Objective alignment method for e-beam metrology apparatus and e-beam metrology apparatus

Abstract

The application provides an objective lens alignment method of an electron beam measuring device and the electron beam measuring device. The objective lens alignment method of the electron beam measuring device comprises the following steps: adding a periodic oscillation current to a starting current value of an objective lens to obtain an actual image offset of an image generated by an electron beam under a preset current of each deflection coil; obtaining a current value optimal solution of each deflection coil based on a preset physical model according to the preset current of each deflection coil and the actual image offset; and adding the periodic oscillation current to the starting current value of the objective lens and calculating an actual image amplitude at the time when each deflection coil is the current value optimal solution, and confirming an alignment state of the objective lens according to the actual image amplitude. According to the scheme of the application, the current value optimal solution is inversely solved through the preset physical model, the complexity of algorithm operation is reduced, and the stability of calculation is ensured on the basis of taking into account the algorithm operation efficiency.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to an objective lens alignment method and an electron beam measurement device. Background Technology

[0002] In electron beam measurement equipment, objective lens alignment essentially involves aligning the objective lens with the optical axis of the electron beam, ensuring the electron beam passes through the center of the objective lens. Precise alignment is fundamental for obtaining clear images and accurate measurement results. However, in actual measurements, the optimal hardware parameters can drift to some extent over time, necessitating periodic calibration of certain hardware parameters.

[0003] Objective lens alignment, as a crucial calibration process, requires automation. Traditional objective lens alignment methods rely on manual operation, making it difficult to guarantee consistency and reliability in high-throughput and high-precision applications. With the advancement of electron beam metrology towards the nanoscale and high-throughput directions, automated objective lens alignment technology is becoming an inevitable trend. Oscillating objective current technology has emerged as a core technology for improving accuracy and automation in automated alignment systems, and is widely used in semiconductor manufacturing, lithography equipment alignment, nanofabrication, and precision measurement.

[0004] One such technique is oscillating objective current alignment, which involves applying minute periodic fluctuations to the current in the objective lens and monitoring the offset caused by these fluctuations to electron beam imaging. Key challenges in automated objective alignment technology primarily involve improving the accuracy, efficiency, and automation level of objective alignment.

[0005] Existing technologies for automatic objective lens alignment in electron beam measurement equipment adjust the current of the deflection coils in the X and Y directions by applying oscillating objective lens current, using a step-search method to locate the deflection coil current value with the smallest image amplitude. However, this step-search method requires the electron beam to continuously and repeatedly scan a specific area of ​​the sample, which can easily lead to charge accumulation and charging effects. When charging effects exist on the sample surface, the electron beam will drift, and the image will shift accordingly. This shift is not caused by objective lens misalignment but is an additional interference, ultimately affecting the accuracy and success rate of automatic objective lens alignment. Furthermore, the aforementioned step-search method requires acquiring a large number of images. The number of images acquired directly affects the execution efficiency of automated objective lens alignment, significantly reducing the performance of existing automatic objective lens alignment solutions. Summary of the Invention

[0006] One objective of this invention is to reduce the complexity of the algorithm by establishing a physical model to solve for the optimal current value, thereby ensuring computational stability while maintaining algorithm efficiency.

[0007] A further objective of this invention is to iteratively update valid data based on a random sampling consensus algorithm, thereby effectively reducing the risk of alignment failure and improving the accuracy of the algorithm.

[0008] Another further objective of this invention is to achieve automated objective lens alignment, eliminate alignment errors caused by manual operation, and ensure the stability and reliability of observation results.

[0009] Specifically, the present invention provides a method for aligning the objective lens of an electron beam measurement device, comprising:

[0010] Given the preset currents of each deflection coil, a periodic oscillating current is added to the initial current value of the objective lens to obtain the actual image offset of the image generated by the electron beam. The currents of each deflection coil are used to control different directions of motion of the electron beam.

[0011] Based on the preset current of each deflection coil and the actual image offset, the optimal solution for the current value of each deflection coil is obtained according to the preset physical model; and

[0012] When each deflection coil has the optimal current value, a periodic oscillating current is added to the initial current value of the objective lens, and the actual image amplitude is calculated. The alignment state of the objective lens is then confirmed based on the actual image amplitude.

[0013] Optionally, each deflection coil includes a first deflection coil for controlling a first direction of motion of the electron beam and a second deflection coil for controlling a second direction of motion of the electron beam; and

[0014] The physical model is

[0015] in, The transformation matrix θ represents the relationship between the actual image offset and the rotation angle of the currents in the first and second deflection coils. x S is used to characterize the scaling relationship between the actual image offset and the current of the first deflection coil. y ΔC is used to characterize the scaling relationship between the actual image offset and the current of the second deflection coil. x ΔC y ΔX and ΔY represent the current changes of the first and second deflection coils relative to their initial current values, respectively; ΔX and ΔY represent the initial image offsets in the first and second motion directions, respectively, when the first and second deflection coils are at their initial current values, after adding a periodic oscillating current to the initial current value of the objective lens; ΔX i ΔY iThe actual image offset in the first and second motion directions is calculated by adding a periodic oscillating current to the initial current value of the objective lens under the changed current conditions of the first and second deflection coils, respectively.

[0016] Optionally, the step of obtaining the optimal solution for the current value of each deflection coil based on a preset physical model according to the preset current of each deflection coil and the actual image offset includes:

[0017] Solve for the transformation matrix; and

[0018] The optimal solution for the current value is obtained by inversely solving the transformation matrix.

[0019] Optionally, given the preset currents of each deflection coil, the step of adding a periodic oscillating current to the initial current value of the objective lens to obtain the actual image offset of the image generated by the electron beam includes:

[0020] The first deflection coil and the second deflection coil are In this case, the actual image offset is calculated by adding a periodic oscillating current to the initial current value of the objective lens.

[0021] The first deflection coil and the second deflection coil are In this case, a periodic oscillating current is added to the initial current value of the objective lens, and the actual image offset is calculated.

[0022] The first deflection coil and the second deflection coil are In this case, a periodic oscillating current is added to the initial current value of the objective lens, and the actual image offset is calculated.

[0023] The first deflection coil and the second deflection coil are In this case, a periodic oscillating current is added to the initial current value of the objective lens, and the actual image offset is calculated. Where Cx0 and Cy0 are the initial current values ​​of the first deflection coil and the second deflection coil, respectively, and ΔC is the current change of the first deflection coil or the second deflection coil compared to the initial current values ​​Cx0 and Cy0;

[0024] The steps to solve for the transformation matrix include:

[0025] Substituting the actual image offsets mentioned above into the physical model, we obtain the formula.

[0026] And solve the transformation matrix using the least squares method.

[0027] Optionally, the steps of inversely solving for the optimal current value based on the transformation matrix include:

[0028] First, based on the transformation matrix and the formula Solving for the results

[0029] Then according to Based on formula The optimal solution for the current value is obtained by solving the problem.

[0030] Optionally, the step of confirming the alignment of the objective lens based on the actual image amplitude includes:

[0031] Determine whether the actual image amplitude is less than or equal to a preset threshold; and

[0032] If so, confirm that the objective lens is successfully aligned, and

[0033] When the actual image amplitude exceeds a preset threshold, the data is iteratively updated using a random sampling consensus algorithm. The updated data is then substituted into the physical model to solve for the optimal solution of the updated transformation matrix and current value.

[0034] The process is repeated, where the optimal current values ​​for the first and second deflection coils are found. Then, a periodic oscillating current is added to the initial current value of the objective lens, and the actual image amplitude is calculated.

[0035] Optionally, the step of iteratively updating the data according to the random sampling consensus algorithm also includes:

[0036] Record the actual number of times the data is updated iteratively, and

[0037] If the actual image amplitude is greater than a preset threshold, determine whether the actual number of occurrences is less than a preset number of occurrences; and

[0038] If so, execute the step of iteratively updating the data according to the random sampling consensus algorithm.

[0039] If not, restore the initial current values ​​of the first and second deflection coils.

[0040] Optionally, the step of obtaining the actual image offset may include:

[0041] Determine the position of the reference pattern on the sample within the preset imaging field of view;

[0042] Obtain the initial current values ​​of the first deflection coil and the second deflection coil.

[0043] With the first and second deflection coils as initial current values, a periodic oscillating current is added to the initial current value of the objective lens, and images are acquired in real time. The initial image offset is calculated based on the position of the reference pattern and converted into the initial image amplitude; and

[0044] Confirm the alignment of the objective lens based on the initial image amplitude.

[0045] Optionally, the first direction of motion and the second direction of motion are orthogonal, and

[0046] The steps to convert the initial image offset into the initial image amplitude include:

[0047] According to the formula The initial image amplitude was calculated.

[0048] According to another aspect of the present invention, an electron beam measurement device is also provided, including a memory, a processor, and a computer program stored in the memory and running on the processor, wherein the processor executes the computer program to implement the objective lens alignment method of any of the above-described electron beam measurement devices.

[0049] The objective lens alignment method of the electron beam measurement device of the present invention, under the condition of preset current of each deflection coil, adds a periodic oscillating current to the initial current value of the objective lens to obtain the actual image offset of the image generated by the electron beam. Based on the preset current of each deflection coil and the actual image offset, the optimal solution of the current value of each deflection coil is obtained according to a preset physical model. When the current value of each deflection coil is the optimal solution, a periodic oscillating current is added to the initial current value of the objective lens and the actual image amplitude at this time is calculated. The alignment state of the objective lens is confirmed according to the actual image amplitude. The optimal solution of the current value is solved by reversing the preset physical model, which reduces the complexity of the algorithm operation and ensures the stability of the calculation while taking into account the efficiency of the algorithm operation.

[0050] Furthermore, the objective lens alignment method of the electron beam measurement device of the present invention, when the actual image amplitude is greater than a preset threshold, iteratively updates the data according to the random sampling consensus algorithm, and uses the updated data to substitute into the physical model to solve for the optimal solution of the updated transformation matrix and current value. Iteratively updating the effective data according to the random sampling consensus algorithm effectively reduces the risk of alignment failure and improves the accuracy of the algorithm; it can realize automated objective lens alignment, eliminate alignment errors caused by manual operation, and ensure the stability and reliability of the observation results.

[0051] The above and other objects, advantages and features of the present invention will become more apparent to those skilled in the art from the following detailed description of specific embodiments of the invention in conjunction with the accompanying drawings. Attached Figure Description

[0052] The following sections will describe some specific embodiments of the invention in detail by way of example and not limitation, with reference to the accompanying drawings. The same reference numerals in the drawings denote the same or similar parts or portions. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0053] Figure 1 This is a schematic diagram of an objective lens alignment method for an electron beam measurement device according to an embodiment of the present invention;

[0054] Figure 2 This is a detailed flowchart of an objective lens alignment method for an electron beam measurement device according to an embodiment of the present invention;

[0055] Figure 3 This is a schematic diagram of an SEM image in an objective lens alignment method of an electron beam measurement device according to an embodiment of the present invention;

[0056] Figure 4 This is a schematic diagram of a computer program product according to an embodiment of the present invention;

[0057] Figure 5 This is a schematic diagram of a computer-readable storage medium according to an embodiment of the present invention; and

[0058] Figure 6 This is a schematic diagram of an electron beam measurement device according to an embodiment of the present invention. Detailed Implementation

[0059] This embodiment provides a method for aligning the objective lens of an electron beam measurement device. By solving the optimal solution of the current value through a preset physical model, the complexity of the algorithm is reduced, and the stability of the calculation is guaranteed while taking into account the efficiency of the algorithm. Figure 1 This is a schematic diagram of an objective lens alignment method for an electron beam measurement device according to an embodiment of the present invention. Figure 1 As shown, the objective lens alignment method of the electron beam measurement device in this embodiment generally includes:

[0060] Step S102: Under the preset current conditions of each deflection coil, add a periodic oscillating current to the initial current value of the objective lens to obtain the actual image offset of the image generated by the electron beam.

[0061] Step S104: Based on the preset current of each deflection coil and the actual image offset, obtain the optimal solution of the current value of each deflection coil according to the preset physical model.

[0062] Step S106: When each deflection coil has the optimal current value, add a periodic oscillation current to the initial current value of the objective lens and calculate the actual image amplitude at this time. Confirm the alignment state of the objective lens based on the actual image amplitude.

[0063] In the above steps, the current of each deflection coil in step S102 is used to control different directions of motion of the electron beam. In a specific embodiment, each deflection coil includes a first deflection coil for controlling a first direction of motion of the electron beam and a second deflection coil for controlling a second direction of motion of the electron beam. In a preferred embodiment, the first and second directions of motion are orthogonal. For example, the first direction of motion can be the X direction, and the second direction of motion can be the Y direction.

[0064] It should be noted that the current in the deflection coil is primarily used to control the scanning trajectory of the electron beam on the sample surface. The current in the objective lens is mainly used to control the magnetic field strength of the objective lens, thereby adjusting the focusing state and beam spot size of the electron beam. In electron beam metrology equipment, the synergistic effect of the deflection coil current and the objective lens current enables precise control and high-quality measurement of the electron beam. Specifically, by precisely adjusting the deflection coil current and the objective lens current, electron beam metrology equipment can achieve multiple functions such as high-resolution imaging, dimensional measurement, and compositional analysis of samples.

[0065] In one specific embodiment, the preset physical model in step S104 is used to describe the relationship between the current change value of each deflection coil and the change value of the image offset obtained by adding a periodic oscillating current to the initial current value of the objective lens. The periodic oscillating current added to the initial current value of the objective lens is based on the current of each deflection coil before and after the change. The image offset refers to the offset of the image generated using the electron beam.

[0066] By changing the current of each deflection coil and adding a periodic oscillating current to the initial current value of the objective lens, the image offset can be changed. Therefore, a physical model can be established between the current change value of each deflection coil and the change in image offset obtained by adding a periodic oscillating current to the initial current value of the objective lens, based on the current conditions of each deflection coil before and after the change. In a specific embodiment, the physical model may include a transformation matrix, which can convert the current change value of each deflection coil into the change value of image offset.

[0067] The steps for obtaining the optimal current value of each deflection coil based on a preset physical model, using the preset current of each deflection coil and the actual image offset, can specifically include: solving the transformation matrix; and solving for the optimal current value based on the transformation matrix. The optimal current value refers to the actual image offset and amplitude obtained by adding a periodic oscillating current to the initial current value of the objective lens, given that the current values ​​of each deflection coil are optimal.

[0068] In step S106, assuming each deflection coil has the optimal current value, a periodic oscillating current is added to the initial current value of the objective lens, and the actual image amplitude is calculated. The alignment status of the objective lens is confirmed based on the actual image amplitude. Specifically, if the actual image amplitude is less than or equal to a preset threshold, the objective lens can be determined to be successfully aligned. An actual image amplitude less than or equal to the preset threshold indicates that the actual image amplitude and actual image offset are very small, meeting the alignment conditions; therefore, the objective lens can be determined to be successfully aligned.

[0069] In summary, the objective lens alignment method of the electron beam measurement device in this embodiment can achieve automated objective lens alignment, eliminate alignment errors caused by manual operation, and ensure the stability and reliability of the observation results. It abandons the traditional step search method and solves the optimal solution of the current value through a preset physical model, quickly obtaining a relatively convergent result, reducing the complexity of the algorithm operation, and ensuring the stability of the calculation while taking into account the efficiency of the algorithm operation.

[0070] In some optional embodiments, the electron beam measurement device can achieve higher technical effects through further optimization and configuration of the above steps. The objective lens alignment method of the electron beam measurement device in this embodiment will be described in detail below with reference to an optional execution flow of this embodiment. This embodiment is only an example of the execution flow. In specific implementation, the execution order and running conditions of some steps can be modified according to specific implementation requirements. Figure 2 This is a detailed flowchart of an objective lens alignment method for an electron beam measurement device according to an embodiment of the present invention. The objective lens alignment method of the electron beam measurement device includes the following steps:

[0071] Step S202: Determine the position of the reference pattern on the sample within the preset imaging field of view;

[0072] Step S204: Obtain the initial current values ​​of the first deflection coil and the second deflection coil;

[0073] Step S206: With the first deflection coil and the second deflection coil as the initial current values, add a periodic oscillation current to the initial current value of the objective lens and acquire images in real time. Calculate the initial image offset at this time based on the position of the reference pattern and convert it into the initial image amplitude.

[0074] Step S208: Determine whether the amplitude of the initial image is greater than a preset threshold. If yes, proceed to step S210; otherwise, proceed to step S220.

[0075] Step S210: Determine that the objective lens is not aligned;

[0076] Step S212, establish a physical model

[0077] Step S214: Solve for the transformation matrix, and then use the transformation matrix to find the optimal solution for the current value.

[0078] Step S216: If the first deflection coil and the second deflection coil are the optimal solutions for current values, add a periodic oscillation current to the initial current value of the objective lens and calculate the actual image amplitude at this time.

[0079] Step S218: Determine whether the actual image amplitude is less than or equal to a preset threshold. If yes, proceed to step S220; otherwise, proceed to step S222.

[0080] Step S220: Confirm that the objective lens is successfully aligned;

[0081] Step S222: Iteratively update the data according to the random sampling consensus algorithm, and use the updated data to substitute into the physical model to solve for the optimal solution of the updated transformation matrix and current value, and return to execute step S216.

[0082] Figure 3 This is a schematic diagram of an SEM image in the objective lens alignment method of an electron beam measurement device according to an embodiment of the present invention. Specifically, a scanning electron microscope (SEM) scans the sample surface with an electron beam, collects signals such as secondary electrons and backscattered electrons emitted by the sample, and generates an image reflecting the surface morphology of the sample after processing. The image acquired by the scanning electron microscope can be called an SEM image. Step S202 determines the position of the reference pattern on the sample within a preset imaging field of view, which facilitates subsequent steps in determining the image offset based on the position of the reference pattern. In a specific embodiment, the position of the reference pattern on the sample can be the position of a uniquely characteristic photoresist pattern on the sample.

[0083] It should be noted that this embodiment assumes that each deflection coil includes a first deflection coil for controlling the first direction of motion of the electron beam and a second deflection coil for controlling the second direction of motion of the electron beam. Step S204 obtains the initial current values ​​of the first and second deflection coils, where the initial current value of the first deflection coil can be Cx0 and the initial current value of the second deflection coil can be Cy0. Step S206, with the first and second deflection coils as initial current values, adds a periodic oscillation current to the initial current value of the objective lens and acquires images in real time. The initial image offset is calculated based on the position of the reference pattern and converted into the initial image amplitude. The initial current value of the objective lens can be OL0, and the periodic oscillation current can be ΔOL.

[0084] Step S206 calculates the initial image offset based on the position of the reference pattern and converts it into the initial image amplitude. Here, ΔX and ΔY represent the initial image offsets in the first and second motion directions, respectively, when the first and second deflection coils are both at their initial current values, and a periodic oscillating current is added to the initial current value of the objective lens. The initial image offset can be conveniently and accurately determined based on the position of the reference pattern. This initial image offset refers to the offset of the reference pattern before and after adding the periodic oscillating current to the initial current value of the objective lens, given the initial current values ​​of the first and second deflection coils.

[0085] In one specific embodiment, the first motion direction and the second motion direction are orthogonal, and the step of converting the initial image offset into the initial image amplitude may include: according to the formula... The initial image amplitude is calculated. Subsequent calculations of the actual image amplitude follow a similar method: first, the actual image offset is obtained, and then the actual image amplitude is calculated based on the actual image offset.

[0086] The alignment status of the objective lens can be confirmed based on the initial image amplitude. Specifically, step S208 determines whether the initial image amplitude is greater than a preset threshold. If the result of step S208 is negative, i.e., the initial image amplitude is less than or equal to the preset threshold, step S220 is executed to confirm that the objective lens is successfully aligned. An initial image amplitude less than or equal to the preset threshold indicates that the initial image amplitude and initial image offset are very small, meeting the alignment conditions; therefore, the objective lens alignment can be confirmed as successful. The initial current values ​​of the first and second deflection coils are directly used, without the need to establish a physical model to solve for the optimal current value.

[0087] If the judgment result in step S208 is yes, i.e., the initial image amplitude is greater than the preset threshold, then step S210 is executed to determine that the objective lens is not aligned. At this time, step S212 can be executed to establish a physical model. in The transformation matrix θ represents the relationship between the actual image offset and the rotation angle of the currents in the first and second deflection coils. x S is used to characterize the scaling relationship between the actual image offset and the current of the first deflection coil. y This is used to characterize the scaling relationship between the actual image offset and the current of the second deflection coil.

[0088] ΔC x ΔC y These represent the current changes of the first and second deflection coils compared to their initial current values, respectively. ΔX i ΔY iThe actual image offset in the first and second motion directions is calculated by adding a periodic oscillating current to the initial current value of the objective lens under the changed current conditions of the first and second deflection coils, respectively.

[0089] After establishing the physical model, step S214 can be executed to solve the transformation matrix, and the optimal solution for the current value can be obtained by inversely solving the transformation matrix. In a specific embodiment, under the preset current of each deflection coil, adding a periodic oscillating current to the initial current value of the objective lens to obtain the actual image offset of the image generated by the electron beam may include: the first deflection coil and the second deflection coil are... In this case, the actual image offset is calculated by adding a periodic oscillating current to the initial current value of the objective lens. The first deflection coil and the second deflection coil are In this case, a periodic oscillating current is added to the initial current value of the objective lens, and the actual image offset is calculated. The first deflection coil and the second deflection coil are In this case, a periodic oscillating current is added to the initial current value of the objective lens, and the actual image offset is calculated. The first deflection coil and the second deflection coil are In this case, a periodic oscillating current is added to the initial current value of the objective lens, and the actual image offset is calculated. Where ΔC is the change in current of the first deflection coil or the second deflection coil relative to the initial current values ​​Cx0 and Cy0.

[0090] The steps to solve the transformation matrix may include: substituting the actual image offsets mentioned above into the physical model to obtain the formula. And solve the transformation matrix using the least squares method.

[0091] The steps for inversely solving the optimal current value based on the transformation matrix may include: first, based on the transformation matrix and the formula... Solving for the results Then according to Based on formula The optimal solution for the current value is obtained by solving the problem.

[0092] As mentioned earlier, the optimal current value refers to the solution where, given the optimal current values ​​for both the first and second deflection coils, adding a periodic oscillating current to the initial objective current value results in the smallest possible actual image offset and amplitude. Therefore, the actual image offset... Minimum is Substituting the case into the physical model It can be obtained

[0093] The least squares method, a mathematical approach to fitting data or solving linear equations by minimizing the sum of squared errors, can achieve optimal fitting results when there are deviations between measured data and theoretical models by selecting parameters that minimize the sum of squared errors across all data points. The least squares method can be used to achieve rapid convergence of the optimal solution for the current value.

[0094] After obtaining the optimal current value, steps S216 and S218 can be executed. If the first and second deflection coils have the optimal current values, a periodic oscillating current is added to the initial current value of the objective lens, and the actual image amplitude is calculated. It is then determined whether the actual image amplitude is less than or equal to a preset threshold. If the result of step S218 is yes, i.e., the actual image amplitude is less than or equal to the preset threshold, step S220 is executed to confirm successful objective lens alignment. An actual image amplitude less than or equal to the preset threshold indicates that the actual image amplitude and actual image offset are very small, meeting the alignment conditions; therefore, the objective lens alignment can be confirmed as successful.

[0095] If the judgment result in step S218 is negative, i.e., the actual image amplitude is greater than the preset threshold, then step S222 is executed. The data is iteratively updated according to the random sampling consensus algorithm, and the updated data is substituted into the physical model to solve for the optimal solution of the updated transformation matrix and current value. Then, the process returns to step S216. If the actual image amplitude is greater than the preset threshold, it indicates that the actual image amplitude and actual image offset are large, failing to meet the alignment conditions, and further adjustments are needed.

[0096] The Random Sample Consensus (RANSAC) algorithm iteratively estimates mathematical model parameters from datasets containing noisy or erroneous data. Its core principle is distinguishing between data that fits the model and noisy or erroneous data. Specifically, it randomly selects the minimum number of samples from the dataset. For example, to solve for a 2D matrix in a physical model, at least four datasets are needed. The model is used to validate all data, and the data that fits the model is statistically analyzed. After multiple iterations, the effective data with the smallest error is selected.

[0097] Solve for the updated transformation matrix and the optimal solution for the current value, return to step S216, and re-execute the step of adding a periodic oscillating current to the initial current value of the objective lens and calculating the actual image amplitude at this time when the first deflection coil and the second deflection coil have the optimal current values, so as to determine whether the objective lens is successfully aligned based on the actual image amplitude.

[0098] In a preferred embodiment, the step of iteratively updating the data according to the random sample consensus algorithm may further include: recording the actual number of times the data is iteratively updated. Furthermore, if the actual image amplitude is greater than a preset threshold, it is determined whether the actual number is less than a preset number; and if so, the step of iteratively updating the data according to the random sample consensus algorithm is executed; if not, the initial current values ​​of the first deflection coil and the second deflection coil are restored.

[0099] In other words, if the actual image amplitude is greater than the preset threshold, but the actual number of iterations is less than the preset number, the data can continue to be updated iteratively using the random sampling consensus algorithm to find the optimal current value, aiming to make the actual image amplitude less than or equal to the preset threshold, thus completing the objective lens alignment. However, if the actual image amplitude is greater than the preset threshold, but the actual number of iterations is greater than or equal to the preset number, it indicates that the number of iterations is too high, and there is no need to waste any more time. In this case, the iteration can be stopped, and the initial current values ​​of the first and second deflection coils can be restored.

[0100] It should be noted that the transformation matrix in the above embodiments... The matrix is ​​a 2x2 matrix. In other embodiments, it can be set to other types of matrices depending on the actual situation, such as a 2x3 matrix or a 3x3 matrix. However, this would increase the amount of computation during the solution process, leading to reduced computational efficiency. Therefore, preferably, a 2x2 matrix can be used. Such a second-order matrix.

[0101] In summary, the objective lens alignment method of the electron beam measurement device in this embodiment reduces the complexity of the algorithm by inversely solving the optimal solution of the current value through a preset physical model, and ensures the stability of the calculation while taking into account the efficiency of the algorithm. Iteratively updating the effective data according to the random sampling consensus algorithm effectively reduces the risk of alignment failure and improves the accuracy of the algorithm. It can realize automated objective lens alignment, eliminate alignment errors caused by manual operation, and ensure the stability and reliability of the observation results.

[0102] This embodiment also provides a computer program product, a computer-readable storage medium, and an electron beam measurement device. Figure 4 This is a schematic diagram of a computer program product 500 according to an embodiment of the present invention. Figure 5 This is a schematic diagram of a computer-readable storage medium 300 according to an embodiment of the present invention. Figure 6 This is a schematic diagram of an electron beam measurement device 400 according to an embodiment of the present invention.

[0103] Computer program product 500 includes computer program 310, which, when executed by processor 410, implements the objective lens alignment method of any of the aforementioned electron beam measurement devices. Computer-readable storage medium 300 stores the aforementioned computer program 310, which, when executed by processor 410, implements the objective lens alignment method of any of the aforementioned electron beam measurement devices. Electron beam measurement device 400 may include memory 420, processor 410, and computer program 310 stored in memory 420 and running on processor 410, and when processor 410 executes computer program 310, it implements the objective lens alignment method of any of the aforementioned electron beam measurement devices.

[0104] The computer program 310 used to perform the operations of the present invention may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-related instructions, microcode, firmware instructions, status setting data, integrated circuit configuration data, or source code or object code written in any combination of one or more programming languages ​​and procedural programming languages.

[0105] Computer program 310 may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the latter case, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0106] In some embodiments, in order to perform aspects of the present invention, electronic circuits including, for example, programmable logic circuits, field-programmable gate arrays (FPGAs) or programmable logic arrays (PLAs) can execute computer-readable program instructions to personalize the electronic circuits by utilizing state information of computer-readable program instructions.

[0107] For the purposes of this embodiment, computer program product 500 is a related product containing computer program 310. For the purposes of this embodiment, computer-readable storage medium 300 is a tangible device capable of holding and storing computer program 310, and can be any device capable of containing, storing, communicating, propagating or transmitting computer program 310 for use by or in conjunction with an instruction execution system, apparatus or device.

[0108] More specific examples (a non-exhaustive list) of computer-readable storage media 300 include the following: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable optical disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, and any suitable combination of the foregoing.

[0109] It should be noted that the logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be specifically implemented in any machine-readable storage medium for use by, or in conjunction with, an instruction execution system, apparatus or device (such as a computer-based system, a processor-based system or other system that can fetch and execute instructions from, an instruction execution system, apparatus or device).

[0110] It should be understood that various parts of the present invention can be implemented using hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented using software or firmware stored in memory and executed by a suitable instruction execution system.

[0111] Electron beam measurement equipment 400 may include computer equipment, such as a server, desktop computer, laptop computer, tablet computer, or smartphone. In some examples, the computer equipment may be a cloud computing node. The computer equipment can be described in the general context of computer system executable instructions (such as program modules) executed by a computer system. Typically, program modules may include routines, programs, object programs, components, logic, data structures, etc., that perform specific tasks or implement specific abstract data types. The computer equipment may be implemented in a distributed cloud computing environment where tasks are performed by remote processing devices linked through a communication network. In a distributed cloud computing environment, program modules may reside on local or remote computing system storage media, including storage devices.

[0112] The computer device may include a processor 410 adapted to execute stored instructions and a memory 420 that provides temporary storage space for the operation of the instructions during operation. The processor 410 may be a single-core processor, a multi-core processor, a computing cluster, or any other configuration. The memory 420 may include random access memory (RAM), read-only memory, flash memory, or any other suitable storage system.

[0113] The processor 410 can be connected via a system interconnect (e.g., PCI, PCI-Express, etc.) to an I / O interface (input / output interface) suitable for connecting a computer device to one or more I / O devices (input / output devices). I / O devices may include, for example, a keyboard and indicating devices, where indicating devices may include a touchpad or touchscreen, etc. I / O devices may be built-in components of the computer device or may be external devices connected to the computing device.

[0114] The processor 410 can also be linked via a system interconnect to a display interface suitable for connecting computer devices to display devices. The display device may include a display screen that is a built-in component of the computer device. The display device may also include a computer monitor, television, or projector, etc., externally connected to the computer device. Furthermore, a network interface controller (NIC) may be adapted to connect computer devices to a network via a system interconnect. In some embodiments, the NIC may use any suitable interface or protocol (such as an Internet Minicomputer System Interface) to transmit data. The network may be a cellular network, a radio network, a wide area network (WAN), a local area network (LAN), or the Internet, etc. Remote devices can connect to the computing device via the network.

[0115] Therefore, those skilled in the art should recognize that although numerous exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications conforming to the principles of the present invention can be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Thus, the scope of the present invention should be understood and construed as covering all such other variations or modifications.

Claims

1. A method for aligning the objective lens of an electron beam measurement device, comprising: Given the preset currents of each deflection coil, a periodic oscillating current is added to the initial current value of the objective lens to obtain the actual image offset of the image generated by the electron beam. The currents of each deflection coil are used to control different directions of motion of the electron beam. Based on the preset current of each deflection coil and the actual image offset, the optimal solution for the current value of each deflection coil is obtained according to a preset physical model; and When each of the deflection coils is the optimal solution for the current value, the periodic oscillation current is added to the initial current value of the objective lens and the actual image amplitude at this time is calculated. The alignment state of the objective lens is then confirmed based on the actual image amplitude. Each of the deflection coils includes a first deflection coil for controlling a first direction of motion of the electron beam and a second deflection coil for controlling a second direction of motion of the electron beam; and the physical model is as follows: ,in, The transformation matrix θ represents the relationship between the actual image offset and the rotation angle of the currents in the first and second deflection coils. This is used to characterize the relationship between the actual image offset and the scaling factor of the current in the first deflection coil. This is used to characterize the scaling relationship between the actual image offset and the current of the second deflection coil; , These are the current changes of the first deflection coil and the second deflection coil compared to their initial current values, respectively. , The initial image offset in the first motion direction and the second motion direction is calculated by adding the periodic oscillation current to the initial current value of the objective lens when both the first deflection coil and the second deflection coil are at the initial current value. , The actual image offset in the first motion direction and the second motion direction is calculated by adding the periodic oscillation current to the initial current value of the objective lens under the changed current conditions of the first deflection coil and the second deflection coil, respectively. The steps of obtaining the optimal solution for the current value of each deflection coil based on the preset current of each deflection coil and the actual image offset according to the preset physical model include: solving the transformation matrix; and solving the optimal solution for the current value based on the transformation matrix.

2. The method according to claim 1, wherein, The steps for obtaining the actual image offset of the electron beam image by adding a periodic oscillating current to the initial current value of the objective lens, under the preset current conditions of each deflection coil, include: In the first deflection coil and the second deflection coil are In this case, the periodic oscillation current is added to the initial current value of the objective lens to calculate the actual image offset. ; In the first deflection coil and the second deflection coil are In this case, the periodic oscillation current is added to the initial current value of the objective lens, and the actual image offset is calculated. ; In the first deflection coil and the second deflection coil are In this case, the periodic oscillation current is added to the initial current value of the objective lens, and the actual image offset is calculated. ; In the first deflection coil and the second deflection coil are In this case, the periodic oscillation current is added to the initial current value of the objective lens, and the actual image offset is calculated. ,in , The initial current values ​​of the first deflection coil and the second deflection coil are respectively. The first deflection coil or the second deflection coil compared to the initial current value , The change in current; The steps for solving the transformation matrix include: Substituting the actual image offsets mentioned above into the physical model, we obtain the formula. ;as well as The transformation matrix is ​​solved using the least squares method.

3. The method according to claim 2, wherein the step of inversely solving for the optimal solution of the current value based on the transformation matrix includes: First, based on the transformation matrix and the formula... Solving for the results ; Based on the above Based on formula The optimal solution for the current value is obtained by solving the problem. .

4. The method according to claim 1, wherein the step of confirming the alignment state of the objective lens based on the actual image amplitude includes: Determine whether the actual image amplitude is less than or equal to the preset threshold; as well as If so, confirm that the objective lens is successfully aligned, and When the actual image amplitude is greater than the preset threshold, the data is iteratively updated according to the random sampling consensus algorithm, and the updated data is substituted into the physical model to solve for the optimal solution of the updated transformation matrix and the current value. as well as The steps of adding the periodic oscillation current to the initial current value of the objective lens and calculating the actual image amplitude at this time are repeated, assuming that the first deflection coil and the second deflection coil are the optimal solutions for the current values.

5. The method of claim 4, wherein the step of iteratively updating the data according to the random sampling consensus algorithm further comprises: Record the actual number of times the data is updated iteratively, and If the actual image amplitude is greater than the preset threshold, determine whether the actual number of times is less than the preset number of times; as well as If so, execute the step of iteratively updating the data according to the random sampling consensus algorithm. If not, restore the initial current values ​​of the first deflection coil and the second deflection coil.

6. The method of claim 1, further comprising, prior to the step of obtaining the actual image offset: Determine the position of the reference pattern on the sample within the preset imaging field of view; Obtain the initial current values ​​of the first deflection coil and the second deflection coil. With the first deflection coil and the second deflection coil at the initial current value, the periodic oscillation current is added to the initial current value of the objective lens and the image is acquired in real time. The initial image offset at this time is calculated according to the position of the reference pattern and converted into the initial image amplitude. as well as The alignment status of the objective lens is confirmed based on the initial image amplitude.

7. The method according to claim 6, wherein, The first direction of motion and the second direction of motion are orthogonal, and The step of converting the initial image offset into the initial image amplitude includes: According to the formula The initial image amplitude was calculated.

8. An electron beam measurement device, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, wherein the processor executes the computer program to implement the objective lens alignment method of the electron beam measurement device according to any one of claims 1 to 7.

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