Calibration method, scanning electron microscope, control device and storage medium

Abstract

The present application discloses a calibration method, a scanning electron microscope, a control device and a storage medium. The calibration method of the parameters of a scanning electron microscope provided in the embodiment of the present application includes: collecting images of a standard sample located on a sample stage under different focusing currents; reading the signal-to-noise ratio of the image; recording the focusing current value corresponding to the highest value of the signal-to-noise ratio; obtaining the current actual working distance; based on the actual working distance, fitting the working distance and the focusing current value to obtain a first relationship; and calibrating the scanning electron microscope based on the first relationship. In this way, the working distance parameters of the scanning electron microscope can be accurately calibrated using the calibration method provided in the embodiment of the present application, so that the scanning electron microscope can achieve the automatic focusing function, thereby realizing accurate measurement of the sample size and optimal imaging, and the calibration method is universal and applicable to all scanning electron microscopes.

Description

Technical Field

[0001] The present application relates to the technical field of scanning electron microscopes, and in particular to a calibration method, a scanning electron microscope, a control device and a storage medium. Background Art

[0002] In related technologies, the calibration method of key parameters of scanning electron microscopes is usually completed before the machine leaves the factory. It is mainly based on mechanical distance and is closely related to the working condition of the high-precision sample stage. There is no universal calibration method, and the calibration process of each device is different. After a scanning electron microscope is used for a long time, the parameters of the scanning electron microscope will change, affecting the test accuracy, and additional calibration is required. Summary of the invention

[0003] Embodiments of the present application provide a calibration method, a scanning electron microscope, a control device, and a storage medium.

[0004] The calibration method of the scanning electron microscope parameters provided in the embodiment of the present application includes:

[0005] Collect images of a standard sample on a sample stage at different focusing currents;

[0006] reading a signal-to-noise ratio of the image;

[0007] Record the focusing current value corresponding to the highest value of the signal-to-noise ratio;

[0008] Get the current actual working distance;

[0009] Based on the actual working distance, fitting and associating the working distance with the focusing current value to obtain a first relationship;

[0010] The scanning electron microscope is calibrated based on the first relationship.

[0011] In this way, the calibration method provided in the embodiment of the present application can be used to accurately calibrate the working distance parameters of the scanning electron microscope, so that the scanning electron microscope can achieve the automatic focusing function, thereby realizing accurate measurement of the sample size and optimal imaging, and the calibration method is universal and applicable to all scanning electron microscopes.

[0012] In certain embodiments, acquiring images of a standard sample on a sample stage at different focusing currents comprises:

[0013] Adjust to obtain different focusing currents;

[0014] An image of at least one of the standard samples is acquired at each of the focusing currents.

[0015] In certain embodiments, before acquiring images of the standard sample on the sample stage at different focusing currents, the calibration method further comprises:

[0016] Select the Z-axis height of the translation stage;

[0017] The standard sample is destigmatized and focused at a predetermined magnification under a predetermined accelerating voltage.

[0018] In certain embodiments, before acquiring images of the standard sample on the sample stage at different focusing currents, the calibration method further comprises:

[0019] According to the Z-axis travel of the translation stage, measure the distance Z from the highest point of the sample stage to the electron microscope pole shoe. min , and measure the distance Z from the lowest point of the sample stage to the electron microscope pole shoe max ;

[0020] Measure the height H of the standard sample;

[0021] The current actual working distance is calculated according to the following formula:

[0022] WD=|ZZ min |-H;

[0023] Wherein, WD is the current working distance.

[0024] In some embodiments, the step of fitting and associating the working distance with the focusing current value to obtain a first relationship based on the actual working distance includes:

[0025] Adjusting the Z-axis height of the translation stage to obtain different Z-axis heights;

[0026] Under different Z-axis height values, the corresponding actual working distance is calculated and the corresponding focusing current value is obtained;

[0027] Nonlinear fitting is performed on different actual working distances and corresponding focusing current values ​​to obtain the first relationship.

[0028] In some embodiments, the calibration method further comprises:

[0029] measuring the actual length of the standard sample;

[0030] The ratio of the actual length to the characteristic length of the standard sample is used as a scaling factor;

[0031] Fitting the working distance and the scaling factor to obtain a second relationship;

[0032] The scanning electron microscope is calibrated based on the second relationship.

[0033] In some embodiments, fitting the working distance and the scaling factor to obtain a second relationship includes:

[0034] Adjusting the Z-axis height of the translation stage to obtain different Z-axis heights;

[0035] Under different Z-axis height values, the corresponding actual working distance and the corresponding scaling factor are calculated;

[0036] Nonlinear fitting is performed on different actual working distances and corresponding scaling coefficients to obtain the second relationship.

[0037] The scanning electron microscope provided in the embodiment of the present application includes: an objective lens, a sample stage, a displacement stage, a memory and a controller. The sample stage is used to carry the sample to be tested, and the sample stage is spaced apart from the objective lens; the displacement stage is connected to the sample stage; the memory is used to store a computer program; and the controller is used to execute the computer program to implement the calibration method described in any of the above embodiments.

[0038] The control device provided in the embodiment of the present application includes an acquisition module, a reading module, a recording module, an acquisition module, a fitting module and a calibration module. The acquisition module is used to acquire images of a standard sample located on a sample stage under different focusing currents. The reading module is used to read the signal-to-noise ratio of the image. The recording module is used to record the focusing current value corresponding to the highest value of the signal-to-noise ratio. The acquisition module is used to obtain the current actual working distance. The fitting module is used to fit the working distance and the focusing current value based on the actual working distance to obtain a first relationship. The calibration module is used to calibrate the scanning electron microscope based on the first relationship.

[0039] A computer program is stored on a computer-readable storage medium provided in an embodiment of the present application. When the program is executed by a processor, the calibration method described in any of the above embodiments is implemented.

[0040] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0042] Figure 1 It is a flow chart of the calibration method of the embodiment of the present application;

[0043] Figure 2 is a schematic structural diagram of a scanning electron microscope according to an embodiment of the present application;

[0044] Figure 3 is a schematic diagram of a module of a control device in an embodiment of the present application;

[0045] Figure 4 It is a flow chart of the calibration method of the embodiment of the present application;

[0046] Figure 5 is another schematic flow chart of the calibration method according to an embodiment of the present application;

[0047] Figure 6 It is another flow chart of the calibration method of the embodiment of the present application;

[0048] Figure 7 is another flow chart of the calibration method according to the embodiment of the present application;

[0049] Figure 8 is a schematic diagram of the fitting results of the working distance and the focusing current value under different accelerating voltages of the calibration method according to the embodiment of the present application;

[0050] Fig. 9 is another flow chart of the calibration method according to the embodiment of the present application;

[0051] Fig.10 is another flow chart of the calibration method according to the embodiment of the present application;

[0052] Fig.11 is an example diagram of the relationship between the scaling factor difference and the working distance of the calibration method according to the embodiment of the present application;

[0053] Fig.12 is a measurement data diagram of an embodiment of a calibration method according to an embodiment of the present application;

[0054] Fig.13 This is a measurement data diagram of another embodiment of the calibration method according to the embodiment of the present application.

[0055] Description of main component symbols:

[0056] Scanning electron microscope 10, objective lens 11, sample stage 12, translation stage 13, memory 14, controller 15, sample chamber 16, electron gun 17, electron microscope pole piece 18, control device 20, acquisition module 21, reading module 22, recording module 23, acquisition module 24, fitting module 25, calibration module 26. DETAILED DESCRIPTION

[0057] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as limiting the present application.

[0058] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0059] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or mutual communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0060] In the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0061] The disclosure below provides many different embodiments or examples to realize the different structures of the present application. In order to simplify the disclosure of the present application, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present application. In addition, the present application can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplification and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed. In addition, the various specific processes and material examples provided by the present application, but those of ordinary skill in the art can appreciate the application of other processes and / or the use of other materials.

[0062] See also Figure 1 and Figure 2 The calibration method of the scanning electron microscope 10 parameters provided in the embodiment of the present application includes:

[0063] S10: collecting images of the standard sample on the sample stage 12 at different focusing currents;

[0064] S20: read the signal-to-noise ratio of the image;

[0065] S30: recording the focusing current value corresponding to the highest signal-to-noise ratio;

[0066] S40: obtaining the current actual working distance;

[0067] S50: Based on the actual working distance, fitting and associating the working distance with the focusing current value to obtain a first relationship;

[0068] S60: Calibrate the scanning electron microscope 10 based on the first relationship.

[0069] In this way, the calibration method provided in the embodiment of the present application can be used to accurately calibrate the working distance parameters of the scanning electron microscope 10, so that the scanning electron microscope 10 can achieve an automatic focusing function, thereby realizing accurate measurement of the sample size and optimal imaging, and the calibration method is universal and applicable to all scanning electron microscopes 10.

[0070] See also Figure 2 The scanning electron microscope 10 provided in the embodiment of the present application includes an objective lens 11, a sample stage 12, a displacement stage 13, a memory 14 and a controller 15. The sample stage 12 is used to carry the sample to be tested. The displacement stage 13 is connected to the sample stage 12. The memory 14 is used to store a computer program. The controller 15 is used to execute the computer program to implement the calibration method described in any of the above embodiments.

[0071] In other words, the controller 15 is used to collect images of the standard sample located on the sample stage 12 under different focusing currents; it is also used to read the signal-to-noise ratio of the image; it is also used to record the focusing current value corresponding to the highest signal-to-noise ratio; it is also used to obtain the current actual working distance; and it is used to fit the working distance and the focusing current value based on the actual working distance to obtain a first relationship; and it is used to calibrate the scanning electron microscope 10 based on the first relationship.

[0072] Specifically, the scanning electron microscope 10 is also called a scanning electron microscope, which can be used to obtain clear quality images. The scanning electron microscope 10 can also include a sample chamber 16 and an electron gun 17, the sample stage 12 and the displacement stage 13 are accommodated in the sample chamber 16, and the electron gun 17 is used to emit a high-energy electron beam. The working principle of the scanning electron microscope 10 is to use a focused very narrow high-energy electron beam to scan the sample to be tested, and to stimulate various physical information through the interaction between the electron beam and the sample to be tested, and to collect, amplify, and re-image the information to achieve the purpose of characterizing the microscopic morphology of the sample to be tested.

[0073] More specifically, the greater the acceleration voltage, the higher the energy of the electron beam. The acceleration voltage usually selected is 1kv-30kv. When the electron beam hits the sample surface, secondary electrons, backscattered electrons, and Auger electrons are generated. Secondary electrons are the main signal source of the scanning electron microscope 10. Secondary electrons are collected by secondary electron detectors and can then be imaged on a computer connected to the scanning electron microscope 10. The more secondary electrons generated at a certain point, the stronger the signal, which is manifested as a brighter image.

[0074] Among them, there are many parameters of the scanning electron microscope 10, and the acceleration voltage, working distance, magnification and detector type will affect the image quality. At the same time, these parameters are usually displayed in the detection result parameter column below the image. Among them, the acceleration voltage and the detector type are the hardware parameters of the scanning electron microscope 10, and the working distance and magnification are the results obtained through relevant calculations and software processing. Therefore, it is possible to associate the working distance and magnification with other parameters to achieve accurate calibration of key parameters, which is conducive to improving the imaging effect of the image and the accuracy of measuring the characteristic size of the sample.

[0075] See also Figure 3 The control device 20 provided in the embodiment of the present application includes an acquisition module 21, a reading module 22, a recording module 23, an acquisition module 24, a fitting module 25 and a calibration module 26. The acquisition module 21 is used to acquire images of the standard sample located on the sample stage 12 under different focusing currents. The reading module 22 is used to read the signal-to-noise ratio of the image. The recording module 23 is used to record the focusing current value corresponding to the highest signal-to-noise ratio. The acquisition module 24 is used to obtain the current actual working distance. The fitting module 25 is used to fit the working distance and the focusing current value based on the actual working distance to obtain a first relationship. The calibration module 26 is used to calibrate the scanning electron microscope 10 based on the first relationship.

[0076] Specifically, after the standard sample is fixed on the sample stage 12, the sample chamber 16 needs to be evacuated because the filament of the electron beam will quickly oxidize and become ineffective in the ordinary atmosphere. The selection of the standard sample has the following requirements: the standard sample will not be decomposed by the electron beam, the standard sample has good stability under the scanning of the electron beam, the standard sample has conductivity, and the size of the standard sample is suitable for the installation of the sample stage 12.

[0077] The standard sample may be pre-treated, cleaned and dried. To prevent the standard sample from being contaminated and affecting the analysis results, the standard sample may be ultrasonically cleaned with a solvent. In addition, a wet standard sample will release water vapor to affect the vacuum environment in the sample chamber 16, and the surface of the water-containing standard sample is prone to deformation, resulting in distorted results, so the standard sample also needs to be dried.

[0078] The sample chamber 16 is controlled to be in a vacuum environment, and the distance between the sample stage 12 and the objective lens 11 is adjusted according to the size of the standard sample to facilitate observation of the standard sample. Under a certain acceleration voltage, the beam is turned on to eliminate astigmatism and focus the standard sample.

[0079] The standard sample can be a solder ball, a grating ruler, etc. After selecting the standard sample, the height H of the standard sample can be measured first. The standard sample is fixed on the sample stage 12, and the sample chamber 16 is evacuated. A Z-axis height Z of the fixed displacement stage 13 is turned on at a certain acceleration voltage, and the standard sample is de-astigmatized and focused at a fixed magnification. After reading the corresponding focusing current value in the software, an image of the scanning electron microscope 10 is collected, and then the value of the focusing current is adjusted to observe whether the image reaches the optimal state, collect images under different focusing current values, read the signal-to-noise ratio of the image under different focusing current values, and record the focusing current value corresponding to the highest signal-to-noise ratio.

[0080] The actual working distance of the current scanning electron microscope 10 can be calculated by the height H of the standard sample and the current Z-axis height Z of the displacement stage 13. Thus, the focusing current value corresponding to the actual working distance under the acceleration voltage can be determined. The Z-axis height Z of the displacement stage 13 is adjusted to ensure that the other parameters of the scanning electron microscope 10 remain unchanged, and the focusing current value corresponding to the highest value of the signal-to-noise ratio is tested at different working distances. The working distance and the focusing current value are nonlinearly fitted to obtain the first relationship, and the relationship between the working distance and the focusing current value under the acceleration voltage can be associated.

[0081] See also Figure 4 In some embodiments, collecting images of a standard sample on the sample stage 12 at different focusing currents includes:

[0082] S11: Adjust to obtain different focusing currents;

[0083] S12: Acquire an image of at least one standard sample at each focusing current.

[0084] In this way, the image of the standard sample is observed by adjusting the focusing current to find the image with the highest signal-to-noise ratio at the working distance, that is, the image with good imaging effect and good focusing effect. Specifically, in the process of adjusting the focusing current, images under different focusing currents are collected, and the signal-to-noise ratios of different focused images are read by the image processing software of the scanning electron microscope 10, and the focusing current value corresponding to the highest signal-to-noise ratio is recorded.

[0085] In some embodiments, the acquisition module 21 is used to adjust to obtain different focusing currents, and is also used to acquire an image of at least one standard sample at each focusing current.

[0086] In some embodiments, the controller 15 is used to adjust to obtain different focusing currents, and is also used to acquire an image of at least one standard sample under each focusing current.

[0087] See also Figure 5 In some embodiments, before acquiring images of the standard sample on the sample stage 12 at different focusing currents, the calibration method further comprises:

[0088] S01: Select the Z-axis height Z of the translation stage 13;

[0089] S02: Under a predetermined acceleration voltage and at a predetermined magnification, the standard sample is destigmatized and focused.

[0090] Thus, after the Z-axis height of the translation stage 13 is selected, the working distance of the scanning electron microscope 10 can be determined based on the Z-axis height of the translation stage 13, and destigmatizing the standard sample can improve the imaging effect and image clarity. In one embodiment, the predetermined magnification can be 5000x.

[0091] In some embodiments, the controller 15 is used to select the Z-axis height of the translation stage 13 and is also used to perform destigmatization and focusing on the standard sample at a predetermined magnification under a predetermined acceleration voltage.

[0092] See also Figure 6 In some embodiments, before acquiring images of the standard sample on the sample stage 12 at different focusing currents, the calibration method further comprises:

[0093] S03: According to the Z-axis travel of the translation stage 13, measure the distance Zmin from the highest point of the sample stage 12 to the electron microscope pole shoe 18, and measure the distance Zmax from the lowest point of the sample stage 12 to the electron microscope pole shoe 18;

[0094] S04: Measure the height H of the standard sample;

[0095] The current actual working distance is calculated according to the following formula:

[0096] WD=|Z-Zmin|-H;

[0097] Wherein, WD is the current working distance.

[0098] In this way, the current actual working distance can be calculated based on the distance from the highest point of the sample stage 12 to the electron microscope pole shoe 18 and the height H of the measured standard sample, so that the focusing current value corresponding to the highest signal-to-noise ratio at the working distance can be determined.

[0099] In some embodiments, the control device 20 also includes a measuring module and a calculating module. The measuring module is used to measure the distance Zmin from the highest point of the sample stage 12 to the electron microscope pole shoe 18 and the distance Zmax from the lowest point of the sample stage 12 to the electron microscope pole shoe 18 according to the Z-axis travel of the translation stage 13, and to measure the height H of the standard sample.

[0100] In some embodiments, the controller 15 is used to measure the distance Zmin from the highest point of the sample stage 12 to the electron microscope pole shoe 18 and the distance Zmin from the lowest point of the sample stage 12 to the electron microscope pole shoe 18 according to the Z-axis travel of the translation stage 13. max , and the height H used to measure the standard sample.

[0101] It should be noted that the electron microscope pole shoe 18 is arranged on the side of the objective lens 11 close to the sample stage 12. When the standard sample is observed by the scanning electron microscope 10, when the working distance of the scanning electron microscope 10 needs to be adjusted, the height position of the objective lens 11 remains unchanged, and the position of the sample stage 12 is adjusted by the translation stage 13 to adjust the working distance. It should be noted that the working distance is the distance between the electron microscope pole shoe 18 and the sample.

[0102] It is worth mentioning that the distance from the highest point of the sample stage 12 to the electron microscope pole shoe 18 is Z min It refers to the distance from the sample stage 12 to the electron microscope pole shoe 18 when the sample stage 12 moves to the highest point, and the distance Z from the lowest point of the sample stage 12 to the electron microscope pole shoe 18 max It refers to the distance from the sample stage 12 to the electron microscope pole shoe 18 when the sample stage 12 moves to the lowest point.

[0103] Since the movable stroke of the sample stage 12 is limited, the movable stroke of the sample stage 12 is the difference between the distance Zmax from the lowest point of the sample stage 12 to the electron microscope pole shoe 18 and the distance Zmin from the highest point of the sample stage 12 to the electron microscope pole shoe 18. Therefore, the Z-axis height Z of the translation stage 13 should be selected within the numerical range of the movable stroke of the sample stage 12.

[0104] When the image of the standard sample is observed by the scanning electron microscope 10, the selected working distance is related to the height H of the standard sample and the Z-axis height Z of the displacement stage 13. The working distance WD of the scanning electron microscope 10 is the difference between the absolute value of the difference between the Z-axis height Z of the displacement stage 13 and the distance Zmin from the highest point of the sample stage 12 to the electron microscope pole shoe 18 and the height H of the standard sample, that is, WD = |Z-Zmin|-H. By calculating the working distance WD of the scanning electron microscope 10, the focusing current value corresponding to the working distance can be known.

[0105] See also Figure 7 In some embodiments, based on the actual working distance, fitting the working distance and the focusing current value to obtain a first relationship includes:

[0106] S51: adjusting the Z-axis height of the translation stage 13 to obtain different Z-axis heights;

[0107] S52: Under different Z-axis height values, the corresponding actual working distance is calculated and the corresponding focusing current value is obtained;

[0108] S53: Perform nonlinear fitting on different actual working distances and corresponding focusing current values ​​to obtain a first relationship.

[0109] In this way, by adjusting the Z-axis height of the translation stage 13, calculating different corresponding actual working distances and obtaining corresponding focusing current values, and performing nonlinear fitting on different actual working distances and corresponding focusing current values, a first relationship between the working distance and the focusing current value under a predetermined voltage can be obtained.

[0110] In some embodiments, the fitting module 25 is used to adjust the Z-axis height of the translation stage 13 to obtain different Z-axis heights, and is also used to calculate the corresponding actual working distance and obtain the corresponding focusing current value at different Z-axis height values, and is also used to perform nonlinear fitting on different actual working distances and corresponding focusing current values ​​to obtain a first relationship.

[0111] In some embodiments, the controller 15 is used to adjust the Z-axis height of the translation stage 13 to obtain different Z-axis heights, and is also used to calculate the corresponding actual working distance and obtain the corresponding focusing current value at different Z-axis height values, and is also used to perform nonlinear fitting on different actual working distances and corresponding focusing current values ​​to obtain a first relationship.

[0112] The working distance and the focusing current value are fitted to obtain a first relationship, and the process of calibrating the working distance parameter of the scanning electron microscope 10 based on the first relationship is as follows: according to the Z-axis travel of the displacement stage 13, the distance Zmin from the highest point of the sample stage 12 to the electron microscope pole shoe 18 is measured, and the distance Zmax from the lowest point of the sample stage 12 to the electron microscope pole shoe 18 is measured, and a standard sample is selected. The standard sample can be a solder ball and a grating ruler, etc., and the height H of the standard sample is measured. The standard sample is fixed on the sample stage 12 and vacuumed. A Z-axis height Z of the displacement stage 13 is fixed, and the beam is turned on at a certain acceleration voltage to eliminate astigmatism and focus the standard sample at a fixed magnification. After reading the corresponding focusing current value in the software, the image of the scanning electron microscope 10 is collected; then the focusing current is adjusted left and right to observe whether the image reaches the optimal state, and images under different focusing current values ​​are collected.

[0113] In the image processing software, read the signal-to-noise ratio of the image under different focusing current values, and record the focusing current value corresponding to the highest signal-to-noise ratio. Calculate the current actual working distance WD = |Z-Zmin|-H to determine the focusing current value corresponding to the actual working distance under the acceleration voltage. Adjust the Z-axis height Z of the displacement stage 13 to ensure that the other parameters of the scanning electron microscope 10 remain unchanged, and test the corresponding focusing current value under different Z values. Perform nonlinear fitting on the working distance and the focusing current value to obtain the first relationship, which can be used to associate the relationship between the working distance and the focusing current value under the acceleration voltage.

[0114] Repeat the above steps at other accelerating voltages to correlate the working distance and focusing current values ​​at other accelerating voltages. Finally, the accurate calibration of the working distance of the scanning electron microscope 10 can be obtained, which is conducive to obtaining high-quality images. The scanning electron microscope 10 can also realize the automatic focusing function according to the corresponding parameter connection, simplify the sample operation, and facilitate the user to simplify the use.

[0115] In one embodiment, nonlinear fitting is performed on the actual working distance and the corresponding focusing current value at accelerating voltages of 5 kv, 10 kv, 15 kv, 20 kv and 25 kv, respectively, to obtain the first relationship between the working distance and the focusing current value at different voltages, such as Figure 8 As shown, the first relationship between the working distance and the focusing current value at the working voltage of 30 kv can be deduced according to the first relationship between the working distance and the focusing current value at the accelerating voltages of 5 kv, 10 kv, 15 kv, 20 kv, and 25 kv.

[0116] In related technologies, the calibration method for key parameters of a scanning electron microscope is usually debugged before the machine leaves the factory. This type of calibration method usually does not cover the entire working parameter range of the electron microscope, and the error is obvious when using a low acceleration voltage.

[0117] In the calibration method provided by the implementation of the present application, the working distance and focusing current value of the scanning electron microscope 10 can be nonlinearly fitted under multiple acceleration voltage conditions to obtain a first relationship, that is, the relationship between the working distance and the focusing current value under multiple acceleration voltages can be associated, ensuring that the calibration method provided by the implementation of the present application can cover the entire working parameter range of the scanning electron microscope 10.

[0118] See also Fig. 9 In some embodiments, the calibration method further comprises:

[0119] S70: Measure the actual length of the standard sample;

[0120] S80: The ratio of the actual length to the characteristic length of the standard sample is used as a scaling factor;

[0121] S90: fitting and associating the working distance with the scaling factor to obtain a second relationship;

[0122] S100: Calibrate the scanning electron microscope 10 based on the second relationship.

[0123] In this way, after calibrating the working distance of the scanning electron microscope 10 based on the first relationship, the second relationship can be obtained by fitting the working distance and the zoom factor to calibrate the magnification parameter of the scanning electron microscope 10, thereby realizing accurate calibration of the magnification of the scanning electron microscope 10 and achieving the function of automatic focusing, which can realize accurate measurement of the sample size and optimal imaging.

[0124] In some embodiments, the control device 20 further includes a measurement module and a calculation module, wherein the measurement module is used to measure the characteristic length of the standard sample, and the calculation module is used to use the ratio of the characteristic length to the actual length of the standard sample as a scaling factor. The fitting module 25 is used to fit the working distance and the scaling factor to obtain a second relationship. The calibration module 26 is used to calibrate the scanning electron microscope 10 based on the second relationship.

[0125] In some embodiments, the controller 15 is used to measure the characteristic length of the standard sample, to use the ratio of the characteristic length to the actual length of the standard sample as a scaling factor, to fit the working distance and the scaling factor to obtain a second relationship, and to calibrate the scanning electron microscope 10 based on the second relationship.

[0126] Among them, the characteristic length of the standard sample is obtained by measuring the software of the scanning electron microscope 10. After calibrating the working distance parameters of the scanning electron microscope 10 based on the first relationship, select the standard sample, and the standard sample can be mainly a grating ruler with a standard size. Measure the height H and actual length of the standard sample, fix the standard sample on the sample stage 12, and perform vacuum operation. Fix a Z-axis height Z of the translation stage 13, turn on the beam at a certain acceleration voltage, and eliminate aberration and focus the standard sample at a fixed magnification (for example, 5000x). Observe whether the image reaches the optimal state, and collect images under different focusing conditions. In the image processing software, read the signal-to-noise ratio of different focused images, and record the working distance value corresponding to the highest signal-to-noise ratio.

[0127] After the working distance parameter of the scanning electron microscope 10 is calibrated based on the first relationship, the working distance and the corresponding focusing current value are nonlinearly fitted to obtain the first relationship. Therefore, the corresponding working distance can be obtained according to the focusing current value corresponding to the highest signal-to-noise ratio value.

[0128] Use the software's built-in measurement tool to measure the characteristic length of the standard sample. Calculate the ratio of the actual length of the standard sample to the characteristic length of the standard sample as the scaling factor. By changing the Z-axis height of the stage, the corresponding scaling factor can be tested at different working distances. By fitting the scaling factor with the working distance, automatic and accurate calibration of the magnification can be obtained.

[0129] See also Fig.10 In some embodiments, fitting the working distance to the scaling factor to obtain a second relationship includes:

[0130] S91: adjusting the Z-axis height of the translation stage 13 to obtain different Z-axis heights;

[0131] S92: Under different Z-axis height values, the corresponding actual working distance and the corresponding scaling factor are calculated;

[0132] S93: Perform nonlinear fitting on different actual working distances and corresponding scaling coefficients to obtain a second relationship.

[0133] In this way, by adjusting the Z-axis height of the translation stage 13 , the relationship between the working distance and the zoom factor can be obtained by performing nonlinear fitting on different working distances and corresponding zoom factors, so as to calibrate the magnification parameters of the scanning electron microscope 10 .

[0134] In some embodiments, the fitting module 25 is used to adjust the Z-axis height of the translation stage 13 to obtain different Z-axis heights, and is also used to calculate the corresponding actual working distance and the corresponding scaling factor at different Z-axis height values, and is used to perform nonlinear fitting on different actual working distances and corresponding scaling factors to obtain a second relationship.

[0135] In some embodiments, the controller 15 is used to adjust the Z-axis height of the translation stage 13 to obtain different Z-axis heights, and is also used to calculate the corresponding actual working distance and the corresponding scaling factor at different Z-axis height values, and is used to perform nonlinear fitting on different actual working distances and corresponding scaling factors to obtain a second relationship.

[0136] In one embodiment, at a predetermined acceleration voltage, at different Z-axis height values, the corresponding actual working distance and the corresponding scaling factor are obtained, and after nonlinear fitting of the different actual working distances and the corresponding scaling factors, the second relationship is obtained as follows: Fig.11 shown.

[0137] After the working distance parameter of the scanning electron microscope 10 is calibrated based on the first relationship, the working distance is fitted and associated with the scaling factor to obtain a second relationship. The process of calibrating the working distance parameter of the scanning electron microscope 10 based on the second relationship is as follows: a standard sample is selected, and the standard sample can be a grating ruler, and the height H and the actual length of the standard sample are measured. The standard sample is fixed on the sample stage 12 and vacuumed. The Z-axis height Z of a translation stage 13 is fixed, and the beam is turned on at a certain acceleration voltage to eliminate stigmation and focus the standard sample at a fixed magnification (for example, 5000x).

[0138] After reading the corresponding focusing current value in the software, collect 10 images of the scanning electron microscope; observe whether the image reaches the optimal state, and collect images under different focusing conditions. In the image processing software, read the signal-to-noise ratio of the different focused images, and record the working distance value corresponding to the highest signal-to-noise ratio value.

[0139] Use the software's built-in measurement tool to measure the characteristic length of the standard sample. Calculate the ratio of the actual length of the standard sample to the characteristic length of the standard sample as the scaling factor. By changing the Z-axis height of the stage, the corresponding scaling factor can be tested at different working distances, and the scaling factor can be fitted and associated with the working distance. Repeat the above steps at other accelerating voltages to associate the relationship between the working distance and the scaling factor at other accelerating voltages.

[0140] Finally, the accurate calibration of the zoom factor of the scanning electron microscope 10 can be obtained, which is conducive to obtaining high-quality images. The scanning electron microscope 10 can also realize the automatic focusing function according to the corresponding parameter connection, simplify the sample operation, and simplify the user's use.

[0141] In summary, the above calibration method can be used to accurately calibrate the working distance and magnification of the scanning electron microscope 10, achieve the automatic focusing function, and realize accurate measurement of sample size and optimal imaging. It is easy to operate and has the advantages of versatility and high precision.

[0142] A computer program is stored on a computer-readable storage medium provided in an embodiment of the present application. When the program is executed by a processor, the calibration method described in any of the above embodiments is implemented.

[0143] In one embodiment, a standard sample is placed on scanning electron microscope No. 1 10, and data is collected, the relationship between the working distance and the focusing current value is fitted, and the working distance and the scaling factor are fitted according to the calibration method provided in the embodiment of the present application. The distance Zmin from the highest point of the sample stage 12 of the scanning electron microscope 10 to the electron microscope pole shoe 18 is measured to be 74.8 mm, the height H of the standard sample is 3.62 mm, and when the Z-axis height Z of the translation stage 13 is 63 mm, the working distance WD of the scanning electron microscope 10 is 8.18 mm.

[0144] In another embodiment, a standard sample is placed on the No. 2 scanning electron microscope 10, and data is collected, the relationship between the working distance and the focusing current value is fitted, and the working distance and the scaling factor are fitted according to the calibration method provided in the embodiment of the present application. The distance Zmin from the highest point of the sample stage 12 of the scanning electron microscope 10 to the electron microscope pole shoe 18 is measured to be 75.2 mm, the height H of the standard sample is 3.62 mm, and when the Z-axis height Z of the translation stage 13 is 63 mm, the working distance WD of the scanning electron microscope 10 is 8.58 mm.

[0145] Under different acceleration voltages and working distances, according to the calibration results, the accuracy of the scaling factor and the accuracy of the working distance of the No. 1 scanning electron microscope 10 and the No. 2 scanning electron microscope 10 are checked. The standard for qualified calibration is set as follows: when the working distance WD of the scanning electron microscope 10 is less than 20 and the acceleration voltage is greater than or equal to 10 kV, the error range is ±3%, and in other cases, the error range is ±5%.

[0146] The final calibration result of SEM No. 1 is as follows: Fig.12 The final calibration result of SEM No. 2 is shown in Fig.13 It should be noted that Fig.12 and Fig.13 The "Z-axis height" is the Z-axis height Z of the translation stage 13, the "recommended WD" is the working distance measured according to the calibration method of the embodiment of the present application, and the "measured WD" is the actually measured working distance, that is, the distance between the electron microscope pole shoe 18 and the sample. The error value of the working distance is the ratio of the absolute value of the difference between the recommended WD and the measured WD to the recommended WD.

[0147] "Size (H)" is the size of the standard sample in the horizontal direction measured by the calibration method according to the embodiment of the present application. "Size (V)" is the size of the standard sample in the vertical direction measured by the calibration method according to the embodiment of the present application. Among them, the size of the standard sample in the horizontal direction and the size of the standard sample in the horizontal direction are both 10. The size error value of the standard sample in the horizontal direction is the ratio of the absolute value of the difference between the recommended WD and the measured WD to the recommended WD.

[0148] Depend on Fig.12 It can be seen that when the working distance WD of scanning electron microscope No. 1 is less than 20 and the acceleration voltage is ≥10kV, the error range is between ±3%. In other cases, the error range is between ±5%. Therefore, it can be confirmed that the working distance and magnification parameters of scanning electron microscope No. 1 are calibrated successfully through the calibration method of the embodiment of the present application.

[0149] Depend on Fig.13 It can be seen that when the working distance WD of the No. 2 scanning electron microscope is less than 20 and the acceleration voltage is greater than or equal to 10 kV, the error range is between ±3%, thereby confirming that the calibration method of the embodiment of the present application is qualified for the calibration of the working distance and magnification parameters of the No. 2 scanning electron microscope.

[0150] In summary, using the calibration method provided by the implementer of the present application to calibrate the working distance and magnification of the scanning electron microscope 10 is beneficial for the scanning electron microscope 10 to obtain high-quality images and accurately measure the characteristic dimensions of the sample. At the same time, it can also realize the automatic focusing function according to the corresponding parameter connection, simplify the sample operation, and help simplify user use. The calibration method is also universal and can be applied to all scanning electron microscopes 10, and is simple to operate, and the working distance and magnification parameters can be adjusted at any time.

[0151] In the description of this specification, the description with reference to the terms "one embodiment", "certain embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiments or examples are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0152] Although the embodiments of the present application have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present application, and that the scope of the present application is defined by the claims and their equivalents.

Claims

1. A method for calibrating parameters of a scanning electron microscope, characterized in that: include: Collect images of a standard sample on a sample stage at different focusing currents; reading a signal-to-noise ratio of the image; Record the focusing current value corresponding to the highest value of the signal-to-noise ratio; Get the current actual working distance; Based on the actual working distance, fitting and associating the actual working distance with the focusing current value to obtain a first relationship; calibrating the scanning electron microscope based on the first relationship; Before acquiring images of the standard sample on the sample stage under different focusing currents, the calibration method further comprises: Select the Z-axis height of the translation stage; Under a predetermined accelerating voltage, destigmatizing and focusing the standard sample at a predetermined magnification; Before acquiring images of the standard sample on the sample stage under different focusing currents, the calibration method further comprises: According to the Z-axis travel of the translation stage, measure the distance Zmin from the highest point of the sample stage to the electron microscope pole shoe, and measure the distance Zmax from the lowest point of the sample stage to the electron microscope pole shoe; Measure the height H of the standard sample; The actual working distance is calculated according to the following formula: WD=|Z-Zmin|-H; Wherein, WD is the actual working distance, Z is the current Z-axis height of the translation stage, Zmin is the distance from the sample stage to the electron microscope pole shoe when the sample stage moves to the highest point, and H is the height of the standard sample; The calibration method further comprises: measuring the actual length of the standard sample; The ratio of the actual length to the characteristic length of the standard sample is used as a scaling factor; Fitting and associating the actual working distance with the scaling factor to obtain a second relationship; The scanning electron microscope is calibrated based on the second relationship.

2. The calibration method according to claim 1, characterized in that: The collecting of images of the standard sample on the sample stage under different focusing currents comprises: Adjust to obtain different focusing currents; An image of at least one of the standard samples is acquired at each of the focusing currents.

3. The calibration method according to claim 1, characterized in that: The step of fitting and associating the actual working distance with the focusing current value to obtain a first relationship based on the actual working distance includes: Adjust the Z-axis height of the translation stage to obtain different Z-axis heights; Under different Z-axis height values, the corresponding actual working distance is calculated and the corresponding focusing current value is obtained; Nonlinear fitting is performed on different actual working distances and corresponding focusing current values ​​to obtain the first relationship.

4. The calibration method according to claim 1, characterized in that: The step of fitting and associating the actual working distance with the scaling factor to obtain a second relationship comprises: Adjust the Z-axis height of the translation stage to obtain different Z-axis heights; Under different Z-axis height values, the corresponding actual working distance and the corresponding scaling factor are calculated; Nonlinear fitting is performed on different actual working distances and corresponding scaling coefficients to obtain the second relationship.

5. A scanning electron microscope, characterized in that: include: Objective lens; The sample stage is used to carry the sample to be tested, and the sample stage is spaced apart from the objective lens: A displacement stage connected to the sample stage; a memory for storing a computer program; and A controller, wherein the controller is used to execute the computer program to implement the calibration method according to any one of claims 1 to 4.

6. A control device, characterized in that: Used to implement the calibration method according to any one of claims 1 to 4, comprising: An acquisition module, used for acquiring images of a standard sample located on a sample stage under different focusing currents; A reading module, used for reading the signal-to-noise ratio of the image; A recording module, used for recording the focusing current value corresponding to the highest value of the signal-to-noise ratio; An acquisition module is used to obtain the current actual working distance; A fitting module, configured to obtain a first relationship by fitting the actual working distance and the focusing current value based on the actual working distance; A calibration module is used to calibrate the scanning electron microscope based on the first relationship.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the calibration method according to any one of claims 1 to 4 is implemented.

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