Molecule removal method and molecule removal device

Abstract

To provide a molecule removal method and a molecule removal device that can remove molecular components of which removal is difficult by only a molecular distillation method.SOLUTION: A molecule removal method for removing molecule components from a base oil has: a process (a) in which in the state that a container, in which there are the base oil and a stirrer located in the base oil, is arranged in a chamber, the interior of the chamber is evacuated; and a process (b) in which in the state that a pressure in the chamber becomes less than 1 mPa by evacuation, the stirrer is rotated to stir the base oil.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a molecule removal method and molecule removal device used when refining a lubricant by removing low-molecular components from a base oil. [Background technology]

[0002] Fluorine-based lubricants are used as lubricants for sliding parts such as sample stages mounted in devices equipped with vacuum chambers, such as electron microscopes. Fluorine-based lubricants have a wide vaporization temperature range, and molecules (gases) such as fluorine are easily released into the surrounding environment. Patent Document 1 (JP 2017-25324 A) discloses a method for reducing the amount of released molecules (gases) by removing low-boiling and high-boiling components from a polymer composition using molecular distillation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-25324 Summary of the Invention [Problem to be solved by the invention]

[0004] The method of removing molecular components by molecular distillation, as disclosed in Patent Document 1, involves distillation in a vacuum environment with the evaporation surface and condensation surface closely spaced apart, but if the base oil contains a large amount of low-molecular-weight components, the molecular components may not be sufficiently removed.If low-molecular-weight components such as fluorine-based compounds are not sufficiently removed, the low-molecular-weight components may gasify in the vacuum chamber of an electron microscope, for example, and adhere to the semiconductor wafer being observed or the inner wall of the vacuum chamber, potentially becoming a source of secondary gas generation.

[0005] The technology described in the present disclosure aims to provide a molecular removal method and molecular removal device that enable the removal of molecular components that are difficult to remove by molecular distillation alone. [Means for solving the problem]

[0006] A brief summary of a representative embodiment of the present invention will be given below.

[0007] One embodiment of the molecular removal method is a molecular removal method for removing molecular components from a base oil, and includes the steps of: (a) evacuating the chamber while a container containing the base oil and a stirrer placed in the base oil is placed in the chamber; and (b) rotating the stirrer to stir the base oil while the pressure in the chamber is reduced to less than 1 mPa due to the evacuation.

[0008] One embodiment of the molecular removal device is a molecular removal device that stirs base oil and removes molecular components from the base oil, and includes a chamber, a vacuum pump that can evacuate the atmosphere in the chamber to a pressure of less than 100 μPa, a container that can be placed in the chamber, a stirrer that is placed in the container and includes a magnet, and a rotation unit that is configured to rotate the stirrer by rotating a magnetic field, and the base oil placed in the container is stirred by the rotation of the stirrer. [Effects of the Invention]

[0009] The effects obtained by the representative inventions disclosed in this application will be briefly explained as follows.

[0010] According to the present disclosure, a molecule removal method and molecule removal device are provided that enable the removal of molecular components that are difficult to remove by molecular distillation alone. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing a part of a molecule removal device according to an embodiment. [Figure 2] 1 is a schematic diagram showing a part of a molecule removal device according to an embodiment. [Figure 3]1 is a schematic diagram showing a molecule removal device according to an embodiment; [Figure 4] 1 is a flow chart showing a molecule removal method according to an embodiment. [Figure 5] 1 is a schematic diagram showing a molecule removal device according to an embodiment; [Figure 6] 10A and 10B are perspective views showing examples of shapes of the stirring bar according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all drawings for explaining the embodiments, components having the same functions are designated by the same reference numerals, and repeated explanations thereof will be omitted. Furthermore, in the following embodiments, explanations of identical or similar parts will not be repeated unless specifically required. Furthermore, in the drawings for explaining the embodiments, hatching may be used even in plan views or perspective views to make the configuration easier to understand. Furthermore, in the drawings for explaining the embodiments, hatching may be omitted in cross-sectional views to make the configuration easier to understand.

[0013] (Embodiment) Unlike optical microscopes, which use light (visible light) to reflect off an object to make a magnified observation, there are electron microscopes that use an electron beam (a beam of charged particles) to obtain a magnified image of the object. Electron microscopes are used to observe (image) a sample placed inside a microscope tube whose interior can be evacuated. The stage on which the sample is placed is slidable, allowing the position or angle of the sample to be adjusted.

[0014] In order for the stage to slide smoothly, it is necessary to apply a lubricant between the stage and its support. If the base oil that constitutes this lubricant contains molecules (high molecular weight components and low molecular weight components), dust generation due to wear between the stage and its support becomes a problem. Therefore, it is important to remove the high molecular weight components and low molecular weight components from the base oil at the stage of refining the lubricant. Removal of the high molecular weight components can be performed by molecular distillation, as described in Patent Document 1. In molecular distillation, for example, 10 -2 Pa or 10 -3 The base oil is heated under a vacuum of 100 Pa to remove molecules (high molecular weight components) that are low boiling point components. This embodiment relates to a molecule removal method and device that enables the removal of low molecular weight components that cannot be removed by molecular distillation. In this application, a high molecular weight refers to a molecule having 1000 or more atomic connections within a single molecule, and a low molecular weight refers to a molecule having less than 1000 atomic connections within a single molecule.

[0015] FIG. 1 is a schematic diagram showing a part of a molecule removal device according to the present embodiment, which is used to remove low-molecular components from a fluorine-based lubricant (hereinafter referred to as base oil) used in sliding parts such as the stage of an electron microscope.

[0016] 1, the molecular removal device of this embodiment includes a rotation unit 104, a container 102 arranged on the rotation unit 104, a stirrer (rotor) 106 arranged in the container 102, and a vacuum chamber 101 capable of accommodating the container 102 and the stirrer 106. A base oil 103 is accommodated in the container 102, and the stirrer 106 is sunk to the bottom of the base oil 103.

[0017] The rotation unit 104 and the stirrer 106 are magnetic stirrers that can rotate the stirrer 106 without contacting each other. A magnetic stirrer is a device that uses the rotation of a magnetic field to rotate the stirrer and stir a liquid. The rotation unit 104 has a motor inside it that rotates a magnet inside the rotation unit 104, thereby rotating the magnetic field outside the rotation unit 104. The rotation speed of this motor is variable. The stirrer 106 is a bar magnet sealed in glass and has, for example, a cylindrical (rod-like or cocoon-like) shape with rounded corners. The stirrer 106 equipped with a bar magnet also rotates in conjunction with the rotation of the magnet rotated by the motor inside the rotation unit 104. The stirrer 106 rotates around an axis perpendicular to the mounting surface, which is the top surface of the rotation unit 104, and the bottom surface inside the container 102. The stirrer 106 rotates around an axis that passes through the center of its extension direction and is perpendicular to the extension direction.

[0018] The rotation unit 104 rotates a magnetic field from outside the vacuum chamber 101 and the container 102, which can rotate the stirrer 106. For this reason, here the rotation unit 104 is disposed outside the vacuum chamber 101. Although it is possible to dispose the rotation unit 104 inside the vacuum chamber 101, there is a risk that the rotation unit 104 may generate unwanted gas components, so it is desirable that the rotation unit 104 be disposed outside the vacuum chamber 101.

[0019] Next, a method for removing low molecular weight components (hereinafter, sometimes referred to as gas) contained in the base oil 103 using these mechanisms will be specifically described.

[0020] When gas (low molecular weight component) 107 is present in base oil 103, evaporation 111 occurs, in which gas 107 is released from the surface of base oil 103 into space (outside base oil 103). In addition, although not shown, condensation may occur, in which gas 107 in space enters base oil 103. For this reason, in order to evaporate and remove gas 107 from base oil 103, it is necessary to create an environment around base oil 103 with little gas 107.

[0021] The vacuum chamber 101 is maintained at a pressure of less than 100 μPa (10 -5 This is a vacuum device that can create a high vacuum (on the order of Pa) and constantly evacuate. By using this vacuum chamber 101, an environment with little gas 107 can be realized inside the vacuum chamber 101. By placing base oil 103 inside the vacuum chamber 101, the gas 107 that has evaporated from the surface of the base oil 103 can be discharged outside the vacuum chamber 101 by evacuation and removed, and condensation of the gas 107 can be prevented.

[0022] Here, in order to evaporate the gas 107 contained in the base oil 103, it is important to expose the entire base oil 103 to a high vacuum environment.

[0023] 2, a stirrer 106 and base oil 103 are placed in the same container 102, and the stirrer 106, which has a built-in magnet, is rotated without contact by a rotation unit 104, thereby stirring the base oil 103. This generates a vortex 105 on the surface (oil surface, upper surface) of the base oil 103. The generation of the cone-shaped vortex 105 makes it possible to expose the entire base oil 103 to a high-vacuum environment.

[0024] Furthermore, it is desirable that the rotation speed when rotating the stirrer 106 by the rotation unit 104 is set to a speed at which a vortex 105 is generated in the base oil 103, but the stirrer 106 is not exposed to the outside of the base oil 103. This increases the surface area of ​​the base oil 103 exposed to the high vacuum environment, thereby increasing the evaporation efficiency of the gas 107. In other words, it is desirable to set the rotation speed so that the stirrer 106 is covered by the base oil 103 below the vortex 105, even when the base oil 103 is generated. Furthermore, by stirring the base oil 103, the base oil 103 near the surface of the container 102 is also exposed to the high vacuum environment, thereby increasing the evaporation efficiency of the gas 107.

[0025] As a method of stirring the base oil 103, a propeller-type or oar-type stirrer with a rotating shaft can also be used to expose the entire base oil to a high vacuum. However, in this case, the presence of a rotating shaft hanging down from above the container 102 into the container 102 reduces the surface area of ​​the base oil 103 exposed to a high vacuum. In other words, compared to a propeller-type or oar-type stirrer, non-contact stirring using the stirrer 106 and rotating unit 104 shown in FIG. 1 can increase the surface area of ​​the base oil 103 exposed to a high vacuum and is easier to clean. Furthermore, the stirrer 106, which rotates without contact with the rotating unit 104, has a smaller contact area with the base oil 103 compared to a propeller-type or oar-type stirrer with a rotating shaft, which prevents gas 107 adhering to the stirrer 106 from being mixed into the base oil 103.

[0026] In this manner, in this embodiment, the base oil 103 contained in the container 102 is stirred by the stirrer 106 in the high vacuum environment of the vacuum chamber 101, thereby effectively removing the gas 107 from the base oil 103.

[0027] Next, a specific embodiment of the molecule removal device of this embodiment will be described using Fig. 3, and a molecule removal method for removing gas 107 from base oil 103 will be described using the flow chart of Fig. 4. Of the components of the molecule removal device shown in Fig. 3, the same components as those in the schematic diagrams of Fig. 1 and Fig. 2 are designated by the same reference numerals.

[0028] 3, the molecular removal device of this embodiment includes a rotation unit 104, a container 102 arranged on the rotation unit 104, a stirrer 106 arranged in the container 102, and a vacuum chamber 101 capable of accommodating the container 102 and the stirrer 106. A base oil 103 is accommodated in the container 102, and the stirrer 106 is sunk to the bottom of the base oil 103.

[0029] A dry pump 108 that performs vacuum evacuation is connected to the vacuum chamber 101, and a turbomolecular pump 109 is connected to the dry pump 108. In other words, the turbomolecular pump 109 is connected to the vacuum chamber 101 via the dry pump 108. The dry pump 108 and the turbomolecular pump 109 are vacuum pumps. A vacuum gauge 112 is connected between the vacuum chamber 101 and the dry pump 108 to check the degree of vacuum inside the vacuum chamber 101. A computer system 110 is connected to each of the rotation unit 104, the dry pump 108, and the turbomolecular pump 109. The computer system 110 controls the rotation unit 104 that rotates the stirrer 106, and controls the operation of the dry pump 108 and the turbomolecular pump 109.

[0030] Next, the function of the molecule removal device and the molecule removal method will be specifically described with reference to FIGS.

[0031] In STEP 201 of FIG. 4, a container 102 containing a base oil (lubricant) 103 and a stirring bar 106 is placed in a vacuum chamber 101.

[0032] The next step 202 and subsequent steps are automatically performed using the computer system 110. In step 202, the computer system 110 starts processing, which causes the dry pump 108 and turbo molecular pump 109 to operate, thereby starting evacuation.

[0033] Next, in STEP 203, the degree of vacuum of the vacuum gauge 112 is confirmed by the computer system 110, and the degree of vacuum is set to less than 1 mPa (10 -4 Here, by evacuating to less than 1 mPa, the gas 107 in the vacuum chamber 101 is reduced to create an environment in which condensation into the base oil 103 and the accompanying chemical changes do not occur.

[0034] Next, in STEP 204, the rotation unit 104 is rotated in response to a rotation command from the computer system 110. This causes the magnet in the stirrer 106 to rotate without contact with the rotation unit 104, starting to stir the base oil 103. The convection generated by the rotation of the stirrer 106 generates a vortex 105 in the base oil 103. This increases the surface area of ​​the base oil 103 exposed to the vacuum environment, enhancing the effect of evaporation 111 of the gas 107.

[0035] Next, in STEP 205, the processing time required to remove the gas 107 contained in the base oil 103 is counted in the computer system 110, and after the processing time has elapsed, the process proceeds to the next STEP.

[0036] Next, in STEP 206, stirring is stopped. That is, in order to end the process, a stop command is sent from the computer system 110 to stop the rotation of the rotating unit 104 and the stirring bar 106.

[0037] Next, in STEP 207, the evacuation is stopped. That is, the computer system 110 issues a stop command to the dry pump 108 and the turbo molecular pump 109, and the vacuum gauge 112 confirms that the pressure inside the vacuum chamber 101 has been replaced with atmospheric pressure, and the process ends.

[0038] The molecule removal device is a device that has the function of removing the gas 107 from the base oil 103 in the above manner.

[0039] When the molecular removal device is used to repeatedly remove small molecules, gas 107 adheres to the inner wall of vacuum chamber 101. A configuration for removing this adhered gas 107 will be described with reference to FIG.

[0040] As shown in Fig. 5, a heater 113 is disposed inside the vacuum chamber 101. The container 102, base oil 103, and stirrer 106 are removed from the vacuum chamber 101. The process of removing the attached gas 107 does not need to be performed by placing the vacuum chamber 101 on the rotation unit 104. The heater 113 is connected to a computer system 110, and heating is controlled by the computer system 110.

[0041] The surface of the vacuum chamber 101 is heated by a heater 113, thereby releasing (desorbing) 114 the gas 107 adhering to the inner wall of the vacuum chamber 101. Here, in order to more reliably release the gas 107, it is desirable to heat the surface of the vacuum chamber 101 to 100°C or higher. It is also desirable to heat for 6 hours or more. The inside of the vacuum chamber 101 is evacuated using a dry pump 108 and a turbo molecular pump 109, thereby discharging the gas 107 released from the inner wall of the vacuum chamber 101 to the outside of the vacuum chamber 101. This makes it possible to remove the gas 107 adhering to the vacuum chamber 101.

[0042] Figure 6 shows several examples of the stirrer 106. Figure 6 is a perspective view showing several example shapes of the stirrer 106. In Figure 6, from the left, rod-shaped (cocoon-shaped), cross-shaped, and single-sided cross-disc-shaped stirrers 106 are shown.

[0043] The shape of the stirrer 106 may be rod-shaped (cocoon-shaped) as described above. This can also be said to be a shape in which two extensions extend from the center in opposite directions on the same axis. The shape of the stirrer 106 may be a cross shape having four extensions extending from the center in this way. The number of extensions is not limited to two or four, and may be any other number. The shape of the stirrer 106 may also be a one-sided cross-shaped disk shape with a cross-shaped protrusion on the top surface of the disk. The cross-shaped protrusion may also be provided on the bottom surface of the disk. Other shapes can be adopted for the shape of the stirrer 106. For example, the shape of the stirrer 106 may be a rod with corners, a rod with bulges on both ends, an ellipse, or a rod with a bulge in the center.

[0044] In this embodiment, the stirrer 106 has been described as having a structure in which a magnet is covered with glass. If the surface of the stirrer 106 is made of glass, there is little risk of damaging the container 102, which is also made of glass. In other words, it is possible to prevent the generation of dirt in the base oil 103 due to friction between the stirrer 106 and the container 102. If such friction is not a problem and any material is not corroded by the base oil 103, it is possible to select a material for the surface of the stirrer 106. For example, it is also possible to use a stirrer 106 in which a magnet is covered with ceramic.

[0045] <Effects of this embodiment> In this embodiment, a molecular removal device is used that stirs base oil in a container and removes molecular components from the base oil. This molecular removal device includes a chamber, a vacuum pump capable of evacuating the atmosphere in the chamber to a pressure of less than 100 μPa, a container that can be placed in the chamber, a stirrer that is placed in the container and includes a magnet, and a rotation unit that is configured to rotate the stirrer by rotating a magnetic field. Using this molecular removal device, a first step of evacuating the chamber with the container containing the base oil and the stirrer placed in the base oil placed in the chamber is performed, and a second step of rotating the stirrer to stir the base oil when the pressure in the chamber is reduced to less than 1 mPa due to the evacuation.

[0046] By rotating the stirrer as described above, a vortex is generated on the surface of the base oil, which increases the surface area of ​​the base oil exposed to the high vacuum environment. This increases the gas evaporation efficiency. Therefore, we provide a molecular removal method and molecular removal device that enable the removal of molecular components that are difficult to remove using molecular distillation alone.

[0047] Furthermore, when the removal of small molecules is repeatedly performed, small molecular components such as fluorine-based compounds adhere to the inner wall of the vacuum chamber of the molecular removal device, deteriorating the degree of vacuum in the vacuum chamber. In this embodiment, the small molecular components (gas 107) adhering to the inner wall of the vacuum chamber can be removed by using a heater 113 as shown in FIG.

[0048] The invention made by the present inventors has been specifically described above based on the embodiments, but it goes without saying that the present disclosure is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit of the present disclosure. [Explanation of symbols]

[0049] 101 Vacuum Chamber 102 Container 103 Base oil 104 Rotating Unit 105 Vortex 106 Stirrer 107 Gas 108 Dry Pump 109 Turbomolecular Pump 110 Computer Systems 111 Evaporation 112 Vacuum Gauge 113 Heater 114 Release

Claims

1. A molecular removal method for removing molecular components from a base oil, comprising: (a) evacuating the chamber while a container containing the base oil and a stirrer disposed in the base oil is placed in the chamber; (b) rotating the stirrer to stir the base oil in a state where the pressure in the chamber is reduced to less than 1 mPa by the exhaust; A molecular removal method comprising:

2. The molecule removal method according to claim 1, The stirrer has a built-in magnet, The stirring bar is rotated by a rotation unit disposed outside the container rotating a magnetic field, The molecule removal method, wherein the stirrer rotates without contacting the rotating unit.

3. The molecule removal method according to claim 2, The method for removing molecules, wherein the stirring bar and the rotating unit constitute a magnetic stirrer.

4. The molecule removal method according to claim 1, In the step (b), a vortex is generated on the surface of the base oil by rotating the stirrer.

5. The molecule removal method according to claim 4, In the step (b), the stirring bar below the vortex is covered with the base oil.

6. A molecular removal device that agitates a base oil and removes molecular components from the base oil, a chamber; a vacuum pump capable of evacuating the atmosphere in the chamber to a pressure of less than 100 μPa; a container positionable within the chamber; a stirrer including a magnet and placed in the container; a rotation unit configured to rotate the stirrer by rotating a magnetic field; Equipped with A molecule removal device that stirs the base oil contained in the container by rotating the stirrer.

7. 7. The molecular removal device according to claim 6, a computer system for controlling the rotary unit; The computer system causes the rotation unit to rotate a magnetic field, thereby rotating the stirrer, while the pressure in the chamber is less than 1 mPa.

8. 7. The molecular removal device according to claim 6, A molecular removal device that generates a vortex on the surface of the base oil by rotating the stirrer within the base oil.

9. 7. The molecular removal device according to claim 6, further comprising a heater disposed within the chamber; A molecular removal device that releases molecular components attached to the inner wall of the chamber by heating the heater.

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