Double-objective-lens structure, electron microscope and use method of double-objective-lens structure

Abstract

The invention discloses a double-objective structure, an electron microscope and a using method, and belongs to the field of electron microscopes, first, second and third extension parts are conical, the tail end of the first extension part and the tail end of the third extension part form an opening, the tail end of the second extension part extends into the opening, and in an immersion mode, a second coil, a second pole shoe and a third pole shoe work; the magnetic field leaks to the sample from the second gap, so that the sample is immersed in the magnetic field, the part with the maximum field intensity is positioned between the tail end of the third pole shoe and the sample, an extremely short effective focal length is obtained, and higher resolution is further obtained; in the non-immersion mode, the first coil, the first pole shoe and the second pole shoe work, the magnetic field is limited in the first gap and does not leak to a sample, the maximum field intensity position is located between the tail ends of the first pole shoe and the second pole shoe, under the same working distance, a longer effective focal length is usually achieved, the immersion mode and the non-immersion mode are achieved, and the non-immersion mode can also achieve high resolution. And the current required during high-energy imaging is small, so that high-energy electronic imaging is facilitated.

Description

Technical Field

[0001] The present invention relates to the field of electron microscopes, and in particular to a dual-objective lens structure, an electron microscope comprising the dual-objective lens structure, and a method for using the dual-objective lens structure. Background Art

[0002] The resolution of a high-resolution field emission scanning electron microscope mainly depends on the aberration of the objective lens. From the perspective of electron optics, the spherical aberration coefficient Cs and chromatic aberration coefficient Cc of the objective lens are positively correlated with the focal length of the objective lens. The shorter the focal length, the smaller the aberration, and therefore the higher the resolution. In order to obtain a shorter effective focal length during imaging, especially to improve the resolution of the system during low-energy imaging, the current mainstream design is to use a magnetic immersion objective lens. However, the application scenario of the magnetic immersion objective lens is usually high resolution, and it cannot take into account the requirements of large field of view, large beam current and high-energy low-current imaging at the same time. At the same time, the magnetic immersion objective lens cannot observe magnetic samples, which limits the application scenarios of the instrument.

[0003] In order to solve the problem that magnetic immersion objectives cannot observe magnetic samples, a triple-pole double-objective lens structure has been developed, which can simultaneously realize the dual functions of magnetic immersion objectives and non-magnetic immersion objectives. However, in the current design, the imaging focal length is very long in the non-magnetic immersion mode, resulting in low resolution; and in the magnetic immersion mode, the current required for high-energy imaging is large, and the coil generates a lot of heat, which is not conducive to the thermal stability of the system. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, one of the objects of the present invention is to provide a dual objective lens structure with an immersion mode and a non-immersion mode. The non-immersion mode can achieve high-resolution imaging of magnetic samples (for example, 1.5nm@1kV, 1mm) and high-energy electron low-current imaging (for example, 1.6A@30kV, 5.5mm, 800 turns of coil); in the immersion mode, it can achieve low-voltage high-resolution imaging of non-magnetic samples (0.7nm@1kV, 1mm).

[0005] In order to overcome the shortcomings of the prior art, the second object of the present invention is to provide an electron microscope with an immersion mode and a non-immersion mode. The non-immersion mode can achieve high-resolution imaging of magnetic samples (for example, 1.5nm@1kV, 1mm), high-energy electron low-current imaging (for example, 1.6A@30kV, 5.5mm, 800 turns of coil), and the immersion mode can achieve low-voltage high-resolution imaging of non-magnetic samples (0.7nm@1kV, 1mm).

[0006] In order to overcome the deficiencies of the prior art, a third object of the present application is to provide a dual objective lens structure use method with immersion mode and non-immersion mode, the non-immersion mode can realize high-resolution imaging of magnetic samples (for example, 1.5 nm@1kV, 1mm), low-current imaging of high-energy electrons (for example, 1.6A@30kV, 5.5mm, coil 800 turns), and the immersion mode can realize low-voltage high-resolution imaging of non-magnetic samples (0.7nm@1k V , 1mm).

[0007] One of the objects of the present application is achieved by adopting the following technical solutions:

[0008] A dual objective lens structure, comprising a first pole piece, a second pole piece, a third pole piece, a first coil and a second coil, the first coil is installed between the first pole piece and the second pole piece, the second coil is installed between the second pole piece and the third pole piece, the first pole piece comprises a first extension, the first extension is tapered and forms a channel for electron beam movement, the second pole piece comprises a second extension, the third pole piece comprises a third extension, the second extension and the third extension are both tapered, the second extension is located between the first extension and the third extension, the end of the first extension and the end of the third extension form an opening, the end of the second extension extends into the opening, a first gap is formed between the end of the second extension and the end of the first extension, a second gap is formed between the end of the second extension and the end of the third extension, in the axial direction of the channel, the second gap is located between the first gap and the sample, when the dual objective lens structure is in immersion mode, the second coil, the second pole piece and the third pole piece work, the magnetic field generated by the second coil leaks from the second gap to the sample, so that the sample is immersed in the magnetic field, at this time, the place with the maximum magnetic field strength is located between the end of the third pole piece and the sample; when the dual objective lens structure is in non-immersion mode, the first coil, the first pole piece and the second pole piece work, the magnetic field generated by the first coil partially leaks at the first gap and does not leak to the sample, at this time, the place with the maximum magnetic field strength is located between the end of the first pole piece and the end of the second pole piece.

[0009] Further, in the axial direction of the channel, the end of the second extension is located between the end of the first extension and the end of the third extension.

[0010] Further, the third pole piece further comprises a horizontal part, the horizontal part extends from the end of the third extension and is horizontally arranged, the horizontal part extends towards the direction of the channel, and the second gap is formed between the end of the third extension and the outer wall of the second extension.

[0011] Furthermore, the outer wall of the first extending portion and the inner wall of the second extending portion form the first gap, and the width of the first gap is smaller than the width of the second gap.

[0012] Furthermore, the inner diameter of the end of the first pole shoe is greater than or equal to the inner diameter of the end of the second pole shoe.

[0013] Furthermore, the inner diameter of the end of the third pole shoe is greater than the inner diameter of the end of the second pole shoe.

[0014] Furthermore, the distance from the point where the magnetic field intensity is maximum to the sample surface is the effective focal length, and the distance from the pole shoe mouth to the sample surface is the working distance. When the dual objective lens structure is in non-immersion mode, the effective focal length is much larger than the working distance; when the dual objective lens structure is in immersion mode, the effective focal length is smaller than the working distance.

[0015] Furthermore, when the dual objective lens structure is in non-immersion mode, the dual objective lens structure is suitable for high-resolution scanning of magnetic samples, large beam analysis, and low-current imaging at high energy; when the dual objective lens structure is in immersion mode, the dual objective lens structure is suitable for low-energy high-resolution scanning of non-magnetic samples.

[0016] The second object of the present invention is achieved by adopting the following technical solution:

[0017] An electron microscope comprises any one of the above-mentioned double objective lens structures.

[0018] The third object of the present invention is achieved by adopting the following technical solution:

[0019] A method for using any of the above dual objective lens structures comprises the following steps:

[0020] When the dual objective lens structure is in immersion mode, the second coil, the second pole shoe, and the third pole shoe are in operation, and the magnetic field generated by the second coil leaks from the second gap to the sample, so that the sample is immersed in the magnetic field. At this time, the maximum magnetic field intensity is located between the end of the third pole shoe and the sample;

[0021] When the dual objective lens structure is in non-immersion mode, the first coil, the first pole shoe and the second pole shoe are working, and the magnetic field generated by the first coil is partially leaked at the first gap and does not leak to the sample. At this time, the maximum magnetic field strength is located between the end of the first pole shoe and the end of the third pole shoe.

[0022] Compared with the prior art, the first pole shoe of the dual objective lens structure of the present invention includes a first extension portion, the first extension portion is tapered and forms a channel for the movement of the electron beam, the second pole shoe includes a second extension portion, the third pole shoe includes a third extension portion, the second extension portion and the third extension portion are both tapered, the second extension portion is located between the first extension portion and the third extension portion, the end of the first extension portion and the end of the third extension portion form an opening, the end of the second extension portion extends into the opening, a first gap is formed between the end of the second extension portion and the end of the first extension portion, a second gap is formed between the end of the second extension portion and the end of the third extension portion, in the axial direction of the channel, the second gap is located between the first gap and the sample, and when the dual objective lens structure is in immersion mode, the second coil, the third coil and the fourth coil are in immersion mode. When the second pole shoe and the third pole shoe are working, the magnetic field generated by the second coil leaks from the second gap to the sample so that the sample is immersed in the magnetic field. At this time, the maximum magnetic field strength is located between the end of the third pole shoe and the sample; when the dual objective lens structure is in non-immersion mode, the first coil, the first pole and the second pole shoe are working, and the magnetic field generated by the first coil partially leaks at the first gap and does not leak to the sample. At this time, the maximum magnetic field strength is located between the end of the first pole shoe and the end of the third pole shoe. Through the above design, the dual objective lens structure of the present application has an immersion mode and a non-immersion mode. The non-immersion mode can achieve high-resolution imaging of magnetic samples and high-energy electron low-current imaging. In the immersion mode, the dual objective lens structure can achieve low-energy and high-resolution imaging of non-magnetic samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the dual objective lens structure of the present invention;

[0024] Figure 2 for Figure 1 Schematic diagram of the local structure of the double objective lens structure;

[0025] Figure 3 is a schematic diagram of the immersion mode of the dual objective lens structure of the present invention;

[0026] Figure 4 for Figure 3 Schematic diagram of magnetic field intensity in immersion mode of a dual objective lens structure;

[0027] Figure 5 Schematic diagram of the non-immersion mode of the dual objective lens structure of the present invention;

[0028] Figure 6 for Figure 5 Schematic diagram of the magnetic field intensity in the non-immersion mode of the dual-objective lens structure.

[0029] In the figure: 10, first pole piece; 11, top; 12, first extension; 120, first end face; 20, second pole piece; 21, spacing part; 22, second extension; 220, second end face; 30, third pole piece; 31, vertical part; 32, third extension; 33, horizontal part; 40, first coil; 50, second coil; 60, channel; 70, sample; 80, electron beam. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0032] Please refer to Figures 1-2 The double objective lens structure of the present application comprises a first pole piece 10, a second pole piece 20, a third pole piece 30, a first coil 40 and a second coil 50. The first pole piece 10 is located inside the second pole piece 20, and the second pole piece 20 is located inside the third pole piece 30. The first coil 40 is installed between the first pole piece 10 and the second pole piece 20, and the second coil 50 is installed between the second pole piece 20 and the third pole piece 30. The first pole piece 10, the second pole piece 20 and the third pole piece 30 are all made of ferromagnetic material and are used to confine the magnetic field. The first coil 40 and the second coil 50 are used to generate the magnetic field.

[0033] The first pole piece 10 comprises a top 11 and a first extension 12 extending from the top 11. The top 11 is horizontally arranged and in the form of a plate body, and the top 11 confines the upper magnetic field. The first extension 12 extends from the inner edge of the top 11 and is in the form of a taper. The first extension 12 forms a channel 60, and the diameter of the channel 60 near the top 11 is larger than the diameter of the channel 60 near the end of the first extension 12, so that the diameter of the channel 60 gradually decreases to form a taper, facilitating the detection of the secondary electron signal and the installation of the detector. A first end face 120 is arranged at the end of the first extension 12 away from the top 11, and the first end face 120 is located on the inner wall of the first extension 12 and is parallel to the axis of the channel 60, so that the end of the channel 60 is in the form of a cylinder.

[0034] The second pole piece 20 includes a spacer portion 21 and a second extension portion 22 extending from the end of the spacer portion 21. The spacer portion 21 extends vertically and is generally cylindrical. The second extension portion 22 is conical. The end of the second extension portion 22 is provided with a second end surface 220. The second end surface 220 is located on the inner wall of the second extension portion 22 and is parallel to the axis of the channel 60. In the vertical direction, the lowest point of the second end surface 220 is lower than the lowest point of the first extension portion 12.

[0035] The third pole shoe 30 includes a vertical portion 31, a third extension portion 32, and a horizontal portion 33. The vertical portion 31 extends vertically to form a cylindrical structure. The vertical portion 31 is located at the edge of the top 11 and surrounds the top 11. The third extension portion 32 extends from the bottom of the vertical portion 31. The third extension portion 32 is tilted to form a conical structure. The horizontal portion 33 extends from the end of the third extension portion 32 and is arranged horizontally. At this time, an opening is formed between the end of the horizontal portion 33 and the end of the first extension portion 12. The second pole shoe 20 is located between the first pole shoe 10 and the third pole shoe 30, and the end of the second extension portion 22 extends into the opening. A second gap is formed between the end of the horizontal portion 33 and the second extension portion 22. A first gap is formed between the second extension portion 22 and the first extension portion 12 of the first pole shoe 10. The first gap is located above the second gap, that is, the second gap is located between the first gap and the sample 70.

[0036] The first coil 40 is installed between the first pole shoe 10 and the second pole shoe 20 , and the second coil 50 is installed between the second pole shoe 20 and the third pole shoe 30 .

[0037] Please continue reading Figure 3 as well as Figure 4 , when the dual objective lens structure is in immersion mode, the second pole shoe 20, the third pole shoe 30 and the second coil 50 are working, and the magnetic field generated by the second coil 50 leaks from the second gap to the sample 70, so that the sample 70 is immersed in the magnetic field. The sample 70 is a non-magnetic sample. The magnetic field strength is as follows Figure 4As shown by the middle red line, the position of the maximum magnetic field strength is between the end of the third pole piece 30 and the sample 70. The distance between the position of the maximum magnetic field strength and the surface of the sample 70 is the effective focal length f, and the distance between the end of the pole piece (the end of the third pole piece 30) and the surface of the sample 70 is the working distance D. At this time, the effective focal length f is smaller than the working distance D. Since the effective focal length f is very small, a shorter focal length imaging can be obtained when the double objective structure is in the immersion mode, and a resolution of 0.7 nm@1kV 1mm can be achieved. Since only the magnetic field on the left side of the sample 70 is used for focusing, a larger excitation is required, and a higher resolution can be obtained as long as the current is sufficient. Therefore, the immersion mode is suitable for high-resolution scanning of non-magnetic samples, and is suitable for low-voltage short focal length work. When high-resolution scanning is performed, it is calculated that when the scanning voltage is 1KV, the effective focal length can be less than 1mm; when the scanning voltage is 5KV, the effective focal length can be less than 1mm. When applied to high-energy short working distance analysis, the scanning voltage is 30KV, the effective focal length is 7mm, and the current needs to be 2A, so the second coil 50 generates too much heat, and the cooling capacity of the system is required to be higher.

[0038] Please continue to refer to Figure 5 and Figure 6 When the double objective structure is in the non-immersion mode, the first pole piece 10, the second pole piece 20 and the first coil 40 work at this time, and the magnetic field generated by the first coil 40 partially leaks from the first gap. Since the first gap is located above the second gap, the first gap is far away from the sample 70, and therefore the sample 70 is not exposed to the magnetic field, and the sample 70 is a magnetic sample. At this time, the position of the maximum magnetic field strength is between the end of the first pole piece 10 and the end of the third pole piece 30, the effective focal length f is greater than the working distance D, and a resolution of 1.5 nm@1kV 1mm can be achieved when imaging. Since all the magnetic field is used for focusing, the required current is smaller under the same effective focal length. For example, when 30kV imaging is performed, the required current is 1.6A for an effective focal length of 5.5mm, and the required current is 2.25A in the immersion mode. The required current in the immersion mode is 1.4 times that in the non-immersion mode, and the heat generated is 2 times.

[0039] The double objective structure of the application can realize magnetic imaging and non-magnetic imaging. When magnetic imaging is performed, the non-immersion mode is used, and a resolution of 1.5 nm@1kV 1mm can be achieved. At the same time, high-energy electron low-current imaging can be realized in this mode. When non-magnetic imaging is performed, the immersion mode is used, and a resolution of 0.7 nm@1kV 1mm can be achieved.

[0040] The application also discloses an electron microscope comprising the double objective structure.

[0041] The application also discloses a use method of the double objective structure, comprising the following steps:

[0042] When the double objective structure is in the immersion mode, the second coil 50, the second pole shoe 20 and the third pole shoe 30 work, the magnetic field generated by the second coil 50 leaks from the second gap to the sample 70, so that the sample 70 is immersed in the magnetic field, and at this time, the position with the maximum magnetic field strength is located between the end of the third pole shoe 30 and the sample 70;

[0043] When the double objective structure is in the non-immersion mode, the first coil 40, the first pole shoe and the second pole shoe 20 work, the magnetic field generated by the first coil 40 partially leaks at the first gap and does not leak to the sample 70, and at this time, the position with the maximum magnetic field strength is located between the end of the first pole shoe 10 and the end of the third pole shoe 30.

[0044] The above embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as the limitation of the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are equivalent modifications and evolutions of the above embodiments according to the essential technology of the present application, and these all belong to the protection scope of the present application.

Claims

1. A dual objective lens structure, comprising a first pole shoe, a second pole shoe, a third pole shoe, a first coil, and a second coil, characterized in that: The first coil is installed between the first pole shoe and the second pole shoe, and the second coil is installed between the second pole shoe and the third pole shoe. The first pole shoe includes a first extension portion, which is conical and forms a channel for the movement of the electron beam. The second pole shoe includes a second extension portion, and the third pole shoe includes a third extension portion. The second extension portion and the third extension portion are both conical. The second extension portion is located between the first extension portion and the third extension portion. The end of the first extension portion and the end of the third extension form an opening. The end of the second extension extends into the opening. A first gap is formed between the end of the second extension and the end of the first extension. The end of the second extension is in contact with the A second gap is formed at the end of the third extension portion. In the axial direction of the channel, the second gap is located between the first gap and the sample. When the dual objective lens structure is in the immersion mode, the second coil, the second pole shoe and the third pole shoe are in operation, and the magnetic field generated by the second coil leaks from the second gap to the sample so that the sample is immersed in the magnetic field. At this time, the maximum strength of the magnetic field is located between the end of the third pole shoe and the sample. When the dual objective lens structure is in the non-immersion mode, the first coil, the first pole shoe and the second pole shoe are in operation, and the magnetic field generated by the first coil partially leaks at the first gap and does not leak to the sample. At this time, the maximum strength of the magnetic field is located between the end of the first pole shoe and the end of the second pole shoe.

2. The dual objective lens structure according to claim 1, wherein: Along the channel axis direction, the end of the second extension portion is located between the end of the first extension portion and the end of the third extension portion.

3. The dual objective lens structure according to claim 1, wherein: The third pole shoe also includes a horizontal portion, which extends from the end of the third extension portion and is horizontally arranged. The horizontal portion extends toward the direction of the channel, and the second gap is formed between the end of the horizontal portion away from the third extension portion and the outer wall of the second extension portion.

4. The dual objective lens structure according to claim 3, wherein: The outer wall of the first extending portion and the inner wall of the second extending portion form the first gap, and the width of the first gap is smaller than the width of the second gap.

5. The dual objective lens structure according to claim 1, wherein: The inner diameter of the end of the first pole shoe is greater than or equal to the inner diameter of the end of the second pole shoe.

6. The dual objective lens structure according to claim 5, wherein: The inner diameter of the end of the third pole shoe is greater than the inner diameter of the end of the second pole shoe.

7. The dual objective lens structure according to claim 1, wherein: The distance from the point where the magnetic field intensity is maximum to the sample surface is the effective focal length, and the distance from the pole shoe mouth to the sample surface is the working distance. When the dual objective lens structure is in non-immersion mode, the effective focal length is much greater than the working distance; when the dual objective lens structure is in immersion mode, the effective focal length is less than the working distance.

8. The dual objective lens structure according to claim 1, wherein: When the dual objective lens structure is in non-immersion mode, the dual objective lens structure is suitable for high-resolution scanning of magnetic samples, large beam analysis, and low-current imaging at high energy; when the dual objective lens structure is in immersion mode, the dual objective lens structure is suitable for low-energy high-resolution scanning of non-magnetic samples.

9. An electron microscope, characterized in that: Comprising the dual objective lens structure as described in any one of claims 1-8.

10. A method for using the dual objective lens structure according to any one of claims 1 to 8, characterized in that: The following steps are involved: When the dual objective lens structure is in immersion mode, the second coil, the second pole shoe, and the third pole shoe are in operation, and the magnetic field generated by the second coil leaks from the second gap to the sample, so that the sample is immersed in the magnetic field. At this time, the maximum magnetic field intensity is located between the end of the third pole shoe and the sample; When the dual objective lens structure is in non-immersion mode, the first coil, the first pole shoe and the second pole shoe are working, and the magnetic field generated by the first coil is partially leaked at the first gap and does not leak to the sample. At this time, the maximum magnetic field strength is located between the end of the first pole shoe and the end of the third pole shoe.

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