Electron microscope, centering deviation correction method thereof and computer readable storage medium

Abstract

The invention discloses an electron microscope and a centering deviation correction method thereof, and a computer readable storage medium, and the centering deviation correction method comprises the steps: determining the excitation current of an astigmatism coil, and calculating the centering deviation of the astigmatism coil according to the excitation current of the astigmatism coil and a function relation between the excitation current of the astigmatism coil and an astigmatism centering compensation current; the astigmatism centering compensation current is a current which needs to compensate a centering coil for correcting centering deviation caused by changes of excitation current of the astigmatism coil; and performing current compensation on the centering coil according to the astigmatism centering compensation current. According to the invention, the centering coil can be used for automatically compensating the centering deviation caused by the change of the excitation current of the astigmatism coil, and the image center is almost not moved when the excitation current of the astigmatism coil is changed.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electron microscopy, in particular to an electron microscope, a method for correcting centering deviation of the electron microscope, and a computer readable storage medium. BACKGROUND

[0002] An electron microscope is a high-resolution microscope that uses a focused high-energy electron beam to irradiate a sample surface and obtains surface topography and composition information of the sample by detecting signals generated by the interaction between the incident electron beam and the sample.

[0003] In the electron optical system of an electron microscope, an electron beam is focused on a sample surface by a series of electromagnetic lenses (such as condenser lenses and objective lenses). These electromagnetic lenses may have problems such as uneven magnetic field and manufacturing errors, which may cause astigmatism, i.e., the focusing ability of the electron beam in different directions (usually X and Y directions) is inconsistent, resulting in an electron beam spot that is not a perfect circle but an ellipse or a stretched shape, thereby causing local blurring, stretching or different clarity in different directions of the image. Therefore, astigmatism compensation is needed for the electron microscope. Astigmatism compensation is a key operation for eliminating astigmatism phenomena such as image blurring or stretching distortion by correcting the axial symmetry of the electron beam, and the core lies in the synergistic optimization of hardware calibration and software algorithm. Usually, an astigmatism coil is provided on the electron microscope to perform astigmatism compensation, and by adjusting the excitation current of the astigmatism coil, stretching and distortion in different directions are eliminated.

[0004] In order to accurately focus the electron beam on the target position of the sample, the electron beam is often subjected to centering operation, which aims to regulate the position of the electron beam in the electron optical system so that it is focused on the target position along the ideal optical axis.

[0005] Adjusting the excitation current of the astigmatism coil can only eliminate the influence of astigmatism on the image, but may cause the shift of the electron beam optical axis, resulting in centering deviation and movement of the image center. SUMMARY

[0006] The present application provides a centering deviation correction method for an electron microscope, an electron microscope and a computer readable storage medium to solve the technical problem of electron beam optical axis movement caused by adjusting the excitation current of the astigmatism coil.

[0007] In a first aspect, the present application provides a centering deviation correction method for an electron microscope, comprising:

[0008] determining the excitation current of the astigmatism coil;

[0009] According to the excitation current of the stigmator coil and a function relationship between the excitation current of the stigmator coil and the stigmator centering compensation current, the stigmator centering compensation current is obtained, which is a current needed to compensate the centering coil to correct the deviation of the centering caused by the change of the excitation current of the stigmator coil;

[0010] According to the stigmator centering compensation current, the current compensation is performed on the centering coil.

[0011] In some embodiments, the centering coil includes a first centering coil, and the stigmator centering compensation current of the first centering coil is determined by the following function relationship:

[0012] Align1Xb = stigX * a + stigY * b,

[0013] Align1Yb = stigX * c + stigY * d,

[0014] wherein Align1Xb and Align1Yb respectively represent the stigmator centering compensation current of the first centering coil in X direction and Y direction, stigX and stigY respectively represent the excitation current of the stigmator coil in X direction and Y direction, and a, b, c and d are respectively a first coefficient, a second coefficient, a third coefficient and a fourth coefficient.

[0015] In some embodiments, the first coefficient a, the second coefficient b, the third coefficient c and the fourth coefficient d are determined by the following method:

[0016] a plurality of first reference coefficients are obtained, for each of the first reference coefficients, the stigmator centering compensation current of the first centering coil in X direction is calculated by using the first reference coefficient under different excitation currents of the stigmator coil, a plurality of images are obtained by imaging based on the excitation current of the stigmator coil and the stigmator centering compensation current of the first centering coil in X direction, the image center variation degree of the plurality of images is obtained, a first interval between two first reference coefficients with the minimum image center variation degree is obtained, and a value in the first interval is selected as the first coefficient a;

[0017] a plurality of second reference coefficients are obtained, for each of the second reference coefficients, the stigmator centering compensation current of the first centering coil in X direction is calculated by using the second reference coefficient under different excitation currents of the stigmator coil, a plurality of images are obtained by imaging based on the excitation current of the stigmator coil and the stigmator centering compensation current of the first centering coil in X direction, the image center variation degree of the plurality of images is obtained, a second interval between two second reference coefficients with the minimum image center variation degree is obtained, and a value in the second interval is selected as the second coefficient b;

[0018] a plurality of third reference coefficients are obtained, for each of the third reference coefficients, a Y direction stigmator compensation current of the first pair of middle coils is calculated by using the third reference coefficient under different excitation currents of the stigmator coils, imaging is performed based on the excitation current of the stigmator coils and the Y direction stigmator compensation current of the first pair of middle coils, a plurality of images are obtained, and a degree of change of image centers of the plurality of images is obtained; a third interval between two third reference coefficients with the smallest degree of change of image centers is obtained, and a value in the third interval is selected as the third coefficient c;

[0019] a plurality of fourth reference coefficients are obtained, for each of the fourth reference coefficients, a Y direction stigmator compensation current of the first pair of middle coils is calculated by using the fourth reference coefficient under different excitation currents of the stigmator coils, imaging is performed based on the excitation current of the stigmator coils and the Y direction stigmator compensation current of the first pair of middle coils, a plurality of images are obtained, and a degree of change of image centers of the plurality of images is obtained; a fourth interval between two fourth reference coefficients with the smallest degree of change of image centers is obtained, and a value in the fourth interval is selected as the fourth coefficient d.

[0020] In some embodiments, the calculation of the X direction stigmator compensation current of the first pair of middle coils by using the first reference coefficient under different excitation currents of the stigmator coils and the imaging based on the excitation current of the stigmator coils and the X direction stigmator compensation current of the first pair of middle coils to obtain a plurality of images comprises:

[0021] different variation amounts ΔstigX and different variation amounts ΔstigY are added to the initial excitation currents stigX0 and stigY0 of the stigmator coils respectively to obtain the excitation currents of the stigmator coils;

[0022] the X direction stigmator compensation current Align1Xb is calculated according to the excitation current of the stigmator coils and the first reference coefficient, and the excitation current of the first pair of middle coils in the X direction is calculated according to the initial excitation current Align1X0 and the stigmator compensation current Align1Xb of the first pair of middle coils in the X direction;

[0023] a plurality of images are obtained by imaging a plurality of times based on the excitation current of the stigmator coils and the excitation current of the first pair of middle coils;

[0024] the calculation of the X direction stigmator compensation current of the first pair of middle coils by using the second reference coefficient under different excitation currents of the stigmator coils and the imaging based on the excitation current of the stigmator coils and the X direction stigmator compensation current of the first pair of middle coils to obtain a plurality of images comprises:

[0025] The initial excitation currents stigX0 and stigY0 of the stigmator coils are respectively added with different variation amounts ΔstigX and ΔstigY to obtain the excitation currents of the stigmator coils;

[0026] The stigmator compensation current Align1Xb in the X direction is calculated according to the excitation current of the stigmator coils, the second reference coefficient and the determined first coefficient a, and the excitation current of the first aligner coil in the X direction is calculated according to the initial excitation current Align1X0 of the first aligner coil in the X direction and the stigmator compensation current Align1Xb;

[0027] Multiple imaging is performed based on the excitation current of the stigmator coils and the excitation current of the first aligner coil to obtain multiple different images.

[0028] In some embodiments, the excitation current of the first aligner coil in the X direction is calculated according to the initial excitation current Align1X0 of the first aligner coil in the X direction and the stigmator compensation current Align1Xb, including:

[0029] The excitation current of the first aligner coil in the X direction is calculated by calculating the current sum of the initial excitation current Align1X0 of the first aligner coil in the X direction, the variation amount ΔAlign1X and the stigmator compensation current Align1Xb.

[0030] In some embodiments, the stigmator compensation current of the first aligner coil in the Y direction is calculated according to the third reference coefficient under different excitation currents of the stigmator coils, and multiple images are obtained by imaging based on the excitation current of the stigmator coils and the stigmator compensation current of the first aligner coil in the Y direction, including:

[0031] The initial excitation currents stigX0 and stigY0 of the stigmator coils are respectively added with different variation amounts ΔstigX and ΔstigY to obtain the excitation currents of the stigmator coils;

[0032] The stigmator compensation current Align1Yb in the Y direction is calculated according to the excitation current of the stigmator coils and the third reference coefficient, and the excitation current of the first aligner coil in the Y direction is calculated according to the initial excitation current Align1Y0 of the first aligner coil in the Y direction and the stigmator compensation current Align1Yb;

[0033] Multiple imaging is performed based on the excitation current of the stigmator coils and the excitation current of the first aligner coil to obtain multiple different images;

[0034] the fourth reference coefficient, and the third coefficient c to obtain the stigmator current of the stigmator; and

[0035] the initial stigmator current stigX0 and the initial stigmator current stigY0 of the stigmator are added with different variation amounts ΔstigX and ΔstigY respectively to obtain the stigmator current of the stigmator;

[0036] the fourth reference coefficient, and the third coefficient c to obtain the stigmator current of the stigmator; and

[0037] the initial stigmator current stigX0 and the initial stigmator current stigY0 of the stigmator are added with different variation amounts ΔstigX and ΔstigY respectively to obtain the stigmator current of the stigmator;

[0038] the initial stigmator current stigX0 and the initial stigmator current stigY0 of the stigmator are added with different variation amounts ΔstigX and ΔstigY respectively to obtain the stigmator current of the stigmator;

[0039] the initial stigmator current stigX0 and the initial stigmator current stigY0 of the stigmator are added with different variation amounts ΔstigX and ΔstigY respectively to obtain the stigmator current of the stigmator;

[0040] the initial stigmator current stigX0 and the initial stigmator current stigY0 of the stigmator are added with different variation amounts ΔstigX and ΔstigY respectively to obtain the stigmator current of the stigmator;

[0041] the initial stigmator current stigX0 and the initial stigmator current stigY0 of the stigmator are added with different variation amounts ΔstigX and ΔstigY respectively to obtain the stigmator current of the stigmator;

[0042] The step of selecting a value from the second interval as the second coefficient b includes:

[0043] The process iteratively selects multiple values ​​from the second interval as new second reference coefficients. For each second reference coefficient, under different excitation currents of the astigmatic coil, the astigmatic alignment compensation current in the X direction of the first alignment coil is calculated using the second reference coefficient. Based on the excitation current of the astigmatic coil and the astigmatic alignment compensation current in the X direction of the first alignment coil, imaging is performed to obtain multiple images. The degree of change of the image center of the multiple images is obtained, and the second interval between the two second reference coefficients with the smallest degree of change of the image center is obtained. This process continues until the absolute value of the difference between the two smallest degree of change of the image center is less than the second difference threshold. Finally, a value is selected from the final second interval as the second coefficient b.

[0044] The step of selecting a value from the third interval as the third coefficient c includes:

[0045] The process iteratively selects multiple values ​​from the third interval as new third reference coefficients. For each third reference coefficient, under different excitation currents of the astigmatic coil, the astigmatic centering compensation current in the Y direction of the first centering coil is calculated using the third reference coefficient. Based on the excitation current of the astigmatic coil and the astigmatic centering compensation current in the Y direction of the first centering coil, imaging is performed to obtain multiple images. The degree of change of the image center of the multiple images is obtained, and the third interval between the two third reference coefficients with the smallest degree of change of the image center is obtained. This process continues until the absolute value of the difference between the two smallest degree of change of the image center is less than the third difference threshold. Finally, a value is selected from the final third interval as the third coefficient c.

[0046] The step of selecting a value from the fourth interval as the fourth coefficient d includes:

[0047] The process iteratively selects multiple values ​​from the fourth interval as new fourth reference coefficients. For each fourth reference coefficient, under different excitation currents of the astigmatic coil, the astigmatic alignment compensation current in the Y direction of the first alignment coil is calculated using the fourth reference coefficient. Imaging is performed based on the excitation current of the astigmatic coil and the astigmatic alignment compensation current in the Y direction of the first alignment coil to obtain multiple images. The degree of change of the image center of the multiple images is obtained, and the fourth interval between the two fourth reference coefficients with the smallest degree of change of the image center is obtained. This process continues until the absolute value of the difference between the two smallest degree of change of the image center is less than the fourth difference threshold. Finally, a value is selected from the final fourth interval as the fourth coefficient d.

[0048] In some embodiments, the current compensation of the centering coil according to the stigmator centering compensation current comprises:

[0049] calculating the current sum of the initial excitation current of the first centering coil in the X direction Align1X0 and the stigmator centering compensation current of the first centering coil in the X direction Align1Xb to obtain the excitation current of the first centering coil in the X direction, and inputting the first centering coil;

[0050] calculating the current sum of the initial excitation current of the first centering coil in the Y direction Align1Y0 and the stigmator centering compensation current of the first centering coil in the Y direction Align1Yb to obtain the excitation current of the first centering coil in the Y direction, and inputting the first centering coil.

[0051] In some embodiments, the centering coil further comprises a second centering coil, and the stigmator centering compensation current of the second centering coil is determined according to a functional relationship between the stigmator centering compensation current of the second centering coil and the stigmator centering compensation current of the first centering coil.

[0052] In some embodiments, the second centering coil is an objective lens centering coil, and the functional relationship between the stigmator centering compensation current of the second centering coil and the stigmator centering compensation current of the first centering coil is:

[0053] Align2Xb = a * Align1Xb,

[0054] Align2Yb = β * Align1Yb,

[0055] wherein Align2Xb and Align2Yb represent the stigmator centering compensation current of the objective lens centering coil in the X direction and the Y direction respectively, and a and β represent the fifth coefficient and the sixth coefficient respectively.

[0056] In some embodiments, the fifth coefficient a and the sixth coefficient β are determined by the following method:

[0057] obtaining a plurality of fifth reference coefficients, for each of the fifth reference coefficients, imaging based on the excitation current of the objective lens coil and the stigmator centering compensation current of the second centering coil in the X direction under different excitation currents of the objective lens coil to obtain a plurality of images, obtaining the degree of change of the image center of the plurality of images, selecting a fifth interval between two fifth reference coefficients with the smallest degree of change of the image center, and selecting a value in the fifth interval as the fifth coefficient a;

[0058] a plurality of sixth reference coefficients are obtained, for each of the sixth reference coefficients, a plurality of images are obtained by imaging based on the excitation current of the objective lens coil and the compensation current of the astigmatism of the second pair of middle coils in the Y direction under different excitation currents of the objective lens coil, and a variation degree of image center of the plurality of images is obtained; a sixth interval between two sixth reference coefficients with the smallest variation degree of image center is obtained, and a value in the sixth interval is selected as the sixth coefficient β.

[0059] In some embodiments, a plurality of images are obtained by imaging based on the excitation current of the objective lens coil and the compensation current of the astigmatism of the second pair of middle coils in the X direction under different excitation currents of the objective lens coil, including:

[0060] The excitation current of the objective lens coil is obtained based on the image magnification, the compensation amount OLb and the initial excitation current OL0 of the objective lens coil.

[0061] The compensation current of the astigmatism of the second pair of middle coils in the X direction Align2Xb is calculated according to the compensation current of the astigmatism of the first pair of middle coils Align1Xb and the fifth reference coefficient.

[0062] The excitation current of the second pair of middle coils in the X direction is calculated according to the initial excitation current Align2X0 of the second pair of middle coils in the X direction and the compensation current of the astigmatism of the second pair of middle coils Align2Xb.

[0063] A plurality of different images are obtained by imaging based on the excitation current of the objective lens coil and the excitation current of the second pair of middle coils.

[0064] A plurality of images are obtained by imaging based on the excitation current of the objective lens coil and the compensation current of the astigmatism of the second pair of middle coils in the Y direction under different excitation currents of the objective lens coil, including:

[0065] The excitation current of the objective lens coil is obtained based on the image magnification, the compensation amount OLb and the initial excitation current OL0 of the objective lens coil.

[0066] The compensation current of the astigmatism of the second pair of middle coils in the Y direction Align2Yb is calculated according to the compensation current of the astigmatism of the first pair of middle coils Align1Yb and the sixth reference coefficient.

[0067] The excitation current of the second pair of middle coils in the Y direction is calculated according to the initial excitation current Align2Y0 of the second pair of middle coils in the Y direction and the compensation current of the astigmatism of the second pair of middle coils Align2Yb.

[0068] Based on the excitation current of the objective lens coil and the excitation current of the second centering coil, multiple imaging is performed to obtain multiple different images.

[0069] In some embodiments, the selecting a value from the fifth interval as the fifth coefficient a comprises:

[0070] The selecting multiple values from the fifth interval as new fifth reference coefficients is iteratively performed, for each of the fifth reference coefficients, imaging is performed under different excitation currents of the objective lens coil to obtain multiple images, the image center variation degree of the multiple images is obtained, the step of obtaining the fifth interval between the two fifth reference coefficients with the minimum image center variation degree is performed until the absolute value of the difference between the two minimum image center variation degrees is less than the fifth difference threshold value, and a value is selected from the final fifth interval as the fifth coefficient a.

[0071] The selecting a value from the sixth interval as the sixth coefficient b comprises:

[0072] The selecting multiple values from the sixth interval as new sixth reference coefficients is iteratively performed, for each of the sixth reference coefficients, imaging is performed under different excitation currents of the objective lens coil to obtain multiple images, the image center variation degree of the multiple images is obtained, the step of obtaining the sixth interval between the two sixth reference coefficients with the minimum image center variation degree is performed until the absolute value of the difference between the two minimum image center variation degrees is less than the sixth difference threshold value, and a value is selected from the final sixth interval as the sixth coefficient b.

[0073] In some embodiments, the obtaining the image center variation degree of the multiple images comprises:

[0074] Taking one of the multiple images as a reference image, the displacement amounts of the image centers of the other images relative to the image center of the reference image are calculated and added to obtain the image center variation degree of the multiple images.

[0075] In some embodiments, the current compensation of the centering coil according to the astigmatism centering compensation current comprises:

[0076] The current sum of the initial excitation current Align2X0 of the second centering coil X direction and the astigmatism centering compensation current Align2Xb of the second centering coil X direction is calculated to obtain the excitation current of the second centering coil X direction, and the second centering coil is inputted.

[0077] The sum of the initial excitation current Align2Y0 of the second pair of centering coils in the Y direction and the astigmatism centering compensation current Align2Yb of the second pair of centering coils in the Y direction is calculated to obtain the excitation current of the second pair of centering coils in the Y direction, and the second pair of centering coils is input.

[0078] In a second aspect, the present application provides an electron microscope, comprising an astigmatism coil, a centering coil and a processor, wherein the processor is configured to execute the centering deviation correction method of the first aspect.

[0079] In a third aspect, the present application provides a computer readable storage medium, wherein a computer executable program or instruction is stored in the computer readable storage medium, and the computer executable program or instruction is executed by a processor to implement the centering deviation correction method of the first aspect.

[0080] The centering deviation correction method of the electron microscope, the electron microscope and the computer readable storage medium provided by the present application can establish the functional relationship between the excitation current of the astigmatism coil and the astigmatism centering compensation current in advance, wherein the astigmatism centering compensation current is the current required to compensate the centering coil to correct the centering deviation caused by the change of the excitation current of the astigmatism coil; the astigmatism centering compensation current is obtained according to the excitation current of the astigmatism coil and the functional relationship between the excitation current of the astigmatism coil and the astigmatism centering compensation current, and the current compensation of the centering coil is performed according to the astigmatism centering compensation current, so that when the excitation current of the astigmatism coil changes, the centering deviation caused by the change of the excitation current of the astigmatism coil can be automatically compensated by the centering coil, and the image center can hardly move when the excitation current of the astigmatism coil changes. BRIEF DESCRIPTION OF DRAWINGS

[0081] Figure 1 FIG. 1 is a structural schematic diagram of an electron microscope according to an embodiment;

[0082] Figure 2 FIG. 2 is a flowchart of a centering deviation correction method of an electron microscope according to an embodiment;

[0083] Figure 3 FIG. 3 is a flowchart of determining a first coefficient a in an embodiment;

[0084] Figure 4 FIG. 4 is a flowchart of calculating the astigmatism centering compensation current of the first pair of centering coils in the X direction by using the first reference coefficient under different excitation currents of the astigmatism coil, and imaging based on the excitation current of the astigmatism coil and the astigmatism centering compensation current of the first pair of centering coils in the X direction to obtain multiple images in some embodiments;

[0085] Figure 5is a flow chart of calculating the Y direction stigmator compensation current of the first pair of middle coils using the third reference coefficient under different excitation currents of the stigmator coils in some embodiments, and imaging based on the excitation current of the stigmator coils and the Y direction stigmator compensation current of the first pair of middle coils to obtain multiple images;

[0086] Figure 6 is a flow chart of determining the fifth coefficient a in an embodiment;

[0087] Figure 7 is a flow chart of obtaining multiple images based on the excitation current of the objective lens coils and the X direction stigmator compensation current of the second pair of middle coils under different excitation currents of the objective lens coils in some embodiments. DETAILED DESCRIPTION

[0088] The application will be further described in details through specific embodiments and the accompanying drawings. In different embodiments, similar elements are associated with similar element labels. In the following embodiments, many details are described in order to make the application better understood. However, those skilled in the art can easily recognize that some features can be omitted in different cases, or can be replaced by other elements, materials or methods. In some cases, some operations related to the application are not shown or described in the specification in order to avoid the core part of the application being overwhelmed by too much description, and it is not necessary to describe these related operations in detail for those skilled in the art according to the description in the specification and general technical knowledge in the art.

[0089] In addition, the features, operations or characteristics described in the specification can be combined in any appropriate way to form various embodiments. At the same time, the steps or actions in the method description can also be sequentially adjusted or adjusted in a manner that is obvious to those skilled in the art. Therefore, the order in the specification and the drawings is only for the purpose of clearly describing a certain embodiment, and does not mean that it is the necessary order, unless otherwise stated that a certain order must be followed.

[0090] In this paper, the serial number of a component or physical quantity, such as "first", "second", etc., is only used to distinguish the described object, and has no technical meaning, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of technical features indicated. The meaning of "multiple" is two or more. And the "connection" and "coupling" in the application include direct and indirect connection (coupling) unless otherwise specified.

[0091] Please refer to Figure 1The present application provides an electron microscope, which can be a scanning electron microscope SEM or a critical dimension scanning electron microscope CD-SEM, etc., comprising a condenser, a diaphragm, an objective lens OL, a stigmator, a centering coil and a processor (not shown in the figure). The condenser is used to shrink and shape the beam spot size of the electron beam. In some embodiments, multiple condensers can be provided, such as the condenser CL1 and the condenser CL2 in Figure 1 The diaphragm is used to control the beam current and the convergence angle, and to affect the beam spot size and aberration. The objective lens OL is used to accurately focus the electron beam on the sample surface. The centering coil is used to center the electron beam, and the position of the electron beam is adjusted by adjusting the excitation current of the centering coil. In some embodiments, multiple centering coils can be provided at different positions to center the electron beams at different positions, such as the centering coil Align1 and the centering coil Align2 in Figure 1 The processor is configured to perform the centering deviation correction method of the electron microscope provided by the present application.

[0092] In order to compensate for the centering deviation caused by stigmation adjustment, the centering deviation correction method provided by the present application utilizes the centering coil of the electron microscope, and obtains the stigmation centering compensation current from the excitation current of the stigmator coil according to the functional relationship between the excitation current of the stigmator coil and the stigmation centering compensation current, and inputs the centering coil to compensate or correct the centering deviation. When the excitation current of the stigmator coil changes, the centering coil can automatically correct the centering deviation.

[0093] Please refer to Figure 2 The centering deviation correction method of the electron microscope in some embodiments of the present application comprises steps 10-30, which are described in detail below.

[0094] Step 10: Determine the excitation current of the stigmator coil.

[0095] Any existing stigmation compensation algorithm can be used to determine the excitation current of the stigmator coil.

[0096] Step 20: Obtain the stigmation centering compensation current according to the excitation current of the stigmator coil and the functional relationship between the excitation current of the stigmator coil and the stigmation centering compensation current.

[0097] The astigmatism-on-center compensation current is a current needed to compensate the centering coil for correcting the centering deviation caused by the change of the excitation current of the astigmatism coil. The functional relationship between the excitation current of the astigmatism coil and the astigmatism-on-center compensation current can be established in advance. The astigmatism-on-center compensation current actually needed to compensate the centering coil for realizing the centering of the electron beam under different excitation currents of the astigmatism coil can be collected. The functional relationship between the excitation current of the astigmatism coil and the astigmatism-on-center compensation current is fitted by using the collected data, for example, polynomial fitting.

[0098] The excitation current of the centering coil includes the excitation current in the X direction and the excitation current in the Y direction. Correspondingly, the astigmatism-on-center compensation current can include the astigmatism-on-center compensation current in the X direction and the astigmatism-on-center compensation current in the Y direction. The functional relationship between the excitation current of the astigmatism coil and the astigmatism-on-center compensation current in the X direction and the astigmatism-on-center compensation current in the Y direction can be established respectively, so as to be used for determining the astigmatism-on-center compensation current in the X direction and the astigmatism-on-center compensation current in the Y direction respectively.

[0099] Step 30: compensating the current of the centering coil according to the astigmatism-on-center compensation current.

[0100] Specifically, the excitation current of the centering coil after compensation is the current sum of the initial excitation current for completing the initial centering and the astigmatism-on-center compensation current. Before using the electron microscope to detect the sample, the initial centering can be performed by using the centering coil. Assuming that the initial excitation currents of the centering coil in the X direction and the Y direction are AlignX0 and AlignY0 respectively after the initial centering is performed by using the centering coil, and the astigmatism-on-center compensation currents in the X direction and the Y direction are AlignXb and AlignYb respectively, then the excitation currents of the centering coil in the X direction and the Y direction after the current compensation are AlignX = AlignX0 + AlignXb and AlignY = AlignY0 + AlignYb respectively.

[0101] The centering deviation correction method of the electron microscope provided in the present application uses the centering coil to correct the centering deviation caused by the adjustment of the astigmatism. The functional relationship between the excitation current of the astigmatism coil and the astigmatism-on-center compensation current can be established in advance. Subsequently, the astigmatism-on-center compensation current is obtained according to the excitation current of the astigmatism coil and the functional relationship between the excitation current of the astigmatism coil and the astigmatism-on-center compensation current. The current of the centering coil is compensated according to the astigmatism-on-center compensation current. Therefore, when the excitation current of the astigmatism coil changes, the excitation current of the centering coil also changes to compensate the centering deviation caused by the change of the excitation current of the astigmatism coil, so that the image center can hardly move when the excitation current of the astigmatism coil is changed.

[0102] In some embodiments, the centering coils include a first pair of centering coils, which are preferably arranged near the stigmator coils to directly compensate for the effect of the variation of the excitation current of the stigmator coils. For example, the first pair of centering coils can be Figure 1 Align1 in the above formula, the electron beam can be returned to the center of the diaphragm or the condenser CL2.

[0103] The excitation current of the stigmator coils includes an X-direction excitation current and a Y-direction excitation current. In some embodiments, the stigmator-compensation current of the first pair of centering coils is determined by the following function relationship:

[0104] Align1Xb=stigX*a+stigY*b,

[0105] Align1Yb=stigX*c+stigY*d,

[0106] wherein Align1Xb and Align1Yb represent the X-direction and Y-direction stigmator-compensation currents of the first pair of centering coils, stigX and stigY represent the X-direction and Y-direction excitation currents of the stigmator coils, and a, b, c and d are the first, second, third and fourth coefficients, respectively.

[0107] Please refer to Figure 3 In some embodiments, the first coefficient a is determined by the following steps.

[0108] Step 110: Obtain a plurality of first reference coefficients.

[0109] In one embodiment, the plurality of first reference coefficients can be selected from a preset coefficient interval. For example, the plurality of first reference coefficients can be selected at equal intervals from the coefficient interval. Assuming that the minimum value of the coefficient interval is i and the maximum value is j, five first reference coefficients can be selected by bisection method: i, (j-i) / 4+i, (j-i) / 2+i, j-(j-i) / 4 and j. The minimum value and the maximum value of the coefficient interval and the number of the first reference coefficients can be set as needed.

[0110] Step 120: For each first reference coefficient, the first reference coefficient is used to calculate the X-direction stigmator-compensation current of the first pair of centering coils under different excitation currents of the stigmator coils, imaging is performed based on the excitation currents of the stigmator coils and the X-direction stigmator-compensation current of the first pair of centering coils, a plurality of images are obtained, and the image center variation degree of the plurality of images is obtained.

[0111] Specifically, the exciting current of the astigmatism coil can be adjusted multiple times, and after each adjustment, the astigmatism compensation current Align1Xb of the X direction of the first pair of middle coils is calculated according to Align1Xb=stigX*a+stigY*b, the exciting current of the X direction of the first pair of middle coils is adjusted according to the astigmatism compensation current Align1Xb of the X direction, and the image of the sample is collected under the adjusted exciting current of the astigmatism coil and the exciting current of the first pair of middle coils, so as to obtain multiple images. The second coefficient b can be set to 0, and if the second coefficient b is determined, it can be set to the determined value. The sample can be a round ball or the like.

[0112] For each image, it can be compared with a reference image to determine the degree of change of the image center. Considering that the feature pattern in the image can be stretched, in an embodiment of the present application, the degree of change of the image center is not measured by taking the edge of the image as the reference point, but the distance or displacement of the center of the obvious mark such as the round ball in the image relative to the center of the same mark in the reference image is used to measure the degree of change of the image center.

[0113] In some embodiments, the degrees of change of the image centers of the multiple images are obtained, including: taking one of the multiple images as a reference image, calculating the displacement of the image center of the other images relative to the image center of the reference image and adding them up to obtain the degree of change of the image centers of the multiple images.

[0114] For example, when the first reference coefficient is 0.03, 5 images are collected, denoted as image 1, image 2, image 3, image 4 and image 5, and the displacement of the image center of image 1, image 2, image 4 and image 5 relative to the image center of image 3 is calculated and added up, respectively, taking image 3 as the reference image, then the degree of change of the image center of the first reference coefficient 0.03 is obtained. Assuming that the displacement of the image center of image 1, image 2, image 4 and image 5 relative to the image center of image 3 is 5, 3, 2 and 4 respectively, then the degree of change of the image center is 5+3+2+4=14.

[0115] Step 130: obtaining a first interval between two first reference coefficients with the smallest degree of change of the image center, and selecting a value from the first interval as the first coefficient a.

[0116] For example, five first reference coefficients i, (j-i) / 4+i, (j-i) / 2+i, j-(j-i) / 4 and j are obtained, five images are obtained for each first reference coefficient, the image center variation degree of the five images obtained for each first reference coefficient is obtained, and it is assumed that the image center variation degrees of the first reference coefficients i and (j-i) / 4+i are the smallest, the first interval is [i, (j-i) / 4+i], and a value in the first interval is selected as the first coefficient a. For example, a value in the first interval is randomly selected or the middle value is taken as the first coefficient a.

[0117] Similarly, in some embodiments, the second coefficient b is determined by the following method: a plurality of second reference coefficients are obtained, for each second reference coefficient, the astigmatism compensation current of the first pair of middle coils in the X direction is calculated by using the second reference coefficient under different excitation currents of the astigmatism coil, imaging is performed based on the excitation current of the astigmatism coil and the astigmatism compensation current of the first pair of middle coils in the X direction, a plurality of images are obtained, and the image center variation degree of the plurality of images is obtained; a second interval between two second reference coefficients with the smallest image center variation degree is obtained, and a value in the second interval is selected as the second coefficient b.

[0118] For details, reference can be made to the determination method of the first coefficient a. It should be noted that the determination order of the first coefficient a and the second coefficient b is not limited, the first coefficient a can be determined first and then the second coefficient b, or the second coefficient b can be determined first and then the first coefficient a.

[0119] In some embodiments, the third coefficient c is determined by the following method: a plurality of third reference coefficients are obtained, for each third reference coefficient, the astigmatism compensation current of the first pair of middle coils in the Y direction is calculated by using the third reference coefficient under different excitation currents of the astigmatism coil, imaging is performed based on the excitation current of the astigmatism coil and the astigmatism compensation current of the first pair of middle coils in the Y direction, a plurality of images are obtained, and the image center variation degree of the plurality of images is obtained; a third interval between two third reference coefficients with the smallest image center variation degree is obtained, and a value in the third interval is selected as the third coefficient c.

[0120] For details, reference can be made to the determination method of the first coefficient a.

[0121] Similarly, in some embodiments, a plurality of fourth reference coefficients are obtained, for each fourth reference coefficient, a stigmator compensation current in the Y direction of the first pair of middle coils is calculated using the fourth reference coefficient under different excitation currents of the stigmator coils, imaging is performed based on the excitation current of the stigmator coils and the stigmator compensation current in the Y direction of the first pair of middle coils, a plurality of images are obtained, and a degree of change in image center of the plurality of images is obtained; a fourth interval between two fourth reference coefficients with the smallest degree of change in image center is obtained, and a numerical value in the fourth interval is selected as the fourth coefficient d.

[0122] For example, the first coefficient a can be determined as follows. It should be noted that the determination order of the third coefficient c and the fourth coefficient d is not limited, and the third coefficient c can be determined first and then the fourth coefficient d, or the fourth coefficient d can be determined first and then the third coefficient c.

[0123] The above-mentioned embodiments of determining the first coefficient a, the second coefficient b, the third coefficient c and the fourth coefficient d are as follows. For each reference coefficient, a stigmator compensation current in a corresponding direction of the first pair of middle coils is calculated using the reference coefficient under different excitation currents of the stigmator coils, imaging is performed based on the excitation current of the stigmator coils and the stigmator compensation current in the corresponding direction of the first pair of middle coils, a plurality of images are obtained, an interval between two reference coefficients with the smallest degree of change in image center of the plurality of images is obtained, and a numerical value in the interval is selected as the coefficient. In other words, for each reference coefficient, a test is performed to evaluate the correction effect, and finally a numerical value between two reference coefficients with the best correction effect is selected as the coefficient, so that a coefficient with a better correction effect can be obtained.

[0124] For example, the first coefficient a can be determined as follows. It should be noted that the determination order of the third coefficient c and the fourth coefficient d is not limited, and the third coefficient c can be determined first and then the fourth coefficient d, or the fourth coefficient d can be determined first and then the third coefficient c. Figure 4 In some embodiments, the above-mentioned steps of calculating a stigmator compensation current in the X direction of the first pair of middle coils using the first reference coefficient under different excitation currents of the stigmator coils, and performing imaging based on the excitation current of the stigmator coils and the stigmator compensation current in the X direction of the first pair of middle coils to obtain a plurality of images include steps 121-123, which are described below.

[0125] Step 121: different change amounts ΔstigX and ΔstigY are added to the initial excitation currents stigX0 and stigY0 of the stigmator coils respectively to obtain excitation currents of the stigmator coils.

[0126] Wherein, the initial exciting current stigX0 and stigY0 are initial values given to the exciting current of the stigmator coil in X direction and Y direction, respectively, and the exciting current of the stigmator coil in X direction and Y direction when the stigmator compensation is completed can be used as the initial exciting current stigX0 and stigY0. The adjustment of the exciting current of the stigmator coil is realized by adding a set variation ΔstigX to the initial exciting current stigX0 and a set variation ΔstigY to stigY0. The variations ΔstigX and ΔstigY used in each adjustment are different. The variations ΔstigX and ΔstigY can be set according to experience and actual needs.

[0127] Step 122: calculating the stigmator compensation current Align1Xb in X direction according to the exciting current of the stigmator coil and the first reference coefficient, and calculating the exciting current of the first alignment coil in X direction according to the initial exciting current Align1X0 of the first alignment coil in X direction and the stigmator compensation current Align1Xb.

[0128] According to the above function relationship, Align1Xb = stigX * a + stigY * b, the exciting current of the first alignment coil in X direction is Align1X = Align1X0 + Align1Xb.

[0129] In an embodiment, the exciting current of the first alignment coil in X direction is also adjusted, that is, a variation ΔAlign1X of the exciting current of the first alignment coil in X direction is introduced. Then, the exciting current of the first alignment coil in X direction is calculated according to the initial exciting current Align1X0 of the first alignment coil in X direction and the stigmator compensation current Align1Xb, which includes: calculating the current sum of the initial exciting current Align1X0 of the first alignment coil in X direction, the variation ΔAlign1X and the stigmator compensation current Align1Xb to obtain the exciting current of the first alignment coil in X direction, that is, Align1X = Align1X0 + ΔAlign1X + Align1Xb.

[0130] Step 123: performing multiple imaging based on the exciting current of the stigmator coil and the exciting current of the first alignment coil to obtain multiple different images.

[0131] In one embodiment, the electron beam is first mechanically centered, and then the excitation current of the wobble (i.e. periodically varying) objective lens is adjusted, and the excitation current of the first centering coil is adjusted to ensure that the electron beam passes through the center of the condenser / objective lens, thereby completing the initial centering. At this time, the excitation currents of the first centering coil in the X and Y directions are respectively the initial excitation currents Align1X0 and Align1Y0 in the X and Y directions, which in a physical sense represent the excitation current size of the first centering coil given by the control board, for example, Align1X0 = 10, which means that the excitation current of the first centering coil given by the control board is 10 mA. At this time, Align1Xb and Align1Yb are 0.

[0132] Then, the initial values stigX0 and stigY0 are assigned to the excitation currents of the stigmation coils in the X and Y directions according to the common stigmation compensation algorithm.

[0133] For each first reference coefficient, 5 images are collected, and the changes ΔstigX, ΔstigY and ΔAlign1X used for imaging each time are shown in the following table:

[0134] image ΔstigX ΔstigY ΔAlign1X 1 -20 -20 -10 2 -10 -10 -5 3 0 0 0 4 10 10 5 5 20 20 10

[0135] For example, when the first reference coefficient is -0.03, the first row of the table is checked to obtain StigX = stigX0 - 20 and StigY = stigY0 - 20, and assuming b = 0, then Align1Xb = (stigX0 - 20)*(-0.03) + (stigY0 - 20)*0, and Align1X = Align1X0 - 10 + Align1Xb, and the first image is collected. Then, the second row of the table is checked to obtain StigX = stigX0 - 10 and StigY = stigY0 - 10, and then Align1Xb = (stigX0 - 10)*(-0.03) + (stigY0 - 10)*0, and Align1X = Align1X0 - 5 + Align1Xb, and the second image is collected. In this way, 5 images are finally obtained.

[0136] The above table includes positive and negative changes of different sizes, thereby being able to cover a variety of changes.

[0137] After the first coefficient a is determined, the determined first coefficient a can be used for the determination of the subsequent second coefficient b. That is, the above-mentioned step of calculating the X-direction stigmation compensation current of the first pair of coils under different excitation currents of the stigmation coil using the second reference coefficient, imaging based on the excitation current of the stigmation coil and the X-direction stigmation compensation current of the first pair of coils, and obtaining multiple images includes: adding different variation amounts ΔstigX and different variation amounts ΔstigY to the initial excitation currents stigX0 and stigY0 of the stigmation coil respectively to obtain the excitation current of the stigmation coil; calculating the X-direction stigmation compensation current Align1Xb according to the excitation current of the stigmation coil, the second reference coefficient and the determined first coefficient a, and calculating the X-direction excitation current of the first pair of coils according to the initial excitation current Align1X0 of the first pair of coils and the stigmation compensation current Align1Xb; and imaging multiple times based on the excitation current of the stigmation coil and the excitation current of the first pair of coils to obtain multiple different images.

[0138] For details, please refer to steps 121-123, which will not be repeated here.

[0139] For details, please refer to steps 121-123, which will not be repeated here. Figure 5 In some embodiments, the above-mentioned step of calculating the Y-direction stigmation compensation current of the first pair of coils under different excitation currents of the stigmation coil using the third reference coefficient, imaging based on the excitation current of the stigmation coil and the Y-direction stigmation compensation current of the first pair of coils, and obtaining multiple images includes steps 124-126, which will be described in detail below.

[0140] Step 124: adding different variation amounts ΔstigX and different variation amounts ΔstigY to the initial excitation currents stigX0 and stigY0 of the stigmation coil respectively to obtain the excitation current of the stigmation coil. For details, please refer to step 121.

[0141] Step 125: calculating the Y-direction stigmation compensation current Align1Yb according to the excitation current of the stigmation coil and the third reference coefficient, and calculating the Y-direction excitation current of the first pair of coils according to the initial excitation current Align1Y0 of the first pair of coils and the stigmation compensation current Align1Yb.

[0142] According to the above function relationship, Align1Yb= stigX*c+stigY*d, the X-direction excitation current of the first pair of coils Align1Y=Align1Y0+ Align1Yb.

[0143] In one embodiment, considering that the variation of astigmatism coil excitation current results in the change of centering result, the variation amount of excitation current of the first centering coil in Y direction, ΔAlign1Y, is introduced to offset the change. Then the excitation current of the first centering coil in Y direction is calculated according to the initial excitation current of the first centering coil in Y direction, Align1Y0, and the astigmatism centering compensation current, Align1Yb, and includes: calculating the current sum of the initial excitation current of the first centering coil in Y direction, Align1Y0, the variation amount ΔAlign1Y, and the astigmatism centering compensation current, Align1Yb, to obtain the excitation current of the first centering coil in Y direction, that is, Align1Y = Align1Y0 + ΔAlign1Y + Align1Yb.

[0144] Step 126: based on the excitation current of the astigmatism coil and the excitation current of the first centering coil, multiple imaging is performed to obtain multiple different images.

[0145] In one specific embodiment, 5 images are collected for each third reference coefficient, and the variation amounts ΔstigX, ΔstigY, and ΔAlign1Y used in each imaging are shown in the following table:

[0146] image ΔstigX ΔstigY ΔAlign1Y 1 -20 -20 -10 2 -10 -10 -5 3 0 0 0 4 10 10 5 5 20 20 10

[0147] For example, when the third reference coefficient is 0.02, the first row in the table is checked to obtain StigX = stigX0-20, StigY = stigY0-20, and assuming d = 0, then Align1Yb = (stigX0-20)*0.02+(stigY0-20)*0, and Align1Y = Align1Y0-10+Align1Yb, and the first image is collected; then the second row in the table is checked to obtain StigX = stigX0-10, StigY = stigY0-10, then Align1Yb = (stigX0-10)*0.02+(stigY0-10)*0, and Align1Y = Align1Y0-5+Align1Yb, and the second image is collected; and so on, finally 5 images are obtained.

[0148] The above table includes positive and negative variation amounts of different sizes, so as to cover various change conditions.

[0149] After the third coefficient c is determined, the determined third coefficient c can be used to determine the fourth coefficient d. That is, the step of calculating the image center variation degree of the plurality of images, calculating the image center variation degree of the plurality of images, and calculating the image center variation degree of the plurality of images includes: adding different variation amounts ΔstigX and different variation amounts ΔstigY to the initial excitation currents stigX0 and stigY0 of the stigmation coil respectively to obtain the excitation currents of the stigmation coil; calculating the X-direction stigmation compensation current Align1Yb according to the excitation currents of the stigmation coil, the second reference coefficient, and the determined third coefficient c, and calculating the Y-direction excitation current of the first pair of coils according to the initial excitation current Align1Y0 of the first pair of coils and the stigmation compensation current Align1Yb; and performing multiple imaging based on the excitation currents of the stigmation coil and the excitation currents of the first pair of coils to obtain a plurality of different images.

[0150] For details, refer to steps 124-126, which will not be repeated here.

[0151] In some embodiments, in order to improve the accuracy of the first coefficient a, the first interval can be iteratively optimized to gradually narrow the first interval, and the first coefficient a is selected in the final first interval. Specifically, selecting a value from the first interval as the first coefficient a includes: iteratively selecting a plurality of values from the first interval as new first reference coefficients, for each first reference coefficient, calculating the X-direction stigmation compensation current of the first pair of coils under different excitation currents of the stigmation coil using the first reference coefficient, imaging based on the excitation currents of the stigmation coil and the X-direction stigmation compensation current of the first pair of coils, obtaining a plurality of images, obtaining the image center variation degree of the plurality of images, and obtaining the first interval between the two first reference coefficients with the smallest image center variation degree, until the absolute value of the difference between the two smallest image center variation degrees is less than the first difference threshold, and selecting a value from the final first interval as the first coefficient a.

[0152] For example, assuming that the image center variation degrees of the first reference coefficients 0.01 and 0.02 are the smallest, it is indicated that the first coefficient a falls between 0.01 and 0.02, a plurality of values are iteratively obtained as new first reference coefficients in the interval [0.01, 0.02], the image center variation degrees corresponding to each of the first reference coefficients are obtained, if the absolute value of the difference between the two smallest image center variation degrees is less than the first difference threshold, a value is selected from the first interval between the two first reference coefficients with the smallest image center variation degrees as the first coefficient a, otherwise a plurality of values are iteratively obtained as new first reference coefficients, and the image center variation degrees corresponding to each of the first reference coefficients are obtained until the absolute value of the difference between the two smallest image center variation degrees is less than the first difference threshold. Assuming that the final first interval is [0.0155, 0.0157], a value is selected therefrom as the first coefficient a, for example, the average of the endpoints (0.0155+0.0157) / 2 = 0.0156 is taken as the first coefficient a.

[0153] Similarly, in some embodiments, a value is selected from the second interval as the second coefficient b, including: iteratively selecting a plurality of values from the second interval as new second reference coefficients, for each second reference coefficient, under different excitation currents of the stigmator coil, the second reference coefficient is used to calculate the stigmator compensation current in the X direction of the first pair of central coils, imaging is performed based on the excitation current of the stigmator coil and the stigmator compensation current in the X direction of the first pair of central coils to obtain a plurality of images, the image center variation degrees of the plurality of images are obtained, the second interval between the two second reference coefficients with the smallest image center variation degrees is obtained, until the absolute value of the difference between the two smallest image center variation degrees is less than the second difference threshold, and a value is selected from the final second interval as the second coefficient b.

[0154] Similarly, in some embodiments, a value is selected from the third interval as the third coefficient c, including: iteratively selecting a plurality of values from the third interval as new third reference coefficients, for each third reference coefficient, under different excitation currents of the stigmator coil, the third reference coefficient is used to calculate the stigmator compensation current in the Y direction of the first pair of central coils, imaging is performed based on the excitation current of the stigmator coil and the stigmator compensation current in the Y direction of the first pair of central coils to obtain a plurality of images, the image center variation degrees of the plurality of images are obtained, the third interval between the two third reference coefficients with the smallest image center variation degrees is obtained, until the absolute value of the difference between the two smallest image center variation degrees is less than the third difference threshold, and a value is selected from the final third interval as the third coefficient c.

[0155] Similarly, in some embodiments, the fourth coefficient d is selected from the fourth interval, including: iteratively selecting multiple values from the fourth interval as new fourth reference coefficients, for each fourth reference coefficient, calculating the Y direction astigmatism compensation current of the first pair of centering coils under different excitation currents of the astigmatism coil using the fourth reference coefficient, imaging based on the excitation current of the astigmatism coil and the Y direction astigmatism compensation current of the first pair of centering coils to obtain multiple images, obtaining the image center variation degree of the multiple images, and obtaining the fourth interval between the two fourth reference coefficients with the smallest image center variation degree, until the absolute value of the difference between the two smallest image center variation degrees is less than the fourth difference threshold value, and selecting a value from the final fourth interval as the fourth coefficient d.

[0156] In some embodiments, the first coefficient a=tan(A), the second coefficient b=tan(B), the third coefficient c=tan(C), and the fourth coefficient d=tan(D), and determining the first coefficient a, the second coefficient b, the third coefficient c, and the fourth coefficient d specifically refers to determining the parameters A, B, C, and D.

[0157] In practice, the coefficients are usually small, and the tan function is used to represent the coefficients, which can improve the resolution because the slope near zero is small.

[0158] After the first coefficient a, the second coefficient b, the third coefficient c, and the fourth coefficient d are determined, the subsequent astigmatism compensation current of the first pair of centering coils can be calculated according to the excitation current of the astigmatism coil to perform current compensation, thereby correcting the centering deviation caused by astigmatism compensation. Therefore, the current compensation of the centering coil according to the astigmatism compensation current in step 30 includes: calculating the current sum of the initial excitation current Align1X0 of the X direction of the first pair of centering coils and the astigmatism compensation current Align1Xb of the X direction of the first pair of centering coils to obtain the excitation current of the X direction of the first pair of centering coils, and inputting the first pair of centering coils; calculating the current sum of the initial excitation current Align1Y0 of the Y direction of the first pair of centering coils and the astigmatism compensation current Align1Yb of the Y direction of the first pair of centering coils to obtain the excitation current of the Y direction of the first pair of centering coils, and inputting the first pair of centering coils.

[0159] That is, Align1X==Align1X0+Align1Xb, Align1Y=Align1Y0+Align1Yb, and the corresponding currents are input to the first pair of centering coils accordingly.

[0160] In some embodiments, the centering coil further includes a second pair of centering coils, and the astigmatism compensation current of the second pair of centering coils is determined according to the functional relationship between the astigmatism compensation current of the first pair of centering coils to correct the change of the centering effect caused by the change of the excitation current of the first pair of centering coils.

[0161] In some embodiments, the second pair of centering coils is an objective lens centering coil capable of returning the electron beam to the center of the objective lens, for example, Align2 in Figure 1 The functional relationship between the astigmatism centering compensation current of the second pair of centering coils and the astigmatism centering compensation current of the first pair of centering coils is:

[0162] Align2Xb= α*Align1Xb,

[0163] Align2Yb= β*Align1Yb,

[0164] Wherein, Align2Xb and Align2Yb represent the astigmatism centering compensation current of the objective lens centering coil in the X direction and the Y direction respectively, and α and β are the fifth coefficient and the sixth coefficient respectively.

[0165] Please refer to Figure 6 In some embodiments, the fifth coefficient α is determined by the following steps.

[0166] Step 210: Obtain a plurality of fifth reference coefficients.

[0167] In an embodiment, the plurality of fifth reference coefficients can be selected from a preset coefficient interval, for example, a plurality of first reference coefficients are selected at equal intervals from the coefficient interval. The minimum value, the maximum value of the coefficient interval, and the number of the fifth reference coefficients can be set as needed.

[0168] Step 220: For each fifth reference coefficient, based on the excitation current of the objective lens coil and the astigmatism centering compensation current of the second pair of centering coils in the X direction, imaging is performed under different excitation currents of the objective lens coil to obtain a plurality of images, and the image center variation degree of the plurality of images is obtained.

[0169] Specifically, the excitation current of the objective lens coil can be adjusted multiple times. After each adjustment, the astigmatism centering compensation current Align2Xb of the second pair of centering coils in the X direction is calculated according to the above function relationship, the excitation current of the second pair of centering coils in the X direction is adjusted according to the astigmatism centering compensation current Align2Xb in the X direction, and the image of the sample is collected under the adjusted excitation current of the objective lens coil and the excitation current of the second pair of centering coils, thereby obtaining a plurality of images.

[0170] The measurement method of the image center variation degree can refer to step 120.

[0171] Step 230: Obtain the fifth interval between the two fifth reference coefficients with the smallest image center variation degree, and select a value from the fifth interval as the fifth coefficient α.

[0172] For details, please refer to step 130.

[0173] Similarly, in some embodiments, the sixth coefficient β is determined by the following method: obtaining a plurality of sixth reference coefficients, for each sixth reference coefficient, based on the excitation current of the objective coil and the astigmatism compensation current of the second pair of centering coils in the Y direction, a plurality of images are obtained under different excitation currents of the objective coil, and the image center variation degree of the plurality of images is obtained; obtaining the sixth interval between the two sixth reference coefficients with the smallest image center variation degree, and selecting a value in the sixth interval as the sixth coefficient β.

[0174] For a specific reference, refer to the determination method of the fifth coefficient α. It should be noted that the determination order of the fifth coefficient α and the sixth coefficient β is not limited. The fifth coefficient α can be determined first and then the sixth coefficient β, or the sixth coefficient β can be determined first and then the fifth coefficient α.

[0175] The above-mentioned implementation of determining the fifth coefficient α and the sixth coefficient β, for each reference coefficient, the astigmatism compensation current of the corresponding direction of the second pair of centering coils is calculated based on the excitation current of the objective coil and the astigmatism compensation current of the corresponding direction of the second pair of centering coils under different excitation currents of the objective coil, a plurality of images are obtained, and the interval between the two reference coefficients with the smallest image center variation degree is obtained. Select a value as the coefficient, which is equivalent to testing each reference coefficient under different excitation currents of the objective coil, evaluating its correction effect on the electron beam at the objective coil, and finally selecting a value between the two reference coefficients with the best correction effect as the coefficient, so as to obtain a coefficient with better correction effect.

[0176] For a specific reference, refer to the determination method of the fifth coefficient α. It should be noted that the determination order of the fifth coefficient α and the sixth coefficient β is not limited. The fifth coefficient α can be determined first and then the sixth coefficient β, or the sixth coefficient β can be determined first and then the fifth coefficient α. Figure 7 In some embodiments, the above-mentioned step of imaging based on the excitation current of the objective coil and the astigmatism compensation current of the second pair of centering coils in the X direction under different excitation currents of the objective coil to obtain a plurality of images includes steps 221-223, which are described in detail below.

[0177] Step 221: based on the image magnification, the compensation amount OLb and the initial excitation current OL0 of the objective coil, the excitation current of the objective coil is obtained.

[0178] The initial excitation current OL0 of the objective coil is an initial value of the excitation current of the objective coil, and the excitation current of the objective coil when the initial centering is completed can be used as the initial excitation current OL0. Under the same conditions, the fluctuation ranges of the excitation current of the objective coil are different under different image magnifications, for example, the excitation current of the objective coil fluctuates by 10 mA under an image magnification of 1 k, and the excitation current of the objective coil fluctuates by 1 mA under an image magnification of 100 k. Under different image magnifications, the fluctuation ranges of the wobble objective current function are different. Therefore, the image magnification is considered in the adjustment of the excitation current of the objective coil in the embodiment. A coefficient is used to represent the fluctuation range of the excitation current of the objective coil under different image magnifications, which is called a mag coefficient, and the mag coefficient is different under different image magnifications.

[0179] The excitation current OL of the objective coil can be calculated according to the following formula:

[0180] OL = OL0+ mag * OLb.

[0181] The compensation amount OLb used each time is different, so that different excitation currents of the objective coil are obtained. The compensation amount OLb can be set according to experience and actual needs.

[0182] Step 222: The astigmatic centering compensation current Align2Xb of the second centering coil in the X direction is calculated according to the astigmatic centering compensation current Align1Xb of the first centering coil and the fifth reference coefficient, and the excitation current of the second centering coil in the X direction is calculated according to the initial excitation current Align2X0 of the second centering coil in the X direction and the astigmatic centering compensation current Align2Xb of the second centering coil.

[0183] According to the above function relationship, Align2Xb = a * Align1Xb, the excitation current of the second centering coil in the X direction is Align2X = Align2X0 + Align2Xb.

[0184] Step 223: Multiple imaging is performed based on the excitation current of the objective coil and the excitation current of the second centering coil, and multiple different images are obtained.

[0185] In a specific embodiment, 5 images are collected for each fifth reference coefficient, and the compensation amount OLb used each time is shown in the following table:

[0186] image OLb 1 -2 2 -1 3 0 4 1 5 2

[0187] For example, if the image magnification is 100k, the mag coefficient is 0.5, OL0=1200mA, and the fifth reference coefficient is 0.02, the first row of the table is searched to obtain OL=1200mA+0.5*(-2)mA=1199mA, and the excitation current of the second pair of middle coils in the X direction is calculated according to Align2Xb=0.02*Align1Xb and Align2X=Align2X0+Align2Xb, and then the first image is acquired; the second row of the table is searched to obtain OL=1200mA+0.5*(-1)mA=1199.5mA, and the second image is acquired; and the above steps are repeated to obtain the OL of the third to fifth rows as 1200mA, 1200.5mA, and 1201mA, respectively, and finally five images are obtained.

[0188] The above table includes different positive and negative compensation amounts, thereby covering various changes of the excitation current of the objective lens coil.

[0189] In some embodiments, the step of imaging, based on the excitation current of the objective lens coil and the astigmatism compensation current of the second pair of middle coils in the Y direction, under different excitation currents of the objective lens coil to obtain multiple images includes: obtaining the excitation current of the objective lens coil based on the image magnification, the compensation amount OLb, and the initial excitation current OL0 of the objective lens coil; calculating the astigmatism compensation current Align2Yb of the second pair of middle coils in the Y direction according to the astigmatism compensation current Align1Yb of the first pair of middle coils and the sixth reference coefficient; calculating the excitation current of the second pair of middle coils in the Y direction according to the initial excitation current Align2Y0 of the second pair of middle coils in the Y direction and the astigmatism compensation current Align2Yb of the second pair of middle coils; and performing multiple imaging based on the excitation current of the objective lens coil and the excitation current of the second pair of middle coils to obtain multiple different images.

[0190] For details, refer to steps 221-223, which are not described here.

[0191] In some embodiments, to improve the accuracy of the fifth coefficient a, the fifth interval can also be iteratively optimized, and the fifth interval is gradually reduced, and the fifth coefficient a is selected in the final fifth interval. Specifically, selecting a value from the fifth interval as the fifth coefficient a includes: iteratively selecting multiple values from the fifth interval as new fifth reference coefficients, for each fifth reference coefficient, imaging under different excitation currents of the objective lens coil to obtain multiple images, obtaining the image center variation degree of the multiple images, obtaining the fifth interval between the two fifth reference coefficients with the smallest image center variation degree, until the absolute value of the difference between the two smallest image center variation degrees is less than the fifth difference threshold, and selecting a value from the final fifth interval as the fifth coefficient a.

[0192] Similarly, in some embodiments, the sixth coefficient β is selected from the sixth interval, including: iteratively selecting multiple values from the sixth interval as new sixth reference coefficients, for each sixth reference coefficient, imaging under different excitation currents of the objective lens coil to obtain multiple images, obtaining the image center variation degree of the multiple images, obtaining the sixth interval between the two sixth reference coefficients with the smallest image center variation degree, until the absolute value of the difference between the two smallest image center variation degrees is less than the sixth difference threshold, and selecting a value from the final sixth interval as the sixth coefficient β.

[0193] In some embodiments, the fifth coefficient α and the sixth coefficient β are also expressed by tan function, that is, the fifth coefficient α=tan(k) and the sixth coefficient β=tan(l), and the specific determination of the fifth coefficient α and the sixth coefficient β is the determination of the parameters k and l.

[0194] After the fifth coefficient α and the sixth coefficient β are determined, the astigmatism compensation current of the second pair of centering coils can be calculated according to the excitation current of the astigmatism coil to compensate the current of the second pair of centering coils, so as to correct the change of the centering effect caused by the change of the excitation current of the first pair of centering coils. In step 30, the current compensation of the centering coil according to the astigmatism compensation current includes: calculating the current sum of the initial excitation current Align2X0 of the second pair of centering coils in the X direction and the astigmatism compensation current Align2Xb of the second pair of centering coils in the X direction to obtain the excitation current of the second pair of centering coils in the X direction, and inputting the second pair of centering coils; calculating the current sum of the initial excitation current Align2Y0 of the second pair of centering coils in the Y direction and the astigmatism compensation current Align2Yb of the second pair of centering coils in the Y direction to obtain the excitation current of the second pair of centering coils in the Y direction, and inputting the second pair of centering coils.

[0195] That is, Align2X==Align2X0+Align2Xb, Align2Y=Align2Y0+Align2Yb, and the corresponding current is input to the second pair of centering coils accordingly.

[0196] The centering deviation correction method of the electron microscope provided in the application utilizes the centering deviation caused by the astigmatism adjustment of the centering coil, and obtains the astigmatism compensation current of the centering coil according to the function relationship between the excitation current of the astigmatism coil and the astigmatism compensation current, and compensates the current of the centering coil according to the astigmatism compensation current. Therefore, when the excitation current of the astigmatism coil changes, the excitation current of the centering coil will also change to compensate the centering deviation caused by the change of the excitation current of the astigmatism coil, so that the image center hardly moves when the excitation current of the astigmatism coil changes.

[0197] Those skilled in the art can understand that all or part of the functions of various methods in the above embodiments can be realized by hardware or by a computer program. When all or part of the functions in the above embodiments are realized by a computer program, the program can be stored in a computer readable storage medium, which can include a read-only memory, a random access memory, a magnetic disk, an optical disk, a hard disk, and the like. The above functions are realized by executing the program by a computer. For example, the program is stored in a memory of a device, and the above functions are realized by executing the program in the memory by a processor. In addition, when all or part of the functions in the above embodiments are realized by a computer program, the program can also be stored in a storage medium such as a server, another computer, a disk, an optical disk, a flash disk, or a mobile hard disk, and is saved in a memory of a local device by downloading or copying, or the system of the local device is updated, and the above functions are realized by executing the program in the memory by a processor.

[0198] The above application of specific examples to the present application is described, which is only used to help understand the present application and does not limit the present application. For those skilled in the art, according to the idea of the present application, a number of simple deductions, deformations or substitutions can be made.

Claims

1. A method for correcting centering deviation in an electron microscope, characterized in that, include: Determine the excitation current of the astigmatic coil; Based on the excitation current of the astigmatic coil and the functional relationship between the excitation current of the astigmatic coil and the astigmatic alignment compensation current, the astigmatic alignment compensation current is obtained. The astigmatic alignment compensation current is the current that needs to be used to compensate the alignment coil to correct the alignment deviation caused by the change of the excitation current of the astigmatic coil. The centering coil is current-compensated according to the astigmatic centering compensation current.

2. The centering deviation correction method as described in claim 1, characterized in that, The centering coil includes a first centering coil, and the astigmatic centering compensation current of the first centering coil is determined by the following functional relationship: Align1Xb=stigX*a+stigY*b, Align1Yb=stigX*c+stigY*d, Wherein, Align1Xb and Align1Yb represent the astigmatic alignment compensation currents in the X and Y directions of the first alignment coil, respectively; stigX and stigY represent the excitation currents in the X and Y directions of the astigmatic coil, respectively; and a, b, c, and d are the first coefficient, the second coefficient, the third coefficient, and the fourth coefficient, respectively.

3. The centering deviation correction method as described in claim 2, characterized in that, The first coefficient a, the second coefficient b, the third coefficient c, and the fourth coefficient d are determined in the following way: Multiple first reference coefficients are obtained. For each first reference coefficient, under different excitation currents of the astigmatic coil, the astigmatic alignment compensation current in the X direction of the first centering coil is calculated using the first reference coefficient. Imaging is performed based on the excitation current of the astigmatic coil and the astigmatic alignment compensation current in the X direction of the first centering coil to obtain multiple images. The degree of change of the image center of the multiple images is obtained. A first interval between the two first reference coefficients with the smallest degree of change of the image center is obtained, and a value is selected from the first interval as the first coefficient a. Multiple second reference coefficients are obtained. For each second reference coefficient, under different excitation currents of the astigmatic coil, the astigmatic alignment compensation current in the X direction of the first centering coil is calculated using the second reference coefficient. Imaging is performed based on the excitation current of the astigmatic coil and the astigmatic alignment compensation current in the X direction of the first centering coil to obtain multiple images. The degree of change of the image center of the multiple images is obtained. A second interval between the two second reference coefficients with the smallest degree of change of the image center is obtained, and a value is selected from the second interval as the second coefficient b. Multiple third reference coefficients are obtained. For each third reference coefficient, under different excitation currents of the astigmatic coil, the astigmatic centering compensation current in the Y direction of the first centering coil is calculated using the third reference coefficient. Imaging is performed based on the excitation current of the astigmatic coil and the astigmatic centering compensation current in the Y direction of the first centering coil to obtain multiple images. The degree of change of the image center of the multiple images is obtained. A third interval between the two third reference coefficients with the smallest degree of change of the image center is obtained, and a value is selected from the third interval as the third coefficient c. Multiple fourth reference coefficients are obtained. For each fourth reference coefficient, under different excitation currents of the astigmatic coil, the astigmatic centering compensation current in the Y direction of the first centering coil is calculated using the fourth reference coefficient. Imaging is performed based on the excitation current of the astigmatic coil and the astigmatic centering compensation current in the Y direction of the first centering coil to obtain multiple images. The degree of change of the image center of the multiple images is obtained. A fourth interval between the two fourth reference coefficients with the smallest degree of change of the image center is obtained, and a value is selected from the fourth interval as the fourth coefficient d.

4. The centering deviation correction method as described in claim 3, characterized in that, Under different excitation currents of the astigmatic coil, the astigmatic alignment compensation current in the X direction of the first centering coil is calculated using the first reference coefficient. Based on the excitation current of the astigmatic coil and the astigmatic alignment compensation current in the X direction of the first centering coil, imaging is performed to obtain multiple images, including: By adding different changes ΔstigX and ΔstigY to the initial excitation currents stigX0 and stigY0 of the astigmatic coil, the excitation current of the astigmatic coil is obtained. The astigmatic alignment compensation current Align1Xb in the X direction is calculated based on the excitation current of the astigmatic coil and the first reference coefficient. The excitation current of the first alignment coil in the X direction is calculated based on the initial excitation current Align1X0 and the astigmatic alignment compensation current Align1Xb in the X direction. Multiple imaging operations are performed based on the excitation current of the astigmatic coil and the excitation current of the first centering coil to obtain multiple different images. Under different excitation currents of the astigmatic coil, the astigmatic alignment compensation current in the X direction of the first centering coil is calculated using the second reference coefficient. Imaging is then performed based on the excitation current of the astigmatic coil and the astigmatic alignment compensation current in the X direction of the first centering coil to obtain multiple images, including: By adding different changes ΔstigX and ΔstigY to the initial excitation currents stigX0 and stigY0 of the astigmatic coil, the excitation current of the astigmatic coil is obtained. The astigmatic alignment compensation current Align1Xb in the X direction is calculated based on the excitation current of the astigmatic coil, the second reference coefficient, and the determined first coefficient a. The excitation current of the first alignment coil in the X direction is calculated based on the initial excitation current Align1X0 in the X direction and the astigmatic alignment compensation current Align1Xb. Multiple imaging operations are performed based on the excitation current of the astigmatic coil and the excitation current of the first centering coil to obtain multiple different images.

5. The centering deviation correction method as described in claim 4, characterized in that, The excitation current in the X direction of the first centering coil is calculated based on the initial excitation current Align1X0 in the X direction and the astigmatic centering compensation current Align1Xb, including: The excitation current in the X direction of the first centering coil is obtained by calculating the sum of the initial excitation current Align1X0, the change ΔAlign1X, and the astigmatic centering compensation current Align1Xb in the X direction of the first centering coil.

6. The centering deviation correction method as described in claim 3, characterized in that, Under different excitation currents of the astigmatic coil, the astigmatic alignment compensation current in the Y direction of the first centering coil is calculated using the third reference coefficient. Based on the excitation current of the astigmatic coil and the astigmatic alignment compensation current in the Y direction of the first centering coil, imaging is performed to obtain multiple images, including: By adding different changes ΔstigX and ΔstigY to the initial excitation currents stigX0 and stigY0 of the astigmatic coil, the excitation current of the astigmatic coil is obtained. The astigmatic alignment compensation current Align1Yb in the Y direction is calculated based on the excitation current of the astigmatic coil and the third reference coefficient. The excitation current in the Y direction of the first alignment coil is calculated based on the initial excitation current Align1Y0 in the Y direction and the astigmatic alignment compensation current Align1Yb. Multiple imaging operations are performed based on the excitation current of the astigmatic coil and the excitation current of the first centering coil to obtain multiple different images. Under different excitation currents of the astigmatic coil, the astigmatic alignment compensation current in the Y direction of the first centering coil is calculated using the fourth reference coefficient. Based on the excitation current of the astigmatic coil and the astigmatic alignment compensation current in the Y direction of the first centering coil, imaging is performed to obtain multiple images, including: By adding different changes ΔstigX and ΔstigY to the initial excitation currents stigX0 and stigY0 of the astigmatic coil, the excitation current of the astigmatic coil is obtained. The astigmatic alignment compensation current Align1Yb in the Y direction is calculated based on the excitation current of the astigmatic coil, the fourth reference coefficient, and the determined third coefficient c. The excitation current in the Y direction of the first alignment coil is calculated based on the initial excitation current Align1Y0 in the Y direction of the first alignment coil and the astigmatic alignment compensation current Align1Yb. Multiple imaging operations are performed based on the excitation current of the astigmatic coil and the excitation current of the first centering coil to obtain multiple different images.

7. The centering deviation correction method as described in claim 6, characterized in that, The excitation current in the Y direction of the first centering coil is calculated based on the initial excitation current Align1Y0 in the Y direction and the astigmatic centering compensation current Align1Yb, including: The excitation current in the Y direction of the first centering coil is obtained by calculating the sum of the initial excitation current Align1Y0, the change ΔAlign1Y, and the astigmatic centering compensation current Align1Yb in the Y direction.

8. The centering deviation correction method according to any one of claims 3 to 7, characterized in that, The step of selecting a value from the first interval as the first coefficient a includes: The process iteratively selects multiple values ​​from the first interval as new first reference coefficients. For each first reference coefficient, under different excitation currents of the astigmatic coil, the astigmatic alignment compensation current in the X direction of the first centering coil is calculated using the first reference coefficient. Based on the excitation current of the astigmatic coil and the astigmatic alignment compensation current in the X direction of the first centering coil, imaging is performed to obtain multiple images. The degree of change of the image center of the multiple images is obtained, and the first interval between the two first reference coefficients with the smallest degree of change of the image center is obtained. This process continues until the absolute value of the difference between the two smallest degree of change of the image center is less than a first difference threshold. Finally, a value is selected from the final first interval as the first coefficient a. The step of selecting a value from the second interval as the second coefficient b includes: The process iteratively selects multiple values ​​from the second interval as new second reference coefficients. For each second reference coefficient, under different excitation currents of the astigmatic coil, the astigmatic alignment compensation current in the X direction of the first alignment coil is calculated using the second reference coefficient. Based on the excitation current of the astigmatic coil and the astigmatic alignment compensation current in the X direction of the first alignment coil, imaging is performed to obtain multiple images. The degree of change of the image center of the multiple images is obtained, and the second interval between the two second reference coefficients with the smallest degree of change of the image center is obtained. This process continues until the absolute value of the difference between the two smallest degree of change of the image center is less than the second difference threshold. Finally, a value is selected from the final second interval as the second coefficient b. The step of selecting a value from the third interval as the third coefficient c includes: The process iteratively selects multiple values ​​from the third interval as new third reference coefficients. For each third reference coefficient, under different excitation currents of the astigmatic coil, the astigmatic centering compensation current in the Y direction of the first centering coil is calculated using the third reference coefficient. Based on the excitation current of the astigmatic coil and the astigmatic centering compensation current in the Y direction of the first centering coil, imaging is performed to obtain multiple images. The degree of change of the image center of the multiple images is obtained, and the third interval between the two third reference coefficients with the smallest degree of change of the image center is obtained. This process continues until the absolute value of the difference between the two smallest degree of change of the image center is less than the third difference threshold. Finally, a value is selected from the final third interval as the third coefficient c. The step of selecting a value from the fourth interval as the fourth coefficient d includes: The process iteratively selects multiple values ​​from the fourth interval as new fourth reference coefficients. For each fourth reference coefficient, under different excitation currents of the astigmatic coil, the astigmatic alignment compensation current in the Y direction of the first alignment coil is calculated using the fourth reference coefficient. Imaging is performed based on the excitation current of the astigmatic coil and the astigmatic alignment compensation current in the Y direction of the first alignment coil to obtain multiple images. The degree of change of the image center of the multiple images is obtained, and the fourth interval between the two fourth reference coefficients with the smallest degree of change of the image center is obtained. This process continues until the absolute value of the difference between the two smallest degree of change of the image center is less than the fourth difference threshold. Finally, a value is selected from the final fourth interval as the fourth coefficient d.

9. The centering deviation correction method according to any one of claims 1 to 8, characterized in that, The step of performing current compensation on the centering coil based on the astigmatic centering compensation current includes: Calculate the sum of the initial excitation current Align1X0 in the X direction of the first centering coil and the astigmatic centering compensation current Align1Xb in the X direction of the first centering coil to obtain the excitation current in the X direction of the first centering coil, and input it into the first centering coil. Calculate the sum of the initial excitation current Align1Y0 in the Y direction of the first centering coil and the astigmatic centering compensation current Align1Yb in the Y direction of the first centering coil to obtain the excitation current in the Y direction of the first centering coil, and input it into the first centering coil.

10. The centering deviation correction method according to any one of claims 2 to 9, characterized in that, The centering coil also includes a second centering coil, and the astigmatic centering compensation current of the second centering coil is determined according to the functional relationship between it and the astigmatic centering compensation current of the first centering coil.

11. The centering deviation correction method as described in claim 10, characterized in that, The second centering coil is the objective lens centering coil. The functional relationship between the astigmatism centering compensation current of the second centering coil and the astigmatism centering compensation current of the first centering coil is as follows: Align2Xb= α *Align1Xb, Align2Yb= β *Align1Yb, Wherein, Align2Xb and Align2Yb represent the astigmatism compensation currents in the X and Y directions of the objective lens centering coil, respectively. α and β These are the fifth and sixth coefficients, respectively.

12. The centering deviation correction method as described in claim 11, characterized in that, Fifth coefficient α and the sixth coefficient β Determined in the following ways: Multiple fifth reference coefficients are obtained. For each fifth reference coefficient, imaging is performed based on the excitation current of the objective lens coil and the astigmatism centering compensation current in the X direction of the second centering coil under different excitation currents of the objective lens coil to obtain multiple images. The degree of change of the image center of the multiple images is obtained. Obtain the fifth interval between the two fifth reference coefficients with the smallest change in image center, and select a value from the fifth interval as the fifth coefficient. α ; Multiple sixth reference coefficients are obtained. For each sixth reference coefficient, under different excitation currents of the objective lens coil, imaging is performed based on the excitation current of the objective lens coil and the astigmatism centering compensation current in the Y direction of the second centering coil to obtain multiple images. The degree of image center change of the multiple images is obtained. A sixth interval between the two sixth reference coefficients with the smallest degree of image center change is obtained, and a value is selected from the sixth interval as the sixth coefficient. β .

13. The centering deviation correction method as described in claim 12, characterized in that, Under different excitation currents of the objective lens coil, imaging is performed based on the excitation current of the objective lens coil and the astigmatism centering compensation current in the X direction of the second centering coil to obtain multiple images, including: The excitation current of the objective lens coil is obtained based on the image magnification, the compensation amount OLb, and the initial excitation current OL0 of the objective lens coil. The astigmatism compensation current Align2Xb of the second centering coil in the X direction is calculated based on the astigmatism compensation current Align1Xb of the first centering coil and the fifth reference coefficient. The excitation current of the second centering coil in the X direction is calculated based on the initial excitation current Align2X0 of the second centering coil in the X direction and the astigmatic centering compensation current Align2Xb of the second centering coil. Multiple imaging operations are performed based on the excitation current of the objective lens coil and the excitation current of the second centering coil to obtain multiple different images; Under different excitation currents of the objective lens coil, imaging is performed based on the excitation current of the objective lens coil and the astigmatism centering compensation current in the Y direction of the second centering coil to obtain multiple images, including: The excitation current of the objective lens coil is obtained based on the image magnification, the compensation amount OLb, and the initial excitation current OL0 of the objective lens coil. The astigmatism compensation current Align2Yb of the second centering coil in the Y direction is calculated based on the astigmatism compensation current Align1Yb of the first centering coil and the sixth reference coefficient. The excitation current in the Y direction of the second centering coil is calculated based on the initial excitation current Align2Y0 in the Y direction of the second centering coil and the astigmatic centering compensation current Align2Yb of the second centering coil. Multiple imaging operations are performed based on the excitation current of the objective lens coil and the excitation current of the second centering coil to obtain multiple different images.

14. The centering deviation correction method as described in claim 12, characterized in that, The fifth coefficient is selected from the fifth interval. α ,include: The process iteratively selects multiple values ​​from the fifth interval as new fifth reference coefficients. For each fifth reference coefficient, imaging is performed under different excitation currents of the objective lens coil to obtain multiple images. The degree of change in the image center of each image is obtained, and the fifth interval between the two fifth reference coefficients with the smallest degree of change in the image center is determined. This process continues until the absolute value of the difference between the two smallest degree of change in the image center is less than a fifth difference threshold. Finally, a value is selected from the final fifth interval as the fifth coefficient. α ; The value is selected from the sixth interval as the sixth coefficient. β ,include: The process iteratively selects multiple values ​​from the sixth interval as new sixth reference coefficients. For each sixth reference coefficient, imaging is performed under different excitation currents of the objective lens coil to obtain multiple images. The degree of change in the image center of these multiple images is obtained. The sixth interval between the two sixth reference coefficients with the smallest degree of change in the image center is then determined. This process continues until the absolute value of the difference between the two smallest degree of change in the image center is less than a sixth difference threshold. Finally, a value is selected from the final sixth interval as the sixth coefficient. β .

15. The centering deviation correction method according to any one of claims 4 to 14, characterized in that, The acquisition of the degree of change in the image center of the multiple images includes: Using one of the multiple images as a reference image, the displacement of the image center of the other images relative to the image center of the reference image is calculated and added together to obtain the degree of change of the image center of the multiple images.

16. The centering deviation correction method according to any one of claims 10 to 15, characterized in that, The step of performing current compensation on the centering coil based on the astigmatic centering compensation current includes: Calculate the sum of the initial excitation current Align2X0 in the X direction of the second centering coil and the astigmatic centering compensation current Align2Xb in the X direction of the second centering coil to obtain the excitation current in the X direction of the second centering coil, and input it into the second centering coil. Calculate the sum of the initial excitation current Align2Y0 in the Y direction of the second centering coil and the astigmatic centering compensation current Align2Yb in the Y direction of the second centering coil to obtain the excitation current in the Y direction of the second centering coil, and input it into the second centering coil.

17. An electron microscope, characterized in that, It includes a deflection coil, a centering coil, and a processor, the processor being configured to perform the centering deviation correction method as described in any one of claims 1 to 16.

18. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer-executable program or instructions, which, when executed by a processor, are used to implement the alignment deviation correction method as described in any one of claims 1 to 16.

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