Vacuum system of scanning electron microscope

Abstract

The invention relates to the technical field of microscopes, and discloses a scanning electron microscope vacuum system, which comprises an electron gun; the lens cone is connected with the electron gun through the first valve; the sample chamber is connected with the lens cone through a sixth valve; a first air inlet of the molecular pump is connected with the electron gun, and a second air inlet is connected with the lens barrel through a fifth valve; the molecular pump is connected with the sample chamber through a fourth valve; the mechanical pump is connected with the sample chamber through a third valve; the scanning electron microscope vacuum system has a low vacuum mode of closing the fourth valve and the sixth valve and opening the first valve, the third valve and the fifth valve; 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 can be freely switched between a low vacuum mode and a high vacuum mode; in addition, the scanning electron microscope vacuum system uses devices as few as possible, the cost is low, the size is reduced, and the space is saved.

Description

Technical Field

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

[0002] Scanning electron microscope, also known as SEM, is a high-resolution microscope. SEM can obtain high-definition images by scanning the electron beam on the surface of the sample; specifically, the sample surface is scanned line by line using a focused electron beam in a vacuum environment. The focused electron beam bombards the sample surface to generate secondary electrons or backscattered electrons. The generation efficiency of secondary electrons or backscattered electrons is related to the morphology or material of the sample surface; 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, that is, the secondary electron image or backscattered electron image of the scanning electron microscope is obtained. After the secondary electron image or backscattered electron image is magnified thousands to hundreds of thousands of times, the surface image of the sample can be observed to achieve the purpose of observing the microscopic morphology of the sample.

[0003] When ordinary scanning electron microscopes are working, they usually only have high vacuum mode. The electron optical tube and sample chamber of the scanning electron microscope must be in a high vacuum environment, and the sample must be free of water and conductive. Otherwise, in the process of observing the microscopic morphology of the sample, it is easy to produce charging effects, causing image drift and image distortion, which seriously affects the observation of the image and even makes it difficult to see the image clearly. Therefore, non-conductive samples must be treated with conductivity before observation, usually by spraying a conductive film layer on the surface of the sample, and the excess electrons on the sample are led away by the conductive film layer.

[0004] For low vacuum SEM, in low vacuum mode, ionized ions or gas molecules can be used to neutralize the generated charge, thereby eliminating the charging effect when the sample is not sprayed with a conductive film. For water-containing and non-conductive samples such as biological samples, the low vacuum SEM can achieve observation of secondary electrons and backscattered electrons without spraying a conductive film, and can maintain the most intrinsic structure of biological samples and quickly image.

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

[0007] The present invention provides a scanning electron microscope vacuum system, 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; 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 the 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 the low vacuum mode, the vacuum pressure adjustment range in the sample chamber described in the present application is larger and has wider adaptability. At the same time, by setting the first pressure difference diaphragm, in the 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: The present application adopts the above technical solution, and by setting 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, and most of the electrons reaching the sample are prevented from being scattered, thereby ensuring the quality of the image obtained subsequently.

[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 signals; 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 operation efficiency.

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

[0020] Optionally, a second pressure difference diaphragm is provided between the electron gun and the lens barrel. Beneficial effect: The present application adopts the above technical solution, and further provides a second pressure difference diaphragm. In the low vacuum mode, the pressure difference between the electron gun and the lens barrel is as small as possible, while having a sufficiently large diaphragm size, so that the total pressure difference between the electron gun and the lens barrel is large, ensuring that the medium vacuum state of the lens barrel and the high vacuum state of the electron gun can work at the same time; at the same time, ensuring that the low vacuum state of the sample chamber and the high vacuum state of the electron gun can work at the same time.

[0021] Optionally, it also includes:

[0022] The 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 the first vacuum gauge 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 implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying 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 the 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] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the 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 creative work are within the scope of protection of the present invention.

[0034] The vacuum system of the existing low vacuum type scanning electron microscope is relatively complex, generally including a large number of vacuum pumps, vacuum valves and vacuum gauges, the cost is high, the adjustable range of vacuum pressure is small, and the stabilization time of vacuum pressure after adjustment is long. Due to the above reasons, the present application proposes an improved vacuum system for scanning electron microscope.

[0035] like Figure 1 to Figure 2 A specific embodiment of the scanning electron microscope vacuum system shown includes: 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 in the present application can be used for a low vacuum type scanning electron microscope, and can work in both a low vacuum mode and a high vacuum mode. 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 through the 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 through the 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 the upper air inlet is connected to the electron gun 1 through a pipeline. The second air inlet of the molecular pump 13 is connected to the lens barrel 2 through the fifth valve 9; the second air inlet is the middle air inlet of the molecular pump 13, and the middle air inlet is connected to the lens barrel 2 through the pipeline through the fifth valve 9. The molecular pump 13 is connected to the bottom of the sample chamber 4 through the fourth valve 8. The mechanical pump 18 is connected to the sample chamber 4 through the 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 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, 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 in 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 in 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 be maintained in 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 without spraying a conductive film layer. In the case of biological samples, etc., without spraying 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 in a high vacuum state, and samples with good conductivity can be observed at high magnification.

[0037] Further, the first differential pressure 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 the 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, obtaining an error signal, and then processing the error signal through the PID link 16 to obtain a control signal, and controlling the opening of the seventh valve 11 in real time through 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, and the vacuum proportional valve can accurately adjust the gas flow into the sample chamber 4. In low vacuum mode, the molecular pump 13 extracts the gas in the sample chamber 4, and the second vacuum gauge 15 simultaneously monitors the change of the vacuum degree in the sample chamber 4, and feeds back the actual vacuum degree signal to the controller. The controller controls the opening change of the vacuum proportional valve according to the PID algorithm through the PID link 16 according to the error signal, and finally makes the measured value of the second vacuum gauge 15 approximately equal to the vacuum degree setting value, thereby realizing the constant control of the vacuum degree in the sample chamber 4. The vacuum degree in the sample chamber 4 can be arbitrarily adjusted within the range of 2Pa to 1000Pa according to the needs of the scanning electron microscope, and the stabilization time of the vacuum pressure in the sample chamber 4 after adjustment is less than 0.5min.

[0039] like Figure 1 As shown, a second differential pressure diaphragm 17 is provided between the electron gun 1 and the lens barrel 2. In the low vacuum mode, the vacuum pressure in the electron gun 1, the lens barrel 2 and the sample chamber 4 is determined by the balance between the inflow and the outflow, and the gas molecules always flow from the place with relatively low vacuum to the place with relatively high vacuum, and the flow rate is controlled by the first differential pressure diaphragm 5 and the second differential pressure diaphragm 17; the flow rate of the gas depends on the size of the first differential pressure diaphragm 5 and the second differential pressure diaphragm 17, and the pressure difference between the first differential pressure diaphragm 5 and the second differential pressure diaphragm 17. The first differential pressure diaphragm 5 and the second differential pressure diaphragm 17 can make the pressure difference between the first differential pressure diaphragm 5 and the second differential pressure diaphragm 17 as small as possible, while having a sufficiently large diaphragm size, so that the total pressure difference between the sample chamber 4 and the electron gun 1 is large, ensuring that the high vacuum state of the electron gun 1 and the low vacuum state of the sample chamber 4 can work simultaneously.

[0040] like Figure 1 As shown, the vacuum system of the scanning electron microscope described in the present application further includes: an eighth valve 12; the eighth valve 12 is connected to the sample chamber 4. When replacing the sample in the sample chamber 4, the eighth valve 12 is opened to deflate the sample chamber 4 to break the vacuum state in the sample chamber 4 and facilitate the replacement of the sample in the sample chamber 4; in the low vacuum mode and the high vacuum mode, the eighth valve 12 is in a closed state. Specifically, the gas in the sample chamber 4 is nitrogen. The eighth valve 12 is a vacuum deflation 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 also includes: a first vacuum gauge 14, the 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.

[0043] Although the embodiments of the present invention have been described in conjunction with 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, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A vacuum system for a scanning electron microscope, characterized in that: include: Electron gun (1); A lens barrel (2) 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), wherein a first air inlet is connected to the electron gun (1), and a second air inlet of the molecular pump (13) is connected to the lens barrel (2) via a fifth valve (9); 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 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 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 a 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.

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: Also includes: a seventh valve (11), connected to the sample chamber (4), and for 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 suitable for obtaining the vacuum degree in the sample chamber (4) in real time; A controller is signal-connected to the seventh valve (11) and the second vacuum gauge (15); in a low vacuum mode, the controller is suitable for comparing a vacuum setting value with an actual vacuum degree in a sample chamber (4) obtained by the second vacuum gauge (15) to obtain an error signal, and then the error signal is processed by a 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 rate input into the sample chamber (4), so that the actual vacuum degree in the sample chamber (4) is equal to the vacuum setting value.

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

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

6. The scanning electron microscope vacuum system according to any one of claims 1 to 4, 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.

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

8. The scanning electron microscope vacuum system according to any one of claims 1 to 4, characterized in that: The mechanical pump (18) is connected to the exhaust port of the molecular pump (13) via a second valve (6); in a low vacuum mode and a high vacuum mode, the second valve (6) is in an open state.

9. The scanning electron microscope vacuum system according to any one of claims 1 to 4, 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.

10. The scanning electron microscope vacuum system according to any one of claims 1 to 4, 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.

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