Abstract:
The present invention aims at providing an ion milling device that can set a high-precision processing area with a simple structure. In order to achieve the above object, there is proposed an ion milling device including a sample holder that holds a sample and a mask partially restricting irradiation of the sample with an ion beam, in which the sample holder includes a first contact surface that contacts with an end surface of the sample located on a passing orbit side of the ion beam, and a second contact surface that contacts with an end surface of the mask so that the mask is located at a position spaced apart from the ion beam more than the first contact surface.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an ion milling device, and particularly to a sample holding table for the ion milling device that produces a sample for an electron scanning microscope, and an ion milling device that processes the sample placed on the sample holding table. 
       BACKGROUND ART 
       [0002]    The ion milling device is a device that smoothly mills a sample without any stress with the use of a physical sputtering phenomenon in which ions of argon or the like generated within an anode are accelerated to about 10 kV or lower (in order to reduce a damage on the sample), and the sample is irradiated with the ions not converged to sputter sample atoms from a sample surface. 
         [0003]    The amount of sample milled by irradiating the sample with an ion beam depends on composition of the sample, an irradiation angle of the ion beam, a crystal orientation, or an acceleration voltage of the ion. However, when the sample is set so that the irradiation angle of the ion beam becomes 90 degrees, a difference in the milled amount depending on the composition of the sample can be reduced, and a multi-layer film of multiple composition can be also smoothly processed. 
         [0004]    In this situation, in the irradiation of the sample with the ion beam, in order to prevent a position other than anion milling target position from being irradiated with the ion beam, a plate (hereinafter also called “shield” or “mask”) for blocking the ion beam is arranged in the ion beam irradiation direction (note: ion source side=ion gun side) of the sample at a processing target position. The sample is exposed from the shield by several hundred microns or lower, and irradiated with the ion beam, and an exposed sample portion is physically sputtered, and milled, to thereby obtain a smooth sample surface. 
         [0005]    PTL 1 discloses that a micrometer for regulating a mask position is disposed for the purpose of accurately setting a processing area (exposed area of the sample to the ion beam). 
       CITATION LIST 
     Patent Literature 
       [0006]    PTL 1: JP-A-2009-245783 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    The sample to be subjected to ion milling is, for example, an observation sample by an electron microscope, and frequently very fine. The micrometer disclosed in PTL 1 is a tool effective in setting the processing area of such a fine sample. However, its structure becomes very complicated more as the target sample is finer. Further, because a sample holder becomes larger by microscale, a work within a limited space is difficult. 
         [0008]    An ion milling device having a sample holder intended to set a high-precision processing area with a simple structure will be described below. 
       Solution to Problem 
       [0009]    According to one mode for achieving the above object, there is proposed below an ion milling device including: an ion source for irradiating a sample with an ion beam; and a sample stage disposed within a vacuum chamber for the sample to be irradiated with the ion beam, in which a sample holder that holds the sample, and a mask that partially limits irradiation of the sample with the ion beam is provided, and the sample holder includes a first contact surface that contacts with an end surface of the sample located on a passing orbit side of the ion beam, and a second contact surface that contacts with an end surface of the mask so that the mask is located at a position spaced apart from the ion beam more than the first contact surface. 
       Advantageous Effects of Invention 
       [0010]    According to the above configuration, the ion milling device having the sample holder intended to set a high-precision processing area with a simple structure can be provided. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]      FIG. 1  is a diagram illustrating an example of a sample table. 
           [0012]      FIG. 2  is a diagram illustrating an example in which a sample is fitted onto the sample table. 
           [0013]      FIG. 3  is a diagram illustrating one example of a sample holder in which the sample and a shield (mask) are fitted onto the sample table. 
           [0014]      FIG. 4  is a diagram illustrating another example of the sample holder. 
           [0015]      FIG. 5  is an illustrative view of the details of the sample holder. 
           [0016]      FIG. 6  is a diagram illustrating an outline of an ion milling device (side plan view). 
           [0017]      FIG. 7  is a diagram illustrating the outline of the ion milling device (top view). 
           [0018]      FIG. 8  is a diagram illustrating a positional relationship among an ion beam trajectory, the sample, and a mask during ion milling. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0019]    As the amount of exposure (processing area) of a sample to an ion beam in an ion milling device, there is a regulation method of regulating an intended amount of exposure by a precision fine movement mechanism such as a micrometer having at least one direction (one axis) in which the sample fitted onto the sample table and the shield arranged on an ion beam irradiation side of the sample are made independent from each other. However, a structure of a sample holder is complicated, the number of components increases, and external diameters are large, the sample cannot be observed (hereinafter called “sharing of the sample holder”, etc.) by an electron scanning microscope while the sample is kept to be installed in the sample holder, and the manufacturing costs are high. 
         [0020]    For that reason, in this embodiment, a sample holder structure is proposed in which a protrusion structure for holding an end surface of a sample processing surface, and a protrusion structure for holding a shield end surface are used for a surface of a sample table for fixing the sample on which the sample is placed, and relative position of the respective protrusion structures is predetermined in dimension so that the irradiation of the sample with the ion beam has an intended sample exposure amount. 
         [0021]    A groove is formed in a part of the protrusion structure for holding the sample processing surface end surface of the sample table, and the sample holder is not directly irradiated with the ion beam that penetrates through the sample. With this configuration, the shield can be fixed directly to the sample holder, and the sample can be arranged between the shield and the sample table. 
         [0022]    Also, an outer shape of the sample holder is set to, for example, about φ70 mm or lower so that the sample holder can be shared with the electron scanning microscope. As a result, a cap for sealing the sample placed on the sample table from an outside air can be installed on the sample holder depending on the intended use. Also, in this case, the sample holder outer shape including the cap is set to a dimension of about φ70 mm×60 mm in height or lower so that the sample holder can be shared with the electron scanning microscope. 
         [0023]    According to the configuration described above, it is unnecessary to regulate the shield by the precision fine movement mechanism such as the micrometer having the independent one direction (one axis) or more, the structure is simple, the number of components is small, and the external dimension can be reduced. Also, the electron scanning microscope and the sample holder can be shared while the sample is kept to be placed on the sample holder. 
         [0024]    A more specific structure will be described below.  FIG. 1  is a diagram illustrating an example of the sample holder of the sample to be ion-milled. A sample end surface placement protrusion  2  and a shield end surface installation protrusion  3  for enabling precise positioning of a sample end surface are disposed on a sample table  1  in advance. An example in which a sample  4  is placed on the sample table  1  is illustrated in  FIG. 2 . An end surface of the sample  4  is placed in close contact with the sample end surface placement protrusion  2  of the sample table  1 . An example of the shield installation after the sample  4  has been placed on the sample table  1  is illustrated in  FIG. 3 . After the sample  4  has been placed on the sample table  1 , the sample table  1  is fixed to a sample holder  5  so that an end surface of a shield  6  installed on the sample holder  5  in advance comes in close contact with the shield installation protrusion  4  of the sample table  1 . 
         [0025]    A relative position of the protrusion structure is predetermined in dimension so that the irradiation of the sample with the ion beam becomes an intended sample exposure amount, as a result of which the sample can be placed with various sample exposure amounts. Also, because the sample exposure amount is predetermined, there is no need to move the shield. Further, there is no need to fix the sample to the sample table by a conductive tape or paste. 
         [0026]    As described above, the first embodiment has a feature that the sample is placed with a given sample exposure amount without any provision of the fine movement mechanism of the independent shield of the sample holder or the sample stage in the ion milling device. 
         [0027]    Subsequently, a second embodiment will be described with reference to  FIG. 4 . An example for sealing the sample holder  5  from the outside air is illustrated in  FIG. 4 . The sample holder  5  has a structure for mounting a cap  7  thereon, and a seal material  8  is incorporated into the cap  7  so that an interior of the sample holder  5  can be sealed from the outside air by the aid of the seal material  8 . The cap  7  is removed in a sample chamber or a sample exchange chamber which is evacuated in the ion milling device or the electron scanning microscope whereby the sample can be processed and the sample can be observed without bringing the sample in contact with the outside air. 
         [0028]      FIGS. 6 and 7  illustrate the configuration of the ion milling device. An ion source  601  and a sample stage  8  are installed on side surfaces of a vacuum chamber  606 .  FIG. 6  is a side view, and  FIG. 7  is a top view. 
         [0029]    A sample holder fine movement mechanism  604  is mounted on a sample unit base  603 . In a mounting method, a lower surface of the sample holder fine movement mechanism  604  is brought into contact with an upper surface of the sample unit base  603 , and fixed by a screw or the like. The sample holder fine movement mechanism  604  is configured to be rotationally tilted at an arbitrary angle with respect to an optical axis (a direction perpendicular to a paper plane in  FIG. 6 ) of the ion beam, a rotational tilt direction and a tilt angle are controlled by a control device not shown. The sample holder fine movement mechanism  604  is rotationally tilted so that a sample  502  placed on the sample holder fine movement mechanism  604  can be set at a given angle with respect to the optical axis of the ion beam. Further, the sample stage  605  is disposed to tilt a sample holder  501  in a direction parallel to the paper plane, which is perpendicular to a rotating axis of a tilt rotary motion, in addition to the tilt rotary motion. The tilting movement (tilt with a rotating shaft indicated by a dashed line in  FIG. 6 ) of the sample holder fine movement mechanism  604  is mainly configured to continuously conduct the tilting movement in a section processing mode for processing a section of the sample. Also, the sample holder fine movement mechanism  604  is configured to be movable from front to back and from side to side in a direction perpendicular to the optical axis of the ion beam, that is, in an X-direction and a Y-direction. 
         [0030]    The sample unit base  603  is arranged through the sample stage  605  (rotating mechanism) mounted on a flange  607  serving as a part of a container wall of the vacuum chamber  606 . When the flange  607  is pulled out along a linear guide  608 , and the vacuum chamber  606  is opened to an atmospheric state, the sample unit base  603  is pulled out to an external of the vacuum chamber. In this way, a sample stage pull-out mechanism is configured. During ion beam processing, the flange  607  is closed, and evacuation is conducted by a vacuum exhaust system  609 . 
         [0031]      FIGS. 6 and 7  illustrate a configuration of the ion milling device that can conduct both of cross-section milling and plane milling. A processing observation window  610  and an openable shutter  611  are disposed in an upper surface of the vacuum chamber  606 . The shutter  611  is installed for preventing sputtered particle from being deposited on the processing observation window  610 . The vacuum chamber  606  is formed into a boxed-shape that forms a space for forming a normal vacuum atmosphere, or formed into a shape based on the box. The observation window is disposed above the box (a direction opposite to a direction of a gravitational field under a gravitational environment), and the ion source is disposed on a side wall of the box (a plane adjacent to the upper surface of the box in a direction perpendicular to the direction of the gravitational field). That is, the processing observation window is disposed in a wall surface of the vacuum chamber in a direction orthogonal to the tilt axis of the sample stage and an plane including an irradiation orbit of the ion beam. As will be described later, aside from the provision of a vacuum-sealable window, an optical microscope or an electron microscope can be installed in the processing observation window opening. 
         [0032]      FIG. 8  is a diagram illustrating a positional relationship among an ion beam optical axis  801 , the sample  502 , and a mask  503  during cross-sectional processing. A rotating axis  802  corresponds to a dashed line in  FIG. 6 . The sample holder fine movement mechanism  604  conducts a continuous tilting movement with the rotating axis  802  as a center, and irradiates the sample with the ion beam in that state to conduct the cross-section processing. 
         [0033]    An outline of the sample holder  501  mounted on the sample holder fine movement mechanism  604  will be described with reference to  FIG. 5 . In  FIG. 5 , a flange portion of the sample holder  5  in  FIG. 4  is omitted. Also, when the sample holder  501  is really fitted to the sample holder fine movement mechanism  604 , an ion beam irradiation portion  508  is located to the top. The sample holder  501  is fixed to push the sample  502  to be ion-milled and the mask  503  which is a shield material against the sample holder  501 . Mask fixing knobs  505  are threaded, and the knobs are rotated to press mask pressing members  504  downward. 
         [0034]    The sample  502  is located to be partially exposed from the mask  503  when viewed from an ion beam irradiation direction, and the ion beam is applied to the ion beam irradiation portion  508  to process the cross-section of the sample. 
         [0035]    In this example, the sample holder  501  includes a sample contact portion  506  and a mask contact portion  507 . Contact surfaces  509  (first contact surface) with the sample are formed on an ion beam passing orbit center side more than contact surfaces  510  (second contact surface) with the mask so that the sample  502  is located closer to the ion beam optical axis center than the ion beam passing orbit side end surface of the mask  503 . A space between the two contact surfaces  509  and the sample configures an ion beam passing opening, and a gap is formed between the two contact surfaces  509  for the purpose of ensuring the passing opening of the ion beam while contacting with the ends of the sample  502  and the mask  503 . Also, an opening  511  (groove) is formed in the sample table on which the sample  502  is placed so that the sample  502  is not directly irradiated with the ion beam. 
         [0036]    With the above configuration in which the opening through which the ion beam passes is ensured while providing the respective regions that contact with the end surface of the sample which is irradiated with the ion beam, and the end surface of the mask which is irradiated with the ion beam, the mask and the sample can be installed without conducting any precise positional regulation. In particular, in this embodiment, a gap P is formed between the contact surfaces  509  of the sample and the contact surface  510  of the mask in a direction perpendicular to the irradiation direction of the ion beam, and the processing area as large as the gap P can be set without requiring the precise regulation. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           501  sample holder 
           502  sample 
           503  mask 
           504  mask pressing member 
           505  mask fixing knob 
           506  sample contact portion 
           507  mask contact portion 
           508  ion beam irradiation portion 
           509 ,  510  contact surface