Patent Publication Number: US-2013248733-A1

Title: Charged particle beam apparatus and method of irradiating charged particle beam

Description:
TECHNICAL FIELD 
     The present invention relates to, for example, a charged particle beam apparatus and a method of irradiating charged particle beam. 
     BACKGROUND ART 
     In recent years, focused ion beam (FIB) apparatuses are used for producing thin film samples for observation of (scanning) transmission electron microscope ((S)TEM). Specifically, in producing thin film samples for analyzing defects of semiconductor devices, FIB apparatus is a necessary tool. 
     In recent years, structural objects are being miniaturized in various industries such as the energy industry like fuel cell or solar cell and the industries using organic materials like organic electro-luminescence (EL) displays, with the semiconductor industry at the top of list. Improving processing techniques for observation samples and analysis samples is thus needed. For example, devices with node size of 30 nm or less are being applied in state of the art devices. In producing thin film samples of such devices for (S)TEM, nanometer-order processing accuracy is required. In addition, as structural objects become miniaturized and complicated, roughness of process cross-section (curtaining pattern) due to mixed light elements and heavy elements becomes a larger issue for (S)TEM observation samples. Therefore, in finally finishing (S)TEM observation thin film samples, it is required to accurately remove damaged layers and curtaining patterns in desired regions. 
     In order to solve the problem above, Patent Literature 1 indicates a method of using, for removing damaged layers, a second ion beam (argon ion) that is different from a first ion beam (gallium ion) used for thin film processing. 
     In addition, Patent Literature 2 indicates a method for removing damaged layers by irradiating an argon ion onto a film sample piece using an ion milling apparatus. 
     In addition, Patent Literature 3 describes a method for decreasing damaged layers wherein energy of an ion beam used for finish processing is made lower than energy of an ion beam used for main processing. Further, it is also indicated that decrease in throughput can be suppressed by finish-processing the sample being inclined with respect to the ion beams. 
     In addition, as a problem other than damaged layers, vertical cross-sections cannot be obtained by irradiating focused ion beams vertically with respect to the surface of samples. This is because the shape of focused ion beams is focused at the focused location. Thus a thin film sample is not appropriate as that for (S)TEM observation if it doesn&#39;t have a cross section that is vertical with respect to the surface of sample. 
     As a method for preventing this problem, Patent Literature 4 indicates a method for obtaining a vertical cross section by irradiating an ion beam with a sample being inclined by a predetermined angle. The processing is generally performed with the surface of sample being inclined by 3 to 5 degree with respect to the center axis of ion beam. 
     In addition, Patent Literature 5 describes a technique that can change the angle of ion beam with respect to the surface of sample from 75 degree to 90 degree using an angle changing electrode. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: JP Patent Publication (Kokai) No. 2004-264145 A 
         Patent Literature 2: JP Patent Publication (Kokai) No. 2002-277364 A 
         Patent Literature 3: JP Patent Publication (Kokai) No. 2007-193977 A 
         Patent Literature 4: JP Patent Publication (Kokai) No. H08-5528 A (1996) 
         Patent Literature 5: JP Patent Publication (Kokai) No. 2002-148159 A 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in techniques described in Patent Literatures 1 to 3, there is a significant restriction in irradiation direction of ion beam. Therefore, it is difficult to irradiate ion beams onto desired regions of sample only and to irradiate ion beams with optimal angle. 
     As the technique described in Patent Literature 4, in a technique where samples are inclined with respect to ion beams, it is also difficult to irradiate ion beams with desired angles onto desired regions by sample inclination only. 
     Furthermore, in the technique described in Patent Literature 5, the angle of ion beams with respect to sample surfaces can be changed. However, it is impossible to irradiate ion beams with angles more than it. Thus it is difficult to irradiate ion beams with desired angles onto desired regions. 
     The objective of the present invention is to achieve a charged particle beam apparatus and a method of irradiating charged particle beam that can irradiate charged particle beams onto desired regions of sample surfaces with wide range of angles. 
     Solution to Problem 
     A charged particle beam apparatus according to the present invention comprises: an ion beam column; a sample chamber with the ion beam column attached to it; a sample stage located in the sample chamber; an electrode unit that is located in the sample chamber and changes a trajectory of an ion beam so that the ion beam is irradiated onto a sample supported by the sample stage; and an electrode unit movement control unit that moves the electrode unit. 
     The electrode unit can change a trajectory of the ion beam generated from the ion beam column by changing an angle between the ion beam and an extended line of a center axis of the ion beam column. Thus the ion beam can be irradiated onto samples supported by the sample stage. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to achieve a charged particle beam apparatus and a method of irradiating charged particle beam that can irradiate charged particle beams onto desired regions of sample surfaces with wide range of angles. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic configuration diagram of a charged particle beam apparatus according to an example 1 of the present invention. 
         FIG. 2  is a diagram showing an example of an ion beam trajectory in the example 1 of the present invention. 
         FIG. 3  is a diagram showing another example of an ion beam trajectory in the example 1 of the present invention. 
         FIG. 4  is a diagram explaining another example of an ion beam trajectory in the example 1 of the present invention. 
         FIG. 5  is a diagram showing another example of an ion beam trajectory in the example 1 of the present invention. 
         FIG. 6  is a comparative explanation diagram between the method for removing damaged layer according to the example 1 of the present invention and another example of the present invention. 
         FIG. 7  is a schematic configuration diagram of a charged particle beam apparatus according to an example 2 of the present invention. 
         FIG. 8  is a diagram showing an example of an ion beam trajectory in the example 2 of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the present invention, an electrode unit for bending a trajectory of a charged particle is provided in a sample chamber of a charged particle beam apparatus comprising an ion beam column. The charged particle beams are bended by an electric field generated by the electrode unit to be irradiated onto a sample. 
     Hereinafter, embodiments of the present invention will be described with reference to attached drawings. However, the embodiments described below are merely examples for implementing the present invention, and it is not intended to limit the technical scope of the present invention. 
     EXAMPLES 
     Example 1 
     Explanation for Configuration of Charged Particle Beam Apparatus 
       FIG. 1  is a schematic overall configuration diagram of a charged particle beam apparatus according to an example 1 of the present invention. 
     In  FIG. 1 , the charged particle beam apparatus comprises: an ion beam column  201   a ; a sample chamber  203 ; an electrode unit  204  that is provided in the sample chamber  203 , is capable of being applied of electric voltages, is movable in any direction, and is capable of adjusting its inclination angle; an electrode controller  211  that controls a location and an angle of the electrode unit  204 ; an electric voltage supplying device  205  for applying an electric voltage to the electrode unit  204 ; an electric voltage controller  212  that controls the electric voltage supplying device  205 ; and an integration computer  213  that controls overall operations of the charged particle beam apparatus. 
     The charged particle beam apparatus further comprises: an ion beam scan controller  214  for controlling a scan of an ion beam  201   b  generated from the ion beam column  201   a ; a detector  206  for obtaining a scanning ion microscope (SIM) image; a detector controller  215  that provides the integration computer  213  with the detected information; a controller (such as a keyboard, a mouse)  216  for operators to input various instructions such as irradiation conditions or electric voltage conditions and location conditions of electrodes; and a display  217  that displays the obtained SIM images. 
     The charged particle beam apparatus further comprises: an ammeter  207  for using the electrode unit  204  as a second detector; and an ammeter controller  218  that performs processing such as amplifying electric current values detected by the ammeter  207 . An electric current measuring signal from the ammeter controller  218  is provided to the integration computer  213 . 
     The ion beam column  201   a  is a system that includes all configurations necessary for FIB, such as an ion source for generating the ion beam  201   b , a lens for focusing the ion beam  201   b , a deflection system for scanning and shifting ion beams. The ion beam column  201   a  is equipped in the sample chamber  203 . Gallium ion is typically used for the ion beam  201   b . However, any ion species can be used for the purpose of processing. 
     The ion beam  201   b  is not limited to focused ion beams and it can be a broad ion beam. In the example 1 of the present invention, a FIB column  201   a  is provided. However, two or more than two of ion beam columns can be provided. For example, a configuration with a Ga focused ion beam column and an Ar focused ion beam column may be allowed. 
     The electric voltage supplying device  205  supplying electric voltages to the electrode unit  204  can be modulated. Each of controllers can communicate with each other, and is controlled by the integration computer  213 . 
     In the example 1, a detector  206  for obtaining SIM images is provided. However, a configuration with two or more than two of same or different detectors may be allowed. For example, a secondary electron detector and a secondary ion detector may be equipped. 
     Other than above-mentioned configurations, a sample stage, a gas deposition unit, a micro sampling unit, and the like are equipped in the sample chamber  203 . A sample  202  can be placed on a sample stage  219  (shown in  FIG. 2 ) for carrying samples. The sample stage  219  can perform in-plane movement, rotation, and inclination. The sample stage  219  can also move portions required for ion beam processing or observation to positions where ion beams are irradiated. 
     Other than semiconductor materials, iron and steel, light metal, polymer molecule, and the like can be expected as the sample  202 . The gas deposition unit that is used for producing protection films or markings stores deposition gases that form deposition films by irradiating charged particle beams, and can provide the gases from a nozzle tip as required. 
     The micro sampling unit picks up specific portions of the sample  202  by using with processing or cutting of the sample  202  by FIB. The micro sampling unit includes a probe that can be moved in the sample chamber  203  by a probe driving unit. The probe is utilized for picking out small sample pieces formed in the sample  202  and for contacting with the sample surface to provide electric potentials to the sample. 
     The detector controller  215  may comprise a circuit or a processing unit that processes a detection signal from the detector  206  for imaging it. Each of driving mechanisms such as the sample stage, the deposition unit, and the micro sampling unit has control circuits respectively. Those control circuits can communicate with each other and are controlled by one or a plurality of computers in integrated manner. 
       FIG. 2 ,  FIG. 3 , and  FIG. 4  are magnified diagrams around the sample  202  shown in  FIG. 1 . 
       FIG. 2  shows a case where an electrode included in the electrode unit  204  is a planar electrode  304 . It shows that an ion beam  301   c  from a tip  301   a  of the ion beam column  201   a  is bended and is irradiated onto the sample  202  supported by the sample stage  219 . In this case, it is possible to change the irradiation position and the irradiation angle of the ion beam  301   c  on the sample  202  by changing the location (the location in the direction along the extended line of the center axis of the ion beam column  201   a , the location in the direction perpendicular to the extended line of the center axis of the ion beam column  201   a ) and the inclination angle α (the inclination angle with respect to the surface perpendicular to the extended line of the center axis of the ion beam column  201   a ) of the planar electrode  304 .  FIG. 2(A)  shows a case where the inclination angle is α A  and  FIG. 2(B)  shows a case where the inclination angle is α B . 
       FIG. 3  shows a case where an electrode included in the electrode unit  204  is a spherical electrode  404 . In this case, it is possible to change the irradiation position and the irradiation angle of the ion beam on the sample  202  by horizontally moving the spherical electrode  404  (move in the direction perpendicular to the extended line of the center axis of the ion beam column  201   a ).  FIG. 3(A)  is a case where the distance between the extended line of the center axis of the ion beam column  201   a  and the center of the spherical electrode  404  is L A .  FIG. 3(B)  is a case where the distance between the extended line of the center axis of the ion beam column  201   a  and the center of the spherical electrode  404  is L B . L A  is larger than L B . 
       FIG. 4  shows a case where an electrode included in the electrode unit  204  is a parabola-shaped (paraboloidal surface shape) electrode  504 . The figure indicates that it is possible to suppress expansion of irradiation position of the ion beam  301   c  by using the parabola-shaped electrode  504 . 
     If an electrode in which electrodes with shapes shown in  FIGS. 2 ,  3 , and  4  are combined is used, it is possible to achieve various irradiation positions and irradiation angles by changing the location, inclination angle, and rotation angle of the electrode. In addition, it is also possible to change irradiation positions and irradiation angles by modulating the voltage applied to the electrode. In other words, it is possible to irradiate ion beams onto desired locations with desired angles by combining electrode shape, electrode voltage, electrode position, irradiation direction of ion beam, and sample movement. Specifically, it is possible to irradiate ion beams onto sample surfaces with wide range of angles by changing the angle of the planar electrode  304  from being perpendicular to the extended line of the center axis of the ion beam column  201   a  to being horizontal. 
     Alternatively, it is possible to irradiate ion beams across the surface of sample  202  by changing the angle between the ion beam  301   c  and the extended line of the center axis of the ion beam column  201   a  using the electrode unit  204 , and by moving the electrode unit  204  from side to side and up and down with the changed beam angle being kept. 
     In addition, as shown in  FIG. 5 , it is also possible to achieve desired irradiation locations and irradiation angles of the sample  202  by using a plurality of an electrode  604   a  (spherical electrode), an electrode  604   b  (planar electrode) simultaneously. For example, it is possible to place the spherical electrode  604   a  (a first electrode unit) near the tip  301   a  of the ion beam column  201   a  and to place the planar electrode  604   b  (a second electrode unit) near the sample  202 . 
     For the purpose of bending the trajectory of the ion beam  301   c , the electrode unit  204  can be supported in any manner. For example, an electrode supporting unit may be additionally provided, or the electrode can be attached instead of the micro sampling probe. Of course, the micro sampling probe itself can be an alternative of the electrode. In a case where a plurality of the sample stages  219  is provided, the electrode unit  204  can be supported on one of the sample stages  219 . For example, in a charged particle beam apparatus comprising: a sample stage with a XYZ driving mechanism, an inclination mechanism, and a rotation mechanism (eucentric stage); and a (S)TEM common sample holder, the electrode unit  204  for bending trajectories of ions can be supported by the eucentric stage and the sample can be supported by the (S)TEM common sample holder. In this case, the electrode controller  211  can be configured to control the operations of the stage supporting the electrode unit  204 . 
     In addition, other than planar electrode, spherical electrode, and parabola-shaped electrode, a polyhedral electrode can be applied as an example of above-mentioned electrodes. 
     Explanation for Irradiating Ion Beams in any Direction 
     It is possible to irradiate ion beams from any direction by equipping, in a sample chamber, an electrode for bending ion trajectories in a charged particle beam apparatus having above-mentioned configurations and being capable of irradiating ion beams. Hereinafter, an explanation for such effects will be provided. 
     When processing a sample with heavy element and light element being mixed using ion beams, the processing result will be uneven due to the difference of sputtering rate, thus threads are formed in cross sections. For example, in a portion where heavy element and light element are present alternately in upper portions of the sample, the sputtering rate for such a portion will be decreased and threads will be formed in processing cross sections. This thread can be removed or decreased by arbitrarily changing irradiation direction of ion beams so that the sputtering rate will be even. 
     In addition, in producing thin film samples for (S)TEM, it is possible to prevent surface unevenness in observed regions by employing irradiation direction of ion beams such that the heavy element region is placed under the observed regions of the sample. 
     According to the example 1 of the present invention, it is possible to irradiate ion beams from such irradiation directions. 
     In addition, it is possible to remove damaged layers due to irradiation of ion beams efficiently. 
       FIG. 6(A)  shows a method for removing damaged layers where the present invention is not employed. If the surface  202   a  of the sample  202  is processed using an ion beam  301   b , a damaged layer  721  is formed in the sample  202 . The ion beam  301   b  used for removing the damaged layer  721  is irradiated from the same direction as the main processing beam. Therefore, as shown in  FIG. 6(A) , a very small portion of the ion beam  301   b  (a portion of side portion of the ion beam  301   b ) is used for removing the damaged layer  721 . Thus it is very ineffective. 
     In contrast, in the example shown in  FIG. 6(B)  where the present invention is applied, the surface  202   a  of the sample  202  is processed using the ion beam  301   b  with the planar electrode  304  being moved from the shown location. After that, the sample  202  is moved and the planar electrode  304  is moved to the shown location, thereby bending the ion beam  301   b  using the planar electrode  304  to irradiate the damaged layer  721 . According to such operation, the ion beam  301   b  can be utilized with small loss to remove the damaged layer  721  efficiently. 
     In addition, it is also possible to remove surface unevenness by controlling the location and inclination of the electrode  304  to irradiate the sample  202  at desired regions with desired angles. For example, it is possible to efficiently remove surface roughness generated by irradiating ion beams. At that time, in addition to the location and inclination of the electrode  304 , the location and inclination of the sample  202  may be adjusted. 
     In addition, in producing thin film samples for (S)TEM, as indicated in Patent Literature 4, a method for obtaining vertical processing cross sections is employed in which a sample is inclined and then ion beams are irradiated. However, if the irradiation directions of ion beams can be arbitrarily selected, it is possible to obtain vertical processing cross sections without inclining samples. Furthermore, it is possible to intensively remove thick portions of the thin film (skirt portion) efficiently by irradiating ion beams from the bottom. 
     Furthermore, the present invention is significantly beneficial in terms of observation in that ion beams can be irradiated from any direction. For example, it is possible to obtain SIM images from various directions even for a sample stage without inclination mechanism and rotation mechanism. For example, it is possible to obtain SIM images observed from bottom of column or SIM images observed from horizontal directions with respect to the optical axis. As a result, it is possible to more precisely analyze the three-dimensional structure of samples. Note that an electrode can be used as a detector in obtaining SIM images. 
     By the way, in  FIG. 1 , if the electrode  204  in which a positive voltage is applied is placed near the sample  202 , most of secondary electrons emitted from the sample  202  are attracted by the electric voltage of the electrode  204 , thus cannot reach the detector  206 . Therefore, it is difficult for the detector  206  to obtain SIM images. 
     Then, the electric current arriving at the electrode  204  is measured using the ammeter  207 , and the measured electric current signal is provided to the integration computer  213  through the ammeter controller  218 . The integration computer  213  obtains SIM images according to the electric current signal provided from the ammeter controller  218 . Therefore, SIM images can be obtained even if the electrode  204  is placed near the sample  202 . 
     If the electrode  204  with a negative charge applied to it is placed near the sample  202 , the same thing can be said for secondary ions emitted from the sample  202 . 
     As such, it is possible to efficiently remove amorphous layers and roughness of observed surfaces that are formed by irradiating focused ion beams and to more precisely know how the sample is being processed. 
     Low Magnification Observation 
     Next, a description will be provided explaining that observable ranges with low magnification can be expanded according to the example 1 of the present invention. 
     As the example 1 of the present invention, the travel distance of ion beams can be extended by irradiating ion beams onto the sample  202  in bypassing manner. The scannable range of ion beams depends on the distance from the emitted point of the ion beam column  201   a  and the sample  202 . As the distance becomes longer, the observed region becomes wider. 
     Therefore, according to the example 1 of the present invention, the scan range of focused ion beams can be expanded. In other words, observable range with low magnification can be expanded. This is beneficial in searching field of views. Further, it can be utilized when wider range is desired to be processed. 
     As discussed above, according to the example 1 of the present invention, the electrode  204  such as the electrode  304 ,  404 ,  504  is placed in the sample chamber  203 , the electrode  204  being capable of adjusting its location in the direction along the extended line of the center axis of the ion beam column  201   a , the location in the direction perpendicular to the extended line, and the inclination angle α (the inclination angle with respect to the surface perpendicular to the extended line of the center axis of the ion beam column  201   a ). The ion beam  301   c  bended by the electrode  304  and the like is irradiated onto the surface of sample  202 . Thus a charged particle beam apparatus and a method of irradiating charged particle beam that can irradiate ion beams onto desired regions of sample surface inclined by any angle of wide range with respect to the sample surface can be achieved. 
     As discussed above, according to the example 1 of the present invention, an apparatus that can efficiently remove damaged layers and surface roughness that are formed on the surface irradiated by ion beams in FIB processing can be provided. 
     Furthermore, the distance between the point where ion beams are emitted from the ion beam column  201   a  and the sample surface can be extended. Therefore, the scan range can be expanded, thus the observed range with low magnification can be expanded. 
     Example 2 
     Explanation for Configuration of Charged Particle Beam Apparatus 
       FIG. 7  is a schematic overall configuration diagram of a charged particle beam apparatus according to an example 2 of the present invention. 
     In addition to the apparatus configuration in the example 1, the charged particle beam apparatus in the example 2 comprises: a SEM column  807   a ; and an electron beam scan controller  818  for controlling a scan of an electron beam  807   b  of the SEM column  807   a . Other configurations are the same as the example 1. 
     The SEM column  807   a  is a system that includes all configurations necessary for SEM, such as an electron source for generating electron beams, a lens for focusing the electron beam, and a deflection system for scanning and shifting electron beams. 
     The charged particle beam apparatus according to the example 2 of the present invention is an apparatus that can SEM-observe cross sections of the sample  202  processed by FIB on site. 
     In the example 2 of the present invention, the ion beam column  201   a  is placed vertically and the SEM column  807   a  is placed with inclination. However, they are not limited to such configurations. The ion beam column  201   a  can be placed with inclination and the SEM column  807   a  can be placed vertically. In addition, both of the ion beam column  201   a  and the SEM column  807   a  can be placed with inclinations. 
     The charged particle beam device may have a triple column configuration with a Ga focused ion beam column, an Ar focused ion beam column, and an electron beam column. In addition, in the example 2 of the present invention, the detector for obtaining SEM images, the detector controller that provides the integration computer with the detected information, and the display that displays SEM images generated from the detection signals are the same as those for SIM images. However, the charged particle beam apparatus may have one or more than one of detectors, detector controllers, and displays as the mechanism for obtaining and displaying SEM images. 
     SEM Observation of Processing State 
     A description will be provided explaining SEM-observation of processing state in the example 2 of the present invention. 
     In the example 2 of the present invention in which the charged particle beam apparatus comprises the SEM column  807   a , the processing state of the ion beam  201   b  can be SEM-observed from various directions by irradiating electrons with bended trajectories onto the sample  202 . 
     When observing the front surface of the sample  202 , the processing state can be SEM-observed by irradiating the electron beam  807   b  from the SEM column  807   a  onto the front surface of the sample  202 , as shown in  FIG. 7 . 
     In addition, as shown in  FIG. 8 , a parabola-shaped electrode  904  is placed so that the trajectory of the electron beam  807   c  from the SEM column  807   a  is bended to the sample  202  placed at the location where the ion beam  301   c  emitted from the tip  301   a  of the ion beam column  201   a  is irradiated. According to this, the back side  923  of the sample  202  viewed from the SEM column  807   a  can be observed. Therefore, the processing state can be identified at both sides of the thin film sample  202 , thus sample processing accuracy can be improved. 
     When SEM-observing the sample back side  923  viewed from the SEM column  807   a  during processing samples by irradiating the ion beam  201   b , the acceleration voltage of the ion beam  301   c  is preferably set higher than the acceleration voltage of the electron beam  807   c . That can achieve the electron trajectory as shown in  FIG. 8  with very small influence on the ion beam  301   c.    
     On the other hand, when SEM-observing during processing samples using the ion beam  201   b  with trajectories bended by the electrode  204 , the acceleration voltage of the ion beam  807   c  is preferably set higher than the acceleration voltage of the electron beam  201   b . That can achieve SEM observation with very small influence on the electron beam  807   b.    
     In addition, the travel distance of the electron beam  807   b  can be extended by irradiating the electron beam  807   b  onto the sample  202  in bypassing manner. This enables to expand the observable range with low magnification in SEM observation, as in the case of SIM observation. 
     According to the example 2 of the present invention, the same advantageous effect as that of the example 1 can be achieved. In addition, as described above, desired locations of the sample surface during processing by ion beams can be observed by SEM. 
     Both in the example 1 and 2 of the present invention, electric fields are used for changing the trajectories of charged particles. However, magnetic fields also can be used for changing the trajectories of charged particles. For example, the trajectories of charged particles can be changed by placing coils or permanent magnets in the sample chamber. 
     In addition, thin film samples of state-of-the-art devices or functional materials can be produced with high quality, processing efficiency improves significantly, and analyzing accuracy in (S)TEM improves significantly. 
     Furthermore, the FIB-SEM apparatus provides an apparatus that can SEM-observe the front surface of the sample as well as the back surface. In producing thin film samples, the both sides can be observed without moving the sample, thus processing accuracy and processing reproducibility improves significantly. 
     REFERENCE SIGNS LIST 
       201   a : ion beam column,  201   b ,  301   b ,  301   c : ion beam, 202: sample,  202   a : sample surface,  203 : sample chamber,  204 : electrode unit,  205 : electric voltage supplying device,  206 : detector,  207 : ammeter,  211 : electrode controller,  212 : electric voltage controller,  213 : integration computer,  214 : ion beam scan controller,  215 : detector controller,  216 : controller,  217 : display,  218 : ammeter controller,  219 : sample stage,  721 : damaged layer,  301   a : ion beam column tip,  304 ,  604   b : planar electrode,  404 ,  604   a : spherical electrode,  504 ,  904 : parabola electrode,  807   a : scanning electron microscope column,  807   b : electron beam,  807   c : electron beam,  818 : electron beam scan controller,  923 : sample back surface