Scanning electron microscope and use method thereof

Abstract

The invention discloses a scanning electron microscope and a use method thereof, and belongs to the field of electron microscopes, a first permanent magnet of a condenser is located in a first outer pole shoe, a first opening and a second opening are formed between a first inner pole shoe and the first outer pole shoe, and the first opening and the second opening are arranged along the optical axis of the condenser; a second permanent magnet of the objective lens is installed between a second outer pole shoe and a second inner pole shoe, a third opening and a fourth opening are formed between the second inner pole shoe and the second outer pole shoe and are arranged along the optical axis of the objective lens, and electron beams in the optical axis are focused to the center of the third opening through magnetic fields of the first opening and the second opening. The influence of the magnetic field of the third opening on electron beams is reduced; a permanent magnet is adopted to generate a magnetic field without heating; the four openings are arranged on the optical axis, so that magnetic field interference to the surroundings is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electron microscopes, and in particular to a scanning electron microscope and a method of using the scanning electron microscope. BACKGROUND

[0002] Scanning electron microscope is a high-end analytical characterization equipment, widely used in scientific research, industry and other fields. The mainstream commercial electron microscope system usually adopts a coil to generate a focusing magnetic field, and a high magnetic permeability material around the coil is used to concentrate the magnetic field into a very narrow space for electron beam focusing. Due to the large current (2A) required for focusing high-energy electrons, the coil generates Joule heat, causing the coil temperature to be as high as 70-80 degrees or more. Therefore, commercial equipment is usually equipped with a water chiller and other cooling equipment to stabilize the temperature of the system, which not only increases the equipment investment, but also introduces vibration, electromagnetic and other interference.

[0003] One method to reduce power consumption is to use a permanent magnet. The permanent magnet generates a magnetic field without heat, so the system does not need a water chiller and other cooling equipment. However, according to Ampere's law, the magnetic field integral along a closed loop is proportional to the current enclosed by the loop. Therefore, when using a pole shoe to surround the permanent magnet for electron beam focusing, two openings need to be left, and the magnetic fields generated by the two openings are in opposite directions.

[0004] However, when using a permanent magnet, the prior art places one opening on the optical axis for focusing and the other outside the optical axis to decouple the effects of the magnetic fields generated by the two openings on the electron beam. However, this solution causes the magnetic field leaked by the opening outside the optical axis to interfere with the surrounding and control system, and the electromagnetic interference from the environment also affects the performance of the entire lens through this opening. SUMMARY

[0005] To overcome the shortcomings of the prior art, one of the purposes of the present application is to provide a low-power scanning electron microscope without interference caused by magnetic field leakage outside the optical axis.

[0006] To overcome the shortcomings of the prior art, the second purpose of the present application is to provide a method for using a low-power scanning electron microscope without interference caused by magnetic field leakage outside the optical axis.

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

[0008] A scanning electron microscope comprises an objective lens and a condenser, the condenser comprises a first outer pole piece, a first inner pole piece and a first permanent magnet, the first permanent magnet is located inside the first outer pole piece, the first inner pole piece and the first outer pole piece form a first opening and a second opening, the first opening and the second opening are arranged along the optical axis of the condenser, the objective lens comprises a second outer pole piece, a second inner pole piece and a second permanent magnet, the second permanent magnet is installed between the second outer pole piece and the second inner pole piece, the second inner pole piece and the second outer pole piece form a third opening and a fourth opening, the third opening and the fourth opening are arranged along the optical axis of the objective lens, the optical axis of the condenser and the optical axis of the objective lens are located on the same straight line, the magnetic field of the first opening and the second opening focuses the electron beam in the optical axis on the third opening, reducing the influence of the magnetic field of the third opening on the electron beam.

[0009] Further, the objective lens further comprises a coil, the coil is installed between the second inner pole piece and the second outer pole piece, the coil adjusts the magnetic field intensity of the fourth opening.

[0010] Further, the condenser further comprises a coil, the coil is installed inside the first outer pole piece, the coil adjusts the magnetic field intensity of the first opening and the second opening to adjust the optical path in the optical axis of the condenser.

[0011] Further, the first opening and the second opening are both axial openings and face the optical axis of the condenser.

[0012] Further, the cross section of the first outer pole piece is rectangular, the first outer pole piece is provided with a notch on one side of the optical axis, the cross section of the first inner pole piece is rectangular, the first inner pole piece extends from the inside of the first outer pole piece to the notch, the upper side of the first inner pole piece and the top of the notch form the first opening; the lower side of the first inner pole piece and the bottom of the notch form the second opening.

[0013] Further, the third opening is an axial opening and faces the optical axis of the objective lens, the fourth opening faces the optical axis of the objective lens to form a non-immersion objective lens, or the opening faces downward to form a radial opening to form an immersion objective lens.

[0014] Further, the top of the second outer pole piece is rectangular and the bottom is conical, the second inner pole piece is conical, the second inner pole piece is located inside the second outer pole piece, and the fourth opening is located between the end of the second outer pole piece and the end of the second inner pole piece.

[0015] Further, the working distance of the scanning electron microscope is 1mm-10mm.

[0016] The second purpose of the application is achieved by the following technical solutions:

[0017] A method for using any of the above scanning electron microscopes, comprising the following steps:

[0018] The magnetic fields of the first opening and the second opening of the condenser lens focus the electron beam at the third opening, reducing the influence of the magnetic field of the third opening on the electron beam;

[0019] The electron beam is focused on the sample on the sample stage under the action of the magnetic field of the fourth opening for scanning imaging;

[0020] Adjusting the electron beam energy or setting a coil in the condenser lens adjusts the optical path;

[0021] Adjusting the coil current in the objective lens changes the magnetic field strength of the fourth opening to focus the focal length of different working distances and different imaging energies.

[0022] Further, the working distance of the scanning electron microscope is 1mm-10mm, and the current excitation range of the coil in the objective lens is-0.45A to +0.45A.

[0023] Compared with the prior art, the condenser lens of the scanning electron microscope of the application comprises a first outer pole piece, a first inner pole piece and a first permanent magnet, the first permanent magnet is located inside the first outer pole piece, the first inner pole piece and the first outer pole piece form a first opening and a second opening, the first opening and the second opening are arranged along the optical axis of the condenser lens, the objective lens comprises a second outer pole piece, a second inner pole piece and a second permanent magnet, the second permanent magnet is installed between the second outer pole piece and the second inner pole piece, the second inner pole piece and the second outer pole piece form a third opening and a fourth opening, the third opening and the fourth opening are arranged along the optical axis of the objective lens, the optical axis of the condenser lens and the optical axis of the objective lens are located on the same straight line, the magnetic field of the first opening and the second opening focuses the electron beam in the optical axis at the third opening, reducing the influence of the magnetic field of the third opening on the electron beam; through the above design, the permanent magnet is used to generate the magnetic field, which will not heat; the first opening, the second opening, the third opening and the fourth opening are all arranged on the optical axis, which will not cause magnetic field interference; the magnetic field of the first opening and the second opening focuses the electron beam in the optical axis at the third opening, reducing the influence of the magnetic field of the third opening on the electron beam. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The structure of the scanning electron microscope of the application is shown in the figure;

[0025] Figure 2 The magnetic field distribution of the scanning electron microscope of the application at different coil currents is shown in the figure; Figure 1

[0026] Figure 3 ​The electron beam and the magnetic field distribution diagram when the coil current is -0.45A;

[0027] Figure 4 The electron beam and the magnetic field distribution diagram when the coil current is 0.45A.

[0028] In the figure: 10, condenser; 11, first outer pole shoe; 12, first inner pole shoe; 13, first permanent magnet; 14, first opening; 15, second opening; 20, objective lens; 21, second outer pole shoe; 22, second inner pole shoe; 23, second permanent magnet; 24, coil; 25, third opening; 26, fourth opening; 30, sample stage; 40, electron beam. DETAILED DESCRIPTION

[0029] 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.

[0030] 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.

[0031] Please refer to Figure 1 The scanning electron microscope comprises a condenser 10, an objective lens 20 and a sample stage 30, which are located on the same straight line, and the objective lens 20 is located between the condenser 10 and the sample stage 30.

[0032] The condenser 10 comprises a first outer pole shoe 11, a first inner pole shoe 12 and a first permanent magnet 13. The first outer pole shoe 11 is annular in structure to form an optical axis (electron channel). The cross section of the first outer pole shoe 11 is hollow rectangular, and a notch is arranged on the inner side of the rectangle. The first permanent magnet 13 is fixed to the inside of the first outer pole shoe 11, and is used to generate a magnetic field. The first inner pole shoe 12 is annular and linear in cross section. The first inner pole shoe 12 is installed in the inside of the first outer pole shoe 11 and extends to the notch at the end. The upper side of the first inner pole shoe 12 and the top of the notch form a first opening 14, and the lower side of the first inner pole shoe 12 and the bottom of the notch form a second opening 15. The first opening 14 and the second opening 15 are both axial openings, which are directed to the optical axis. The first outer pole shoe 11 can also be installed with a coil (not shown in the figure) to adjust the optical path.

[0033] The objective lens 20 comprises a second outer pole piece 21, a second inner pole piece 22, a second permanent magnet 23 and a coil 24. The second outer pole piece 21 is in the shape of a ring to form an optical axis (electron channel). The optical axis of the objective lens 20 is in line with the optical axis of the condenser lens 10. The top of the cross section of the second outer pole piece 21 is rectangular, and the bottom of the cross section of the second outer pole piece 21 is conical. The second inner pole piece 22 is inside the second outer pole piece 21, and the second permanent magnet 23 and the coil 24 are installed between the second inner pole piece 22 and the second outer pole piece 21. The second permanent magnet 23 is used to generate a magnetic field, and the coil 24 is used to adjust the strength of the magnetic field. The second inner pole piece 22 is conical, and the third opening 25 is formed between the top of the second inner pole piece 22 and the top of the second outer pole piece 21, and the fourth opening 26 is formed between the bottom of the second inner pole piece 22 and the bottom of the second outer pole piece 21. The third opening 25 is an axial opening, which is directed towards the optical axis, and the fourth opening 26 is directed towards the optical axis and forms an acute angle with the optical axis.

[0034] The sample stage 30 is located at the bottom of the fourth opening 26.

[0035] The scanning electron microscope is along the optical axis direction, and the first opening 14, the second opening 15, the third opening 25 and the fourth opening 26 are sequentially arranged.

[0036] When the scanning electron microscope is used, the electron beam 40 is injected along the optical axis, and under the action of the magnetic field of the first opening 14 and the second opening 15, the electron beam 40 is focused on the center of the magnetic field of the third opening 25, so that the focusing ability of the third opening 25 to the electron beam 40 is weak, and the whole is equivalent to a single conventional objective lens. The condenser lens 10 has a reduction ratio greater than 1.5. Under the action of the magnetic field of the fourth opening 26, the electron beam 40 is focused on the sample on the sample stage 30 for scanning.

[0037] Please continue to refer to Figure 2 By adjusting the current of the coil 24 of the objective lens 20, the magnetic field strength of the fourth opening 26 of the objective lens 20 can be changed, which is used to focus the focal length of different working distances and different imaging energies. Although the magnetic field strength of the third opening 25 also changes, the electron beam 40 is focused on the center of this field distribution, which does not affect the electron optical path of the whole system, and realizes the controllable focusing of the objective lens 20.

[0038] Please continue to refer to Figure 3 For the imaging energy of the electron beam 40 of 5kV, the current of the coil 24 of the objective lens 20 is -0.45A, which offsets part of the magnetic field generated by the second permanent magnet 23, and realizes the weak focusing of the long distance (10mm).

[0039] Please continue to refer to Figure 4For the electron beam 40 imaging energy of 5kV, the coil 24 current of the objective lens 20 is 0.45A, which is further enhanced on the magnetic field generated by the second permanent magnet 23, so as to realize strong focusing with a short working distance (1mm).

[0040] Through the above design, the scanning electron microscope can realize controllable focusing imaging with a large working distance of 1-10mm and a large imaging energy of 100V-10kV. Through the integrated permanent magnet, the maximum current excitation of the system only needs +-0.45A, which is 0.15 times of the conventional objective lens 1.3A. Combined with the condenser 10, the heat generation power of the whole system is only 0.07 times of the conventional electromagnetic system. The two-stage lens combination of the condenser 10 and the objective lens 20 further reduces the height of the lens barrel.

[0041] The application also discloses a use method of the scanning electron microscope.

[0042] The magnetic field of the first opening 14 and the second opening 15 of the condenser 10 focuses the electron beam 40 on the third opening 25, so as to reduce the influence of the magnetic field of the third opening 25 on the electron beam 40.

[0043] The electron beam 40 is focused on the sample on the sample stage 30 under the action of the magnetic field of the fourth opening 26 to realize scanning imaging.

[0044] The energy of the electron beam 40 or the coil 24 in the condenser 10 is adjusted to adjust the light path.

[0045] The current of the coil 24 in the objective lens 20 is adjusted to change the magnetic field intensity of the fourth opening 26, so as to focus the focal length of different working distances and different imaging energies.

[0046] The working distance of the scanning electron microscope is 1mm-10mm, and the current excitation range of the coil 24 in the objective lens 20 is -0.45A to +0.45A.

[0047] Compared with the prior art, the scanning electron microscope adopts a permanent magnet to generate a magnetic field, which does not generate heat. The first opening 14, the second opening 15, the third opening 25 and the fourth opening 26 are all arranged on the optical axis, which does not generate magnetic field interference. The magnetic field of the first opening 14 and the second opening 15 focuses the electron beam 40 in the optical axis on the third opening 25, so as to reduce the influence of the magnetic field of the third opening 25 on the electron beam 40.

[0048] The above embodiments only express several implementation manners of the present application, the description is more specific and detailed, but 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, several 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 scanning electron microscope comprising an objective lens, characterized in that: The scanning electron microscope further comprises a condenser including a first outer pole piece, a first inner pole piece and a first permanent magnet, the first permanent magnet is located inside the first outer pole piece, the first inner pole piece and the first outer pole piece form a first opening and a second opening, the first opening and the second opening are arranged along the optical axis of the condenser, the objective lens includes a second outer pole piece, a second inner pole piece and a second permanent magnet, the second permanent magnet is installed between the second outer pole piece and the second inner pole piece, the second inner pole piece and the second outer pole piece form a third opening and a fourth opening, the third opening and the fourth opening are arranged along the optical axis of the objective lens, the optical axis of the condenser and the optical axis of the objective lens are located on the same straight line, the magnetic field of the first opening and the second opening focuses the electron beam in the optical axis on the third opening, and the influence of the magnetic field of the third opening on the electron beam is reduced.

2. The scanning electron microscope of claim 1, wherein: The objective lens further comprises a coil installed between the second inner pole piece and the second outer pole piece, and the coil adjusts the magnetic field intensity of the fourth opening.

3. The scanning electron microscope of claim 1, wherein: The condenser further comprises a coil installed in the first outer pole piece, and the coil adjusts the magnetic field intensity of the first opening and the second opening to adjust the optical path in the optical axis of the condenser.

4. The scanning electron microscope of claim 1, wherein: The first opening and the second opening are axial openings and face the optical axis of the condenser.

5. The scanning electron microscope of claim 4, wherein: The first outer pole piece has a rectangular cross section, the first outer pole piece is provided with a notch on one side of the optical axis, the first inner pole piece has a rectangular cross section, the first inner pole piece extends from the inside of the first outer pole piece to the notch, and the upper side of the first inner pole piece and the top of the notch form the first opening; the lower side of the first inner pole piece and the bottom of the notch form the second opening.

6. The scanning electron microscope of claim 1, wherein: The third opening is an axial opening and faces the optical axis of the objective lens, and the fourth opening faces the optical axis of the objective lens, which is a non-immersion objective lens; the fourth opening is a downward radial opening, which is an immersion objective lens.

7. The scanning electron microscope of claim 6, wherein: The top of the second outer pole piece is rectangular and the bottom is conical, the second inner pole piece is conical, the second inner pole piece is located inside the second outer pole piece, and the fourth opening is located between the end of the second outer pole piece and the end of the second inner pole piece.

8. The scanning electron microscope of claim 1, wherein: The working distance of the scanning electron microscope is 1mm-10mm.

9. A method of using a scanning electron microscope as claimed in any one of claims 1 to 8, characterised in that, The steps include: The magnetic field of the first opening and the second opening of the condenser focuses the electron beam on the third opening, and the influence of the magnetic field of the third opening on the electron beam is reduced; The electron beam is focused on the sample on the sample stage under the action of the magnetic field of the fourth opening to perform scanning imaging; Adjust the electron beam energy or set the coil in the condenser to adjust the optical path; Adjust the coil current in the objective lens to change the magnetic field intensity of the fourth opening to focus the focal length of different working distances and different imaging energies.

10. The method of using a scanning electron microscope according to claim 9, wherein: The working distance of the scanning electron microscope is 1mm-10mm, and the current excitation range of the coil in the objective lens is-0.45A to +0.45A.

Images