Patent Publication Number: US-2022238296-A1

Title: Charged Particle Beam Apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a charged particle beam apparatus. 
     BACKGROUND ART 
     A scanning electron microscope (SEM), a scanning transmission electron microscope (STEM), or a focused ion beam apparatus (FIB) is an apparatus that can execute nano-level observation and analysis and is used as an essential tool in various fields such as a semiconductor field, a material field, or a medical field. In various fields including the semiconductor field where miniaturization is progressing, further improvement of image resolution or processing accuracy is required. 
     WO-A-2016/174891 (PTL 1) discloses that a spherical aberration correction effect is obtained by using an electrode of a circular aperture and an electrode of an annular aperture in combination and applying a voltage between the two electrodes. JP-A-2016-46263 (PTL 2) discloses an aberration correction apparatus including: an aberration correction unit that applies a voltage between a first conductive element and a second conductive element, the first conductive element being arranged on an axis and the second conductive element being arranged rotationally symmetrical about the first conductive element; and an annular aperture that is provided in front of or in rear of the aberration correction unit. In this aberration correction apparatus, the spherical aberration correction effect is obtained by causing an annular beam formed by the annular aperture or the aberration correction unit to propagate through the aberration correction unit. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: WO-A-2016/174891 
         PTL 2: JP-A-2016-46263 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     Both of the electrode of the annular aperture in the aberration correction apparatus disclosed in the PTL 1 and the annular aperture or the aberration correction unit in the aberration correction apparatus disclosed in PTL 2 include an on-axis light shielding unit and an off-axis light shielding unit in order to form an annular beam. When the on-axis light shielding unit and the off-axis light shielding unit are irradiated with a charged particle beam, there is a difference in charged particle dose between the on-axis light shielding unit and the off-axis light shielding unit, and thus there is a difference in surface potential between the on-axis light shielding unit and the off-axis light shielding unit. Therefore, the charged particle beam is affected by an unintentional deflection action when transmitting through the annular aperture, and thus desired performance cannot be obtained. 
     Solution to Problem 
     According to one embodiment of the present invention, there is provided a charged particle beam apparatus including: a charged particle beam source that emits a charged particle beam; an objective lens that focuses the charged particle beam on a sample; a charged particle beam aperture stop and an electrode that are arranged on an optical axis between the charged particle beam source and the objective lens; and a power supply that applies a voltage between the charged particle beam aperture stop and the electrode, in which the voltage that is applied from the electrode to the charged particle beam aperture stop by the power supply is a voltage having a polarity opposite to a charge of the charged particle beam, the electrode includes an annular aperture, and the charged particle beam aperture stop includes a plurality of apertures that are arranged at positions overlapping the annular aperture of the electrode when viewed in a direction along the optical axis. 
     In addition, according to another embodiment of the present invention, there is provided a charged particle beam apparatus including: a charged particle beam source that emits a charged particle beam; an objective lens that focuses the charged particle beam on a sample; a charged particle beam aperture stop and an on-axis electrode that are arranged on an optical axis between the charged particle beam source and the objective lens; an off-axis electrode that is provided to surround the on-axis electrode; and a power supply that applies a voltage between the on-axis electrode and the off-axis electrode, in which the voltage that is applied from the on-axis electrode to the off-axis electrode by the power supply is a voltage having a polarity opposite to a charge of the charged particle beam, and the charged particle beam aperture stop includes a plurality of apertures that are arranged at positions overlapping a gap between the on-axis electrode and the off-axis electrode when viewed in a direction along the optical axis. 
     Advantageous Effects of Invention 
     A charged particle beam apparatus capable of stably obtaining a spherical aberration correction effect can be provided. 
     Other objects and new characteristics will be clarified with reference to description of the specification and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view illustrating a charged particle beam apparatus according to a first embodiment. 
         FIG. 2A  is a diagram illustrating an aperture shape and an arrangement of a charged particle beam aperture stop and an electrode. 
         FIG. 2B  is a diagram illustrating the aperture shape and the arrangement of the charged particle beam aperture stop and the electrode. 
         FIG. 3  is a diagram illustrating an aperture shape and an arrangement of the charged particle beam aperture stop and the electrode. 
         FIG. 4  is a diagram illustrating an aperture shape and an arrangement of the charged particle beam aperture stop and the electrode. 
         FIG. 5A  is a diagram illustrating an example of an aberration correction unit and a holder. 
         FIG. 5B  is a diagram illustrating an example of the aberration correction unit and the holder. 
         FIG. 6  is a schematic view illustrating a charged particle beam apparatus according to a second embodiment. 
         FIG. 7  is a schematic view illustrating a charged particle beam apparatus according to a third embodiment. 
         FIG. 8  is a schematic view illustrating a charged particle beam aperture stop, an on-axis electrode, and an off-axis electrode. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     New characteristics and effects of the present invention will be described using the drawings. Embodiments are merely examples for implementing the present invention and do not limit the technical scope of the present invention. In addition, common configurations in the respective drawings are represented by the same reference numerals. 
     First Embodiment 
       FIG. 1  illustrates the outline of a charged particle beam apparatus according to a first embodiment. The charged particle beam apparatus includes, as main components: a charged particle beam source  101  that forms a charged particle beam; an acceleration electrode  102  that accelerates the charged particle beam emitted from the charged particle beam source  101 ; first and second condenser lenses  103  and  104  that condense the charged particle beam emitted from the charged particle beam source  101 ; an objective lens  105  that focuses the charged particle beam on a sample; a sample chamber  115  where a sample  114  is arranged; and a detector  116  that detects secondary charged particles emitted from the sample. 
     In addition, on an optical axis between the first condenser lens  103  and the second condenser lens  104 , a plurality of apertures are arranged on a circumference, and a charged particle beam aperture stop  121  that shields a part of the charged particles emitted from the charged particle beam source  101  and an electrode  122  having an annular shape are arranged. The charged particle beam aperture stop  121  and the electrode  122  are held by a holder  120  in a state of being electrically insulated from each other by an insulating material  123 . A power supply  108  can apply a predetermined voltage between the charged particle beam aperture stop  121  and the electrode  122 . 
     As controllers that control the respective components of the charged particle optical systems, the charged particle beam apparatus includes: a charged particle beam source controller  151  that controls the charged particle beam source  101 ; an acceleration electrode controller  152  that controls the acceleration electrode  102 ; first and second condenser lens controllers  153  and  154  that control the first and second condenser lenses  103  and  104 ; an objective lens controller  155  that controls the objective lens  105 ; a power supply controller  158  that controls the power supply  108 ; and a detector controller  156  that controls the detector  116 . The controllers are controlled by an integrated computer  170  that controls an overall operation of the charged particle beam apparatus and constructs a charged particle beam image. The integrated computer  170  is connected to a controller (for example, a keyboard or a mouse)  171  and a display  172 , and an operator can input various instructions such as irradiation conditions, voltage conditions of the charged particle beam aperture stop, or position conditions from the controller  171  and can cause the display  172  to display an acquired image or a control screen. The components of the charged particle beam apparatus illustrated in  FIG. 1  are a part of the charged particle beam apparatus, and it is needless to say that the charged particle beam apparatus includes a component that is essential for the charged particle beam apparatus, for example, a deflection system for scanning and shifting a charged particle beam. 
     In addition, in the example shown in  FIG. 1 , the two condenser lenses  103  and  104  are provided. However, the number of condenser lenses for controlling the charged particles incident on the objective lens  105  is not limited. The objective lens  105  includes a lens of a type that prevents a magnetic field from leaking to the outside of a magnetic path. However, the objective lens  105  may be a lens of a type that allows a magnetic field to leak to the outside of a magnetic path or may be a compound objective lens including both of a lens of the type that allows a magnetic field to leak and a lens of the type that prevents a magnetic field from leaking. In addition, each of the condenser lenses  103  and  104  and the objective lens  105  may be an electrostatic lens or an objective lens where a magnetic lens and an electrostatic lens are combined as in a booster optical system or a retarding optical system for the above-described purposes, or may be a lens of any type for the purpose of focusing the charged particle beam on the sample  114 . In addition, the detector that detects the secondary charged particles may be arranged in the sample chamber  115 , or may be arranged in a column containing the charged particle optical systems. For the purpose of detecting the secondary charged particles, the number and the arrangement locations of the detectors are not limited. A plurality of charged particle beam columns may be provided. 
     In the first embodiment, the voltage that is applied between the charged particle beam aperture stop  121  and the electrode  122  is a voltage that undergoes the divergence action when the charged particle beam transmits through the aperture of the electrode  122  having an annular shape. That is, when the charged particle beam is an electron beam having negative charge, the electrode  122  applies a positive voltage to the charged particle beam aperture stop  121 . On the other hand, when the charged particle beam is an electron beam having positive charge, the electrode  122  applies a negative voltage to the charged particle beam aperture stop  121 . As long as the above-described conditions are satisfied, a method of applying the voltage between the charged particle beam aperture stop  121  and the electrode  122  is not limited. As illustrated in  FIG. 1 , the power supply  108  may be connected to the charged particle beam aperture stop  121  such that the electrode  122  functions as a reference potential (GND), the power supply  108  may be connected to the electrode  122  such that the charged particle beam aperture stop  121  functions as a reference potential (GND), or the power supply may be connected to both the charged particle beam aperture stop  121  and the electrode  122 . 
     Next, an example of an aperture shape and an arrangement of the charged particle beam aperture stop  121  and the electrode  122  will be shown.  FIG. 2A  is a perspective view, and  FIG. 2B  is a plan view in a direction Z along the optical axis of  FIG. 2A . In a charged particle beam aperture stop  121   a , a plurality of circular apertures  201   a  to  201   d  are arranged on a circumference. An electrode  122   a  includes: an on-axis electrode portion  202 ; a ring-shaped off-axis electrode portion  203 ; and beams  204   a  to  204   d  that hold the on-axis electrode portion  202  using the off-axis electrode portion  203 . The power supply  108  applies a predetermined voltage between the charged particle beam aperture stop  121   a  and the electrode  122   a . In addition, as illustrated in  FIG. 2B , the plurality of circular apertures  201   a  to  201   d  of the charged particle beam aperture stop  121   a  are arranged at positions overlapping an annular aperture  205  that is formed by the on-axis electrode portion  202  and the off-axis electrode portion of the electrode  122   a.    
     As a result, the influence of a difference in surface potential between the on-axis electrode portion  202  and the off-axis electrode portion  203  that is caused when the electrode  122   a  is directly irradiated with the charged particle beam as in the related art can be reduced. In addition, the annular aperture of the electrode  122   a  is irradiated with the charged particle beams transmitted through the circular apertures  201  of the charged particle beam aperture stop  121   a , and the charged particle doses of the charged particle beams transmitted through the circular apertures  201  are substantially the same. As a result, a stable spherical aberration correction effect can be obtained. When the charged particle beam aperture stop  121   a  is directly irradiated with the charged particle beam, there may be a difference in surface potential around the circular aperture, and a conductor portion that configures the aperture stop for the aperture is widened. Therefore, as compared to the electrode  122   a  where the on-axis electrode portion  202  and the off-axis electrode portion  203  are connected through only the beams  204 , a difference in surface potential in the charged particle beam aperture stop  121   a  can be easily alleviated, and there is no deflection action on the charged particle beam to be transmitted. 
     In this case, the aperture of the charged particle beam aperture stop  121   a  needs to be provided to prevent the occurrence of anisotropy in the charged particle beam when the charged particle beam transmitted through the charged particle beam aperture stop  121  and the electrode  122  is focused on one point by an electron lens. 
     In the example illustrated in  FIGS. 2A and 2B , the plurality of circular apertures  201   a  to  201   d  are arranged such that the centers thereof are on a circumference C and they are line-symmetric to two axes perpendicular to each other. Here, a center O of the circumference C is arranged to overlap the center of the annular aperture  205  of the electrode  122  when viewed in the direction Z along the optical axis, and the center O of the circumference C and the center of the annular aperture  205  are arranged on the optical axis in the charged particle beam apparatus. 
     The size of the circumference C is a size overlapping at least the annular aperture  205 . In addition, the plurality of circular apertures  201   a  to  201   d  have the same size, and the diameter of the circular apertures  201  is less than or equal to the width of the annular aperture  205  (difference between the radius of the aperture portion of the off-axis electrode portion  203  and the radius of the on-axis electrode portion  202 ). Further, when the charged particle beam aperture stop  121  and the electrode  122  are laminated, they are laminated such that the circular apertures  201   a  to  201   d  and the beams  204   a  to  204   d  do not overlap each other. 
     In the embodiment, the shape and the arrangement are not limited to those shown in  FIGS. 2A and 2B , and various modification examples can be adopted as long as the influence of the difference in surface potential between the on-axis electrode portion  202  and the off-axis electrode portion  203  can be reduced and the anisotropy of the charged particle beam caused by the charged particle beam aperture stop  121  can be reduced to be in an allowable range. 
     For example, as the number of circular apertures provided in the charged particle beam aperture stop  121  increases, the anisotropy is not likely to occur in the charged particle beam that is focused on the sample.  FIG. 3  illustrates an example where 12 circular apertures are arranged on the circumference. When the circular apertures are provided in the charged particle beam aperture stop  121 , the circular apertures are arranged such that all of a 2k number (where k represents an integer) of circular apertures have the same size and an angle between lines connecting the center of the charged particle beam aperture stop  121  and centers of the circular apertures adjacent to each other is (180/k)°.  FIG. 3  corresponds to a case where k=6. 
     Further, the aperture shape provided in the charged particle beam aperture stop  121  is not limited to a circular shape. The aperture shape may be an oval shape, an elliptical shape, or a curved oval shape illustrated in  FIG. 4 . A 2k number (where k represents an integer) of circular apertures may be arranged such that the aperture shape is a shape that is line-symmetric to the diameter of the charged particle beam aperture stop  121 , all the circular apertures have the same size, and an angle between symmetry axes of the apertures adjacent to each other is (180/k)°. When the aperture shape is not circular, the centroids of the apertures are placed on the circumference C.  FIG. 4  corresponds to a case where k=2. 
     In the example of the charged particle beam apparatus illustrated in  FIG. 1 , one set including the charged particle beam aperture stop  121  and the electrode  122  is mounted on the holder  120 . Plural sets including the charged particle beam aperture stops  121  and the electrodes  122  may be mounted on the holder  120  to be switched therebetween.  FIG. 5A  illustrates an example of the holder  120  that supports an aberration correction unit  501   a  and an aberration correction unit  501   b . The aberration correction units  501  includes a combination of the charged particle beam aperture stop  121  and the electrode  122 , and are attachable and detachable to and from the holder  120  on a basis of the unit. By replacing the aberration correction units  501  on a basis of the unit, when the aberration correction unit that is contaminated is replaced or when different aberration correction units are mounted, the replacement of the aberration correction unit corresponding to a desire of a user can be easily performed. For example, in the example of  FIG. 5A , the aperture shape of the charged particle beam aperture stop varies between the two aberration correction units  501 . 
     The structure of the aberration correction units  501  will be described using  FIG. 5B . The holder  120  is a conductor, and a voltage is applied between the charged particle beam aperture stop  121   a  and the electrode  122   a . Therefore, the holder  120  and the charged particle beam aperture stop  121   a  are electrically insulated from each other by an insulating unit case  502  having a cylindrical shape, and the charged particle beam aperture stop  121   a  and the electrode  122   a  are electrically insulated from each other by an insulating ring  507 . Here, it is desirable that the insulating material such as the unit case  502  and the insulating ring  507  are invisible from a path of the charged particle beam. Thus, as in the cross-sectional view of  FIG. 5B , in the unit case  502 , a lower spacer  504 , the electrode  122 , an intermediate spacer  505 , the insulating ring  507 , an upper spacer  506 , and the charged particle beam aperture stop  121  are accommodated in order from below (the sample side), and are fixed to an opening portion of the holder  120  by a pressing screw  503 . All of the lower spacer  504 , the intermediate spacer  505 , and the upper spacer  506  are conductors. This way, the upper spacer  506  having a small inner diameter and the intermediate spacer  505  having a large inner diameter are arranged between the charged particle beam aperture stop  121  and the electrode  122  through the insulating ring  507 , and the insulating ring  507  is invisible from the optical axis by an inner wall of the upper spacer  506 . 
     Second Embodiment 
       FIG. 6  illustrates the outline of a charged particle beam apparatus according to a second embodiment. The charged particle beam apparatus according to the second embodiment is different from that of the first embodiment in that the charged particle beam apparatus includes: a beam tube  112  that is arranged in a range from the acceleration electrode  102  to the vicinity of a lower end of the objective lens  105 ; a beam tube power supply  113  that applies a voltage to the beam tube; and a beam tube power supply controller  159  that controls the beam tube power supply  113 . The other apparatus configurations are the same as the apparatus configurations of the first embodiment. In the configuration of  FIG. 6 , the electrode  122  is electrically connected to the beam tube  112 , and a voltage is applied from the power supply  108  to the charged particle beam aperture stop  121 . However, a configuration in which the charged particle beam aperture stop  121  is electrically connected to the beam tube and a voltage is applied from the power supply  108  to the electrode  122  may be adopted, or a configuration in which voltages different from that of the beam tube  112  are applied to both of the charged particle beam aperture stop  121  and the electrode  122  may be adopted. 
     In addition, in the example of  FIG. 6 , the single beam tube power supply  113  and the single beam tube power supply controller  159  are provided. When the beam tube is divided halfway or is electrically insulated, a plurality of beam tube power supplies and a plurality of beam tube power supply controllers corresponding to the divided beam tube can be provided. 
     Third Embodiment 
       FIG. 7  illustrates the outline of a charged particle beam apparatus according to a third embodiment. The charged particle beam apparatus according to the third embodiment is different from that of the second embodiment in that, instead of the electrode  122 , the charged particle beam apparatus includes: an on-axis electrode  124 ; an off-axis electrode  125 ; an on-axis electrode power supply  130  that applies a voltage to the on-axis electrode  124 ; and an on-axis electrode power supply controller  160  that controls the on-axis electrode power supply  130 . The other apparatus configurations are the same as the apparatus configurations of the second embodiment. In the configuration of  FIG. 7 , the charged particle beam aperture stop  121  and the off-axis electrode  125  are electrically connected to the beam tube  112 , and a voltage is applied from the on-axis electrode power supply  130  to the on-axis electrode  124 . However, a configuration in which a voltage different from that of the beam tube  112  is applicable to each of the charged particle beam aperture stop  121 , the on-axis electrode  124 , and the off-axis electrode  125  may be adopted. 
       FIG. 8  is a schematic view illustrating the charged particle beam aperture stop  121 , the on-axis electrode  124 , and the off-axis electrode  125 . The cylindrical off-axis electrode  125  is arranged to surround the columnar on-axis electrode  124 , and the on-axis electrode  124  and the off-axis electrode  125  are arranged on the sample side further than the charged particle beam aperture stop  121 . In the example of  FIG. 8 , the shape of the on-axis electrode is columnar. However, as long as an electric field generated from the electrode is directed in a direction perpendicular to the optical axis of the charged particle beam, the shape of the on-axis electrode is not limited. The aperture shape and the arrangement in the charged particle beam aperture stop  121  and the arrangement of the charged particle beam aperture stop  121 , the on-axis electrode  124 , and the off-axis electrode  125  are the same as those of the first embodiment. The annular aperture  205  of the electrode  122  in the first embodiment may be replaced with a gap between the on-axis electrode  124  and the off-axis electrode  125 . In addition, the center of the circumference where the centroids of the plurality of apertures of the charged particle beam aperture stop  121  are arranged is arranged to overlap a central axis of the on-axis electrode  124  when viewed in the direction Z along the optical axis. 
     The voltage that is applied to the on-axis electrode  124  is a voltage that undergoes the divergence action outside the axis when the charged particle beam transmits through the vicinity of the on-axis electrode  124 . That is, when the charged particle beam is an electron beam having negative charge, a positive voltage is applied to the off-axis electrode  125 . On the other hand, when the charged particle beam is an electron beam having positive charge, a negative voltage is applied to the off-axis electrode  125 . 
     REFERENCE SIGNS LIST 
     
         
         
           
               101 : charged particle beam source 
               102 : acceleration electrode 
               103 : first condenser lens 
               104 : second condenser lens 
               105 : objective lens 
               108 : power supply 
               112 : beam tube 
               113 : beam tube power supply 
               114 : sample 
               115 : sample chamber 
               116 : detector 
               120 : holder 
               121 : charged particle beam aperture stop 
               122 : electrode 
               123 : insulating material 
               124 : on-axis electrode 
               125 : off-axis electrode 
               130 : on-axis electrode power supply 
               151 : charged particle beam source controller 
               152 : acceleration electrode controller 
               153 : first condenser lens controller 
               154 : second condenser lens controller 
               155 : objective lens controller 
               156 : detector controller 
               158 : power supply controller 
               159 : beam tube power supply controller 
               160 : on-axis electrode power supply controller 
               170 : integrated computer 
               171 : controller 
               172 : display 
               201 : circular aperture 
               202 : on-axis electrode portion 
               203 : off-axis electrode portion 
               204 : beam 
               205 : annular aperture 
               501 : aberration correction unit 
               502 : unit case 
               503 : pressing screw 
               504 : lower spacer 
               505 : intermediate spacer 
               506 : upper spacer 
               507 : insulating ring