A scanning electron microscope vacuum system

Abstract

The present invention relates to the field of microscope technology, and discloses a scanning electron microscope vacuum system, comprising: an electron gun; a lens barrel connected to the electron gun through a first valve; a sample chamber connected to the lens barrel through a sixth valve; a molecular pump first air inlet connected to the electron gun, and a second air inlet connected to the lens barrel through a fifth valve; a molecular pump connected to the sample chamber through a fourth valve; a mechanical pump connected to the sample chamber through a third valve; the scanning electron microscope vacuum system has a low vacuum mode in which the fourth valve and the sixth valve are closed, and the first valve, the third valve, and the fifth valve are opened; and a high vacuum mode in which the third valve and the fifth valve are closed, and the first valve, the fourth valve, and the sixth valve are opened. The scanning electron microscope vacuum system of the present application can be freely switched between the low vacuum mode and the high vacuum mode; and the scanning electron microscope vacuum system of the present application uses as few components as possible, has low cost, reduces volume, and saves space.

Description

Technical Field

[0001] The present invention relates to the technical field of microscopes, in particular to a vacuum system for a scanning electron microscope. Background Art

[0002] A scanning electron microscope (SEM), also known as a scanning electron microscope (SEM), is a high-resolution microscope. It can obtain high-definition images by scanning the sample surface with an electron beam. Specifically, a focused electron beam is used to scan the sample surface line by line in a vacuum environment. The focused electron beam bombards the sample surface, generating secondary electrons or backscattered electrons. The efficiency of generating secondary electrons or backscattered electrons is related to the surface morphology or material of the sample. The secondary electrons or backscattered electrons generated on the sample surface are collected, and the position of the sample surface scanned by the focused electron beam and the number of secondary electrons or backscattered electrons generated are expressed in the form of a two-dimensional image. This results in a secondary electron image or backscattered electron image of the SEM. After magnifying the secondary electron image or backscattered electron image by thousands to hundreds of thousands of times, the surface image of the sample can be observed, thereby achieving the purpose of observing the sample's microscopic morphology.

[0003] Conventional scanning electron microscopes typically operate only in high-vacuum mode. The electron optical tube and sample chamber must be in a high-vacuum environment, and the sample must be free of water and electricity. Otherwise, charging effects can easily occur during observation of the sample's microscopic morphology, causing image drift and distortion, seriously affecting observation and even making the image difficult to see clearly. Therefore, non-conductive samples must be treated with a conductive coating before observation. This is usually done by spraying a conductive film on the sample surface to remove excess electrons from the sample.

[0004] Low-vacuum SEMs, operating in low-vacuum mode, can neutralize the generated charge using ionized ions or gas molecules, eliminating the charging effect without coating the sample with a conductive coating. For aqueous and non-conductive samples, such as biological samples, low-vacuum SEMs enable observation of secondary and backscattered electrons without the need for a conductive coating, maintaining the sample's essential structure and enabling rapid imaging.

[0005] The present application proposes a novel scanning electron microscope vacuum system that is different from the existing scanning electron microscope vacuum system structure, so as to reduce the number of components used, reduce the volume and lower the cost. Summary of the Invention

[0006] In view of this, the present invention provides an improved scanning electron microscope vacuum system, which is different from the structure of the existing scanning electron microscope vacuum system, so as to reduce the number of components used, reduce the volume and lower the cost.

[0007] The present invention provides a vacuum system for a scanning electron microscope, comprising:

[0008] electron gun;

[0009] a lens barrel connected to the electron gun via a first valve;

[0010] A first differential pressure diaphragm is provided between the sample chamber and the lens barrel; the sample chamber and the lens barrel are connected via a sixth valve;

[0011] A molecular pump, wherein the first air inlet is connected to the electron gun, the second air inlet of the molecular pump is connected to the lens barrel through a fifth valve; and the molecular pump is connected to the bottom of the sample chamber through a fourth valve;

[0012] a mechanical pump connected to the sample chamber via a third valve;

[0013] The vacuum system of the scanning electron microscope has a low vacuum mode in which the fourth valve and the sixth valve are closed and the first valve, the third valve and the fifth valve are opened; and a high vacuum mode in which the third valve and the fifth valve are closed and the first valve, the fourth valve and the sixth valve are opened; in the low vacuum mode, the vacuum degree in the electron gun is less than 5×e -3 Pa, the vacuum degree in the lens barrel is greater than 1×e -2 Pa, and the vacuum degree in the lens barrel is less than 1Pa, the vacuum degree in the sample chamber is greater than 1Pa, and the vacuum degree in the sample chamber is less than 1000Pa; in high vacuum mode, the vacuum degree in the electron gun, the vacuum degree in the lens barrel, and the vacuum degree in the sample chamber are all less than 5×e -3 Pa. Beneficial effects: The scanning electron microscope vacuum system described in the present application can be freely switched between low vacuum mode and high vacuum mode; and, the scanning electron microscope vacuum system described in the present application uses as few devices as possible, has low cost, reduces volume, saves space, saves materials and costs. In low vacuum mode, the vacuum pressure in the sample chamber described in the present application has a larger adjustment range and wider adaptability. At the same time, by setting the first pressure difference diaphragm, in low vacuum mode, the pressure difference between the sample chamber and the lens barrel is as small as possible, and the diaphragm size is large enough, so that the total pressure difference between the sample chamber and the lens barrel is large, ensuring that the medium vacuum state of the lens barrel and the low vacuum state of the sample chamber can work at the same time.

[0014] Optionally, the first pressure difference diaphragm is located below the objective lens provided at the bottom of the lens barrel. Beneficial Effect: This application adopts the above technical solution, and by arranging the first pressure difference diaphragm at the bottom of the lens barrel, the distance that the focused electron beam passes through the high-pressure section is reduced, thereby preventing most electrons reaching the sample from being scattered, thereby ensuring the quality of the image subsequently obtained.

[0015] Optionally, it also includes:

[0016] a seventh valve connected to the sample chamber, and inputting gas into the sample chamber through the seventh valve;

[0017] a second vacuum gauge connected to the sample chamber, wherein the second vacuum gauge is suitable for obtaining the vacuum degree in the sample chamber in real time;

[0018] The controller is connected to the seventh valve and the second vacuum gauge by signal; in the low vacuum mode, the controller is suitable for comparing the vacuum setting value with the actual vacuum in the sample chamber obtained by the second vacuum gauge to obtain an error signal, and then the error signal is processed by the PID link to obtain a control signal, and the opening of the seventh valve is controlled in real time by the control signal to control the gas flow input into the sample chamber so that the actual vacuum in the sample chamber is equal to the vacuum setting value. Beneficial effect: The present application adopts the above technical solution. In the low vacuum mode, the stabilization time of the vacuum pressure in the sample chamber after adjustment is short, which significantly improves the operating efficiency.

[0019] Optionally, the seventh valve is a vacuum proportional valve.

[0020] Optionally, a second pressure differential diaphragm is provided between the electron gun and the lens barrel. Beneficial Effect: This application adopts the above technical solution and further provides a second pressure differential diaphragm. In the low vacuum mode, the pressure differential between the electron gun and the lens barrel is as small as possible, while having a sufficiently large diaphragm size. This results in a large total pressure differential between the electron gun and the lens barrel, ensuring that the medium vacuum state of the lens barrel and the high vacuum state of the electron gun can operate simultaneously; at the same time, it ensures that the low vacuum state of the sample chamber and the high vacuum state of the electron gun can operate simultaneously.

[0021] Optionally, it also includes:

[0022] An eighth valve is connected to the sample chamber. When the sample in the sample chamber is replaced, the eighth valve is opened to deflate the sample chamber. In the low vacuum mode and the high vacuum mode, the eighth valve is in a closed state.

[0023] Optionally, the gas in the sample chamber is nitrogen.

[0024] Optionally, the mechanical pump is connected to the exhaust port of the molecular pump via a second valve; in the low vacuum mode and the high vacuum mode, the second valve is in an open state.

[0025] Optionally, it also includes:

[0026] The first vacuum gauge is connected to the electron gun and is suitable for obtaining the vacuum degree in the electron gun in real time.

[0027] Optionally, the first valve, the third valve, the fourth valve, the fifth valve and the sixth valve are all vacuum isolation valves. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 A schematic diagram of the connection of a vacuum system for a scanning electron microscope provided in an embodiment of the present invention;

[0030] Figure 2 Schematic diagram of the closed-loop control principle for adjusting the vacuum degree in the sample chamber in a low vacuum mode provided in an embodiment of the present invention.

[0031] Description of reference numerals:

[0032] 1. Electron gun; 2. Mirror tube; 3. First valve; 4. Sample chamber; 5. First differential pressure diaphragm; 6. Second valve; 7. Third valve; 8. Fourth valve; 9. Fifth valve; 10. Sixth valve; 11. Seventh valve; 12. Eighth valve; 13. Molecular pump; 14. First vacuum gauge; 15. Second vacuum gauge; 16. PID link; 17. Second differential pressure diaphragm; 18. Mechanical pump. DETAILED DESCRIPTION

[0033] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0034] Existing low-vacuum scanning electron microscope (SEM) vacuum systems are relatively complex, typically including a large number of vacuum pumps, vacuum valves, and vacuum gauges, resulting in high costs. The adjustable range of vacuum pressure is narrow, and the stabilization time after vacuum pressure adjustment is long. For these reasons, the present application proposes an improved SEM vacuum system.

[0035] like Figures 1 to 2 A specific embodiment of a scanning electron microscope vacuum system is shown, comprising: an electron gun 1, a lens barrel 2, a sample chamber 4, a molecular pump 13, and a mechanical pump 18. The scanning electron microscope vacuum system described herein can be used in a low-vacuum scanning electron microscope, operating in both low-vacuum and high-vacuum modes. The lens barrel 2 is an electron optical lens barrel.

[0036] like Figure 1 As shown, the lens barrel 2 is connected to the electron gun 1 via a first valve 3. A first differential pressure stop 5 is provided between the sample chamber 4 and the lens barrel 2; the sample chamber 4 and the lens barrel 2 are connected via a sixth valve 10. The first air inlet of the molecular pump 13 is connected to the electron gun 1. The first air inlet is the upper air inlet of the molecular pump 13 and is connected to the electron gun 1 via a pipe. The second air inlet of the molecular pump 13 is connected to the lens barrel 2 via a fifth valve 9; the second air inlet is the middle air inlet of the molecular pump 13 and is connected to the lens barrel 2 via a pipe through the fifth valve 9. The molecular pump 13 is connected to the bottom of the sample chamber 4 via a fourth valve 8. The mechanical pump 18 is connected to the sample chamber 4 via a third valve 7. The vacuum system of the scanning electron microscope has a low vacuum mode in which the fourth valve 8 and the sixth valve 10 are closed and the first valve 3, the third valve 7, and the fifth valve 9 are open; and a high vacuum mode in which the third valve 7 and the fifth valve 9 are closed and the first valve 3, the fourth valve 8, and the sixth valve 10 are open. In the low vacuum mode, the vacuum degree in the electron gun 1 is less than 5×e -3 Pa, in a high vacuum state; the vacuum degree in the lens barrel 2 is greater than 1×e -2 Pa, and the vacuum degree in the lens barrel 2 is less than 1Pa, which is a medium vacuum state; the vacuum degree in the sample chamber 4 is greater than 1Pa, and the vacuum degree in the sample chamber 4 is less than 1000Pa, which is a low vacuum state; in the high vacuum mode, the vacuum degree in the electron gun 1, the vacuum degree in the lens barrel 2, and the vacuum degree in the sample chamber 4 are all less than 5×e -3 Pa. In low vacuum mode, the vacuum pressure in the sample chamber 4 can be adjusted within the range of 2Pa to 1000Pa. In low vacuum mode, while the sample chamber 4 is in a low vacuum state, the electron gun 1 can maintain a high vacuum environment required for operation. In low vacuum mode, ionized ions or gas molecules can be used to neutralize the generated charges, thereby eliminating the charging effect under the condition that the conductive film layer is not sprayed. When biological samples are not sprayed with a conductive film layer, the observation of secondary electrons and backscattered electrons without charging effects can be achieved. In high vacuum mode, the electron gun 1, the lens barrel 2 and the sample chamber 4 are all connected and are in a high vacuum state, which allows for high-magnification observation of samples with good conductivity.

[0037] Furthermore, the first pressure difference diaphragm 5 is located below the objective lens provided at the bottom of the lens barrel 2. Specifically, the first valve 3, the third valve 7, the fourth valve 8, the fifth valve 9 and the sixth valve 10 are all vacuum isolation valves.

[0038] like Figure 1As shown, the scanning electron microscope vacuum system described in the present application also includes: a seventh valve 11, a second vacuum gauge 15 and a controller. The seventh valve 11 is connected to the sample chamber 4, and gas is input into the sample chamber 4 through the seventh valve 11; in high vacuum mode, the seventh valve 11 is in a closed state. The second vacuum gauge 15 is connected to the sample chamber 4, and the second vacuum gauge 15 is suitable for obtaining the vacuum degree in the sample chamber 4 in real time. The controller is signal-connected to the seventh valve 11 and the second vacuum gauge 15. Figure 2 As shown, in the low vacuum mode, the controller is suitable for comparing the vacuum setting value with the actual vacuum degree in the sample chamber 4 obtained by the second vacuum gauge 15 to obtain an error signal, and then the error signal is processed by the PID link 16 to obtain a control signal, and the opening of the seventh valve 11 is controlled in real time by the control signal to control the gas flow input into the sample chamber 4 so that the actual vacuum degree in the sample chamber 4 is equal to the vacuum setting value. Specifically, the seventh valve 11 is a vacuum proportional valve. The vacuum pressure in the sample chamber 4 is determined by the balance between the inflow and outflow, the outflow gas flow is determined by the pumping speed of the mechanical pump 18, and the gas flow into the sample chamber 4 is controlled by the vacuum proportional valve, which can accurately adjust the gas flow into the sample chamber 4. In low vacuum mode, molecular pump 13 extracts gas from sample chamber 4, while second vacuum gauge 15 simultaneously monitors changes in the vacuum level within sample chamber 4 and feeds back the actual vacuum level signal to the controller. Based on the error signal, the controller, via PID link 16, controls the opening of the vacuum proportional valve according to a PID algorithm, ultimately ensuring that the measured value of second vacuum gauge 15 is approximately equal to the set vacuum level, thereby achieving constant control of the vacuum level within sample chamber 4. The vacuum level within sample chamber 4 can be adjusted within a range of 2 Pa to 1000 Pa to meet the needs of scanning electron microscopy imaging. The stabilization time of the vacuum pressure within sample chamber 4 after adjustment is less than 0.5 minutes.

[0039] like Figure 1 As shown, a second pressure diaphragm 17 is provided between the electron gun 1 and the lens barrel 2. In low vacuum mode, the vacuum pressure within the electron gun 1, lens barrel 2, and sample chamber 4 is determined by the balance between inflow and outflow. Gas molecules always flow from areas with relatively low vacuum to areas with relatively high vacuum. The gas flow rate is controlled by the first and second pressure diaphragms 5 and 17. The gas flow rate depends on the sizes of the first and second pressure diaphragms 5 and 17, as well as the pressure difference between the first and second pressure diaphragms 5 and 17. The first and second pressure diaphragms 5 and 17 minimize the pressure difference between the first and second pressure diaphragms 5 and 17 while maintaining a sufficiently large diaphragm size to ensure a large total pressure difference between the sample chamber 4 and the electron gun 1, ensuring that the electron gun 1 can operate in a high vacuum state and the sample chamber 4 can operate in a low vacuum state simultaneously.

[0040] like Figure 1 As shown, the vacuum system of the scanning electron microscope described in this application also includes an eighth valve 12. The eighth valve 12 is connected to the sample chamber 4. When the sample in the sample chamber 4 is replaced, the eighth valve 12 is opened to release the air in the sample chamber 4, thereby breaking the vacuum state in the sample chamber 4 and facilitating the replacement of the sample in the sample chamber 4. In low vacuum mode and high vacuum mode, the eighth valve 12 is closed. Specifically, the gas in the sample chamber 4 is nitrogen. The eighth valve 12 serves as a vacuum release valve.

[0041] like Figure 1 As shown, the mechanical pump 18 is connected to the exhaust port of the molecular pump 13 through the second valve 6; in the low vacuum mode and the high vacuum mode, the second valve 6 is in an open state.

[0042] like Figure 1 As shown, the scanning electron microscope vacuum system described in the present application further includes: a first vacuum gauge 14, which is connected to the electron gun 1 and is suitable for obtaining the vacuum degree in the electron gun 1 in real time.

[0043] Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention. Such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A scanning electron microscope vacuum system, characterized in that: include: Electron gun (1); A lens barrel (2) is connected to the electron gun (1) via a first valve (3); A first differential pressure diaphragm (5) is provided between the sample chamber (4) and the lens barrel (2); the sample chamber (4) and the lens barrel (2) are connected via a sixth valve (10); A molecular pump (13), a first air inlet of which is connected to the electron gun (1), a second air inlet of which is connected to the lens barrel (2) via a fifth valve (9); and the molecular pump (13) is connected to the bottom of the sample chamber (4) via a fourth valve (8); a mechanical pump (18) connected to the sample chamber (4) via a third valve (7); The scanning electron microscope vacuum system has a low vacuum mode in which the fourth valve (8) and the sixth valve (10) are closed and the first valve (3), the third valve (7) and the fifth valve (9) are opened; and a high vacuum mode in which the third valve (7) and the fifth valve (9) are closed and the first valve (3), the fourth valve (8) and the sixth valve (10) are opened. In the low vacuum mode, the vacuum degree in the electron gun (1) is less than 5×e －3 Pa, the vacuum degree in the lens barrel (2) is greater than 1×e －2 Pa, and the vacuum degree in the lens barrel (2) is less than 1 Pa, the vacuum degree in the sample chamber (4) is greater than 1 Pa, and the vacuum degree in the sample chamber (4) is less than 1000 Pa; in high vacuum mode, the vacuum degree in the electron gun (1), the vacuum degree in the lens barrel (2), and the vacuum degree in the sample chamber (4) are all less than 5×e －3 Pa; Also includes: a seventh valve (11) connected to the sample chamber (4) and inputting gas into the sample chamber (4) through the seventh valve (11); a second vacuum gauge (15) connected to the sample chamber (4), wherein the second vacuum gauge (15) is adapted to obtain the vacuum degree in the sample chamber (4) in real time; The controller is connected to the seventh valve (11) and the second vacuum gauge (15) by signal. In the low vacuum mode, the controller is suitable for comparing the vacuum setting value with the actual vacuum degree in the sample chamber (4) obtained by the second vacuum gauge (15) to obtain an error signal, and then the error signal is processed by the PID link (16) to obtain a control signal, and the opening of the seventh valve (11) is controlled in real time by the control signal to control the gas flow input into the sample chamber (4) so ​​that the actual vacuum degree in the sample chamber (4) is equal to the vacuum setting value.

2. The scanning electron microscope vacuum system according to claim 1, characterized in that: The first pressure difference diaphragm (5) is located below the objective lens provided at the bottom of the lens barrel (2).

3. The scanning electron microscope vacuum system according to claim 1, characterized in that: The seventh valve (11) is a vacuum proportional valve.

4. The scanning electron microscope vacuum system according to any one of claims 1 to 3, characterized in that: A second pressure difference diaphragm (17) is provided between the electron gun (1) and the lens barrel (2).

5. The scanning electron microscope vacuum system according to any one of claims 1 to 3, characterized in that: Also includes: The eighth valve (12) is connected to the sample chamber (4). When the sample in the sample chamber (4) is replaced, the eighth valve (12) is opened to deflate the sample chamber (4). In the low vacuum mode and the high vacuum mode, the eighth valve (12) is in a closed state.

6. The scanning electron microscope vacuum system according to claim 5, characterized in that: The gas in the sample chamber (4) is nitrogen.

7. The vacuum system for a scanning electron microscope according to any one of claims 1 to 3, characterized in that: The mechanical pump (18) is connected to the exhaust port of the molecular pump (13) via a second valve (6); in low vacuum mode and high vacuum mode, the second valve (6) is in an open state.

8. The vacuum system for a scanning electron microscope according to any one of claims 1 to 3, characterized in that: Also includes: A first vacuum gauge (14) is connected to the electron gun (1), and the first vacuum gauge (14) is suitable for obtaining the vacuum degree in the electron gun (1) in real time.

9. The vacuum system for a scanning electron microscope according to any one of claims 1 to 3, characterized in that: The first valve (3), the third valve (7), the fourth valve (8), the fifth valve (9) and the sixth valve (10) are all vacuum isolation valves.

Images