Patent Publication Number: US-2022216030-A1

Title: Sample Loading Method and Charged Particle Beam Apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2021-001503 filed Jan. 7, 2021, the disclosure of which is hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a sample loading method and a charged particle beam apparatus. 
     Description of Related Art 
     In a case in which a biological sample or a polymer material is observed with an electron microscope such as a transmission electron microscope or a scanning transmission electron microscope, when the sample is irradiated with an electron beam, the sample may be damaged and the sample may not be able to be observed in a normal state. When the sample is cooled to a liquid nitrogen temperature or lower, damage to the sample can be reduced even if the sample is irradiated with an electron beam, and the sample can be observed in a normal state. 
     When a cooled sample is loaded into an electron microscope in a vacuum state, crystalline ice (frost) should not adhere to the sample. When crystalline ice adheres to the sample, a thickness of the sample increases and a resolution of an image decreases. 
     For example, JP-A-2015-88237 discloses a charged particle beam apparatus which includes a sample container that can be connected to a sample exchange chamber via a gate valve. This charged particle beam apparatus can evacuate the inside of the sample container in a state in which the gate valve is closed. In this charged particle beam apparatus, since the inside of the sample container can be evacuated in a state in which the gate valve is closed, the gate valve can be opened after the inside of the sample container is made to become a vacuum state to solidify liquid nitrogen. As a result, a sample can be loaded from the sample container into the sample exchange chamber even in a state in which liquid nitrogen remains in the sample container. In addition, it is possible to prevent crystalline ice from adhering to the sample. 
     As described above, in the charged particle beam apparatus, when a cooled sample is loaded, it is necessary to reduce the adhesion of crystalline ice to the sample. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention, there is provided a sample loading method of loading a cooled sample into a sample exchange chamber of a charged particle beam apparatus, the method including: 
     attaching a sample container in which a sample and liquid nitrogen are accommodated to the sample exchange chamber via a gate valve; 
     evacuating a space between a liquid surface of the liquid nitrogen and the gate valve in a state in which the gate valve is closed; 
     discharging the liquid nitrogen in the sample container after the space between the liquid surface of the liquid nitrogen and the gate valve has been evacuated; 
     evacuating a space in the sample container after the liquid nitrogen in the sample container has been discharged; and 
     opening the gate valve after the space in the sample container has been evacuated. 
     According to a second aspect of the invention, there is provided a charged particle beam apparatus including: 
     a sample chamber; 
     a sample exchange chamber connected to the sample chamber; 
     a sample container which is capable of being attached to the sample exchange chamber via a gate valve and accommodates a sample and liquid nitrogen; 
     a discharge mechanism for discharging the liquid nitrogen in the sample container; 
     an evacuation system for evacuating a space in the sample container; and 
     a control unit that controls the gate valve, the discharge mechanism, and the evacuation system, 
     the control unit performing processing of: 
     causing the evacuation system to evacuate a space between a liquid surface of the liquid nitrogen in the sample container attached to the sample exchange chamber and the gate valve in a state in which the gate valve is closed; 
     causing the discharge mechanism to discharge the liquid nitrogen in the sample container after the evacuation system has evacuated the space between the liquid surface of the liquid nitrogen and the gate valve; 
     causing the evacuation system to evacuate the space in the sample container after the discharge mechanism has discharged the liquid nitrogen in the sample container; and 
     opening the gate valve after the evacuation system has evacuated the space in the sample container. 
     According to a third aspect of the invention, there is provided a charged particle beam apparatus including: 
     a sample chamber; 
     a sample exchange chamber connected to the sample chamber; 
     a sample container which is capable of being attached to the sample exchange chamber via a gate valve and accommodates a sample and liquid nitrogen; 
     a discharge mechanism for discharging the liquid nitrogen in the sample container; 
     an evacuation system for evacuating a space between a liquid surface of the liquid nitrogen and the gate valve and a space in the sample container; and 
     a control unit that controls the evacuation system, 
     the control unit causing the evacuation system to evacuate the space between the liquid surface of the liquid nitrogen and the gate valve for only a set period of time, and 
     the set period of time being set as a period of time during which the liquid nitrogen does not solidify. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a configuration of a transmission electron microscope according to the first embodiment. 
         FIG. 2  is a flowchart illustrating an example of a sample loading method in a transmission electron microscope according to the first embodiment. 
         FIG. 3  is a diagram schematically illustrating a sample loading step. 
         FIG. 4  is a diagram schematically illustrating a sample loading step. 
         FIG. 5  is a diagram schematically illustrating a sample loading step. 
         FIG. 6  is a diagram schematically illustrating a sample loading step. 
         FIG. 7  is a diagram schematically illustrating a sample loading step. 
         FIG. 8  is a diagram schematically illustrating a sample loading step. 
         FIG. 9  is a diagram schematically illustrating a sample loading step. 
         FIG. 10  is a diagram illustrating a main part of a transmission electron microscope according to a modification example of the first embodiment. 
         FIG. 11  is a diagram illustrating a configuration of a transmission electron microscope according to the second embodiment. 
         FIG. 12  is a flowchart illustrating an example of a sample introduction process of a control unit. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     According to an embodiment of the invention, there is provided a sample loading method of loading a cooled sample into a sample exchange chamber of a charged particle beam apparatus, the method including: 
     attaching a sample container in which the sample and liquid nitrogen are accommodated to the sample exchange chamber via a gate valve; 
     evacuating a space between a liquid surface of the liquid nitrogen and the gate valve in a state in which the gate valve is closed; 
     discharging the liquid nitrogen in the sample container after the space between the liquid surface of the liquid nitrogen and the gate valve has been evacuated; 
     evacuating a space in the sample container after the liquid nitrogen in the sample container has been discharged; and 
     opening the gate valve after the space in the sample container has been evacuated. 
     In such a sample loading method, because the liquid nitrogen in the sample container is discharged after the space between the liquid surface of the liquid nitrogen and the gate valve has been evacuated, the adhesion of crystalline ice to the sample can be reduced. 
     According to another embodiment of the invention, there is provided a charged particle beam apparatus including: 
     a sample chamber; 
     a sample exchange chamber connected to the sample chamber; 
     a sample container which is capable of being attached to the sample exchange chamber via a gate valve and accommodates a sample and liquid nitrogen; 
     a discharge mechanism for discharging the liquid nitrogen in the sample container; 
     an evacuation system for evacuating a space in the sample container; and 
     a control unit that controls the gate valve, the discharge mechanism, and the evacuation system, 
     the control unit performing processing of: 
     causing the evacuation system to evacuate a space between a liquid surface of the liquid nitrogen in the sample container attached to the sample exchange chamber and the gate valve in a state in which the gate valve is closed; 
     causing the discharge mechanism to discharge the liquid nitrogen in the sample container after the evacuation system has evacuated the space between the liquid surface of the liquid nitrogen and the gate valve; 
     causing the evacuation system to evacuate the space in the sample container after the discharge mechanism has discharged the liquid nitrogen in the sample container; and 
     opening the gate valve after the evacuation system has evacuated the space in the sample container. 
     In such a charged particle beam apparatus, because the liquid nitrogen in the sample container is discharged after the space between the liquid surface of the liquid nitrogen and the gate valve has been evacuated, the adhesion of crystalline ice to the sample can be reduced. 
     According to still another embodiment of the invention, there is provided a charged particle beam apparatus including: 
     a sample chamber; 
     a sample exchange chamber connected to the sample chamber; 
     a sample container which is capable of being attached to the sample exchange chamber via a gate valve and accommodates a sample and liquid nitrogen; 
     a discharge mechanism for discharging the liquid nitrogen in the sample container; 
     an evacuation system for evacuating a space between a liquid surface of the liquid nitrogen and the gate valve and a space in the sample container; and 
     a control unit that controls the evacuation system, 
     the control unit causing the evacuation system to evacuate the space between the liquid surface of the liquid nitrogen and the gate valve for only a set period of time, and 
     the set period of time being set as a period of time during which the liquid nitrogen does not solidify. 
     Because such a charged particle beam apparatus includes the evacuation system for evacuating the space between the liquid surface of the liquid nitrogen and the gate valve, the adhesion of crystalline ice to the sample can be reduced. Further, in such a charged particle beam apparatus, because the space between the liquid surface of the liquid nitrogen and the gate valve can be evacuated only for only the period of time during which the liquid nitrogen does not solidify, it is possible to prevent the solidified liquid nitrogen from adhering to the sample. 
     Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings. It is noted that the following embodiments do not unduly limit the scope of the invention as stated in the claims. Further, all of the components described in the following embodiments are not necessarily essential requirements of the invention. 
     Furthermore, although a transmission electron microscope for observing and analyzing a sample by irradiating the sample with an electron beam will be described below as an example of the charged particle beam apparatus according to the invention, the charged particle beam apparatus according to the invention may be an apparatus for observing and analyzing a sample by irradiating the sample with a charged particle beam other than an electron beam (an ion beam or the like). 
     1. First Embodiment 
     1.1. Configuration of Transmission Electron Microscope 
     First, a transmission electron microscope according to a first embodiment will be described with reference to the drawings.  FIG. 1  is a diagram illustrating a configuration of a transmission electron microscope  100  according to the first embodiment. 
     As illustrated in  FIG. 1 , the transmission electron microscope  100  includes a sample container  2 , a sample chamber  10 , a sample holder  20 , a sample exchange chamber  30 , a storage  40 , a cooling unit  50 , a first transport device  60 , a second transport device  70 , an evacuation system  80 , and a discharge mechanism  90 . 
     The sample container  2  is a container for accommodating a sample. In the illustrated example, a magazine  4  and liquid nitrogen  5  are accommodated in the sample container  2 . A plurality of cartridges  6  can be attached to the magazine  4 . The sample is fixed to the cartridges  6 . The magazine  4  is immersed in the liquid nitrogen  5 . That is, the sample is immersed in the liquid nitrogen  5 . Therefore, the sample can be maintained at a liquid nitrogen temperature in the sample container  2 . The sample container  2  functions as a transport container for transporting the sample in a cooled state. 
     Although the case in which the magazine  4  is accommodated in the sample container  2  is described here, the cartridges  6  and the sample may be directly accommodated in the sample container  2 . 
     The sample chamber  10  is provided in a lens barrel  12 . Although not shown, an electron source, an irradiation optical system for irradiating a sample with an electron beam emitted from the electron source, and an image capturing optical system for capturing a transmission electron microscope image with the electron beam transmitted through a sample are disposed in the lens barrel  12 . Further, although not shown, the transmission electron microscope  100  includes a detector for detecting an image captured by an image capturing system, a detector for detecting X-rays emitted from a sample, and the like. 
     The sample chamber  10  includes a space between an upper pole and a lower pole of a pole piece of an objective lens (not shown). The sample chamber  10  is evacuated by an evacuation device. The sample holder  20  is disposed in the sample chamber  10 , and the cartridges  6  are attached to a tip end of the sample holder  20 . 
     The sample holder  20  is positioned by a goniometer stage  24 . The goniometer stage  24  can tilt the sample held by the sample holder  20 . For example, in the transmission electron microscope  100 , the sample can be tilted with respect to two axes orthogonal to each other. 
     An attachment portion to which the cartridges  6  are attached is provided at the tip end of the sample holder  20 . By attaching the cartridges  6  to the sample holder  20 , it is possible to observe the sample in the transmission electron microscope  100 . 
     The sample exchange chamber  30  is connected to the sample chamber  10 . A gate valve  32  is provided between the sample exchange chamber  30  and the sample chamber  10 . Although not shown, the sample exchange chamber  30  is evacuated by an evacuation device such as a turbo molecular pump and is maintained in a vacuum state. 
     The sample container  2  is attached to the sample exchange chamber  30 . The sample container  2  is attached to the sample exchange chamber  30  via a gate valve  34 . In a case in which the sample container  2  is attached to the sample exchange chamber  30 , the gate valve  34  is disposed between the sample exchange chamber  30  and the sample container  2 . The sample container  2  is attachable and detachable with respect to the sample exchange chamber  30 . 
     In the illustrated example, the sample container  2  is attached to the sample exchange chamber  30  via a connecting portion  36 . The connecting portion  36  is connected to the sample exchange chamber  30 . The sample container  2  is attachable and detachable with respect to the connecting portion  36 . An evacuation pipe  84  of the evacuation system  80  and a discharge pipe  94  of the discharge mechanism  90  are connected to the connecting portion  36 . 
     In a state in which the sample container  2  is connected to the connecting portion  36 , a vacuum seal  38  is disposed between the connecting portion  36  and the sample container  2 . The vacuum seal  38  is, for example, an O-ring. When the sample container  2  is attached to the sample exchange chamber  30  by the vacuum seal  38 , the inside of the sample exchange chamber  30  and the inside of the sample container  2  can be made airtight. 
     The storage  40  is provided in the sample exchange chamber  30 . The storage  40  can accommodate the plurality of cartridges  6 . The storage  40  is cooled by the cooling unit  50 . Therefore, the sample can be stored in a cooled state. The storage  40  is formed of, for example, a material having a high thermal conductivity. 
     The cooling unit  50  cools the storage  40 . The cooling unit  50  includes, for example, a tank  52  containing liquid nitrogen and a heat conductive member  54   a  that thermally connects the tank  52  and the storage  40 . When the heat conductive member  54   a  is cooled with the liquid nitrogen contained in the tank  52 , the storage  40  is cooled. 
     The cooling unit  50  further cools a chuck device  64  of the first transport device  60  and a chuck device  74  of the second transport device  70 . The cooling unit  50  includes a heat conductive member  54   b  that thermally connects the tank  52  and the chuck device  64  and a heat conductive member  54   c  that thermally connects the tank  52  and the chuck device  74 . Each of the heat conductive member  54   a , the heat conductive member  54   b , and the heat conductive member  54   c  is, for example, a copper wire. 
     The first transport device  60  transports the cartridges  6  between the sample container  2  and the sample exchange chamber  30 . That is, the first transport device  60  transports the sample between the sample container  2  and the sample exchange chamber  30 . Here, the first transport device  60  transports the cartridges  6  by transporting the magazine  4 . 
     The first transport device  60  includes a transport rod  62  and the chuck device  64  provided at a tip end of the transport rod  62 . In the first transport device  60 , it is possible to grip the magazine  4  using the chuck device  64 . The first transport device  60  transports the magazine  4  between the sample container  2  and the sample exchange chamber  30  by moving the magazine  4  gripped by the chuck device  64  in a vertical direction. 
     The second transport device  70  transports the cartridges  6  between the sample exchange chamber  30  and the sample chamber  10 . That is, the second transport device  70  transports the sample between the sample exchange chamber  30  and the sample chamber  10 . The second transport device  70  takes the cartridges  6  out of the magazine  4  gripped by the first transport device  60 . The second transport device  70  transports the taken-out cartridges  6  from the sample exchange chamber  30  to the sample chamber  10  and attaches the cartridges  6  to the sample holder  20 . Further, the second transport device  70  removes the cartridges  6  from the sample holder  20  and transports the cartridges  6  from the sample chamber  10  to the sample exchange chamber  30 . 
     The second transport device  70  includes a transport rod  72  and the chuck device  74  provided at a tip end of the transport rod  72 . In the second transport device  70 , it is possible to grip the cartridges  6  using the chuck device  74 . The second transport device  70  transports the cartridges  6  between the sample exchange chamber  30  and the sample chamber  10  by moving the cartridges  6  gripped by the chuck device  74  in a horizontal direction. 
     The second transport device  70  further transfers the cartridges  6  between the magazine  4  gripped by the first transport device  60  and the storage  40 . For example, the second transport device  70  takes the cartridges  6  out of the magazine  4  gripped by the first transport device  60  and attaches the cartridges  6  to the storage  40 . Further, the second transport device  70  takes the cartridges  6  out of the storage  40  and transports the taken-out cartridges  6  to the sample chamber  10 . 
     The first transport device  60  and the second transport device  70  can transport the cartridges  6  to the sample container  2 , the sample exchange chamber  30 , the storage  40 , and the sample chamber  10 . 
     The evacuation system  80  includes an evacuation device  82 , the evacuation pipe  84 , and a gate valve  86 . The evacuation device  82  evacuates the inside of the sample container  2  via the evacuation pipe  84 . The evacuation device  82  is, for example, a scroll pump. The evacuation pipe  84  is provided with the gate valve  86 . The evacuation pipe  84  constitutes an evacuation path between the evacuation device  82  and the sample container  2 . When the gate valve  86  is opened, the inside of the sample container  2  is evacuated. When the inside of the sample container  2  is evacuated with the evacuation system  80 , the inside of the sample container  2  can be made to become a vacuum state. 
     The discharge mechanism  90  discharges the liquid nitrogen  5  in the sample container  2 . The discharge mechanism  90  includes a suction member  92 , the discharge pipe  94 , a gate valve  96 , and the evacuation device  82 . The evacuation device  82  functions as a part of the evacuation system  80  and also functions as a part of the discharge mechanism  90 . 
     The suction member  92  is disposed in the sample container  2  when the sample container  2  is attached to the sample exchange chamber  30 . The suction member  92  is connected to the discharge pipe  94 . The discharge pipe  94  connects the suction member  92  and the evacuation device  82 . The discharge pipe  94  is provided with the gate valve  96 . When the gate valve  96  is opened, the liquid nitrogen  5  is discharged from the sample container  2 . 
     1.2. Sample Loading Method 
     Next, a sample loading method of loading a cooled sample into the sample exchange chamber  30  in the transmission electron microscope  100  will be described. Hereinafter, the case in which the sample is fixed to the cartridges  6  will be described. 
       FIG. 2  is a flowchart illustrating an example of the sample loading method in the transmission electron microscope  100 .  FIGS. 3 to 9  are diagrams each schematically illustrating a sample loading step. In  FIGS. 4 to 9 , only a main part of the transmission electron microscope  100  is illustrated for convenience. 
     First, as illustrated in  FIG. 3 , the sample container  2  in which the cartridges  6  and the liquid nitrogen  5  are accommodated is prepared (S 100 ). 
     The cartridges  6  and the liquid nitrogen  5  are accommodated in the sample container  2 . The cartridges  6  are immersed in the liquid nitrogen  5 . As a result, the sample can be kept cooled to the liquid nitrogen temperature. In the example illustrated in  FIG. 3 , the plurality of cartridges  6  are accommodated in the magazine  4 . A liquid surface of the liquid nitrogen  5  is located above an upper surface of the magazine  4 . 
     Next, as illustrated in  FIG. 4 , the sample container  2  in which the cartridges  6  and the liquid nitrogen  5  are accommodated is attached to the sample exchange chamber  30  (S 102 ). 
     As illustrated in  FIG. 4 , the sample container  2  is attached to the connecting portion  36 . At this time, the gate valve  34  is closed. Since the vacuum seal  38  is disposed between the sample container  2  and the connecting portion  36 , the inside of the sample exchange chamber  30  and the inside of the sample container  2  can be made airtight. 
     An atmosphere exists in a space  7  between the liquid surface of the liquid nitrogen  5  and the gate valve  34 . The atmosphere existing in the space  7  is enclosed when the sample container  2  is attached to the sample exchange chamber  30 . The space  7  is a space above the liquid surface of the liquid nitrogen  5 . In the illustrated example, the space  7  is a space defined by the liquid surface of the liquid nitrogen  5 , the gate valve  34 , an inner wall of the connecting portion  36 , and an inner surface of the sample container  2 . 
     As illustrated in  FIG. 5 , the space  7  between the liquid surface of the liquid nitrogen  5  and the gate valve  34  is evacuated in a state in which the gate valve  34  is closed (S 104 ). 
     Specifically, first, the gate valve  86  is opened, and the space  7  is evacuated by the evacuation device  82  via the evacuation pipe  84 . Then, the gate valve  86  is closed immediately after a period of time during which the liquid nitrogen  5  does not solidify has elapsed. That is, a period of time from opening the gate valve  86  to closing the gate valve  86  is the period of time during which the liquid nitrogen  5  does not solidify. The period of time during which the liquid nitrogen  5  does not solidify is a period of time from when the evacuation of the space  7  is started until a pressure in the sample container  2  decreases and the liquid nitrogen  5  starts to solidify. 
     The transmission electron microscope  100  includes a control unit  88  that controls the evacuation system  80 . The control unit  88  causes the evacuation system  80  to evacuate the space  7  for only a set period of time. The set period of time is set as a period of time during which the liquid nitrogen  5  does not solidify. It is possible to know in advance the period of time during which liquid nitrogen  5  does not solidify by conducting an experiment under the same conditions as in this step S 104 . 
     The control unit  88  controls the gate valve  86 . The control unit  88  opens the gate valve  86  for only a set period of time which is set in advance. The control unit  88  includes a timer. The timer starts measurement at a timing when the gate valve  86  is opened and notifies of a timing when the set period of time has elapsed. When the control unit  88  receives the notification from the timer, the control unit  88  closes the gate valve  86 . 
     In the above, the control unit  88  opens or closes the gate valve  86 , but the user may manually open or close the gate valve  86 . 
     As illustrated in  FIG. 6 , the liquid nitrogen  5  in the sample container  2  is discharged (S 106 ). 
     The liquid nitrogen  5  in the sample container  2  can be discharged using the discharge mechanism  90 . Specifically, the gate valve  96  is opened. As a result, the liquid nitrogen  5  in the sample container  2  is sucked out from the suction member  92  and discharged through the discharge pipe  94 . The liquid nitrogen  5  is vaporized while passing through the discharge pipe  94  and is evacuated by the evacuation device  82 . 
     As illustrated in  FIG. 7 , the space in the sample container  2  is discharged (S 108 ). 
     Specifically, the gate valve  86  is opened, and the space in the sample container  2  is evacuated by the evacuation device  82  via the evacuation pipe  84 . At this time, the gate valve  96  is open in the example illustrated in  FIG. 7 , but the gate valve  96  may be closed. 
     As illustrated in  FIG. 8 , when the pressure in the space in the sample container  2  becomes equal to or lower than a predetermined pressure, the gate valve  34  is opened (S 110 ). The transmission electron microscope  100  has a vacuum gauge for measuring the pressure in the space in the sample container  2 . From the measurement result of this vacuum gauge, it is possible to know the pressure in the space in the sample container  2 . 
     As illustrated in  FIG. 9 , the magazine  4  is transported from the sample container  2  to the sample exchange chamber  30  by the first transport device  60  (S 112 ). Next, the gate valve  34  is closed (S 114 ). Further, the gate valve  86  and the gate valve  96  are closed. 
     Through the above steps, the magazine  4  can be loaded into the sample exchange chamber  30 . 
     1.3. Effect 
     The sample loading method in the transmission electron microscope  100  includes the step S 102  of attaching the sample container  2  in which the cartridges  6  and the liquid nitrogen  5  are accommodated to the sample exchange chamber  30  via the gate valve  34 , the step S 104  of evacuating the space  7  in a state in which the gate valve  34  is closed, the step S 106  of discharging the liquid nitrogen  5  in the sample container  2  after the space  7  has been evacuated, the step S 108  of evacuating the space in the sample container  2  after the liquid nitrogen  5  in the sample container  2  has been discharged, and the step S 110  of opening the gate valve  34  after the space in the sample container  2  has been evacuated. 
     As described above, in the sample loading method in the transmission electron microscope  100 , the space  7  between the liquid surface of the liquid nitrogen  5  and the gate valve  34  is evacuated before the liquid nitrogen  5  in the sample container  2  is discharged. Therefore, the adhesion of crystalline ice to the sample can be reduced. 
     For example, in a case in which the liquid nitrogen  5  in the sample container  2  is discharged without the space  7  being evacuated, when the liquid surface of the liquid nitrogen  5  is lowered, the cartridges  6  are exposed to the atmosphere existing in the space  7  and the crystalline ice adheres to the sample. In the sample loading method in the transmission electron microscope  100 , the cartridges  6  are not exposed to the atmosphere because the space  7  is evacuated before the liquid nitrogen  5  in the sample container  2  is discharged. Therefore, the adhesion of crystalline ice to the sample can be reduced. 
     In the sample loading method in the transmission electron microscope  100 , in the step S 104  of evacuating the space  7 , the space  7  is evacuated only for only a period of time during which the liquid nitrogen  5  does not solidify. Therefore, it is possible to prevent the solidified liquid nitrogen  5  from adhering to the sample. 
     In the transmission electron microscope  100 , the control unit  88  causes the evacuation system  80  to evacuate the space  7  for only the set period of time, and the set period of time is set to the period of time during which the liquid nitrogen  5  does not solidify. Therefore, in the transmission electron microscope  100 , the space  7  can be evacuated only for only the period of time during which the liquid nitrogen  5  does not solidify, and thus it is possible to prevent the solidified liquid nitrogen  5  from adhering to the sample. 
     1.4. Modification Example 
     Next, a modification example of the transmission electron microscope  100  according to the first embodiment will be described. Hereinafter, points different from the above example of the transmission electron microscope  100  will be described, and description of the same points will be omitted.  FIG. 10  is a diagram illustrating a main part of a transmission electron microscope  101  according to the modification example of the first embodiment. 
     As illustrated in  FIG. 10 , the evacuation system  80  includes a second evacuation device  182  in addition to the evacuation device  82  (hereinafter also referred to as a “first evacuation device  82 ”). Further, the evacuation system  80  includes an evacuation pipe  184  and a gate valve  186 . 
     The second evacuation device  182  evacuates the space in the sample container  2  via the evacuation pipe  184  and the evacuation pipe  84 . An ultimate pressure of the second evacuation device  182  is lower than an ultimate pressure of the first evacuation device  82 . The first evacuation device  82  is, for example, a scroll pump, and the second evacuation device  182  is, for example, a turbo molecular pump. 
     The evacuation pipe  184  connects the second evacuation device  182  and the evacuation pipe  84 . The evacuation pipe  184  is provided with a gate valve  186 . The gate valve  86  and the gate valve  186  can switch between a state in which the space in the sample container  2  is evacuated using the first evacuation device  82  and a state in which the space in the sample container  2  is evacuated using the second evacuation device  182 . 
     A sample loading method in the transmission electron microscope  101  is similar to the sample loading method in the transmission electron microscope  100  described above except that the second evacuation device  182  is used in the step S 108  of evacuating the space in the sample container  2  illustrated in  FIG. 2 . 
     That is, in the sample loading method in the transmission electron microscope  101 , the first evacuation device  82  is used in the step S 104  of evacuating the space  7 , and the second evacuation device  182  is used in the step S 108  of evacuating the space in the sample container  2 . Therefore, in the sample loading method in the transmission electron microscope  101 , for example, the pressure in the sample container  2  can be made lower (a higher degree of vacuum) than in the case in which the first evacuation device  82  is used in the step S 108 . As a result, the adhesion of crystalline ice to the sample can be further reduced. 
     2. Second Embodiment 
     2.1. Configuration of Transmission Electron Microscope 
     Next, a transmission electron microscope according to a second embodiment will be described with reference to the drawings.  FIG. 11  is a diagram illustrating a configuration of a transmission electron microscope  200  according to the second embodiment. Hereinafter, in the transmission electron microscope  200  according to the second embodiment, the members having the same functions as the constituent members of the transmission electron microscope  100  according to the first embodiment are designated by the same reference signs, and detailed description thereof will be omitted. 
     As illustrated in  FIG. 11 , the transmission electron microscope  200  includes a control unit  210 . 
     The control unit  210  controls the gate valve  34 , the evacuation system  80 , and the discharge mechanism  90 . The control unit  210  further controls the first transport device  60 . The control unit  210  performs, for example, a sample loading process of loading the sample from the sample container  2  into the sample exchange chamber  30 . 
     The control unit  210  includes, for example, a central processing unit (CPU) and a storage device (a random access memory (RAM), a read only memory (ROM), and the like). The control unit  210  performs various control processes by executing a program stored in the storage device by the CPU. 
     2.2. Sample Loading Method 
     In the transmission electron microscope  200 , the control unit  210  performs steps S 104  to S 114  of  FIG. 2 . 
       FIG. 12  is a flowchart illustrating an example of the sample loading process of the control unit  210 . 
     When a user attaches the sample container  2  to the sample exchange chamber  30  and then issues an instruction to start sample loading (hereinafter also referred to as a “start instruction”) to the control unit  210 , the control unit  210  starts the sample loading process. The control unit  210  determines that the user has issued the start instruction in a case in which, for example, an operation of pressing a sample loading start button (not shown) is performed. 
     In a case in which the control unit  210  determines that the start instruction has been issued (Yes in S 200 ), the control unit  210  causes the evacuation system  80  to evacuate the space  7  between the liquid surface of the liquid nitrogen  5  and the gate valve  34  (S 202 ). 
     The control unit  210  opens the gate valve  86  as illustrated in  FIG. 5 . As a result, the space  7  is evacuated by the evacuation device  82 . The control unit  210  opens the gate valve  86  for only a set period of time which is set in advance. This period of time is set as a period of time during which the liquid nitrogen  5  does not solidify. The control unit  210  starts time measurement at a timing when the gate valve  86  is opened and closes the gate valve  86  at a timing when the set period of time has elapsed. 
     The control unit  210  may include a timer for measuring the period of time during which the liquid nitrogen  5  does not solidify. This timer may be used to measure the period of time during which the gate valve  86  is open. 
     Next, the control unit  210  causes the discharge mechanism  90  to discharge the liquid nitrogen  5  in the sample container  2  (S 204 ). The control unit  210  opens the gate valve  96  as illustrated in  FIG. 6 . As a result, the liquid nitrogen  5  in the sample container  2  is sucked out from the suction member  92  and discharged through the discharge pipe  94 . 
     Next, the control unit  210  causes the evacuation system  80  to evacuate the space in the sample container  2  (S 206 ). The control unit  210  opens the gate valve  86  as illustrated in  FIG. 7 . As a result, the space in the sample container  2  is evacuated by the evacuation device  82 . The transmission electron microscope  200  has a vacuum gauge for measuring the pressure in the space in the sample container  2 . 
     The control unit  210  starts monitoring a pressure in the space in the sample container  2  (S 208 ). The control unit  210  receives the measurement result of the pressure in the space in the sample container  2  output from the vacuum gauge and monitors the pressure. In a case in which the control unit  210  determines that the pressure in the space in the sample container  2  is equal to or lower than a predetermined pressure (Yes in S 210 ), the control unit  210  opens the gate valve  34  as illustrated in  FIG. 8  (S 212 ). 
     As illustrated in  FIG. 9 , the control unit  210  causes the first transport device  60  to transport the magazine  4  from the sample container  2  to the sample exchange chamber  30  (S 214 ). The control unit  210  closes the gate valve  34  after the magazine  4  has been loaded into the sample exchange chamber  30  (S 216 ). Further, the control unit  210  closes the gate valve  86  and the gate valve  96 . Then, the control unit  210  ends the sample loading process. 
     2.3. Effect 
     In the transmission electron microscope  200 , the control unit  210  performs the process S 202  of causing the evacuation system  80  to evacuate the space  7  in a state in which the gate valve  34  is closed, the process S 204  of causing the discharge mechanism  90  to discharge the liquid nitrogen  5  in the sample container  2  after the process S 202 , a process S 206  of causing the evacuation system  80  to evacuate the space in the sample container  2  after the process S 204 , and a process S 212  of opening the gate valve  34  after the process S 206 . Therefore, in the transmission electron microscope  200 , the sample can be easily loaded from the sample container  2  into the sample exchange chamber  30 . Further, in the transmission electron microscope  200 , when the sample is loaded from the sample container  2  into the sample exchange chamber  30 , the adhesion of crystalline ice to the sample can be reduced. 
     3. Other 
     The invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the gist of the invention. 
     In the first embodiment and the second embodiment described above, the case in which the charged particle beam apparatus according to the invention is a transmission electron microscope has been described, but the charged particle beam apparatus according to the invention is not particularly limited as long as it is an apparatus using a charged particle beam such as an electron or ion beam. The charged particle beam apparatus according to the invention may include, for example, an electron microscope such as a scanning transmission electron microscope (STEM) or a scanning electron microscope (SEM), an electron probe microanalyzer (EPMA), a focused ion beam apparatus (FIB apparatus), an electron beam exposure apparatus, or the like. 
     The above-described embodiments and modification example are merely examples, and the invention is not limited thereto. For example, each embodiment and the modification example can be combined as appropriate. 
     The invention is not limited to the above-described embodiments, and various modifications can be made. For example, the invention includes configurations that are substantially the same as the configurations described in the embodiments. Substantially same configurations means configurations that are the same in function, method, and results, or configurations that are the same in objective and effects, for example. The invention also includes configurations in which non-essential elements described in the embodiments are replaced by other elements. The invention also includes configurations having the same effects as those of the configurations described in the embodiments, or configurations capable of achieving the same objectives as those of the configurations described in the embodiments. The invention further includes configurations obtained by adding known art to the configurations described in the embodiments. 
     Some embodiments of the invention have been described in detail above, but a person skilled in the art will readily appreciate that various modifications can be made from the embodiments without materially departing from the novel teachings and effects of the invention. Accordingly, all such modifications are assumed to be included in the scope of the invention.