlation processing, and then the cross-section data at the same position is selected.

[0085] Furthermore, the phase shift determination module may preferably include:

[0086] The distance dx(π) of x corresponding to half a period is determined by the positions of two adjacent maxima and minima of the self-convolution and cross-convolution values. The distance dx(2π) of x corresponding to one period is calculated to be 2dx(π). dx(π) and dx(2π) represent the distances of x corresponding to half a period and one period of the shadow moiré image.

[0087] The phase shift dp0 corresponding to the stage or grating movement dz0 can be obtained from the position difference dx0 between the maximum value of the self-convolution value and the maximum value of the cross-convolution value in the x direction:

[0088] dp0=2π*dx0 / dx(2π)(1);

[0089] Height difference calculation module, specifically including:

[0090] The height of the sample (or) grating that needs to be moved for a given phase shift is:

[0091] dz(π / 2)=(π / 2)*dz0 / dp0(2);

[0092] dz(2π / 3)=(2π / 3)*dz0 / dp0(3);

[0093] dz(2π)=2π*dz0 / dp0(4).

[0094] Furthermore, it is preferred that the range of the cross-section data in the x-direction be selected to include data of one period or multiple periods;

[0095] When determining the maximum and / or minimum positions of the self-convolution value or the cross-convolution value, the convolution result is first interpolated;

[0096] The interpolation method is linear interpolation, spline interpolation or high-order function interpolation;

[0097] When determining the maximum and / or minimum positions of the self-convolution value or the cross-convolution value, the x-coordinate of the point where the convolution value is maximum or minimum is directly selected in pixels, or a sine function is fitted to the convolution and the maximum and minimum positions are calculated from the fitting parameters;

[0098] The calculation of the shadow moiré phase shift dp0 corresponding to the stage or grating moving height dz0 is calculated from the original shadow moiré image;

[0099] The phase shift corresponding to the moving height dz0 is obtained according to the ratio of the x distance that the original shadow moiré moves due to the moving height dz0 to the x distance of one period.

[0100] Those skilled in the art will appreciate that the contents disclosed in this disclosure may be subject to various modifications and improvements. For example, the various devices or components described above may be implemented through hardware, software, firmware, or a combination of some or all of the three.

[0101] Flowcharts are used in this disclosure to illustrate the steps of the methods according to the embodiments of the present disclosure. It should be understood that the preceding or following steps do not necessarily need to be performed in exact order. Instead, the various steps may be performed in reverse order or simultaneously. Furthermore, other operations may be added to these processes.

[0102] Those skilled in the art will appreciate that all or part of the steps in the above method can be performed by instructing the relevant hardware through a computer program, and the program can be stored in a computer-readable storage medium, such as a read-only memory, a magnetic disk, or an optical disk. Alternatively, all or part of the steps in the above embodiment can also be implemented using one or more integrated circuits. Accordingly, each module / unit in the above embodiment can be implemented in the form of hardware or in the form of software functional modules. The present disclosure is not limited to any particular combination of hardware and software.

[0103] Unless otherwise defined, all terms used herein have the same meaning as commonly understood by those skilled in the art to which the present disclosure belongs. It should also be understood that terms such as those defined in common dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and should not be interpreted in an idealized or highly formal sense unless expressly defined as such herein.

[0104] The above is an illustration of the present disclosure and should not be considered as a limitation thereof. Although several exemplary embodiments of the present disclosure have been described, it will be readily understood by those skilled in the art that many modifications may be made to the exemplary embodiments without departing from the novel teachings and advantages of the present disclosure. Therefore, all such modifications are intended to be included within the scope of the present disclosure as defined by the claims. It should be understood that the above is an illustration of the present disclosure and should not be considered as limited to the specific embodiments disclosed, and modifications to the disclosed embodiments and other embodiments are intended to be included within the scope of the appended claims. The present disclosure is defined by the claims and their equivalents.

[0105] Throughout this specification, the use of sample terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the exemplary use of these terms does not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0106] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

Claims

1. A method for determining the height difference of a single-step phase shift of a shadow moiré pattern, characterized in that: include: Using a verified sample, placing the sample at a first position, and acquiring a first shadow moiré image of the sample; Moving the sample or the grating by an arbitrary distance less than a phase shift of one period, and acquiring a second shadow moiré image of the sample; Performing a self-convolution process on the first shadow moiré image to obtain a self-convolution value, and performing a cross-convolution or cross-correlation process on the first shadow moiré image and the second shadow moiré image to obtain a cross-convolution value; Obtaining the number of pixels of the shadow moiré phase shifted by one period according to two adjacent maximum or minimum values ​​of the self-convolution value and the cross-convolution value; Obtaining a phase shift of the moving distance according to a position difference between a maximum value or a minimum value of the self-convolution value and the cross-convolution value, wherein the unit of the position difference is the number of pixels; Based on the given phase shift amount, the height difference of the grating or stage required to be moved is calculated.

2. The method for determining the height difference of a single-step phase shift of shadow moiré according to claim 1, wherein: Also includes: Before performing the self-convolution processing on the first shadow moiré image and the inter-convolution processing on the first shadow moiré image and the second shadow moiré image, performing a smoothing and noise reduction processing on the first shadow moiré image and the second shadow moiré image; The smoothing and noise reduction processing is one or more of mean filtering, Gaussian filtering, median filtering or filtering with a custom kernel.

3. The method for determining the height difference of a single-step phase shift of shadow moiré according to claim 1, wherein: The performing self-convolution processing on the first shadow moiré image to obtain a self-convolution value, and performing cross-convolution or cross-correlation processing on the first shadow moiré image and the second shadow moiré image to obtain a cross-convolution value, specifically includes: Selecting cross-sectional data in the x-direction of the first shadow moiré image to perform autoconvolution or autocorrelation processing, and selecting cross-sectional data at the same position as that of the first shadow moiré image to perform cross-convolution or cross-correlation processing on the second shadow moiré image; The two-dimensional data of the first shadow moiré image is subjected to autoconvolution or autocorrelation processing, and the two-dimensional image data of the second shadow moiré image at the same position as that of the first shadow moiré image is subjected to cross-convolution or cross-correlation processing, and then the cross-line data at the same position is selected.

4. The method for determining the height difference of a single-step phase shift of shadow moiré according to claim 1, wherein: The step of obtaining the number of pixels of the shadow moiré phase shifted by one period based on two adjacent maximum or minimum values ​​of the self-convolution value and the cross-convolution value specifically includes: Determine the distance dx(π) of x corresponding to half a period based on the positions of two adjacent maxima and minima of the self-convolution and cross-convolution values; calculate the distance dx(2π)=2dx(π) of x corresponding to one period, where dx(π) and dx(2π) represent the distances of x corresponding to half a period and one period of the shadow moiré image; The phase shift amount of the moving distance dz is obtained according to the position difference between the maximum value or the minimum value of the self-convolution value and the cross-convolution value, specifically including: The phase shift dp0 corresponding to the stage or grating movement dz0 can be obtained from the position difference dx0 between the maximum value of the self-convolution value and the maximum value of the cross-convolution value in the x direction: dp0=2π*dx0 / dx(2π) (1); The step of calculating the height difference of the required moving grating or stage based on the given phase shift amount specifically includes: The height of the sample or grating that needs to be moved for a given phase shift is: dz(π / 2)=(π / 2)*dz0 / dp0 (2); dz(2π / 3)=(2π / 3)*dz0 / dp0 (3); dz(2π)=2π*dz0 / dp0 (4).

5. The method for determining the height difference of a single-step phase shift of shadow moiré according to claim 3, wherein: Also includes: The range of the cross-section data in the x-direction selects one or more cycles of data; When determining the maximum and / or minimum position of the self-convolution value or the cross-convolution value, first interpolate the convolution result; The interpolation method is linear interpolation, spline interpolation or high-order function interpolation; When determining the maximum and / or minimum positions of the self-convolution value or the cross-convolution value, directly select the x-coordinate of the point where the convolution value is maximum or minimum, in pixels, or perform sinusoidal function fitting on the convolution and calculate the maximum and minimum positions from the fitting parameters; The calculation of the shadow moiré phase shift dp0 corresponding to the stage or grating moving height dz0 is calculated from the original shadow moiré image; The phase shift corresponding to the moving height dz0 is obtained according to the ratio of the x distance that the original shadow moiré moves due to the moving height dz0 to the x distance of one period.

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