Abstract:
In this invention, vibrations generated by a freezer from a cooling mechanism for cooling an ion source emitter tip are prevented from being transmitted to the emitter tip as much as possible, while the cooling capability of the cooling mechanism is improved widely. The ion beam device ( 10 ) is equipped with: an ion source housing ( 22 ) provided with an emitter tip ( 45 ) and defining an ion source chamber ( 27 ) supplied with an ionization gas or gas molecules; a gas pot ( 51 ) provided in the ion source chamber ( 27 ) so as to be thermally connected to the emitter tip ( 45 ) and accommodated so as to have no direct physical contact with a cooling stage ( 57 ) of a freezer ( 52 ); and a spacer ( 59 ) provided on the peripheral surface of the cooling stage ( 57 ) housed by the gas pot ( 51 ) and maintaining a given interval or greater between the peripheral surface of the cooling stage ( 57 ) and the internal peripheral surface of the gas pot ( 52 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an ion beam device which includes an ion microscope, an ion beam, processing observation device and the like, a freezer used for cooling of an emitter tip of an ion source in the ion beam device, and a method of mounting a cooling mechanism to the ion beam device. 
       BACKGROUND ART 
       [0002]    It is possible to observe a sample surface structure by scanning an electron beam and irradiating the sample with the electron beam and detecting secondary charged particles released from the sample at that time. An example of such electron beam devices is a scanning electron microscope (hereinafter, also referred to as the SEM). 
         [0003]    Meanwhile, it is also possible to observe a sample surface structure by scanning an ion beam instead of the electron beam and irradiating the sample with the ion beam and detecting secondary charged particles released from the sample at that time. An example of such ion beam devices is a scanning ion microscope (hereinafter, also abbreviated as the SIM). In particular, when the sample is irradiated with the ion beam using ion species of a light mass, such as hydrogen and helium, in the ion beam device such as the scanning ion microscope, sputtering action relatively decreases, which is preferable to observe the sample. 
         [0004]    A gas field ionization ion source is preferably used as an ion source of such an ion beam device. The gas field ionization ion source is the ion source that ionizes a gas using an electric field generated by an emitter tip and generates an ion beam. The gas field ionization ion source is configured to include a gas ionization chamber containing the emitter tip which has a needle shape and to which a high voltage can be applied, and an ionization gas (ion material gas) is supplied to the gas ionization chamber from the gas source via a gas supply piping. 
         [0005]    In the gas field ionization ion source, when the ionization gases (or gas molecules) supplied from the gas supply piping approaches a distal end of the needle-shaped emitter tip to which the high voltage is applied and an intense electric field is applied, electrons inside the gases (gas molecules) tunnel through a potential barrier, which has been reduced by the intense electric field, due to a quantum tunneling effect, and the gases (gas molecules) are released as positive ions. These released ions are used as the ion beam in the ion beam device. 
         [0006]    The gas field ionization ion source can generate an ion beam having a narrow energy width. In addition, a size of the ion generation source is small, and thus, it is possible to generate a fine ion beam. 
         [0007]    Meanwhile, it is necessary to obtain an ion beam, with a high current density on a sample in order to observe the sample at a high signal to noise ratio (S/N ratio) in the ion beam device including the scanning ion microscope. In order for this, it is necessary to increase an ion radiation angle current density of the gas field ionization ion source. A molecular density of the ionization gas in the vicinity of the emitter tip may be increased in order to increase the ion radiation angle current density. 
         [0008]    In this case, a gas molecular density per unit pressure is inversely proportional to temperature of the gas. In this regard, it is desirable to cool the emitter tip to cryogenic temperature and decrease the temperature of the ionization gas in the vicinity of the emitter tip. Accordingly, it is possible to increase the molecular density of the ionization gas in the vicinity of the emitter tip by cooling the emitter tip to the cryogenic temperature. 
         [0009]    On the other hand, it is necessary to prevent vibration of a freezer, which is an ion beam device cooling mechanism that cools the emitter tip to the cryogenic temperature, from being transmitted to the emitter tip in order to observe the sample with high resolution in the ion beam, device including the scanning ion microscope. Thus, PTL 1 discloses an ion beam device cooling mechanism provided with a function of preventing transmission of vibration caused by a refrigerator to an emitter tip of a gas field ionization ion source, the ion beam device cooling mechanism in which the mechanical refrigerator and a helium gas pot are combined. A helium gas (inert gas) is stored in the helium gas pot as a cooling medium gas for cooling of the gas field ionization ion source. 
       CITATION LIST 
     Patent Literature 
       [0010]    PTL 1: WO 2009/147894 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0011]    The inventor of the present application has conducted extensive studies on an ion beam device which is provided with an ion beam device cooling mechanism so as to cool an emitter tip to cryogenic temperature and to prevent vibration caused by a freezer from being transmitted to the emitter tip, and as a result, has obtained the following findings. 
         [0012]    In the ion beam device cooling mechanism disclosed in PTL 1, a gas pot that transmits coldness to the emitter tip and a cooling stage of the refrigerator are likely to have direct physical contact with each other at the time of assembling a vacuum chamber of a device main body and the refrigerator. Thus, when the gas pot and the cooling stage of the refrigerator are brought into direct physical contact with each other, vibration of a main body of the refrigerator is also transmitted to the gas pot. In general, the gas pot is fixed to the vacuum chamber defining a gas ionization chamber of the ion beam device rigidly, that is, mechanically firmly so that a positional relationship thereof is not deviated. Thus, when the gas pot vibrates, the vacuum, chamber of the ion beam device also vibrates in response thereto. In addition, the vacuum chamber and the emitter tip of the gas field ionization ion source are also rigidly fixed to each other, and thus, the emitter tip also vibrates when the vacuum chamber vibrates. As a result, the emitter tip vibrates, it is difficult for a released ion beam to be sufficiently converged, and it is difficult to perform high-resolution observation. 
         [0013]    In order to prevent this problem, it is necessary to make a gap (interval) between the gas pot and the cooling stage of the refrigerator wide such that the pot and the cooling stage have no direct physical contact with each other. However, the gas pot is not sufficiently cooled by the cooling stage when the gap between the gas pot and the cooling stage is made wide. 
         [0014]    Meanwhile, the gas pot and the emitter tip are thermally connected to each other, and thus, the emitter tip is not sufficiently cooled when the gas pot is not sufficiently cooled. When the emitter tip is not sufficiently cooled, it is difficult to lower the temperature of the ionization gas in the vicinity of the emitter tip to be the cryogenic temperature. Further, when it is difficult to lower the temperature of the ionization gas in the vicinity of the emitter tip to be the cryogenic temperature, the molecular density of the ionization gas in the vicinity of the emitter tip decreases. As a result, it is difficult to increase the ion radiation angle current density, and it is difficult to obtain the ion beam with a high current density on the sample. Thus, it is difficult to observe the sample at the high signal to noise ratio in the ion beam device such as the scanning ion microscope. 
         [0015]    The present invention has solved the various problems in the conventional ion beam device based on the above-described findings acquired regarding the ion beam device cooling mechanism, and an object thereof is to provide an ion beam, device which prevents vibration caused by a freezer in an ion beam device cooling mechanism from being transmitted to an ion source as much as possible and enables significant improvement in cooling performance of the ion beam device cooling mechanism. 
       Solution to Problem 
       [0016]    An ion beam device according to the present invention includes: an ion source housing that is provided with an emitter tip to generate an ion and defines an ion source chamber supplied with an ionization gas or gas molecules; a cooling pot that is provided in the ion source chamber so as to be thermally connected to the emitter tip and contains a cooling stage of a freezer so as to have no direct physical contact therebetween; and a spacer that maintains a given interval or greater between a peripheral surface of the cooling stage and an internal peripheral surface of the cooling pot. 
         [0017]    In addition, a freezer used in an ion beam device according to the present invention includes: a cooling stage that is contained in a cooling pot, which is provided in an ion source chamber so as to be thermally connected to an emitter tip, so as to have no direct physical contact with the cooling pot and cools the cooling pot via a heat conducting medium; and a spacer that maintains a given interval or greater between a peripheral surface of the cooling stage and an internal peripheral surface of the cooling pot. 
         [0018]    In addition, a method of mounting a cooling mechanism to an ion beam device according to the present invention includes: containing a cooling stage to cool a cooling pot in the cooling pot which is provided in an ion source chamber so as to be thermally connected to an emitter tip maintaining a spacer in a normal temperature state, the spacer configured using a material whose volume shrinks in a cooling state with respect to the normal temperature state; and causing the spacer to be in the cooling state in a state of being contained in the cooling pot so as to separate a peripheral surface of the spacer and an internal peripheral surface of the cooling pot. 
       Advantageous Effects of Invention 
       [0019]    According to the present invention, it is possible to set a gap between a gas pot and the cooling stage to be narrow without causing the direct physical contact between the gas pot as the cooling pot and the cooling stage of the freezer, and to hold positioning of the gas pot with respect to the cooling stage. Thus, it is possible to reduce transmission of vibration from the cooling stage to the emitter tip via the gas pot as much as possible, to favorably perform cooling of the gas pot using the cooling stage, and to improve cooling performance in the emitter tip and in the vicinity of the emitter tip. 
         [0020]    Accordingly, it is possible to obtain the following effects as the ion beam device. 
         [0021]    (1) It is possible to perform higher-sensitivity inspection of a sample using the ion beam device. 
         [0022]    (2) It is possible to improve detection reproducibility of a defect in inspection results. 
         [0023]    Incidentally, other objects, configurations, and effects will be apparent from the following description of embodiments. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0024]      FIG. 1  is a schematic configuration diagram of a scanning ion microscope as an ion beam device according to a first embodiment of the present invention. 
           [0025]      FIG. 2  is a partially enlarged view of a cooling stage unit and a gas pot section forming an ion beam device cooling mechanism of the scanning ion microscope illustrated in  FIG. 1 . 
           [0026]      FIG. 3  is a diagram illustrating the cooling stage unit section and the gas pot section which are separated before being assembled as the cooling stage unit and gas pot section illustrated in  FIG. 2 . 
           [0027]      FIG. 4  is a diagram in which the cooling stage unit section and the gas pot section illustrated in  FIG. 3  are assembled. 
           [0028]      FIGS. 5( a ) to 5( c )  are explanatory diagrams of a cooling stage unit which does not include a spacer as a comparative example relating to position adjustment between a fin and a gas pot. 
           [0029]      FIGS. 6( a ) and 6( b )  are views for comparison between a normal temperature state and a cooling state in the cooling stage unit and gas pot section illustrated in  FIG. 2 . 
           [0030]      FIGS. 7( a ) and 7( b )  are configuration diagrams of a modified example of an assembly obtained by connecting and fixing a fin to a cooling stage. 
           [0031]      FIG. 8  is a configuration diagram of a cooling mechanism that includes a heat conducting medium adjusting mechanism. 
           [0032]      FIGS. 9( a ) to 9( c )  are explanatory diagrams of an operation state of a cooling mechanism that does not include the heat conducting medium adjusting mechanism as a comparative example. 
           [0033]      FIG. 10  is a schematic configuration diagram of a scanning ion microscope as an ion beam device according to a second embodiment of the present invention. 
           [0034]      FIG. 11  is a partially enlarged view of a cooling stage unit and a gas pot section forming an ion beam device cooling mechanism of the ion beam device illustrated in  FIG. 10 . 
           [0035]      FIG. 12  is a diagram illustrating the cooling stage unit section and the gas pot section which are separated before being assembled as the cooling stage unit and gas pot section illustrated in  FIG. 11 . 
           [0036]      FIGS. 13( a )  and  13  ( b ) are views for comparison between a normal temperature state and a cooling state in the cooling stage unit and the gas pot section illustrated in  FIG. 11 . 
           [0037]      FIGS. 14( a ) and 14( b )  are configuration diagrams of a modified example of an assembly obtained by connecting and fixing a fin to a cooling stage. 
           [0038]      FIG. 15  is a configuration diagram of an example of an ion beam device in which a scanning ion microscope and a mass spectrometer are combined. 
           [0039]      FIG. 16  is a configuration diagram of another example relating to the ion beam device in which the scanning ion microscope and the mass spectrometer are combined illustrated in  FIG. 15 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0040]    First, characteristics of an ion beam device will be described before describing embodiments of the present invention. 
         [0041]    The ion beam device is sensitive to information on a sample surface as compared to an electron beam device using an electron beam such as an SEM. This is because an excitation region of secondary charged particles is localized by the sample surface in irradiation with an ion beam, as compared to irradiation with the electron beam. In addition, a diffraction effect of the ion beam can be ignored in the ion beam device. Aberration is generated due to the diffraction effect in the electron beam because it is difficult to ignore a property of the electron as a wave. On the contrary, the property as the wave can be ignored in the ion beam since ions have a heavier mass than electrons. 
         [0042]    An example of the ion beam device taking advantage of such a characteristic is a scanning ion microscope. The scanning ion microscope is a device that observes a surface structure of a sample by scanning an ion beam and irradiating the sample with the ion beam, and detecting secondary charged particles released from the sample. In particular, when the sample is irradiated with ion species of a light mass, such as hydrogen and helium, sputtering action relatively decreases, which is preferable to observe the sample. 
         [0043]    In addition, another example of the ion beam device is a transmission ion microscope. The transmission ion microscope is a device that is capable of obtaining information reflecting an internal structure of a sample by irradiating the sample with an ion beam and detecting ions transmitted through the sample. The transmission ion microscope is preferable to observe the sample as a proportion of the ions transmitting through the sample becomes large if the sample is irradiated with ion species with a light mass, such as hydrogen and helium. 
         [0044]    In addition, still another example of the ion beam device is a focused ion beam device (hereinafter, also abbreviated as the FIB). The focused ion beam device is a device that processes a sample using sputtering action by irradiating the sample with ion species with a heavy mass, conversely, such, as argon, xenon, and gallium which are preferable to process the sample using the sputtering action. In particular, a focused ion beam device (FIB) that uses a liquid metal ion source (hereinafter, also abbreviated as the LMIS) as an ion source to generate an ion beam is known as a focused ion beam processing observation device. 
         [0045]    In addition, an FIB-SEM device, which is a device obtained by combining the scanning electron microscope (SEM) and the focused ion beam device (FIB), has been also used in recent years. The FIB-SEM device can form a square hole at a desired point in a sample by irradiating the sample with a focused ion beam (FIB), and perform SEM observation of a cross-section of the sample. In the FIB-SEM device, an ion source is not limited to the liquid metal ion source, and the sample can be processed even by generating a gas ion, such as argon and xenon, and irradiating the sample with the generated gas ion using a plasma ion source or a gas field ionization ion source as the ion source. 
         [0046]    The present invention can be applied in ion beam devices such as the ion microscopes and the ion beam processing observation device described above, and an ion beam device in which the ion beam, devices are combined, such as the device obtained by combining the ion beam processing observation device and the ion microscope. In addition, the present invention can be also applied to ion beam devices in which an ion beam device and a device other than the ion beam device are combined such as an analysis and inspection device obtained by applying an ion microscope and an electron microscope, a device obtained by combining an ion microscope and amass spectrometer, and a device obtained by combining an ion microscope, an electron microscope, and a mass spectrometer. 
         [0047]    Hereinafter, the ion beam device in which the ion beam devices are combined, and the ion beam devices in which the ion beam device and the devices other than the ion beam device are combined are also collectively referred to as the ion beam device. Accordingly, the ion beam device according to the present invention is not limited to the above-described devices as long as the ion beam device is a device using an ion source, and particularly, a device using a gas field ionization ion source. 
         [0048]    Hereinafter, a description will be given by exemplifying a scanning ion microscope, which is a kind of ion beam devices, regarding embodiments of the ion beam device according to the present invention, a freezer used in the ion beam device, and a method of mounting a cooling mechanism to the ion beam device, with reference to drawings. Incidentally, the drawings are used solely for understanding of the present invention, and do not limit specific configurations of the ion beam device according to the present invention, the cooling mechanism of the device, and the like, or kinds of the ion beam device, and do not uselessly restrict the scope of the claims. 
       First Embodiment 
       [0049]      FIG. 1  is a schematic configuration diagram of a scanning ion microscope as an ion beam device according to a first embodiment of the present invention. 
         [0050]      FIG. 2  is a partially enlarged view of a cooling stage unit and a gas pot section forming an ion beam device cooling mechanism of the scanning ion microscope illustrated in  FIG. 1 . 
         [0051]      FIG. 3  is a diagram illustrating the cooling stage unit section and the gas pot section which are separated before being assembled as the cooling stage unit and the gas pot section illustrated in  FIG. 2 . 
         [0052]      FIG. 4  is a diagram in which the cooling stage unit section and the gas pot section illustrated in  FIG. 3  are assembled. 
         [0053]    As illustrated in the drawing, a scanning ion microscope  10  as the ion beam device includes an ion source  20  to generate an ion beam  21 , a column (lens barrel)  30  provided with a beam irradiation system  31 , a sample chamber  40  in which a sample  41  as an observation target is contained and arranged, an ion beam device cooling mechanism  50  (hereinafter, also abbreviated as the cooling mechanism  50 ) to cool the ion source  20 , and a control device  90  to perform control of each unit of the microscope. 
         [0054]    In the illustrated example, the sample chamber  40  and the column  30  are configured to be integrated by a vacuum chamber  32 . Furthermore, the vacuum chamber  32  also serving as a sample chamber housing and the column forms a device main body  11  of the ion beam, device  10  together with an ion source housing  22  of the ion source  20 . The vacuum chamber  32 , that is, the device main body  11  of the ion beam, device  10  is mounted and fixed to a base plate  15  that is supported by a base stand  13 , arranged on a floor  12 , with an anti-vibration mechanism  14  interposed therebetween. 
         [0055]    The anti-vibration mechanism  14  is configured using, for example, anti-vibration rubber, a spring, a damper, or combinations thereof. The anti-vibration mechanism  14  attenuates vibration transmitted from the floor  12  to the base plate  15  via the base stand  13 . Accordingly, the vibration transmitted from the floor  12  to the device main body  11  is reduced to a level that does not cause a problem in practical use of the scanning ion microscope  10 . 
         [0056]    The vacuum chamber  32  includes the sample chamber  40  and the column  30  in an internal portion thereof, and the internal portion of the chamber is held in vacuum. In order for this, the vacuum chamber  32  is connected with a vacuum exhaust system  33  for vacuum exhaust of atmosphere inside the chamber. In the illustrated example, the vacuum exhaust system  33  is configured such that a vacuum exhaust equipment  34 , such as a vacuum pump, is connected to an exhaust port of the vacuum chamber  32  formed in the base plate  15  via a vacuum exhaust pipe  35 . In this case, the vacuum exhaust system  33  is also provided with an anti-vibration mechanism (not illustrated), for example, at an intermediate portion of the vacuum exhaust pipe  35  or a connection portion with the vacuum exhaust equipment  34  or the base plate  15  using, for example, a damping member such as bellows, packing, and a seal. Accordingly, driving vibration of the vacuum exhaust equipment  34  to be transmitted to the base plate  15  and the device main body  11  via the vacuum exhaust pipe  35  is also reduced to a level that does not cause a problem, in practical use of the scanning ion microscope  10 . 
         [0057]    In the illustrated example, it is configured such that the sample chamber  40  and the column  30  to store the beam irradiation system  31  are vertically arranged in an integrated manner in a plate thickness direction of the base plate  15  inside the vacuum chamber  32 . 
         [0058]    The sample chamber  40  is provided with a sample stage  42  on which a sample  41  is placed to be moved inside the sample chamber  40 , and a secondary particle detector  43  that detects a secondary particle generated from the sample  41  due to the irradiation with the ion beam  21 . In addition, a sample loading and unloading port (not illustrated) is formed in a peripheral wall of the sample chamber section of the vacuum chamber  32 . The sample loading and unloading port is usually sealed in an airtight manner by a lid that can block or open the port. The sample  41  as the observation target is loaded to or unloaded from the sample chamber  40  through the sample loading and unloading port. 
         [0059]    The sample stage  42  includes a mounting surface to which the loaded sample  41  is mounted and a drive mechanism that causes movement (also including rotating and inclination) of the mounting surface. The sample stage  42  displaces an ion beam irradiation position and changes an irradiation direction on the mounted sample  41  in response to the movement of the mounting surface. The secondary particle detector  43  detects the secondary particle generated from the sample  41  due to the irradiation with the ion beam  21 , and outputs a signal of the detection to an image generation unit inside the control device  90 . 
         [0060]    The beam irradiation system  31  is configured to include a lens that focuses and scans the ion beam  21  released from the ion source  20 , a deflector, and the like. In the illustrated example, the beam irradiation system  31  is fixedly arranged inside the vacuum chamber  32  above the sample chamber  40 , that is, in the column  30  such that an optical axis thereof extends in the plate thickness direction of the base plate  15  which is vertical to the plate surface of the base plate  15 . The beam irradiation system  31  drives and controls each unit of the lens, the deflector, and the like based on a control signal supplied from an irradiation control unit inside the control device  90  such that a desired position on a surface of the sample mounted to the sample stage  42  is irradiated with the ion beam  21  generated by the ion source  20 . 
         [0061]    Meanwhile, a gas field ionization ion source (hereinafter, also abbreviated as the gas ion source) is used as the ion source  20  to generate the ion beam  21  in the present embodiment. The gas ion source  20  has a configuration in which the ion source housing  22  thereof is integrally fixed to the vacuum chamber  32  such that an optical axis of the ion beam  21  to be generated becomes coaxial with the optical axis of the beam irradiation system  31 . In the illustrated example, the ion source housing  22  includes an ion source containing housing portion  23  that is continuously provided at an upper part of the vacuum chamber  32 , and a pot containing housing portion (cooling mechanism housing portion)  24  that projects outwardly in a horizontal direction from a side surface of the ion source containing housing portion  23  to be parallel with the plate surface of the base plate  15 . Accordingly, a gas ionization chamber  25  is formed inside the ion source containing housing portion  23 , and a pot containing chamber  26  is formed inside the pot containing housing portion  24 . The two chambers  25  and  26  usually communicate with each other via a communication port  28  in a connecting portion between the ion source containing housing portion  23  and the pot containing housing portion  24 , and an integrated ion source chamber  27  is configured by combining both the chambers  25  and  26 . In addition, a projecting end of the pot containing housing portion  24  is opened toward the horizontal direction as a cooling mechanism mounting port  29 . The ion source chamber  27  and the inside of the column  30  of the vacuum chamber  32  are connected only via a passage hole  37  formed at a bulkhead  36  that defines the two chambers. The passage hole  37  is formed on the bulkhead  36  to penetrate therethrough in accordance with a position of the optical axis of the beam irradiation system  31 . 
         [0062]    Incidentally, the description has been given in the present embodiment regarding the configuration in which an extending direction of the pot containing chamber  26  in the pot containing housing portion  24  and an opening direction of the cooling mechanism mounting port  29  are the horizontal direction, the extending direction and the opening direction are not necessarily limited to the horizontal direction. For example, both the directions may be configured to be the vertical direction. 
         [0063]    The gas ion source  20  includes an emitter tip  45  and an extraction electrode  46  in the gas ionization chamber  25  of the ion source housing  22 . A gas supply piping  48  to supply an ionization gas from a gas source  47  and a vacuum, exhaust pipe  39  of a vacuum exhaust system  49  for vacuum exhaust of atmosphere inside the ion source chamber  27  are configured to be connected to the gas ionization chamber  25  in a communicating manner. 
         [0064]    The emitter tip  45  is configured using a needle-shaped electrode to which a high voltage can be applied. The emitter tip  45  is connected to a gas ion source control unit inside the control device  90  such that the high voltage is applied by the control of the gas ion source control unit, and an intense electric field, can be generated from the needle-shaped electrode. The emitter tip  45  generates positive ions as electrons inside the gas molecules tunnel a potential barrier reduced by the intense electric field from the needle-shaped electrode of the emitter tip  45  due to a quantum tunneling effect when the gas molecules of the ionization gas approaches. The extraction electrode  46  is connected to the gas ion source control unit inside the control device  90 , and extracts the positive ions generated by the emitter tip  45  so as to be released as the ion beam when being applied with an extraction voltage by control of the gas ion source control unit. The emitter tip  45  and the extraction electrode  46  are fixedly arranged in the ion source containing housing portion  23  such that the optical axis of the ion beam  21  to be released becomes coaxial with the passage hole  37  of the bulkhead  36  and the optical axis of the beam irradiation system  31 . Incidentally, the ionization gas supplied to the ion source chamber  27  passing through the gas supply piping  48  may be the gas molecules. 
         [0065]    An anti-vibration mechanism using a damping member, such as bellows, packing, and a seal, is also provided in the middle of the gas supply piping  48 , a connection portion thereof, and the like. Accordingly, driving vibration of the gas source  47  of the ionization gas to be transmitted to the ion source housing  22  via the gas supply piping  48  is also reduced to a level that does not cause a problem in practical use of the scanning ion microscope  11 . Similarly, an anti-vibration mechanism using a damping member, such as bellows, packing, and a seal, is also provided in the middle of the vacuum exhaust pipe  39 , a connection portion thereof, and the like. Accordingly, driving vibration of a vacuum exhaust equipment  38  to be transmitted to the ion source housing  22  via the vacuum exhaust pipe  39  is also reduced to a level that does not cause a problem, in practical use of the scanning ion microscope  11 . Incidentally, the vacuum exhaust equipment  39  that performs the vacuum exhaust inside the ion source chamber  27  can be shared with the vacuum exhaust equipment  34  that performs the exhaust of the vacuum chamber  32 . 
         [0066]    The ion beam  21  generated by the emitter tip  45  of the gas ion source  20  and released from the extraction electrode  46  enters the inside of the vacuum chamber  32  via the passage hole  37 , is appropriately focused, deflected or scanned by the beam irradiation system  31 , and causes an observation point on the sample  40  mounted to the sample stage  42  inside the sample chamber  40  to be irradiated therewith. At this time, secondary charged particles released from the observation point on the sample  40  due to the irradiation with the ion beam  21  are detected by the secondary particle detector  43 , and an observation image of an irradiation point of the ion beam is generated based on the detection signal from the secondary particle detector  43  in the image generation unit inside the control device  90 . The control device  90  causes this generated observation image to be displayed on a display unit of an input/output device  91  so as to be visually confirmed. 
         [0067]    Meanwhile, a gas pot  51  of the cooling mechanism (ion beam device cooling mechanism)  50  is contained and arranged in the pot containing chamber  26  of the ion source chamber  27 . Before describing the arrangement of the gas pot  51  contained in the pot containing chamber  26 , first, a description will be given regarding the entire configuration of the cooling mechanism  50  included in the scanning ion microscope  10  according to the present embodiment. 
         [0068]    The cooling mechanism  50  cools the emitter tip  45  to cryogenic temperature in order to increase a molecular density of an ionization gas in the gas ionization chamber  25  section around the emitter tip  45 , and lowers temperature of an ionization gas around the emitter tip  45 . The cooling mechanism  50  is configured using a cooling mechanism in which a mechanical freezer  52  and the gas pot  51  are combined. 
         [0069]    In the present embodiment, a Gifford-McMahon cooler (GM cooler) is used as the mechanical freezer  52  of the cooling mechanism  50 . Incidentally, a pulse tube freezer, a Stirling freezer or the like may be also used as the mechanical freezer  52  without being limited to the GM cooler. 
         [0070]    The freezer  52  includes a freezer main body  53  and a compressor  54 , and the freezer main body  53  and the compressor  54  are connected to each other via a high-pressure piping  55  and a low-pressure piping  56 . The freezer  52  has a structure in which coldness is generated by periodically expanding a high-pressure working gas inside the freezer main body  53 . 
         [0071]    The compressor  54  compresses the working gas made of, for example, a helium, gas to a high-pressure state, and supplies the compressed gas to the freezer main body  53  via the high-pressure piping  55 . The working gas with lowered pressure after being used to generate the coldness in the freezer main body  53  is collected by the compressor  54  via the low-pressure piping  56 . The collected working gas is compressed again by the compressor  54 . 
         [0072]    For example, the freezer main body  53  includes a cylinder (not illustrated) provided with a displacer, which is integrated with a built-in coldness accumulator, so as to be reciprocatingly movable, a displacer driving means (not illustrated) that causes the displacer to reciprocate in the cylinder, and a valve mechanism which causes the inside of the cylinder to communicate with the high-pressure piping  55  or the low-pressure piping  56  in accordance with the movement of the displacer inside the cylinder so as to cause the working gas to flow in and out. Further, it is configured such that a section including an expansion chamber side inside the cylinder defined by the displacer projects from a housing surface thereof in a rod shape as a cooling stage  57  to cool a thermal load. 
         [0073]    In the illustrated example, the cooling stage  57  has a stepped rod shape in which a stage  57   b  whose outer shape viewed in an axis direction is formed to be smaller than an outer shape of a base  57   a  is formed to be coaxial and projects from the base  57   a  formed to project on a housing surface of the freezer main body  53 . A stage distal end side of the cooling stage  57  is a most cooling face, and thus, a base  58   a  of a fin  58  is tightly fixed to the cooling stage  57  in a coaxial manner at a stage distal end  57   c.  The fin  58  is formed using a material having a high heat conducting property (heat dissipation property), for example, oxygen-free copper, to achieve enlargement of the area of the most cooling face of the cooling stage  57 . Along with this, an outer shape of the fin  58  vertical to the axis direction, which is viewed in the axis direction of the cooling stage  57 , is larger than the outer shape of the stage  57   b  of the cooling stage  57  so as to have a large diameter. 
         [0074]    In addition, a spacer  59  is attached to a peripheral surface of the stage  57   b  of the cooling stage  57  so as to surround the peripheral surface of the stage  57   b.  The spacer  59  is formed to have an external peripheral edge projecting outwardly in a radial direction than an external peripheral edge of the fin  58 , in relation to the radial direction having the axis of the cooling stage  57  as the center, in the state of being mounted to the stage  57   b.    
         [0075]    Incidentally, it is possible to use various specific forms, for example, a tubular spacer that surrounds the entire peripheral surface of the stage  57   b  of the cooling stage  57 , a spacer piece assembly obtained by arranging a plurality of spacer pieces side by side with a predetermined interval along a circumferential direction of the stage  57   b  so as to partially surround the peripheral surface of the stage  57   b,  and the like, as a specific form of the spacer  59  based on the above-described viewpoint. 
         [0076]    In addition, it is possible to use various shapes of the external peripheral edge, for example, a circular shape of the external peripheral edge projecting at least with respect to the external peripheral edge of the fin  58  in an entire region along the circumference thereof, a polygonal shape in which corners of the external peripheral edge project at least with respect to the external peripheral edge of the fin  58  partially only at a plurality of points along the circumference thereof, even in the case where the spacer  59  is the tubular spacer, for example, in relation to the shape of the external peripheral edge obtained by viewing the spacer  59  in the state of being mounted to the stage  57   b  of the cooling stage  57  in the axis direction thereof. 
         [0077]    In the present embodiment, it is assumed to use the tubular spacer, which surrounds the entire peripheral surface of the stage  57   b  in the state of being mounted to the stage  57   b  of the cooling stage  57 , and has the external peripheral edge projecting outwardly in the radial direction more than each external peripheral edge of the base  57   a  and the fin  58  over the entire region along the circumference thereof, as the spacer  59 . Hereinafter, the cooling stage  57  in the state of being assembled with the fin  58  and the spacer  59  will be referred to as a cooling stage unit  60 . 
         [0078]    Further, in the present embodiment, the spacer  59  has a heat insulating property and further, has temperature reversibility in terms of its size so that spacer  59  contracts and the volume thereof decreases as compared to a normal temperature state when being cooled from normal temperature (for example, corresponding to room temperature of a room in which the scanning ion microscope  10  is provided), and returns to substantially the same size when returning to the normal temperature. Thus, the spacer  59  has the temperature reversibility in terms of a size of the external peripheral edge viewed in the axis direction thereof so that the external peripheral edge contracts as compared to the normal temperature state when being cooled and returns to the original size when returning to the normal temperature. The above-described spacer  59  is configured using a porous material, for example foamed resin. 
         [0079]    A peripheral surface of a spacer mounting portion  60   a  of the cooling stage unit  60  is configured to project outwardly in a radial direction in the entire region along the circumference thereof more than a peripheral surface of a fin portion  60   b  of the cooling stage unit  60  at the normal temperature, in relation to the radial direction having an axis of the cooling stage unit  60  as the center. 
         [0080]    Meanwhile, the gas pot  51  includes a pot main body  61  having a bottomed-cylindrical shape whose one end is blocked and the other end is opened, and has a structure such that a stage containing chamber  62 , which can contain the fin  58  of the cooling stage unit  60  and the stage  57   b  of the cooling stage  57  provided with the spacer  59 , is included in the pot main body  61 . In the present embodiment, a length in an axial direction of the stage containing chamber  62  is set to be appropriately longer than a length obtained by adding a length of an axial direction of the spacer mounting portion  60   a  in the cooling stage unit  60  (length in an axial direction of the stage  57   b  of the cooling stage  57  mounting the spacer  59 ) and a length in an axial direction of the fin portion  60   b  (length in an axial direction of the fin  58  that is tightly fixed to the stage  57   b  of the cooling stage  57 ). Accordingly, it is configured such that it is possible to form an end face gap g 1  (see  FIG. 2 ) between a distal end portion of the fin  58  in the axial direction and a containing chamber bottom  61   c  of the pot main body  61  in a state where the cooling stage unit  60  is contained in the stage containing chamber  62 . 
         [0081]    Incidentally, it is configured such that a part of the base  57   a,  formed to project on the housing surface of the freezer main body  53 , is also contained in the stage containing chamber  62  of the pot main body  61  in the illustrated example. Thus, an outer shape of the spacer mounting portion  60   a  vertical to the axial direction viewed in the axis direction of the cooling stage unit  60  is larger than an outer shape of the base  57   a  vertical to the axis direction, and an external peripheral edge of the spacer mounting portion  60   a  projects outwardly in the radial direction more than the external peripheral edge of the base  57   a  in the entire region along the circumference thereof. However, when the base  57   a  formed to project on the housing surface of the freezer main body  53  is not contained in the stage containing chamber  62  of the pot main body  61  at all, the base  57   a  is hardly brought into contact with an internal peripheral surface of the pot main body  61  serving as a wall surface of the stage containing chamber  62 . Thus, the configuration in which the external peripheral edge of the spacer mounting portion  60   a  projects outwardly in the radial direction more than the external peripheral edge of the base  57   a  is not indispensable. 
         [0082]    In addition, a cross-sectional shape of the stage containing chamber  62  vertical to the axis is a cross-sectional shape which has no step and is uniform in the entire region along the axial direction, and is a cross-sectional shape formed in accordance with an external peripheral surface shape of the spacer mounting portion  60   a  of the cooling stage unit  60 . A size of this cross-sectional shape (length of the stage containing chamber  62  in the radial direction) is set to be a size that enables contact with the spacer mounting portion  60   a  of the cooling stage unit  60  in a normal temperature state, that is, the external peripheral edge of the spacer  59  in a non-contracted state in the cooling stage unit  60 . Accordingly, it is configured such that the cooling stage unit  60  causes the spacer  59  to have contact with the internal peripheral surface of the pot main body  61  serving as the wall surface of the stage containing chamber  62  in the normal temperature state, the cooling stage unit  60  becomes coaxial with the pot main body  61  in the state of being contained in the stage containing chamber  62 , and a gap g 2  (see  FIG. 2 ) is formed around the circumference of the fin portion  60   b  between the external peripheral edge of the fin portion  60   b  of the cooling stage unit  60  and the internal peripheral surface of the pot main body  61 , in the illustrated example. Incidentally, a gap length of the gap g 2  is not necessarily formed to have a same gap length at the entire region around the circumference of the fin portion  60   b.    
         [0083]    Accordingly, a non-contact space  67  having the gaps g 1  and g 2  is formed between the fin portion  60   b  of the cooling stage unit  60  and a bottom-side main body portion  61   a  of the pot main body  61 . In addition, it is configured such that a gap g 3  (see  FIG. 2 ) is also formed between the peripheral surface of the base  57   a  and the internal peripheral surface of the pot main body  61  when the peripheral surface of the base  57   a  formed to project on the housing surface of the freezer main body  53  and the internal peripheral surface of the pot main body  61  are superimposed on each other. 
         [0084]    The pot main body  61  is configured by coaxially joining and fixing the bottom-side main body portion  61   a  having a portion to contain the fin portion  60   b  of the cooling stage unit  60  and an opening-side main body portion  61   b  having a portion to contain the spacer mounting portion  60   a  of the cooling stage unit  60  to be integrated. The bottom-side main body portion  61   a  is configured using a heat conducting material, but the opening-side main body portion  61   b  is configured using a heat insulating material (material having extremely lower thermal conductivity than the bottom-side main body portion  61   a ). Accordingly, it is configured such that a portion of the gas pot  51  to be cooled by the fin  58 , which is tightly fixed to the stage  57   b  of the cooling stage  57  and the stage distal end  57   c  as the most cooling face of the cooling stage  57 , can be limited to the bottom-side main body portion  61   a.  At the same time, the entry of heat from the outside to the cooled bottom-side main body portion  61   a  is performed using the opening-side main body portion  61   b  made of the heat insulating material, and thus, the heat is blocked and reduced by the opening-side main body portion  61   b.  Accordingly, speed of cooling the bottom-side main body portion  61   a  of a gas pot  51  performed by the cooling stage  57  is improved, and improvement in cooling efficiency is achieved. 
         [0085]    The cooling mechanism  50  is configured by arranging the fin portion  60   b  and the spacer mounting portion  60   a  of the cooling stage unit  60 , inserted from an opening on the other end side of the pot main body  61  of the gas pot  51 , to be contained in the stage containing chamber  62  in such a manner that the cooling stage unit  60  and the gas pot  51  are coaxial, and connecting the gas pot  51  to the freezer main body  53  to be integrated. Further, when the cooling stage unit  60  is arranged to be contained in the stage containing chamber  62 , only the external peripheral edge of the spacer mounting portion  60   a  of the cooling stage unit  60  can be in contact with the internal peripheral surface of the gas pot  51 , and the other peripheral surface portion including the fin portion  60   b  of the cooling stage unit  60  is configured not to nave contact with the internal peripheral surface of the gas pot  51 . 
         [0086]    On the other hand, the bottom-side main body portion  61   a  of the pot main body  61  configured using the heat conducting material is thermally connected to the emitter tip  45  provided in the ion source containing housing portion  23  of the ion source housing  22  via a cooling conduction mechanism  70 . 
         [0087]    The cooling conduction mechanism  70  is configured to include, for example a gold-plated copper mesh portion, and the cooling conduction mechanism  70  itself can be deformed, such as deflected or bent, by deformation of the copper mesh portion. Accordingly, even if relative arrangement between the bottom-side main body portion  61   a  of the pot main body  61  and the emitter tip  45  is slightly deviated, the cooling conduction mechanism  70  is configured to be capable of absorbing the deviation and connecting and holding the bottom-side main body portion  61   a  and the emitter tip  45  without being damaged as the copper mesh portion is deformed. 
         [0088]    The connection between the gas pot  51  and the freezer main body  53  is performed using a tubular bellows  63  that is stretchable. The tubular bellows  63  is configured to include an internal peripheral surface capable of opposing the peripheral surface of the base  57   a  to be separated by a predetermined distance without abutment of the peripheral surface of the base  57   a  in a state where the cooling stage unit  60  is coaxially interpolated. The tubular bellows  63  includes a pot connecting frame  65 , at one end side, which can be joined with an attachment flange  64  integrally formed at the other end of the pot main body  61  of the gas pot  51 . The other end side of the tubular bellows  63  is tightly fixed to the freezer main body  53 . 
         [0089]    In the present embodiment, the gas pot  51  is arranged to be contained in the pot containing housing portion  24  through the cooling mechanism mounting port  29  of the ion source housing  22  in advance at the time of connecting the gas pot  51  and the freezer main body  53  using the tubular bellows  63 . For example, a state is formed in which the attachment flange  64  of the pot main body  61  is airtightly attached to an attachment flange  66  formed at the projecting end of the pot containing housing portion  24  using a seal member such as packing (not illustrated). On the other hand, the other end side of the tubular bellows  63  is tightly fixed to the freezer main body  53 , and the state where the cooling stage unit  60  is coaxially interpolated is formed. Thus, the connection between the gas pot  51  and the freezer main body  53  is performed by airtightly joining and connecting the pot connecting frame  65  of the tubular bellows  63  fixed, in advance, to the freezer main body  53  with the attachment flange  64  of the pot main body  61  or the attachment flange  66  of the pot containing housing portion  24  using the seal member such as packing (not illustrated). At this time, the fin portion  60   b  and the spacer mounting portion  60   a  of the cooling stage unit  60  are arranged in the stage containing chamber  62  of the gas pot  51  to be coaxial with the gas pot  51  through an opening on the other end side of the pot main body  61 . 
         [0090]    In the state where the pot connecting frame  65  of the tubular bellows  63  is airtightly joined and connected with the attachment flange  64  of the pot main body  61  or the attachment flange  66  of the pot containing housing portion  24 , a vibration suppressing space  68 , which is airtightly defined from the external atmosphere (atmosphere of the room in which the scanning ion microscope  10  is provided), is formed between the internal peripheral surface of the tubular bellows  63  and the peripheral surface of the base  57   a  formed to project on the housing surface of the freezer main body  53 , and the non-contact, space  67  is formed inside the stage containing chamber  62 . 
         [0091]    Thereafter, a heat conducting medium is stored in the non-contact space  67 , and a vibration damping medium is stored in the vibration suppressing space  68 . In the present embodiment, the communication between the non-contact space  67  and the vibration suppressing space  68  inside the gas pot  51  is caused by the spacer  59  whose volume has been reduced when the bottom-side main body portion  61   a  of the pot main body  61  is cooled by the cooling stage unit  60 . Thus, the same kind of medium, for example, a helium gas is used as the heat conducting medium and the vibration damping medium. Accordingly, the same helium gas is fed into the non-contact, space  67  and the vibration suppressing space  68 , and is stored in each of the two spaces  67  and  68  to be isolated from the helium gas as the ionization gas that has been supplied to the gas ionization chamber  25 . Hereinafter, the heat conducting medium and the vibration damping medium made of the common helium gas will be collectively referred to as a heat conducting medium  69 . 
         [0092]    Regarding the feeding of the heat conducting medium  69  into each of the two spaces  67  and  68 , the present embodiment is configured such that, if the helium gas is fed into any one side of the two spaces  67  and  68 , the helium gas is also fed into the other side. That is, the spacer  59  attached to the stage  57   b  of the cooling stage  57  is configured using the foamed resin, and a peripheral surface thereof is microscopically a large uneven surface and has a number of fine microscopic clearances in the present embodiment, and thus, the medium can be fed into the other side through the fine microscopic clearances only by feeding the medium into any one side of the two spaces  67  and  68  even in a case where the peripheral surface of the spacer  59  is in contact with the internal peripheral surface of the opening-side main body portion  61   b  of the pot main body  61  in the entire region along the circumferential direction in the normal temperature state. Thus, it is configured such that a separate gas supply piping (not illustrated) connected to the gas source  47  of the same helium gas communicates with the vibration suppressing space  68  inside the gas pot  51  and enables the heat conducting medium  69  to be stored in the non-contact space  67  and the vibration suppressing space  68  in the illustrated example, which is similar to the gas supply piping  48 . 
         [0093]    On the other hand, the freezer main body  53  is mounted and fixed onto a support, stand  83  different from the base plate  15  to which the device main body  11  of the scanning ion microscope  10  is mounted and fixed such that the axis direction of the cooling stage unit  60  projecting in the rod shape is aligned with a height position of the cooling mechanism mounting port  29  provided in the pot containing housing portion  24  of the ion source housing  22 . In the present embodiment, an opening direction of the cooling mechanism mounting port  29  in the ion source housing  22  is oriented in the horizontal direction, when an attitude of the device main body  11  is in a horizontal state. Accordingly, the freezer main body  53  is also mounted and fixed onto the support stand  83  facing the freezer main body  53  such that the axis direction of the cooling stage unit  60  becomes the horizontal direction. Incidentally, the mounting attitude of the freezer main body  53  on the support stand  83  is changed depending on a change of a containing direction of the gas pot  51  (direction of the cooling mechanism mounting port  29 ) in the pot containing housing portion  24  of the ion source housing  22 . 
         [0094]    The support stand  83  has a structure which includes a base stand  84 , a fulcrum  85 , and a position adjusting and fixing mechanism  87 . The fulcrum  85  is erected on the base stand  84  and has a length in accordance with a height position of the pot containing housing portion  23  of the scanning ion microscope  10 . The position adjusting and fixing mechanism  87  includes a mounting portion  88  to which the freezer main body  53  is mounted and fixed, and is attached and fixed to the attachment portion  86  of the fulcrum  85 . The position adjusting and fixing mechanism  87  has a structure which enables elevation, rotation or inclination of the mounting portion  88  within a range of a predetermined amount, and is capable of finely adjusting an attitude state of the freezer main body  53  mounted and fixed to the mounting portion  88  in a tolerable range based on the predetermined amount range. 
         [0095]    Next, a description will be given regarding the assembly of the cooling mechanism  50  and position adjustment between the fin  58  and the gas pot  51  performed by the spacer  59  at the time of assembly relating to the cooling mechanism  50  provided in the scanning ion microscope  10  according to the present embodiment, on the basis of  FIG. 1  to  FIG. 6( b )   
         [0096]      FIG. 3  corresponds to a state in which the freezer  60  in which the fin  58  is joined and fixed to the cooling stage  57  and the gas pot  51  attached to the ion source containing housing portion  23  of the ion source housing  22  are not yet assembled. 
         [0097]    In  FIG. 3 , the illustrated arrow indicates the containing direction in which the fin portion  60   b  and the spacer mounting portion  60   a  of the cooling stage unit  60  is inserted through the other-end-side opening of the pot main body  61  of the gas pot  51  and is arranged to be contained in the stage containing chamber  62  such that the cooling stage unit  60  and the gas pot  51  become coaxial. Such containing work of the cooling stage unit  60  into the stage containing chamber  62  of the gas pot  51  is performed under the normal temperature. 
         [0098]      FIG. 4  corresponds to a state after the freezer  60  in which the fin  58  is joined and fixed to the cooling stage  57  and the gas pot  51  attached to the ion source containing housing portion  23  of the ion source housing  22  have been assembled. Incidentally, the non-contact space  67  and the vibration suppressing space  68  formed by the assembly is not sealed with the heat conducting medium  69  yet in the illustrated state. Thus, the spacer  59  remains in the normal temperature state without being cooled. Incidentally,  FIGS. 3 and 4  do not illustrate the ion source housing  22  to which the gas pot  51  has been rigidly attached in advance before the assembly. 
         [0099]    Only the spacer mounting portion  60   a  of the cooling stage unit  60  is contained in the pot main body  61  at the time of containing the cooling stage unit  60  in the stage containing chamber  62  of the gas pot  51  as illustrated in  FIG. 3 , and only the external peripheral edge of the tubular spacer  59  in the non-contracted state is contained in the pot main body  61  in the case of the present embodiment, while being in contact with and supported by the internal peripheral surface of the pot main body  61  over the entire region around the circumference thereof which serves as the wall surface of the stage containing chamber  62 . Thus, it is possible to arrange the cooling stage unit  60  to be coaxial with the pot main body  61  forming the stage containing chamber  62 . That is, the cooling stage unit  60  can be arranged in the stage containing chamber  62  without any deviation or inclination of the axis thereof from the axis of the pot main body  61 . 
         [0100]    Further, the pot connecting frame  65  is airtightly joined and connected to the attachment flange  64  of the pot main body  61  or the attachment flange  66  of the pot containing housing portion  24  using the seal member such as packing (not illustrated) in a state where the external peripheral edge of the spacer  59  in the non-contracted state is in contact with and supported by the internal peripheral surface of the pot main body  61  over the entire region around the circumference thereof serving as the wall surface of the stage containing chamber  62 , and thus, the coaxiality of the cooling stage unit  60  and the pot main body  61  is not compromised even in such joining and connection. 
         [0101]    In addition, if the size of the shape of the external peripheral edge of the spacer mounting portion  60   a  viewed in the axis direction of the cooling stage unit  60  is smaller than the size of the internal peripheral shape of the stage containing chamber  62  viewed in the axis direction of the pot main body  61 , only the external peripheral edge of the spacer mounting portion  60   a  of the cooling stage unit  60  can be in contact with the internal peripheral surface of the gas pot  51 , and the other peripheral surface portion including the fin portion  60   b  of the cooling stage unit  60  has no contact with the internal peripheral surface of the gas pot  51 . In this manner, even when only a part of the spacer  59  along the circumference thereof is in contact with the internal peripheral surface of the pot main body  61  serving as the wall surface of the stage containing chamber  62 , the contact portion of the spacer  59  regulates contact between the other portion of the cooling stage unit  60  and the internal peripheral surface of the pot main body  61 . In this case, only the contact portion of the spacer mounting portion  60   a  of the cooling stage unit  60  is supported by the internal peripheral surface of the pot main body  61 , but an inclination angle θ expressed by inclination of the axis of the pot main body  61  with respect to the axis of the cooling stage unit  60  is reliably suppressed to be a value or smaller, the value obtained when the part of the spacer  59  corresponding to the contact portion of the spacer mounting portion  60   a  is in contact with the internal peripheral surface of the stage containing chamber  62 . 
         [0102]    Incidentally, the case where the size of the shape of the external peripheral edge of the spacer mounting portion  60   a  viewed in the axis direction of the cooling stage unit  60  is smaller than the size of the internal peripheral shape of the stage containing chamber  62  viewed in the axis direction of the pot main body  61  includes a case where the shape of the external peripheral edge of the spacer mounting portion  60   a  viewed in the axis direction of the cooling stage unit  60  is similar to the internal peripheral shape of the stage containing chamber  62  viewed in the axis direction of the pot main body  61 , a case where both the shapes are different from each other, and the like. 
         [0103]      FIGS. 5( a ) to 5( c )  are explanatory diagrams of a cooling stage unit which does not include the spacer as a comparative example relating to position adjustment between a fin and a gas pot. 
         [0104]      FIG. 5( a )  corresponds to a state where the freezer  60  in which the fin  58  is joined and fixed to the cooling stage  57  and the gas pot  51  attached to the ion source containing housing portion  23  of the ion source housing  22  are not yet assembled. In  FIG. 5( a ) , the illustrated arrow indicates a containing direction in which the cooling stage unit  60  is contained in the stage containing chamber  62  of the gas pot  51 .  FIGS. 5( b ) and 5( c )  correspond to states after the freezer  60  in which the fin  58  is joined and fixed to the cooling stage  57  and the gas pot  51  attached to the ion source containing housing portion  23  of the ion source housing  22  have been assembled. Incidentally, the respective units have the same configurations as those in the cooling mechanism  50  according to the present embodiment illustrated in  FIGS. 1 to 3  except that the spacer  59  is not provided, and thus, will be denoted by the same reference signs, and detailed individual description thereof will be omitted. 
         [0105]    In the cooling stage unit  60  according to the comparative example configured using an assembly in which the fin  58  is connected and fixed to the cooling stage  57  and the spacer  59  is not provided, a clearance having a length, which corresponds to a sum of a length of a spacer non-mounting portion  60   a ′ and a length of the fin portion  60   b  in the axis direction, is formed between the external peripheral surface of the cooling stage unit  60  and the internal peripheral surface of the gas pot  51 . Thus, the tolerance greater than necessary is given with respect to eccentricity of the cooling stage unit  60  in the stage containing chamber  62  and the inclination of the cooling stage unit  60 , expressed by the inclination angle θ, in the stage containing chamber  62 . 
         [0106]    Accordingly, even if the cooling stage unit  60  is positioned with respect to the stage containing chamber  62  such that the cooling stage unit  60  becomes coaxial with the gas pot  51  and the clearance is formed between the external peripheral surface of the cooling stage unit  60  and the internal peripheral surface of the gas pot  51  before the assembly of the freezer  60  and the gas pot  51 , the tolerance with respect to the eccentricity and the inclination of the cooling stage unit  60  is in the state of being greater than necessary. As a result, when the pot connecting frame  65  is actually joined and connected to the pot main body  61  or the attachment flanges  64  and  66  of the pot containing housing portion  24 , there may occur a case where the cooling stage unit  60  becomes eccentric in the stage containing chamber  62  or the cooling stage unit  60  is inclined as illustrated in  FIGS. 5( b ) and 5( c )  so that the fin portion  60   b  is brought into contact with the internal peripheral surface of the stage containing chamber  62 . 
         [0107]    Meanwhile, relating to the assembly of the cooling mechanism  50 , only a predetermined amount of the heat conducting medium  69  is fed into a space of the gas pot  51  incorporated with the cooling stage  57  to seal the space when the assembly of the freezer  60  in which the fin  58  is joined and fixed to the cooling stage  57  and the gas pot  51  attached to the ion source containing housing portion  23  of the ion source housing  22  is completed in the scanning ion microscope  10 . At this time, even when the spacer  59  is configured as the tubular spacer  59  that is in contact with the internal peripheral surface of the pot main body  61  over the entire region along the circumferential direction thereof as in the present embodiment, it is possible to feed the heat conducting medium  69  into the other side even by feeding the heat conducting medium  69  into any one side of the two spaces  67  and  68  since the spacer  59  is formed, using the porous material with the heat insulating property. For example, when the heat conducting medium  69  is fed into the vibration suppressing space  68 , the heat conducting medium  69  can be fed up to the non-contact space  67  at an inner portion of the gas pot  51  through the microscopic clearance in the spacer  59  even using the tubular spacer  59  that is in contact with the internal peripheral surface of the pot main body  61  over the entire region along the circumference thereof.  FIG. 2  corresponds to the cooling stage unit  60  and the gas pot  51  section in the state where the heat conducting medium  69  is fed into and stored in the non-contact space  67  and the vibration suppressing space  68 . 
         [0108]    In the cooling mechanism  50  of the scanning ion microscope  10  according to the present embodiment assembled in this manner, the spacer  59  contracts when being cooled so that the volume thereof decreases as compared to the normal temperature state. Then, the external peripheral edge of the peripheral surface of the spacer  59  that has been brought into contact with the internal peripheral surface of the pot main body  61  is separated from the internal peripheral surface of the pot main body  61 , and the cooling stage unit  60  has no direct physical contact with the internal peripheral surface of the pot main body  61  in the entire region along the circumference thereof. Accordingly, a clearance S (see  FIGS. 6( a ) and 6( b ) ) is formed between the cooling stage unit  60  and the internal peripheral surface of the pot main body  61 . 
         [0109]    In addition, the cooling is performed using coldness obtained by the cooling stage unit  60  of the freezer  52  configured to cool the emitter tip  45  to generate the ion beam  21 . Thus, the cooling is performed at operation temperature of the ion beam device during the cooling. This operation temperature of the ion beam device corresponds to, for example, cooling temperature of the emitter tip set in response to a peak of an ion current (for example, several K to several tens of K when the ionization gas is the helium gas). 
         [0110]      FIGS. 6( a ) and 6( b )  are views for comparison between the normal temperature state and a cooling state in the cooling stage unit and gas pot section illustrated in  FIG. 2 .  FIG. 6( a )  illustrates the cooling stage unit and gas pot section in the normal temperature state, and  FIG. 6( b )  illustrates the cooling stage unit and gas pot section in the normal temperature state. 
         [0111]    Accordingly, when the external peripheral surface of the cooling stage unit  60  and the internal peripheral surface of the gas pot  51  are in contact with each other at the time of completing the assembly in the assembly of the freezer  60  and the gas pot  51 , the internal peripheral surface of the gas pot  51  is only in contact with the spacer  59  in the external peripheral surface of the cooling stage unit  60  in the present embodiment. Thus, the clearance S is reliably secured between the external peripheral surface of the cooling stage unit  60  and the internal peripheral surface of the pot main body  61 , in the entire region along the circumferential direction thereof, due to the contraction of the spacer  59  between the cooling stage unit  60  and the gas pot  51  whose relative arrangement positions are fixed at the time of completing the assembly in a situation where the scanning ion microscope  10  is used and the freezer  52  is driven. Along with this, further, it is unnecessary to take into consideration of the contact between the fin portion  60   b  of the cooling stage unit  60  and the internal peripheral surface of the pot main body  61  as illustrated in  FIGS. 5( a ) to 5( c )  at a step of positioning the cooling stage unit  60  with respect to the stage containing chamber  62  when the freezer  60  and the ion source housing  22  are assembled and fixed. Accordingly, assembly work of assembling the freezer  60  and the ion source housing  22  becomes easy and efficient. 
         [0112]    To be specific, the positional relationship between the external peripheral edge of the fin  58  and the internal peripheral surface of the pot main body  61  can be roughly set in response to a size of the clearance S specified by the spacer  59 . In addition, it is possible to prevent the inclination angle θ exceeding the tolerable range from being generated between the cooling stage unit  60  and the gas pot  51  when the cooling stage unit  60  is arranged to be contained in the stage containing chamber  62  of the gas pot  51 . As a result, the clearance S is reliably secured between the external peripheral surface of the cooling stage unit  60  and the internal peripheral surface of the pot main body  61  in the entire region along the circumference thereof, and it is possible to prevent the direct physical contact between the fin  58  and the internal peripheral surface of the pot main body  61 . It is possible to more strictly design the gap g 2  between the external peripheral edge of the fin  58  and the internal peripheral surface of the pot main body  61  than ever before by managing the size of the shape of the external peripheral edge of the spacer  59  viewed in the axis direction thereof between the normal temperature state and the cooling state although it is difficult to visually confirm the state after the assembly of the freezer  60  and the ion source housing  22 . 
         [0113]    In addition, the spacer  59  of the cooling mechanism  50  has the temperature reversibility so that the spacer  59  returns to the original size when returning to the normal temperature. Accordingly, for example, when the freezer  60  is separated from the device main body  11  integrated with the ion source housing  22  in order for maintenance of the freezer  52 , or when the ion source housing  22  is separated from the freezer  52  and the vacuum chamber  32  in order to replace the emitter tip  45 , the spacer  59  can be used in the assembly again at the time of assembling the freezer  60  or the ion source housing  22  again after completing such work. 
         [0114]    Further, this configuration of the cooling mechanism  50  to prevent the direct physical contact between the fin  58  and the internal peripheral surface of the pot main body  61  prevents the vibration transmitted from the cooling mechanism  50  to the emitter tip  45  from being transmitted to the ion source housing  22  to which the emitter tip  45  and the gas pot  51  of the cooling mechanism  50  are rigidly connected in order for anti-vibration of the emitter tip  45 . 
         [0115]    In this case, there are major kinds of vibration, such as the vibration generated by the freezer main body  53  of the freezer  52 , the vibration of the compressor  54  to be transmitted to the freezer main body  53  via the high-pressure piping  55  and the low-pressure piping  56 , and the vibration from the floor  12  to be transmitted to the freezer main body  53  via the support stand  83  and the position adjusting and fixing mechanism  87 , as the vibration which has a risk of being transmitted to the emitter tip  45  from the cooling mechanism  50  via the ion source housing  22 . The vibration from the freezer main body  53  is mechanical vibration generated by the own device, and is mainly cause as the displacer repeats the reciprocation at high speed inside the cylinder. In addition, the vibration from the floor  12  also includes the vibration of the compressor  54 . Further, the both kinds of vibration correspond to the vibration that is transmitted from the freezer main body  53 . Meanwhile, the freezer  52  is also driven when the scanning ion microscope  10  is used, the spacer  59  contracts due to the coldness generated by the cooling stage unit  60 , the cooling stage unit  60  has no direct physical contact with the internal peripheral surface of the pot main body  61  at the distal end thereof and in the entire region along the circumference thereof, the end face gap g 1  is formed between the cooling stage unit  60  and the containing chamber bottom  61   c  of the pot main body  61 , and the clearance S is formed between the cooling stage unit  60  and the internal peripheral surface of the pot main body  61 . Thus, the vibration transmitted from the freezer main body  53  is not transmitted to the gas pot  51 , that is, the ion source housing  22  via the cooling stage unit  60 , and particularly via the fin  58  thereof. As a result, the freezer main body  53  and the ion source housing  22  have only indirect physical contact with each other with the bellows  63  interposed therebetween, and thus, the vibration transmitted from the freezer main body  53  is reduced to a level that does not cause the problem in practical use by elasticity and stretchability of the bellows  63  and the heat conducting medium  69  as the vibration damping medium stored in the vibration suppressing space  68  inside the bellows  63 . 
         [0116]    Incidentally, the factors causing the vibration transmitted from the freezer main body  53  have been exemplified, but the vibration source is not limited only to the exemplified factors. In addition, the description has been given by exemplifying the pot containing housing portion  24  in which the containing direction of the cooling stage unit  60  of the freezer  52  with respect to the stage containing chamber  62  is the horizontal direction as a mechanism for reduction of the vibration transmitted from the freezer main body  53 . However, the present invention can be applied also to an ion beam, device which includes the pot containing housing portion  24  in which the containing direction of the cooling stage unit  60  is set to a direction other than the horizontal direction. 
         [0117]    Accordingly, the vibration from the freezer main body  53  is not transmitted to the gas pot  51  rigidly attached to the ion source housing  22  at the time of using the scanning ion microscope  10  according to the present embodiment, and thus, there is no problem that the emitter tip  45  vibrates and the ion beam  21  is hardly focused. In addition, there is no need of setting the gap between the gas pot  51  and the cooling stage unit  60 , and particularly between the fin  58  and the internal peripheral surface of the gas pot  51  to be wide more than enough taking into consideration of the prevention of contact therebetween in order to avoid the above-described problem. Thus, it is unnecessary to set the gap g 2  between the internal peripheral surface of the gas pot  51  and the external peripheral edge of the fin  52  to be wide to prevent the vibration from the freezer main body  53  from being transmitted to the ion source housing  22  and to the emitter tip  45  via the gas pot  51 , and thus, it is possible to prevent a situation that the cooling temperature of the emitter tip  45  tends to be higher than the original cooling temperature of the freezer  52  caused as cooling performance of the ionization gas deteriorates. 
         [0118]    Next, cooling performance of the scanning ion microscope  10  according to the present embodiment will be described on the basis of  FIG. 2 . 
         [0119]    A distal-end-side portion of the stage  57   b  of the cooling stage  57  becomes a low temperature portion which is cold in the freezer  52 . Thus, the cooling efficiency with respect to the gas pot  51  becomes more favorable as the area of the low temperature portion increases in the case of cooling the gas pot  51  using the heat conducting medium  64 . Thus, the fin  58  is joined and fixed to the distal end  57  of the cooling stage  57  so as to enlarge the surface area of the low temperature portion of the cooling stage  57 . In addition, the gas pot  51  is configured such that the bottom-side main body portion  61   a  is formed using the heat conducting material and the opening-side main body portion  61   b  is formed using the heat insulating material so as to limit a main cooled portion to the bottom-side main body portion  61   a  formed using the heat conducting material, and the heat entry to the opening-side main body portion  61   b,  which has been cooled by the fin  58 , is reduced by the opening-side main body portion  61   b  formed using the heat insulating material. 
         [0120]    In addition, it is preferable to set the end face gap g 1  between the fin  58  and the containing chamber bottom  61   c  of the pot main body  61  in a vibration direction to be large from a viewpoint of preventing the vibration transmitted from the freezer main body  53 , and particularly, the vibration generated as the displacer repeats reciprocation at high speed inside the cylinder from being transmitted to the gas pot  51 . When the end face gap g 1  is set to be large, however, the cooling performance of the fin  58  with respect to the containing chamber bottom  61   c  of the pot main body  61  decreases. Thus, it is preferable to set the side surface gap g 2  between the fin  58  and the internal peripheral surface of the pot main body  61  as narrow as possible in order to complement such a decrease in cooling performance of the fin  58  with respect to the containing chamber bottom  61   c  of the pot main body  61  to improve the cooling efficiency. In regard to this point, it is possible to roughly set the positional relationship between the external peripheral edge of the fin  58  and the internal peripheral surface of the pot main body  61  in response to the size of the clearance S specified by the spacer  59  in the present embodiment, and thus, it is possible to easily and accurately narrow the side surface gap g 2 . 
         [0121]    Accordingly, the gas pot  51  is configured so as to narrow the side surface gap g 2  to narrow down a cooling target to the bottom-side main body portion  61   a,  and to be protected from the heat entry from the outside by the opening-side main body portion  61   b  to be capable of efficiently using the coldness of the fin  58  for the cooling thereof. 
         [0122]    In addition, it is possible to achieve further improvement in cooling performance by configuring an assembly obtained by connecting and fixing the fin  58  to the cooling stage  57  as illustrated in  FIGS. 7( a ) and 7( b )  in relation to the cooling performance of the cooling stage unit  60  with respect to the gas pot  51 . 
         [0123]      FIGS. 7( a ) and 7( b )  are configuration diagrams of a modified example of the assembly obtained by connecting and fixing the fin to the cooling stage. Incidentally, when a configuration of the assembly is described, the same components as those of the assembly illustrated in  FIG. 3  will be denoted by the same reference signs, and the detailed description thereof will be omitted. 
         [0124]    Relating to the assembly in the cooling stage unit  60  obtained by joining and fixing the fin  58  to the cooling stage  57 , the cooling performance of the cooling stage unit  60  with respect to the gas pot  51  is improved as the contact area therebetween increases, that is, each efficiency of heat conduction of joining and fixing surfaces thereof is higher. From this viewpoint, both the joining and fixing surfaces are not completely flat but are uneven surfaces when the respective surfaces are microscopically viewed. Thus, concave surfaces of the uneven surfaces have no contact with each other when the cooling stage  57  and the fin  58  are simply joined and fixed to each other, thereby decreasing the contact area. 
         [0125]    Thus, the cooling stage unit  60  illustrated, in  FIG. 7( a )  is configured such that a thermally conductive sheet  95  made of a soft material and has favorable heat conduction, such as indium, is interposed and sandwiched between the cooling stage  57  and the fin  58  in advance before joining and fixing both the cooling stage  57  and the fin  58 . Accordingly, the thermally conductive sheet  95  is deformed to bury the uneven surfaces generated in the respective joining and fixing surfaces at the time of joining and fixing the fin  58  to the cooling stage  57 , thereby improving the efficiency of heat conduction between both the joining and fixing surfaces. 
         [0126]    On the contrary, a thermally conductive film  96  made of a soft material which is soft and has favorable heat conduction, such as gold plating, is formed on a surface of the fin  58  to be joined and fixed to the cooling stage  57  in the cooling stage unit  60  illustrated in  FIG. 7( b ) . Accordingly, the thermally conductive film  96  is deformed to bury the uneven surfaces generated in the respective joining and fixing surfaces at the time of joining and fixing the fin  58  to the cooling stage  57 , thereby improving the efficiency of heat conduction between both the joining and fixing surfaces. 
         [0127]    In addition, it is possible to achieve further improvement in cooling performance, in relation to the cooling performance of the cooling stage unit  60  with respect to the gas pot  51 , by providing a heat conducting medium adjusting mechanism  100 , which adjusts a storage amount of the heat conducting medium  69  in each of the vibration suppressing space  68  and the non-contact space  67  as illustrated in  FIG. 8 , in the cooling mechanism  50 . 
         [0128]      FIG. 8  is a configuration diagram of a cooling mechanism that includes a heat conducting medium adjusting mechanism. 
         [0129]      FIGS. 9( a ) to 9( c )  are explanatory diagrams of an operation state of a cooling mechanism that does not include the heat conducting medium adjusting mechanism as a comparative example. 
         [0130]    Incidentally, in the description of a configuration of the cooling mechanism that includes the heat conducting medium adjusting mechanism according to the present example, the same or similar components as those in the configuration of the cooling mechanism illustrated in  FIG. 2  will be denoted by the same reference signs, and the detailed description thereof will be omitted. 
         [0131]    As illustrated in  FIG. 8 , the heat conducting medium adjusting mechanism  100  is configured to include a heat conducting medium supply mechanism  101  which supplies the heat conducting medium  69  to each of the vibration suppressing space  68  and the non-contact space  67  of the cooling mechanism  50  to be stored therein, and a heat conducting medium discharge mechanism  102  which discharges the stored heat conducting medium  69  from each of the vibration suppressing space  68  and the non-contact space  67  of the cooling mechanism  50 . 
         [0132]    The heat conducting medium supply mechanism  101  includes a heat conducting medium source  103  and a regulator  104 , and is connected to a heat conducting medium port  105  formed in the pot connecting frame  65  via an anti-vibration mechanism (not illustrated). On the other hand, the heat conducting medium discharge mechanism  102  includes the check valve  106  and the pressure gauge  107  and is connected to a heat conducting outlet  108  formed in the pot connecting frame  65  via an anti-vibration mechanism (not illustrated). 
         [0133]    Meanwhile, when heating is performed to sharpen the emitter tip  45  in the case of the scanning ion microscope  10  illustrated in  FIG. 1 , for example, the heat of the emitter tip  45  is transmitted from the cooling conduction mechanism  70  to the bottom-side main body portion  61   a  of the pot main body  61  formed using the heat conducting material in the gas pot  51 , and the non-contact space  67  of the cooling mechanism  50  and the heat conducting medium  69  stored in the vibration suppressing space  68  communicating with the non-contact space  67  are heated. Accordingly, the non-contact space  67 , the heat conducting medium  64 , and the respective heat conducting media  69  are expanded and each volume thereof increases. Along with this, the bellows  63  of the cooling mechanism  50  is deformed to be stretchable as illustrated in  FIG. 9( b )  from an initial state illustrated in  FIG. 9( a ) , and the cooling stage unit  60  is extruded outwardly inside the stage containing chamber  62 . As a result, the positional relationship between the fin  58  and the containing chamber bottom  61   c  of the pot main body  61 , which is formed using the heat conducting material, of the gas pot  51  is changed to be separated from each other, and it becomes difficult to perform the cooling efficiently. 
         [0134]    In addition, for example, when the cooling using the cooling mechanism  50  is performed from the room temperature, the heat conducting medium  69  stored in the non-contact space  67  and the vibration suppressing space  68  contracts and is decreased in volume as the temperature of the gas pot  51  is cooled. Along with this, the bellows  63  of the cooling mechanism  50  is deformed to contract as illustrated in  FIG. 9( c )  from the initial state illustrated in  FIG. 9( a ) , and the cooling stage unit  60  retracts toward the inner portion side of the stage containing chamber  62 . As a result, the positional relationship between the fin  58  and the containing chamber bottom  61   c  of the pot main body  61  is changed to approach each other, and the gap g 1  between the fin  58  and the containing chamber bottom  61   c  of the gas pot  51  decreases. Further, when the gap g 1  is not formed so that the fin  58  and the containing chamber bottom  61   c  of the gas pot  51  are brought into contact with each other, the vibration from the freezer  60  is transmitted to the gas pot  51 , thereby causing vibration of the emitter tip  45  in the ion source housing  22 . 
         [0135]    The heat conducting medium adjusting mechanism  100  adjusts a variation of the cooling stage unit  60  based on such a pressure change of the heat conducting medium  69  such that the pressure of the heat conducting medium  69  becomes constant by adjusting the amount of the heat conducting medium  69  in each of the non-contact space  67  and the vibration suppressing space  68 . 
         [0136]    To be specific, when there is an indication that the bellows  63  is deformed to be stretchable and the cooling stage unit  60  is extruded outwardly inside the stage containing chamber  62  as illustrated in  FIG. 9( b ) , the heat conducting medium adjusting mechanism  100  discharges the heat conducting medium  69  corresponding to the increased volume from the heat conducting medium discharge mechanism  102 . On the other hand, when there is an indication that the bellows  63  is deformed to contract and the cooling stage unit  60  retracts to the inner portion side of the stage containing chamber  62  as illustrated in  FIG. 9( c ) , the heat conducting medium adjusting mechanism  100  supplies the heat conducting medium  69  corresponding to the decreased volume from the heat conducting medium supply mechanism  101 . 
         [0137]    In this manner, the positional relationship with the containing chamber bottom  61   c  of the pot main body  61  is held in a given state as illustrated in  FIG. 8  regardless of the temperature variation of the heat conducting medium  69  in the cooling mechanism  50  including the heat conducting medium adjusting mechanism  100 , thereby achieving the further improvement in cooling performance of the cooling mechanism  50 . 
       Second Embodiment 
       [0138]    A description will be given regarding a scanning ion microscope  10 ′ as an ion beam device according to a second embodiment of the present invention on the basis of  FIGS. 10 to 13 ( b ). Incidentally, each unit having the same or similar configuration as that in the scanning ion microscope  10  according to the first embodiment will be denoted by the same reference sign in the drawing when the description is given, and the redundant description will be omitted. 
         [0139]      FIG. 10  is a schematic configuration diagram of the scanning ion microscope as the ion beam device according to the second embodiment of the present invention. 
         [0140]      FIG. 11  is a partially enlarged view of a cooling stage unit and a gas pot section forming an ion beam device cooling mechanism of the ion beam device illustrated in  FIG. 10 . 
         [0141]      FIG. 12  is a diagram illustrating the cooling stage unit section and the gas pot section which are separated before being assembled as the cooling stage unit and the gas pot section illustrated in  FIG. 11 . 
         [0142]      FIGS. 13( a ) and 13( b )  are views for comparison between a normal temperature state and a cooling state in the cooling stage unit and the gas pot section illustrated in  FIG. 11 . 
         [0143]    As illustrated in  FIG. 10 , the scanning ion microscope  10 ′ according to the present embodiment is different from the scanning ion microscope  10  according to the first embodiment illustrated in  FIG. 1  first in terms that the ion source chamber  27  of the ion source containing housing portion  23  is defined into an inner space  27   i  in which the emitter tip  45  is contained and an outer space  27   o  around the inner space  27   i  by a radiation shield  111 , and the gas ionization chamber  25  is formed using the defined space  27   i.  Accordingly, downsizing of the gas ionization chamber  25 , which is a target to be cooled by the cooling mechanism  50 , is achieved in the scanning ion microscope  10 ′ according to the present embodiment, as compared to the scanning ion microscope  10  illustrated in  FIG. 1  in which the gas ionization chamber  25  becomes the inside of the ion source chamber  27 . 
         [0144]    In addition, the scanning ion microscope  10 ′ according to the present embodiment is different from the scanning ion microscope  10  according to the first embodiment illustrated in  FIG. 1  in terms that the freezer  52  in a two-stage cooling system including two large and small cylinders provided with the displacer, which is integrated with a built-in coldness accumulator and is reciprocatingly movable, for example, is used as the freezer  52  of the cooling mechanism  50 , and the cooling stage unit  60  is configured to include a high-temperature-side cooling stage unit portion  60 H to cool the radiation shield  111  to cryogenic temperature and a low-temperature-side cooling stage unit portion  60 L to cool the emitter tip  45  to cryogenic temperature which is lower temperature than the radiation shield  111 , along with the employing of the configuration in which the gas ionization chamber  25  is further defined by the radiation shield  111  inside the ion source chamber  27 . 
         [0145]    In the present embodiment, the radiation shield  111  is attached and fixed to the ion source housing  22  so as to open a releasing direction of the ion beam  21  and surrounds the emitter tip  45  inside the ion source containing housing portion  23  as illustrated in  FIG. 10 . The radiation shield  111  is configured using, for example, a gold-plated copper mesh or the like, and prevents entry of heat from outside into the gas ionization chamber  25 . An open end of the gas supply piping  48  to supply an ionization gas passes through the space  27   o  and is opened at the space  27   i  so as to supply the ionization gas or gas molecules to the space  27   i  serving as the gas ionization chamber  25 . In addition, a passage hole  112 , configured to allow the cooling conduction mechanism  70 , which transmits coldness generated by the cooling stage unit  60  of the cooling mechanism  50  to the emitter tip  45 , to pass therethrough in a non-contact manner is formed in the radiation shield  111 . 
         [0146]    On the other hand, in the present embodiment, the cooling stage unit  60  has a structure such that the cooling stage unit  60  is formed by coaxially connecting the two high-temperature-side and low-temperature-side cooling stage unit portions  60 H and  60 L at two stages according to the use of the freezer  52  of the two-stage cooling system in the cooling mechanism  50 , and the pot main body  61  of the gas pot  51  also has a structure obtained by continuously providing two high-temperature-side and low-temperature-side pot main body portions  61 H and  61 L to be coaxial with each other. 
         [0147]    As illustrated in  FIGS. 11 to 13 ( b ), the cooling stage unit portions  60 H and  60 L are configured such that a size of the low-temperature-side cooling stage unit portion  60 L on a distal end side, which has a storage  57   b L including an expansion chamber side inside the small cylinder on the low temperature side is smaller than a size of the high-temperature-side cooling stage unit portion  60 H on a proximal end side which has a stage  57   b H including an expansion chamber side inside the large cylinder on the high temperature side. Further, the respective cooling stage unit portions  60 H and  60 L are configured such that the fin  58  ( 58 H or  58 L) has a larger outer shape viewed in the axial direction than the stage  57   b  ( 57   b H or  57   b L). 
         [0148]    Furthermore, a spacer mounting portion  60   a H, provided with a tubular spacer  59 H that surrounds a peripheral surface of the stage  57   b H in the entire region around the circumference of the stage  57   b H, of the high-temperature-side cooling stage unit portion  60 H is configured to have a larger outer shape vertical to the axis direction which is viewed in the axial direction than the fin portion  60   b H, and an external peripheral edge of the spacer mounting portion  60   a H projects outwardly in the radial direction more than an external peripheral edge of the fin portion  60   b H in the entire region along the circumference thereof. Similarly, a spacer mounting portion  60   a L, provided with a tubular spacer  59 L that surrounds a peripheral surface of the stage  57   b L in the entire region around the circumference of the stage  57   b L, of the low-temperature-side cooling stage unit portion  60 L is configured to have a larger outer shape vertical to the axis direction which is viewed in the axial direction than the fin portion  60   b L, and an external peripheral edge of the spacer mounting portion  60   a L projects outwardly in the radial direction more than an external peripheral edge of the fin portion  60   b L in the entire region along the circumference thereof. Further, the fin portion  60   b H of the high-temperature-side cooling stage unit portion  60 H is configured to have the larger outer shape vertical to the axis direction which is viewed in the axial direction than the fin portion  60   b L of the low-temperature-side cooling stage unit portion  60 L, and the external peripheral edge of the fin portion  60   b H projects outwardly in the radial direction more than the external peripheral edge of the fin portion  60   b L in the entire region along the circumference thereof. The above-described spacers  59 H and  59 L are configured using a porous material, for example foamed resin. 
         [0149]    Meanwhile, the pot main body  61  of the gas pot  51  obtained by continuously providing the two pot main body portions  61 H and  61 L on the high temperature side and the low temperature side to be coaxial has a stepped-cylindrical shape with a bottom whose one end is blocked and the other end is opened, and has a configuration in which the pot main body portion  61 H containing the high-temperature-side cooling stage unit portion  60 H on the one end side and the pot main body portion  61 L containing the low-temperature-side cooling stage unit portion  60 L on the other end side are integrated via a stepped portion  116 . Further, a high-temperature-side stage containing chamber  62 H is formed in the pot main body portion  61 H. 
         [0150]    A cross-sectional shape of the high-temperature-side stage containing chamber  62 H vertical to the axis is a cross-sectional shape which has no step and is uniform in the entire region along the axial direction, and is a cross-sectional shape formed in accordance with an external peripheral surface shape of the spacer mounting portion  60   a H of the high-temperature-side cooling stage unit portion  60 H. A size of this cross-sectional shape (length of the high-temperature-side stage containing chamber  62 H in the radial direction) is set to be a size that enables contact with the spacer mounting portion  60   a H of the high-temperature-side cooling stage unit portion  60 H in a normal temperature state, that is, the external peripheral edge of the spacer  59 H in a non-contracted state in the cooling stage unit  60 . In addition, a length of the high-temperature-side stage containing chamber  62 H in the axial direction is set to be appropriately longer than a length obtained by adding a length of the spacer mounting portion  60   a H in the axial direction and a length of the fin portion  60   b H in the axial direction in the high-temperature-side cooling stage unit portion  60 H. 
         [0151]    The low-temperature-side stage containing chamber  62 L is formed to be coaxial with the high-temperature-side stage containing chamber  62 H, and communicates with the high-temperature-side stage containing chamber  62 H. A cross-sectional shape of the low-temperature-side stage containing chamber  62 L vertical to the axis is a cross-sectional shape which has no step and is uniform in the entire region along the axial direction, and is a cross-sectional shape formed in accordance with an external peripheral surface shape of the spacer mounting portion  60   a L of the low-temperature-side cooling stage unit portion  60 L. A size of this cross-sectional shape (length of the low-temperature-side stage containing chamber  62 L in the radial direction) is set to be a size that enables contact with the spacer mounting portion  60   a L of the low-temperature-side cooling stage unit portion  60 L in a normal temperature state, that is, the external peripheral edge of the low-temperature-side spacer  59 L in a non-contracted state. In addition, a length of the low-temperature-side stage containing chamber  62 L in the axial direction is set to be appropriately longer than a length of the fin portion  60   b L of the low-temperature-side cooling stage unit portion  60 L in the axial direction. 
         [0152]    Furthermore, a length of the stage containing chamber  62 , which is formed in the pot main body portion  61  and includes the high-temperature-side stage containing chamber  62 H and the low-temperature-side stage containing chamber  62 L, in the axial direction is set to be appropriately longer than a length obtained by adding the length of the high-temperature-side cooling stage unit portion  60 H in the axial direction and the length of the low-temperature-side cooling stage unit portion  60 L in the axial direction. 
         [0153]    Further, each of the pot main body portions  61 H and  61 L is configured by joining and fixing the opening-side main body portion  61   b  ( 61   b H or  61   b H) formed using a heat insulating material and the bottom-side main body portion  61   a  ( 61   a H or  61   a H) formed using the heat conducting material to be coaxially integrated with each other along the axial direction. 
         [0154]    Accordingly, the high-temperature-side non-contact space  67 H is formed between the fin portion  60   b H of the high-temperature-side cooling stage unit portion  60 H and the bottom (cross section)-side main body portion  61   a H of the pot main body portion  61 H. In addition, the low-temperature-side non-contact space  67 L is formed between the fin portion  60   b L of the low-temperature-side cooling stage unit portion  60 L and the bottom-side main body portion  61   a L of the pot main body portion  61 L. Further, the heat conducting medium  69  is stored in each of the high-temperature-side non-contact space  67 H and the low-temperature-side non-contact space  67 L. Further, in the gas pot  51 , the bottom-side main body portion  61   a H of the high-temperature-side pot main body portion  61 H of the pot main body  61  is cooled by coldness of the fin portion  60   b H of the high-temperature-side cooling stage unit portion  60 H to the cryogenic temperature, and the bottom-side main body portion  61   a L of the low-temperature-side pot main body portion  61 L of the pot main body  61  is cooled by coldness of the fin portion  60   b L of the low-temperature-side cooling stage unit portion  60 L to still lower cryogenic temperature. 
         [0155]    Further, the bottom-side main body portion  61   a H of the high-temperature-side pot main body portion  61 H of the pot main body  61  formed using the heat conducting material is thermally connected to the radiation shield  111  provided in the ion source containing housing portion  23  of the ion source housing  22  via the high-temperature-side cooling conduction mechanism  70 H configured to include a gold-plated copper mesh portion, for example. In addition, the bottom-side main body portion  61   a L of the low-temperature-side pot main body portion  61 L of the pot main body  61  formed using the heat conducting material is thermally connected to the emitter tip  45  provided in the ion source containing housing portion  23  of the ion source housing  22  via a low-temperature-side cooling conduction mechanism  70 L. 
         [0156]    Even in the scanning ion microscope  10 ′ according to the present embodiment, the same action and effects as those in the scanning ion microscope  10  according to the first embodiment are achieved regarding the assembly of the cooling mechanism  50 , position adjustment between the fin  58  and the gas pot  51  performed by the spacer  59  at the time of assembly relating to the cooling mechanism  50 , and the cooling performance of the scanning ion microscope  10 ′. 
         [0157]    For example, it is preferable to set an end face gap g 1 H between the fin  58 H and the stepped portion  116  of the pot main body  61  and an end face gap g 1 L between the fin  58 L and the containing chamber bottom  61   c  of the pot main body  61  in a vibration direction to be large from a viewpoint of preventing the vibration transmitted from the freezer main body  53 , and particularly, the vibration generated as the displacer repeats reciprocation at high speed inside the cylinder from being transmitted to the gas pot  51 . When the end face gaps g 1 H and g 1 L are set to be large, however, each cooling performance of the fins  58 H and  58 L with respect to the stepped portion  116  and the containing chamber bottom  61   c  of the pot main body  61  decreases. Thus, it is preferable to set a side surface gap g 2 H or g 2 L between the fin  58 H or  58 L and the internal peripheral surface of the pot main body  61  as narrow as possible in order to complement the decreases in cooling performance of the fins  58 H and  58 L with respect to the stepped portion  116  and the containing chamber bottom  61   c  of the pot main body  61  to improve the cooling efficiency. In regard to this point, it is possible to roughly set the positional relationship between the external peripheral edge of the fin  58 H or  58 L and the internal peripheral surface of the pot main body  61  in response to the size of the clearance S specified by the spacer  59 H or  59 L in the present embodiment, and thus, it is possible to easily and accurately narrow the side surface gap g 2 H or g 2 L. 
         [0158]    Incidentally, the description has been given in the illustrated example regarding the case of using the same material for the two spacers  59 H and  59 L, but the material of the spacer  59  may be changed between the high-temperature-side spacer  59 H and the low-temperature-side spacer  59 L. In addition, for example, a specific form of the spacer  59 , such as the tubular spacer and a spacer piece assembly, or a shape of the external peripheral edge viewed in the axis direction, such as a circular shape and a polygonal shape, may be changed between the high-temperature-side spacer  59 H and the low-temperature-side spacer  59 L. 
         [0159]      FIGS. 14( a ) and 14( b )  are configuration diagrams of a modified example of an assembly obtained by connecting and fixing a fin to a cooling stage. Incidentally, when a configuration of the assembly is described, the same components as those of the assembly illustrated in  FIGS. 7( a ), 7( b )  and  12  will be denoted by the same reference signs, and the detailed description thereof will be omitted. 
         [0160]    The cooling stage unit  60  illustrated in  FIG. 14( a )  is configured such that the thermally conductive sheet  95  ( 95 H or  95 L) made of a soft material and has favorable heat conduction, such as indium, is interposed and sandwiched between the stage  57   b  ( 57   b H or  57   b L) and the fin  58  ( 58 H or  58 L) in advance before joining and fixing both the stage  57   b  and the fin  58 . Accordingly, the thermally conductive sheet  95  is deformed to bury the uneven surfaces generated in the respective joining and fixing surfaces at the time of joining and fixing the fin  58  to the stage  57   b,  thereby improving the efficiency of heat conduction between both the joining and fixing surfaces. 
         [0161]    On the contrary, a thermally conductive film  96  ( 96 H or  96 L) made of a soft material which is soft and has favorable heat conduction, such as gold plating, is formed on a surface of the fin  58  ( 58 H or  58 L) to be joined and fixed to the stage  57   b  ( 57   b H or  57   b L) in the cooling stage unit  60  illustrated in  FIG. 14( b ) . Accordingly, the thermally conductive film  96  is deformed to bury the uneven surfaces generated in the respective joining and fixing surfaces at the time of joining and fixing the fin  58  to the cooling stage  57 , thereby improving the efficiency of heat conduction between both the joining and fixing surfaces. 
       Third Embodiment 
       [0162]    An ion beam device according to the present embodiment will be described regarding the ion beam device obtained by combining the ion beam device and the device other than the ion beam device by exemplifying an ion beam device in which a mass spectrometer  121  as an optional item, for example, is attached to the vacuum chamber  32  of the scanning ion microscope  10  according to the first embodiment illustrated in  FIGS. 1 to 4  on the basis of the drawings. Incidentally, the overlapping description with that for the scanning ion microscope  10  illustrated in  FIGS. 1 to 4  will be omitted in the following description. 
         [0163]      FIG. 15  is a configuration diagram of an example of the ion beam device in which the scanning ion microscope and the mass spectrometer are combined. 
         [0164]    As illustrated in  FIG. 15 , in the ion beam device in which the mass spectrometer  121  as the optional item, for example, is attached to the vacuum chamber  32  of the scanning ion microscope  10  illustrated in  FIG. 1 , the device main body  11  of the scanning ion microscope  10  mounted and fixed to the base stand  13  is inclined by the inclination angle θ as a position of the center of gravity of the device main body  11  of the scanning ion microscope  10  is changed from a position of the center of gravity in the standard configuration in which the mass spectrometer  121  is not provided. 
         [0165]    Even in such a case, the scanning ion microscope  10  forming the ion beam device is provided with the position adjusting and fixing mechanism  87  capable of finely adjusting an attitude state of the freezer main body  53  mounted and fixed to the mounting portion  88  within a tolerable range, and thus, it is possible to adjust a mounting attitude of the freezer main body  53  on the support stand  83  such that a direction of the cooling stage unit  60  of the freezer  52  becomes coaxial with a containing direction of the gas pot  51  by adjusting an attachment angle of the mounting portion  88  in response to a change of the containing direction of the gas pot  51  (direction of the cooling mechanism mounting port  29 ) in the pot containing housing portion  24  of the ion source housing  22  caused by the inclination of the device main body  11 . 
         [0166]    Accordingly, if the device main body of the ion beam device is inclined, the same action and effects as those in the scanning ion microscope  10  illustrated in  FIG. 1  are achieved regarding the assembly of the cooling mechanism  50 , position adjustment between the fin  58  and the gas pot  51  performed by the spacer  59  at the time of assembly, and the cooling performance of the scanning ion microscope  10 . 
         [0167]      FIG. 16  is a configuration diagram of another example relating to the ion beam device in which the scanning ion microscope and the mass spectrometer are combined illustrated in  FIG. 15 . 
         [0168]    In the present example, a containing direction adjusting and fixing mechanism  89  is provided, which is capable of finely adjusting the containing direction of the gas pot  51  (direction of the cooling mechanism mounting port  29 ) in the pot containing housing portion  24  of the ion source housing  22  within the tolerable range with respect to the ion source containing housing portion  23  in a connection portion between the ion source containing housing portion  23  and the pot containing housing portion  24  in the ion source housing  22  of the scanning ion microscope  10 . 
         [0169]    Even in the present example, even if the device main body of the ion beam device is inclined, the same action and effects as those in the scanning ion microscope  10  illustrated in  FIG. 1  are achieved regarding the assembly of the cooling mechanism  50 , position adjustment between the fin  58  and the gas pot  51  performed by the spacer  59  at the time of assembly, and the cooling performance of the scanning ion microscope  10 . 
         [0170]    In addition, the cooling conduction mechanism  70  is configured using a gold-plated copper mesh, and can be deformed, for example, deflected or bent, by deformation of the copper mesh portion in the present example. Thus, even if the containing direction of the gas pot  51  is changed with respect to the ion source containing housing portion  23 , the cooling conduction mechanism  70  can be deformed, for example, deflected or bent, in response to the change. Accordingly, even when the cooling conduction mechanism  70  is cut or the like, the transmission of coldness is not blocked. 
         [0171]    Incidentally, embodiments of the present invention are not limited only to the specific configurations of the embodiments described above. For example, in the case of the spacer piece assembly in which the plurality of spacer pieces are arranged side by side with the predetermined interval along the circumferential direction of the stage  57   b  to partially surround the peripheral surface of the stage  57   b,  the spacer pieces can be also provided on the internal peripheral surface of the gas pot  51 . 
         [0172]    In addition, it is unnecessary to implement the respective examples described above independently from each other, but a plurality of examples can be applied at the same time without restricting the scope of the claims. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           10  scanning ion microscope 
           11  device main body 
           12  floor 
           13  base stand 
           14  anti-vibration mechanism 
           15  base plate 
           20  ion source (gas ion source) 
           21  ion beam 
           22  ion source housing 
           23  ion source containing housing portion 
           24  pot containing housing portion (cooling mechanism housing portion) 
           25  gas ionization chamber 
           26  pot containing chamber 
           27  ion source chamber 
           28  communication port 
           29  cooling mechanism mounting port 
           30  column (lens barrel) 
           31  beam irradiation system 
           32  vacuum chamber 
           33  vacuum exhaust system 
           34  vacuum exhaust equipment 
           35  vacuum exhaust pipe 
           36  bulkhead 
           37  passage hole 
           38  vacuum exhaust equipment 
           39  vacuum exhaust pipe 
           40  sample chamber 
           41  sample 
           42  sample stage 
           43  secondary particle detector 
           45  emitter tip 
           46  extraction electrode 
           47  gas source 
           48  gas supply piping 
           49  vacuum exhaust system 
           50  ion beam device cooling mechanism (cooling mechanism) 
           52  freezer 
           53  freezer main body 
           54  compressor 
           55  high-pressure piping 
           56  low-pressure piping 
           57  cooling stage 
           57   a  base 
           57   b  stage 
           57   c  stage distal end 
           58  fin 
           58   a  base 
           59  spacer 
           60  cooling stage unit 
           60   a  spacer mounting portion 
           60   b  fin portion 
           61  pot main body 
           61   a  bottom-side main body portion 
           61   b  opening-side main body portion 
           61   c  containing chamber bottom 
           62  stage containing chamber 
           63  bellows 
           64  attachment flange 
           65  pot connecting frame 
           66  attachment flange 
           67  non-contact space 
           68  vibration suppressing space 
           69  heat conducting medium 
           70  cooling conduction mechanism 
           83  support stand 
           84  base stand 
           85  fulcrum 
           86  attachment plate 
           87  position adjusting and fixing mechanism 
           88  mounting portion 
           89  containing direction adjusting and fixing mechanism 
           90  control device 
           91  input/output device 
           95  thermally conductive sheet 
           96  thermally conductive film 
           100  heat conducting medium adjusting mechanism 
           101  heat conducting medium supply mechanism 
           102  heat conducting medium discharge mechanism 
           103  heat conducting medium source 
           104  regulator 
           105  heat conducting medium port 
           106  check valve 
           107  pressure gauge 
           108  heat conducting outlet 
           111  radiation shield 
           112  passage hole 
           116  stepped portion 
           121  mass spectrometer 
       
     
         [0261]    All publications, patents, and patent applications cited herein are incorporated herein by reference in their entirety.