Abstract:
With conventional optical axis adjustment, a charged particle beam will not be perpendicularly incident to a sample, affecting the measurements of a pattern being observed. Highly precise measurement and correction of a microscopic inclination angle are difficult. Therefore, in the present invention, in a state where a charged particle beam is irradiated toward a sample, a correction of the inclination of the charged particle beam toward the sample is performed on the basis of secondary electron scanning image information from a reflector plate. From the secondary electron scanning image information, a deviation vector for charged particle beam deflectors is adjusted, causing the charged particle beam to be perpendicularly incident to the sample. At least two stages of charged particle beam deflectors are provided.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to a charged particle beam device and is applicable, for example, to a charged particle beam device for correcting charged particle beam inclination. 
       BACKGROUND ART 
       [0002]    Along with a progress of recent semiconductor devices, semiconductor measurement and inspection techniques are becoming increasingly important. A scanning electron microscope represented by a critical dimension-scanning electron microscope (CD-SEM) is a device for observing a pattern formed on a semiconductor device by performing electron beam scanning over a sample and then detecting a secondary electron emitted from the sample. In order to perform highly precise measurement and inspection on the device like this, it is required to set device conditions properly. 
         [0003]    For example, optical axis adjustment of an electron microscope has been disclosed as an optical axis adjustment method using a deflector and a wobbler method in JP 2000-331911 A (PTL 1), JP 2008-084823 A (PTL 2), and JP 2011-054426 A (PTL 3). The deflector deflects an electron beam emitted from an electron source. The wobbler method periodically changes an excitation current of an objective lens. 
       CITATION LIST 
     Patent Literatures 
       [0004]    PTL 1: JP 2000-331911 A 
         [0005]    PTL 2: JP 2008-084823 A 
         [0006]    PTL 3: JP 2011-054426 A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    Recently, device patterns with deep grooves and deep holes are remarkably increasing, making observation of the patterns with a scanning electron microscope very difficult. In observation with a scanning electron microscope, inclined incidence of an electron beam on a sample surface may cause a pattern to be observed unevenly. Inclined incidence of the electron beam would not have much influence on a pattern with a small aspect ratio. However, in a case of patterns with deep grooves and deep holes having the aspect ratio of several tens, such as a NAND flash memory and a contact hole in recent years, inclined incidence of the electron beam would cause unevenness in observation of the pattern, leading to a failure in high-precision measurement. 
         [0008]    Techniques described in PTL 1, PTL 2 and PTL 3 are techniques to perform automatic adjustment of an optical axis of the electron beam so as to achieve a state in which an observed pattern does not move when wobbling of the objective lens is executed. Each of the literatures describes a technique to allow the electron beam to pass through a center of an electron lens included in the electron microscope. 
         [0009]    Unfortunately, however, since a mechanical tolerance is inevitably present in an actual device, a plurality of electron lenses is not arranged concentrically. With such a device state, even when an electron beam is emitted through the center of the objective lens arranged immediately above the sample, the electron beam is incident with inclination to the objective lens. Accordingly, the electron beam is not incident perpendicularly to the sample even at a stage when the electron beam reaches the sample. On a device pattern with the aspect ratio of several tens as described above, when the electron beam has an inclination angle of about 0.10, it might have a non-negligible influence on the measurement. From the above, in observation of patterns with a deep groove and a deep hole in recent years, it is necessary to achieve an optical axis of an electron beam that passes through the center of the objective lens and is incident perpendicularly to the sample. 
         [0010]    An object of the present disclosure is to provide a method to correct a microscopic inclination angle of a charged particle beam. 
         [0011]    Other objects and novel features will become apparent from description and attached drawings of the present disclosure. 
       Solution to Problem 
       [0012]    Typical techniques of the present disclosure will be briefly described as below. 
         [0013]    In a charged particle beam inclination correction method, inclination correction of the charged particle beam is performed based on information, obtained on a reflector plate, regarding a scanned image with an emitted charged particle emitted from a sample. The reflector plate is arranged between a charged particle source and an objective lens to focus the charged particle beam. 
       Advantageous Effects of Invention 
       [0014]    According to the above-described charged particle beam inclination correction method, it is possible to correct a microscopic inclination angle of the charged particle beam. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  is a diagram illustrating a configuration of a scanning electron microscope. 
           [0016]      FIG. 2  is a diagram illustrating inclined incidence of a primary electron beam to a sample. 
           [0017]      FIGS. 3( a ) and 3( b )  are diagrams illustrating dimensional measurement values.  FIG. 3( a )  illustrates a case where the primary electron beam is not inclined.  FIG. 3( b )  illustrates a case where the primary electron beam is inclined. 
           [0018]      FIG. 4  is a diagram illustrating a change in a secondary electron trajectory by an objective lens. 
           [0019]      FIG. 5  is a diagram illustrating a black point image formed by a secondary electron scanning image. 
           [0020]      FIG. 6  is a diagram illustrating deviation of the black point due to inclination of the primary electron beam. 
           [0021]      FIG. 7  is a diagram illustrating a change in the inclination of the primary electron beam by a two-stage deflector. 
           [0022]      FIG. 8  is a diagram illustrating a sequence for correcting inclination of the primary electron beam. 
           [0023]      FIG. 9  is a diagram illustrating correction of inclination of the primary electron beam by measuring a deviation amount of a black point. 
           [0024]      FIG. 10  is a diagram illustrating parallelism adjustment between an objective lens and a sample. 
           [0025]      FIGS. 11( a ) and 11( b )  are diagrams illustrating pattern shading due to inclination of the primary electron beam. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0026]    Hereinafter, embodiments and examples will be described with reference to the drawings. Note that, in the description below, a same sign will be put to same components and repetitive description will be omitted. In the following, a scanning electron microscope (SEM) that performs electron beam scanning over a sample will be described as an example. The technique is not limited to this but is applicable, for example, to other charged particle beam devices including a focused ion beam (FIB) device. The present embodiment describes merely an exemplary scanning electron microscope. The present technique is applicable to a scanning electron microscope having a configuration different from the present embodiment. 
       EMBODIMENT 
       [0027]      FIG. 1  is a diagram illustrating a configuration of a scanning electron microscope.  FIG. 1  illustrates a device state in which mechanical axis deviation is occurring for the purpose of exhibiting a concept of electron beam inclination correction. 
         [0028]    In a scanning electron microscope  101 , an extraction electric field is formed between a field emission cathode  1  and an extraction electrode  2  by a power supply V 1  and a primary electron beam  3  is extracted. The power supply V 1  is controlled by a first high-voltage control circuit  41 . 
         [0029]    The primary electron beam (charged particle beam)  3  extracted in this manner is accelerated by a voltage applied to an acceleration electrode  4  by a power supply V 2 , and undergoes focusing by a condenser lens  5  and scanning deflection by an upper scanning deflector (first deflector)  6  and a lower scanning deflector (second deflector)  7 . Between the acceleration electrode  4  and the condenser lens  5 , an objective aperture  8  for controlling intensity and an aperture angle of the primary electron beam  3  is arranged. Deflection intensity of each of the upper scanning deflector  6  and the lower scanning deflector  7  is adjusted so as to perform two-dimensional scanning over a sample  11  disposed on a holder  10  with a center of an objective lens  9  as a fulcrum. The power supply V 2  is controlled by the first high-voltage control circuit  41 . The condenser lens  5  is controlled by a converging lens control circuit  42 . The upper scanning deflector  6  and the lower scanning deflector  7  are controlled by a first deflection control circuit  45 . The holder  10  is controlled by a sample fine movement control circuit  48 . 
         [0030]    The primary electron beam  3  deflected by the upper scanning deflector  6  and by the lower scanning deflector  7  is further accelerated by an acceleration voltage in a later stage in an acceleration cylinder  12  provided at a passage in the objective lens  9 . The primary electron beam  3  accelerated in the later stage is sharply focused by lens action of the objective lens  9 . A tubular cylinder  13  is grounded and forms an electric field that accelerates the primary electron beam  3 , between the tubular cylinder  13  and the acceleration cylinder  12  to which a voltage is applied by a power supply V 3 . The objective lens  9  is controlled by an objective lens control circuit  46 . The power supply V 3  is controlled by a second high-voltage control circuit  47 . 
         [0031]    Electrons such as secondary electrons or back-scattered electrons emitted from a sample are accelerated in a direction opposite to the direction of the emitted primary electron beam  3  by a negative voltage (retarding voltage) applied to the sample by a power supply V 4  and an electric field formed between the tubular cylinder  13  and the acceleration cylinder  12 . The secondary electrons  14  collide with a reflector plate  15  and are converted into tertiary electrons (charged particles)  16 , which are guided to a detector  17  so as to form an SEM image. The reflector plate  15  has a hole through which the primary electron beam  3  passes, and is arranged between the condenser lens  5  and the objective lens  9 . The power supply V 4  is controlled by a third high-voltage control circuit  49 . The tertiary electron  16  detected at the detector  17  is transmitted to a control device  50  via a signal control circuit. 
         [0032]    Between the condenser lens  5  and the reflector plate  15 , an upper deflector  18  and a lower deflector  19  for deflecting the primary electron beam  3  are arranged. These deflectors have a deflecting action by one or both of a magnetic field and an electric field. Deflection intensity of each of the upper deflector  18  and the lower deflector  19  is adjusted such that the primary electron beam  3  passes through the center of the objective lens  9  and is directed onto the sample  11 . The upper deflector  18  and the lower deflector  19  are adjusted by a second deflection control circuit  43 . 
         [0033]    The electron detected at the detector  17  is amplified by an amplifier  44  and displayed on an image display device  51  in synchronization with a scanning signal supplied to the upper scanning deflector  6  and to the lower scanning deflector  7 . An obtained image is stored in a frame memory  502 . It is possible to configure such that a current or voltage applied to each of components of the scanning electron microscope illustrated in  FIG. 1  is controlled by the control device  50  provided separately from a scanning electron microscope main body  54 . Specifically, the control device  50  applies a current or a voltage to each of the components of the scanning electron microscope via the first high-voltage control circuit  41 , the converging lens control circuit  42 , the second deflection control circuit  43 , the first deflection control circuit  45 , the objective lens control circuit  46 , the second high-voltage control circuit  47 , the third high-voltage control circuit  49 , and the sample fine movement control circuit  48 . The control device  50  includes a CPU  501 , the frame memory  502 , and a storage device  503  for storing programs and data. Programs and data are input into the control device  50  via an input device  52 . 
         [0034]    Next, a case where the primary electron beam is incident with inclination to a sample and a problem caused by this will be described with reference to  FIGS. 2, 3 ( a ), and  3 ( b ). 
         [0035]      FIG. 2  is a diagram illustrating inclined incidence of the primary electron beam to the sample.  FIGS. 3( a ) and 3( b )  are diagrams illustrating dimensional measurement values.  FIG. 3( a )  illustrates a case where the primary electron beam is not inclined.  FIG. 3( b )  illustrates a case where the primary electron beam is inclined. 
         [0036]    An ordinary optical axis adjustment includes execution of wobbling that periodically changes an excitation current of an electron lens such as the condenser lens  5  and the objective lens  9  and then, adjustment is performed so as to achieve a state in which a pattern image of the sample  11  does not move at the time of wobbling. At this time, the primary electron beam  3  passes through the center of each of the electron lenses. Unfortunately, however, since a mechanical tolerance is inevitably present in an actual device, each of the electron lenses is not arranged concentrically. Accordingly, as illustrated in  FIG. 2 , even when the primary electron beam  3  passes through an objective lens center  20  immediately above the sample  11 , the primary electron beam  3  is incident with inclination to the sample  11 . With this configuration, even when the primary electron beam  3  passes through the objective lens center  20 , the primary electron beam  3  is not incident on an intersection of the sample  11  and an optical axis  55  of the objective lens  9 . 
         [0037]    Inclined incidence, in this manner, of the primary electron beam  3  to the sample  11  would cause a problem when a deep groove pattern  21  is measured. Specifically, as illustrated in  FIG. 3( a ) , in a case where the primary electron beam  3  is not inclined, a width of a groove bottom is measured as a dimensional measurement value  22 . In contract, as illustrated in  FIG. 3( b ) , in a case where the primary electron beam  3  is inclined, the pattern is observed unevenly, leading to an observation result with a dimensional measurement value  23 . This means that an obtained dimensional measurement value does not reflect a real width of the groove bottom. 
         [0038]    In a case where the primary electron beam  3  is not inclined and passes through the objective lens center  20 , the primary electron beam  3  reaches a position on the optical axis, and thus, an emission position of the secondary electron  14  is to be on the optical axis. In contrast, in a case where the primary electron beam  3  passes through the objective lens center  20  and reaches at a position off-axis from the optical axis  55 , the primary electron beam  3  is inclined with respect to the sample  11 . This would cause the secondary electron  14  to be emitted from an off-axis position  56  from the optical axis  55 , meaning there is a correlation between the inclination angle of the primary electron beam  3  and the emission position of the secondary electron  14 . 
         [0039]    Hereinafter, a method to correct inclination of the primary electron beam  3  with respect to the sample  11  and a device to achieve the correction will be described with reference to  FIGS. 4 to 6 . 
         [0040]      FIG. 4  is a diagram illustrating a change in a secondary electron trajectory by the objective lens.  FIG. 5  is a diagram illustrating a black point image formed by a secondary electron scanning image.  FIG. 6  is a diagram illustrating a position deviation of the black point due to inclination of the primary electron beam. 
         [0041]    In the present embodiment, inclination correction of the primary electron beam  3  is performed by monitoring the emission position of the secondary electron  14  in observation of a scanning image of the secondary electron  14  on the reflector plate  15 . The reason for performing inclination correction of the primary electron beam  3  with respect to the sample in observation of the scanning image of the secondary electron  14  lies in its capability of performing high-precision inclination angle correction. As illustrated in  FIG. 4 , in a case where the emission position of the secondary electron  14  changes by a distance  24   a  on the sample  11 , trajectories of the secondary electron  14  before/after the change would be a trajectory  25   a  and a trajectory  25   b  respectively, due to a lens action of the objective lens  9 . Along with this, the distance  24   a  would be enlarged to be a distance  24   b  when it is projected on the reflector plate  15 . Accordingly, it is possible to perform high-precision observation of inclination of the primary electron beam  3 . 
         [0042]    Similarly to the primary electron beam  3 , the secondary electron  14  emitted from the sample  11  undergoes a scanning deflection action of the upper scanning deflector  6  and the lower scanning deflector  7 . In observation of a low-magnification SEM image with an increased scanning deflection amount in each of the upper scanning deflector  6  and the lower scanning deflector  7 , wide-range scanning of the secondary electron  14  is performed on the reflector plate  15 , and as a result, a scanning image on the reflector plate  15  with the secondary electron  14  would be observed on the detector  17 , as illustrated in  FIG. 5 . A black point  26  within a screen corresponds to an opening that allows the primary electron beam  3  to pass through, provided on the reflector plate  15 . At an opening portion, a luminance is low because the secondary electron  14  passes through the reflector plate  15  and thus is not detected. In other words, the reflector plate  15  has an opening that allows the secondary electron  14  to pass through. Although not illustrated in  FIG. 1 , in a case where the detector  17  is arranged at a position closer to the condenser lens  5  rather than to the reflector plate  15 , a contrast is inversed to cause the scanning image on the reflector plate  15  to be observed as a while point image. The following will be described on an assumption that the black point image is obtained. 
         [0043]    The secondary electron  14  generated on the optical axis and the secondary electron  14  generated at an off-axis position have different trajectories. Accordingly, the position of a black point of an obtained black point image on the reflector plate  15  changes depending on whether the primary electron beam  3  is inclined or not. In a case where the primary electron beam  3  is not inclined, the secondary electron  14  is emitted from a position on the optical axis. The secondary electron  14  emitted perpendicularly undergoes deflection by the objective lens  9 , and thus, forms a black point  27  at a center of an SEM image as illustrated in  FIG. 6 . In contrast, in a case where the primary electron beam  3  is inclined, the secondary electron is emitted from an off-axis position. In this case, even when emission is performed perpendicularly, the secondary electron undergoes deflection by the objective lens  9  as illustrated in  FIG. 4 , and thus, forms a black point  28  at a position deviating from the center of the SEM image. 
         [0044]    It is understandable, from the above, that in a state where the primary electron beam  3  passes through the center of the objective lens  9  and is not inclined with respect to the sample  11 , the black point position does not move but only the size of the black point changes when wobbling of the objective lens  9  is executed. Accordingly, in order to achieve a state where the primary electron beam  3  is not inclined, it may be appropriate to change the trajectory of the primary electron beam  3  using the upper deflector  18  and the lower deflector  19  while executing wobbling of the objective lens  9  for that period, and to set, onto the device, conditions of the upper deflector  18  and the lower deflector  19  that minimize the amount of movement of the black point position. Wobbling of the objective lens  9  is executed by changing the excitation current of the objective lens  9 . The deflector to change the trajectory of the primary electron beam  3  would be satisfactory if it includes at least two stages of the upper deflector  18  and the lower deflector  19 . Alternatively, the deflector may have three or more stages. 
         [0045]    Note that a technique to change the black point position is not limited to wobbling of the objective lens  9 . Another technique may be used as long as it can change the trajectory of the secondary electron  14 . For example, it is allowable to execute wobbling of a retarding voltage (deceleration voltage) applied to the sample  11  or a voltage of the acceleration cylinder  12  (acceleration cylinder voltage). 
         [0046]    In summary, in the present embodiment, a two-stage charged particle beam deflector is arranged between a charged particle source and an objective lens used to focus a charged particle beam. The charged particle beam deflector deflects a charged particle beam emitted from the charged particle source. A current or voltage with an inverted phase is applied to the two-stage charged particle beam deflector so as to swing back the charged particle beam to cause the charged particle beam to pass through the objective lens center. At this state, a secondary electron emitted from a sample by charged particle beam irradiation is deflected by a lens effect of the objective lens and when reaching a reflector plate arranged between the charged particle source and the objective lens. At this time, wobbling of the objective lens is executed while a deviation vector of the charged particle beam is being changed by the two-stage charged particle beam deflector, and a secondary electron scanning image is observed on the reflector plate at this time. Under conditions of the two-stage charged particle beam deflector under which the amount of movement of a reflector plate scanning image caused by an objective wobbler is minimized, a device state allowing the charged particle beam to pass through the objective lens center and to be incident perpendicularly to the sample is achieved. 
         [0047]    According to the embodiment, by observing a secondary electron trajectory, it is possible to correct an inclination angle of the charged particle beam with respect to the sample. A change of the trajectory of the secondary electron is enlarged by the objective lens in observation on the reflector plate, it is possible to correct the inclination angle with high precision. Furthermore, there is no need to perform a preliminary measurement of the inclination angle. Even in a case where the inclination angle is changed by charged electricity, it is possible to allow the charged particle beam to be incident perpendicularly to the sample. 
       Example 1 
       [0048]      FIG. 7  is a diagram illustrating a change in the inclination of the primary electron beam by a two-stage deflector.  FIG. 8  is a diagram illustrating a sequence for correcting inclination of the primary electron beam.  FIG. 9  is a diagram illustrating a deviation amount of the black point position when wobbling of the objective lens  9  is executed. 
         [0049]    With reference to  FIGS. 7 and 8 , an exemplary flow of primary electron beam inclination correction in a case where the centers of the condenser lens  5  and the objective lens  9  deviate due to mechanical axis deviation  53 , as illustrated in  FIG. 1 , will be described. In ordinary adjustment to cause the primary electron beam to pass through the electron lens center, the primary electron beam would have an axis that passes through the center of each of the condenser lens  5  and the objective lens  9 . Accordingly, the trajectory would be like a primary electron beam trajectory  29  and be incident with inclination to the sample  11 . At a stage where the primary electron beam passes through the condenser lens  5 , the beam has deviated by a distance of  57  with respect to the optical axis  55 . 
         [0050]    In order to correct the inclination angle with respect to the sample  11 , the upper deflector  18  and the lower deflector  19  are started to operate (step S 1  in  FIG. 8 ). A current or voltage with an inversed phase is applied to the upper deflector  18  and the lower deflector  19 . The primary electron beam deflected by the upper deflector  18  changes from the trajectory  29  to a trajectory  30 , and then, is swung back by the lower deflector  19  in an inversed direction to be a trajectory  31 . At this time, an upper/lower stage ratio of deflection intensities of the upper deflector  18  and the lower deflector  19  is adjusted such that the primary electron beam passes through the center of the objective lens  9  (step S 2 ). 
         [0051]    For adjustment of the upper/lower stage ratio, it may be appropriate to use an ordinary axis adjustment technique of achieving a state in which a pattern on the sample  11  does not move when wobbling of the objective lens  9  is executed (steps S 3  and S 4 ). For example, it is possible to fix the deflection intensity of any one of the upper deflector  18  and the lower deflector  19  and change the deflection intensity of the other deflector so as to set, as a condition, the upper/lower stage ratio that achieves a state in which a wobbling image does not move (step S 5 ). Note that the magnitude of applied current or voltage to each of the upper deflector  18  and the lower deflector  19  when the upper/lower stage ratio is obtained may be arbitrarily determined as long as it is within a range to allow observation of the SEM image. 
         [0052]    However, performing adjustment of the upper/lower stage ratio of the upper deflector  18  and the lower deflector  19  alone would leave the primary electron beam in a state of still being incident with inclination to the sample  11 . Inclination angle correction is, therefore, performed by changing the deviation vector of each of the upper deflector  18  and the lower deflector  19  while maintaining the upper/lower stage ratio at this time (step S 6 ). 
         [0053]    Whether the primary electron beam is incident perpendicularly to the sample is determined by executing wobbling of the objective lens  9  while changing the deviation vector of each of the upper deflector  18  and the lower deflector  19  (step S 7 ), and observing the black point image at that time (step S 8 ). The horizontal axis in  FIG. 9  corresponds to the deviation vector of the upper deflector  18  and the lower deflector  19 .  FIG. 9  illustrates an exemplary measurement in which the deviation amount of the black point is measured while, at first, a phase of the deviation vector alone is changed for 360°, and then, the magnitude of the deviation vector is changed. Accordingly, an interval between the peaks or between the bottoms corresponds to a deviation phase of 360°. A plurality of peaks and bottoms exists because the magnitude of the deviation vector has been changed. Each of peaks  91 ,  92 , and  93  has different magnitude of deflection. 
         [0054]    In  FIG. 9 , the deviation vector that minimizes the deviation amount of the black point is determined (step S 9 ). Herein, the deviation amount of the black point at the time of wobbling is minimized in the deviation vector indicated by a broken line  32 . Accordingly, when the setting of the deviation vector of each of the upper deflector  18  and the lower deflector  19  has been performed according to the condition of the broken line  32  (step S 10 ) and when the primary electron beam has been deflected with this state, it is expected that the inclination angle of the primary electron beam with respect to the sample  11  has been corrected, namely, the primary electron beam is incident perpendicularly to the sample. 
         [0055]    As described above, according to the present embodiment, it is possible to set, with high precision, conditions of the primary electron beam that passes through the center of the objective lens and is incident perpendicularly to the sample. Furthermore, even in a case where an inclination of the primary electron beam is changed due to an influence of charged electricity, or the like, it is possible to correct the inclination including the influence of the charged electricity. Accordingly, this correction method can be a significant technique in SEM observation of a sample with deep grooves and deep holes having possibility of strong charged electricity. 
       Example 2 
       [0056]      FIG. 10  is a diagram illustrating parallelism adjustment between the objective lens and the sample. 
         [0057]    In order to reduce the deviation amount of the black point in the deviation vector illustrated by the broken line  32  in  FIG. 9  to zero, it is required to arrange the objective lens  9  and the sample  11  in parallel with each other. When the objective lens  9  and the sample  11  are not arranged in parallel with each other, the secondary electron would be deflected when reaching the reflector plate  15 . To cope with this, as illustrated in  FIG. 10 , it is possible to configure such that an inclination mechanism may be provided on the holder  10  so as to operate as indicated by an arrow  94 . This operation can be used to set the condition to a sample inclination condition in which the deviation amount of the black point becomes zero in the deviation vector indicated by the broken line  32 . With this configuration, it is possible adjust the parallelism between the objective lens  9  and the sample  11  with high precision. 
       Example 3 
       [0058]      FIGS. 11( a ) and 11( b )  are diagrams illustrating pattern shading due to inclination of the primary electron beam.  FIG. 11( a )  is a sectional view of the sample and  FIG. 11( b )  is an observation pattern of the sample. 
         [0059]    By using the technique of the present embodiment, it is possible to set the conditions not only for correcting inclination of an electron beam but also, conversely, for allowing the electron beam to have a large inclination. For this, it may be appropriate, in  FIG. 9 , to set a deviation vector of the upper deflector  18  and the lower deflector  19  to the peak conditions having an increased deviation amount of the black point. By causing the electron beam  3  to be incident to the sample  11  with large inclination in a case where there is unevenness in height on the observation pattern, it is possible to provide shading (gradation) as illustrated in a pattern shading  33  generated by inclination of the primary electron beam illustrated in  FIG. 11( b ) . This makes it possible to apply the technique to unevenness determination of the sample. 
         [0060]    The present invention made by the present inventor has been described in detail according to the embodiments and the examples. It is understandable that the present invention is not limited to the above-described embodiments and examples but can also be modified in a variety of forms. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  field emission cathode 
           2  extraction electrode 
           3  primary electron beam 
           4  acceleration electrode 
           5  condenser lens 
           6  upper scanning deflector 
           7  lower scanning deflector 
           8  objective aperture 
           9  objective lens 
           10  holder 
           11  sample 
           12  acceleration cylinder 
           13  tubular cylinder 
           14  secondary electron 
           15  reflector plate 
           16  tertiary electron 
           17  detector 
           18  upper deflector 
           19  lower deflector 
           20  objective lens center 
           21  deep groove pattern 
           22  dimensional measurement value of groove bottom width when primary electron beam is not inclined 
           23  dimensional measurement value of groove bottom width when primary electron beam is inclined 
           24   a  deviation amount of secondary electron emitting position on sample 
           24   b  deviation amount of secondary electron emitting position on reflector plate 
           25   a  trajectory of secondary electron emitted from off-axis position 
           25   b  trajectory of secondary electron emitted from off-axis position 
           26  black point 
           27  black point position when primary electron beam is not inclined 
           28  black point position when primary electron beam is inclined 
           29  primary electron beam trajectory with mechanical axis deviation 
           30  trajectory of primary electron beam deflected by upper deflector 
           31  trajectory primary electron beam swung back by lower deflector 
           32  upper/lower deflector condition for correcting inclination of primary electron beam with respect to sample 
           33  pattern shading due to inclination of primary electron beam 
           41  first high-voltage control circuit 
           42  converging lens control circuit 
           43  second deflection control circuit 
           44  amplifier 
           45  first deflection control circuit 
           46  objective lens control circuit 
           47  second high-voltage control circuit 
           48  sample fine movement control circuit 
           49  third high-voltage control circuit 
           50  control device 
           501  CPU 
           502  frame memory 
           503  storage device 
           51  image display device 
           52  input device 
           53  mechanical axis deviation 
           55  optical axis 
           56  off-axis position from optical axis 
           57  distance of deviation with respect to optical axis 
           91 ,  92 ,  93  peak 
           94  arrow 
         V 1 , V 2 , V 3 , V 4  power supply