Opposed Compressor-Driven Scanning Electron Microscope Refrigeration System and Method

Abstract

The present invention relates to the technical field of cooling of electron microscope sample stages, and provides a refrigeration system and method for a scanning electron microscope driven by an opposed compressor. The refrigeration system provided by the present invention includes a first vacuum chamber, a second vacuum chamber, an opposed compressor, a refrigerator, and a sample stage. The refrigerator is located inside the first vacuum chamber, the sample stage is located inside the second vacuum chamber, the opposed compressor is located outside the first vacuum chamber and is flexibly connected to the refrigerator, and the cold head of the refrigerator is connected to the sample stage. For the refrigeration system of the scanning electron microscope driven by the opposed compressor provided by the present invention, the opposed compressor drives the refrigerator to refrigerate, and the cold quantity generated by the refrigerator is transferred to the sample stage to reduce the temperature of the sample stage, so as to meet the temperature requirements of different sample measurement environments, and the applicability is high; the opposed compressor and the refrigerator are respectively located outside and inside the first vacuum chamber, are separated from each other, and are flexibly connected between the two, reducing the vibration of the sample stage.

Description

Technical Field

[0001] The present invention relates to the technical field of cooling of electron microscope sample stages, and particularly to a refrigeration system and method for a scanning electron microscope driven by an opposed compressor. Background Art

[0002] Currently, a scanning electron microscope can only measure the sample temperature at room temperature, with a narrow scope of application and being unable to measure samples with special requirements for the temperature environment. To solve this problem, the common practice now is to use liquid ammonia as a cold source and further as the cold head of the scanning electron microscope. The specific cooling method is to introduce liquid nitrogen into the scanning electron microscope to directly cool the sample stage. This cooling method has several problems: First, the cooling temperature range is narrow. Using liquid nitrogen, the temperature can only be around 77K, with a limited cooling temperature range. Second, the temperature control accuracy is not high. It is difficult to achieve high-precision temperature control by controlling the liquid nitrogen flow rate. Usually, the temperature fluctuation is as high as 1 - 2K or even higher. Third, introducing liquid nitrogen into the scanning electron microscope inevitably introduces vibrations, which will significantly affect the observation of the microscopic morphology at high magnifications. Fourth, the usual temperature control mode is to use electric heating technology, and the refrigerator or cold source usually needs to be in a working state all the time, heating to the corresponding temperature by electricity, resulting in an obvious problem of wasted cooling capacity. Summary of the Invention

[0003] (1) Technical Problems to be Solved

[0004] One of the objectives of the present invention is to provide a refrigeration system for a scanning electron microscope driven by an opposed compressor to solve the problems of the limited cooling temperature range of the existing scanning electron microscope refrigeration system and the low measurement accuracy caused by the easy vibration of the sample stage.

[0005] Another objective of the present invention is to provide a method for cooling using the above scanning electron microscope system driven by an opposed compressor. (2) Summary of the Invention

[0007] To solve one of the above technical problems, the present invention provides a refrigeration system for a scanning electron microscope driven by an opposed compressor, including a first vacuum chamber and a second vacuum chamber, and further including an opposed compressor, a refrigerator, and a sample stage. The refrigerator is located in the first vacuum chamber, the sample stage is located in the second vacuum chamber, the opposed compressor is located outside the first vacuum chamber and is flexibly connected to the refrigerator, and the cold head of the refrigerator is connected to the sample stage.

[0008] Wherein, the opposed compressor is installed on a first base, and a first vibration damping unit is installed below the first base.

[0009] Among them, the refrigerator and the second vacuum chamber are installed on the second base, and a second vibration damping unit is installed below the second base.

[0010] Among them, the hot end of the refrigerator is rigidly connected to the second base.

[0011] Among them, the refrigerator is a pulse tube refrigerator.

[0012] Among them, the cold end of the refrigerator is connected to the sample stage through a flexible pipeline.

[0013] Among them, the first vacuum chamber communicates with the second vacuum chamber.

[0014] Among them, the vacuum degrees of the first vacuum chamber and the second vacuum chamber are respectively 0 Pa to 10 5 Pa.

[0015] Among them, the opposed compressor includes a first piston and a second piston, and the first piston and the second piston move towards each other.

[0016] To solve the second of the above technical problems, the present invention provides a method for cooling using the scanning electron microscope refrigeration system driven by the above-mentioned opposed compressor, including:

[0017] After the vacuum degrees of the first vacuum chamber and the second vacuum chamber reach the requirements, start the opposed compressor, and the refrigerator releases cold to cool the sample stage. When the temperature of the sample stage drops to the preset temperature, reduce the input electric work of the opposed compressor; when the temperature of the sample stage is higher than the preset temperature, increase the input electric work of the opposed compressor.

[0018] (III) Beneficial effects

[0019] The scanning electron microscope refrigeration system driven by the opposed compressor provided by the present invention drives the refrigerator to refrigerate by the opposed compressor, and the cold generated by the refrigerator is transferred to the sample stage to reduce the temperature of the sample stage, so as to meet the temperature requirements of different sample measurement environments. Compared with the existing liquid ammonia cooling, the achievable temperature range is wider and the applicability is high; the opposed compressor and the refrigerator are respectively located outside and inside the first vacuum chamber, and are separated from each other and flexibly connected, thereby reducing the vibration transmitted from the opposed compressor and the refrigerator to the sample stage and improving the accuracy of sample observation. Description of the drawings

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0021] Figure 1 It is a schematic structural diagram of a scanning electron microscope refrigeration system driven by an opposed compressor according to an embodiment of the present invention;

[0022] In the figure: 10, the first vacuum chamber; 11, the flexible pipeline; 20, the second vacuum chamber; 30, the opposed compressor; 31, the first piston; 32, the second piston; 40, the refrigerator; 41, the flexible conveying pipeline; 50, the sample stage; 51, the electron gun; 60, the first base; 70, the first vibration damping unit; 80, the second base; 90, the second vibration damping unit. Detailed implementation manners

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0024] In the description of the present invention, it should be noted that, unless otherwise clearly defined and limited, the terms "installation", "connection", and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0025] The scanning electron microscope refrigeration system driven by an opposed compressor provided by the embodiment of the present invention, as Figure 1 shown, includes a first vacuum chamber 10, a second vacuum chamber 20, an opposed compressor 30, a refrigerator 40, and a sample stage 50. Among them, the opposed compressor 30 is located in the first vacuum chamber 10 and is flexibly connected to the refrigerator 40 through a flexible pipeline 11. The refrigerator 40 is located in the first vacuum chamber 10, the sample stage 50 is located in the second vacuum chamber 20, and the cold head of the refrigerator 40 is connected to the sample stage 50.

[0026] During use, the opposed compressor 30 drives the refrigerator 40 to refrigerate. The cooling capacity generated by the refrigerator 40 is transferred to the sample stage 50 to lower the temperature of the sample stage 50. In the embodiment of the present invention, the temperature of the sample stage 50 can be greatly reduced, so as to meet the temperature requirements of different sample measurement environments. Compared with the existing liquid ammonia cooling, a wider temperature range can be achieved, and the applicability is high. In the embodiment of the present invention, the opposed compressor 30 and the refrigerator 40 are respectively located outside and inside the first vacuum chamber 10, that is, they are separated from each other, and are flexibly connected through a flexible pipe 11, so as to reduce the vibration transmitted from the opposed compressor 30 and the refrigerator 40 to the sample stage 50 and improve the accuracy of sample observation.

[0027] In addition, when the sample stage 50 needs to maintain a constant temperature during the observation of the microscopic morphology of the sample, the opposed compressor 30 needs to continuously work. There is a corresponding relationship between the output electric work of the opposed compressor 30 and the cooling capacity output by the refrigerator 40. Specifically, when the output electric work of the opposed compressor 30 is large, the refrigerator 40 outputs more cooling capacity, the sample stage 50 cools down quickly, and the temperature changes greatly; when the output electric work of the opposed compressor 30 is small, the refrigerator 40 outputs less cooling capacity, and the temperature change of the sample stage 50 is not obvious. Since the opposed compressor 30 is always in a working state, its vibration is not conducive to the observation of the sample by the scanning electron microscope.

[0028] Specifically, the refrigeration system further includes a control device. A temperature sensor is provided on the sample stage 50, and the temperature sensor is in signal connection with the control device. The control device controls the output electric work of the opposed compressor 30 according to the temperature value collected by the temperature sensor. When the temperature value collected by the temperature sensor is within the preset temperature range, the control device controls the opposed compressor 30 to reduce the output electric work; as the observation work progresses, the temperature of the sample stage 50 in the second vacuum chamber 20 gradually increases. When the temperature value collected by the temperature sensor is not within the preset temperature range, the control device controls the opposed compressor 30 to increase the output electric work, drives the refrigerator 40 to output more cooling capacity, and quickly reduces the temperature of the sample stage 50 to ensure that the temperature of the sample stage 50 is generally maintained within the set temperature range. In addition, an electron gun 51 is provided above the sample stage 50, and the electron gun 51 extends into the second vacuum chamber 20 for observing the sample on the sample stage 50.

[0029] Among them, the refrigerator 40 is a pulse tube refrigerator. As a cold source, the cold head of the pulse tube refrigerator has no moving parts and no vibration itself, further reducing the vibration transmitted from external devices to the sample stage 50. Further, the sample stage 50 and the pulse tube refrigerator are flexibly connected through a flexible conveying pipe 41 to reduce the vibration transmitted from the opposed compressor 30 and the pulse tube refrigerator to the sample stage 50.

[0030] In the embodiment of the present invention, the opposed compressor 30 is fixedly mounted on the first base 60, and the first vibration reduction unit 70 is installed below the first base 60. The vibration is eliminated by means of the first vibration reduction unit 70 below the first base 60 to prevent it from affecting the sample observation. The refrigerator 40 and the second vacuum chamber 20 are both mounted on the second base 80, and the second vibration reduction unit 90 is installed below the second base 80. Specifically, the hot end of the refrigerator 40 is fixed to the second base 80 by bolts to achieve a hard connection, thereby using the second vibration reduction unit 90 and the second base 80 already existing in the scanning electron microscope to reduce the vibration of the refrigerator 40, thereby preventing the refrigerator 40 from introducing a new vibration source to affect the stability of the sample stage 50, while reducing the number of vibration reduction units and bases, and reducing costs.

[0031] In addition, in order to reduce the number of vacuum pumps, the first vacuum chamber 10 is connected to the second vacuum chamber 20. Therefore, the vacuum pump of the scanning electron microscope can create a vacuum environment in the first vacuum chamber 10 while evacuating the second vacuum chamber 20. Specifically, the vacuum degree in the first vacuum chamber 10 and the second vacuum chamber 20 is the same, both within the range of 0Pa to 10 5 Pa, that is, between 0 Pa and normal pressure, so that the refrigerator 40 and the scanning electron microscope are in a vacuum environment with the same vacuum degree.

[0032] The opposed compressor 30 is a linear compressor, which includes a first piston 31 and a second piston 32. The first piston 31 and the second piston 32 move toward each other, which can reduce the vibration caused by the piston movement. The control device controls the temperature of the sample stage 50 by controlling the movement amplitude of the first piston 31 and the second piston 32. The higher the temperature, the smaller the movement amplitude of the first piston 31 and the second piston 32, and the correspondingly less electric power is consumed.

[0033] The scanning electron microscope refrigeration system driven by the opposed compressor in the embodiment of the present invention has good vibration reduction effect and can observe the microscopic morphology of samples at different temperatures. In addition, the present invention also provides a method for refrigeration using the above refrigeration system.

[0034] First, evacuate the first vacuum chamber 10 and the second vacuum chamber 20 until the vacuum degree meets the vacuum degree requirement of the scanning electron microscope (the vacuum degree is between 0Pa and 10Pa). 5(between Pa), start the opposed compressor 30, and the refrigerator 40 flexibly connected to the opposed compressor 30 provides cooling capacity to the sample stage 50 for cooling. When the temperature of the sample stage 50 drops to the preset temperature, reduce the input electric power of the opposed compressor 30, reduce the motion amplitudes of the first piston 31 and the second piston 32, and the temperature of the sample stage 50 begins to rise; when the temperature of the sample stage 50 is higher than the preset temperature, increase the input electric power of the opposed compressor 30, increase the motion amplitudes of the first piston 31 and the second piston 32, and the temperature of the sample stage 50 begins to drop. Precisely control the temperature of the sample stage 50 by repeatedly adjusting the input electric power of the opposed compressor 30. Among them, the control process of the opposed compressor 30 is automatically controlled by the control device according to the temperature data collected by the temperature sensor.

[0035] The following specifically describes the specific control process when the temperature of the sample stage 50 is set to 4K.

[0036] After the vacuum degrees of the first vacuum chamber 10 where the refrigerator 40 is located and the second vacuum chamber 20 where the scanning electron microscope is located meet the requirements, start the opposed compressor 30, and the first piston 31 and the second piston 32 start to move towards each other, and the cold-end temperature of the refrigerator 40 begins to drop. At this time, the flexible conveying pipeline 41 transfers the cooling capacity at the cold end of the refrigerator 40 to the sample stage 50. After the temperature of the sample stage 50 drops to the set temperature of 4K, gradually reduce the input electric power of the opposed compressor 30, and the motion amplitudes of the first piston 31 and the second piston 32 decrease. At this time, the temperature of the sample stage 50 begins to rise; when the temperature of the sample stage 50 is higher than 4K, gradually increase the input electric power of the opposed compressor 30, and the motion amplitudes of the first piston 31 and the second piston 32 increase. At this time, the temperature of the sample stage 50 begins to drop; therefore, the temperature of the sample stage 50 can be precisely controlled by repeatedly adjusting the input electric power of the opposed compressor 30.

[0037] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art can understand and implement it without creative labor.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A scanning electron microscope refrigeration system driven by an opposed compressor, comprising a first vacuum chamber and a second vacuum chamber, characterized in that, It further includes an opposed compressor, a refrigerator and a sample stage. The refrigerator is located within the first vacuum chamber, the sample stage is located within the second vacuum chamber, the opposed compressor is located outside the first vacuum chamber and is flexibly connected to the refrigerator, and the cold head of the refrigerator is connected to the sample stage.

2. The scanning electron microscope refrigeration system driven by an opposed compressor according to claim 1, characterized in that, The opposed compressor is mounted on a first base, and a first vibration damping unit is mounted below the first base.

3. The scanning electron microscope refrigeration system driven by an opposed compressor according to claim 1 or 2, characterized in that, The refrigerator and the second vacuum chamber are mounted on a second base, and a second vibration damping unit is mounted below the second base.

4. The scanning electron microscope refrigeration system driven by an opposed compressor according to claim 3, characterized in that, The hot end of the refrigerator is rigidly connected to the second base.

5. The scanning electron microscope refrigeration system driven by an opposed compressor according to claim 1, characterized in that, The refrigerator is a pulse tube refrigerator.

6. The scanning electron microscope refrigeration system driven by an opposed compressor according to claim 1 or 5, characterized in that, The cold end of the refrigerator and the sample stage are connected through a flexible pipe.

7. The scanning electron microscope refrigeration system driven by an opposed compressor according to claim 1, characterized in that, The first vacuum chamber communicates with the second vacuum chamber.

8. The scanning electron microscope refrigeration system driven by an opposed compressor according to claim 7, characterized in that, The vacuum degrees of the first vacuum cavity and the second vacuum cavity are respectively 0 Pa to 10 5 Pa.

9. The scanning electron microscope refrigeration system driven by an opposed compressor according to claim 1, characterized in that, The opposed compressor includes a first piston and a second piston, and the first piston and the second piston move towards each other.

10. A method for cooling using the scanning electron microscope refrigeration system driven by an opposed compressor according to any one of claims 1 to 9, characterized in that, Comprising: After the vacuum degrees of the first vacuum chamber and the second vacuum chamber meet the requirements, start the opposed compressor. The refrigerator releases cold to cool down the sample stage. When the temperature of the sample stage drops to the preset temperature, reduce the input electric power of the opposed compressor; when the temperature of the sample stage is higher than the preset temperature, increase the input electric power of the opposed compressor.

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