Field emission scanning electron microscope

Abstract

The application discloses a field emission scanning electron microscope, which comprises a source-beam-angle-of-field control mirror, an objective lens, an image-beam-angle-of-field control mirror arranged between the source-beam-angle-of-field control mirror and the objective lens, and an aperture arranged between the source-beam-angle-of-field control mirror and the image-beam-angle-of-field control mirror, wherein the source-beam-angle-of-field control mirror is provided with a first pole piece, the image-beam-angle-of-field control mirror is provided with a second pole piece, and the objective lens is provided with a third pole piece; and a centering coil is arranged between at least one of the first pole piece and the aperture, the aperture and the second pole piece, and the second pole piece and the third pole piece. According to the field emission scanning electron microscope, the beam current can be adjusted and the beam angle can be optimized, the degree of freedom of the electron beam adjustment is effectively improved, and the centering effect of the electron beam and the magnetic lens is improved.

Description

Technical Field

[0001] This invention relates to the field of electron microscopy, and more specifically, to a field emission scanning electron microscope. Background Technology

[0002] Field emission scanning electron microscope (FESEM) is a type of electron microscope that is widely used for the detection of semiconductors, inorganic non-metallic materials and devices due to its advantages such as high resolution, large depth of field, more three-dimensional images, and wide adjustable magnification range.

[0003] Field emission scanning electron microscopy (FEM) requires continuously adjustable electron beam current to meet the analytical needs of various scenarios. Some related technologies employ a system scheme of a single aperture, beam control mirror, and image-side beam angle control mirror. This allows for optimized resolution or optimal depth of field under different beam currents.

[0004] However, when switching between different operating conditions, the two magnetic lenses, the beam control mirror and the image-side angle control mirror, will frequently change in conjunction, resulting in the problem that the electron beam and the center of the magnetic lens cannot maintain good alignment, which affects the adjustable range of the magnetic lens, as well as the imaging quality and stability. Summary of the Invention

[0005] The present invention aims to at least solve one of the technical problems existing in the prior art. Therefore, one object of the present invention is to provide a field emission scanning electron microscope that enables continuous adjustment of the electron beam current and effectively improves the alignment effect between the electron beam and the magnetic lens.

[0006] A field emission scanning electron microscope according to an embodiment of the present invention includes a source beam angle control mirror, an objective lens, an image beam angle control mirror disposed between the source beam angle control mirror and the objective lens, and an aperture disposed between the source beam angle control mirror and the image beam angle control mirror. The source beam angle control mirror is provided with a first pole shoe, the image beam angle control mirror is provided with a second pole shoe, and the objective lens is provided with a third pole shoe. At least one of the following locations is provided: between the first pole shoe and the aperture, between the aperture and the second pole shoe, and between the second pole shoe and the third pole shoe.

[0007] According to an embodiment of the field emission scanning electron microscope of the present invention, the source-side beam angle control mirror, the image-side beam angle control mirror, and the objective lens constitute a three-stage converging system, which can achieve a high degree of decoupling between adjustable beam current and optimized beam angle. Furthermore, by providing a centering coil at at least at one of the following locations—between the first pole piece and the aperture, between the aperture and the second pole piece, and between the second and third pole pieces—and by rationally setting the number and arrangement of the centering coils, the degree of freedom of electron beam adjustment can be effectively improved, the centering effect between the electron beam and the magnetic lens can be enhanced, thereby contributing to improved imaging quality and stability of the field emission scanning electron microscope.

[0008] In addition, the field emission scanning electron microscope according to the above embodiments of the present invention may also have the following additional technical features:

[0009] According to some embodiments of the present invention, the centering coil is provided between the first pole piece and the aperture, between the aperture and the second pole piece, and between the second pole piece and the third pole piece.

[0010] According to some embodiments of the present invention, a pair of centering coils are provided between the first pole piece and the aperture, and a centering coil is provided between the aperture and the second pole piece, and between the second pole piece and the third pole piece.

[0011] According to some embodiments of the present invention, the centering coil between the first pole piece and the aperture is located inside the source beam angle control mirror, the first pole piece is disposed at the end of the source beam angle control mirror away from the image beam angle control mirror, and the centering coil is disposed at the end of the source beam angle control mirror close to the image beam angle control mirror.

[0012] According to some embodiments of the present invention, the centering coil between the aperture and the second pole piece is located inside the image-square beam angle control mirror, the second pole piece is disposed at the end of the image-square beam angle control mirror near the objective lens, and the centering coil is disposed at the end of the image-square beam angle control mirror away from the objective lens.

[0013] According to some embodiments of the present invention, the centering coil between the second pole shoe and the third pole shoe is located inside the objective lens, the third pole shoe is located at the end of the objective lens away from the image-square beam angle control mirror, and the centering coil is located at the end of the objective lens near the image-square beam angle control mirror.

[0014] According to some embodiments of the present invention, the source-side beam angle control mirror includes a first magnetic lens core, the image-side beam angle control mirror includes a second magnetic lens core, the objective lens includes a third magnetic lens core, the inner diameter of the first pole piece is smaller than the inner diameter of the first magnetic lens core, the inner diameter of the second pole piece is smaller than the inner diameter of the second magnetic lens core, and the inner diameter of the third pole piece is smaller than the inner diameter of the third magnetic lens core.

[0015] According to some embodiments of the present invention, the source beam angle control mirror, the image beam angle control mirror, and the objective lens are independently configured.

[0016] According to some embodiments of the present invention, the field emission scanning electron microscope further includes a microscope tube, an electron gun, a vacuum differential aperture, and a shut-off valve. The microscope tube has a first vacuum chamber and a second vacuum chamber. The vacuum differential aperture and the shut-off valve are disposed between the first vacuum chamber and the second vacuum chamber. The electron gun and the source beam angle control mirror are disposed in the first vacuum chamber, and the image beam angle control mirror and the objective lens are disposed in the second vacuum chamber.

[0017] According to some embodiments of the present invention, the third pole shoe includes an upper pole shoe and a lower pole shoe, which are spaced apart to form an air extraction channel.

[0018] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0020] Figure 1 This is a schematic diagram of the structure of the microscope tube of a field emission scanning electron microscope according to an embodiment of the present invention.

[0021] Figure label:

[0022] Field emission scanning electron microscope 100;

[0023] Source beam angle control mirror 10; first pole shoe 11; first magnetic lens core 12; first housing 13;

[0024] Aperture 20;

[0025] Image beam angle control mirror 30; second magnetic lens core 31; second pole shoe 32; second housing 33;

[0026] Objective lens 40; third magnetic lens core 41; third pole shoe 42; upper pole shoe 421; lower pole shoe 422; evacuation channel 423; third housing 43; astigmatism reducer 44; scanning deflection system 45; upper deflector 451; lower deflector 452;

[0027] Centering coil 50; first centering coil 51; second centering coil 52; third centering coil 53; electron gun 71. Detailed Implementation

[0028] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0029] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0030] In the description of this invention, "first feature" and "second feature" may include one or more of the features, "multiple" means two or more, "above" or "below" the second feature may include the first and second features being in direct contact, or the first and second features being in contact through another feature between them, and "above," "over," and "on top" the second feature may include the first feature being directly above or diagonally above the second feature, or simply indicate that the first feature is at a higher horizontal level than the second feature.

[0031] A field emission scanning electron microscope 100 according to an embodiment of the present invention is described below with reference to the accompanying drawings.

[0032] In practical applications of field emission scanning electron microscopy (FEM), the electron beam needs to be focused into a nanoscale microfocal spot, giving the beam a specific current and beam angle. Generally, the focal spot and beam angle should be as small as possible to achieve higher resolution and greater depth of field. Simultaneously, the landing beam current needs to be adjustable over a wide range to meet the analytical needs of various scenarios. For example, a large landing beam current is required when a good imaging signal-to-noise ratio is needed or when using it as an electron probe for microscopic analysis; while a moderate or smaller beam current is required when high-resolution or large depth-of-field imaging is needed, or when reducing electron beam irradiation on the sample.

[0033] In some related technologies, a multi-aperture diaphragm is generally used to switch beam levels to achieve beam adjustment in different scenarios, and then a condenser lens is used for fine-tuning the beam. However, adjusting the beam size using a multi-aperture diaphragm has the following drawbacks: First, the beam adjustment is discontinuous; second, switching the multi-aperture diaphragm is time-consuming and requires high precision in mechanical movement, making alignment and calibration difficult; third, the biggest drawback is that adjusting the beam will cause the beam angle to deviate from the optimal angle; the greater the deviation, the greater the reduction in resolution.

[0034] In some related technologies, electromagnetic adjustment is used, that is, a coil generates a magnetic field to control the electron beam path in order to switch to different apertures. However, this can only solve part of the problem of adjusting the beam size using multiple apertures.

[0035] Reference Figure 1 As shown, the field emission scanning electron microscope 100 according to an embodiment of the present invention may include: a source beam angle control mirror 10, an objective lens 40, an image beam angle control mirror 30, and an aperture 20.

[0036] Specifically, the image square beam angle control mirror 30 can be positioned between the source square beam angle control mirror 10 and the objective lens 40, and the aperture 20 can be positioned between the source square beam angle control mirror 10 and the image square beam angle control mirror 30. Figure 1 As shown in the vertical direction, the source beam angle control mirror 10, aperture 20, image beam angle control mirror 30, and objective lens 40 are arranged sequentially from top to bottom, forming the electron beam converging system of the field emission scanning electron microscope 100, enabling uninterrupted beam current adjustment. For example, the electron beam converging system can also be automatically optimized based on electron optics calculations, improving imaging performance such as resolution under most operating conditions without changing the limiting resolution. In practical applications, the source beam angle control mirror 10 is closest to the electron gun 71, and the objective lens 40 is closest to the surface of the sample being inspected.

[0037] The source-square beam angle control mirror 10 and aperture 20 enable continuous, wide-range adjustment of the beam current to meet the analytical needs of various application scenarios. The image-square beam angle control mirror 30 can be used to change the beam angle and beam spot size of the electron beam, achieving optimal resolution or best depth of field under different beam currents, thus improving imaging quality under more conditions. In some embodiments, the optimal value of the image-square beam angle control mirror 30 needs to be obtained through electro-optical calculations. The objective lens 40 can be used for final focusing of the electron beam, further reducing and focusing the electron beam onto the surface of the sample being tested to improve imaging quality.

[0038] Furthermore, by setting the source-side beam angle control mirror 10 and the image-side beam angle control mirror 30, the electron beam spot size can be continuously adjusted to meet the analysis needs of various scenarios. This also allows the aperture 20 to adopt a single-aperture structure, eliminating the need for a multi-aperture structure, resulting in a simpler structure and enhanced operational stability and reliability.

[0039] Furthermore, the source-side beam angle control mirror 10 may be equipped with a first pole piece 11, the image-side beam angle control mirror 30 may be equipped with a second pole piece 32, and the objective lens 40 may be equipped with a third pole piece 42. By setting pole piece structures in each magnetic lens (i.e., the source-side beam angle control mirror 10, the image-side beam angle control mirror 30, and the objective lens 40), a better linear distribution of the magnetic field can be obtained, which is beneficial for realizing the focusing effect of the magnetic field established by the pole piece structure on the electron beam, and for obtaining an electron beam with a smaller beam spot. This, in turn, can reduce the size of the imaging unit and improve the resolution of the analytical imaging.

[0040] Furthermore, the inventors discovered that by using only the source beam angle control mirror 10, the aperture 20, and the image beam angle control mirror 30 in conjunction, the source beam angle control mirror 10 and the image beam angle control mirror 30 will frequently change in tandem when switching between different operating conditions. This results in a problem where the electron beam and the center of the magnetic lens cannot maintain good alignment, which affects the adjustable range, imaging quality, and stability of the magnetic lens.

[0041] Therefore, to address the problem of the electron beam and magnetic lens centers not maintaining good alignment, this application may further include an alignment coil 50. Specifically, an alignment coil 50 may be provided at least at one of the following locations: between the first pole piece 11 and the aperture 20, between the aperture 20 and the second pole piece 32, and between the second pole piece 32 and the third pole piece 42. The alignment coil 50 can form an alignment system to improve the alignment effect between the electron beam and each magnetic lens.

[0042] For example, the centering coil 50 can be positioned between the first pole piece 11 and the aperture 20, thereby ensuring that the deflected electron beam is concentric with the aperture 20, and that the electron beam passes through the center of the aperture 20 during its movement. As another example, the centering coil 50 can be positioned between the aperture 20 and the second pole piece 32, thereby ensuring that the deflected electron beam is aligned with the image-side beam angle control mirror 30, and that the electron beam passes through the center of the image-side beam angle control mirror 30, which is also the center of the second pole piece 32, during its movement. Yet another example is that the centering coil 50 can be positioned between the second pole piece 32 and the third pole piece 42, thereby ensuring that the deflected electron beam is aligned with the objective lens 40, and that the electron beam passes through the center of the objective lens 40, which is also the center of the third pole piece 42, during its movement.

[0043] This improves the alignment between the electron beam and the aperture 20 or the magnetic lens, enhances the freedom of electron beam adjustment, avoids affecting the adjustable range of the magnetic lens, and improves the imaging quality and stability of the field emission scanning electron microscope 100.

[0044] According to an embodiment of the field emission scanning electron microscope 100 of the present invention, the source-side beam angle control mirror 10, the image-side beam angle control mirror 30, and the objective lens 40 constitute a three-stage converging system, which can achieve a high degree of decoupling between adjustable beam current and optimized beam angle. Furthermore, by providing a centering coil 50 at at least one of the following locations: between the first pole piece 11 and the aperture 20, between the aperture 20 and the second pole piece 32, and between the second pole piece 32 and the third pole piece 42, and by rationally setting the number and arrangement of the centering coils 50, the degree of freedom of electron beam adjustment can be effectively improved, the centering effect between the electron beam and the magnetic lens can be improved, and thus the imaging quality and stability of the field emission scanning electron microscope 100 can be enhanced.

[0045] It should be noted that the embodiments of the present invention do not impose special limitations on the number and position of the centering coils 50. For example, one centering coil 50 may be set between the first pole piece 11 and the aperture 20, or multiple centering coils 50 may be set. Furthermore, the centering coil 50 located between the first pole piece 11 and the aperture 20 may be completely located outside the source beam angle control mirror 10, or partially located outside the source beam angle control mirror 10. These are all within the protection scope of the embodiments of the present invention.

[0046] For example, in some embodiments, such as Figure 1 As shown, centering coils 50 are provided between the first pole piece 11 and the aperture 20, between the aperture 20 and the second pole piece 32, and between the second pole piece 32 and the third pole piece 42. This allows for sufficient degrees of freedom in adjusting the electron beam, resulting in better centering of the electron beam. The centering coils 50 at the three positions can be designated as the first centering coil 51, the second centering coil 52, and the third centering coil 53, respectively.

[0047] Therefore, during the movement of the electron beam, it passes through the source-side beam angle control mirror 10 and, under the action of the first pair of center coils 51, can pass through the center of the aperture 20. Since a second pair of center coils 52 is provided between the aperture 20 and the second pole piece 32, for example, the second pair of center coils 52 and the image-side beam angle control mirror 30 maintain a relatively large distance within an allowable range, mutual interference between the magnetic fields of the second pair of center coils 52 and the second pole piece 32 can be avoided. The electron beam passing through the center of the aperture 20 can pass through the center of the image-side beam angle control mirror 30 under the deflection effect of the second pair of center coils 52. Furthermore, since a third pair of center coils 53 is provided between the second pole piece 32 and the third pole piece 42, the electron beam passing through the center of the image-side beam angle control mirror 30 can pass through the center of the objective lens 40 under the deflection effect of the third pair of center coils 53.

[0048] By setting the first centering coil 51, the second centering coil 52, and the third centering coil 53, the movement path of the electron beam can pass through several fixed points, eliminating the need for physical adjustment to achieve the centering effect of the electron beam. This helps to ensure good centering between the electron beam and the magnetic lens throughout the process, improves the reliability, repeatability, and automation of the field emission scanning electron microscope 100, and further enhances the actual usage efficiency of the field emission scanning electron microscope 100.

[0049] For example, in some embodiments, such as Figure 1 As shown, a pair of centering coils 50 can be provided between the first pole piece 11 and the aperture 20, that is, the first centering coil 51 can be a pair of centering coils 50. For example, the pair of centering coils 50 can be arranged vertically, that is, one centering coil 50 is close to the aperture 20, and the other centering coil 50 is far away from the aperture 20. Furthermore, a centering coil 50 can be provided between the aperture 20 and the second pole piece 32, and between the second pole piece 32 and the third pole piece 42. This not only ensures good centering of the electron beam throughout the entire process, improving image quality and stability, but also facilitates the adjustment of the electron beam angle by the centering coils 50, which is beneficial to ensuring the centering effect of the electron beam. Moreover, the small number of centering coils 50 and the overall simplicity help to maintain a larger distance between the centering coils 50 and the pole pieces, avoiding interference between the field of convergence and the field of convergence of the magnetic lens.

[0050] Specifically, for example, there is a large gap between the first centering coil 51 and the second centering coil 52, meaning the electron beam travels a long distance from the first centering coil 51 to the second centering coil 52. By setting a pair of centering coils 50 between the first pole piece 11 and the aperture 20, the electron beam passes through the center of the aperture 20 under the action of the first centering coil 51. The centering coil 50 of the first centering coil 51 closer to the aperture 20 can make the deflection angle of the electron beam away from the center of the image-side beam angle control mirror 30 smaller. This makes it easier for the second centering coil 52 to adjust the deflection angle of the electron beam, causing it to deflect towards and pass through the center of the image-side beam angle control mirror 30, thereby achieving the centering effect of the electron beam. The second centering coil 52 has a better centering effect.

[0051] In some specific embodiments, such as Figure 1 As shown, the field emission scanning electron microscope 100 may further include an astigmatism reducer 44, for example, an on-axis octet astigmatism reducer 44. The astigmatism reducer 44 may be located below and adjacent to the centering coil 50 between the second and third pole shoes 32. By providing the astigmatism reducer 44, it can provide a correction magnetic field opposite to the non-uniform magnetic field of the objective lens 40, allowing the objective lens 40 to ultimately form a symmetrical magnetic field, thereby generating a finely focused electron beam and improving image quality.

[0052] In some embodiments of the field emission scanning electron microscope 100, including an astigmatism reducer 44, such as Figure 1 As shown, the field emission scanning electron microscope 100 may also include a scanning deflection system 45, which is used to deflect the electron beam. For example, the electron beam can be scanned in a grid pattern on the surface of the sample to be tested in a certain time and space order to achieve the effect of analyzing the surface morphology of the sample to be tested.

[0053] Specifically, the scanning deflection system 45 can be composed of an upper deflector 451 and a lower deflector 452, both located below the astigmatism reducer 44, forming a dual-deflection structure. The lower deflector 452 is kept as low as possible, with its lower end adjacent to the third pole piece 42 on the objective lens 40. In some embodiments, the lower deflector 452 may be adjacent to the upper pole piece 421 of the third pole piece 42. This allows the distance between the scanning deflection system 45 and the centering coil 50 to be as large as possible, avoiding problems such as mutual interference.

[0054] To avoid the magnetic field generated by the pole shoes overlapping with the magnetic field generated by the centering coil 50, such as Figure 1As shown, taking the example of a centering coil 50 located between the first pole piece 11 and the aperture 20, this centering coil 50 can be located inside the source beam angle control mirror 10. Furthermore, the first pole piece 11 can be located at the end of the source beam angle control mirror 10 furthest from the image beam angle control mirror 30 (e.g., Figure 1 The centering coil 50 can be located at the end of the source beam angle control mirror 10 near the image beam angle control mirror 30 (as shown above). Figure 1 (As shown at the lower end). In other words, the first pole piece 11 and the centering coil 50 are located at opposite ends of the source beam angle control mirror 10, as shown in the figure. Figure 1 In the vertical direction shown, the first pole piece 11, the centering coil 50, and the image beam angle control mirror 30 are arranged in sequence. A certain distance can be maintained between the first pole piece 11 and the centering coil 50.

[0055] Therefore, on the one hand, the magnetic fields generated by the first pole piece 11 and the centering coil 50 can be prevented from interfering with each other, and the magnetic field of the first pole piece 11 can be prevented from affecting the deflection and centering effect of the centering coil 50 on the electron beam, which is beneficial to improving imaging quality; on the other hand, repeated iterative adjustments or calibrations are avoided in subsequent alignment, which is beneficial to improving imaging efficiency.

[0056] Taking an alignment coil 50 located between aperture 20 and the second pole piece 32 as an example, such as Figure 1 As shown, the centering coil 50 can be located inside the image-side beam angle control mirror 30. Furthermore, the second pole piece 32 can be located at the end of the image-side beam angle control mirror 30 closer to the objective lens 40, and the centering coil 50 can be located at the end of the image-side beam angle control mirror 30 furthest from the objective lens 40. In other words, the second pole piece 32 and the centering coil 50 are located at opposite ends of the image-side beam angle control mirror 30, as shown in the diagram. Figure 1 In the vertical direction shown, the second pole piece 32, the centering coil 50, and the objective lens 40 are arranged in sequence. The first pole piece 11 and the centering coil 50 can maintain a certain distance.

[0057] Therefore, on the one hand, the magnetic fields generated by the second pole shoe 32 and the centering coil 50 can be prevented from interfering with each other, and the magnetic field of the second pole shoe 32 can be prevented from affecting the deflection and centering effect of the centering coil 50 on the electron beam, which is beneficial to improving imaging quality; on the other hand, repeated iterative adjustments or calibrations are avoided in subsequent alignment, which is beneficial to improving imaging efficiency.

[0058] Taking the example of a centering coil 50 located between the second pole shoe 32 and the third pole shoe 42, as follows: Figure 1 As shown, the centering coil 50 can be located inside the objective lens 40. Furthermore, the third pole piece 42 can be located at the end of the objective lens 40 furthest from the image-side beam angle control mirror 30, and the centering coil 50 can be located at the end of the objective lens 40 closest to the image-side beam angle control mirror 30. In other words, the third pole piece 42 and the centering coil 50 are located at opposite ends of the objective lens 40, as shown in the diagram. Figure 1 In the vertical direction shown, the image beam angle control mirror 30, the centering coil 50, and the third pole piece 42 are arranged in sequence. The third pole piece 42 and the centering coil 50 can maintain a certain distance.

[0059] Therefore, on the one hand, the magnetic fields generated by the third pole shoe 42 and the centering coil 50 can be prevented from interfering with each other, and the magnetic field of the third pole shoe 42 can be prevented from affecting the deflection and centering effect of the centering coil 50 on the electron beam, which is beneficial to improving imaging quality; on the other hand, repeated iterative adjustments or calibrations are avoided in subsequent alignment, which is beneficial to improving imaging efficiency.

[0060] According to some embodiments of the present invention, such as Figure 1 As shown, the source-side beam angle control mirror 10 may include a first magnetic lens core 12, the image-side beam angle control mirror 30 may include a second magnetic lens core 31, and the objective lens 40 may include a third magnetic lens core 41. Thus, each magnetic lens core can generate a converging magnetic field in its corresponding magnetic lens, such as generating a rotationally symmetric non-uniform magnetic field, thereby achieving the effect of electron beam focusing imaging.

[0061] For example, such as Figure 1 As shown, the source-square beam angle control mirror 10 may further include a first housing 13, with the first magnetic lens core 12 disposed within the first housing 13 to prevent the first magnetic lens core 12 from being exposed. The image-square beam angle control mirror 30 may further include a second housing 33, with the second magnetic lens core 31 disposed within the second housing 33 to prevent the second magnetic lens core 31 from being exposed. The objective lens 40 may further include a third housing 43, with the third magnetic lens core 41 disposed within the third housing 43 to prevent the third magnetic lens core 41 from being exposed.

[0062] Furthermore, the inner diameter of the first pole piece 11 is smaller than the inner diameter of the first magnetic lens core 12 to form an ultrashort magnetic lens. For example, one end of the first pole piece 11 located within the source-side beam angle control mirror 10 can extend towards the centerline of the source-side beam angle control mirror 10, so that the inner diameter of the first pole piece 11 is smaller than the inner diameter of the first magnetic lens core 12. The inner diameter of the second pole piece 32 is smaller than the inner diameter of the second magnetic lens core 31 to form an ultrashort magnetic lens. For example, one end of the second pole piece 32 located within the image-side beam angle control mirror 30 can extend towards the centerline of the image-side beam angle control mirror 30, so that the inner diameter of the second pole piece 11 is smaller than the inner diameter of the second magnetic lens core 12. The inner diameter of the third pole piece 42 is smaller than the inner diameter of the third magnetic lens core 41 to form an ultrashort magnetic lens. For example, one end of the third pole piece 42 located inside the objective lens 40 can extend towards the centerline of the objective lens 40 so that the inner diameter of the third pole piece 11 is smaller than the inner diameter of the third magnetic lens core 12.

[0063] Since the magnetic field range generated by the ultrashort magnetic lens is much shorter than the focal length, it can effectively avoid the overlap of magnetic fields between the magnetic lenses and mutual interference, thus avoiding affecting the focusing effect of each magnetic lens on the electron beam. On the other hand, it helps to prevent the magnetic field of the magnetic lens from coinciding with the magnetic field of the centering coil 50, which can reduce the repeated iterative adjustment or calibration work in subsequent use.

[0064] According to some embodiments of the present invention, such as Figure 1 As shown, the source-side beam angle control mirror 10, the image-side beam angle control mirror 30, and the objective lens 40 can be set independently. This allows for relatively independent structure and function of each magnetic lens, facilitating production and assembly, and also making it easier to adjust the position of each magnetic lens. Furthermore, each magnetic lens can be tested independently, and even if problems arise, maintenance can be performed independently, which helps reduce maintenance costs.

[0065] According to some embodiments of the present invention, the field emission scanning electron microscope 100 may further include a microscope tube, an electron gun 71, a vacuum differential aperture, and a shut-off valve. Specifically, the microscope tube may have a first vacuum chamber and a second vacuum chamber. The first vacuum chamber is located above the second vacuum chamber. The vacuum differential aperture and the shut-off valve are disposed between the first and second vacuum chambers. Furthermore, the shut-off valve can open or close the vacuum differential aperture to create a vacuum difference or isolation between the first and second vacuum chambers. In other words, the vacuum levels in the first and second vacuum chambers may be different, and each vacuum chamber can maintain a relatively stable operating pressure, which is beneficial for ensuring the vacuum stability of each vacuum chamber.

[0066] Furthermore, the electron gun 71 and the source beam angle control mirror 10 can be located in the first vacuum chamber, while the image beam angle control mirror 30 and the objective lens 40 can be located in the second vacuum chamber. The microscope tube can serve to fix the electron gun 71 and each magnetic lens, which helps to ensure the steady-state operation of the field emission scanning electron microscope 100. During operation, by closing the isolation valve, the working environment pressure of the electron gun 71 and the source beam angle control mirror 10 can be different from the working environment pressure of the image beam angle control mirror 30 and the objective lens 40, allowing the devices in the two vacuum chambers to operate normally without interfering with each other.

[0067] For example, since the electron beam needs to be emitted from the objective lens 40 onto the surface of the sample being tested, and the end of the objective lens 40 closest to the sample is connected to the chamber where the sample is located, the pressure in the second vacuum chamber is greater than the pressure in the first vacuum chamber. In other words, the vacuum level of the first vacuum chamber is greater than that of the second vacuum chamber, which is beneficial for ensuring that the working states of the devices in each vacuum chamber are relatively independent and do not interfere with each other.

[0068] According to some embodiments of the present invention, such as Figure 1As shown, the third pole piece 42 may include an upper pole piece 421 and a lower pole piece 422. Furthermore, the upper pole piece 421 and the lower pole piece 422 may be spaced apart to form a evacuation channel 423. Specifically, since the objective lens 40 is closer to the sample being tested, and one end of the objective lens 40 is connected to the chamber containing the sample, gas in the chamber can easily enter the space between the upper pole piece 421 and the lower pole piece 422 of the third pole piece 42. In some embodiments where the upper pole piece 421 of the third pole piece 42 has a pole piece vacuum differential aperture, gas in the chamber containing the sample is evacuated through this space. The pole piece vacuum differential aperture in the upper pole piece 421 prevents gas from passing upwards through the electron beam channel (i.e., the electron beam channel in the objective lens 40). This arrangement can achieve a large vacuum differential gradient between the upper pole piece 421 and the lower pole piece 422, making the gas pressure at the lower end of the pole piece vacuum differential aperture significantly lower than the chamber gas pressure, thereby maintaining a high vacuum at the upper end of the pole piece vacuum differential aperture. In this state, the chamber pressure is high, and the electron beam can still reach the sample under test after passing through the vacuum differential aperture of the pole shoe for scanning imaging. It can achieve characterization and observation of the sample under test at higher pressures of 10 Pa to 1000 Pa, enabling the field emission scanning electron microscope 100 to characterize volatile samples such as those containing water or gas. At the same time, for non-conductive samples, it can reduce the charging effect on the surface of the sample and eliminate the need for pretreatment processes such as gold or carbon sputtering on the sample surface.

[0069] Other configurations and operations of the field emission scanning electron microscope 100 according to embodiments of the present invention are known to those skilled in the art and will not be described in detail here.

[0070] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0071] In the description of this specification, the references to terms such as "embodiment," "specific embodiment," and "example" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0072] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A field emission scanning electron microscope, characterized in that, The system includes a source-side beam angle control lens, an objective lens, an image-side beam angle control lens disposed between the source-side beam angle control lens and the objective lens, and an aperture disposed between the source-side beam angle control lens and the image-side beam angle control lens. The source-side beam angle control lens has a first pole piece, the image-side beam angle control lens has a second pole piece, and the objective lens has a third pole piece. Alignment coils are provided between the first pole piece and the aperture, between the aperture and the second pole piece, and between the second pole piece and the third pole piece; The centering coil between the first pole piece and the aperture is located inside the source-side beam angle control lens; the centering coil between the aperture and the second pole piece is located inside the image-side beam angle control lens; and the centering coil between the second pole piece and the third pole piece is located inside the objective lens.

2. The field emission scanning electron microscope according to claim 1, characterized in that, A pair of centering coils are provided between the first pole piece and the aperture, and a centering coil is provided between the aperture and the second pole piece, and between the second pole piece and the third pole piece.

3. The field emission scanning electron microscope according to claim 1, characterized in that, The first pole piece is located at the end of the source beam angle control mirror away from the image beam angle control mirror, and the centering coil is located at the end of the source beam angle control mirror close to the image beam angle control mirror.

4. The field emission scanning electron microscope according to claim 1, characterized in that, The second pole shoe is located at the end of the image beam angle control mirror near the objective lens, and the centering coil is located at the end of the image beam angle control mirror away from the objective lens.

5. The field emission scanning electron microscope according to claim 1, characterized in that, The third pole shoe is located at the end of the objective lens away from the image-square beam angle control mirror, and the centering coil is located at the end of the objective lens closer to the image-square beam angle control mirror.

6. The field emission scanning electron microscope according to claim 1, characterized in that, The source beam angle control mirror includes a first magnetic lens core, the image beam angle control mirror includes a second magnetic lens core, and the objective lens includes a third magnetic lens core. The inner diameter of the first pole piece is smaller than the inner diameter of the first magnetic lens core, the inner diameter of the second pole piece is smaller than the inner diameter of the second magnetic lens core, and the inner diameter of the third pole piece is smaller than the inner diameter of the third magnetic lens core.

7. The field emission scanning electron microscope according to claim 1, characterized in that, The source beam angle control mirror, the image beam angle control mirror, and the objective lens are independently configured.

8. The field emission scanning electron microscope according to claim 1, characterized in that, It also includes a lens barrel, an electron gun, a vacuum differential aperture, and a shut-off valve. The lens barrel has a first vacuum chamber and a second vacuum chamber. The vacuum differential aperture and the shut-off valve are located between the first vacuum chamber and the second vacuum chamber. The electron gun and the source beam angle control mirror are located in the first vacuum chamber, and the image beam angle control mirror and the objective lens are located in the second vacuum chamber.

9. The field emission scanning electron microscope according to claim 1, characterized in that, The third pole shoe includes an upper pole shoe and a lower pole shoe, which are spaced apart to form an air extraction channel.

Images