CN115732298A

CN115732298A - Scanning electron microscope

Info

Publication number: CN115732298A
Application number: CN202211477788.6A
Authority: CN
Inventors: 阴达; 张伟; 尹朋飞; 卢志钢
Original assignee: Chinainstru and Quantumtech Hefei Co Ltd
Current assignee: Chinainstru and Quantumtech Hefei Co Ltd
Priority date: 2022-11-23
Filing date: 2022-11-23
Publication date: 2023-03-03

Abstract

The invention discloses a scanning electron microscope, which comprises a tungsten filament electron gun, a voltage tube, a magnetic lens and a sample stage. The tungsten filament electron gun comprises a cathode, wherein the cathode is connected with a negative potential, and the negative potential is a negative voltage to the ground; the voltage tube and the tungsten filament electron gun are arranged at intervals, a channel is formed in the voltage tube and is used for allowing an electron beam emitted by the tungsten filament electron gun to pass through, the voltage tube is connected with a positive potential, and the positive potential is a positive voltage to the ground; the magnetic lens surrounds the voltage tube and is used for converging the electron beam; the sample stage is arranged on one side of the voltage tube, which is away from the tungsten filament electron gun, and is used for bearing a sample. The voltage tube is connected with a positive potential, and a larger electric field is formed between the voltage tube and the cathode, so that the filament tip surface of the tungsten filament electron gun has higher field intensity, the limitation of space charge effect on beam brightness is overcome, the beam brightness is obviously improved, and the resolution of a scanning electron microscope based on the tungsten filament as an electron source is improved.

Description

Scanning electron microscope

Technical Field

The invention relates to the technical field of microscopes, in particular to a scanning electron microscope.

Background

The scanning electron microscope is an electron optical microscopic imaging device which scans a sample by using a probe which is converged into a superfine electron beam, collects signal electrons generated after the interaction of the electron beam and the sample, and realizes the imaging of the sample by synchronizing a signal acquisition time sequence and a scanning time sequence. When the scanning electron microscope works, the energy of the electron beam is generally adjustable within the range of below 30kV. Among them, the low landing voltage condition of 3kV or less is one of the most important and widely used working conditions. However, at low landing voltage, the imaging resolution of the scanning electron microscope is limited by the brightness of the electron beam, chromatic aberration due to energy dispersion, and diffraction aberration. Electron sources of a scanning electron microscope can be classified into thermal emission electron sources and field emission electron sources according to the emission mechanism. The tungsten filament electron gun is a thermal emission electron source, and the operating temperature of the tungsten filament is 2600K to 2800K. The resolution bottleneck of the tungsten filament scanning electron microscope is mainly limited by factors such as beam brightness and chromatic aberration. The existing tungsten filament scanning electron microscope has lower resolution under low landing voltage.

Disclosure of Invention

The invention provides a scanning electron microscope.

The scanning electron microscope of the embodiment of the present invention includes:

the tungsten filament electron gun comprises a cathode, wherein the cathode is connected with a negative potential, and the negative potential is a negative voltage to the ground;

the voltage tube is arranged at intervals with the tungsten filament electron gun, a channel is formed in the voltage tube and is used for allowing an electron beam emitted by the tungsten filament electron gun to pass through, the voltage tube is connected with a positive potential, and the positive potential is a positive earth voltage;

a magnetic lens surrounding the voltage tube for converging the electron beam;

the sample stage is arranged on one side, away from the tungsten filament electron gun, of the voltage tube and used for bearing a sample.

In the scanning electron microscope of the embodiment of the invention, the voltage tube is connected with a positive potential, and a larger electric field is formed between the voltage tube and the cathode, so that the surface of the tip end of the filament of the tungsten filament electron gun has higher field intensity, thereby overcoming the suppression of space charge effect on the thermionic emission of the tungsten filament, namely overcoming the limitation of the space charge effect on the beam brightness, thereby obviously improving the beam brightness and further improving the resolution of the scanning electron microscope based on the tungsten filament as an electron source.

In some embodiments, the voltage tube and the tungsten filament electron gun are both in a vacuum environment, and the channel formed in the voltage tube is a vacuum channel.

In certain embodiments, the positive potential is in the range of no less than 8kV.

In certain embodiments, the negative potential ranges from-100V to-30 kV.

In certain embodiments, the voltage tube is a continuous structure along an axial direction of the voltage tube.

In some embodiments, the number of the magnetic lenses is multiple, the magnetic lenses include a first electrical coil, the magnetic field generated by the first electrical coil can be controlled by adjusting the magnitude of the current, and the first electrical coil surrounds the voltage tube.

In some embodiments, the scanning electron microscope further comprises an objective lens disposed between the sample stage and the magnetic lens, the objective lens surrounding the voltage tube, and a retardation field formed between an end of the voltage tube remote from the tungsten filament electron gun and the objective lens.

In some embodiments, the objective lens includes a second electrically-conductive coil and a metal cover having a ring cavity and a C-shaped cross section, the second electrically-conductive coil surrounds the ring cavity of the metal cover, a magnetic field formed by the second electrically-conductive coil forms a strong magnetic field at the opening of the ring cavity of the metal cover of the C-shaped, the intensity of the magnetic field can be adjusted by adjusting the current of the second electrically-conductive coil, and the magnetic field can be closed by closing the current of the second electrically-conductive coil.

In certain embodiments, the metal cover is made of a high magnetic permeability material.

In some embodiments, the second energized coil, the metal shield, and the voltage tube are coaxial.

In some embodiments, two end edges of the opening of the metal cover extend to one end of the voltage tube far away from the tungsten filament electron gun to form an upper pole shoe and a lower pole shoe respectively, the magnetic field generated by the second electrified coil is conducted to the upper pole shoe and the lower pole shoe, and a strong magnetic field is formed between the upper pole shoe and the lower pole shoe.

In some embodiments, the retarding field is formed between the lower pole piece and an end of the voltage tube distal from the tungsten filament electron gun and the objective lens.

In some embodiments, the scanning electron microscope further comprises a detector for detecting signal electrons generated after the electron beam interacts with the sample.

In certain embodiments, the detector comprises a first detector spaced from the sample stage, the first detector being disposed radially to one side of the voltage tube.

In some embodiments, the detector comprises a second detector disposed within the voltage tube, the second detector being provided with a through hole for the passage of the electron beam.

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.

Drawings

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

fig. 1 is a schematic configuration diagram of a scanning electron microscope according to an embodiment of the present invention.

Description of the main element symbols: a scanning electron microscope 1000; a tungsten filament electron gun 100; a cathode 10; an anode 20; a voltage tube 200; a channel 300; an electron beam 30; a magnetic lens 400; a sample stage 500; a first energized coil 410; an objective lens 600; an upper pole piece 610; a lower pole piece 620; a second electrified coil 630; a metal cap 640; an annular cavity 641; a retarding field 700; a detector 800; a first detector 810; a second detector 820; a through hole 821.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.

In the description of the present invention, it is to 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", and the like, indicate orientations and positional relationships based on those shown in the drawings, and are used only for convenience of description and simplicity of description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be considered as limiting the present invention. Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", may explicitly or implicitly include one or more of the described features. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; may be mechanically connected, may be electrically connected or may be in communication with each other; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

In the present invention, unless otherwise expressly stated or limited, "above" or "below" a first feature means that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact with each other via another feature therebetween. Also, the first feature being "on," "above" and "over" the second feature includes the first feature being directly on and obliquely above the second feature, or merely indicating that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly under and obliquely below the second feature, or simply meaning that the first feature is at a lesser elevation than the second feature.

The following disclosure provides many different embodiments or examples for implementing different features of the invention. To simplify the disclosure of the present invention, the components and arrangements of specific examples are described below. Of course, they are merely examples and are not intended to limit the present invention. Furthermore, the present invention may repeat reference numerals and/or letters in the various examples, such repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. In addition, the present invention provides examples of various specific processes and materials, but one of ordinary skill in the art may recognize applications of other processes and/or uses of other materials.

Referring to fig. 1, a scanning electron microscope 1000 according to an embodiment of the present invention includes a tungsten filament electron gun 100, a voltage tube 200, a magnetic lens 400, and a sample stage 500. The tungsten filament electron gun 100 comprises a cathode 10, wherein the cathode 10 is connected with a negative potential, and the negative potential is a negative voltage to the ground; the voltage tube 200 is arranged at an interval with the tungsten filament electron gun 100, a channel 300 is formed in the voltage tube, the channel 300 is used for the electron beam 30 emitted by the tungsten filament electron gun 100 to pass through, the voltage tube 200 is connected with a positive potential, and the positive potential is a positive voltage to the ground; the magnetic lens 400 surrounds the voltage tube 200 to converge the electron beam 30; the sample stage 500 is disposed on a side of the voltage tube 200 facing away from the tungsten filament electron gun 100, and is configured to carry a sample.

In the scanning electron microscope 1000 according to the embodiment of the present invention, the voltage tube 200 is connected to a positive potential, and a large electric field is formed between the voltage tube 200 and the cathode 10, so that the filament tip surface of the tungsten filament electron gun 100 has a high field strength, thereby overcoming the suppression of the space charge effect on the thermionic emission of the tungsten filament, that is, overcoming the limitation of the space charge effect on the beam brightness, thereby significantly improving the beam brightness, and further improving the resolution of the scanning electron microscope 1000 based on the tungsten filament as an electron source.

Specifically, the tungsten filament electron gun 100 may be used to emit tungsten filament thermoelectrons, and the minimum value of the electron probe beam spot generated by the electron beam 30 emitted by the tungsten filament electron gun 100 and the signal intensity generated after the electron beam 30 interacts with the sample determine the limit resolution and the imaging quality of the scanning electron microscope 1000.

The cathode 10 of the tungsten filament electron gun 100 may be at a negative potential of-1 kV, -2kV, etc. since the sample stage 500 is usually at the same voltage as ground, the negative voltage of the cathode 10 to ground corresponds to the energy of tungsten filament thermal electrons landing on the sample. The voltage tube 200 may have a positive potential to ground of 8kV or more.

The channel 300 may be formed in the voltage tube 200. An electron beam 30 from a tungsten filament lamp electron source may reach the sample stage 500 through the channel 300 and interact with the sample at the sample stage 500 to generate signal electrons. The voltage tube 200 is connected to a positive potential, which enhances the electric field strength on the surface of the tip of the tungsten filament, thereby overcoming the suppression of the space charge effect on the thermionic emission of the tungsten filament, i.e., overcoming the limitation of the space charge effect on the beam brightness, thereby significantly improving the beam brightness, and further improving the resolution of the scanning electron microscope 1000 based on the tungsten filament as an electron source. Meanwhile, the channel 300 in the voltage tube 200 forms an electric field, and electrons have higher energy and lower space charge density when flying in the section, so that the effect (Boerscheffect) of increasing energy dispersion caused by coulomb interaction between the electrons is reduced, the monochromaticity of the electron beam is improved, and the imaging resolution of the scanning electron microscope 1000 under low pressure is improved.

The magnetic lens 400 may be commercially available or custom made, and embodiments of the present invention are not limited to a specific model of the magnetic lens 400. The electron beam 30 is converged while passing through the magnetic lens 400. Further, the channel 300 may partially coincide with the focusing optical path of the magnetic lens 400.

The sample stage 500 is a platform for holding a sample, and the sample may be fixed on the sample stage 500 so that the electron beam 30 may scan a specific surface of the sample. A voltage tube 200 is disposed between the sample stage 500 and the tungsten filament electron gun 100, and the electron beam 30 emitted from the tungsten filament electron gun 100 can reach the sample stage 500 through a passage 300 at the voltage tube 200 and react with a sample on the sample stage 500.

Referring to fig. 1, in some embodiments, the voltage tube 200 and the tungsten filament electron gun 100 are both in a vacuum environment, and the channel 300 formed in the voltage tube 200 is a vacuum channel.

As such, the propagation resistance of the electron beam 30 in the voltage tube 200 is low compared to a non-vacuum environment, and thus the beam brightness of the electron beam 30 is hardly reduced.

Referring to fig. 1, in some embodiments, the voltage tube 200 is connected to a positive potential in a range of 8kV or more. When the positive potential is less than 8kV, the effect of the space charge effect is more obvious along with the reduction of the positive voltage, and the inhibition effect on the surface emission of the tip of the filament is enhanced, so that the beam brightness is reduced; meanwhile, coulomb interaction of electrons in the flight process of the channel 300 is strengthened, electron energy distribution is widened, energy dispersion is increased, and the resolution of the scanning electron microscope 1000 is reduced. When the positive potential is not lower than 8kV, the electric field intensity on the surface of the tip of the tungsten filament electron gun 100 filament is larger, so that the inhibition of space charge effect on emission can be overcome, the coulomb interaction in the electron beam 30 is reduced, the beam brightness is improved, and the energy dispersion is reduced.

Referring to fig. 1, in some embodiments, the negative potential connected to the cathode 10 is in the range of-100V to-30 kV.

The range of the negative potential can be adjusted, for example, the negative potential can be-1 kV, -10kV, -30kV, and in the range of-100V to-30 kV, and the user can adjust the voltage according to the microscopic imaging and analysis characterization requirements of different scenes. Wherein, when the negative potential ranges from-1 kV to-3 kV, i.e. the landing energy of the electrons ranges from 1keV to 3keV, the irradiation damage of the electron beam 30 to the sample is reduced, and the characterization of the biological and other irradiation-sensitive samples is advantageous. Meanwhile, the secondary electron emission coefficient of the sample under specific low energy is close to 1, which is beneficial to realizing the balance of injected electrons and emergent electrons, thereby avoiding adverse effects and the like caused by the charge of the sample. At very low landing voltages, new mechanisms for the interaction of incident electrons and the sample also occur, creating new contrast and thus obtaining more new information on the sample surface.

For an operating condition with a landing voltage of 1kV, the potential difference between the cathode 10 and the anode 20 is-1 kV when the voltage tube 200 is omitted and the anode 20 is grounded. When a positive potential of 8kV or more with respect to ground is applied to the voltage tube 200, the potential difference between the cathode 10 and the voltage tube 200 is 9kV or more, and compared with the case where the voltage tube 200 is omitted and the anode 20 is grounded, the potential difference between the cathode 10 and the voltage tube 200 is increased by 9 times or more, which greatly increases the electric field strength of the filament surface, thereby overcoming the limitation of space charge effect on the beam brightness, and further improving the resolution of the scanning electron microscope 1000.

Referring to fig. 1, in some embodiments, the voltage tube 200 is a continuous structure along the axial direction of the voltage tube 200.

In this manner, the potential at all positions of the voltage tube 200 is equal, so that the energy of the electron beam 30 in the voltage tube 200 is kept at a higher level, thereby reducing aberrations caused by coulomb interactions of the electron beam 30.

When the voltage tube 200 is a discontinuous structure, a metal cover may be sleeved around the voltage tube 200 to prevent electrons from leaking to affect other parts of the sem 1000.

In other embodiments, the voltage tube 200 may be a multi-segment structure, each segment being coaxially disposed to form a continuous channel 300 for the electron beam 30 to pass through, each segment having equal positive potential to ground and being in a vacuum environment; the voltage tube 200 may be connected to the anode 20, or may be connected to another power source;

in other embodiments, the voltage tube 200 may not be under vacuum.

In other embodiments, to avoid external interference and facilitate later installation and maintenance, the voltage tube 200 is hermetically connected between each segment of the structure.

In other embodiments, in order to control other actions of the electron beam 30, the positive ground potential of each segment of the voltage tube 200 is changed according to the corresponding action, or the positive ground potential of each segment of the voltage tube 200 may not be equal.

Referring to fig. 1, in some embodiments, the number of the magnetic lenses 400 is multiple, the magnetic lenses 400 include a first electrical coil 410, a magnetic field generated by the first electrical coil 410 can be controlled by adjusting the magnitude of the current, and the first electrical coil 410 surrounds the voltage tube 200.

In this manner, the plurality of magnetic lenses 400 can compress the electron beam 30 emitted from the tungsten filament electron gun 100 to the sample in multiple stages, so that the source spot (i.e., the electrons initially emitted from the tungsten filament electron gun 100) is converged into an image spot (electron probe beam spot) having a predetermined size.

Specifically, the number of the magnetic lenses 400 may be three, four, five, or more, and the embodiment of the invention does not limit the specific number of the magnetic lenses 400. The number of the magnetic lenses 400 is three, and the three magnetic lenses 400 are arranged up and down along the axial direction of the voltage tube 200. The number of magnetic lenses 400 and the arrangement direction of the magnetic lenses 400 are illustrated only for one illustration, and are not to be construed as limiting the embodiments of the present invention.

Referring to fig. 1, in some embodiments, the sem 1000 further includes an objective lens 600 disposed between the stage 500 and the magnetic lens 400, the objective lens 600 surrounds the voltage tube 200, and a retardation field 700 is formed between an end of the voltage tube 200 away from the w filament electron gun 100 and the objective lens 600.

In this manner, the objective lens 600 can focus the electron beam 30 to obtain a high resolution sample image at a certain focal length. The arrangement of the voltage tube 200 at the objective lens 600 may apply an electric field at the objective lens 600 to improve aberrations such as spherical aberration and chromatic aberration. The retardation field 700 can decelerate the high-energy electron beam 30 within the voltage tube 200 to a lower energy, and the formed retardation lens can improve the aberrations such as spherical aberration and chromatic aberration at a low landing voltage.

In particular, the objective lens 600 may be commercially available or customized, and the embodiment of the present invention does not particularly limit the model of the objective lens 600. The electron beam 30 emitted from the tungsten filament electron gun 100 may contact the sample on the sample stage 500 after being converged by the magnetic lens 400 and focused by the objective lens 600. The objective lens 600 may be composed of a magnetic lens 400, and a scan coil may be disposed in a cavity at the center of the magnetic lens 400, and the scan coil is used to deflect the electron beam 30 and perform a regular scan on the surface of the sample, so as to obtain a related image of the sample. The voltage tube 200 may be disposed around the main optical axis of the objective lens 600. The objective lens 600 includes an upper pole piece 610 and a lower pole piece 620, and a gap exists between the upper pole piece 610 and the lower pole piece 620, and the voltage tube 200 may be partially located in the gap. The deceleration field 700 is an electric field for decelerating the electron beam 30.

Referring to fig. 1, in some embodiments, the objective lens 600 includes a second electrically conductive coil 630 and a metal cover 640 having a C-shaped cross section and having an annular cavity 641, the second electrically conductive coil 630 surrounds the annular cavity 641 of the metal cover 640, a magnetic field formed by the second electrically conductive coil 630 forms a strong magnetic field at an opening of the annular cavity 641 of the C-shaped metal cover 640, the intensity of the magnetic field can be adjusted by adjusting the current of the second electrically conductive coil 630, and the magnetic field can be turned off by turning off the current of the second electrically conductive coil 630.

In this way, the electron beam can be focused by the magnetic field generated by the objective lens 600, and the electron beam 30 can also be focused by the electric field generated by the voltage tube 200.

In particular, the objective lens 600 and the voltage tube 200 herein are in the form of a combination of an electric lens and a lens capable of generating a magnetic field. It will be appreciated that the degree of focus of the electron beam 30, i.e. the spot size of the electron beam 30 falling on the sample, can be adjusted by adjusting the magnitude of the current in the objective lens 600 through the second energized coil 630.

When the voltage tube 200 is not energized and the second energizing coil 630 is energized, the objective lens 600 acts as a lens capable of generating a magnetic field, in which case the electron beam 30 can be focused, and the magnitude of the magnetic field formed by the objective lens 600 can be controlled by adjusting the magnitude of the current of the second energizing coil 630.

When the second electrifying coil 630 is not electrified and the voltage tube 200 is electrified, the objective lens 600 has no magnetic field at this time, so that the electron beam 30 cannot be focused, but the electron beam 30 can be focused according to the decelerating field 700, and at this time, the electric field intensity of the decelerating field 700 can be adjusted by adjusting the voltage of the voltage tube 200, so that the focusing degree of the electron beam 30 can be controlled.

When the second current-carrying coil 630 is energized and the voltage tube 200 is energized, the objective lens 600 and the voltage tube 200 may form a compound form of an electric lens and a lens capable of generating a magnetic field, and in this case, the current magnitude of the second current-carrying coil 630 and/or the potential magnitude of the voltage tube 200 may be adjusted to adjust parameters such as the degree of focusing of the electron beam 30.

Referring to fig. 1, in some embodiments, the metal shield 640 is made of a high magnetic permeability material.

As such, the metal cover 640 made of a high permeability material may direct the magnetic field generated by the second energized coil 630 toward the opening, resulting in a greater magnetic field strength at the opening as compared to a low permeability material.

In particular, metal shield 640 may be a ferromagnetic material, an iron alloy, or other relatively high magnetic permeability material for providing a low reluctance path for the magnetic field generated by second powered coil 630.

Referring to fig. 1, in some embodiments, second energizing coil 630, metal cap 640, and voltage tube 200 are coaxial.

Thus, the electric field and the magnetic field acting on the electron beam 30 are in the same axial direction, and the focusing effect of the electron beam 30 is better.

Referring to fig. 1, in some embodiments, two end edges of the opening of the metal cap 640 extend to an end of the voltage tube 200 away from the tungsten filament electron gun 100 to form an upper pole piece 610 and a lower pole piece 620, respectively, and the magnetic field generated by the second current-carrying coil 630 is guided to the upper pole piece 610 and the lower pole piece 620, so that a strong magnetic field is formed between the upper pole piece 610 and the lower pole piece 620.

In this way, the strong magnetic field formed between the upper pole piece 610 and the lower pole piece 620 can be combined with the electric lens and a lens capable of generating a magnetic field formed between the voltage tube 200, and the focusing degree of the electron beam 30 can be adjusted by adjusting the current passing through the second current-carrying coil 630.

Referring to fig. 1, in some embodiments, a retardation field 700 is formed between the lower pole piece and an end of the voltage tube 200 remote from the tungsten filament electron gun 100 and the objective lens 600.

Thus, the retardation field 700 can decelerate the high-energy electron beam 30 originally in the voltage tube 200 to a lower energy, and the formed retardation lens can improve aberrations such as spherical aberration and chromatic aberration at a low landing voltage.

Specifically, an end of the voltage tube 200 remote from the tungsten filament electron gun 100 may be spaced apart from the lower pole piece 620 of the objective lens 600, and the end of the voltage tube 200 naturally forms an axisymmetric electrode. The lower pole piece 620 is generally grounded, and the electron beam 30 emitted from the tungsten-filament electron gun 100 is negatively charged and receives a force opposite to the direction of the electric field with respect to the electric field generated in the voltage tube 200 and directed toward the sample, and thus reaches the electric field area to be decelerated. The retardation field 700 is thus formed between the axisymmetric electrode and the lower pole piece 620 of the objective lens 600, and the objective lens 600 and the voltage tube 200 therein form a retardation field electric lens.

Further, the magnetic field generated by the magnetic lens 400 near one end of the sample stage 500 and the deceleration field 700 generated by the lower end of the voltage tube 200 and the lower pole piece 620 of the objective lens 600 form a certain overlap region, which is a composite field of the electric field and the magnetic field, so that the magnetic lens 400 and the deceleration field 700 form an electromagnetic composite objective lens. Compared with the magnetic lens 400 without the retardation field 700, the electromagnetic composite objective lens effectively reduces the spherical aberration coefficient and the chromatic aberration coefficient of the objective lens 600, and particularly under the conditions of small distance between a sample and the objective lens 600 and low landing voltage, the effect of reducing the aberration is more remarkable, so that the size of the beam spot of the electron probe is reduced, and the resolution of the scanning electron microscope 1000 is improved.

Referring to fig. 1, in some embodiments, the sem 1000 further includes a detector 800, wherein the detector 800 is configured to detect signal electrons generated by the interaction between the electron beam 30 and the sample.

In this manner, signal electrons generated by the interaction of the electron beam 30 with the sample can be detected by the detector 800.

Specifically, the probe 800 may be disposed inside the voltage tube 200, or may be disposed outside the voltage tube 200. The electron beam 30 interacts with the sample to generate signal electrons, the signal electrons are emitted to various directions, and the detector 800 can detect a part of the signal electrons, and the sample is imaged by synchronizing the signal acquisition timing and the scanning timing. When the distance between the sample and the objective lens 600 is small, most of the signal electrons are attracted by the electric field to move upwards, are focused by the magnetic field and then are dispersed, and about 80-90% of the signal electrons reach the detector 800 in the voltage tube 200.

The dashed arrows in the figure show part of the trajectory of the signal electrons. It should be noted that this is merely an example and should not be construed as limiting the embodiments of the present invention.

Referring to fig. 1, in some embodiments, the detector 800 includes a first detector 810 spaced apart from the sample stage 500, the first detector 810 being disposed on a radial side of the voltage tube 200.

In this manner, the first probe 810 is disposed at one side in the radial direction of the voltage tube 200, which can be more easily installed and maintained.

The term "one side of the voltage tube 200 in the radial direction" refers to the outside of the voltage tube 200, and in combination with the "first detector 810 spaced apart from the sample stage 500", it is understood that the first detector 810 is disposed at the periphery of the sample stage 500 and not inside the voltage tube 200.

Referring to fig. 1, in some embodiments, the detector 800 includes a second detector 820, the second detector 820 is disposed in the voltage tube 200, and the second detector 820 is provided with a through hole 821 for passing the electron beam 30.

In this manner, the second detector 820 is disposed above the objective lens 600, below the magnetic lens 400 near the sample, and is disposed inside the voltage tube 200. On the one hand, when the sample is closer to the objective lens 600, more signal electrons more easily enter the voltage tube 200 and are accelerated to be detected by the second detector 820, so that the signal intensity detected by the second detector 820 is high. On the other hand, the distance between the specimen and the objective lens 600 when observing the specimen can be shortened, and substantially all of the signal electrons generated by the interaction between the electron beam 30 and the specimen surface enter the voltage tube 200 and reach the second detector 820. The collection efficiency of the first detector 810 is typically 15% -30%, and the collection efficiency of the second detector 820 can reach 80% -90%.

Specifically, the signal electrons mostly rise into the voltage tube 200 directly through the pole piece of the objective lens 600 and are accelerated by the electric field to reach the second detector 820, and finally, an image of the sample can be presented. The through hole 821 allows the electron beam 30 to pass through the second probe 820. Compared to the first detector 810, the second detector 820 has higher collection efficiency because the sample corresponding to the second detector 820 can be closer to the objective lens 600.

Compared with the first detector 810, the signal intensity of the second detector 820 is several times higher, and since the compression ratio of the source spot is positively correlated with the beam size, the second detector 820 can be used for imaging under smaller beam, so that the beam spot of the electron probe of the scanning electron microscope 1000 becomes smaller, and the imaging resolution and the imaging quality of the scanning electron microscope 1000 are higher.

It will be appreciated that in a scanning electron microscope 1000 with a tungsten filament as the electron source, a smaller electron probe beam spot relies on higher magnification compression of the tungsten filament electron gun 100, which means a reduction in landing beam current under the constraint that the aperture angle cannot be excessive. The diaphragm is an entity that limits the electron beam 30 in the scanning electron microscope 1000, the diaphragm can filter electrons far from the main optical axis in the electron beam 30, the diaphragm can block part of electrons emitted from the tungsten filament electron gun 100, and the diaphragm can be disposed above the second detector 820, so as to avoid affecting the contact between signal electrons and the second detector 820 and avoid affecting the detection efficiency of the second detector 820. The improvement of the signal electron collection efficiency means that imaging with higher signal-to-noise ratio can be realized by using lower landing beam current, so that a smaller electron probe beam spot can be obtained by increasing the compression ratio of the magnetic lens 400 to the tungsten filament electron gun 100. Meanwhile, the extremely short distance between the sample and the objective lens 600 is beneficial to further reducing the aberration coefficient of the objective lens 600, and the reduction of the aberration coefficient of the objective lens 600 can correspondingly reduce the size of the electron probe beam spot, and the minimum value of the electron probe beam spot determines the limit resolution of the scanning electron microscope 1000.

Referring to fig. 1, in one embodiment, a scanning electron microscope 1000 according to an embodiment of the invention has the following features: firstly, the voltage tube 200 is adjusted to a positive potential of 8kV to 10kV to the ground; secondly, a decelerating field 700 is arranged between one end of the voltage tube 200 far away from the tungsten filament electron gun 100 and a lower pole shoe 620 of the objective lens 600, so that the magnetic lens 400 and the decelerating field 700 form an electromagnetic composite objective lens; finally, a second detector 820 is disposed at a specific location of the channel 300. Combining the above factors, the imaging resolution of the scanning electron microscope 1000 is 1nm-2nm, 2nm-2.5nm, 2.5nm-3.5nm respectively under landing voltages of 30kV, 3kV, 1kV. For comparison, the imaging resolutions of the traditional scanning electron microscope are respectively 3nm, 8nm and 20nm under landing voltages of 30kV, 3kV and 1 kV; the imaging resolution of an entrance-level field emission scanning electron microscope at a landing voltage of 1kV is about 3nm. It can be seen that the resolution and imaging quality of the scanning electron microscope 1000 of the embodiments of the present invention is greatly improved over conventional scanning electron microscopes and is close to that of access gate-level field emission scanning electron microscopes.

For an operating condition with a landing voltage of 1kV, the voltages of the cathode 10 and the voltage tube 200 will increase by more than 9 times compared to when the voltage tube 200 is omitted and the anode 20 is grounded, which greatly increases the electric field strength of the filament surface, and the lower the landing voltage, the greater the improvement factor of the beam brightness by this way. Therefore, at a positive voltage of 8-10kV, the emission surface of the tungsten filament electron gun 100 generates a stronger attractive electric field to overcome the limitation of space charge effect on the beam brightness, thereby improving the imaging resolution of the scanning electron microscope 1000. The arrangement of the retarding field 700 enables the retarding field 700 and the magnetic field generated by the magnetic lens 400 to form an electromagnetic compound objective lens, thereby reducing aberrations such as spherical aberration and chromatic aberration and improving the imaging quality of the scanning electron microscope 1000. The second detector 820 is disposed in the voltage tube 200, so that the detection efficiency of the second detector 820 is improved, the signal intensity detected by the second detector 820 is high, and the resolution and the imaging quality of the scanning electron microscope 1000 are improved.

In some embodiments, the tungsten filament electron gun 100 includes a gun head spaced from the voltage tube 200, the gun head including a cathode 10 and a grid, the gun head being configured to emit an electron beam 30.

Specifically, the grid of the tungsten filament electron gun 100 is used to control the surface electric field intensity of the cathode 10 so as to change the beam size of the electron beam 30 emitted from the cathode 10 of the gun head.

In some embodiments, the upper end of the voltage tube 200 is formed with the anode 20 of the tungsten filament electron gun 100.

Through the anode 20 of the tungsten filament electron gun 100 formed at the upper end of the voltage tube 200, the anode 20 can directly supply power to the voltage tube 200, a large potential difference is formed between the voltage tube 200 and the cathode 10, so that under the same emission beam, the tip surface of the tungsten filament has high field intensity, the electron beam 30 can overcome the suppression of space charge effect on tungsten filament thermionic emission, the beam brightness is remarkably improved, the imaging signal-to-noise ratio is further improved, and the resolution of the scanning electron microscope 1000 based on the tungsten filament as an electron source is improved.

In the description herein, references to the description of the terms "one embodiment," "certain embodiments," "an illustrative embodiment," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

While embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to the 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 scanning electron microscope, comprising:

a magnetic lens surrounding the voltage tube for converging the electron beam;

2. The scanning electron microscope of claim 1, wherein the voltage tube and the tungsten filament electron gun are both in a vacuum environment, and the channel formed in the voltage tube is a vacuum channel.

3. The scanning electron microscope of claim 1, wherein the positive potential is in a range of no less than 8kV.

4. The scanning electron microscope of claim 1, wherein the negative potential is in a range of-100V to-30 kV.

5. The scanning electron microscope of claim 1, wherein the voltage tube is a continuous structure along an axial direction of the voltage tube.

6. The scanning electron microscope of claim 1, wherein the number of the magnetic lenses is plural, the magnetic lenses comprise a first current-carrying coil, the magnetic field generated by the first current-carrying coil can be controlled by adjusting the magnitude of the current, and the first current-carrying coil surrounds the voltage tube.

7. The scanning electron microscope of claim 1, further comprising an objective lens disposed between the sample stage and the magnetic lens, the objective lens surrounding the voltage tube, a retarding field being formed between an end of the voltage tube distal from the tungsten filament electron gun and the objective lens.

8. The SEM according to claim 7, wherein the objective lens comprises a second electrified coil and a metal cover which is C-shaped in cross section and has a ring cavity, the second electrified coil surrounds the ring cavity of the metal cover, the magnetic field formed by the second electrified coil forms a strong magnetic field at the opening of the ring cavity of the metal cover which is C-shaped, the intensity of the magnetic field can be adjusted by adjusting the current of the second electrified coil, and the magnetic field can be closed by closing the current of the second electrified coil.

9. The scanning electron microscope of claim 8, wherein the metal shield is made of a high magnetic permeability material.

10. The scanning electron microscope of claim 8, wherein the second energizing coil, the metal shield, and the voltage tube are coaxial.

11. The scanning electron microscope of claim 8, wherein two end edges of the metal cap at the opening extend to an end of the voltage tube away from the tungsten filament electron gun to form an upper pole piece and a lower pole piece, respectively, and the magnetic field generated by the second electrified coil is guided to the upper pole piece and the lower pole piece, and a strong magnetic field is formed between the upper pole piece and the lower pole piece.

12. The scanning electron microscope of claim 11, wherein the retarding field is formed between the lower pole piece and an end of the voltage tube distal from the tungsten filament electron gun and the objective lens.

13. The scanning electron microscope of claim 1, further comprising a detector for detecting signal electrons generated after the electron beam interacts with the sample.

14. The scanning electron microscope of claim 13, wherein the detector comprises a first detector spaced from the sample stage, the first detector being disposed on a radial side of the voltage tube.

15. A scanning electron microscope according to claim 13 wherein the probe comprises a second probe disposed within the voltage tube, the second probe being provided with a through hole for the passage of the electron beam.