Low-spherical-aberration objective lens suitable for 15KV compact electron microscope

Abstract

The invention relates to the technical field of low-spherical-aberration objective lenses of 15KV compact electron microscopes, and discloses a low-spherical-aberration objective lens suitable for a 15KV compact electron microscop.The low-spherical-aberration objective lens comprises an electromagnetic lens shell, a coil is arranged in the electromagnetic lens shell, a pole shoe area is formed in the electromagnetic lens shell, and a sample rod is installed in the electromagnetic lens shell in a sliding mode; the pole shoe area is located at the protruding end, close to the optical axis, of the electromagnetic lens shell, has the function of concentrating a magnetic field and is located at the top of the coil. According to the low-spherical-aberration objective lens suitable for the 15KV compact electron microscope, through the arrangement of the low-spherical-aberration objective lens, in the use process, the advantages that the compact structure of the 15KV electron microscope can be kept, and low sample damage is kept can be achieved, the technical difficulty of a spherical-aberration mode corrector is reduced, and the working efficiency is improved. And meanwhile, the device has the characteristics of high-resolution transmission-type electron microscope imaging principle and low aberration of a high-intensity magnetic field objective lens, so that the actual resolution capability and the resolution of an imaging mode are improved, and the instrument cost is greatly reduced.

Description

Technical Field

[0001] The invention relates to the technical field of low spherical aberration objective lenses for 15kV compact electron microscopes, in particular to a low spherical aberration objective lens suitable for 15kV compact electron microscopes. Background Art

[0002] Spherical aberration is a type of lens aberration and one of the main reasons affecting imaging resolution. Low spherical aberration objective is a type of electromagnetic lens objective design, often paired with a spherical aberration corrector to form an aberration-corrected electron microscope. An aberration-corrected electron microscope uses a multi-pole magnetic field and electric field difference correction device to act as a concave lens to correct high-order aberrations. It is an analytical instrument used in the fields of materials science, physics, basic medicine, and chemical engineering.

[0003] In the prior art, only large floor-standing transmission electron microscopes with an accelerating voltage of 200kV or higher or large floor-standing transmission electron microscopes with a low accelerating voltage equipped with an aberration corrector can achieve a resolution slightly greater than an atom. The former can only rely on the advantages of low spherical aberration and chromatic aberration of a large accelerating voltage system and a strong magnetic field mirror group in exchange for a resolution slightly greater than an atom. However, in addition to the huge accelerating voltage system and the huge size of the mirror group, the 200keV high-energy electrons also cause irreversible and destructive radiation damage to the observed samples, including ionization, chemical etching, atomic displacement, and sample heating. The latter low-accelerating voltage transmission electron microscope equipped with an aberration corrector is still limited by the bottleneck of the volume, manufacturing, and installation costs of the floor-standing type. Therefore, it is necessary to invent a low spherical aberration objective lens suitable for a 15KV compact electron microscope to solve the above problems. Summary of the invention

[0004] The object of the present invention is to provide a low spherical aberration objective lens suitable for a 15KV compact electron microscope to solve the problems raised in the above background technology.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical solution: a low spherical aberration objective lens suitable for a 15KV compact electron microscope, comprising an electromagnetic lens housing, a coil is arranged inside the electromagnetic lens housing, and a pole shoe area is formed, and a sample rod is slidably installed inside the electromagnetic lens housing.

[0006] The pole shoe area is located at the protruding end of the electromagnetic lens housing at the near optical axis position, and the pole shoe area is located at the top of the coil. The top of the electromagnetic lens housing is provided with an astigmatism corrector and an aberration corrector.

[0007] A sample rod insertion hole is provided at corresponding positions of the electromagnetic lens housing and the sample rod, and the sample rod is slidably installed inside the sample rod insertion hole provided inside the electromagnetic lens housing.

[0008] Preferably, the theory of the low spherical aberration objective lens of the compact transmission and scanning integrated electron microscope is known from the focal length (f) of the electron lens and the Cs / Cc formula. The larger the ampere-turn number (NI) of the corresponding electron track position h(z) in the magnetic field, the stronger the magnetic intensity (B(z)) on the z-axis, the more concentrated the magnetic field (dB(z) / dz), and the smaller the focal length and the aberration coefficient become.

[0009] Preferably, the theoretical formula of the low spherical aberration objective lens is:

[0010]

[0011] Preferably, the electromagnetic lens housing adopts an iron shell with a heat-conducting structure to maintain the heat dissipation of the coil and maintain a high magnetic field strength.

[0012] Compared with the prior art, the present invention provides a low spherical aberration objective lens suitable for a 15KV compact electron microscope, which has the following beneficial effects:

[0013] 1. The low spherical aberration objective lens suitable for 15KV compact electron microscope can maintain the compact structure of 15kv electron microscope, maintain the advantages of low sample damage, reduce the technical difficulty of spherical aberration mode correction device, and has the characteristics of high-resolution transmission electron microscope imaging principle and low aberration of strong magnetic field objective lens, which improves the actual resolving power and the resolution of imaging mode and greatly reduces the cost of the instrument.

[0014] 2. The low spherical aberration objective lens suitable for a 15KV compact electron microscope, through the astigmatism corrector and the aberration corrector, can theoretically achieve atomic or subatomic resolution during use. The low accelerating voltage compact electron microscope, which is originally limited by the large chromatic aberration coefficient caused by the low accelerating voltage and the large spherical aberration coefficient of the electromagnetic lens with a weaker magnetic field, can achieve atomic or subatomic resolution. At the same time, the controlled spherical aberration coefficient of the low spherical aberration objective lens is 1mm, which can further compress the size of the corrector, reduce the multipole field intensity requirement, and avoid the generation of more high-order aberrations.

[0015] 3. This low spherical aberration objective lens for 15KV compact electron microscope is equipped with a 15kv low acceleration voltage system, a two-stage adjustable magnifying lens group and a scanning coil and an electromagnetic lens for collecting transmitted electrons. During use, the electron gun can be equipped with traditional continuous electron light sources such as thermal ionization and field emission, or equipped with a pulse light source. Through the electromagnetic lens, different light sources can be appropriately adjusted. The strong magnetic field in-lens design can effectively reduce spherical aberration. In the short focal length mode, the sample rod is assembled to enable the system to scan, realizing the function of the low spherical aberration objective lens to work in both scanning and transmission electron microscope modes. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative labor:

[0017] Figure 1 It is a schematic diagram of the planar structure of the low spherical aberration objective lens of the present invention;

[0018] Figure 2 This is a schematic diagram of the planar structure of the low spherical aberration objective lens of the present invention after the physical design and assembly are completed;

[0019] Figure 3 Schematic diagram of a compact transmission / scanning integrated electron microscope system with a low spherical aberration objective lens.

[0020] In the figure: 1. Electromagnetic lens housing; 2. Coil; 3. Pole shoe area; 4. Sample rod. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0023] See also Figure 1-2 The present invention provides a technical solution: a low spherical aberration objective lens suitable for a 15KV compact electron microscope, comprising an electromagnetic lens housing 1, a coil 2 is arranged inside the electromagnetic lens housing 1, and a pole shoe area 3 is formed, and a sample rod 4 is slidably installed inside the electromagnetic lens housing 1.

[0024] The pole shoe region 3 is located at one end of the electromagnetic lens housing 1 away from the coil 2 , and the pole shoe region 3 is located at the top of the coil 2 . The top of the electromagnetic lens housing 1 is provided with an astigmatism corrector and an aberration corrector.

[0025] A sample rod insertion hole is provided at corresponding positions of the electromagnetic lens housing 1 and the sample rod 4 , and the sample rod 4 is slidably installed inside the sample rod insertion hole provided inside the electromagnetic lens housing 1 .

[0026] Furthermore, the theory of low spherical aberration objective lens for compact transmission and scanning integrated electron microscope is known from the focal length (f) of the electron lens and the Cs / Cc formula. The larger the ampere-turn number (NI) of the magnetic field corresponding to the electron track position h(z), the stronger the magnetic intensity (B(z)) on the z-axis, the more concentrated the magnetic field (dB(z) / dz), and the smaller the focal length and aberration coefficient.

[0027] Furthermore, the theoretical formula of low spherical aberration objective lens is:

[0028]

[0029] Furthermore, the electromagnetic lens housing 1 adopts an iron shell with a heat-conducting structure, which can maintain the heat dissipation of the coil and maintain a high magnetic field strength.

[0030] In actual operation, when this device is used, by setting up a low spherical aberration objective lens 1, it is possible to maintain a compact structure of a 15kv electron microscope, maintain the advantage of low sample damage, reduce the technical difficulty of the spherical aberration mode corrector, and at the same time have the high-resolution transmission electron microscope imaging principle and the low aberration characteristics of a strong magnetic field objective lens, thereby improving the actual resolving power and the resolution of the imaging mode and significantly reducing the cost of the instrument.

[0031] Through the astigmatism corrector and aberration corrector, the low accelerating voltage compact electron microscope, which was originally limited by the large chromatic aberration coefficient caused by the low accelerating voltage and the large spherical aberration coefficient of the electromagnetic lens with a weak magnetic field, can theoretically achieve atomic or subatomic resolution. At the same time, the controlled spherical aberration coefficient of the low spherical aberration objective lens is 1mm, which can further compress the size of the corrector, reduce the multipole field intensity requirements, and avoid the generation of more high-order aberrations. In addition to the traditional continuous electron light sources such as thermal ionization and field emission, it can be equipped with a pulse light source, a two-stage adjustable magnifying glass group and a scanning coil and an electromagnetic lens for collecting transmitted electrons, which can be appropriately adjusted for different light sources. The objective lens adopts a low spherical aberration in-lens objective lens equipped with a sample rod. The strong magnetic field in-lens design can effectively reduce spherical aberration. In the short focal length mode, the sample rod 4 is equipped to allow the system to scan, realizing the function of the low spherical aberration objective lens working in both scanning and transmission electron microscope modes.

[0032] By converting the general scanning coil into a twelve-pole electrode deflector, the compact transmission / scanning integrated electron microscope equipped with an octopole-quadrupole spherical aberration-chromatic aberration corrector and a low spherical aberration objective lens can use a high-contrast hollow cone dark field scanning imaging mode. To meet the needs of collecting dark field signals, the signal collector includes a secondary electron probe (SE), a backscattered electron probe (BSE), an energy dispersive X-ray spectrometer (EDX) and a dark field detector. This enables the use of an imaging mode with higher contrast on a compact electron microscope.

[0033] Low spherical aberration objectives are strong electromagnetic in-lens lenses and require adjustment of optical parameters according to the architecture of the electronic optical path of the imaging mode used.

[0034] The strength of the electromagnetic lens is determined by the number of coil turns. As the number of coil turns increases, the overall size of the objective lens also increases, which in turn leads to changes in the mechanical assembly of the compact scanning electron microscope (SEM).

[0035] While maintaining a simple mechanical structure of passive cooling for a compact scanning electron microscope (SEM), when the volume of the objective lens increases due to the increase in the ampere-turns of the coil 2, the thermal equilibrium temperature of the coil 2 needs to be modified and analyzed through design to ensure that the coil 2 can provide a stable magnetic field strength.

[0036] The condenser and the lens group in the electron optical path maintain relative positions, and the in-lens objective lens with a strong magnetic field has a shorter focal length, so that the electron beam will be focused within the pole shoe area 3.

[0037] The strong magnetic field of the in-lens objective has the ability to reduce the spherical coefficient and focus the electron beam spot on the sample, which can improve resolution.

[0038] The imaging mode will be changed from a scanning mode with relatively limited resolution to an additional field signal imaging with higher resolution using transmitted electrons. The in-lens low spherical aberration objective lens can increase the resolution limit.

[0039] Coil 2 uses a downward-moving coil, and the internal space of the objective lens needs to be expanded.

[0040] In order to ensure that the ampere-turns of the coil 2 of the in-lens high magnetic field objective lens are increased and the sample rod 4 that passes through the objective lens housing can be used normally, the space inside the objective lens needs to be greatly expanded.

[0041] To ensure that the strong magnetic field does not saturate and overflow, the outer shell will be thickened to maintain the magnetic flux within the material upper limit.

[0042] After the coil 2 is moved, the pole shoe area 3 and the surrounding space are released, leaving the movement space required by the sample rod 4 and the sealed vacuum interface.

[0043] Moving coil 2 downward will increase the magnetic flux saturation pressure of the outer shell and extend the mirror group, and the direction in which the objective lens is expanded belongs to the sample chamber space that was originally unused, so that it can be used to the greatest extent to convert the traditional compact scanning electron microscope (SEM) into a compact transmission / scanning integrated electron microscope (SEM / STEM) The space that cannot be effectively utilized between the integrated electron microscopes releases space for improving traditional compact scanning electron microscope (SEM) components and adding new functional components.

[0044] The thermal balance of coil 2 after the change in ampere-turns is achieved using the passive cooling system of the SEM using a weaker magnetic field electromagnetic lens.

[0045] The increase in the ampere-turns of coil 2 that generates a strong magnetic field with a low spherical aberration objective lens affects the heat generated by coil 2 during operation. It is necessary to keep the resistance of coil 2 within a certain range with temperature change without changing the passive cooling method to avoid the increase in resistance caused by the increase in coil 2 temperature, reduce the current of coil 2, hinder the increase in magnetic field strength and the instability of coil current during operation, resulting in continuous changes in focal length and affecting the uneven size of the electron beam spot during scanning, resulting in a decrease in alternative resolution.

[0046] The working heat generation rate, heat conduction efficiency, surface temperature and shell temperature gradient of the coil 2 will affect the heat dissipation efficiency of the coil 2. A thicker wire diameter is required to reduce the heat generation during operation and the heat accumulation that cannot leave the center of the coil 2.

[0047] The arrangement of the coil 2 with optimized surface area can more effectively conduct the heat from the center of the coil 2 to the surface, thus maintaining a high temperature gradient.

[0048] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

Claims

1. A low spherical aberration objective lens suitable for a 15KV compact electron microscope, comprising an electromagnetic lens housing (1), characterized in that: A coil (2) is arranged inside the electromagnetic lens housing (1), and a pole shoe region (3) is formed therein; a sample rod (4) is slidably mounted inside the electromagnetic lens housing (1); The pole shoe region (3) is located at one end of the electromagnetic lens housing (1) away from the coil (2), and the pole shoe region (3) is located at the top of the coil (2), and an astigmatism corrector and an aberration corrector are arranged on the top of the electromagnetic lens housing (1); A sample rod insertion hole is provided at corresponding positions of the electromagnetic lens housing (1) and the sample rod (4), and the sample rod (4) is slidably mounted inside the sample rod insertion hole provided inside the electromagnetic lens housing (1).

2. The low spherical aberration objective lens suitable for a 15KV compact electron microscope according to claim 1, characterized in that: The theory of the low spherical aberration objective lens of the compact transmission and scanning integrated electron microscope is known from the focal length (f) of the electron lens and the Cs / Cc formula. The larger the ampere-turn number (NI) of the corresponding electron track position h(z) in the magnetic field, the stronger the magnetic intensity (B(z)) on the z-axis, the more concentrated the magnetic field (dB(z) / dz), and the smaller the focal length and the aberration coefficient.

3. The low spherical aberration objective lens suitable for a 15KV compact electron microscope according to claim 1, characterized in that: The theoretical formula of the low spherical aberration objective lens is:

4. The low spherical aberration objective lens suitable for a 15KV compact electron microscope according to claim 1, characterized in that: The electromagnetic lens housing adopts an iron shell with a heat-conducting structure to maintain the heat dissipation of the coil and maintain a high magnetic field strength.

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