Method and system for improving secondary electron collection efficiency in rejection field scanning electron microscope

Abstract

The invention discloses a method and a system for improving secondary electron collection efficiency in a rejection field scanning electron microscope. The method comprises the following steps: acquiring a new straight optical axis condition of a Wien filter when an edge electromagnetic field is not matched; under the new straight optical axis condition, the influence rule of the orientation angle and excitation of the Wien filter on the primary electron transmission characteristic is obtained; determining the position and the size of a secondary electron emission source; according to the position and the size of a secondary electron emission source and the influence rule of the orientation angle and the excitation of the Wien filter on the transmission characteristics of the primary electrons, the excitation and the orientation angle of the Wien filter required when the secondary electrons are completely collected are calculated.

Description

Technical Field

[0001] The present invention relates to the field of electron optical systems, and particularly to a method and a system for improving the secondary electron collection efficiency in a retarding field scanning electron microscope. Background Art

[0002] A retarding field scanning electron microscope (hereinafter referred to as a scanning electron microscope) can observe the in-situ structure of a sample surface without sputtering the sample surface with gold, and has the advantages of low spherical aberration coefficient and small damage to the sample. Therefore, it is widely used in the microscopic structure observation and measurement of biological samples and semiconductor samples. Due to the existence of the retarding field, secondary electrons in the scanning electron microscope are accelerated in the reverse direction to a very high energy. Therefore, an in-lens detector is required to collect secondary electrons. The in-lens detector needs to be provided with a central hole to ensure the smooth passage of primary electrons. However, the central hole will cause some secondary electrons (especially secondary electrons emitted in the central region of the scanning field) to escape, resulting in signal loss, and finally causing a dark area in the collected secondary electron image. To improve the image quality, a Wien filter is usually used to deflect secondary electrons from the direct axis of the system, so that all secondary electrons fall into the effective collection area of the detector, thereby improving the secondary electron collection efficiency. For most Wien filters, due to the different sizes of their electrodes and magnetic poles, there will be a mismatch between the electric field and the magnetic field in the edge region, which also causes the optical axis of the primary electrons to bend and generate aberrations. Even if a multi-pole Wien filter structure is used, due to the processing and installation accuracy limitations of the electrodes (or magnetic poles), there will still be a certain degree of edge electromagnetic field mismatch. Therefore, in the process of using the Wien filter to improve the secondary electron collection efficiency, the influence of the mismatched edge electromagnetic field on the aberrations of primary electrons must be considered.

[0003] The existing aberration theory of the Wien filter can only handle the case where the electromagnetic field is everywhere matched. For the research on the influence of the mismatched edge electromagnetic field on aberrations, at present, most scholars can only use the trajectory tracking method to draw the spot landing distribution on a certain plane by calculating the electron trajectories so as to evaluate the spot. At the same time, for the research on the secondary electron collection efficiency, most scholars also use the trajectory tracking method to calculate the landing distribution of secondary electrons so as to calculate their collection efficiency. This method requires a large number of electron trajectories to be calculated and it is difficult to study the variation law of aberrations. In addition, there is no relevant report on comprehensively considering the influence of the mismatched edge electromagnetic field of the Wien filter on the aberrations of primary electrons and the secondary electron collection efficiency.

[0004] Therefore, if the influence of the mismatched edge electromagnetic field on the aberrations of primary electrons and the secondary electron collection efficiency can be comprehensively considered and accurately calculated, it can effectively guide the design of the electron optical system of the scanning electron microscope, while improving the secondary electron collection efficiency and reducing its influence on the system aberrations. Summary of the Invention

[0005] The object of the present invention is to provide a method and system for improving the secondary electron collection efficiency in a retarding field scanning electron microscope, so as to overcome the problem that it is currently difficult to comprehensively consider the influence of the mismatched electromagnetic fields at the edge of the Wien filter on the primary electron aberration and the secondary electron collection efficiency.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for improving the secondary electron collection efficiency in a retarding field scanning electron microscope, comprising the following steps:

[0008] Step 1: Obtain the new straight optical axis condition of the Wien filter when the edge electromagnetic fields are mismatched;

[0009] Step 2: Under the new straight optical axis condition, obtain the influence law of the orientation angle and excitation of the Wien filter on the primary electron transmission characteristics;

[0010] Step 3: Determine the position and size of the secondary electron emission source;

[0011] Step 4: According to the position and size of the secondary electron emission source, and the influence law of the orientation angle and excitation of the Wien filter on the primary electron transmission characteristics, calculate the excitation and orientation angle of the Wien filter required for complete collection of secondary electrons.

[0012] Further, the obtaining of the new straight optical axis condition of the Wien filter when the edge electromagnetic fields are mismatched is specifically as follows:

[0013] For a Wien filter with mismatched edge electromagnetic field distributions, first use numerical calculation methods to calculate its electric dipole field distribution and magnetic dipole field distribution respectively, and then based on the mismatched electric dipole field distribution and magnetic dipole field distribution, by tracking the optical axis trajectory of a primary electron beam, obtain the Gaussian characteristics of the electron beam and the aberration coefficients within the third order;

[0014] By adjusting the ratio of the electric dipole field excitation V1 and the magnetic dipole field excitation NI1 of the Wien filter so that the optical axis can return to the straight optical axis after passing through the Wien filter, regard the ratio of the electric dipole field excitation V1 and the magnetic dipole field excitation NI1 at this time as the new straight optical axis condition of the Wien filter when the edge electromagnetic fields are mismatched.

[0015] Further, the obtaining of the influence law of the orientation angle and excitation of the Wien filter on the primary electron transmission characteristics under the straight optical axis condition is specifically as follows:

[0016] Under the condition of a straight optical axis, first fix the orientation angle of the Wien filter and keep it unchanged, change the dipole field excitation of the Wien filter, and calculate the Gaussian characteristics of the electron beam and the aberration coefficients within the third order at the corner and the center of the primary electron scanning field respectively. Then, keep the excitation of the Wien filter unchanged, change the orientation angle of the Wien filter, and calculate the Gaussian characteristics of the electron beam and the aberration coefficients within the third order at the corner and the center of the primary electron scanning field again, so as to obtain the influence law of the excitation and orientation angle of the Wien filter on the electron beam transmission characteristics.

[0017] Further, the determination of the position and size of the secondary electron emission source is specifically as follows:

[0018] Take the size of the primary electron beam spot as the size of the secondary electron emission source.

[0019] Further, the determination of the size of the primary electron beam spot is specifically as follows:

[0020] Under the condition of a straight optical axis, according to the design requirements of the scanning field size, determine the excitation of the deflector so that the scanning field range of the primary electrons meets the design requirements. Then, calculate the electron beam transmission characteristics within the third order of the primary electron scanning field at the corner and the center relative to the initial plane without the action of the Wien filter, and calculate the size of the primary electron beam spot according to the electron beam transmission characteristics and the initial conditions of the primary electron beam emission from the initial plane;

[0021] Or, obtain the primary electron beam spot distribution by measuring the current density distribution;

[0022] Or, based on the secondary electron image, indirectly obtain the size of the primary electron beam spot by calculating the image pixel size.

[0023] Further, according to the position and size of the secondary electron emission source, and the influence law of the orientation angle and excitation of the Wien filter on the primary electron transmission characteristics, calculate the excitation and orientation angle of the Wien filter required for complete collection of secondary electrons, specifically as follows:

[0024] On the basis of determining the position and size of the secondary electron emission source, first ensure that the Wien filter is in the closed state and the deflector is in the open state. Select the primary electron beam spot at the corner of the scanning field as the secondary electron emission source, and trace a central reference trajectory R s , calculate the central reference trajectory R s The landing position (x s , y s ) of the detector plane and the off-axis distance At the same time, calculate the current density distribution formed by the secondary electrons emitted at the center of the scanning field in the detector plane and the n% current envelope d SE , where the n% current envelope d SE Is defined as a circular area containing n% of the total current, dSE is the envelope diameter;

[0025] Then ensure that the Wien filter is in the on state and the electric dipole field excitation is V 1w , and the magnetic dipole field excitation is NI 1w , and ensure that the electric dipole field excitation and the magnetic dipole field excitation satisfy the new straight optical axis condition, that is, V 1w : NI 1w = V1:NI1, the deflector is in the off state, select the primary electron beam spot at the center of the scanning field as the secondary electron emission source, and trace a central reference trajectory R w , calculate the central reference trajectory R w The landing position (x w , y w ) on the detector plane and the off-axis distance

[0026] Finally, considering the inner and outer diameter sizes of the detector, when the Wien filter is not turned on, the secondary electrons at the center of the overall secondary electron scanning area escape from the central hole of the detector. Offset the overall secondary electron scanning area along a direction perpendicular to one side of the scanning area so that all secondary electrons fall into the effective collection area of the detector. The calculated Wien filter orientation angle and excitation range required for complete collection of secondary electrons are as follows:

[0027]

[0028] Among them, d o and d i are the outer diameter and inner diameter of the detector, unit: mm; θ w is the Wien filter orientation angle, unit: °; V 1w_max and V 1w_min are the maximum and minimum electric dipole field excitations of the Wien filter required to achieve complete collection of secondary electrons, unit: V; the corresponding maximum and minimum magnetic dipole field excitations NI 1w_max and NI 1w_min (unit: AT) are calculated according to the new straight optical axis condition, that is, NI 1w_max = V 1w_max *NI1 / V1, NI 1w_min = V 1w_min *NI1 / V1.

[0029] Furthermore, after obtaining the Wien filter orientation angle and excitation range required for complete collection of secondary electrons, determine the final Wien filter orientation angle in combination with the influence law of the Wien filter orientation angle on the primary electron aberration. In addition, considering the dipole field excitation redundancy, select (1.05 - 1.1)V 1w_min and (0.9 - 0.95)V 1w_maxThe minimum and maximum electric dipole field excitations of the Wien filter, and (1.05 - 1.1)NI 1w_min and (0.9 - 0.95)NI 1w_max The minimum and maximum magnetic dipole field excitations of the Wien filter.

[0030] A system for improving the secondary electron collection efficiency in a rejection field scanning electron microscope, comprising:

[0031] A first acquisition module: used to acquire the new straight optical axis condition of the Wien filter when the edge electromagnetic field is mismatched;

[0032] A second acquisition module: used to obtain the influence law of the orientation angle and excitation of the Wien filter on the primary electron transmission characteristics under the new straight optical axis condition;

[0033] A determination module: used to determine the position and size of the secondary electron emission source;

[0034] A calculation module: used to calculate the excitation and orientation angle of the Wien filter required for complete secondary electron collection according to the position and size of the secondary electron emission source, and the influence law of the orientation angle and excitation of the Wien filter on the primary electron transmission characteristics.

[0035] A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the steps of the method for improving the secondary electron collection efficiency in the rejection field scanning electron microscope are implemented.

[0036] A computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the steps of the method for improving the secondary electron collection efficiency in the rejection field scanning electron microscope are implemented.

[0037] Compared with the prior art, the present invention has the following beneficial technical effects:

[0038] The method for improving the secondary electron collection efficiency by using a Wien filter proposed by the present invention comprehensively considers the influence of the Wien filter on primary electron aberration and secondary electron current density distribution, and combines the geometric dimensions of the detector inside the lens to obtain the excitation range and orientation angle expression of the Wien filter required for complete secondary electron collection. In this process, the influence of the mismatched electromagnetic field at the edge of the Wien filter on primary electron aberration and the spatial distribution of secondary electron current density is obtained by tracking the reference trajectory instead of calculating a large number of electron trajectories. Compared with the traditional trajectory tracking method, the calculation amount of the trajectory is significantly reduced, and the excitation and orientation angle expression of the Wien filter is given, which is beneficial to the research of the transmission law in the secondary electron collection process and the optimized design of the secondary electron collection system. Description of the Drawings

[0039] The accompanying drawings of the specification are used to provide a further understanding of the present invention and form a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0040] Figure 1 It is a schematic diagram of secondary electron transmission when the Wien filter is closed and the deflector is open;

[0041] Figure 2 It is a schematic diagram of secondary electron transmission when the Wien filter is open and the deflector is closed;

[0042] Figure 3 It is a schematic diagram of the secondary electron scanning area and current density distribution under different excitations of the Wien filter in the detector plane;

[0043] Figure 4 It is a schematic diagram of the calculation model of the scanning electron microscope in the embodiment of the present invention;

[0044] Figure 5 It is a calculation result diagram of the electron beam optical axis returning to the straight optical axis after adjusting the dipole field excitation of the Wien filter;

[0045] Figure 6 It is the influence of the Wien filter excitation on the energy dispersion coefficient of the electron beam at the center and corners of the scanning field;

[0046] Figure 7 It is the influence of the orientation angle of the Wien filter on the energy dispersion coefficient of the electron beam at the center and corners of the scanning field;

[0047] Figure 8 It is when the Wien filter excitation is V 1w = 210V, NI 1w = 14.43AT, the orientation angle is θ w = 49.08°, the secondary electron current density distribution on the detector;

[0048] Figure 9 It is the secondary electron current density distribution on the detector when the Wien filter is not used;

[0049] Figure 10 It is when the Wien filter excitation is V 1w = 210V, NI 1w = 14.43AT, the orientation angle is θ w = 139.08°, the secondary electron current density distribution on the detector;

[0050] Figure 11 It is when the Wien filter excitation is V 1w = 210V, NI 1w = 14.43AT, the orientation angle is θ wThe distribution of the secondary electron current density on the detector when = 229.08°;

[0051] Figure 12 It is when the Wien filter is excited to V 1w = 210V, NI 1w = 14.43AT, and the orientation angle is θ w The distribution of the secondary electron current density on the detector when = 319.08°;

[0052] Figure 13 It is when the Wien filter is excited to V 1w = 210V, NI 1w = 14.43AT, and the orientation angle is θ w The comparison of the primary electron energy dispersion coefficients at 49.08°, 139.08°, 229.08°, and 319.08° respectively. Specific implementation manner

[0053] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0054] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily need to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units does not necessarily need to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products, or devices.

[0055] Embodiment 1

[0056] The present invention provides a method for improving the secondary electron collection efficiency in a retarding field scanning electron microscope, including the following steps:

[0057] First step, find the straight optical axis condition of the Wien filter when the edge electromagnetic fields do not match. For the Wien filter 104 with mismatched edge electromagnetic field distributions, first use numerical calculation methods to calculate its electric dipole field and magnetic dipole field distributions respectively. Then, based on the above mismatched electromagnetic field distributions, by tracing a reference trajectory (optical axis trajectory) of a primary electron beam, obtain the Gaussian characteristics of the electron beam and aberration coefficients within the third order. Since the mismatched edge electromagnetic fields of the Wien filter will cause the primary electron optical axis to deviate from the straight optical axis and introduce aberrations, it is necessary to adjust the ratio of the electric dipole field excitation V1 and the magnetic dipole field excitation NI1 of the Wien filter so that the optical axis can return to the straight optical axis after passing through the Wien filter, thereby reducing the influence on the system aberrations. The ratio of the electric dipole field excitation V1 and the magnetic dipole field excitation NI1 at this time is regarded as the new straight optical axis condition of the Wien filter with mismatched electromagnetic fields.

[0058] Second step, obtain the influence rules of the orientation angle and excitation of the Wien filter on the primary electron transmission characteristics. Under the new straight optical axis condition in the first step, first fix the orientation angle of the Wien filter and change the dipole field excitation of the Wien filter, and calculate the Gaussian characteristics of the electron beam and aberration coefficients within the third order at the corner 101 of the primary electron scanning field and at the center 102 of the primary electron scanning field respectively. Then, fix the excitation of the Wien filter (non-zero excitation) and change the orientation angle of the Wien filter, and calculate the Gaussian characteristics of the electron beam and aberration coefficients within the third order at the corner 101 of the primary electron scanning field and at the center 102 of the primary electron scanning field again. Finally, obtain the influence rules of the excitation and orientation angle of the Wien filter on the electron beam transmission characteristics.

[0059] Third step, determine the secondary electron emission source. In the present invention, the size of the primary electron beam spot is used as the size of the secondary electron emission source. The present invention provides two methods for determining the secondary electron emission source. One method is determined according to the electron beam transmission characteristics and initial conditions. Under the new straight optical axis condition in the first step, the influence of the Wien filter on the primary electron scanning position can be ignored. Therefore, according to the design requirements for the size of the primary electron scanning field 100, determine the excitation of the deflector so that the scanning field range of the primary electrons meets the design requirements. Then, calculate the electron optical characteristics within the third order of the electron beam at the corner 101 of the primary electron scanning field and at the center 102 of the primary electron scanning field without the action of the Wien filter, and calculate the size of the primary electron beam spot according to the electron beam transmission characteristics and the initial conditions of the electron beam emission. Another method is to directly measure or indirectly measure the primary electron beam spot. For example, obtain the primary electron beam spot distribution by measuring the current density distribution, or indirectly obtain the size of the primary electron beam spot by calculating the pixel size of the secondary electron image.

[0060] The fourth step is to calculate the Wien filter excitation and orientation angle required for complete collection of secondary electrons. Based on the position and size of the secondary electron emission source determined in the third step, first ensure that the Wien filter is closed (OFF) and the deflector is open (ON), select the primary electron beam spot at the corner of the scanning field as the secondary electron emission source, and trace a central reference trajectory R s 103, calculate the landing point position (x s ,y s ) and the distance from the axis At the same time, the current density distribution 201 formed by the secondary electrons emitted at the center on the detector plane and the n% current envelope d are calculated. SE , where n% current envelope d SE Defined as the circular area containing n% of the total current, d SE is the envelope diameter. Then ensure that the Wien filter is turned on (ON) and the excitation is V1 (and NI1), the deflector is turned off (OFF), select the primary electron beam spot at the center of the scanning field as the secondary electron emission source, and trace a central reference trajectory R w 107, calculate the landing point position (x w ,y w ) and the distance from the axis Finally, considering the inner and outer diameters of the detector, when the Wien filter is not turned on, the secondary electrons at the center of the entire secondary electron scanning area 202 escape from the central hole of the detector. In order to make all the secondary electrons fall into the effective collection area of the detector, the best offset method is to offset the entire secondary electron scanning area 202 in a direction perpendicular to one side of the scanning area, such as Figure 3 As shown, the Wien filter orientation angle and excitation range required to fully collect secondary electrons can be calculated as shown in formula (1) and formula (2), respectively.

[0061]

[0062] where θ w is the Wien filter orientation angle (unit: °), V 1w_max and V 1w_min are the maximum and minimum electric dipole field excitations (in V) of the Wien filter required to achieve complete collection of secondary electrons, and the corresponding maximum and minimum magnetic dipole field excitations NI 1w_max and NI 1w_min (Unit: AT) can be calculated based on the new straight optical axis condition. According to the symmetry line, θ w +90°、θ w +180° and θ w+270° also meets the above requirements. Therefore, it is necessary to determine the final orientation angle of the Wien filter by combining the influence law of the orientation angle of the Wien filter obtained in the second step on the primary electron aberration. For example, when the energy dispersion is the main factor affecting the primary electron aberration, it is necessary to find the orientation angle corresponding to a smaller energy dispersion according to the variation law of the energy dispersion with the orientation angle; while when the second-order aperture aberration is the main factor affecting the primary electron aberration, it is necessary to find the orientation angle corresponding to a smaller second-order aperture aberration according to the variation law of the second-order aperture aberration with the orientation angle. Then, considering a certain redundancy of the dipole field excitation, (1.05 - 1.1) V 1w_min and (0.9 - 0.95) V 1w_max , as well as (1.05 - 1.1) NI 1w_min and (0.9 - 0.95) NI 1w_max are selected as the minimum and maximum excitations of the Wien filter.

[0063] Example Two

[0064] Taking the calculation of the secondary electron collection in a retarding field scanning electron microscope as an example for illustration, the calculated model is as Figure 4 shown. The model includes a sample stage 301, a retarding electrode 302, an objective lens 303, a Wien filter 104, a deflector 105, and an in-lens detector 106. In the calculated model, the primary electrons are accelerated to 12 keV and decelerated to 1 keV at the sample stage, and the Wien filter is in an equipotential region of 12 kV. The object plane 308 is located at z = 0 mm, the surface of the sample stage is located at z = 264.5 mm, the detector is located at z = 165 mm, and the Wien filter is located at z = 219 mm. First, fix the electric dipole field excitation of the Wien filter at 100 V, and then change the magnetic dipole field excitation. When the magnetic dipole field excitation is 6.872 AT, the optical axis of the electron beam can return to the straight optical axis again after passing through the Wien filter. The calculation results are as Figure 5 shown. Therefore, it can be considered that for an electron beam of 12 keV, when the ratio of the electric and magnetic dipole field excitations is 100 V:6.872 AT, the new straight optical axis condition is satisfied. Under this excitation, set the primary electron scanning field 100 region as a square region of 100 μm × 100 μm, and then calculate the influence of the orientation angle and excitation of the Wien filter on the electron optical properties at the center and corners of the primary electron scanning field respectively. Here, taking the energy dispersion coefficient (DQ) as an example for illustration, the calculation results are as Figure 6 and Figure 7 shown. It can be seen that the energy dispersion coefficient increases with the increase of the excitation of the Wien filter, and the orientation angle of the Wien filter will cause large periodic fluctuations in the energy dispersion coefficient.

[0065] Example Three

[0066] When the Wien filter is in the OFF state and the deflector is in the ON state, trace a secondary electron reference trajectory R emitted from the corner 101 of the primary electron scanning field. s 103, as Figure 1 shown, calculate its landing position (x s , y s ) = (3.24 mm, 0.33 mm) and the off-axis distance And calculate the current density distribution 201 formed by the secondary electrons emitted from the center in the detector plane. During the calculation of the secondary electron current density distribution, it is assumed in the present invention that the diameter of the primary electron beam spot is 10 nm. The 80% current envelope d of the calculated secondary electron current density distribution 201 SE = 2.2 mm. Then turn the Wien filter to the ON state and the electric dipole field excitation V 1w = 100 V (magnetic dipole field excitation NI 1w = 6.872 AT), the deflector is in the OFF state, and trace a secondary electron reference trajectory R w 107, as Figure 2 shown, calculate its landing position (x w , y w ) = (2.26 mm, 0.07 mm) and the off-axis distance The inner diameter d of the detector used i = 2 mm, the outer diameter d o = 22 mm. According to the above parameters and formulas (1) and (2), the orientation angle θ w of the Wien filter can be calculated to be 49.08°, 139.08°, 229.08°, and 319.08°. The minimum electric dipole field excitation is V 1w_min = 204.66 V - 214.41 V, the maximum electric dipole field excitation is V 1w_max = 378.61 V - 399.65 V, the minimum magnetic dipole field excitation is NI 1w_min = 14.064 AT - 16.590 AT, and the maximum magnetic dipole field excitation is NI 1w_max = 26.018 AT - 27.464 AT.

[0067] Example 4

[0068] According to Figure 7 the calculation results, when the orientation angle θ w of the Wien filter is 49.08°, the energy dispersion introduced into the system is the smallest. Therefore, the orientation angle is set to 49.08°. At the same time, according to Figure 6As can be seen from the results shown, the smaller the excitation of the Wien filter, the smaller the energy dispersion introduced into the system. Considering a certain redundancy, the electric dipole field excitation of the Wien filter is set to V 1w = 210 V, NI 1w = 14.43 AT. At this time, the calculation results of the secondary electron current density distribution on the detector plane are as follows Figure 8 shown. It can be seen that all secondary electrons fall into the effective collection area of the detector, achieving 100% collection of secondary electrons. When the Wien filter is not used, the calculation results of the secondary electron current density distribution on the detector plane are as follows Figure 9 shown. At this time, most of the secondary electrons emitted at the center of the scanning field escape from the central hole of the detector, and the collection efficiency is only 11.08%. For comparison, in this example, the electric excitation of the dipole field of the Wien filter is also calculated when it is set to V 1w = 210 V, NI 1w = 14.43 AT. When the orientation angle θ w of the Wien filter in Example 2 is 139.08°, 229.08°, and 319.08°, the secondary electron current density distribution on the detector plane is shown in Figures 10 - 12 respectively, and the influence of the above different orientation angles on the energy dispersion of primary electrons is calculated, and the results are as follows Figure 13 shown. It can be seen from the above results that although the secondary electrons can be 100% collected when the orientation angle θ w of the Wien filter is 49.08°, 139.08°, 229.08°, and 319.08°, the energy dispersion of the system is the smallest when θ w optimally selected in this example is 49.08°, verifying the effectiveness of the method of the present invention.

[0069] Example Five

[0070] The present invention also provides a system for improving the secondary electron collection efficiency in a retarding field scanning electron microscope, including:

[0071] The first acquisition module: used to acquire the new straight optical axis condition of the Wien filter when the edge electromagnetic field is mismatched;

[0072] The second acquisition module: used to obtain the influence law of the orientation angle and excitation of the Wien filter on the primary electron transmission characteristics under the new straight optical axis condition;

[0073] The determination module: used to determine the position and size of the secondary electron emission source;

[0074] The calculation module: used to calculate the excitation and orientation angle of the Wien filter required for complete collection of secondary electrons according to the position and size of the secondary electron emission source, and the influence law of the orientation angle and excitation of the Wien filter on the primary electron transmission characteristics.

[0075] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0076] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to the embodiments of the present invention. It should be understood that each flow and / or block in the flowchart and / or block diagram, as well as the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the functions specified in one Figure 1 one flow or multiple flows and / or blocks Figure 1 or multiple blocks.

[0077] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing devices to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including instruction means that implement the functions specified in one Figure 1 one flow or multiple flows and / or blocks Figure 1 or multiple blocks.

[0078] These computer program instructions can also be loaded onto a computer or other programmable data processing devices, such that a series of operation steps are executed on the computer or other programmable devices to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable devices provide steps for implementing the functions specified in one Figure 1 one flow or multiple flows and / or blocks Figure 1 or multiple blocks.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the scope of its protection. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: after reading the present invention, those skilled in the art can still make various changes, modifications, or equivalent replacements to the specific implementation manners of the invention, but these changes, modifications, or equivalent replacements are all within the scope of the claims of the invention pending approval.

Claims

1. A method for improving the secondary electron collection efficiency in a rejection field scanning electron microscope, characterized in that, It includes the following steps: Step 1: Obtain the new straight optical axis condition of the Wien filter when the edge electromagnetic field is mismatched; Step 2: Under the new straight optical axis condition, obtain the influence law of the orientation angle and excitation of the Wien filter on the primary electron transmission characteristics; Step 3: Determine the position and size of the secondary electron emission source; Step 4: According to the position and size of the secondary electron emission source, and the influence law of the orientation angle and excitation of the Wien filter on the primary electron transmission characteristics, calculate the excitation and orientation angle of the Wien filter required for complete collection of secondary electrons.

2. The method for improving the secondary electron collection efficiency in a retarding field scanning electron microscope according to claim 1, wherein The obtaining of the new straight optical axis condition of the Wien filter when the edge electromagnetic field is mismatched is specifically as follows: For a Wien filter with mismatched edge electromagnetic field distributions, first use numerical calculation methods to calculate its electric dipole field distribution and magnetic dipole field distribution respectively, and then based on the mismatched electric dipole field distribution and magnetic dipole field distribution, by tracking the optical axis trajectory of a primary electron beam, obtain the Gaussian characteristics of the electron beam and the aberration coefficients within the third order; Adjust the ratio of the electric dipole field excitation V1 and the magnetic dipole field excitation NI1 of the Wien filter so that the optical axis can return to the straight optical axis after passing through the Wien filter, and regard the ratio of the electric dipole field excitation V1 and the magnetic dipole field excitation NI1 at this time as the new straight optical axis condition of the Wien filter when the edge electromagnetic field is mismatched.

3. The method for improving the secondary electron collection efficiency in a retarding field scanning electron microscope according to claim 1, characterized in that The obtaining of the influence law of the orientation angle and excitation of the Wien filter on the primary electron transmission characteristics under the new straight optical axis condition is specifically as follows: Under the new straight optical axis condition, first keep the orientation angle of the Wien filter fixed and change the dipole field excitation of the Wien filter, and calculate the Gaussian characteristics of the electron beam and the aberration coefficients within the third order at the corners and the center of the primary electron scanning field respectively. Then keep the excitation of the Wien filter fixed and change the orientation angle of the Wien filter, and calculate the Gaussian characteristics of the electron beam and the aberration coefficients within the third order at the corners and the center of the primary electron scanning field again, to obtain the influence law of the excitation and orientation angle of the Wien filter on the electron beam transmission characteristics.

4. The method for improving the secondary electron collection efficiency in a retarding field scanning electron microscope according to claim 1, wherein The determination of the position and size of the secondary electron emission source is specifically as follows: Take the size of the primary electron beam spot as the size of the secondary electron emission source.

5. The method for improving the secondary electron collection efficiency in a retarding field scanning electron microscope according to claim 4, wherein, The determination of the size of the primary electron beam spot is specifically as follows: Under the straight optical axis condition, according to the design requirements of the scanning field size, determine the excitation of the deflector so that the scanning field range of the primary electrons meets the design requirements, and then calculate the electron beam transmission characteristics within the third order of the primary electron scanning field at the corners and the center relative to the initial plane without the action of the Wien filter respectively. Calculate the size of the primary electron beam spot according to the electron beam transmission characteristics and the initial conditions of the primary electron beam emission from the initial plane; Or, obtain the primary electron beam spot distribution by measuring the current density distribution; Or, based on the secondary electron image, indirectly obtain the size of the primary electron beam spot by calculating the pixel size of the image.

6. The method for improving the secondary electron collection efficiency in a retarding field scanning electron microscope according to claim 2, wherein The calculation of the excitation and orientation angle of the Wien filter required for complete collection of secondary electrons according to the position and size of the secondary electron emission source, and the influence law of the orientation angle and excitation of the Wien filter on the primary electron transmission characteristics is specifically as follows: On the basis of determining the position and size of the secondary electron emission source, first ensure that the Wien filter is in the off state and the deflector is in the on state. Select the primary electron beam spot at the corner of the scanning field as the secondary electron emission source and trace a central reference trajectory R s , and calculate the central reference trajectory R s The landing position (x s , y s ) on the detector plane and the off-axis distance At the same time, calculate the current density distribution formed by the secondary electrons emitted at the center of the scanning field on the detector plane and the n% current envelope d SE , where the n% current envelope d SE is defined as a circular area containing n% of the total current, and d SE is the envelope diameter; Then ensure that the Wien filter is in the on state and the electric dipole field excitation is V 1w , and the magnetic dipole field excitation is NI 1w , and ensure that the electric dipole field excitation and the magnetic dipole field excitation satisfy the new straight optical axis condition, that is, V 1w : NI 1w = V1:NI1, the deflector is in the off state, select the primary electron beam spot at the center of the scanning field as the secondary electron emission source, and trace a central reference trajectory R w , calculate the landing position (x w , y w ) of the central reference trajectory R w on the detector plane and the off-axis distance Finally, considering the inner and outer diameter dimensions of the detector, when the Wien filter is not turned on, the secondary electrons at the center of the overall secondary electron scanning area escape from the central hole of the detector. The overall secondary electron scanning area is shifted along a direction perpendicular to one side of the scanning area, so that all secondary electrons fall into the effective collection area of the detector. The obtained Wien filter orientation angle and excitation range required for complete collection of secondary electrons are as follows: where d o and d i are the outer diameter and inner diameter of the detector, unit: mm; θ w is the Wien filter orientation angle, unit: °; V 1w_max and V 1w_min are the maximum and minimum electric dipole field excitations of the Wien filter required to achieve complete collection of secondary electrons, unit: V; the corresponding maximum and minimum magnetic dipole field excitations NI 1w_max and NI 1w_min , unit: AT, are calculated according to the new straight optical axis condition, i.e., NI 1w_max = V 1w_max *NI1 / V1, NI 1w_min = V 1w_min *NI1 / V1.

7. The method for improving the secondary electron collection efficiency in a rejection field scanning electron microscope according to claim 6, characterized in that After obtaining the Wien filter orientation angle and excitation range required for complete collection of secondary electrons, the final orientation angle of the Wien filter is determined by combining the influence law of the Wien filter orientation angle on the primary electron aberration. In addition, considering the redundancy of the dipole field excitation, (1.05 - 1.1) V 1w_min and (0.9 - 0.95) V 1w_max are respectively selected as the minimum and maximum electric dipole field excitations of the Wien filter, and (1.05 - 1.1) NI 1w_min and (0.9 - 0.95) NI 1w_max are selected as the minimum and maximum magnetic dipole field excitations of the Wien filter.

8. A system for improving the secondary electron collection efficiency in a rejection field scanning electron microscope, characterized in that, Including: The first acquisition module: used to acquire the new straight optical axis condition of the Wien filter when the edge electromagnetic field is mismatched; The second acquisition module: used to obtain the influence law of the Wien filter orientation angle and excitation on the primary electron transmission characteristics under the new straight optical axis condition; The determination module: used to determine the position and size of the secondary electron emission source; The calculation module: used to calculate the Wien filter excitation and orientation angle required for complete collection of secondary electrons according to the position and size of the secondary electron emission source, and the influence law of the Wien filter orientation angle and excitation on the primary electron transmission characteristics.

9. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, the steps of the method for improving the secondary electron collection efficiency in the rejection field scanning electron microscope according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, the steps of the method for improving the secondary electron collection efficiency in the rejection field scanning electron microscope according to any one of claims 1 to 7 are implemented.

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