CN218918782U

CN218918782U - Scanning electron microscope

Info

Publication number: CN218918782U
Application number: CN202223123645.3U
Authority: CN
Inventors: 阴达; 张伟; 尹朋飞; 卢志钢
Original assignee: Chinainstru and Quantumtech Hefei Co Ltd
Current assignee: Guoyi Quantum Technology Hefei Co ltd
Priority date: 2022-11-23
Filing date: 2022-11-23
Publication date: 2023-04-25
Anticipated expiration: 2032-11-23

Abstract

The utility model discloses a scanning electron microscope, which comprises a tungsten filament electron gun, a voltage tube, a sample stage and an objective lens. The tungsten filament electron gun comprises a cathode, wherein the cathode is connected with a negative potential; the negative potential is a negative voltage to ground; the voltage tube and the tungsten filament electron gun are arranged at intervals, a channel is formed in the voltage tube, the channel is used for passing electron beams emitted by the tungsten filament electron gun, the voltage tube comprises a first voltage tube and a second voltage tube which are arranged at intervals, and potential difference is formed between the first voltage tube and the second voltage tube so as to converge the electron beams; the sample platform is arranged at one side of the voltage tube, which is away from the tungsten filament electron gun, and is used for bearing a sample. The objective lens is arranged between the sample stage and the voltage tube, and the objective lens is arranged around the voltage tube. A larger electric field is formed between the first voltage tube and the cathode, so that the limitation of space charge effect on beam brightness is overcome, and the resolution of a scanning electron microscope is further improved.

Description

Scanning electron microscope

Technical Field

The utility model 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 an electron beam probe which is converged into a very fine shape, collects signal electrons generated after the interaction of an electron beam and the sample, and realizes 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 current is generally adjustable in the range below 30kV. Among them, the low landing voltage condition below 3kV is one of the most important and widely used operating conditions. However, at low landing voltages, the brightness of the electron beam, chromatic aberration from astigmatism, and diffraction aberrations limit the imaging resolution of a scanning electron microscope. The electron sources of a scanning electron microscope can be classified into a thermal emission electron source and a field emission electron source according to emission mechanisms. Wherein the tungsten filament electron gun is a heat emission electron source, and the working temperature of the tungsten filament is in the range of 2600K to 2800K. The resolution bottleneck of a tungsten filament scanning electron microscope is mainly limited by factors such as beam brightness, chromatic aberration and the like. The existing tungsten filament scanning electron microscope has lower resolution at low landing voltage.

Disclosure of Invention

The utility model provides a scanning electron microscope.

The scanning electron microscope according to an embodiment of the present utility model includes:

the tungsten filament electron gun comprises a cathode and an anode, wherein the cathode is connected with a negative potential, and the negative potential is 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, the channel is used for passing electron beams emitted by the tungsten filament electron gun, the voltage tube comprises a first voltage tube and a second voltage tube which are arranged at intervals, the first voltage tube is connected with a positive potential, the positive potential is positive to the ground, the second voltage tube is any potential which is higher than a negative potential of a cathode but different from the first voltage tube, and a potential difference is formed between the first voltage tube and the second voltage tube so as to converge the electron beams;

the sample table 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;

and the objective lens is arranged between the sample table and the voltage tube, and the objective lens is arranged around the voltage tube.

In the scanning electron microscope of the embodiment of the utility model, 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 filament tip 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 remarkably improving the beam brightness and further improving the resolution of the scanning electron microscope based on the tungsten filament as an electron source. At the same time, the electron beam can be focused by the magnetic field generated by the objective lens.

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 some embodiments, the number of the first voltage tubes and/or the second voltage tubes is plural, and the first voltage tubes and the second voltage tubes are alternately arranged in the direction of the vacuum channel.

In some embodiments, the number of the first voltage tubes is two, the number of the second voltage tubes is one, and the second voltage tubes are disposed between the two first voltage tubes.

In some embodiments, the range of positive potential of the first voltage tube is not less than 8kV.

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

In some embodiments, a deceleration field is formed between the objective lens and an end of the voltage tube away from the tungsten filament electron gun along the axial direction of the voltage tube.

In some embodiments, the objective lens comprises an energizing coil and a metal cover with a C-shaped section and an annular cavity, the energizing coil surrounds the annular cavity of the metal cover, a magnetic field formed by the energizing coil forms a strong magnetic field at an opening of the annular cavity of the C-shaped metal cover, the intensity of the magnetic field can be adjusted by adjusting the current of the energizing coil, and the magnetic field can be turned off by turning off the current of the energizing coil.

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

In some embodiments, the energizing coil, the metal cover, and the voltage tube are coaxial.

In some embodiments, two end edges of the opening of the metal cover extend to one end, far away from the tungsten filament electron gun, of the voltage tube respectively to form an upper pole shoe and a lower pole shoe, a magnetic field generated by the energizing 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 deceleration field is formed between the lower pole piece and the objective lens and between an end of the voltage tube remote from the tungsten filament electron gun.

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

In some embodiments, the detector includes a first detector disposed spaced apart from the sample stage, the first detector being disposed on a radial 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 electron beam to pass through.

Additional aspects and advantages of the utility model 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 utility model.

Drawings

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

fig. 1 is a schematic view of a scanning electron microscope according to an embodiment of the present utility model.

Description of main reference numerals: a scanning electron microscope 1000; tungsten filament electron gun 100; a cathode 10; an anode 20; a voltage tube 200; a first voltage tube 210; a second voltage tube 220; a channel 300; an electron beam 30; a sample stage 500; an objective lens 600; energizing coil 630; a metal cover 640; an annular cavity 641; an upper pole piece 610; a lower pole piece 620; a deceleration field 700; a detector 800; a first detector 810; a second detector 820; and a through hole 821.

Detailed Description

Embodiments of the present utility model are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary only for explaining the present utility model and are not to be construed as limiting the present utility model.

In the description of the present utility model, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings are merely for convenience in describing the present utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present utility model. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more of the described features. In the description of the present utility model, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.

In the description of the present utility model, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically connected, electrically connected or can be communicated with each other; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the above terms in the present utility model can be understood by those of ordinary skill in the art according to the specific circumstances.

In the present utility model, unless expressly stated or limited otherwise, a first feature "above" or "below" a second feature may include both the first and second features being in direct contact, as well as the first and second features not being in direct contact but being in contact with each other through additional features therebetween. Moreover, a first feature being "above," "over" and "on" a second feature includes the first feature being directly above and obliquely above the second feature, or simply indicating that the first feature is higher in level than the second feature. The first feature being "under", "below" and "beneath" the second feature includes the first feature being directly under and obliquely below the second feature, or simply means that the first feature is less level than the second feature.

The following disclosure provides many different embodiments, or examples, for implementing different features of the utility model. In order to simplify the present disclosure, components and arrangements of specific examples are described below. They are, of course, merely examples and are not intended to limit the utility model. Furthermore, the present utility model may repeat reference numerals and/or letters in the various examples, which are for the purpose of brevity and clarity, and which do not themselves indicate the relationship between the various embodiments and/or arrangements discussed. In addition, the present utility model provides examples of various specific processes and materials, but one of ordinary skill in the art will recognize the application of other processes and/or the use of other materials.

Referring to fig. 1, a scanning electron microscope 1000 according to an embodiment of the present utility model includes a tungsten filament electron gun 100, a voltage tube 200, a sample stage 500, and an objective lens 600. The tungsten filament electron gun 100 comprises a cathode 10, wherein the cathode 10 is connected with a negative potential; the negative potential is a negative voltage to ground; the voltage tube 200 and the tungsten filament electron gun 100 are arranged at intervals, a channel 300 is formed in the voltage tube, the channel 300 is used for passing an electron beam 30 emitted by the tungsten filament electron gun 100, the voltage tube 200 comprises a first voltage tube 210 and a second voltage tube 220 which are arranged at intervals, the first voltage tube is connected with a positive potential, the positive potential is positive to the ground, the second voltage tube is any potential which is higher than negative potential of a cathode but different from the first voltage tube, and a potential difference is formed between the first voltage tube 210 and the second voltage tube 220 so as to converge the electron beam 30; the sample stage 500 is arranged on one side of the voltage tube 200 away from the tungsten filament electron gun 100 and is used for carrying a sample; the objective lens 600 is disposed between the sample stage 500 and the voltage tube 200, and the objective lens 600 is disposed around the voltage tube 200.

In the scanning electron microscope 1000 according to the embodiment of the present utility model, the first voltage tube 210 is connected to the anode 20 of the tungsten filament electron gun 100, and a larger electric field is formed between the first voltage tube 210 and the cathode 10, so that the surface of the tungsten filament electron gun 100 has a higher field strength, thereby overcoming the suppression of space charge effect on thermionic emission of the tungsten filament, that is, overcoming the limitation of space charge effect on beam brightness, so as to significantly improve beam brightness, and further improve the resolution of the scanning electron microscope 1000 based on the tungsten filament as an electron source. Meanwhile, a potential difference is formed between the first voltage tube 210 and the second voltage tube 220 to converge the electron beam 30, and a magnetic field generated by the objective lens 600 can focus the electron beam 30 without using other devices to converge the electron beam 30.

Specifically, the tungsten filament electron gun 100 may be used to emit tungsten filament hot electrons, and the minimum value of electron probe beam spots 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 ultimate resolution and imaging quality of the scanning electron microscope 1000.

The cathode 10 of the electron gun 100 with tungsten filament may have a negative voltage of 1kV, 2kV, etc. to the ground, and since the sample stage 500 is generally at the same voltage as the ground, the negative voltage of the cathode 10 to the ground corresponds to the energy of the hot electrons of the tungsten filament landing on the sample. The anode 20 of the tungsten filament electron gun 100 may be at a positive voltage of 8kV-10kV to ground.

The channel 300 may be formed in the voltage tube 200. An electron beam 30 from a tungsten 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 with a positive potential, so that the electric field intensity of the tip surface of the tungsten filament is enhanced, and the suppression of space charge effect on thermionic emission of the tungsten filament is overcome, namely the limitation of space charge effect on beam brightness is overcome, so that the beam brightness is remarkably improved, and the resolution of the scanning electron microscope 1000 based on the tungsten filament as an electron source is further improved. Meanwhile, the channel 300 in the voltage tube 200 forms an electric field, electrons have higher energy and lower space charge density when the segment flies, so that the effect of energy dispersion increase (Boersch effect) caused by coulomb interaction between electrons is reduced, the monochromaticity of electron beams is improved, and the imaging resolution of the scanning electron microscope 1000 under low pressure is improved.

A potential difference can be formed between the first voltage tube 210 and the second voltage tube 220 by connecting different power sources. For example, the first voltage tube 210 may be connected to the anode 20, the first voltage tube 210 may be a positive voltage of 8kV to ground, the second voltage tube 220 may be connected to another power source, and the second voltage tube 220 may be a positive voltage of 10kV to ground. In this way, a potential difference is formed between the first voltage tube 210 and the second voltage tube 220, that is, an electric field is formed between the first voltage tube 210 and the second voltage tube 220, so that the electron beam 30 is converged when the electron beam 30 passes through the channel 300.

Sample stage 500 is a platform for carrying a sample that may be secured to sample stage 500 such that electron beam 30 may scan a particular surface of the sample.

The objective lens 600 may be commercially available or custom made, and embodiments of the present utility model are not particularly limited to 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 convergence of the voltage tube 200 and focusing of the objective lens 600. The objective lens 600 may be composed of a magnetic lens, and a scanning coil may be disposed in a receiving cavity in the center of the magnetic lens, and the scanning coil is used to deflect the electron beam 30 and perform regular scanning 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.

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.

In this way, the propagation obstruction of the electron beam 30 in the voltage tube 200 is low compared to the non-vacuum environment, and therefore the beam brightness of the electron beam 30 is hardly lowered.

Referring to fig. 1, in some embodiments, the number of the first voltage tubes 210 and/or the second voltage tubes 220 is plural, and the first voltage tubes 210 and the second voltage tubes 220 are alternately arranged along the direction of the channel 300.

As such, the first and

second voltage tubes

210 and 220 are alternately arranged in the direction of the channel 300 such that a plurality of regions having different potential differences may be formed between the first and

second voltage tubes

210 and 220, thereby forming the multi-stage voltage tube 200, so that the electron beam 30 may be condensed multiple times in the channel 300.

Specifically, the first voltage tube 210 may be one, two, three, or more, and the second voltage tube 220 may be one, two, three, or more.

Referring to fig. 1, in some embodiments, the number of the first voltage tubes 210 is two, the number of the second voltage tubes 220 is one, and the second voltage tubes 220 are disposed between the two first voltage tubes 210.

In this way, a potential difference may be formed between the second voltage tube 220 and one voltage tube, and a potential difference may also be formed between the second voltage tube 220 and the other voltage tube, so that two regions having different potential differences may be formed between the first voltage tube 210 and the second voltage tube 220, thereby forming the secondary voltage tube 200, so that the electron beam 30 may be secondarily condensed in the channel 300. For example, both first voltage tubes 210 are at a positive potential of 10kV to ground and the second voltage tube 220 is at a positive potential of 8kV to ground, each first voltage tube 210 forms a potential difference with respect to the second voltage tube 220, so that the electron beam 30 in the channel 300 can be condensed.

Referring to fig. 1, in some embodiments, the positive potential to which the voltage tube 200 is connected is in a range of not less than 8kV. When the positive potential is less than 8kV, the effect of space charge effect becomes more remarkable along with the reduction of positive voltage, and the inhibition effect on the surface emission of the filament tip is enhanced, so that the brightness of the beam current is reduced; at the same time, the coulomb interaction of electrons in the flight process of the channel 300 is enhanced, the electron energy distribution is widened, the 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 of the surface of the filament tip of the tungsten filament electron gun 100 is high, so that the suppression of space charge effect on emission can be overcome, the coulomb interaction in the electron beam 30 is lightened, the beam brightness is improved, and the energy dispersion is reduced.

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

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

For an operating condition with a landing voltage of 1kV, the potential difference between the cathode 10 to 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 to the ground is applied to the first 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 intensity of the filament surface, thereby overcoming the limitation of space charge effect on beam brightness and further improving the resolution of the scanning electron microscope 1000.

Referring to fig. 1, in some embodiments, a deceleration field 700 is formed between an end of the voltage tube 200 away from the tungsten filament electron gun 100 and the objective lens 600 along an axial direction of the voltage tube 200.

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

Specifically, the deceleration field 700 is an electric field for decelerating the electron beam 30, and the electron beam 30 emitted from the tungsten filament electron gun 100 is negatively charged with respect to the electric field generated in the voltage tube 200 and receives a force opposite to the direction of the electric field, and thus reaches the electric field region to be decelerated.

Referring to fig. 1, in some embodiments, an objective lens 600 includes an energizing coil 630 and a metal cover 640 having a C-shaped cross section and an annular cavity 641, the energizing coil 630 surrounds the annular cavity 641 of the metal cover 640, a magnetic field formed by the energizing 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 energizing coil 630, and the magnetic field can be turned off by turning off the current of the energizing coil 630.

Thus, the magnetic field generated by the objective lens 600 can focus the electron beam, and the electric field generated by the voltage tube 200 can also focus the electron beam 30.

Specifically, the objective lens 600 and the voltage tube 200 herein are in the form of an electric lens and a lens capable of generating a magnetic field. It will be appreciated that the degree of focusing of the electron beam 30, i.e. the spot size of the electron beam 30 falling on the sample, may be adjusted by adjusting the amount of current in the objective lens 600 through the energizing coil 630.

When the voltage tube 200 is not voltage and the energizing coil 630 is energized, the objective lens 600 corresponds to a lens capable of generating a magnetic field, at this time, 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 energizing coil 630.

When the energizing coil 630 is not energized and the voltage tube 200 is energized, the objective lens 600 has no magnetic field, so that the electron beam 30 cannot be focused, but the electron beam 30 can be focused according to the retarding field 700, and at this time, the electric field intensity of the retarding 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 power-on coil 630 is powered on and the voltage tube 200 is powered on, the objective lens 600 and the voltage tube 200 may form a composite form of an electric lens and a lens capable of generating a magnetic field, and at this time, the current magnitude of the power-on coil 630 and/or the potential magnitude of the voltage tube 200 may be adjusted to adjust parameters such as the focusing degree of the electron beam 30.

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

In this manner, the metal cover 640 made of the high magnetic permeability material can guide the magnetic field generated by the energizing coil 630 to the opening, compared to the low magnetic permeability material, so that the magnetic field intensity at the opening is larger.

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

Referring to fig. 1, in some embodiments, the energizing coil 630, the metal cover 640, and the 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 edges of the opening of the metal cover 640 extend to the ends of the voltage tube 200, which are far away from the tungsten filament electron gun 100, respectively, to form an upper pole piece 610 and a lower pole piece 620, respectively, and the magnetic field generated by the energizing coil 630 is conducted 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.

Thus, the formation of a strong magnetic field between the upper pole piece 610 and the lower pole piece 620 may form a complex form with the electric lens and a magnetic field generation between the voltage tube 200, and at this time, the degree of focusing of the electron beam 30 may be adjusted by adjusting the magnitude of the current passing through the energizing coil 630.

Referring to fig. 1, in some embodiments, a deceleration field 700 is formed between an end of the voltage tube 200 remote from the tungsten filament electron gun 100 and a lower pole piece 610 of the objective lens 600 along an axial direction of the voltage tube 200.

In this way, the deceleration field 700 can decelerate the original high-energy electron beam 30 in the voltage tube 200 to a lower energy, and the formed deceleration lens can improve the aberration such as spherical aberration and chromatic aberration at 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 610 of the objective lens 600, the end of the voltage tube 200 naturally forming an axisymmetric electrode. The lower pole piece 620 is typically grounded, and the electron beam 30 emitted from the tungsten filament electron gun 100 is negatively charged with respect to the electric field generated in the voltage tube 200 in the direction of the sample, and is subjected to a force opposite to the direction of the electric field, so that it reaches the electric field region and is decelerated. The axisymmetric electrode thus forms a retarding field 700 with the lower pole piece 610 of the objective lens 600, and the objective lens 600 and the voltage tube 200 therein form a retarding field lens.

Further, the magnetic field generated from the objective lens 600 near one end of the sample stage 500 forms a certain overlap region with the deceleration field 700 generated from the lower end of the voltage tube 200 and the lower pole piece 620 of the objective lens 600, and the overlap region is a composite field of the electric field and the magnetic field, so that the objective lens 600 and the deceleration field 700 form an electromagnetic composite objective lens. Compared with the objective lens 600 without the deceleration field 700, the electromagnetic compound 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 reduction effect of the aberration is more remarkable, so that the size of the beam spot of the electronic probe is reduced, and the resolution of the scanning electron microscope 1000 is further improved.

Referring to fig. 1, in some embodiments, the scanning electron microscope 1000 further includes a detector 800, where the detector 800 is configured to detect signal electrons generated by the interaction of the electron beam 30 with the sample.

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

Specifically, the detector 800 may be disposed inside the voltage tube 200 or may be disposed outside the voltage tube 200. After the electron beam 30 interacts with the sample, signal electrons are generated, the signal electrons are emitted to all directions, and the detector 800 can detect a part of the signal electrons, so that the imaging of the sample is realized through synchronization of a signal acquisition time sequence and a scanning time sequence. 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, and are focused by the magnetic field to be dispersed again, and about 80-90% of the signal electrons reach the detector 800 in the voltage tube 200.

The dashed arrow in the figure shows part of the trajectory of the signal electrons. It should be noted that this is only an illustration, and is not to be construed as limiting the embodiments of the present utility model.

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

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

"one radial side of the voltage tube 200" refers to the exterior of the voltage tube 200, and in combination with "the first detector 810 is 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 being disposed in the voltage tube 200, the second detector 820 being provided with a through hole 821 through which the electron beam 30 passes.

Thus, the second detector 820 is disposed above the objective lens 600, below the objective lens 600 near the sample, and is disposed within the voltage tube 200. On the one hand, as the sample is closer to the objective lens 600, more signal electrons more easily enter the voltage tube 200 and are accelerated, so as 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 sample and the objective lens 600 can be shortened when observing the sample, and the signal electrons generated by the interaction between the electron beam 30 and the sample 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 be up to 80% -90%.

Specifically, most of the signal electrons rise into the voltage tube 200 directly through the pole shoe of the objective lens 600 and reach the second detector after being accelerated by the electric field, and finally, an image of the sample can be presented. The through hole 821 allows the electron beam 30 to pass through the second detector 820. Since the second detector 820 corresponds to a sample and the objective lens 600 may be closer in distance than the first detector 810, the collection efficiency of the second detector 820 is higher.

Compared with the first detector 810, the signal intensity of the second detector 820 is several times higher, and because the compression ratio of the source spot is positively correlated with the beam current, the second detector 820 can be used for imaging under a smaller beam current, so that the beam spot of the electron probe of the scanning electron microscope 1000 is 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, smaller electron probe beam spots rely on higher magnification compression of the tungsten filament electron gun 100, which in limiting conditions where the aperture angle cannot be excessive, means a reduction in landing beam. The diaphragm is an entity in the scanning electron microscope 1000 that limits the electron beam 30, and can filter electrons far away from the main optical axis in the electron beam 30, and can shield part of electrons emitted from the tungsten filament electron gun 100, and can be disposed above the second detector 820, so as to avoid affecting signal electrons to contact with the second detector 820 and avoid affecting 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, so that smaller electron probe beam spots can be obtained by increasing the compression ratio of the voltage tube 200 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, the size of the electron probe beam spot can be correspondingly reduced by reducing the aberration coefficient of the objective lens 600, and the minimum value of the electron probe beam spot determines the ultimate resolution and the imaging quality of the scanning electron microscope 1000.

Referring to fig. 1, in a specific embodiment, a scanning electron microscope 1000 according to an embodiment of the present utility model has the following features: firstly, the voltage tube 200 is adjusted to be at a positive potential of 8kV to 10kV relative to the ground; secondly, a deceleration field 700 is arranged between one end of the voltage tube 200 far away from the tungsten filament electron gun 100 and the lower pole piece 610 of the objective lens 600, so that the voltage tube 200 and the deceleration field 700 form an electromagnetic composite objective lens; finally, a second detector 820 is arranged at a specific position of the channel 300. By combining the above factors, the imaging resolution of the scanning electron microscope 1000 is 1nm-2nm, 2nm-2.5nm, 2.5nm-3.5nm at landing voltages of 30kV, 3kV, 1kV, respectively. By contrast, at landing voltages of 30kV, 3kV and 1kV, the imaging resolutions of the traditional scanning electron microscope are 3nm, 8nm and 20nm respectively; the imaging resolution of an entry 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 embodiment of the present utility model are greatly improved over conventional scanning electron microscopes and are close to those of the portal field emission scanning electron microscope.

For an operating condition with a landing voltage of 1kV, the voltage of the cathode 10 and the anode 20 will be increased 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 larger the improvement factor of the beam brightness by this means. Therefore, at a positive voltage of 8-10kV, a stronger attractive electric field is generated on the emission surface of the tungsten filament electron gun 100 to overcome the limitation of space charge effect on beam brightness, thereby improving the imaging resolution of the scanning electron microscope 1000. The arrangement of the retarding field 700 causes the retarding field 700 and the magnetic field generated by the objective lens 600 to form an electromagnetic compound objective lens, thereby reducing aberration 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, and the signal intensity detected by the second detector 820 is high, thereby improving the resolution and imaging quality of the scanning electron microscope 1000.

Referring to fig. 1, in some embodiments, a tungsten filament electron gun 100 includes a gun head spaced from a voltage tube 200, the gun head including a cathode 10 and a grid, the gun head for emitting an electron beam 30.

Specifically, the grid electrode 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 current size of the electron beam 30 emitted from the cathode 10 of the gun head.

Referring to fig. 1, in some embodiments, an anode 20 of a tungsten filament electron gun 100 is formed at an upper end of a voltage tube 200.

The anode 20 of the tungsten filament electron gun 100 formed at the upper end of the voltage tube 200 can directly supply power to the voltage tube 200, a larger potential difference is formed between the voltage tube 200 and the cathode 10, so that the tip surface of the tungsten filament has higher field strength under the same emission beam flow, the electron beam 30 can overcome the suppression of space charge effect on the thermionic emission of the tungsten filament, the beam brightness is obviously 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 of the present specification, reference to the terms "one embodiment," "certain embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples," etc., means 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 utility model. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiments or examples. 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 utility model have been shown and described, it will be understood by those of ordinary skill in the art that: many changes, modifications, substitutions and variations may be made to the embodiments without departing from the spirit and principles of the utility model, the scope of which is defined by the claims and their equivalents.

Claims

1. A scanning electron microscope, comprising:

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

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

3. The scanning electron microscope of claim 2 wherein the number of first voltage tubes and/or the second voltage tubes is plural, the first voltage tubes and the second voltage tubes being alternately arranged in the direction of the vacuum channel.

4. A scanning electron microscope according to claim 3 wherein the number of first voltage tubes is two and the number of second voltage tubes is one, the second voltage tubes being arranged between two of the first voltage tubes.

5. The scanning electron microscope of claim 1 wherein the positive potential is in the range of not less than 8kV.

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

7. The scanning electron microscope of claim 1 wherein a deceleration field is formed between the objective lens and an end of the voltage tube remote from the tungsten filament electron gun along an axial direction of the voltage tube.

8. The electron microscope of claim 1, wherein the objective lens comprises an energizing coil and a metal cover with a C-shaped cross section and an annular cavity, the energizing coil surrounds the annular cavity of the metal cover, a magnetic field formed by the energizing coil forms a strong magnetic field at an opening of the annular cavity of the C-shaped metal cover, the magnetic field strength can be adjusted by adjusting the current of the energizing coil, and the magnetic field can be turned off by turning off the current of the energizing coil.

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

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

11. The electron microscope of claim 8, wherein edges of two ends of the opening of the metal cover extend to one end of the voltage tube, which is far away from the tungsten filament electron gun, respectively, to form an upper pole shoe and a lower pole shoe, respectively, and a magnetic field generated by the energizing 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.

12. The electron microscope of claim 11, wherein a deceleration field is formed between the lower pole piece and the end of the voltage tube remote 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 upon interaction of the electron beam with the sample.

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

15. The scanning electron microscope of claim 13 wherein the detector comprises a second detector disposed within the voltage tube, the second detector being provided with a through hole for the electron beam to pass through.