Scanning electron microscope image distortion correction method and device based on scanning magnetic field compensation

Abstract

The application provides a scanning electron microscope image distortion correction method and device based on scanning magnetic field compensation, and belongs to the technical field of electron microscopes. The scanning electron microscope image distortion correction method based on scanning magnetic field compensation corrects analog signals at the source of scanning signal generation, so that the image is already non-distorted when collected, does not need to occupy a CPU for image processing, and will not cause image resolution to decrease or produce artifacts due to an interpolation algorithm. By adopting a multi-path multiplication type digital-to-analog conversion circuit, scanning vectors in any direction can be accurately synthesized, so that non-orthogonal distortion caused by processing errors of a magnetic field coil is perfectly offset, physical error parameters and user operation parameters are completely decoupled in an algorithm, and the image always remains in a non-distorted state regardless of how the scanning direction is rotated, so that user experience and instrument ease of use are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of electron microscopy, and in particular to a method and apparatus for correcting image distortion in scanning electron microscopes based on scanning magnetic field compensation. Background Technology

[0002] Scanning electron microscopy (SEM) uses a focused electron beam to scan the sample surface using a raster, collecting electron signals to create an image. The scanning coil is the core component that controls the deflection of the electron beam. Ideally, the scanning magnetic fields in the X and Y directions should be strictly orthogonal, and the magnetic field strength generated under the same driving signal should conform to a preset ratio, usually 1:1 or a specific aspect ratio, to ensure that the image does not undergo geometric distortion.

[0003] However, in actual manufacturing and assembly processes, due to limitations in machining precision and coil winding technology, it is often difficult to achieve strict physical orthogonality between the X-axis coil and the Y-axis coil, and their magnetic field efficiencies (Gauss / Ampere) inevitably differ. Furthermore, when operators use the electron beam rotation function to observe samples at different angles, these physical errors couple with the rotation angle, resulting in parallelogram distortion, trapezoidal distortion, or nonlinear stretching in the image.

[0004] Existing calibration methods typically employ software interpolation or simple analog potentiometer adjustments. Software calibration suffers from computational lag and reduced image resolution; analog potentiometer adjustments have low precision, large temperature drift, and cannot adapt to dynamic changes after electron beam rotation, requiring users to recalibrate after changing the scanning angle—a cumbersome process that severely impacts work efficiency and image quality. Therefore, a calibration scheme capable of real-time compensation for hardware errors, with calibration parameters independent of the scanning angle, is urgently needed. Summary of the Invention

[0005] This invention provides a scanning electron microscope image distortion correction method and apparatus based on scanning magnetic field compensation, which solves the shortcomings of the existing correction methods and achieves the effect of improving correction effect and operation independence.

[0006] This invention provides a method for correcting distortion in scanning electron microscope images based on scanning magnetic field compensation, comprising:

[0007] Generate raw X-direction and raw Y-direction scanning signals for driving the scanning coil of a scanning electron microscope;

[0008] Based on the set amplitude correction parameters, phase correction parameters, and electron beam rotation angle, the corresponding digital control coefficients are calculated using the scanning signal correction model.

[0009] Using the original X-direction scanning signal and the original Y-direction scanning signal as reference inputs, and the digital control coefficients as modulation inputs, the original scanning signals are orthogonally coupled and modulated through a multiplicative digital-to-analog converter circuit to output a corrected analog scanning signal.

[0010] The scanning coil is driven by the corrected analog scanning signal to generate a magnetic field, and an image is acquired. The amplitude correction parameter and phase correction parameter are adjusted according to the image distortion until the image distortion is eliminated.

[0011] According to the present invention, a scanning electron microscope image distortion correction method based on scanning magnetic field compensation is provided, wherein the original scanning signal is orthogonally coupled and modulated using a multiplicative digital-to-analog converter circuit to output a corrected analog scanning signal, comprising:

[0012] The original X-direction scanning signal is connected to the reference voltage input terminals of the first and third multiplication-type digital-to-analog converters via a multi-channel multiplication-type digital-to-analog converter, and the original Y-direction scanning signal is connected to the reference voltage input terminals of the second and fourth multiplication-type digital-to-analog converters.

[0013] The calculated digital control coefficients are sent to the digital input terminals of the corresponding multiplication-type digital-to-analog converters via the host computer software.

[0014] The first and second outputs of the multiplicative digital-to-analog converter circuit are superimposed to form an X-direction correction signal; the third and fourth outputs of the multiplicative digital-to-analog converter circuit are superimposed to form a Y-direction correction signal.

[0015] According to the present invention, a scanning electron microscope image distortion correction method based on scanning magnetic field compensation is provided, wherein the digital control coefficient is:

[0016] ;

[0017] ;

[0018] ;

[0019] ;

[0020] Where RcA, RcB, RcC, and RcD are the digital control coefficients corresponding to each channel of the multiplication-type digital-to-analog converter, respectively; M1 and M2 are amplitude correction parameters, t1 and t2 are phase correction parameters; and θ is the electron beam rotation angle.

[0021] According to the present invention, a scanning electron microscope image distortion correction method based on scanning magnetic field compensation is provided, wherein adjusting the amplitude correction parameter and the phase correction parameter according to the image distortion includes:

[0022] By using a circular standard sample and adjusting the amplitude correction parameters, the image can be made to appear as a perfect ellipse or circle.

[0023] Adjusting the phase correction parameters eliminates the rotation angle, gradually bringing the image closer to a perfect circle.

[0024] According to the scanning electron microscope image distortion correction method based on scanning magnetic field compensation provided by the present invention, after adjusting the phase correction parameter to eliminate the rotation angle and gradually making the image approach a perfect circle, the method further includes:

[0025] The geometric parameters of the image are measured using an image measurement tool. The amplitude correction parameters and phase correction parameters are then iteratively fine-tuned based on the deviation between the measured values ​​and the standard values ​​until the image distortion is eliminated.

[0026] According to the present invention, a scanning electron microscope image distortion correction method based on scanning magnetic field compensation, after adjusting the amplitude correction parameter and phase correction parameter according to the image distortion, the method further includes:

[0027] After completing the parameter adjustment, change the electron beam rotation angle and magnification to determine whether the standard sample image is distorted; if distortion occurs, recalculate and update the digital control coefficients until the same set of correction parameters applies to all rotation angles.

[0028] The present invention also provides a scanning electron microscope image distortion correction device based on scanning magnetic field compensation, comprising:

[0029] The generation module is used to generate the raw X-direction scanning signal and the raw Y-direction scanning signal for driving the scanning coil of the scanning electron microscope;

[0030] The first output module is used to calculate the corresponding digital control coefficients based on the set amplitude correction parameters, phase correction parameters and electron beam rotation angle using the scanning signal correction model.

[0031] The second output module is used to take the original X-direction scanning signal and the original Y-direction scanning signal as reference inputs, take the digital control coefficients as modulation inputs, and perform orthogonal coupling modulation on the original scanning signal through a multiplicative digital-to-analog converter circuit to output the corrected analog scanning signal.

[0032] The correction module is used to drive the scanning coil to generate a magnetic field through the corrected analog scanning signal, acquire images, and adjust the amplitude correction parameters and phase correction parameters according to the image distortion until the image distortion is eliminated.

[0033] The present invention also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the scanning electron microscope image distortion correction method based on scanning magnetic field compensation as described above.

[0034] The present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the scanning electron microscope image distortion correction method based on scanning magnetic field compensation as described above.

[0035] The present invention also provides a computer program product, including a computer program that, when executed by a processor, implements the scanning electron microscope image distortion correction method based on scanning magnetic field compensation as described above.

[0036] The scanning electron microscope image distortion correction method and apparatus based on scanning magnetic field compensation provided by this invention corrects the analog signal at the source of the scanning signal generation, so the image is already distortion-free at the time of acquisition. It does not require CPU for image processing and will not cause image resolution degradation or artifacts due to interpolation algorithms. By using a multi-channel multiplicative digital-to-analog converter circuit, it can accurately synthesize scanning vectors in any direction, thereby perfectly offsetting the non-orthogonal distortion caused by the processing error of the magnetic field coil. The physical error parameters and user operation parameters are completely decoupled in the algorithm. No matter how the scanning direction is rotated, the image always remains distortion-free, which greatly improves the user experience and ease of use of the instrument. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0038] Figure 1 This is one of the flowcharts of the scanning electron microscope image distortion correction method based on scanning magnetic field compensation provided by the present invention;

[0039] Figure 2 This is the second flowchart of the scanning electron microscope image distortion correction method based on scanning magnetic field compensation provided by the present invention;

[0040] Figure 3 This is a flowchart of the image distortion correction process provided by the present invention;

[0041] Figure 4 is a schematic diagram of the structure of the scanning electron microscope image distortion correction device based on scanning magnetic field compensation provided by the present invention;

[0042] Figure 5 is a schematic diagram of the structure of the electronic device provided by the present invention. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0044] The following is combined Figure 1 Figure 5 illustrates the scanning electron microscope image distortion correction method and apparatus based on scanning magnetic field compensation according to the present invention.

[0045] like Figure 1 As shown, this invention provides a scanning electron microscope (SEM) image distortion correction method based on scanning magnetic field compensation. This embodiment uses a system calibrated using the scanning signal of a scanning electron microscope as the execution entity to illustrate the specific implementation of the correction method in software and hardware collaborative control. The system as a whole consists of a host computer software terminal and a scanning control hardware terminal, which realize parameter sending and feedback closed loop through a communication interface. The specific steps of the SEM image distortion correction method based on scanning magnetic field compensation in this embodiment are as follows.

[0046] Step 110: Generate the X-direction raw scanning signal and the Y-direction raw scanning signal for driving the scanning coil of the scanning electron microscope;

[0047] Step 120: Based on the set amplitude correction parameters, phase correction parameters and electron beam rotation angle, the corresponding digital control coefficients are calculated using the scanning signal correction model.

[0048] Step 130: Using the original X-direction scanning signal and the original Y-direction scanning signal as reference inputs, and the digital control coefficients as modulation inputs, the original scanning signals are orthogonally coupled and modulated through a multiplicative digital-to-analog converter circuit to output the corrected analog scanning signal.

[0049] Step 140: Drive the scanning coil to generate a magnetic field using the corrected analog scanning signal, acquire an image, and adjust the amplitude correction parameter and phase correction parameter according to the image distortion until the image distortion is eliminated.

[0050] First, raw X-direction and Y-direction scanning signals are generated to drive the scanning coils of the scanning electron microscope. These are typically high-precision sawtooth wave signals, representing the scanning trajectory in an ideal coordinate system. Based on the set amplitude correction parameters, phase correction parameters, and the current electron beam rotation angle, the corresponding digital control coefficients can be calculated using a scanning signal correction model. The amplitude correction parameters are used to compensate for the gain difference between the X and Y coils, and the phase correction parameters are used to compensate for the non-orthogonality of the X and Y coils.

[0051] The signal can be processed using a multiplying digital-to-analog converter (MDAC). The original X-direction scan signal can be connected to the reference voltage input terminals of the first channel (MDAC1) and the third channel (MDAC3); the original Y-direction scan signal can be connected to the reference voltage input terminals of the second channel (MDAC2) and the fourth channel (MDAC4). The host computer software sends the calculated digital control coefficients RcA, RcB, RcC, and RcD to the digital input terminals of the corresponding MDACs. Through this cross-coupling, i.e., mixing the Y component into the X signal and the X component into the Y signal, a linear transformation of the coordinate system is achieved, thereby canceling the physical non-orthogonality of the magnetic field at the electrical level. Based on this, the corrected analog scan signal is used to drive the scanning coil to generate a magnetic field and acquire the image.

[0052] The scanning electron microscope image distortion correction method based on scanning magnetic field compensation provided by the present invention corrects the analog signal at the source of the scanning signal generation, so that the image is already distortion-free at the time of acquisition. It does not require CPU for image processing and will not cause image resolution degradation or artifacts due to interpolation algorithms. By using a multi-channel multiplicative digital-to-analog converter circuit, it can accurately synthesize scanning vectors in any direction, thereby perfectly offsetting the non-orthogonal distortion caused by the processing error of the magnetic field coil. The physical error parameters and user operation parameters are completely decoupled in the algorithm. No matter how the scanning direction is rotated, the image always remains distortion-free, which greatly improves the user experience and ease of use of the instrument.

[0053] In some embodiments, such as Figure 2 As shown, the original scanning signal is orthogonally coupled and modulated using a multiplicative digital-to-analog converter circuit to output a corrected analog scanning signal, including steps 210, 220 and 230.

[0054] Step 210: The original X-direction scanning signal is connected to the reference voltage input terminals of the first and third multiplication-type digital-to-analog converters through a multi-channel multiplication-type digital-to-analog converter, and the original Y-direction scanning signal is connected to the reference voltage input terminals of the second and fourth multiplication-type digital-to-analog converters.

[0055] Step 220: The calculated digital control coefficients are sent down to the digital input terminals of the corresponding multiplication-type digital-to-analog converters via the host computer software.

[0056] Step 230: The first and second outputs of the multiplicative digital-to-analog converter circuit are superimposed to form the X-direction correction signal; the third and fourth outputs of the multiplicative digital-to-analog converter circuit are superimposed to form the Y-direction correction signal.

[0057] The system software provides a visual human-computer interaction interface, allowing operators to adjust and correct parameters M1, M2, t1, and t2 via interface sliders. After scanning a standard sample (such as a circular hole or square grid), the system can determine whether there is elliptical distortion based on the aspect ratio and tilt angle of the standard sample and then modify the above parameters.

[0058] The software calculates the corresponding digital control coefficient (R) in real time based on the correction formula. c A, R c B, R c C, R c (D) A set of digital codes is formed to control the hardware modulation coefficients and sent to the multiplicative DAC module via a high-speed communication interface for dynamically adjusting the modulation ratio of each channel in the hardware. Currently, a set of distortion calibration parameters M1, M2, t1, and t2 are used globally. M1 and M2 are used for amplitude calibration, ranging from [0,2], while t1 and t2 are used for phase calibration, ranging from [-45°, 45°]. The debugging sequence can be to first debug M1 and M2, then adjust t1 and t2. Simultaneously, the adjusted parameters are saved to the server configuration file for real-time access by the client.

[0059] The hardware includes main modules such as a raw scanning signal source, a multiplicative DAC, and a scanning coil driver. The raw scanning waveform generated by the scanning signal generator serves as the external reference voltage (Vref) for the multiplicative DAC, while the digital control code sent from the PC serves as the digital input. The multiplicative DAC performs proportional calculations on the reference voltage. The operator can adjust the output signal amplitude in real time on the client side by adjusting the parameter slider, achieving dynamic adjustment and correction of the voltage ratio in the X / Y directions. Simultaneously, the output signal amplitude can be amplified and modulated again to achieve overall amplitude amplification or reduction of the scan signal after distortion correction. Finally, the output is an analog signal modulated by the distortion correction and amplification factor, which drives the scanning coil to form a scanning magnetic field with consistent amplitude and orthogonal direction.

[0060] In some embodiments, the formula used for correction may be:

[0061] ;

[0062] ;

[0063] ;

[0064] ;

[0065] Where RcA, RcB, RcC, and RcD are the digital control coefficients corresponding to each channel of the multiplication-type digital-to-analog converter; M1 and M2 are amplitude correction parameters, t1 and t2 are phase correction parameters; and θ is the electron beam rotation angle.

[0066] The determination of the correction formula can be based on the principle of vector coordinate transformation. First, an ideal polar coordinate system based on the rotation angle and an actual oblique coordinate system based on the magnetic field phase deviation angle can be constructed. By establishing the mapping relationship between the ideal orthogonal vector and the actual deflection vector, a system of linear equations including the X-scanning direction and the orthogonal Y-scanning direction can be listed and solved to obtain the corrected coordinate component solution. Finally, the mathematical solution is transformed into four key operation control coefficients required by the hardware circuit by combining the amplitude scaling factor, thus realizing the transformation of the complex physical problem of magnetic field distortion into an accurate mathematical linear compensation model.

[0067] In some embodiments, adjusting the amplitude correction parameter and the phase correction parameter according to the image distortion includes: adjusting the amplitude correction parameter to make the image present a perfect ellipse or circle by using a circular standard sample; and adjusting the phase correction parameter to eliminate the rotation angle so that the image gradually approaches a perfect circle.

[0068] Understandably, in the coarse adjustment stage, a circular standard sample, such as the circular holes of a standard grid, can be used. First, adjust the amplitude correction parameters M1 and M2 to determine the changes in the major and minor axes of the image, making the image appear as a perfect ellipse or circle, thus solving the aspect ratio problem. Then, adjust the phase correction parameters t1 and t2 to eliminate the rotation and shearing distortion of the image, making the image approach a perfect circle.

[0069] In some embodiments, after adjusting the phase correction parameter to eliminate the rotation angle and gradually bringing the image closer to a perfect circle, the scanning electron microscope image distortion correction method based on scanning magnetic field compensation further includes: measuring the geometric parameters of the image using an image measurement tool, and iteratively fine-tuning the amplitude correction parameter and the phase correction parameter according to the deviation between the measured value and the standard value until the image distortion is eliminated.

[0070] In the fine-tuning stage, based on the coarse-tuning, geometric parameters of the image, such as the side length and diagonal length of a square grid, can be measured using image measurement tools like software rulers. These parameters are then iteratively fine-tuned based on the deviation between the measured values ​​and standard values ​​until the required accuracy is met.

[0071] After adjusting the amplitude correction parameters and phase correction parameters according to the image distortion, the scanning electron microscope image distortion correction method based on scanning magnetic field compensation also includes: after completing the parameter adjustment, changing the electron beam rotation angle and magnification to determine whether the standard sample image is distorted; if distortion occurs, recalculating and updating the digital control coefficients until the same set of correction parameters is applicable to all rotation angles.

[0072] After parameter adjustments are complete, the electron beam rotation angle and magnification can be changed to determine if distortion has occurred in the standard sample image. If minor distortion occurs, the digital control coefficients are recalculated and updated until the same set of correction parameters applies to all rotation angles. Users will not need to recalibrate regardless of how the image is rotated in subsequent use.

[0073] The standard sample material is preferably a highly conductive metal sample. Non-conductive samples need to be coated with a conductive coating using magnetron sputtering or thermal evaporation coating equipment. The coating should be uniform and should not affect the morphology and size of the sample.

[0074] Understandably, the system's signal feedback module includes an image signal acquisition and feedback module, used to achieve closed-loop optimization of parameter correction. After the scanning coil is driven, the secondary electron signal of the sample is acquired by the detector, pre-amplified, and then sent to the ADC for analog-to-digital conversion. The digital signal is converted into an analog signal, processed by the FPGA image acquisition board, and transmitted to the host computer software. The pixel data acquired by the software is used to create a real-time scan image. The operator then measures the feature dimensions of the standard sample again and further fine-tunes the correction parameters. The new parameters are calculated using formulas and sent back to the DAC, and the system enters the next round of correction, forming a closed-loop process of "measurement-calculation-correction". After multiple iterations, the circular standard sample approaches a perfect circle, or the aspect ratio of the rectangular standard sample approaches 1, and the tilt angle approaches 0°, indicating that the scanning magnetic field has achieved orthogonality and magnification consistency. This closed-loop control mechanism ensures elliptic correction of the scanned image under different electron beam rotation angles and different magnifications.

[0075] The following is in conjunction with the appendix Figure 3 This paper provides a detailed description of the technical solution. Figure 3 The flowchart for SEM rhomboid or elliptical image distortion correction provided in this embodiment includes the following specific steps:

[0076] (1) Calibration begins: SEM built-in circular hole sample (size Ø=100μm), standard sample (size 100μm×100μm square), open the host computer software, and calibration begins.

[0077] (2) Initial settings: The software has built-in correction formulas (Equations 1-4) and provides adjustable parameters: M1 and M2 are used for amplitude calibration (range (0,2), initial value 2), t1 and t2 are used for phase calibration (range (-45°, 45°), initial value 0°); Debugging conditions: Rotation=0°, Acc=20kV, WD≈10mm, Probe=10.

[0078] (3) Scanning image of circular hole sample: After adjusting to a suitable magnification, find the circular hole (Ø=100μm), perform focusing and astigmatism correction, and then acquire the image of the circular hole. Subsequent adjustments are all performed at this magnification.

[0079] (4) Coarse adjustment of parameters: First adjust the amplitude parameters M1 and M2, then adjust the phase parameters t1 and t2.

[0080] Amplitude calibration: M1 and M2 are proportional. Increasing the value of M1 stretches the image vertically along the screen, while decreasing the value of M1 stretches the image horizontally along the screen. The trend of M2 is the opposite. During the debugging process, first fix M2 and adjust M1. Adjust M1 to make the image present a "positive ellipse" state, that is, the major axis and minor axis of the ellipse are located in the horizontal or vertical direction of the screen. Then adjust M1 and M2 again to make the image more "circular". At this time, the "circle" refers to what is observed by the naked eye, without specific measurement, and there is a certain rotation angle.

[0081] Phase calibration: t1 and t2 have a proportional relationship. Increasing the t1 value causes the image to rotate clockwise and stretch along its original vertical direction, while decreasing the t2 value causes the image to rotate counterclockwise and stretch along its original horizontal direction. The trend of t2 is the opposite. Based on the adjustments made to M1 and M2, first adjust t1 within a small range, then adjust t1 to make it round. At this point, the circle is close to a perfect circle, with no visible rotation angle.

[0082] Verification: Return to the scanning field of view, drag the Rotation slider, and verify within the range of (-180°, 180°). If the image of the entire Rotation is approximately circular, it is considered qualified. If the shape of the circle changes under other Rotations, the amplitude and phase calibration is re-performed. Repeat this process until the image is circular across the entire Rotation.

[0083] (5)Parameter fine-tuning: In this step, the parameters M1, M2, t1, and t2 mentioned above are further fine-tuned. Use tools such as software length measurement, click to take a picture, and draw lines around the round hole in a "cross" shape for measurement. When drawing the lines, the horizontal direction should be controlled to ensure that the measured line segments are as close as possible to the diameter of the round hole. Criteria for judging a relatively round round hole: The lengths of the four line segments measured should be within the error range (±3%). If the error is too large, it will increase the difficulty of the next fine-tuning work. If it is not within the error range, the above operations should be repeated until the image meets the requirements. Or use the circle-drawing tool. If the round hole image basically coincides with the circle drawn by the circle-drawing tool, the image is considered to meet the requirements; otherwise, the parameters should be adjusted repeatedly until the image meets the requirements.

[0084] (6)Scanning the image of the rectangular sample: Switch the sample, find a 100μm×100μm rectangular sample, perform focusing and astigmatism elimination, and then collect the image.

[0085] (7)Parameter fine-calibration: This step is carried out on the basis of rough-tuning and fine-tuning to ensure that the error between the scanned rectangular sample image and the true value (100μm×100μm) is within ±0.5%.

[0086] Image acquisition reference measurement: Use the measurement tool to measure the geometric parameters of the grid in the image multiple times to obtain reference data. The geometric parameters include the side length and angle of the grid;

[0087] Initial parameter adjustment: According to the deviation between the reference measurement data and the theoretical target value, adjust the amplitude correction parameters M1, M2 and the phase correction parameters t1, t2; The adjustment amplitude of RangeX / Y is proportional to the percentage deviation of the measurement error.

[0088] Iterative correction: The principle of first correcting the angle and then correcting the side length can be followed, and only one parameter is adjusted preferentially in each iteration; After the parameters are modified, use the new parameters to re-collect the image and measure, compare the measurement results with the target value, and then fine-tune the parameters again according to this; This process is iterated until the geometric parameter errors measured are all controlled within the error range (±0.5%).

[0089] (8)Global verification: Continuously change the Rotation angle and magnification, and observe whether diamond-shaped distortion appears in the grid of the real-time scanning state. Collect images every 15° of Rotation for measurement verification, and switch the scanning gear of the magnification for verification. If distortion or measurement error exceeds the limit is found, modify the parameters until the geometric shapes of the images at all angles meet the accuracy requirements.

[0090] (9)End calibration or continue: Select to end the calibration or continue to adjust the parameters according to the image effect and measurement error.

[0091] The scanning electron microscope image distortion correction device based on scanning magnetic field compensation provided by the present invention will be described below. The scanning electron microscope image distortion correction device based on scanning magnetic field compensation described below can be referred to in correspondence with the scanning electron microscope image distortion correction method based on scanning magnetic field compensation described above.

[0092] As shown in Figure 4, the scanning electron microscope image distortion correction device based on scanning magnetic field compensation according to this embodiment of the invention mainly includes: a generation module 410, a first output module 420, a second output module 430, and a correction module 440.

[0093] The generation module 410 is used to generate the X-direction raw scanning signal and the Y-direction raw scanning signal for driving the scanning coil of the scanning electron microscope;

[0094] The first output module 420 is used to calculate the corresponding digital control coefficients based on the set amplitude correction parameters, phase correction parameters and electron beam rotation angle using the scanning signal correction model.

[0095] The second output module 430 is used to take the original X-direction scanning signal and the original Y-direction scanning signal as reference inputs, take the digital control coefficients as modulation inputs, and perform orthogonal coupling modulation on the original scanning signal through a multiplicative digital-to-analog converter circuit to output the corrected analog scanning signal.

[0096] The correction module 440 is used to drive the scanning coil to generate a magnetic field through the corrected analog scanning signal, acquire images, and adjust the amplitude correction parameters and phase correction parameters according to the image distortion until the image distortion is eliminated.

[0097] The scanning electron microscope image distortion correction device based on scanning magnetic field compensation provided in this embodiment of the invention corrects the analog signal at the source of the scanning signal generation, so that the image is already distortion-free at the time of acquisition. It does not require CPU for image processing and will not cause image resolution degradation or artifacts due to interpolation algorithms. By using a multi-channel multiplicative digital-to-analog converter circuit, it can accurately synthesize scanning vectors in any direction, thereby perfectly offsetting the non-orthogonal distortion caused by the processing error of the magnetic field coil. It completely decouples the physical error parameters from the user operation parameters in the algorithm. No matter how the scanning direction is rotated subsequently, the image always remains distortion-free, which greatly improves the user experience and ease of use of the instrument.

[0098] The following describes the scanning electron microscope image distortion correction system based on scanning magnetic field compensation provided by the present invention. This system can be the correction system described in the foregoing embodiments.

[0099] This invention provides a scanning electron microscope (SEM) image distortion correction system based on scanning magnetic field compensation, mainly comprising: a host computer control module, a scanning signal generator, a signal modulation correction module, and a drive module. This system employs the scanning electron microscope (SEM) image distortion correction method based on scanning magnetic field compensation described in the aforementioned embodiments for image correction.

[0100] The host computer control module is used to provide a human-machine interface, receive input amplitude correction parameters and phase correction parameters, and calculate digital control coefficients based on the electron beam rotation angle and a preset correction model.

[0101] A scan signal generator is used to generate raw analog scan waveforms in the X and Y directions;

[0102] The signal modulation correction module is connected to the host computer control module and the scanning signal generator respectively. It is used to receive the original analog scanning waveform as the reference signal, receive the digital control coefficient as the modulation signal, and output the corrected analog scanning signal through hardware multiplication.

[0103] The drive module, connected to the signal modulation and correction module, is used to amplify the power of the corrected analog scanning signal and drive the scanning coil.

[0104] The host computer control module is typically a PC or an embedded workstation. It provides a user interface (GUI) for users to input or adjust amplitude / phase correction parameters. Simultaneously, it reads the current electron beam rotation angle (θθ) in real time and runs the aforementioned mathematical model algorithm to calculate the four key digital control coefficients.

[0105] The scanning signal generator is used to generate highly linear X / Y raw sawtooth wave signals. The signal modulation and correction module is the core hardware of the system. It includes a four-channel multiplicative digital-to-analog converter (MDAC) and an adder circuit. It receives the raw waveform as an analog reference, receives digital control coefficients as digital gain, performs hardware multiplication and addition operations, and outputs the corrected waveform. The drive module converts the modulated voltage signal into the current signal required to drive the coil and amplifies the power.

[0106] The scanning electron microscope image distortion correction system based on scanning magnetic field compensation may also include an image acquisition feedback module, which acquires images through the SEM detector and transmits them back to the host computer for users or algorithms to judge the distortion situation.

[0107] Figure 5 An example is a schematic diagram of the physical structure of an electronic device, such as... Figure 5As shown, the electronic device may include a processor 510, a communication interface 520, a memory 530, and a communication bus 540, wherein the processor 510, the communication interface 520, and the memory 530 communicate with each other via the communication bus 540. The processor 510 can call logic instructions in the memory 530 to execute a scanning electron microscope image distortion correction method based on scanning magnetic field compensation. This method includes: generating original X-direction and Y-direction scanning signals for driving the scanning coil of the scanning electron microscope; calculating the corresponding digital control coefficients using a scanning signal correction model based on set amplitude correction parameters, phase correction parameters, and electron beam rotation angle; using the original X-direction and Y-direction scanning signals as reference inputs, and the digital control coefficients as modulation inputs, performing orthogonal coupling modulation on the original scanning signals through a multiplicative digital-to-analog converter circuit, and outputting a corrected analog scanning signal; driving the scanning coil to generate a magnetic field through the corrected analog scanning signal, acquiring an image, and adjusting the amplitude correction parameters and phase correction parameters according to the image distortion until the image distortion is eliminated.

[0108] Furthermore, the logical instructions in the aforementioned memory 530 can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0109] On the other hand, the present invention also provides a computer program product, which includes a computer program that can be stored on a non-transitory computer-readable storage medium. When the computer program is executed by a processor, the computer can execute the scanning electron microscope image distortion correction method based on scanning magnetic field compensation provided by the above methods. The method includes: generating an X-direction original scanning signal and a Y-direction original scanning signal for driving the scanning coil of the scanning electron microscope; calculating the corresponding digital control coefficients using a scanning signal correction model based on set amplitude correction parameters, phase correction parameters, and electron beam rotation angle; using the X-direction original scanning signal and the Y-direction original scanning signal as reference inputs, using the digital control coefficients as modulation inputs, orthogonally coupling and modulating the original scanning signal through a multiplicative digital-to-analog converter circuit, and outputting a corrected analog scanning signal; driving the scanning coil to generate a magnetic field through the corrected analog scanning signal, acquiring an image, and adjusting the amplitude correction parameters and phase correction parameters according to the image distortion until the image distortion is eliminated.

[0110] In another aspect, the present invention also provides a non-transitory computer-readable storage medium storing a computer program thereon. When executed by a processor, the computer program implements the scanning electron microscope image distortion correction method based on scanning magnetic field compensation provided by the above methods. The method includes: generating an X-direction original scanning signal and a Y-direction original scanning signal for driving the scanning coil of the scanning electron microscope; calculating the corresponding digital control coefficients using a scanning signal correction model based on set amplitude correction parameters, phase correction parameters, and electron beam rotation angle; using the X-direction original scanning signal and the Y-direction original scanning signal as reference inputs, and the digital control coefficients as modulation inputs, performing orthogonal coupling modulation on the original scanning signal through a multiplicative digital-to-analog converter circuit, and outputting a corrected analog scanning signal; driving the scanning coil to generate a magnetic field through the corrected analog scanning signal, acquiring an image, and adjusting the amplitude correction parameters and phase correction parameters according to the image distortion until the image distortion is eliminated.

[0111] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0112] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for correcting image distortion in scanning electron microscopes based on scanning magnetic field compensation, characterized in that, include: Generate raw X-direction and raw Y-direction scanning signals for driving the scanning coil of a scanning electron microscope; Based on the set amplitude correction parameters, phase correction parameters, and electron beam rotation angle, the corresponding digital control coefficients are calculated using the scanning signal correction model. Using the original X-direction scanning signal and the original Y-direction scanning signal as reference inputs, and the digital control coefficients as modulation inputs, the original scanning signals are orthogonally coupled and modulated through a multiplicative digital-to-analog converter circuit to output a corrected analog scanning signal. The scanning coil is driven by the corrected analog scanning signal to generate a magnetic field, and an image is acquired. The amplitude correction parameter and phase correction parameter are adjusted according to the image distortion until the image distortion is eliminated. The digital control coefficients are: ； ； ； ； Where RcA, RcB, RcC, and RcD are the digital control coefficients corresponding to each channel of the multiplication-type digital-to-analog converter, respectively; M1 and M2 are amplitude correction parameters, t1 and t2 are phase correction parameters; and θ is the electron beam rotation angle.

2. The scanning electron microscope image distortion correction method based on scanning magnetic field compensation according to claim 1, characterized in that, The process of using a multiplicative digital-to-analog converter circuit to orthogonally couple and modulate the original scanning signal, and outputting a corrected analog scanning signal, includes: The original X-direction scanning signal is connected to the reference voltage input terminals of the first and third multiplication-type digital-to-analog converters via a multi-channel multiplication-type digital-to-analog converter, and the original Y-direction scanning signal is connected to the reference voltage input terminals of the second and fourth multiplication-type digital-to-analog converters. The calculated digital control coefficients are sent to the digital input terminals of the corresponding multiplication-type digital-to-analog converters via the host computer software. The first and second outputs of the multiplicative digital-to-analog converter circuit are superimposed to form an X-direction correction signal; the third and fourth outputs of the multiplicative digital-to-analog converter circuit are superimposed to form a Y-direction correction signal.

3. The scanning electron microscope image distortion correction method based on scanning magnetic field compensation according to claim 1, characterized in that, The step of adjusting the amplitude correction parameter and phase correction parameter according to the image distortion includes: By using a circular standard sample and adjusting the amplitude correction parameters, the image can be made to appear as a perfect ellipse or circle. Adjusting the phase correction parameters eliminates the rotation angle, gradually bringing the image closer to a perfect circle.

4. The scanning electron microscope image distortion correction method based on scanning magnetic field compensation according to claim 3, characterized in that, After adjusting the phase correction parameters to eliminate the rotation angle and gradually bring the image closer to a perfect circle, the method further includes: The geometric parameters of the image are measured using an image measurement tool. The amplitude correction parameters and phase correction parameters are then iteratively fine-tuned based on the deviation between the measured values ​​and the standard values ​​until the image distortion is eliminated.

5. The scanning electron microscope image distortion correction method based on scanning magnetic field compensation according to claim 4, characterized in that, After adjusting the amplitude correction parameter and phase correction parameter according to the image distortion, the method further includes: After completing the parameter adjustment, change the electron beam rotation angle and magnification to determine whether the standard sample image is distorted; if distortion occurs, recalculate and update the digital control coefficients until the same set of correction parameters applies to all rotation angles.

6. A scanning electron microscope image distortion correction device based on scanning magnetic field compensation, characterized in that, include: The generation module is used to generate the raw X-direction scanning signal and the raw Y-direction scanning signal for driving the scanning coil of the scanning electron microscope; The first output module is used to calculate the corresponding digital control coefficients based on the set amplitude correction parameters, phase correction parameters and electron beam rotation angle using the scanning signal correction model. The second output module is used to take the original X-direction scanning signal and the original Y-direction scanning signal as reference inputs, take the digital control coefficients as modulation inputs, and perform orthogonal coupling modulation on the original scanning signal through a multiplicative digital-to-analog converter circuit to output the corrected analog scanning signal. The correction module is used to drive the scanning coil to generate a magnetic field through the corrected analog scanning signal, acquire images, and adjust the amplitude correction parameters and phase correction parameters according to the image distortion until the image distortion is eliminated. The digital control coefficients are: ； ； ； ； Where RcA, RcB, RcC, and RcD are the digital control coefficients corresponding to each channel of the multiplication-type digital-to-analog converter, respectively; M1 and M2 are amplitude correction parameters, t1 and t2 are phase correction parameters; and θ is the electron beam rotation angle.

7. A scanning electron microscope image distortion correction system based on scanning magnetic field compensation, comprising image correction using the scanning electron microscope image distortion correction method based on scanning magnetic field compensation as described in any one of claims 1-5, characterized in that, The system includes: The host computer control module is used to provide a human-machine interface, receive input amplitude correction parameters and phase correction parameters, and calculate digital control coefficients based on the electron beam rotation angle and a preset correction model. A scan signal generator is used to generate raw analog scan waveforms in the X and Y directions; The signal modulation correction module is connected to the host computer control module and the scanning signal generator respectively. It is used to receive the original analog scanning waveform as a reference signal, receive the digital control coefficient as a modulation signal, and output the corrected analog scanning signal through hardware multiplication. The driving module, connected to the signal modulation and correction module, is used to amplify the power of the corrected analog scanning signal and drive the scanning coil.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor, characterized in that, When the processor executes the program, it implements the scanning electron microscope image distortion correction method based on scanning magnetic field compensation as described in any one of claims 1 to 5.

9. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the scanning electron microscope image distortion correction method based on scanning magnetic field compensation as described in any one of claims 1 to 5.

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