Abstract:
The present invention is provided to enable a detailed inspection of a specimen and preventing a distortion of an observation image even when a specimen containing an insulating material is partially charged. For a scanning ion microscope utilizing a gas field ionization ion source, a thin film is disposed between an ion optical system and a specimen, and an ion beam is applied to and transmitted through this thin film in order to focus a neutralized beam on the specimen. Furthermore, an electrode for regulating secondary electrons discharged from this thin film is provided in order to eliminate mixing of noises into an observation image.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a scanning ion microscope that can form a specimen image by scanning with uncharged particles and a secondary particle control method. 
     BACKGROUND ART 
     Patent Document 1 and Patent Document 2 disclose focused ion beam (FIB) devices that have gas field ionization ion source (GFIS) and use gas ions such as hydrogen (H2), helium (He), and neon (Ne). Such gas focused ion beams (gas FIB) has an advantageous effect in that they do not bring Ga contamination to the specimen as in a gallium (Ga: metal) focused ion beam (Ga-FIB) from a liquid metal ion source (LMIS), which is used often nowadays. 
     In addition, the energy width of the gas ions extracted from GFIS is narrow and the size of an ion generation source is small in GFIS, and thus GFIS can form minute beams than Ga-FIB. 
     Such gas FIB devices are used as a scanning ion microscope having a high resolution. That is, an image of the specimen is formed by detecting secondary particles emitted from the specimen, synchronizing with the scanning the specimen with the ions. 
     Patent Document 3 discloses a pattern inspection device that use an ion beam, wherein the ion beam that has converged and scanned is neutralized and irradiates onto the specimen. The neutralization is performed by an electron emission source (grid etc. to which negative voltage is applied) which is provided to cross the ion beam. 
     Patent Document 4 discloses a surface analysis device that uses an ion beam, wherein the ion beam is charge-neutralized for irradiation of the specimen. The charge-neutralizing means is provided by exchanging charges in gas (and in a capillary). Here, in order to make energy of uncharged particle beams uniform and to remove particles other than uncharged particles, there are further provided a means for removing multivalent ions as pre-treatment and a means for removing charged particles as post-treatment. 
     Patent Document 5 discloses an analysis apparatus that uses ion beams of high energy (MeV level), wherein ion beams led from vacuum are applied to the specimen in atmospheric pressure such that the ion beams are transmitted through an exit window (pressure bulkhead). The pressure bulkhead is formed by attaching a gold thin film on a metal net-structured object. Here, since the net-structured object partially supports the pressure difference between inside and outside of the pressure bulkhead, the gold thin film through which the ion beams are transmitted can be made relatively thin. Thereby, analysis accuracy has improved. Patent Documents 6, 7 and 8 disclose techniques similar to those in Patent Document 5. Here, for example, methods for cooling the pressure bulkhead, methods for monitoring a beam amount, and methods for reinforcing the pressure bulkhead are disclosed. 
     Patent Document 9 describes an arrangement of a film that can transmit ion beams on an ion beam path in order to remove contamination of low energy that comes from, for example, inner walls, in an ion implantation device. The film is a high polymer thin film. Degradation is prevented by exchanging the film once in every fixed service period. 
     PRIOR TECHNICAL DOCUMENTS 
     Patent Document 
     
         
         Patent Document 1: 
       
    
     Japan Patent Application Publication JP 07-192669 A
     Patent Document 2:   

     Japan International Patent Application Publication JP 2009-517846 W
     Patent Document 3:   

     Japan Patent Application Publication JP 62-298708 A
     Patent Document 4:   

     Japan Patent Application Publication JP 2008-185336 A
     Patent Document 5:   

     Japan Patent Application Publication JP 08-240542 A
     Patent Document 6:   

     Japan Patent Application Publication JP 09-033462 A
     Patent Document 7:   

     Japan Patent Application Publication JP 2010-203805 A
     Patent Document 8:   

     Japan Patent Application Publication JP 2011-095154 A
     Patent Document 9:   

     Japan Patent Application Publication JP 2002-134060 A 
     SUMMARY OF THE INVENTION 
     Object of the Invention 
     In a case where a specimen containing an insulator is observed with a scanning ion microscope, there is an issue that an image of the specimen is distorted with respect to an actual image as a result of the path of the ion beam being locally bent by partial electrification of the specimen. This cannot be completely solved by reducing electrification on the specimen. The best solution is to neutralize the ion beam itself (i.e., remove electric charge). 
     As described above, the ion beam neutralization method described in Patent Document 3 is described as having a grid structure in which negative voltage applied so as to intersect the flight path of the ion beam is applied. 
     Patent Document 4 needs to add, for example, a means for removing remaining ions to the latter stage. Such means serves as a big hindrance when converging ion beams minutely. 
     It should be noted that the conventional thin film utilizing methods described in Patent Documents 6, 7 and 8 do not describe whether the transmitted beam has electric charge. However, since energy of ions is large, existence of electric charge does not influence the measurement and thus it is presumed that the neutralization ratio itself is low. Furthermore, since the conventional thin film utilizing method described in Patent Document 9 does not care about convergence characteristics of the beam, existence of electric charge or secondary electrons in the transmitted beam has not been paid attention. 
     The present invention has been achieved in view of the above-described issues and an object of the present invention is to provide a scanning ion microscope that can observe a specimen minutely and prevent distortion of an observation image even if a specimen containing an insulator is charged partially and a secondary particle control method. 
     Means for Solving the Problem 
     In order to achieve the above-described object, the scanning ion microscope according to the present invention uses a gas field ionization ion source and arranges a thin film onto which ions are irradiated between a specimen and an ion optical system which makes ions converge and deflect onto the specimen. This thin film is supported by an electrically-conductive support member. There is provided a means for controlling an electric potential of the support member Furthermore, there are provided an electrode having an opening between the thin film and the specimen, and a means for controlling the electric potential of the electrode (e.g., power source  83 ). 
     The present invention utilizes that most of the ions applied to the thin film are neutralized after going through a first layer on the surface of the thin film, and are emitted as uncharged particles when transmitting through the thin film. In addition, ions applied to the thin film also emit secondary electrons. There is provided a means for controlling the secondary electrons emitted from the thin film appropriately for preventing a part of the secondary electrons penetrating through the thin film (e.g., power source  84 ). 
     EFFECT OF THE INVENTION 
     According to the present invention, it is possible to observe a specimen minutely and prevent distortion of an observation image even if a specimen containing insulators is charged partially. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an entire configuration of a scanning ion microscope according to a first embodiment of the present invention; 
         FIG. 2  shows a configuration around a thin film of the scanning ion microscope according to the first embodiment of the present invention; 
         FIG. 3  shows a configuration around a thin film of a scanning ion microscope according to a second embodiment of the present invention; 
         FIG. 4  shows a configuration around a thin film of a scanning ion microscope according to a third embodiment of the present invention; 
         FIG. 5  shows a configuration around a thin film of a scanning ion microscope according to a fourth embodiment of the present invention; 
         FIG. 6  shows a configuration around a thin film of a scanning ion microscope according to a fifth embodiment of the present invention; 
         FIG. 7  shows a configuration around a thin film of a scanning ion microscope according to a sixth embodiment of the present invention; 
         FIG. 8  shows a configuration around a thin film of a scanning ion microscope according to a seventh embodiment of the present invention; and 
         FIG. 9  shows a diagram illustrating a situation of neutralization of ion beams of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of scanning ion microscopes according to the present invention will be described in detail with reference to the drawings. 
     &lt;First Embodiment&gt; 
       FIG. 1  shows an entire configuration of a scanning ion microscope according to the present embodiment. The scanning ion microscope  200  according to the present embodiment is configured by incorporating a gas field ionization ion source (GFIS)  100  utilizing helium (He) into a focused ion beam (FIB) device produced for a conventional gallium-liquid metal ion source (Ga-LMIS) instead of the Ga-LMIS. 
     In  FIG. 1 , a scanning ion microscope  200  has a configuration in which a helium (He) ion beam  5  emitted from a GFIS  100  enter into an ion optical system  300  (ion optical series system) which cause the ion beams  5  to converge by the ion optical system  300 , and thus irradiates a specimen  6  placed on a specimen stage  101  with the ion beams  5 . Acceleration voltage of ions is 30 kV. 
     The GFIS  100  includes: an emitter tip  1 ; an extraction electrode  2 ; and a gas discharge outlet  3  of gas supplying piping, which supplies gas for ionization to an apex of the emitter tip. The emitter tip  1  ionizes gas that is supplied from the gas discharge outlet  3  and resides at the apex of the tip with a high voltage (the emitter tip  1  side is positive and the extraction electrode  2  side is negative) applied from the extraction voltage application unit  4  between the emitter tip  1  and the extraction electrode  2 . The extraction electrode  2  extracts ions generated by the emitter tip  1  and emits the ions as an ion beam  5  to the ion optical system  300 . 
     The ion optical system  300  includes: a lens system  102  (lens series system) containing electrostatic lenses  102   a ,  102   b , a beam limiting aperture  102   c , and an aligner  102   d ; and a deflector system  103  (deflector series system) including deflectors  103   a ,  103   b . The ion beam  5  that has entered the ion optical system  300  converges with the electrostatic lenses  102   a ,  102   b  in the ion optical system  300  and is applied to the specimen  6 . At this time, the position where the ion beam  5  is irradiated onto the specimen  6  is adjusted by deflecting the ion beam  5  with the deflectors  103   a ,  103   b.    
     At this time, the lens system  102  including the electrostatic lenses  102   a ,  102   b , the beam limiting aperture  102   c , and the aligner  102   d  is controlled by a lens system controller  105  by controlling the drive of the corresponding drivers (DV)  102   a D- 102   d D. In addition, the lens system controller  105  also controls the ion beam  5  emitted by the ion optical system  300  by controlling the drive of the extraction voltage application unit  4 . Meanwhile, the deflector system  103  containing the deflectors  103   a ,  103   b  is controlled by control of the corresponding drivers (DV)  103   a D,  103   b D by the deflector system controller  106 . 
     An ion controller  120  for controlling the ion optical system  300  is configured with the lens system controller  105  and the deflector system controller  106  together with a plurality of drivers. 
     Secondary electrons  7  generated from the specimen  6  as a result of the above-described irradiation with the ion beam  5  are detected by a secondary particle detector  104  and are converted into digital signals through an A/D signal conversion unit  104 D. Thereafter, the image processing unit  110  forms a secondary electron observation image (image) in which the signal intensity of the digital signal is associated with the deflection intensity, and the image is displayed onto the display unit  110   b . An image formed by the image processing unit  110  is stored in a storage unit  110   a  (image memory). The image thus stored is used for image operations and image display. The user can specify a position to which the ion beam  5  is applied on the screen of the display unit  110   b  while looking into the secondary electron observation image displayed on the display unit  110   b.    
     In  FIG. 1 , an operation to control the entirety of the lens system controller  105 , the deflector system controller  106 , and the image processing unit  110  is omitted. 
     A first feature of the present embodiment is in addition to a fundamental configuration of the scanning ion microscopes a thin film  80  is disposed between the ion optical system  300  and the specimen  6  to neutralize the charge of the ion beam  5  to convert the ion beam  5  into an uncharged particle beam  50  for irradiating the specimen. 
     That is, the present embodiment maintains characteristics of a microscope since the thin film  80  serves as a neutralization means of the ion beam  5  and does not change at all the advancing direction of ions in the ion beam  5  that converge and scan in the ion optical system  300 . The secondary electron image of the specimen  6  is substantially unchanged from that in a case where there is no thin film  80 . However, since kinetic energy of the ion decreases slightly, brightness of the secondary electron image is reduced slightly. In addition, since a small amount of component that has changed in the advancing direction as a result of a scatter in the thin film  80  is mixed also, a small amount of background noise is produced in the secondary electron image. 
     It should be noted that since conventional neutralization means of an ion beam, for example, methods that use charge exchange in gas or capillary penetration, not only have low neutralization ratio but also the advancing direction of the ion beams spreads by experiencing a lot of dispersion, such means cannot be used for the purpose of the microscope according to the present invention. 
     Here, in order for the thin film  80  to function as a neutralization means of an ion beam, it is necessary to meet the following two conditions. A first condition is that an acceleration voltage of the ion beam  5  (which represents kinetic energy upon entering into the thin film  80 ) should be in a low speed to medium speed region, which is from several kV to about 100 kV. 
     When an ion subject to the acceleration voltage in a range from a low speed to medium speed enters into a solid, the speed of the entering ion is overwhelmingly lower than a speed of an electrically-conductive electron in a solid. Accordingly, an electric field produced by the ion is immediately shielded by electrically-conductive electrons. That is, the ion is neutralized. This has been confirmed experimentally also by checking ions that are scattered on a surface of a solid. The ion scattered in a first atomic layer of a surface of a solid comes out mostly unchanged as an ion. The ion scattered in a second atomic layer of a surface of a solid comes out mostly being neutralized. It should be noted that it is possible to provide distinction as to from what depth and by what atom the reflected ions and uncharged particles are scattered according to energy losses by energy discrimination of the reflected ions and uncharged particles with, for example, a semiconductor detector. In addition, the measurement may be performed by removing only ions with an electric field. 
       FIG. 9  shows a diagram illustrating a situation of neutralization of an ion beam in the present invention. The above situation of neutralization of the ion beam will be described now with reference to  FIG. 9 . In this diagram, “+” represents an ion, “N” represents an uncharged particle, and “−” represents an electron. A part of ions in the ion beam  5  that enters the thin film  80  are scattered at the surface. An ion scattered in the first atomic layer on the surface is emitted as an ion  5   b , and an ion scattered in the second atomic layer in the surface is emitted as an uncharged particle  50   b . If an ion is scattered in a location deeper than the second atomic layer, the ion hardly comes out from the thin film  80  but a part of the ions transmit through the thin film  80  as uncharged particles  50   c . Most ions in the ion beam  5  transmit through the thin film  80  as an uncharged particle beam  50  without changing the direction. Excited secondary electrons are emitted from the surface which the ion beam  5  enters and the surface the uncharged particle beam  50  is emitted. It should be noted that the scattered ions, uncharged particles, and secondary electrons are emitted with a broad angle distribution. In addition, re-ionization takes place rarely when the uncharged particle beam  50  is emitted. However, it is not illustrated since the probability is very low. 
     It should be noted that an ion beam having acceleration voltage of MV order, such as those used in RBS or PIXE, transmits through a thin film as ions with no change causing almost no interactions when entering into the thin film, and such an ion beam cannot be used for the present invention. 
     Another condition is that the thickness of the thin film  80  should be sufficiently thin as compared to a flying distance (“range”) of the ion beam  5 . 
     Near the “range”, the probability that an ion that has entered in to a solid scatters increases and the direction of the ions is broadened rapidly, and the ion stops near the “range”. At a distance sufficiently shorter than the range, the ion loses kinetic energy slightly as a result of inelastic scattering (dependent on the distance from the incident location) but the advancing direction is not changed. However, some ions change the advancing direction in a rare case as a result of elastic scattering. Such “range” varies with what the ion is (dependent on its mass), kinetic energy of the ion, and what the solid is (dependent on its element and density), and thus it is difficult to express the above condition with a short expression using an observable matter. 
     As to other expressions, it is considered that it is appropriate to express thickness of the thin film  80  with a transmission factor of the ion beam  5 . Fundamentally, the thickness of the thin film  80  is set such that 50% or more of ions in the ion beam  5  transmits through the thin film  80 . This condition is a practical limit. If this condition is not met, there are produced a lot of beams that have changed the direction as a result of the scattering in the thin film, thus causing a lot of background noise in the secondary electron image, for example. More preferably, it is possible to obtain an image of a specimen in which background noise is reduced by setting the thickness of the thin film  80  such that 90% or more of ions in the ion beam  5  transmit the thin film  80 . It should be noted that the neutralization ratio is reduced when the thickness of the thin film  80  is smaller than a two atom layer, and thus such a case is not suitable for the present invention. 
     Here, ionic species of the ion beam  5  is a monovalent helium ion in the present embodiment. Fundamentally, any ionic species can be used as long as the relation between the energy of the ion beam and the thickness of the thin film meets the above-described conditions (i.e., a multivalent ion or heavier ionic species is sufficient). Therefore, ion sources such as a plasma ion source, a liquid metal ion source, and an ionic liquid ion source can be used for the ion source instead of a gas field ionization ion source. 
     The reason why a helium ion is chosen in the present embodiment is that, since its normal state is gas, the ions come out from the thin film as gas when a small portion of the ions remain inside the thin film, and thus it is not likely to damage the thin film. If the ions are not gas, it is more likely that the ions remain and are accumulated in the thin film, changing the characteristics of the thin film. In this regard, neon ions and argon ions, which are gas, may also be used. In addition, another reason for selecting helium ions is because their transmission capability is high with respect to thin films that are currently available. In this regard, hydrogen ions having lighter mass may also be used. As to a heavy ion, it becomes more likely that thin films are damaged by sputtering. 
     The reason for selecting a gas field ionization ion source as an ion source in the present embodiment is that, since the ion source produces high brightness and the source size is small, it is easy to make an ion beam on the specimen minute and configure a microscope having a high resolution. In addition, since the electric current of the emitted ions is as small as several nA at most and ions turn into gas when neutralized, it is possible to make various kinds of damages done to the thin film  80  small. 
     A second feature of the present embodiment is in arranging an electrode  82  between the thin film  80  and the specimen. By handling the secondary electrons produced as a result of the thin film  80  appropriately, it is possible to avoid producing noise in the secondary electron observation image of the specimen. However, even if there is no such configuration and the secondary electrons are mixed in the image, substantially uniform background noise is reflected on the secondary electron image, and therefore observation of contrast that depends on the specimen can be performed sufficiently by applying suitable bias. 
     A third feature of the present embodiment is that front and back sides of the thin film  80  are kept in vacuum. Accordingly, it is possible to use thinner thin film for the thin film  80  since there is no need to support atmospheric pressure difference. Therefore, it is easier to increase the transmission factor of the ion beam  5 . However, even if gas at or below atmospheric pressure is arranged at the specimen side of the thin film  80 , there is no change in the essence of the present invention (the first feature described above). 
     Here, the thin film  80  is a silicon nitride thin film formed on a silicon substrate. The silicon substrate is etched in a shape of a window and a single silicon nitride thin film is placed in the window portion. The thin film is commercially available for holding specimens of transmission electron microscopes. Thickness of the silicon nitride thin film is 10 nm and the window size is 50 μm square. The thin film  80  is supported by a support body  81  having stainless characteristics and an electric potential thereof is controlled by the power source  83 . Usually, silicon nitride thin films are insulators and electrification may cause problems. However, large electrification is not produced on the silicon nitride thin films since electron hole pairs are produced inside as a result of irradiation of the ion beam  5  and thus the silicon nitride thin films are electrically conductive. Here, broadening the irradiation range of the ion beam  5  onto the outside of the window is effective for reducing the electric potential difference caused by resistance. Such broadening may be done upon performing blanking of the ion beam  5 . 
     An electric potential of the thin film  80  is made to be a ground potential, which is the same as the specimen  6 , by the power source  83 . If the thin film  80  is irradiated with the ion beam  5  by an acceleration voltage of 30 kV, the beam that has transmitted through the thin film  80  is neutralized to be an uncharged particle beam  50 . The uncharged particle beam  50  hardly is scattered in the thin film  80 , and thus applied to the same position on the specimen  6  to which the original ion beam  5  is converged and is deflected. Therefore, when an operation for acquiring a secondary electron observation image of the specimen  6  is caused to perform by the scanning ion microscope  200 , it is possible to acquire an image at the same location. As compared with a case where there is no thin film  80 , the amount of production of the secondary electrons  7  is reduced slightly, and in addition, the secondary electron observation image is not distorted when the specimen  6  is an insulator since the ion beam  5  is bent by the electrification of the specimen  6 . 
     Here, since the ion beam  5  does not converge on the thin film  80 , damage to the thin film  80  by the ion beam  5  is far smaller than damage to the specimen  6 . Furthermore, in the present embodiment, the thin film  80  can move slightly by the thin film slight movement mechanism  800  (thin film moving means) (refer to  FIG. 1 ). Thereby, the degradation can be delayed using the entire region of the thin film  80  uniformly. 
     In addition, the thin film slight movement mechanism  800  can remove the thin film  80  from the ion optical axis of the ion optical system  300 . Thereby, larger secondary electron signals can be obtained when the specimen  6  is electrically-conductive. 
       FIG. 2  shows a configuration near a thin film of the scanning ion microscope according to the first embodiment of the present invention. The periphery of the thin film  80  will be described in detail using  FIG. 2 . When the thin film  80  is irradiated with the ion beam  5 , the secondary electrons  70  transmit through the specimen  6  side of the thin film  80  in addition to the uncharged particle beam  50 . When the secondary electrons  70  are mixed with the secondary electrons  7  produced at the specimen  6  and are detected by the secondary particle detector  104  (refer to  FIG. 1 ), noise is mixed in the secondary electron observation image of the specimen  6 . Accordingly, in the present embodiment, the electric potential of the electrode  82  having an opening in the center is set by the power source  84  appropriately. That is, the secondary electron  70  is sent back to the thin film  80  side by setting the electric potential of the electrode  82  to minus several tens of V with respect to the electric potential of the support body  81  (ground potential in this case). Thereby, noise in the secondary electron observation image of the specimen  6  can be removed. It should be noted that no matter how the electric potential of the electrode  82  is set, the path of the uncharged particle beam  50  is not affected. 
     Now, a method for improving convergence performance of the uncharged particle beam  50  by setting the electric potential of the thin film  80  will be described. In the above descriptions, the acceleration voltage of the ion beam  5  is 30 kV and the electric potential of the thin film  80  (i.e., electric potential of the support body  81 ) is a ground potential, which is the same as the specimen  6 . Convergence performance of the uncharged particle beam  50  in this case is fundamentally the same as convergence performance of the ion beam  5 . 
     Meanwhile, when the electric potential of the thin film  80  is set to a positive high potential, for example, 10 kV, by the power source  83 , and the acceleration voltage of the ion beam  5  is set to 40 kV, which is a value higher for an amount corresponding to the positive high potential, it is possible to improve the convergence performance of the uncharged particle beam  50 . By increasing the acceleration voltage of the ion beam  5  in this setting, the aberration of the ion optical system  300  becomes smaller, improving the convergence of the ion beam  5 . The ion beam  5  slows down immediately before the specimen  6  by being affected from the thin film  80 . This is because the lens effect in this part is small and thus the aberration thus produced is small also. 
     Meanwhile, the acceleration voltage (accelerating energy) of the uncharged particle beam  50  is incident energy of the ion beam  5  onto the thin film  80  ([acceleration voltage of the ion beam  5 ]−[electric potential of the thin film  80 ]) and is 30 kV. This is the same as the above-described case. Accordingly, with such setting, it is possible to improve convergence performance of the uncharged particle beam  50  by making incident energy of the uncharged particle beam  50  onto the specimen  6  the same. That is, it is possible to reduce aperture as compared to the same beam electric current. 
     &lt;Second Embodiment&gt; 
       FIG. 3  shows a configuration near a thin film of the scanning ion microscope according to a second embodiment of the present invention. The scanning ion microscope in the present embodiment is fundamentally the same as that in  FIG. 1  but is different in that there are additional elements near the thin film  80 .  FIG. 3  shows a peripheral portion of the thin film  80 . 
     If the thin film  80  is irradiated with the ion beam  5 , a small amount of reflection particles and secondary electrons  71  are emitted to the side of the ion optical system  300 . When they enter an electrostatic lens or a deflector in the ion optical system  300 , the operation of the ion optical system  300  may become unstable as a result of inducement of unnecessary electrification onto the insulator portion. Accordingly, in the present embodiment, a shielding body  85  having an opening is arranged above the thin film  80  for blocking the reflection particles and secondary electrons  71 . Although a part of the particles enter into the ion optical system  300 , they do not directly enter insulators at least. 
     In addition, in the present embodiment, an electric current detector  86  is connected to the shielding body  85  and thus it is possible to monitor the electric current of the secondary electrons produced by the ion beam  5 . When the amount of electric current flowing into the shielding body decreases largely even though there is irradiation of the ion beam  5 , there is a possibility of abnormalities, such as when the thin film  80  is torn. In the scanning ion microscope in the present embodiment, the system is configured so as to at least alert the user by detecting abnormalities of the thin film  80  with the monitoring of the electric current. It should be noted that abnormalities, such as when the thin film  80  is torn, can be detected by monitoring the electric current flowing into the thin film  80  as well. Specifically, it is preferable if the power source  83  (means for controlling a first electric potential) detects abnormalities of the thin film  80  when the electric current flowing into the thin film  80  becomes a predetermined value or more by monitoring such electric current. 
     &lt;Third Embodiment&gt; 
       FIG. 4  shows a configuration near a thin film of the scanning ion microscope according to a third embodiment of the present invention. The scanning ion microscope in the present embodiment is fundamentally the same as that shown in  FIG. 1  but is different in that there are additional elements near the thin film  80 .  FIG. 4  shows a peripheral portion of the thin film  80 . It has a feature of having a several-molecules layer of ionic liquid  80   a  dispersed on the silicon nitride thin film  80  similar to the first embodiment. Here, C10H15F6N3O4S2 (C 10 H 15 F 6 N 3 O 4 S 2 ) (CAS No. 174899-83-3) is used for the ionic liquid  80   a.    
     In the present embodiment, since the thin film  80  effectively becomes electrically-conductive as a result of the ionic liquid  80   a , restrictions in selecting the material for the thin film  80  itself are freed. That is, the thin film  80  may be a complete insulator. Since the acceleration voltage of the ion beam  5  is low, it is effective even when the electrical conductivity emerging effect as a result of the irradiation is small. 
     In addition, in the present embodiment, the ionic liquid  80   a  solely is damaged by the ion beam  5  and is self-repaired as a result of the flow. Therefore, there is an advantageous effect of prolonging the lifetime of the thin film  80 . It should be noted that the ionic liquid  80   a  shown here is good as long as it is electrically-conductive liquid and is not limited to the above-described composition. 
     &lt;Fourth Embodiment&gt; 
       FIG. 5  shows a configuration near a thin film of the scanning ion microscope according to the fourth embodiment of the present invention. The scanning ion microscope in the present embodiment is fundamentally the same as that shown in  FIG. 1  but is different in the configuration of the thin film  80 .  FIG. 5  shows a peripheral portion of the thin film  80 . In the present embodiment, the ionic liquid  80   a  is impregnated into a net-structured object  80   b  (mesh-structured object) made of carbon (thickness of several nm and average opening size of several μm), thus forming the thin film  80 . The ionic liquid  80   a  is the same as that shown in the third embodiment. 
     From the ion beam  5 , the thin film  80  can be viewed as a thin layer of ionic liquid. This is because there are only few ions scattering at carbon. Therefore, the thin film  80  is electrically-conductive and has self-repairing characteristics as a result of the ionic liquid  80   a . The present embodiment also has an advantageous effect of prolonging the lifetime of the thin film  80 . 
     &lt;Fifth Embodiment&gt; 
       FIG. 6  shows a configuration near a thin film of the scanning ion microscope according to the fifth embodiment of the present invention. The scanning ion microscope in the present embodiment is fundamentally the same as that shown in  FIG. 1  but is different in the configuration of the thin film  80 .  FIG. 6  shows a peripheral portion of the thin film  80 . In the present embodiment, a crystalline body  80   c  is used as the thin film  80 . Specifically, the thin film  80  is formed by partially reducing the thickness of a single crystal silicon substrate by etching. In addition, there is provided a thin film inclining mechanism  801  so as to enable change in the incident angle of the ion beam  5  onto the thin film  80 . 
     Here, there is a channeling phenomenon in the transmission of the ion beam through a crystalline body. That is, the channeling phenomenon is a phenomenon that the transmission capability of an ion beam entering in a specific crystal direction is high. The present embodiment adjusts such that the transmission capability of the ion beam  5  is the highest by inclining the crystalline body  80   c  as appropriate by the thin film inclining mechanism  801 . Thereby, it is possible to prevent excessive scattered particles from existing above the thin film  80 . It should be noted that, when the thin film  80  is constituted by microcrystals, similar effect can be obtained with channeling if the directions of the microcrystals are aligned. 
     &lt;Sixth Embodiment&gt; 
       FIG. 7  shows a configuration near a thin film of the scanning ion microscope according to the sixth embodiment of the present invention. The scanning ion microscope in the present embodiment is fundamentally the same as that shown in  FIG. 1  but is different in portions near the thin film  80 . The portions near the thin film  80  are shown in  FIG. 7 . In the present embodiment, the electrode  82  is replaced with a mesh-structured electrode  82   a . Both the electrode  82  and the mesh-structured electrode  82   a  have a common feature of having an opening in the center portion of the transmission of the uncharged particle beam  50 . The electric potential of the thin film  80  is set to −100V with respect to the specimen  6  by the power source  83 . In addition, the electric potential of the mesh-structured electrode  82   a  is set by the power source  84  to a ground potential, which is the same as the specimen  6 . By such electric potential setting, the secondary electron  70  produced at the thin film  80  is accelerated with 100 V to be irradiated to the specimen  6 . By irradiating the secondary electrons  70  onto the specimen  6 , it is possible to neutralize electrification on the surface if the specimen  6  is an insulator. 
     It should be noted that energy and the direction are completely different between such secondary electrons  70  and the secondary electrons  7  produced at the specimen  6  in an equipotential space surrounded by the specimen  6  and the mesh-structured electrode  82   a . For this reason, it is easy to detect only the secondary electron  7  selectively with an electric field produced at an end of the secondary particle detector  104 , and thus it is possible to achieve both the electrification neutralization and the specimen image formation. Of course, it is also possible to perform intermittently irradiation of the secondary electron  70  onto the specimen  6  by controlling the mesh electrode  82   a . Even if the electric potential of the mesh-structured electrode  82   a  is controlled, there is no influence on the path of the uncharged particle beam  50 . In addition, even if the electrode  82  is not a mesh-structured electrode, it is possible to obtain the same effect as the above. However, in this case, the irradiation amount of the secondary electron  70  onto the specimen  6  is reduced slightly. 
     It should be noted that although the electric potential of the thin film  80  is negative in the present embodiment, it is good as long as the electric potential is relatively negative as compared to the electric potential of the specimen  6 . For example, it is possible to achieve a similar advantageous effect when the thin film  80  has a ground potential and the specimen has a positive electric potential. This case has an advantage that the accelerating energy of the ion beam  5 , that is, the accelerating energy of the uncharged particle beam  50 , can be made constant. 
     That is, it is preferable to accelerate secondary electrons emitted from the thin film  80  with several tens of V to several hundred V and inject them into the specimen  6  by maintaining a first electric potential, which is an electric potential of the support body  81  with respect to the electric potential of the specimen  6 , to negative relatively, and maintaining a second electric potential, which is an electric potential of the electrode  82  with respect to the first electric potential, to positive relatively. 
     &lt;Seventh Embodiment&gt; 
       FIG. 8  shows a configuration near a thin film of the scanning ion microscope according to the seventh embodiment of the present invention. The scanning ion microscope in the present embodiment is fundamentally the same as that shown in  FIG. 1  but is different in that there are additional elements near the thin film  80 . The portions near the thin film  80  are shown in  FIG. 8 . In the present embodiment, there is provided an X ray detector  700  for detecting X rays  72  that come from the specimen  6 . The X ray detector  700  can conduct energy analysis of the X ray and can form a specimen image instead of secondary electron signals from the specimen  6  by outputting a part of the energy distribution as X ray intensity signals. 
     The X rays  72  are emitted from the specimen  6  according to the following setting in the present embodiment. That is, an electric potential of the thin film  80  is set to −10 kV with respect to the specimen  6  by the power source  83 . The electric potential of the electrode  82  is set by the power source  84  between an electric potential of the thin film  80  and a ground potential which is the electric potential of the specimen  6 . According to such electric potential setting, the secondary electron  70  produced in the thin film  80  is accelerated with 10 kV to irradiate the specimen  6 . A characteristic X ray which depends on the material of the specimen  6  is emitted as a result of the secondary electron  70  that is accelerated with several kV or more irradiating the specimen  6 . Scanning by the secondary electrons  70  is performed interlockingly as scanning by the ion beam  5  is performed by the ion optical system  300 . Accordingly, the configuration and setting in the present embodiment are equivalent to configuring an X ray analysis microscope that uses electron beams as a probe. Thus, there are advantageous effects of not only the specimen  6  being minutely observable by the neutral beam but also the material analysis being able to perform easily. 
     It should be noted that although the electric potential of the thin film  80  is negative in the present embodiment, there is a need to only be relatively negative with respect to the electric potential of the specimen  6 . For example, it is possible to obtain similar effects when the thin film  80  has a ground potential and the specimen has a positive electric potential. In this case, there is an advantage that the accelerating energy of the ion beam  5 , that is, the accelerating energy of the uncharged particle beam  50 , can be made constant. 
     That is, at least one of the secondary particle detectors  104  is an X ray detector  700  for X rays emitted from the specimen  6 . It is preferable if the first electric potential, which is an electric potential of the support body  81  with respect to the electric potential of the specimen  6 , is maintained relatively negative, and the second electric potential, which is an electric potential of the electrode  82  with respect to the first electric potential, is maintained relatively positive, and thus the secondary electrons emitted from the thin film  6  are accelerated with several kV to several tens of kV to be injected into the specimen such that the X rays emitted from the specimen are detected. 
     Here, if no special consideration takes place, the spread of the secondary electrons  70  on the specimen  6  is broad, resulting in low resolution of the secondary electrons  70 . Accordingly, in the present embodiment, the diameter of the opening and the electric potential setting of the electrode  82  are devised to have electrostatic lens functionality for the secondary electrons  70 . Thereby, the probe system of the electron beam on the specimen  6  can be made small to some extent. Specifically, resolution of the uncharged particle beam  50  is about 1 nm and resolution of the electron beam is about 1 μm. It should be noted that although the scanning range of the electron beam on the specimen  6  corresponds to the scanning range of the uncharged particle beam  50 , the size is different. Accordingly, the scanning ion microscope in the present embodiment has functionality to perform magnification correction when comparing both specimen images. 
     Although the present embodiment uses electrostatic lens functionality for converging the electron beams, the convergence performance of the electron beam can also be improved more using magnetic field utilizing lens functionality. Neither of the cases affects the path of the uncharged particle beam  50  at all. 
     It should be noted that the thin film  80  of the present invention is not limited to the above-described material and is preferably made of thin material that shows electrical conductivity at least by ion irradiation and is easily transmitted by ion beams. For example, thin films of carbon and metal, and a monomolecular film of electrically-conductive polymer may be used. 
     As described above, according to the scanning ion microscope in the present embodiment, the specimen image is formed by scanning with uncharged particles, and therefore it is possible to observe a specimen containing an insulator without distortion. In addition, since irradiation of electrons emitted from the thin film can be controlled, it is possible to prevent noise contamination in the specimen image. Furthermore, it is possible to prevent electrification of the specimen and perform analysis by making X rays emit from the specimen. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           1 : emitter tip 
           2 : extraction electrode 
           3 : gas outlet portion of gas supply piping 
           4 : extraction voltage application unit (EVA) 
           5 : ion beam 
           6 : specimen 
           7 : secondary electron 
           50 : uncharged particle beam 
           70 : secondary electron 
           71 : reflection particle and secondary electron 
           72 : X ray 
           80 : thin film 
           80   a : ionic liquid 
           80   b : net-structured object (mesh-structured object) 
           80   c : crystalline body 
           81 : support body (support member) 
           82 : electrode 
           82   a : mesh-structured electrode 
           83 ,  84 : power source (PS) 
           85 : shielding body 
           86 : electric current detector (ECD) 
           100 : gas field ionization ion source (GFIS) 
           101 : specimen stage 
           102 : lens system (lens series system) 
           102   a ,  102   b : electrostatic lens 
           102   c : beam limiting aperture 
           102   d : aligner 
           103 : deflector system (deflector series system) 
           103   a ,  103   b : deflector 
           104 : secondary particle detector (SPD) 
           105 : lens system controller (LSC) 
           106 : deflector system controller (DSC) 
           110 : image processing unit (IPU) 
           110   a : storage unit (SU) 
           110   b : display unit (DP) 
           120 : ion controller (ICNT) 
           200 : scanning ion microscope 
           300 : ion optical system (ion optical series system, ISO) 
           700 : X ray detector (XRD) 
           800 : thin film slight movement mechanism (thin film moving means) 
           801 : thin film inclining mechanism (TFIM)