Abstract:
Provided is a charged-particle-beam device capable of simultaneously cancelling out a plurality of aberrations caused by non-uniform distribution of the opening angle and energy of a charged particle beam. The charged-particle-beam device is provided with an aberration generation lens for generating an aberration due to the charged particle beam passing off-axis, and a corrective lens for causing the trajectory of the charged particle beam to converge on the main surface of an objective lens irrespective of the energy of the charged particle beam. The main surface of the corrective lens is disposed at a crossover position at which a plurality of charged particle beams having differing opening angles converge after passing through the aberration generation lens.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a charged-particle-beam device for irradiating charged-particle beams on a specimen. 
       BACKGROUND ART 
       [0002]    An important function of making a 3D observation of a specimen is required for a device for examining a 3D specimen by use of charged-particle beams such as electron beams. When a specimen is subjected to 3D observation by use of an electronic microscope, the stage is tilted thereby to acquire a 3D image of the specimen. However, a mechanical operation is required for tilting the stage or column, which deteriorates throughput or reproducibility of tilt angle. As a method for making a 3D measurement of a specimen without tilting the stage, there is assumed that beams are tilted by use of a deflector. How ever, when beams are tilted (deflected) by a deflector, an aberration is generated and the beam diameter increases. 
         [0003]    PTL 1 describes a technique capable of lowering energy when charged-particle beams pass through a corrector than energy when they pass through a lens whose chromatic aberration is to be corrected, thereby lowering a required specification for lens power supply stability, PTL 1 describes that beams with different energy are converged near the principal plane of a lens thereby to create an achromatic space on the image plane of the lens. 
       CITATION LIST 
     Patent Literature 
       [0004]    PTL 1: Japanese Patent Publication (Kokai) No. 2007-128893 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    A scanning electronic microscope for making a 3D observation of a specimen by tilting electron beams requires that electrons discharged from a chip are focused on a specimen by use of a plurality of optical elements, electron beams are tilted by a deflector, and the tilted beams are scanned on the specimen. In this case, electron beams are tilted, and thus primary electron beams pass off the axis of the lens, and consequently an aberration is generated and a resolution is deteriorated. The electron beams discharged from the chip are not constant in energy and exit angle (opening angle) but are distributed. Therefore, when the electron beams are tilted, an aberration due to a difference in energy and a plurality of aberrations (such as deflected chromatic aberration, deflected coma aberration and high-order chromatic aberration) due to a difference in opening angle are generated, which increases the beam diameter. With the use of the technique described in PTL 1, a high-order chromatic aberration can be prevented from occurring and an achromatic space can be created on the image plane of the lens, but the technique described in PTL 1 has the two following problems. 
         [0006]    (Problem 1) A high-order chromatic aberration can be restricted to some extent, but a mechanism for reversely generating a high-order chromatic aberration is not provided, and thus a generated high-order chromatic aberration cannot be corrected. 
         [0007]    (Problem 2) A method for correcting an aberration due to an opening angle as well as preventing a high-order chromatic aberration from occurring is not described. 
         [0008]    With the technique described in PTL 1, it is assumed that all the above aberrations are difficult to cancel at the same time due to the above problems. In particular, under the condition that a plurality of aberrations stand out as the electron beams are tilted at a larger angle (such as 10 degrees or more), an increase in beam diameter and a deterioration in resolution are remarkable. 
         [0009]    The present invention has been made in terms of the above problems, and an object thereof is to provide a charged-particle-beam device capable of cancelling a plurality of aberrations at the same time generated by energy and opening angles of charged-particle beams which are not constant but are distributed. 
       Solution to Problem 
       [0010]    A charged-particle-beam device according to the present invention includes an aberration generation lens for generating an aberration when charged-particle beams pass off the axis, and a correction lens for focusing trajectories of the charged-particle beams on the principal plane of an objective lens irrespective of energy of the charged-particle beams, wherein the principal plane of the correction lens is arranged at a crossover position where the charged-particle beams with different opening angles pass through the aberration generation lens and then focus. 
       Advantageous Effects of Invention 
       [0011]    With the charged-particle-beam device according to the present invention, it is possible to restrict a resolution from deteriorating even when charged-particle beams are largely deflected. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]      FIG. 1  is a diagram for explaining a structure of an optical system provided in a charged-particle-beam device according to a first exemplary embodiment. 
           [0013]      FIG. 2  is a diagram illustrating a difference of a trajectory of electron beams  2  indicated in a dotted line of  FIG. 1  relative to a center trajectory of electron beams  2  indicated in a bold line of  FIG. 1 . 
           [0014]      FIG. 3  is a diagram illustrating a plurality of trajectories of electron beams  2  with different energy. 
           [0015]      FIG. 4  is a side view illustrating a structure of the charged-particle-beam device according to the first exemplary embodiment. 
           [0016]      FIG. 5  is a side view illustrating a structure of a charged-particle-beam device according to a second exemplary embodiment. 
           [0017]      FIG. 6  is a side view illustrating a structure of a charged-particle-beam device according to a third exemplary embodiment, 
           [0018]      FIG. 7  is a side view illustrating a structure of a charged-particle-beam device according to a fourth exemplary embodiment. 
           [0019]      FIG. 8  is a flowchart for explaining the operations of the charged-particle-beam device according to the fourth exemplary embodiment. 
           [0020]      FIG. 9  is a side view illustrating a structure of a charged-particle-beam device according to a fifth exemplary embodiment. 
           [0021]      FIG. 10  is a side view illustrating a structure of a charged-particle-beam device according to a sixth exemplary embodiment. 
           [0022]      FIG. 11  is a diagram for explaining a structure of an optical system provided in a charged-particle-beam device according to a seventh exemplary embodiment. 
           [0023]      FIG. 12  is a diagram illustrating a plurality of trajectories of electron beams  2  with different energy. 
           [0024]      FIG. 13  is a side view illustrating a structure of the charged-particle-beam device according to the seventh exemplary embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Exemplary Embodiment 
       [0025]      FIG. 1  is a diagram for explaining a structure of an optical system provided in a charged-particle-beam device according to a first exemplary embodiment of the present invention. A scanning electronic microscope (SEM) will be described below as an exemplary charged-particle-beam device. The optical system according to the first exemplary embodiment includes an objective lens  12 , a correction lens  15 , an aberration generation lens  13 , and a condenser lens  11 . The objective lens  12  focuses charged-particle beams (electron beams)  2  on a point P 4  on an image plane Z 4 . The aberration generation lens  13  is configured to have an equivalent property to the objective lens  12 , and generates an aberration when electron beams  2  passing through the condenser lens  11  pass off the axis. The correction lens  15  focuses the electron beams  2  with different energy on the principal plane of the objective lens  12 . The principal plane of the correction lens  15  is arranged to overlap on the object plane of the objective lens  12 . 
         [0026]    The electron beams  2  discharged from an electron source  1  are focused on a point P 1  on a plane Z 1  by the condenser lens  11 . The electron beams  2  focused on the point P 1  are deflected by a deflector  21  installed on Z 1 , and pass off the axis of the aberration generation lens  13 . The aberrations caused by the aberration generation lens  13  are different depending on an opening angle of the electron beams  2 . The electron beams  2  passing through the aberration generation lens  13  focus on a point P 3  on the principal plane Z 3  of the correction lens  15  (the object plane of the objective lens  12 ) irrespective of the opening angles of the electron beams  2 , and cross over on the point P 3 . Some of the electron beams  2  with different opening angles, which pass through a center trajectory, are indicated in a bold line, and others that pass through the other two trajectories are indicated in a line and a dotted line. 
         [0027]    A deflector  27  is arranged on the principal plane Z 3  of the correction lens  15  (the object plane of the objective lens  12 ). The deflector  27  deflects the electron beams  2  and pass them off the axis of the objective lens  12 . The trajectories of the electron beams  2  deflected by the deflector  27  are different depending on the opening angles non-deflected by the deflector  27 , but the electron beams  2  pass through the objective lens  12  and then focus on the point P 4  in any trajectory, and are tilted to be incident on a specimen arranged on the point. 
         [0028]      FIG. 2  is a diagram illustrating a difference of the trajectory of the electron beams  2  indicated in a dotted line of  FIG. 1  relative to the center trajectory of the electron beams  2  indicated in a bold line of  FIG 1 . In  FIG. 2 , an offset relative to the center trajectory on the principal plane of the aberration generation lens  13  and an offset relative to the center trajectory on the principal plane of the objective lens  12  are arranged to be antisymmetric about the principal plane Z 3  of the correction lens  15 . With the arrangement, aberrations generated due to a difference in opening angle of the electron beams  2  can be cancelled. That is, a deflected coma aberration and a deflected chromatic aberration generated between the plane Z 1  and the principal plane Z 3 , and those generated between the principal plane Z 3  and the image plane Z 4  are equal in amount and different in sign to cancel each other 
         [0029]      FIG. 3  is a diagram illustrating a plurality of trajectories of the electron beams  2  with different energy. The electron beams  2  discharged from the chip  1  are deflected by the deflector  21  to be incident into the aberration generation lens  13 . The electron beams  2  with low energy (in a chain line) are strongly affected by the operation of the aberration generation lens  13 , and the electron beams  2  with high energy (in a dotted line) are weakly affected by the operation of the aberration generation lens  13 . Consequently, an offset between the trajectories (color variance) due to a difference in energy is caused. The electron beams  2  with different energy, which are incident into the correction lens  15 , are reversely swung back by the deflector  27  arranged on the principal plane of the correction lens  15  to focus on the principal plane of the objective lens  12 . 
         [0030]    In  FIG. 3 , an offset between the trajectories of the electron beams  2  due to a difference in energy are reversely swung back with reference to the principal plane Z 3  of the correction lens  15 . Consequently, an aberration due to a difference in energy of the electron beams  2  (high-order chromatic aberration proportional to the product of the cube of tilt angle θi and the difference ΔΦ in energy) can be cancelled. That is, the aberration generated between the aberration generation lens  13  and the principal plane Z 3  and the aberration generated between the principal plane Z 3  and the objective lens  12  are equal in amount and different in sign to cancel each other. 
         [0031]    Therefore, in the optical system according to the first exemplary embodiment, while the opening angles of the electron beams  2  are different between the aberration generation lens  13  and the objective lens  12  ( FIG. 1 ), the electron beams  2  with different energy are focused by use of the lenses ( FIG. 3 ). On the other hand, while the electron beams  2  are different in energy in the correction lens  15  ( FIG. 3 ), the electron beams  2  with different opening angles are focused by use of the lens ( FIG. 1 ). An aberration due to a difference in energy and an aberration due to a difference in opening angle (such as deflected chromatic aberration, deflected coma aberration, or high-order chromatic aberration), which are generated when the electron beams  2  are tilted, can be corrected at the same time. 
         [0032]      FIG. 4  is a side view illustrating a structure of the charged-particle-beam device according to the first exemplary embodiment. The exemplary trajectories of the electron beams  2 , which correspond to those in  FIG. 1 , are illustrated. An optical element control unit  35  controls the operations of the lenses and the deflectors. An optical condition storage unit  36  stores the operation parameters such as setting parameters of the lenses and deflection intensities of the deflectors. 
         [0033]    The electron beams  2  discharged from the chip  1  pass through the condenser lens  11  and are limited in opening angle by an objective diaphragm  3  to be focused on the point Pl. The electron beams  2  are deflected by the deflector  21  (a deflector  22  may be further provided) and pass off the axis of the aberration generation lens  13  to be focused on the point P 3  where the correction lens  15  and the deflector  27  are installed. The electron beams  2  are swung back by the deflector  27  to be incident into the objective lens  12 , and are tilted to reach a specimen  52 . It is possible to adjust a focus of the electron beams  2  by a lens intensity of the objective lens  12  and to make an astigmatic adjustment by the excitation amount of a stigma coil  37  installed in the condenser lens  11 . 
       First Exemplary Embodiment: Conclusion 
       [0034]    As described above, in the charged-particle-beam device according to the first exemplary embodiment, the principal plane Z 3  of the correction lens  15  is arranged at a crossover position where the electron beams  2  with different opening angles pass through the aberration generation lens  13  and then focus. Further, the principal plane of the correction lens  15  is arranged to overlap on the object plane of the objective lens  12 . With the arrangement, it is possible to correct an aberration due to a difference in energy of the electron beams  2  and an aberration due to a difference in opening angle of the electron beams  2  at the same time, 
       Second Exemplary Embodiment 
       [0035]      FIG. 5  is a side view illustrating a structure of a charged-particle-beam device according to a second exemplary embodiment of the present invention. According to the second exemplary embodiment, the electron beams  2  are swung back by use of two-stage deflectors  27  and  28  installed between the correction lens  15  and the objective lens  12  instead of the deflector  27  arranged on the principal plane Z 3  of the correction lens  15 . In order to strictly make the aberration correction, it is desirable that the deflector  27  is installed on the principal plane Z 3  of the correction lens  15  to swing back the electron beams  2  as in the first exemplary embodiment, but the deflector  27  may be difficult to arrange at the position in terms of design. In such a case, the electron beams  2  can be swung back by the two-stage deflectors  27  and  28  illustrated in  FIG. 5 . Also in this case, a deterioration in resolution is not practically problematic and the same effects as in the first exemplary embodiment can be expected. 
       Third Exemplary Embodiment 
       [0036]      FIG. 6  is a side view illustrating a structure of a charged-particle-beam device according to a third exemplary embodiment of the present invention. According to the third exemplary embodiment, two-stage deflectors  25  and  26  are installed between the aberration generation lens  13  and the correction lens  15  in order to correct an aberration changing depending on an irradiation angle when the irradiation angle of the electron beams  2  is variously changed. 
         [0037]    When the electron beams  2  pass off the axis of the aberration generation lens  13 , a positional offset proportional to the cube of the correction amount (∞θ P1 ) is generated on the image plane of the aberration generation lens  13  (the principal plane Z 3  of the correction lens  15 ), The two-stage deflectors  25  and  26  correct the positional offset, and correct the trajectory of the electron beams  2  such that the center trajectory (in a bold line) of the electron beams  2  passes through the center of the correction lens  15 . With the corrected trajectory, when an irradiation angle of the electron beams  2  is variously changed, the electron beams  2  can pass through the center of the correction lens  15  without passing off the axis of the correction lens  15 . Thereby, even when an irradiation angle of the electron beam  2  is variously changed, the trajectory of the electron beams  2  can be controlled such that another aberration is not generated by the correction lens  15 . 
       Fourth Exemplary Embodiment 
       [0038]    According to the first to third exemplary embodiments, the aberration generation lens  13  needs to be designed as an equivalent lens to the objective lens  12 . Instead, according to a fourth exemplary embodiment of the present invention, a mechanism for adjusting a lens condition is provided such that aberrations equal in amount and different in sign can he generated for an aberration component of interest in terms of aberrations to be corrected (deflected chromatic aberration and deflected coma aberration in this example), thereby correcting an aberration caused on the objective lens  12 . 
         [0039]      FIG. 7  is a side view illustrating a structure of a charged-particle-beam device according to the fourth exemplary embodiment. According to the fourth exemplary embodiment, an aberration adjustment lens  14  is arranged behind the aberration generation lens  13 , and a correction aberration is generated by use of a combination lens configured of the two lenses. 
         [0040]    A boosting electrode  51  for accelerating the electron beams  2  is installed near the objective lens  12 . The specimen  52  is provided with a mechanism capable of applying a deceleration voltage. In this way, under an environment where an electric field or magnetic field is applied in a superimposed manner, the optical property of the objective lens  12  changes due to an applied voltage to the boosting electrode  51  or a deceleration voltage applied to the specimen  52 . Thus, it is assumed to dynamically cancel an aberration of the changed objective lens  12  due to a combination effect of the aberration adjustment lens  14  behind the aberration generation lens  13 . A stage height measurement device  38  measures a height of the stage where the specimen  52  is placed. 
         [0041]    The electron beams  2  are focused on the point P 1  and deflected by the deflector  21  (or the deflectors  21  and  22 ) thereby to pass off the axis of the aberration generation lens  13  similarly as in the first exemplary embodiment. The aberration generation lens  13  generates deflected aberrations (deflected chromatic aberration and deflected coma aberration) increasing depending on the deflection amount θ P1  by the deflector  21 . Deflectors  23  and  24  correct the trajectory of the electron beams  2  such that they pass through the center of the aberration adjustment lens  14 . The deflected chromatic aberration and the deflected coma aberration generated on the aberration generation lens  13  are reflected on the point P 3  according to a lens magnification of the aberration adjustment lens  14 . A deflected coma aberration and a deflected chromatic aberration generated on the objective lens  12  can be corrected by use of the aberrations reflected on the point P 3 . 
         [0042]    A method for adjusting the generated aberration amount by use of the aberration adjustment lens  14  will be specifically described below. For brief description, there will be assumed that a virtual deflection point when the electron beams  2  are deflected by use of the deflectors  21  and  22  is matched with P 1 . A deflected chromatic aberration and a deflected coma aberration generated on the image plane of the aberration generation lens  13  are expressed in the following Equations. 
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         [0043]    (ΔU Coma ) Cor   _   P2 : The coma aberration amount on P 2  generated by a deflected aberration corrector 
         [0044]    (ΔU C ) Cor   _   P2 : The chromatic aberration amount on P 2  generated by the deflected aberration corrector 
         [0045]    (Cs 13 ) P2 : Spherical aberration coefficient of the lens  13  (image plane definition) 
         [0046]    (Cc 13 ) P2 : Chromatic aberration coefficient of the lens  13  (image plane definition) 
         [0047]    α P2 : Beam opening angle on the image plane of the lens  13   
         [0048]    α P2 *: Complex conjugate of α P2    
         [0049]    θ P2 : Tilt angle on P 2   
         [0050]    θ P2 *: Complex conjugate of θ P2    
         [0051]    ΔΦ: Energy width of the electron beams  2  discharged from the chip  1 . 
         [0052]    Φ P2 : Potential of electron beams on P 2   
         [0053]    The respective aberration amounts reflected on the point P 3  by the aberration enlargement lens  14  are expressed in the following Equations. 
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         [0054]    (ΔU Coma ) Cor   _   P3 : The coma aberration amount on P 3  generated by the deflectors  23  and  24   
         [0055]    (ΔU C ) Cor   _   P3 : The chromatic aberration amount on P 3  generated by the deflectors  23  and  24   
         [0056]    MA 14 : Angle magnification of the aberration adjustment lens  14   
         [0057]    M 14 : Magnification of the aberration adjustment lens  14   
         [0058]    α P3 : Opening angle of the electron beams  2  on P 3   
         [0059]    α P3 *: Complex conjugate of α P3    
         [0060]    Φ P3 : Potential of the electron beams  2  on P 2   
         [0061]    A deflected chromatic aberration and a deflected coma aberration generated by the objective lens  12 , which are defined on the object plane Z 3  of the objective lens  12 , are expressed in the following Equations. 
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         [0062]    (ΔU Coma ) obj   _   P3 : The coma aberration amount generated on the objective lens  12  when the electron beams  2  are tilted (converted into magnitude on P 3 ) 
         [0063]    (ΔU C ) Cor   _   P3 : The chromatic aberration amount generated on the objective lens when the electron beams  2  are tilted (converted into magnitude on P 3 ) 
         [0064]    MA obj : Angle magnification of the objective lens  12   
         [0065]    M obj : Magnification of the objective lens  12   
         [0066]    (Cs obj ) P3 : Spherical aberration coefficient of the objective lens  12  (object plane definition) 
         [0067]    (Cc obj ) P3 : Chromatic aberration coefficient of the objective lens  12  (object plane definition) 
         [0068]    θ P3 : Tilt angle on P 3   
         [0069]    θ P3 *: Complex conjugate of θ P3    
         [0070]    θ i : Tilt angle of beams (specimen plane) 
         [0071]    The sums of the aberration (Equation (1)′, Equation (2)′) reflected on the point P 3  by the aberration enlargement lens  14  and the aberration (Equation (3), Equation (4)) of the objective lens  12  are expressed in the following Equations, respectively. 
         [0000]    
       
         
           
             
               
                 
                   
                       
                   
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                       Math 
                       . 
                       
                           
                       
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         [0072]    (ΔU Coma ) all   _   P4 : The deflected coma aberration amount generated in the entire optical system (specimen plane definition) 
         [0073]    (ΔU C ) Cor   _   P3 : The deflected chromatic aberration amount generated in the entire optical system (specimen plane definition) 
         [0074]    A condition (correction condition) for making Equation (5) an Equation (6) zero at the same time is expressed in the following Equations. Equation (7) is a condition for correcting a deflected chromatic aberration and a deflected coma aberration at the same time, and Equation (8) is a deflection angle given on the points P 1  and P 3  during correction. 
         [0000]    
       
         
           
             
               
                 
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                     Math 
                     . 
                     
                         
                     
                      
                     5 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       
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                         4 
                       
                     
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         [0075]    A condition for correcting a deflected chromatic aberration and a deflected coma aberration at the same time will be considered according to Equation (7). The right side of Equation (7) is determined by the spherical aberration coefficient Cs and the chromatic aberration coefficient Cc of the object plane definition of the objective lens  12 , and indicates a rate at which the deflected coma aberration and the deflected chromatic aberration are generated. Therefore, the right side of Equation (7) indicates a rate at which the deflected chromatic aberration and the deflected coma aberration are generated on the objective lens  12 , and the left side indicates a rate at which the aberrations are created by the aberration generation lens  13  and the aberration adjustment lens  14 . Therefore, under the condition that the right side and the left side match with each other, the deflected chromatic aberration and the deflected coma aberration can be corrected at the same time. 
         [0076]    There will he assumed that the potentials Φ P1 , Φ P2 , and Φ P3  on the points P 1 , P 2 , and P 3  are the same for brief description. In this case, a condition for correcting the deflected chromatic aberration and the deflected coma aberration at the same time is expressed in the following Equation. 
         [0000]    
       
         
           
             
               
                 
                   [ 
                   
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                     . 
                     
                         
                     
                      
                     7 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       1 
                       
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                         14 
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                               13 
                             
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                             obj 
                           
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                            
                           
                               
                           
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                           ) 
                         
                         
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                           3 
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   
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                     7 
                     ) 
                   
                   ′ 
                 
               
             
           
         
       
     
         [0077]    There will be assumed that the intensities of the aberration generation lens  13  and the aberration adjustment lens  14  are adjusted such that the crossover points P 1  and P 3  are fixed and only the crossover point P 2  is vertically moved. When the position of the crossover point P 2  is lifted up, the magnification M 13  of the aberration generation lens  13  decreases. It is known that the following approximations are established between the magnification, and the spherical aberration coefficient Cs and the chromatic aberration coefficient Cc. [Math. 8] 
         [0000]        Cs∝f   3 (1+ M ) 4    (9)
 
         [0000]        Cc∝f (1+ M ) 2    (10)
 
         [0078]    It is seen from Equations (9) and (10) that when the magnification M 13  is lowered, the value of Cs/Cc of the aberration generation lens  13  is lowered. When the position of P 3  is fixed and the position of P 2  is lifted up, the angle magnification MA 14  of the aberration adjustment lens  14  is increased. Consequently, the component (1/MA 14   2 ) in the left side of Equation (7)′ also decreases, thereby lowering a rate (the left side of Equation ( 7 )′) of the deflected chromatic aberration and the deflected coma aberration created by a combination of the aberration generation lens  13  and the aberration adjustment lens  14 . When the points P 1  and P 3  are fixed and the position of P 2  is lowered, the rate (the left side of Equation ( 7 )′) can be increased. The position of the point P 3  can be controlled by the optical element control unit  35 , 
         [0079]      FIG. 8  is a flowchart for explaining the operations of the charged-particle-beam device according to the fourth exemplary embodiment. Each step in  FIG. 8  will be described. 
         [0000]    ( FIG. 8 : steps S 101  to S 102 ) 
         [0080]    An operator determines the optical condition (such as acceleration voltage, booster potential, retarding potential, and object plane position) for observing a specimen, and inputs it into the optical condition storage unit  36  (S 101 ), (Cs obj ) P3  and (Cc obj ) P3  are determined under the optical condition input in step S 101 . The operator moves the specimen stage to the observation position (S 102 ). 
         [0000]    ( FIG. 8 : step S 103 ) 
         [0081]    The stage height measurement device  38  measures a height of the specimen  52 , and stores a working distance based on the measurement result in the optical condition storage unit  36 . A height of the specimen  52  may he estimated based on the excitation amount of the objective lens  12  when not tilted instead of the stage height measurement device  38 . 
         [0000]    ( FIG. 8 : step S 104 ) 
         [0082]    The optical element control unit  35  calculates a setting parameter of each lens according to Equation (7) or Equation (7)′ based on the optical condition stored in the optical condition storage unit  36  in step S 101  and the optical condition measured in step S 103 , and reflects the result on each lens. 
       (FIG.  8 : Steps S 105  to S 106 ) 
       [0083]    The operator inputs a tilt angle of the electron beams  2  into the optical condition storage unit  36  (S 105 ). The optical element control unit  35  determines a deflection intensity of each deflector and a setting intensity of the stigma coil  37  based on the input tilt angle, and the deflection intensity of each deflector when the beams are tilted which is stored in the optical condition storage unit  36 , and reflects them. Step S 106  is directed for adjusting each deflector according to the principle described in  FIG. 1  to  FIG. 3 . 
         [0000]    ( FIG. 8 : steps S 107  to S 108 ) 
         [0084]    The optical element control unit  35  makes focus adjustment and stigma adjustment (S 107 ). An observation image generator (not illustrated) acquires a tilt image of the specimen  52  by use of secondary electrons discharged from the specimen  52  (S 108 ). When the tilt angle is to he changed, the processing returns to S 105 , and when the observation condition is to be changed, the processing returns to S 104 . 
       Fourth Exemplary Embodiment: Conclusion 
       [0085]    As described above, the charged-particle-beam device according to the fourth exemplary embodiment fixes the points P 1  and P 3  and controls the point P 2 , thereby adjusting a rate of the deflected coma aberration and deflected chromatic aberration which are to be generated to a rate thereof generated on the objective lens  12 . Thereby, even when a rate of the deflected chromatic aberration and the deflected coma aberration generated on the objective lens  12  is varied due to a change in working distance, the point P 2  is moved according to the variation amount, thereby correcting the deflected chromatic aberration and the deflected coma aberration at the same time. That is, even when the optical condition of the objective lens  12  is changed, the aberrations on the objective lens  12  can be cancelled due to a combination effect of the aberration generation lens  13  and the aberration adjustment lens  14 . 
       Fifth Exemplary Embodiment 
       [0086]      FIG. 9  is a side view illustrating a structure of a charged-particle-beam device according to a fifth exemplary embodiment of the present invention. According to the fifth exemplary embodiment, the electron beams  2  are tilted by use of the deflector  28  installed in the magnetic field of the objective lens  12 . An aberration generated on the objective lens  12  is different depending on the operations of the objective lens  12  and the deflector  28 . Thus, according to the fifth exemplary embodiment, as in the fourth exemplary embodiment, an aberration generated on the objective lens  12  is dynamically adjusted by a combination effect of the aberration generation lens  13  and the aberration adjustment lens  14 .  FIG. 9  illustrates an exemplary structure in which the electron beams  2  are faced toward the center of the lens by use of the two-stage deflectors  25  and  26  described according to the third exemplary embodiment, but the structure is not limited thereto, 
         [0087]    With the charged-particle-beam device according to the fifth exemplary embodiment, also when an aberration generated on the objective lens  12  is largely varied because the beams are tilted due to a change in the condition of the electromagnetic lens or the trajectory in the lens caused by a deflection in the magnetic field, such as when the objective lens  12  employs an electric/magnetic field lens or when the deflector  28  is arranged as a beam tilt means in the magnetic field of the objective lens  12 , the aberration can be dynamically corrected. 
       Sixth Exemplary Embodiment 
       [0088]      FIG. 10  is a side view illustrating a structure of a charged-particle-beam device according to a sixth exemplary embodiment of the present invention. According to the sixth exemplary embodiment, the two-stage deflectors  23  and  24  deflect a trajectory of the electron beams  2  such that the electron beams  2  pass off the axis of the aberration adjustment lens  14 . According to the sixth exemplary embodiment, a deflected aberration is generated by passing the electron beams  2  off the axis of the aberration adjustment lens  14 , thereby reducing the off-axis amount on the aberration generation lens  13  required for generating the same aberration amount as in the fifth exemplary embodiment. Thereby, the high-order aberration amount to be generated on the aberration generation lens  13  can be restricted, which facilitates each lens to be controlled. 
       Seventh Exemplary Embodiment 
       [0089]      FIG. 11  is a diagram for explaining a structure of an optical system provided in a charged-particle-beam device according to a seventh exemplary embodiment of the present invention. According to the seventh exemplary embodiment, a trajectory focus lens  17  focuses the electron beams  2  with different opening angles on the point P 3  on the principal plane of the correction lens  15  according to the deflection operations of deflectors  30  and  31 . A second correction lens  16  is configured to be equivalent to the correction lens  15 . That is, there is configured, with respect to the second correction lens  16 , such that the electron beams  2  with different energy are focused on the principal plane of the aberration generation lens  13 . The principal plane of the second correction lens  16  is arranged to overlap on the image plane of the aberration generation lens  13 . The electron beams  2  with different opening angles cross over on the point PS on the principal plane of the second correction lens  16  and on the point P 3  on the principal plane of the correction lens  15 . 
         [0090]    With the arrangement of the lenses in  FIG. 11 , when an offset relative to the center trajectory on the principal plane of the aberration generation lens  13  and an offset relative to the center trajectory on the principal plane of the objective lens  12  are arranged to be symmetric about a principal plane Z 6  of the trajectory focus lens  17 . An axial offset of the center trajectory on the principal plane of the aberration generation lens  13  and an axial offset of the center trajectory on the principal plane of the objective lens  12  are arranged to be antisymmetric about the principal plane Z 6  of the trajectory focus lens  17 . Therefore, the entire optical system in  FIG. 11  can produce the same effects as the optical system in  FIG. 1 . 
         [0091]      FIG. 12  is a diagram illustrating a plurality of trajectories of the electron beams  2  with different energy. The principal plane of the trajectory focus lens  17  is arranged to overlap on a crossover position P 6  where the electron beams  2  with different energy pass through the second correction lens  16  and then focus. Thereby, the trajectories of the electron beams  2  with different energy are antisymmetric about the principal plane Z 6  of the trajectory focus lens  17 , and thus the aberrations caused due to a difference in energy are equal in amount and different in sign before and after Z 6  to cancel each other. Therefore, the entire optical system in  FIG. 12  can produce the same effects as the optical system in FIG:  3 . 
         [0092]      FIG. 13  is a side view illustrating a structure of the charged-particle-beam device according to the seventh exemplary embodiment. The electron beams  2  discharged from the chip  1  are focused on the point P 1  by the condenser lens  11 , and pass off the axis of the aberration generation lens  13  by the deflector  21  (or the deflectors  21  and  22 ) to be focused on the point P 5 . The second correction lens  16  is arranged on the point P 5 , and gives the lens operation only to the electron beams  2  with different energy ( FIG. 12 ). The deflector  30  deflects the electron beams  2  toward the center of the trajectory focus lens  17  ( FIG. 11 ). The trajectories with different opening angles are focused on the point P 3  by the lens operation of the trajectory focus lens  17  and the deflector  31 . The subsequent operations are the same as in the first exemplary embodiment. 
         [0093]    The present invention is not limited to the above exemplary embodiments, and encompasses various variants. The above exemplary embodiments have been described in detail for easy understanding of the present invention, and the present invention is not necessarily limited to ones including all the components. Part of the components of an exemplary embodiment may be replaced with the components of other exemplary embodiment, Further, the components of an exemplary embodiment may be added with the components of other exemplary embodiment. Further, part of the components of each exemplary embodiment may be added with other components, deleted, or replaced therewith. 
         [0094]    Each lens (the condenser lens  11 , the aberration generation lens  13 , the aberration adjustment lens  14 , the correction lens  15 , and the objective lens  12 ) provided in the charged-particle-beam device according to the present invention may be of any type of electrostatic type, magnetic field type, and electromagnetic superimposed type. The lenses may be employed in combination. 
         [0095]    There has been described by way of example according to the above exemplary embodiments a scanning electronic microscope in which the electron beams  2  are tilted by a deflector to scan the specimen  52 , thereby acquiring a tilt image of the specimen  52 . The same effects by the above operations can be expected also when the deflector performs image shifting for moving a field of observation. Thereby, image shifting over a lame area can be realized. Therefore, it is possible to acquire a high-resolution beams tilt image in a short time, and it is possible to realize SEM such as semiconductor device suitable for 3D observation of a specimen. 
         [0096]    The charged-particle-beam device according to the present invention is not limited to devices using electron beams as charged-particle beams, and may be applied to general charged-particle-beam devices using other charged-particle beams such as ion microscope or ion processor (FIB). 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1 : Electron source 
           2 : Electron beam 
           3 : Objective diaphragm 
           11 : Condenser lens 
           12 : Objective lens 
           13 : Aberration generation lens 
           14 : Aberration adjustment lens 
           15 : Correction lens 
           16 : Second correction lens 
           17 : Trajectory focus lens 
           21  to  28  and  30  to  31 : Deflector 
           35 : Optical element control unit 
           36 : Optical condition storage unit 
           37 : Stigma coil 
           38 : Stage height measurement device 
           51 : Booster electrode 
           52 : Specimen