Working distance calibration method and system of scanning electron microscope, scanning electron microscope and medium

Abstract

The present application relates to the technical field of scanning electron microscopy, and discloses a working distance calibration method and system for a scanning electron microscope, the scanning electron microscope and a medium. The method comprises the following steps: placing an elevation sample on a sample stage of a scanning electron microscope to be calibrated, adjusting objective lens excitation, changing the focal length of the objective lens, and obtaining objective lens excitation under different accelerating voltages; under the same working distance, fitting different accelerating voltages and corresponding objective lens excitation by using a first fitting model to determine first, second, third, fourth and fifth calibration parameters of the first fitting model; under the same accelerating voltage, fitting different working distances and corresponding objective lens excitation by using a second fitting model to determine the third, fourth and fifth calibration parameters of the second fitting model; and calibrating the scanning electron microscope to be calibrated by using the five calibration parameters. The present application determines multiple calibration parameters by using two fitting models, thereby improving the accuracy of calibration of key parameters of the scanning electron microscope before delivery.

Description

Technical Field

[0001] This invention relates to the field of scanning electron microscopy (SEM) technology, specifically to a method, system, SEM, and medium for calibrating the working distance of an SEM. Background Technology

[0002] A scanning electron microscope (SEM) is a large, precision instrument used for high-resolution micro-area morphology analysis, with wide applications in cutting-edge fields such as nanomaterials technology and life sciences. To ensure the accuracy and validity of information such as image size, magnification, and resolution, key parameters need to be calibrated and adjusted before the equipment leaves the factory. This primarily involves calibrating the magnification, image scale, and scale based on the standard working distance. The premise of this calibration and adjustment is that the actual working distance of the sample (i.e., the distance between the sample and the lower surface of the objective lens) remains constant. When changing the accelerating voltage and magnification to achieve a clear image of the sample again, the working distance read back by the software remains essentially unchanged. The working distance value read back by the software is based on a theoretical model, obtained through a series of mathematical calculations on the lens excitation current value. This theoretical model can be determined through electron optics simulation calculations.

[0003] In practical applications, due to the precision issues of equipment mechanical assembly and electrical systems, when switching acceleration voltages, the working distance value determined by the theoretical model and read back by the software can fluctuate by up to 18%, leading to a decrease in the accuracy of subsequent parameter calibration. Summary of the Invention

[0004] In view of this, the present invention provides a method, system, scanning electron microscope and medium for calibrating the working distance of a scanning electron microscope, in order to solve the problem of low accuracy of parameter calibration and debugging before the scanning electron microscope leaves the factory.

[0005] In a first aspect, the present invention provides a method for calibrating the working distance of a scanning electron microscope, the method comprising:

[0006] Elevation samples with different heights are placed on the sample stage of the scanning electron microscope to be calibrated. Different accelerating voltages are set, and the objective lens focal length is changed by adjusting the objective lens excitation to make the elevation samples clear images. This is to obtain the objective lens excitation when the elevation samples are clearly imaged at different accelerating voltages under a fixed working distance, and the objective lens excitation when the elevation samples are clearly imaged at different working distances under a fixed accelerating voltage. The objective lens focal length when the elevation samples are clearly imaged is equal to the actual working distance of the elevation samples.

[0007] For the same actual working distance, the first fitting model is used to fit different accelerating voltages and corresponding objective excitations to determine the first calibration parameters and the second calibration parameters of the first fitting model.

[0008] For the same accelerating voltage, the second fitting model is used to fit different actual working distances and corresponding objective excitations to determine the third, fourth, and fifth calibration parameters of the second fitting model.

[0009] The scanning electron microscope to be calibrated is calibrated using the first calibration parameter, the second calibration parameter, the third calibration parameter, the fourth calibration parameter, and the fifth calibration parameter.

[0010] The scanning electron microscope (SEM) working distance calibration method provided by this invention determines multiple calibration parameters through two fitting models. This ensures that, under the premise that the actual working distance of the sample remains unchanged, the displayed value of the working distance remains unchanged when the sample is re-imaged clearly, even when the accelerating voltage and magnification are changed. This improves the accuracy of the calibration of key parameters of the SEM before it leaves the factory.

[0011] In one optional implementation, the elevation samples at different heights include: a step sample with multiple steps, each step serving as an elevation sample; the process of determining the working distance of the elevation sample includes:

[0012] Adjust the height of the sample stage so that the top layer of the stepped sample touches the lower pole shoe of the objective lens;

[0013] Based on the number of steps corresponding to the elevation sample and the height of each step, the distance from the elevation sample to the top of the step sample is determined as the working distance of the elevation sample.

[0014] The scanning electron microscope working distance calibration method provided by this invention uses a step sample as an elevation sample to provide a clear and stable physical size reference. The working distance marked by the electron microscope measurement software can be directly compared with the standard value of the step height, which facilitates rapid and repeated measurement and calibration, and provides a reliable benchmark for electron microscope measurement.

[0015] In one optional implementation, a first fitting model is used to represent the relationship between objective lens excitation and accelerating voltage at the same actual working distance. The process of determining the first fitting model includes:

[0016] Based on electron optics theory, the relationship between the objective lens focal length, objective lens excitation, and accelerating voltage of a scanning electron microscope is determined as follows:

[0017]

[0018] Where S and D are the objective lens electron optical constants, f represents the objective lens focal length, N represents the number of turns of the objective lens coil, I represents the current through the objective lens coil, NI represents the objective lens excitation of the scanning electron microscope, and V r Indicates accelerating voltage;

[0019] Based on the relationship between the objective lens focal length, objective lens excitation, and accelerating voltage of a scanning electron microscope, the relationship between objective lens excitation and accelerating voltage is determined as follows when the objective lens focal length remains constant:

[0020] NI∝C(V r ) α Where C represents the first calibration parameter and α represents the second calibration parameter.

[0021] In one optional implementation, the second fitting model is used to represent the relationship between objective excitation and the working distance indicated by the electron microscope software under the same accelerating voltage. The process of determining the second fitting model includes:

[0022] Based on the relationship between the objective focal length, objective excitation, and accelerating voltage of a scanning electron microscope (SEM), the conversion relationship between objective excitation and the working distance indicated by the SEM software is determined as follows when the accelerating voltage remains constant:

[0023] NI = p1(WD) 2 +p2(WD) 1 +p3(WD) 0 Where WD indicates the working distance, p1 indicates the third calibration parameter, p2 indicates the fourth calibration parameter, and p3 indicates the fifth calibration parameter.

[0024] The scanning electron microscope working distance calibration method provided by the present invention performs a first fitting on different accelerating voltages and corresponding objective excitations by fixing the working distance, and then performs a second fitting on different working distances and corresponding objective excitations by fixing the accelerating voltage, and finally obtains the values ​​of five calibration parameters, thereby improving the accuracy of working distance calibration.

[0025] In one optional implementation, a first fitting model is used to fit different accelerating voltages and corresponding objective excitations to determine the first calibration parameters and second calibration parameters of the first fitting model, including:

[0026] The first fitting model is linearized to obtain a linear fitting model.

[0027] Based on different accelerating voltages and corresponding objective lens excitations, the linear fitting model is solved using the least squares method to obtain the first calibration parameter and the second calibration parameter.

[0028] The scanning electron microscope working distance calibration method provided by this invention can accurately adjust the objective lens excitation by fitting the calibration parameters, optimize the electron beam focusing effect, reduce aberrations, and make the electron microscope imaging clearer and with higher resolution, thereby improving the accuracy of sample microstructure measurement. The accurate calibration parameters can ensure that the electron beam can pass through the objective lens in the best state under different accelerating voltages, avoiding problems such as image blurring and distortion caused by excitation and voltage mismatch, and ensuring the reliability of image data.

[0029] In one optional implementation, after calibrating the scanning electron microscope to be calibrated, the method further includes:

[0030] Obtain the actual working distance and the labeled working distance of the calibrated scanning electron microscope when it operates under different accelerating voltages;

[0031] The deviation between the indicated working distance and the actual working distance under different accelerating voltages was calculated, and the calibration accuracy of the scanning electron microscope was evaluated based on the deviation.

[0032] The scanning electron microscope (SEM) working distance calibration method provided by this invention optimizes the functional relationship between accelerating voltage and lens excitation in the SEM system at a fixed working distance, thereby reducing the deviation between the software-indicated working distance value and the actual value (the former is derived from the lens excitation through the functional relationship). This further ensures that the software-displayed values ​​of physical quantities (such as working distance, magnification, and sample feature size) in the SEM measurement system are consistent with the true values, and improves the accuracy and consistency of the equipment's imaging information.

[0033] In a second aspect, the present invention provides a working distance calibration system for a scanning electron microscope, the system comprising:

[0034] The test condition setting module is used to place elevation samples with different heights on the sample stage of the scanning electron microscope to be calibrated, set different accelerating voltages, and change the objective lens focal length by adjusting the objective lens excitation to make the elevation sample clear image. This module obtains the objective lens excitation when the elevation sample is clearly imaged at different accelerating voltages under a fixed working distance, and the objective lens excitation when the elevation sample is clearly imaged at different working distances under a fixed accelerating voltage. The objective lens focal length is equal to the actual working distance of the elevation sample when the elevation sample is clearly imaged.

[0035] The first fitting module is used to fit different acceleration voltages and corresponding objective lens excitations using a first fitting model for the same actual working distance, and to determine the first calibration parameters and the second calibration parameters of the first fitting model.

[0036] The second fitting module is used to fit different actual working distances and corresponding objective lens excitations using the second fitting model for the same accelerating voltage, and to determine the third, fourth, and fifth calibration parameters of the second fitting model.

[0037] The parameter calibration module is used to calibrate the scanning electron microscope to be calibrated using the first calibration parameter, the second calibration parameter, the third calibration parameter, the fourth calibration parameter, and the fifth calibration parameter.

[0038] Thirdly, the present invention provides a scanning electron microscope, comprising: a memory and a processor, wherein the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the computer instructions to perform the method described in the first aspect or any corresponding embodiment thereof.

[0039] Fourthly, the present invention provides a computer-readable storage medium storing computer instructions for causing a computer to perform the method described in the first aspect or any corresponding embodiment thereof.

[0040] Fifthly, the present invention provides a computer program product, including computer instructions for causing a computer to perform the method described in the first aspect or any corresponding embodiment thereof. Attached Figure Description

[0041] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0042] Figure 1 This is a schematic flowchart of a scanning electron microscope working distance calibration method according to an embodiment of the present invention;

[0043] Figure 2 This is a flowchart illustrating another scanning electron microscope working distance calibration method according to an embodiment of the present invention;

[0044] Figure 3 This is a schematic diagram of the physical structure of the step sample used in the working distance calibration method of a scanning electron microscope according to an embodiment of the present invention;

[0045] Figure 4 This is a schematic diagram of the measurement results when the actual working distance is 5 mm in the scanning electron microscope working distance calibration method according to an embodiment of the present invention;

[0046] Figure 5 This is a schematic diagram of measurement results at different actual working distances in the scanning electron microscope working distance calibration method according to an embodiment of the present invention;

[0047] Figure 6 This is a structural block diagram of a scanning electron microscope working distance calibration system according to an embodiment of the present invention;

[0048] Figure 7 This is a schematic diagram of the hardware structure of a computer device according to an embodiment of the present invention. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] This invention provides a method for calibrating the working distance of a scanning electron microscope (SEM), which determines multiple calibration parameters through two fitting models to improve the accuracy of calibration of key parameters of the SEM.

[0051] According to an embodiment of the present invention, a method for calibrating the working distance of a scanning electron microscope is provided. It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions. Furthermore, although a logical order is shown in the flowchart, in some cases, the steps shown or described may be executed in a different order than that shown here.

[0052] This embodiment provides a method for calibrating the working distance of a scanning electron microscope, which can be used in the aforementioned computer system. Figure 1 This is a flowchart of a scanning electron microscope working distance calibration method according to an embodiment of the present invention, such as... Figure 1 As shown, the process includes the following steps:

[0053] Step S101: Place elevation samples with different heights on the sample stage of the scanning electron microscope to be calibrated, set different accelerating voltages, and change the objective lens focal length by adjusting the objective lens excitation to make the elevation samples clear images. This will obtain the objective lens excitation when the elevation samples are clearly imaged at different accelerating voltages under a fixed working distance, and the objective lens excitation when the elevation samples are clearly imaged at different working distances under a fixed accelerating voltage. The objective lens focal length is equal to the actual working distance of the elevation samples when the elevation samples are clearly imaged.

[0054] Specifically, the elevation sample is a standard reference object with a known precise height or thickness, mainly used to calibrate the working distance, magnification, depth of field, or height measurement functions of an electron microscope.

[0055] During scanning electron microscope (SEM) calibration, a single elevation sample is placed on the stage at a time. The stage's position in the XY direction of the horizontal plane is adjusted until the elevation sample appears in the SEM's field of view. Then, the objective excitation is adjusted to ensure a clear image of the elevation sample surface. In SEM, the parameter corresponding to objective excitation is the objective ampere-turns, typically adjusted by changing the current in the objective coil. Changes in current cause changes in the magnetic field strength. Electrons experience a Lorentz force in a magnetic field, and the magnetic field generated by the objective excitation affects the electron's trajectory. In principle, focal length refers to the distance from the point where a parallel electron beam converges after passing through the objective lens to the center of the objective lens. However, when the objective excitation changes, the magnetic field strength changes, altering the magnitude and direction of the Lorentz force on the electrons, thus changing the electron beam's convergence. Increased excitation strengthens the magnetic field, causing the electron beam to converge faster, equivalent to a shorter focal length; decreased excitation weakens the magnetic field, causing the electron beam to converge more slowly, equivalent to a longer focal length.

[0056] When the elevation sample is clearly imaged in the field of view of a scanning electron microscope (SEM), it should be located on the focal plane of the objective lens. At this point, the elevation sample appears clearest. Therefore, when the elevation sample is clearly imaged, the objective lens focal length can be considered equal to the actual working distance of the elevation sample. The actual working distance of the elevation sample is the distance from the lower end of the objective lens pole piece to the objective lens focal point. Since the focal point of an SEM image is essentially on the sample surface, the working distance is often understood as the distance from the lower end of the pole piece to the sample surface. However, strictly speaking, there is a slight difference between the working distance and the objective lens focal length, but this difference is usually negligible. For users, the concept of working distance is more intuitive than that of objective lens focal length.

[0057] For a sample at the same elevation, the accelerating voltage is changed to obtain objective excitations at different accelerating voltages. Then, samples at different elevations are used, and the accelerating voltage is changed to obtain objective excitations corresponding to different accelerating voltages for that sample. In this way, different objective excitations at different elevations and different accelerating voltages can be obtained.

[0058] Step S102: For the same actual working distance, the first fitting model is used to fit different accelerating voltages and corresponding objective lens excitations to determine the first calibration parameters and the second calibration parameters of the first fitting model.

[0059] Specifically, according to calculations based on electron optics theory, the relationship between the focal length of the electron microscope objective, the objective excitation, and the accelerating voltage is expressed as follows:

[0060]

[0061] Where S and D are the objective lens electron optical constants, f represents the objective lens focal length, N represents the number of turns of the objective lens coil, I represents the current through the objective lens coil, NI represents the objective lens excitation of the scanning electron microscope, and V r This indicates the accelerating voltage.

[0062] Based on the above formula (1), it can be seen that for the same actual working distance and the same objective lens focal length, NI∝C(V r ) 0.5 Where C is the first calibration parameter. Existing technologies for calibrating the working distance are all based on NI∝C(V). r ) 0.5 The test results are used to fit a constant coefficient C, which is then used to calculate the objective excitation current and its corresponding working distance software-indicated value when switching accelerating voltages. However, when using the above expression for calibration, the working distance indicated by the software fluctuates by up to 18% when switching accelerating voltages, leading to a decrease in the accuracy of subsequent parameter calibration. Therefore, this embodiment introduces a first fitting model with two calibration parameters, using different expressions to fit different accelerating voltages and corresponding objective excitations to determine the two calibration parameters.

[0063] Step S103: For the same accelerating voltage, the second fitting model is used to fit different actual working distances and corresponding objective lens excitations to determine the third, fourth, and fifth calibration parameters of the second fitting model.

[0064] Specifically, based on the above formula (1), when the accelerating voltage is the same, the relationship between the objective lens focal length and the objective lens excitation is: NI=x1f 2 Using the experimental data on the objective lens focal length and objective lens excitation under the same accelerating voltage, a binary fit is performed to obtain the third calibration parameter x1, the fourth calibration parameter x2, and the fifth calibration parameter x3. The specific fitting process is a mature existing technology and will not be described in detail here.

[0065] Step S104: The scanning electron microscope to be calibrated is calibrated using the first calibration parameter, the second calibration parameter, the third calibration parameter, the fourth calibration parameter, and the fifth calibration parameter.

[0066] Specifically, the final values ​​of the first calibration parameter, the second calibration parameter, the third calibration parameter, the fourth calibration parameter, and the fifth calibration parameter are input into the scanning electron microscope to be calibrated to achieve calibration.

[0067] The scanning electron microscope (SEM) working distance calibration method provided in this embodiment determines multiple calibration parameters through two fitting models. This ensures that, under the premise that the actual working distance of the sample remains unchanged, the software display value of the working distance remains unchanged when the sample is re-imaged clearly, even when the accelerating voltage and magnification are changed. This improves the accuracy of the calibration of key parameters of the SEM before it leaves the factory.

[0068] This embodiment provides a method for calibrating the working distance of a scanning electron microscope, which can be used in the aforementioned computer system. Figure 2This is a flowchart of a scanning electron microscope working distance calibration method according to an embodiment of the present invention, such as... Figure 2 As shown, the process includes the following steps:

[0069] Step S201: Place elevation samples with different heights on the sample stage of the scanning electron microscope to be calibrated, set different accelerating voltages, and change the objective lens focal length by adjusting the objective lens excitation to make the elevation samples clear images. This will obtain the objective lens excitation when the elevation samples are clearly imaged at different accelerating voltages under a fixed working distance, and the objective lens excitation when the elevation samples are clearly imaged at different working distances under a fixed accelerating voltage. When the elevation samples are clearly imaged, the objective lens focal length is equal to the actual working distance of the elevation samples.

[0070] In some optional implementations, elevation samples of different heights include: step samples with multiple steps, each step serving as an elevation sample; the process of determining the working distance of the elevation samples includes:

[0071] Step a1: Adjust the height of the sample stage so that the top layer of the stepped sample touches the lower pole shoe of the objective lens.

[0072] Specifically, such as Figure 3 The diagram shows the structure of the stepped sample. Except for the top layer, each step surface has an electron microscope calibration standard copper mesh attached. The sample is a standard height sample used for internal calibration by the equipment manufacturer. Each step is 5mm high. During calibration, the accuracy of the calibration adjustment is ensured by making the copper mesh clear and straight in the field of view. The stepped sample is placed on the sample stage, with the top layer of the stepped sample close to the lower pole piece of the objective lens. The height of the sample stage is slowly adjusted until the top layer of the stepped sample touches the lower pole piece of the objective lens.

[0073] Step a2: Based on the number of steps corresponding to the elevation sample and the height of each step, determine the distance from the top of the elevation sample to the top of the step sample, which is used as the working distance of the elevation sample.

[0074] Specifically, for stepped samples, the height of each step is the same. Therefore, the distance from the top of the step sample to the elevation sample can be determined according to the number of steps of the elevation sample. For example, if the elevation sample is a standard copper mesh on the third step, then the working distance of the elevation sample is 3×5mm=15mm. This is just an example, but it is not a limitation.

[0075] The scanning electron microscope working distance calibration method provided in this embodiment uses a step sample as an elevation sample to provide a clear and stable physical size reference. The working distance indicated by the electron microscope software can be directly compared with the standard value of the step height, which facilitates rapid and repeated measurement and calibration, and provides a reliable benchmark for electron microscope measurements.

[0076] Step S202: For the same actual working distance, the first fitting model is used to fit different accelerating voltages and corresponding objective lens excitations to determine the first calibration parameters and the second calibration parameters of the first fitting model.

[0077] Specifically, the first fitting model is used to represent the relationship between objective lens excitation and accelerating voltage at the same working distance. The process of determining the first fitting model includes:

[0078] Based on electron optics theory, the relationship between the objective lens focal length, objective lens excitation, and accelerating voltage of a scanning electron microscope is determined as follows:

[0079]

[0080] Where S and D are the objective lens electron optical constants, f represents the objective lens focal length, N represents the number of turns of the objective lens coil, I represents the current through the objective lens coil, NI represents the objective lens excitation of the scanning electron microscope, and V r Indicates accelerating voltage;

[0081] Based on the relationship between the objective lens focal length, objective lens excitation, and accelerating voltage of a scanning electron microscope, the relationship between objective lens excitation and accelerating voltage is determined as follows when the objective lens focal length remains constant:

[0082] NI∝C(V r ) α Where C represents the first calibration parameter and α represents the second calibration parameter.

[0083] Specifically, based on the above formula (1), it can be seen that for the same actual working distance and the same objective lens focal length, NI∝C(V r ) 0.5 Where C is the first calibration parameter. To improve calibration accuracy, a second calibration parameter is introduced, resulting in the relationship between objective excitation and accelerating voltage: NI∝C(V r ) α .

[0084] This embodiment introduces a first fitting model NI∝C(V) with two calibration parameters. r ) α The first fitting model includes: a first calibration parameter C and a second calibration parameter α. In conventional techniques, α = 0.5 is a fixed value. In this embodiment, α is used as a variable. Based on the actual experimental data of different scanning electron microscope equipment, different accelerating voltages and corresponding objective lens excitations, the two calibration parameters are fitted to ensure that the calibration results of different scanning electron microscopes are more accurate.

[0085] In some optional implementations, a first fitting model is used to fit different accelerating voltages and corresponding objective excitations to determine the first calibration parameters and second calibration parameters of the first fitting model, including:

[0086] The first fitting model is linearized to obtain a linear fitting model.

[0087] Specifically, the first fitted model is a nonlinear model, which is linearized to reduce the processing difficulty. For the first fitted model, NI∝C(V) r ) α Linearization is performed by taking the natural logarithm of both sides, resulting in lnNI ∝ lnC + αlnV. r , let Y=lnNI, A=lnC, X=lnV r This transforms the original nonlinear model into a linear model Y∝A+αX, allowing the parameters to be solved using linear regression.

[0088] Based on different accelerating voltages and corresponding objective lens excitations, the linear fitting model is solved using the least squares method to obtain the first calibration parameter and the second calibration parameter.

[0089] Specifically, multiple sets of accelerating voltage data and their corresponding objective excitation data can be obtained through actual measurements using an electron microscope under different operating conditions. To ensure data quality, the raw data needs to be cleaned to remove outliers and noise, avoiding their adverse effects on subsequent fitting results. Taking the natural logarithm of the collected accelerating voltage and objective excitation data respectively, we obtain X = lnV. r And Y = lnNI, so that the data conforms to the form requirement of the linear fitting model Y∝A+αX.

[0090] The least squares method is used to estimate the parameters of the linear fitting model Y∝A+αX. The core idea of ​​the least squares method is to find a set of parameters A and α such that the sum of squared errors between the observed values ​​Y and the fitted values ​​Y' predicted by the model for all data points is minimized. Through mathematical derivation and calculation, the estimated values ​​of parameters A and α can be obtained. Based on the previous linearization transformation relationship, the parameters A obtained by the least squares method are expressed as C=e A The first calibration parameter C is calculated; while the parameter α obtained by directly solving the least squares method is the second calibration parameter.

[0091] After obtaining the calibration parameters, the fitted model can be evaluated to determine whether its fit is good. The evaluation process is a mature existing technology and will not be described in detail here.

[0092] The scanning electron microscope working distance calibration method provided in this embodiment can accurately adjust the objective lens excitation by fitting the calibration parameters, optimize the electron beam focusing effect, reduce aberrations, and make the electron microscope imaging clearer and with higher resolution. This improves the accuracy of measuring the microstructure of the sample. The accurate calibration parameters can ensure that the electron beam can pass through the objective lens in the best condition under different accelerating voltages, avoiding problems such as image blurring and distortion caused by excitation and voltage mismatch, and ensuring the reliability of image data.

[0093] Step S203: For the same accelerating voltage, the second fitting model is used to fit different actual working distances and corresponding objective lens excitations to determine the third, fourth, and fifth calibration parameters of the second fitting model.

[0094] In some optional implementations, a second fitting model is used to represent the relationship between objective excitation and the calibrated working distance under the same accelerating voltage. The process of determining the second fitting model includes:

[0095] Based on the relationship between the objective lens focal length, objective lens excitation, and accelerating voltage of a scanning electron microscope, the relationship between objective lens excitation and the indicated working distance is determined when the accelerating voltage remains constant:

[0096] NI = p1(WD) 2 +p2(WD) 1 +p3(WD) 0 Where WD indicates the working distance, p1 indicates the third calibration parameter, p2 indicates the fourth calibration parameter, and p3 indicates the fifth calibration parameter.

[0097] The scanning electron microscope working distance calibration method provided in this embodiment improves the accuracy of working distance calibration by fixing the working distance, performing a first fitting on different accelerating voltages and corresponding objective excitations, then fixing the accelerating voltage, and performing a second fitting on different working distances and corresponding objective excitations, and finally obtaining the values ​​of five calibration parameters.

[0098] Step S204: The scanning electron microscope to be calibrated is calibrated using the first calibration parameter, the second calibration parameter, the third calibration parameter, the fourth calibration parameter, and the fifth calibration parameter. For details, please refer to [link to relevant documentation]. Figure 1 Step S101 of the illustrated embodiment will not be described again here.

[0099] In some optional implementations, after calibrating the scanning electron microscope to be calibrated, the method further includes:

[0100] Step S205: Obtain the actual working distance and the marked working distance of the calibrated scanning electron microscope when it operates under different accelerating voltages.

[0101] Step S206: Calculate the deviation between the indicated working distance and the actual working distance under different accelerating voltages, and evaluate the calibration accuracy of the scanning electron microscope based on the deviation value.

[0102] Specifically, when the scanning electron microscope to be calibrated is based on NI∝C(V r ) 0.5 During fitting, switch the acceleration voltage; the working distance value indicated by the software is as follows: Figure 4 The blue dotted line indicates the state before correction, based on the scanning electron microscope to be calibrated according to NI∝C(V). r ) 0.5 The software-defined values ​​obtained through fitting. For the same scanning electron microscope to be calibrated, according to NI∝C(V r ) α During fitting, the sample stage height remains constant (working distance remains constant). When switching the accelerating voltage, the working distance value indicated by the software is as follows: Figure 4 The gray dotted lines indicate the corrected scanning electron microscope to be calibrated, based on NI∝C(V). r ) α The software-defined values ​​obtained through fitting. Figure 4 The red dotted line represents the actual working distance. In this embodiment, the height of the sample is 5mm. Figure 4 It can be seen that when the sample stage height remains constant, switching the accelerating voltage, based on NI∝C(V) r ) 0.5 The fitted model yielded a significant deviation between the software-labeled working distance (blue dotted line) and the actual working distance (red dotted line), reaching a maximum of 18%. This deviation is based on NI∝C(V r ) α The software-labeled working distance (gray dotted line) obtained by the fitted model is not completely consistent with the actual working distance (red dotted line), but it greatly reduces the deviation from the actual working distance, and the stability of the deviation value under different acceleration voltages is improved.

[0103] Figure 5 To switch the acceleration voltage for different actual working distances, based on NI∝C(V) r ) 0.5 ,NI∝C(V r ) α The obtained labeled working distance, according to current test data, has a maximum deviation between the labeled working distance and the actual working distance, which is determined by NI∝C(V) before the fitting model optimization. r ) 0.5 The 18% reduction was optimized to NI∝C(V) r ) αBefore optimization, 41% of the total test data had a deviation greater than 5%, and 41% had a deviation greater than 8%. After optimization, approximately 83.3% of the total test data had a deviation less than 4%, and approximately 50% had a deviation less than 2%. The accuracy of subsequent parameter calibrations was greatly improved after the objective working distance software calibration was corrected based on this optimized fitting model.

[0104] The scanning electron microscope (SEM) working distance calibration method provided in this embodiment optimizes the functional relationship between accelerating voltage and lens excitation in the SEM system at a fixed working distance, reducing the deviation between the working distance software-indicated value and the actual value (the former is derived from the lens excitation through the functional relationship). This further ensures that the software-displayed values ​​of physical quantities (such as working distance, magnification, and sample feature size) in the electron microscope measurement system are consistent with the true values, thereby improving the accuracy and consistency of the equipment's imaging information.

[0105] In one specific embodiment, the calibration process of the scanning electron microscope to be calibrated includes:

[0106] (1) Place the stepped sample on the sample stage, with the top layer of the stepped sample close to the surface of the pole shoe under the objective lens.

[0107] (2) Apply the accelerating voltage to 30KV (the accelerating voltage of a scanning electron microscope is generally adjustable within the range of 200V to 30KV), and adjust the z-axis knob of the sample stage to adjust the height of the sample stage so that the top layer of the stepped sample hits the lower pole shoe of the objective lens.

[0108] (3) Adjust the X and Y direction knobs of the sample stage so that the standard copper mesh on the third step of the stepped sample appears in the field of view. At this time, the distance between the standard copper mesh on the third step and the lower surface of the objective lens pole shoe is 15mm.

[0109] (4) Adjust the objective lens excitation so that the surface of the standard copper mesh on the third step can be focused and clearly imaged. At this time, the actual working distance is 15mm. Record the objective lens excitation at this time.

[0110] (5) Keep the sample stage unchanged, switch the accelerating voltage in sequence, and record the objective lens excitation when the surface of the standard copper mesh on the third step is clearly focused and imaged under different accelerating voltages.

[0111] (6) Change the standard copper mesh on the observed step sample, repeat steps (3)-(5) above, and record the objective lens excitation corresponding to the clear imaging of the standard copper mesh under different accelerating voltages when the actual working distances are 10mm, 5mm, 20mm, 25mm, and 30mm, such as... Figure 4 , Figure 5 As shown.

[0112] (7) Fitting based on experimental data (working distance, objective excitation, acceleration voltage): Fix the working distance, fit the objective excitation when clear imaging is achieved under different acceleration voltages with the corresponding acceleration voltage to obtain the first calibration parameter and the second calibration parameter; fix the acceleration voltage, fit the objective excitation when clear imaging is achieved under different working distances with the working distance in a quadratic term to obtain the third calibration parameter, the fourth calibration parameter, and the fifth calibration parameter.

[0113] This embodiment also provides a working distance calibration system for a scanning electron microscope, which is used to implement the above embodiments and preferred embodiments; details already described will not be repeated. As used below, the term "module" can refer to a combination of software and / or hardware that performs a predetermined function. Although the system described in the following embodiments is preferably implemented in software, hardware implementation, or a combination of software and hardware, is also possible and contemplated.

[0114] This embodiment provides a working distance calibration system for a scanning electron microscope, such as... Figure 6 As shown, it includes:

[0115] The test condition setting module 601 is used to place elevation samples with different heights on the sample stage of the scanning electron microscope to be calibrated, set different accelerating voltages, and change the objective lens focal length by adjusting the objective lens excitation to make the elevation samples clear images. This allows for obtaining the objective lens excitation when the elevation samples are clearly imaged at different accelerating voltages under a fixed working distance, as well as the objective lens excitation when the elevation samples are clearly imaged at different working distances under a fixed accelerating voltage. The objective lens focal length is equal to the actual working distance of the elevation samples when the elevation samples are clearly imaged.

[0116] The first fitting module 602 is used to fit different accelerating voltages and corresponding objective lens excitations using a first fitting model for the same actual working distance, and to determine the first calibration parameters and the second calibration parameters of the first fitting model.

[0117] The second fitting module 603 is used to fit different actual working distances and corresponding objective lens excitations using the second fitting model for the same accelerating voltage, and to determine the third, fourth, and fifth calibration parameters of the second fitting model.

[0118] The parameter calibration module 604 is used to calibrate the scanning electron microscope to be calibrated using the first calibration parameter, the second calibration parameter, the third calibration parameter, the fourth calibration parameter, and the fifth calibration parameter.

[0119] Further functional descriptions of the above modules and units are the same as those in the corresponding embodiments described above, and will not be repeated here.

[0120] In this embodiment, the working distance calibration system of the scanning electron microscope is presented in the form of a functional unit. Here, a unit refers to an ASIC (Application Specific Integrated Circuit) circuit, a processor and memory that execute one or more software or fixed programs, and / or other devices that can provide the above functions.

[0121] This invention also provides a scanning electron microscope having the above-described features. Figure 6 The working distance calibration system of the scanning electron microscope shown is illustrated.

[0122] Please see Figure 7 , Figure 7 This is a schematic diagram of the structure of a controller in a scanning electron microscope provided in an optional embodiment of the present invention, as shown below. Figure 7 As shown, the scanning electron microscope includes at least one or more processors 10, a memory 20, and interfaces for connecting the components, including high-speed interfaces and low-speed interfaces. The components communicate with each other via different buses and can be mounted on a common motherboard or otherwise installed as needed. The processors can process instructions executed within the computer device, including instructions stored in or on memory to display graphical information of a GUI on an external input / output device (such as a display device coupled to the interface). In some alternative implementations, multiple processors and / or multiple buses can be used with multiple memories and multiple memory modules, if desired. Similarly, multiple computer devices can be connected, each providing some of the necessary operations (e.g., as a server array, a group of blade servers, or a multiprocessor system). Figure 7 Take a processor 10 as an example.

[0123] Processor 10 may be a central processing unit, a network processor, or a combination thereof. Processor 10 may further include a hardware chip. The hardware chip may be an application-specific integrated circuit (ASIC), a programmable logic device (PLD), or a combination thereof. The programmable logic device may be a complex programmable logic device (CAMP), a field-programmable gate array (FPGA), a general-purpose array logic (GDA), or any combination thereof.

[0124] The memory 20 stores instructions executable by at least one processor 10 to cause the at least one processor 10 to perform the method shown in the above embodiments.

[0125] The memory 20 may include a program storage area and a data storage area. The program storage area may store the operating system and applications required for at least one function; the data storage area may store data created based on the use of the computer device. Furthermore, the memory 20 may include high-speed random access memory and may also include non-transitory memory, such as at least one disk storage device, flash memory device, or other non-transitory solid-state storage device. In some alternative embodiments, the memory 20 may optionally include memory remotely located relative to the processor 10, and these remote memories may be connected to the computer device via a network. Examples of such networks include, but are not limited to, the Internet, intranets, local area networks, mobile communication networks, and combinations thereof.

[0126] The memory 20 may include volatile memory, such as random access memory; the memory may also include non-volatile memory, such as flash memory, hard disk or solid-state drive; the memory 20 may also include a combination of the above types of memory.

[0127] The computer device also includes a communication interface 30 for communicating with other devices or communication networks.

[0128] This invention also provides a computer-readable storage medium. The methods described above according to embodiments of the invention can be implemented in hardware or firmware, or implemented as computer code that can be recorded on a storage medium, or implemented as computer code downloaded via a network and originally stored on a remote storage medium or a non-transitory machine-readable storage medium and then stored on a local storage medium. Thus, the methods described herein can be processed by software stored on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. The storage medium can be a magnetic disk, optical disk, read-only memory, random access memory, flash memory, hard disk, or solid-state drive, etc.; further, the storage medium can also include combinations of the above types of memory. It is understood that computers, processors, microprocessor controllers, or programmable hardware include storage components capable of storing or receiving software or computer code, which, when accessed and executed by the computer, processor, or hardware, implements the methods shown in the above embodiments.

[0129] A portion of this invention can be applied as a computer program product, such as computer program instructions, which, when executed by a computer, can invoke or provide the methods and / or technical solutions according to the invention through the operation of the computer. Those skilled in the art will understand that the forms in which computer program instructions exist in a computer-readable medium include, but are not limited to, source files, executable files, installation package files, etc. Correspondingly, the ways in which computer program instructions are executed by a computer include, but are not limited to: the computer directly executing the instructions, or the computer compiling the instructions and then executing the corresponding compiled program, or the computer reading and executing the instructions, or the computer reading and installing the instructions and then executing the corresponding installed program. Here, the computer-readable medium can be any available computer-readable storage medium or communication medium accessible to a computer.

[0130] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A method for calibrating the working distance of a scanning electron microscope, characterized in that, The method includes: Elevation samples with different heights are placed on the sample stage of the scanning electron microscope to be calibrated. Different accelerating voltages are set, and the objective lens focal length is changed by adjusting the objective lens excitation to make the elevation samples clear images. This is to obtain the objective lens excitation when the elevation samples are clearly imaged at different accelerating voltages under a fixed working distance, and the objective lens excitation when the elevation samples are clearly imaged at different working distances under a fixed accelerating voltage. The objective lens focal length when the elevation samples are clearly imaged is equal to the actual working distance of the elevation samples. For the same actual working distance, a first fitting model is used to fit different accelerating voltages and corresponding objective excitations to determine the first calibration parameters and second calibration parameters of the first fitting model. The first fitting model is used to represent the relationship between objective excitation and accelerating voltage at the same actual working distance. The process of determining the first fitting model includes: based on electron optics theory, determining the relationship between the objective focal length of the scanning electron microscope, objective excitation, and accelerating voltage as follows: in, and The electron optical constant of the objective lens. Indicates the focal length of the objective lens. Indicates the number of turns of the objective lens coil. This indicates the current passing through the objective lens coil. This indicates the objective lens excitation of a scanning electron microscope. This represents the accelerating voltage. Based on the relationship between the objective lens focal length, objective lens excitation, and accelerating voltage of a scanning electron microscope, the relationship between objective lens excitation and accelerating voltage when the objective lens focal length remains constant is determined as follows: ,in, Indicates the first calibration parameter. Indicates the second calibration parameter; For the same accelerating voltage, a second fitting model is used to fit different actual working distances and corresponding objective excitations, determining the third, fourth, and fifth calibration parameters of the second fitting model. The second fitting model represents the relationship between objective excitation and the indicated working distance under the same accelerating voltage. The process of determining the second fitting model includes: based on the objective focal length of the scanning electron microscope, the relationship between objective excitation and accelerating voltage, determining the conversion relationship between objective excitation and the indicated working distance when the accelerating voltage remains constant as follows: ,in, Indicates the working distance. This indicates the third calibration parameter. This indicates the fourth calibration parameter. This indicates the fifth calibration parameter; The scanning electron microscope to be calibrated is calibrated using the first calibration parameter, the second calibration parameter, the third calibration parameter, the fourth calibration parameter, and the fifth calibration parameter.

2. The method according to claim 1, characterized in that, The elevation samples at different heights include: step samples with multiple steps, each step serving as an elevation sample; the process for determining the working distance of the elevation samples includes: Adjust the height of the sample stage so that the top layer of the stepped sample touches the lower pole shoe of the objective lens; Based on the number of steps corresponding to the elevation sample and the height of each step, the distance from the elevation sample to the top of the step sample is determined as the working distance of the elevation sample.

3. The method according to claim 1, characterized in that, The first fitting model is used to fit different accelerating voltages and corresponding objective excitations to determine the first calibration parameters and the second calibration parameters of the first fitting model, including: The first fitting model is linearized to obtain a linear fitting model. Based on different accelerating voltages and corresponding objective lens excitations, the linear fitting model is solved using the least squares method to obtain the first calibration parameter and the second calibration parameter.

4. The method according to claim 1, characterized in that, After calibrating the scanning electron microscope to be calibrated, the method further includes: Obtain the actual working distance and the labeled working distance of the calibrated scanning electron microscope when it operates under different accelerating voltages; The deviation between the indicated working distance and the actual working distance under different accelerating voltages is calculated, and the calibration accuracy of the scanning electron microscope is evaluated based on the deviation.

5. A working distance calibration system for a scanning electron microscope, employing the working distance calibration method for a scanning electron microscope as described in any one of claims 1-4, characterized in that, The system includes: The test condition setting module is used to place elevation samples with different heights on the sample stage of the scanning electron microscope to be calibrated, set different accelerating voltages, and change the objective lens focal length by adjusting the objective lens excitation to make the elevation sample clear image. This module obtains the objective lens excitation when the elevation sample is clearly imaged at different accelerating voltages under a fixed working distance, and the objective lens excitation when the elevation sample is clearly imaged at different working distances under a fixed accelerating voltage. The objective lens focal length is equal to the actual working distance of the elevation sample when the elevation sample is clearly imaged. The first fitting module is used to fit different accelerating voltages and corresponding objective excitations using a first fitting model for the same actual working distance, and to determine the first calibration parameters and second calibration parameters of the first fitting model. The first fitting model is used to represent the relationship between objective excitation and accelerating voltage at the same actual working distance. The process of determining the first fitting model includes: determining the relationship between the objective focal length, objective excitation, and accelerating voltage of the scanning electron microscope according to electron optics theory as follows: in, and The electron optical constant of the objective lens. Indicates the focal length of the objective lens. Indicates the number of turns of the objective lens coil. This indicates the current passing through the objective lens coil. This indicates the objective lens excitation of a scanning electron microscope. This represents the accelerating voltage. Based on the relationship between the objective lens focal length, objective lens excitation, and accelerating voltage of a scanning electron microscope, the relationship between objective lens excitation and accelerating voltage when the objective lens focal length remains constant is determined as follows: ,in, Indicates the first calibration parameter. Indicates the second calibration parameter; The second fitting module is used to fit different actual working distances and corresponding objective excitations using a second fitting model for the same accelerating voltage, and to determine the third, fourth, and fifth calibration parameters of the second fitting model. The second fitting model is used to represent the relationship between objective excitation and the indicated working distance under the same accelerating voltage. The process of determining the second fitting model includes: based on the relationship between the objective focal length of the scanning electron microscope, objective excitation, and accelerating voltage, determining the conversion relationship between objective excitation and indicated working distance when the accelerating voltage remains constant as follows: ,in, Indicates the working distance. This indicates the third calibration parameter. This indicates the fourth calibration parameter. This indicates the fifth calibration parameter; The parameter calibration module is used to calibrate the scanning electron microscope to be calibrated using the first calibration parameter, the second calibration parameter, the third calibration parameter, the fourth calibration parameter, and the fifth calibration parameter.

6. A scanning electron microscope, characterized in that, include: A memory and a processor, the memory and the processor being communicatively connected to each other, the memory storing computer instructions, the processor executing the computer instructions to perform the method of any one of claims 1 to 4.

7. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions for causing a computer to perform the method of any one of claims 1 to 4.

8. A computer program product, characterized in that, Includes computer instructions for causing a computer to perform the method of any one of claims 1 to 4.

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