Patent Publication Number: US-2022230837-A1

Title: Multi-beam image acquisition apparatus and multi-beam image acquisition method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2021-008258 filed on Jan. 21, 2021 in Japan, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a multi-beam image acquisition apparatus and a multi-beam image acquisition method. For example, the invention relates to an image acquisition method of a multi-beam inspection apparatus that performs pattern inspection using a secondary electron image caused by emission of multiple primary electron beams. 
     Related Art 
     In recent years, with the increase in the integration and capacity of a large-scale integrated circuit (LSI), the circuit pattern linewidth required for semiconductor devices has become narrower and narrower. In addition, improving the yield is indispensable for manufacturing the LSI, which requires a high manufacturing cost. However, as represented by 1-gigabit class DRAM (random access memory), the patterns configuring the LSI are on the order of submicron to nanometer. In recent years, with the decrease in the dimensions of LSI patterns formed on a semiconductor wafer, dimensions that should be detected as pattern defects are also extremely small. Therefore, it is necessary to improve the accuracy of a pattern inspection apparatus for inspecting the defects of ultrafine patterns transferred onto the semiconductor wafer. 
     For example, the inspection apparatus irradiates an inspection target substrate with multiple beams using electron beams and detects secondary electrons corresponding to each beam emitted from the inspection target substrate to capture a pattern image. In addition, there is known a method of performing an inspection by comparing a captured measurement image with design data or a measurement image obtained by capturing the same pattern on the substrate. For example, there is a “die to die inspection” in which pieces of measurement image data obtained by imaging the same pattern at different locations on the same substrate are compared with each other or a “die to database inspection” in which design image data (reference image) is generated based on pattern-designed design data and the design image data is compared with a measurement image that serves as measurement data obtained by imaging the pattern. The captured images are transmitted to a comparison circuit as measurement data. The comparison circuit aligns the images with each other and then compares the measurement data and the reference data according to an appropriate algorithm. When the measurement data and the reference data do not match each other, the comparison circuit determines that there is a pattern defect. 
     Here, when an inspection image is acquired by using multiple electron beams, it is required to reduce the pitch between beams in order to realize high resolution. If the pitch between beams is reduced, there is a problem that crosstalk between beams is likely to occur in the detection system. Specifically, when an inspection image is acquired by using multiple electron beams, an E×B (E cross B) separator is arranged on the trajectory of the primary electron beam to separate the secondary electron beam from the primary electron beam. The E×B separator is arranged at the field conjugate position of the primary electron beam where the influence of E×B is small. Then, the primary electron beam is imaged on the target object surface by the objective lens. Between the primary electron beam and the secondary electron beam, the energy of emitted electrons incident on the target object surface and the energy of the generated secondary electrons are different. Therefore, when the primary electron beam forms an intermediate field on the E×B separator, the secondary electron beam forms an intermediate field in front of the E×B separator after passing through the objective lens. For this reason, the secondary electron beam spreads on the E×B separator without forming an intermediate field. As a result, the secondary electrons separated by the E×B separator continue to spread in the detection optical system. Therefore, there is a problem that the aberration occurring in the detection optical system may increase and multiple secondary electron beams may overlap each other on the detector and accordingly, it may be difficult to detect the multiple secondary electron beams individually. In other words, there is a problem that crosstalk between beams is likely to occur. Such a problem is not limited to the inspection apparatus, and may occur similarly in all apparatuses for acquiring an image using multiple electron beams. 
     Here, a technique is disclosed in which a Wien filter configured by a multi-pole lens having a four-stage configuration for correcting on-axis chromatic aberration is arranged in the secondary electron optics away from the primary electron optics and the on-axis chromatic aberration of the secondary electrons after being separated is corrected (see, for example, JP-A-2006-244875). 
     BRIEF SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a multi-beam image acquisition apparatus, includes: 
     a stage on which a substrate is placed; 
     an objective lens configured to image multiple primary electron beams on the substrate by using the multiple primary electron beams; 
     a separator configured to have two or more electrodes for forming an electric field and two or more magnetic poles for forming a magnetic field and configured to separate multiple secondary electron beams emitted due to the substrate being irradiated with the multiple primary electron beams from trajectories of the multiple primary electron beams by the electric field and the magnetic field formed; 
     a deflector configured to deflect the multiple secondary electron beams separated; 
     a lens arranged between the objective lens and the deflector and configured to image the multiple secondary electron beams at a deflection point of the deflector; and 
     a detector configured to detect the deflected multiple secondary electron beams. 
     According to another aspect of the present invention, a multi-beam image acquisition method, includes: 
     imaging multiple primary electron beams on a substrate placed on a stage by using an objective lens; 
     separating multiple secondary electron beams emitted due to the substrate being irradiated with the multiple primary electron beams from trajectories of the multiple primary electron beams by an electric field and a magnetic field formed by using a separator having two or more electrodes for forming an electric field and two or more magnetic poles for forming a magnetic field; 
     deflecting a separated multiple secondary electron beams by using a deflector; 
     imaging the multiple secondary electron beams at a deflection point of the deflector by using a lens arranged between the objective lens and the deflector; and 
     detecting a deflected multiple secondary electron beams by using a detector and outputting data of a secondary electron image based on a signal of the detected multiple secondary electron beams. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a configuration diagram showing the configuration of a pattern inspection apparatus according to Embodiment 1; 
         FIG. 2  is a conceptual diagram showing the configuration of a shaping aperture array substrate according to Embodiment 1; 
         FIGS. 3A and 3B  are diagrams showing an example of the trajectory of multiple secondary electron beams and an example of the trajectory of multiple primary electron beams in a comparative example of Embodiment 1; 
         FIGS. 4A and 4B  are diagrams showing an example of the trajectory of multiple secondary electron beams and an example of the trajectory of multiple primary electron beams in Embodiment 1; 
         FIG. 5  is a diagram showing a relationship between the amount of secondary electrons and energy in Embodiment 1; 
         FIG. 6  is a diagram showing an example of the trajectory of the secondary electron beam between the deflection point and the detection surface in Embodiment 1; 
         FIG. 7  is a diagram showing the 40° deflection trajectory of multiple secondary electron beams in Embodiment 1; 
         FIG. 8  is a diagram showing an example of the distribution of secondary electrons detected by 40° deflection in Embodiment 1; 
         FIG. 9  is a diagram showing the 50° deflection trajectory of multiple secondary electron beams in Embodiment 1; 
         FIG. 10  is a diagram showing an example of the distribution of secondary electrons detected by 50° deflection in Embodiment 1; 
         FIG. 11  is a diagram showing an example of the beam diameter of multiple secondary electron beams on the detection surface of a multi-detector in Embodiment 1 and the comparative example; 
         FIG. 12  is a diagram showing an example of a plurality of chip regions formed on a semiconductor substrate in Embodiment 1; 
         FIG. 13  is a diagram for explaining image acquisition processing in Embodiment 1; 
         FIG. 14  is a configuration diagram showing the configuration of a pattern inspection apparatus according to a modification example of Embodiment 1; and 
         FIG. 15  is a diagram showing an example of the trajectory of multiple secondary electron beams in the modification example of Embodiment 1. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, in an embodiment, an apparatus and a method capable of reducing the aberration occurring in a detection optical system and separating each secondary electron beam of multiple secondary electron beams on the detection surface will be described. 
     In addition, in the embodiment, a multi-electron beam inspection apparatus will be described below as an example of a multi-electron beam image acquisition apparatus. However, the image acquisition apparatus is not limited to the inspection apparatus, and may be any apparatus that acquires an image by using multiple beams. 
     Embodiment 1 
       FIG. 1  is a configuration diagram showing the configuration of a pattern inspection apparatus according to Embodiment 1. In  FIG. 1 , an inspection apparatus  100  for inspecting a pattern formed on a substrate is an example of a multi-electron beam inspection apparatus. The inspection apparatus  100  includes an image acquisition mechanism  150  and a control system circuit  160  (control unit). The image acquisition mechanism  150  includes an electron beam column  102  (electron optical column), an inspection room  103 , a detection circuit  106 , a chip pattern memory  123 , a stage drive mechanism  142 , and a laser length measurement system  122 . An electron gun assembly  201 , an illumination lens  202 , a shaping aperture array substrate  203 , an electromagnetic lens  205 , a batch deflector  212 , a limited aperture substrate  213 , electromagnetic lenses  206  and  207 , a main deflector  208 , a sub-deflector  209 , a beam separator  214 , an electromagnetic lens  217 , a deflector  218 , an electromagnetic lens  224 , a deflector  226 , and a multi-detector  222  are arranged in the electron beam column  102 . 
     A primary electron optics  151  is configured by the electron gun assembly  201 , the electromagnetic lens  202 , the shaping aperture array substrate  203 , the electromagnetic lens  205 , the batch deflector  212 , the limited aperture substrate  213 , the electromagnetic lens  206 , the electromagnetic lens  207  (objective lens), the main deflector  208 , and the sub-deflector  209 . In addition, a secondary electron optics  152  is configured by the electromagnetic lens  207  (objective lens), the electromagnetic lens  217 , the beam separator  214 , the deflector  218 , the electromagnetic lens  224 , and the deflector  226 . The electromagnetic lens  217  is arranged between the electromagnetic lens  207  (objective lens) and the deflector  218  with respect to the trajectory of the secondary electron. In the example of  FIG. 1 , the electromagnetic lens  217  is arranged between the electromagnetic lens  207  (objective lens) and the beam separator  214 . 
     A stage  105  that can move at least in the X and Y directions is arranged in the inspection room  103 . A substrate  101  (target object) to be inspected is arranged on the stage  105 . Examples of the substrate  101  include an exposure mask substrate and a semiconductor substrate, such as a silicon wafer. When the substrate  101  is a semiconductor substrate, a plurality of chip patterns (wafer dies) are formed on the semiconductor substrate. When the substrate  101  is an exposure mask substrate, a chip pattern is formed on the exposure mask substrate. The chip pattern is configured by a plurality of figures. By exposing and transferring the chip pattern formed on the exposure mask substrate to the semiconductor substrate a plurality of times, a plurality of chip patterns (wafer dies) are formed on the semiconductor substrate. Hereinafter, the case where the substrate  101  is a semiconductor substrate will be mainly described. The substrate  101  is arranged on the stage  105 , for example, with the pattern forming surface facing upward. In addition, a mirror  216  that reflects a laser beam for laser length measurement emitted from the laser length measurement system  122  arranged outside the inspection room  103  is arranged on the stage  105 . 
     In addition, the multi-detector  222  is connected to the detection circuit  106  outside the electron beam column  102 . The detection circuit  106  is connected to the chip pattern memory  123 . 
     In the control system circuit  160 , a control computer  110  that controls the entire inspection apparatus  100  is connected to a position circuit  107 , a comparison circuit  108 , a reference image generation circuit  112 , a stage control circuit  114 , a lens control circuit  124 , a blanking control circuit  126 , a deflection control circuit  128 , a retarding control circuit  130 , a storage device  109  such as a magnetic disk drive, a monitor  117 , a memory  118 , and a printer  119  through a bus  120 . In addition, the deflection control circuit  128  is connected to DAC (digital-to-analog conversion) amplifiers  144 ,  146 ,  148 . The DAC amplifier  146  is connected to the main deflector  208 , and the DAC amplifier  144  is connected to the sub-deflector  209 . The DAC amplifier  148  is connected to the deflector  218 . 
     In addition, the chip pattern memory  123  is connected to the comparison circuit  108 . In addition, the stage  105  is driven by the stage drive mechanism  142  under the control of the stage control circuit  114 . In the stage drive mechanism  142 , for example, a drive system such as a three-axis (X-Y-θ) motor for driving in the X, Y, and θ directions in the stage coordinate system is configured, so that the stage  105  can move in the X, Y, and θ directions. As these X motor, Y motor, and θ motor (not shown), for example, step motors can be used. The stage  105  can be moved in the horizontal direction and the rotational direction by a motor of each axis of X, Y, and θ. Then, the moving position of the stage  105  is measured by the laser length measurement system  122  and supplied to the position circuit  107 . The laser length measurement system  122  measures the position of the stage  105  based on the principle of the laser interferometry by receiving light reflected from the mirror  216 . In the stage coordinate system, for example, X, Y, and θ directions of the primary coordinate system are set with respect to the plane perpendicular to the optical axis of multiple primary electron beams  20 . 
     The electromagnetic lens  202 , the electromagnetic lens  205 , the electromagnetic lens  206 , the electromagnetic lens  207 , the electromagnetic lens  217 , the electromagnetic lens  224 , and the beam separator  214  are controlled by the lens control circuit  124 . In addition, the batch deflector  212  is configured by two or more electrodes, and each of the electrodes is controlled by the blanking control circuit  126  through a DAC amplifier (not shown). The sub-deflector  209  is configured by four or more electrodes, and each of the electrodes is controlled by the deflection control circuit  128  through the DAC amplifier  144 . The main deflector  208  is configured by four or more electrodes, and each of the electrodes is controlled by the deflection control circuit  128  through the DAC amplifier  146 . The deflector  218  is a two-stage deflector configured by four or more electrodes, and each of the electrodes is controlled by the deflection control circuit  128  through the DAC amplifier  148 . In addition, the deflector  226  is configured by four or more electrodes, and each of the electrodes is controlled by the deflection control circuit  128  through a DAC amplifier (not shown). The retarding control circuit  130  applies a desired retarding potential to the substrate  101  to adjust the energy of the multiple primary electron beams  20  emitted to the substrate  101 . 
     A high-voltage power supply circuit (not shown) is connected to the electron gun assembly  201 , and a group of electrons emitted from the cathode are accelerated by the application of an acceleration voltage from the high-voltage power supply circuit between a filament and an extraction electrode (not shown) in the electron gun assembly  201 , the application of a voltage to a predetermined extraction electrode (Wenert), and the heating of the cathode at a predetermined temperature, and are emitted as electron beam  200 . 
     Here,  FIG. 1  describes components necessary for explaining Embodiment 1. The inspection apparatus  100  may usually include other necessary components. 
       FIG. 2  is a conceptual diagram showing the configuration of a shaping aperture array substrate according to Embodiment 1. In  FIG. 2 , on the shaping aperture array substrate  203 , holes (openings)  22  having a two-dimensional shape of m 1  columns wide (x direction))×n 1  rows long (y direction)) (m 1  and n 1  are integers of 2 or more) are formed at predetermined arrangement pitches in the x and y directions. In the example of  FIG. 2 , a case where 23×23 holes (openings)  22  are formed is shown. The holes  22  are formed in rectangles having the same dimension and shape. Alternatively, the holes  22  may be circles having the same outer diameter. Parts of the electron beam  200  pass through the plurality of holes  22  to form the multiple primary electron beams  20 . The shaping aperture array substrate  203  is an example of a multi-beam forming mechanism for forming multiple primary electron beams. 
     The image acquisition mechanism  150  acquires an image to be inspected of a figure from the substrate  101  on which the figure is formed by using multiple beams using electron beams. Hereinafter, the operation of the image acquisition mechanism  150  in the inspection apparatus  100  will be described. 
     The electron beam  200  emitted from the electron gun assembly  201  (emission source) are refracted by the electromagnetic lens  202  to illuminate the entire shaping aperture array substrate  203 . As shown in  FIG. 2 , a plurality of holes  22  (openings) are formed on the shaping aperture array substrate  203 , and a region including all of the plurality of holes  22  is illuminated with the electron beam  200 . Parts of the electron beam  200  emitted to the positions of the plurality of holes  22  pass through the plurality of holes  22  on the shaping aperture array substrate  203  to form the multiple primary electron beams  20 . 
     The formed multiple primary electron beams  20  are refracted by the electromagnetic lens  205  and the electromagnetic lens  206 , pass through the beam separator  214 , which is arranged at the intermediate field (field conjugate position: I. I. P.) of each of the multiple primary electron beams  20 , while repeating an intermediate image and crossover, and travel to the electromagnetic lens  207 . In addition, scattered beams can be shielded by arranging the limited aperture substrate  213  having a limited passage hole near the crossover position of the multiple primary electron beams  20 . In addition, all of the multiple primary electron beams  20  can be blanked by collectively deflecting all of the multiple primary electron beams  20  using the batch deflector  212  and shielding all of the multiple primary electron beams  20  with the limited aperture substrate  213 . 
     When the multiple primary electron beams  20  are incident on the electromagnetic lens  207  (objective lens), the electromagnetic lens  207  focuses the multiple primary electron beams  20  on the substrate  101 . In other words, the electromagnetic lens  207  irradiates the substrate  101  with the multiple primary electron beams  20 . The multiple primary electron beams  20  focused on the surface of the substrate  101  (target object) by the objective lens  207  are collectively deflected by the main deflector  208  and the sub-deflector  209 , and are emitted to the irradiation position of each beam on the substrate  101 . In this manner, the primary electron optics  151  irradiates the surface of the substrate  101  with multiple primary electron beams. 
     When the multiple primary electron beams  20  are emitted to a desired position of the substrate  101 , a group of secondary electrons (multiple secondary electron beams  300 ) including reflected electrons, which correspond to the multiple primary electron beams  20 , are emitted from the substrate  101  due to the emission of the multiple primary electron beams  20 . 
     The multiple secondary electron beams  300  emitted from the substrate  101  pass through the electromagnetic lens  207  and travel to the beam separator  214 . 
     Here, the beam separator  214  (E×B separator) has a plurality (two or more) of magnetic poles using a coil and a plurality (two or more) of electrodes. Then, a directional magnetic field is generated by the plurality of magnetic poles. Similarly, a directional electric field is generated by the plurality of electrodes. Specifically, the beam separator  214  generates an electric field and a magnetic field so as to be perpendicular to each other on a plane perpendicular to a direction in which the central beam of the multiple primary electron beams  20  travels (central axis of trajectory). The electric field applies a force in the same direction regardless of the traveling direction of the electron. On the other hand, the magnetic field applies a force according to the Fleming&#39;s left-hand rule. Therefore, the direction of the force acting on the electron can be changed depending on the electron incidence direction. In the multiple primary electron beams  20  incident on the beam separator  214  from above, the force due to the electric field and the force due to the magnetic field cancel each other out. Therefore, the multiple primary electron beams  20  travel straight downward. On the other hand, in the multiple secondary electron beams  300  incident on the beam separator  214  from below, both the force due to the electric field and the force due to the magnetic field act in the same direction. Therefore, the multiple secondary electron beams  300  are bent obliquely upward and separated from the trajectory of the multiple primary electron beams  20 . 
     The multiple secondary electron beams  300 , which are bent obliquely upward and separated from the multiple primary electron beams  20 , are guided to the multi-detector  222  by the secondary electron optics  152 . Specifically, the multiple secondary electron beams  300  separated from the multiple primary electron beams  20  are further bent by being deflected by the deflector  218 , and are projected onto the multi-detector  222  while being refracted in the focusing direction by the electromagnetic lens  224  at a position away from the trajectory of the multiple primary electron beams  20 . In other words, the deflector  218  deflects the multiple secondary electron beams  300  so that the central axis trajectory of the multiple secondary electron beams  300  separated by the beam separator  214  is directed toward the multi-detector  222 . Then, the multiple secondary electron beams  300  whose central axis trajectory is directed toward the multi-detector  222  are projected onto the multi-detector  222  by the electromagnetic lens  224 . The multi-detector  222  (multiple secondary electron beams detector) detects the refracted and projected multiple secondary electron beams  300 . The multi-detector  222  has a plurality of detection elements (for example, diode type two-dimensional sensors (not shown)). Then, each of the multiple primary electron beams  20  collides with a detection element corresponding to each of the multiple secondary electron beams  300  on the detection surface of the multi-detector  222  to generate electrons, thereby generating secondary electron image data for each pixel. The intensity signal detected by the multi-detector  222  is output to the detection circuit  106 . 
       FIGS. 3A and 3B  are diagrams showing an example of the trajectory of multiple secondary electron beams and an example of the trajectory of multiple primary electron beams in a comparative example of Embodiment 1.  FIG. 3A  shows an example of the trajectory of multiple secondary electron beams in the comparative example.  FIG. 3B  shows an example of the trajectory of multiple primary electron beams in the comparative example. The multiple primary electron beams  20  spread through the beam separator  214  arranged at the field conjugate position, and the trajectory of the multiple primary electron beams  20  is bent in the focusing direction by the electromagnetic lens  207  (objective lens) to form an image on the surface of the substrate  101 .  FIG. 3B  shows the trajectory of the central primary electron beam  21  among the multiple primary electron beams  20 . In addition, the energy at the time of emission of the central secondary electron beam  301  corresponding to the central primary electron beam  21 , among the multiple secondary electron beams  300  emitted from the substrate  101 , is smaller than the incidence energy of the central primary electron beam  21  to the substrate  101 . For this reason, under the condition that the primary electron beam is imaged on the surface of the beam separator  214  and the electromagnetic lens  207  focuses the multiple primary electron beams  20  on the substrate  101 , as shown in  FIG. 3A , the trajectory of the central secondary electron beam  301  is bent in the focusing direction by the electromagnetic lens  207  (objective lens), but an intermediate image plane  600  (imaging point) is formed at a position before reaching the beam separator  214 . Thereafter, the central secondary electron beam  301  travels to the beam separator  214  while spreading. Then, in the comparative example, the central secondary electron beam  301  travels to the deflector  218  while further spreading. As a result, the beam diameter D 1  of the central secondary electron beam  301  increases at the position of the deflector  218 . Similarly, the beam diameters of the other secondary electron beams increase. The larger the beam diameter D 1  of each secondary electron beam, the larger the aberration occurring in the deflector  218 . For this reason, even if an attempt is made to make the secondary electron beams after passing through the deflector  218  converge by the lens work of the electromagnetic lens  224 , the beam diameter cannot be reduced on the detection surface of the multi-detector  222 , and the secondary electron beams overlap each other. Therefore, separation between the secondary electron beams may be difficult. As a result, it becomes difficult to detect the secondary electron beams individually. In addition, when the objective lens gives priority to the focusing of the primary electron beam, it is difficult in principle to align the focus of the secondary electron beam with the position of the deflector  218 . 
       FIGS. 4A and 4B  are diagrams showing an example of the trajectory of multiple secondary electron beams and an example of the trajectory of multiple primary electron beams in Embodiment 1.  FIG. 4A  shows an example of the trajectory of multiple secondary electron beams in Embodiment 1.  FIG. 4B  shows an example of the trajectory of multiple primary electron beams in Embodiment 1. In Embodiment 1, as shown in  FIG. 4B , the multiple primary electron beams  20  spread through the beam separator  214  arranged at the field conjugate position and are refracted by the electromagnetic lens  217 . The multiple primary electron beams  20  continue to spread toward the electromagnetic lens  207  (objective lens) even though the trajectory of the multiple primary electron beams  20  is slightly changed by the electromagnetic lens  217 , and the trajectory is bent in the focusing direction by the electromagnetic lens  207  (objective lens) to form an image on the surface of the substrate  101 .  FIG. 4B  shows the trajectory of the central primary electron beam  21  among the multiple primary electron beams  20 . Under the condition that such a primary electron beam is imaged on the surface of the beam separator  214  and the electromagnetic lens  207  focuses the multiple primary electron beams  20  on the substrate  101 , as in the comparative example, the trajectory of the central secondary electron beam  301  is bent in the focusing direction by the electromagnetic lens  207  (objective lens), but an intermediate image plane  600  (imaging point) is formed at a position before reaching the beam separator  214 . 
     Here, in Embodiment 1, the trajectory is bent in the focusing direction by the electromagnetic lens  207  (objective lens) to form the intermediate image plane  600  (imaging point), and the trajectory of the multiple secondary electron beams in the divergence direction is bent in the focusing direction by the electromagnetic lens  217 . At that time, the electromagnetic lens  217  forms an intermediate image plane  601  (imaging point) of the multiple secondary electron beams at the deflection point of the deflector  218 . As described above, the multiple secondary electron beams  300  are refracted by the electromagnetic lens  217  before being separated from the trajectory of the multiple primary electron beams  20 , and as a result, an image of the multiple secondary electron beams  300  is formed on the deflection point of the deflector  218 . The deflection point may be, for example, the intersection of an extension line of a central axis trajectory of the multiple secondary electron beams  300  before deflection and an extension line of a central axis trajectory of the multiple secondary electron beams  300  after deflection by a deflector. In this manner, as shown in  FIG. 4A , the beam diameter of the central secondary electron beam  301  can be reduced at the position of the deflection point in the deflector  218 . Thus, it is possible to suppress the aberration occurring in the deflector  218 . Therefore, the beam diameter can be reduced on the detection surface of the multi-detector  222  by the lens work of the electromagnetic lens  224  after the secondary electron beams pass through the deflector  218 , and an image can be formed on the detection surface of the multi-detector  222  in a state in which the secondary electron beams are separated. As a result, it is possible to detect the secondary electron beams individually. Therefore, the deflection point of the deflector  218  is conjugated to the surface of the substrate  101  and the detection surface of the multi-detector  222 . 
     In addition, it is preferable that the deflector  218  is formed so that its cross section cut by the plane including the central axis of the trajectory of the secondary electron is an arc shape. However, the invention is not limited thereto. The deflector  218  may be formed so that its cross section cut by the plane including the central axis of the trajectory of the secondary electron is a rectangular shape. In Embodiment 1, the position of the midpoint of the length of the central axis in the deflector  218  through which the central secondary electron beam  301  passes is assumed to be the deflection point (or the deflection center). 
       FIG. 5  is a diagram showing a relationship between the amount of secondary electrons and energy in Embodiment 1. In  FIG. 5 , the vertical axis indicates the amount of secondary electrons and the horizontal axis indicates the magnitude of energy. Secondary electrons having different energies are emitted from the substrate  101 . In the example of  FIG. 5 , the energy of the secondary electron has a width of 0&lt;secondary electron &lt;E 0 . In Embodiment 1, the electromagnetic lens  217  is controlled so that the imaging point of the secondary electrons with energy E indicating the peak in the energy distribution shown in  FIG. 5  is formed at the deflection point of the deflector  218 . 
       FIG. 6  is a diagram showing an example of the trajectory of the secondary electron beam between the deflection point and the detection surface in Embodiment 1. In  FIG. 6 , the amount of deflection of the secondary electron by the deflector  218  changes according to the magnitude of its own energy. As shown in the example of  FIG. 6 , a secondary electron  301 - 2  (solid line) having low energy is bent more than a secondary electron  301 - 1  (dotted line) having high energy. Here, at a position that is not conjugated to the deflection point of the deflector  218 , as shown in  FIG. 6 , the trajectory of the secondary electron deviates depending on the magnitude of energy and accordingly, the image is blurred. On the other hand, in Embodiment 1, since the deflection point of the deflector  218  is conjugated to the detection surface of the multi-detector  222 , the secondary electron returns to the center of the trajectory on the detection surface of the multi-detector  222  regardless of the magnitude of energy. Therefore, it is possible to suppress the blurring of the secondary electron beam on the detection surface of the multi-detector  222 . 
       FIG. 7  is a diagram showing the 40° deflection trajectory of multiple secondary electron beams in Embodiment 1. In the example of  FIG. 7 , a case is shown in which the multiple secondary electron beams  300  are deflected by, for example, 40° by the deflector  218 . 
       FIG. 8  is a diagram showing an example of the distribution of secondary electrons detected by 40° deflection in Embodiment 1. In the example of  FIG. 8 , a case of detecting the 3×3 multiple secondary electron beams  300  is shown. By arranging the deflector  218  at a position where the deflection point of the deflector  218  is conjugated to the surface of the substrate  101  and the detection surface of the multi-detector  222 , as shown in  FIG. 8 , the multiple secondary electron beams  300  can be separated and detected on the detection surface of the multi-detector  222  when the multiple secondary electron beams  300  are deflected by, for example, 40°. 
       FIG. 9  is a diagram showing the 50° deflection trajectory of multiple secondary electron beams in Embodiment 1. In the example of  FIG. 9 , a case is shown in which the multiple secondary electron beams  300  are deflected by, for example, 50° by the deflector  218 . 
       FIG. 10  is a diagram showing an example of the distribution of secondary electrons detected by 50° deflection in Embodiment 1. In the example of  FIG. 10 , a case of detecting the 3×3 multiple secondary electron beams  300  is shown. By arranging the deflector  218  at a position where the deflection point of the deflector  218  is conjugated to the surface of the substrate  101  and the detection surface of the multi-detector  222 , as shown in  FIG. 10 , the multiple secondary electron beams  300  can be separated and detected on the detection surface of the multi-detector  222  when the multiple secondary electron beams  300  are deflected by, for example, 50°. 
     As described above, in Embodiment 1, since the deflector  218  is arranged at a position where the deflection point of the deflector  218  is conjugated to the surface of the substrate  101  and the detection surface of the multi-detector  222 , the multiple secondary electron beams  300  can be separated and detected even when the amount of deflection by the deflector  218  is changed. In addition,  FIGS. 7 and 9  show a case of changing the deflection angle by changing the length of the deflector  218 , but the invention is not limited thereto. The same effect can be obtained by changing the applied voltage using the deflector  218  of the same length. Even when the voltage applied to the deflector  218  is changed, the multiple secondary electron beams  300  can be separated and detected by arranging the deflector  218  at the position where the deflection point of the deflector  218  is conjugated to the surface of the substrate  101  and the detection surface of the multi-detector  222 . 
       FIG. 11  is a diagram showing an example of the beam diameter of multiple secondary electron beams on the detection surface of a multi-detector in Embodiment 1 and the comparative example. In the comparative example described above, since the aberration in the deflector  218  increases, the beam diameter of each beam  15  of the multiple secondary electron beams  300  on the detection surface of the multi-detector  222  increases. As a result, as shown in  FIG. 11 , the beams  15  may overlap each other. On the other hand, according to Embodiment 1, since the aberration in the deflector  218  can be suppressed, the beam diameter of each beam  14  of the multiple secondary electron beams  300  on the detection surface of the multi-detector  222  can be reduced. As a result, as shown in  FIG. 11 , it is possible to prevent the beams  14  from overlapping each other. Therefore, the secondary system can have high resolution at the position of the multi-detector  222  (separation on the detection surface is possible). 
     After adjusting the electron optics as described above, inspection processing on the substrate to be inspected is performed. 
       FIG. 12  is a diagram showing an example of a plurality of chip regions formed on a semiconductor substrate in Embodiment 1. In  FIG. 12 , a plurality of chips (wafer dies)  332  are formed in a two-dimensional array in an inspection region  330  of a semiconductor substrate (wafer)  101 . A mask pattern for one chip formed on an exposure mask substrate is transferred to each chip  332  so as to be reduced to, for example, ¼ by an exposure apparatus (stepper) (not shown). 
       FIG. 13  is a diagram for explaining image acquisition processing in Embodiment 1. As shown in  FIG. 13 , the region of each chip  332  is divided into a plurality of stripe regions  32  with a predetermined width in the y direction, for example. The scanning operation of the image acquisition mechanism  150  is performed, for example, for each stripe region  32 . For example, while moving the stage  105  in the −x direction, the scanning operation on the stripe region  32  is performed relatively in the x direction. Each stripe region  32  is divided into a plurality of rectangular regions  33  in the longitudinal direction. The movement of the beam to the target rectangular region  33  is performed by collectively deflecting all of the multiple primary electron beams  20  using the main deflector  208 . 
     In the example of  FIG. 13 , for example, a case of 5×5 multiple primary electron beams  20  is shown. An irradiation region  34  that can be irradiated by one emission of the multiple primary electron beams  20  is defined by (x-direction size obtained by multiplying the x-direction beam-to-beam pitch of the multiple primary electron beams  20  on the surface of the substrate  101  by the number of x-direction beams)×(y-direction size obtained by multiplying the y-direction beam-to-beam pitch of the multiple primary electron beams  20  on the surface of the substrate  101  by the number of y-direction beams). The irradiation region  34  is a field of view of the multiple primary electron beams  20 . Then, each primary electron beam  10  forming the multiple primary electron beams  20  is emitted into a sub-irradiation region  29  surrounded with the x-direction beam-to-beam pitch and the y-direction beam-to-beam pitch in which the beam itself is located, thereby scanning (scanning operation) the inside of the sub-irradiation region  29 . Each primary electron beam  10  is responsible for any of the sub-irradiation regions  29  that are different from each other. Then, each primary electron beam  10  is emitted to the same position in the corresponding sub-irradiation region  29 . The sub-deflector  209  (first deflector) collectively deflects the multiple primary electron beams  20  to scan the surface of the substrate  101  on which patterns are formed with the multiple primary electron beams  20 . In other words, the movement of the primary electron beam  10  in the sub-irradiation region  29  is performed by collectively deflecting all of the multiple primary electron beams  20  using the sub-deflector  209 . This operation is repeated to sequentially irradiate the inside of one sub-irradiation region  29  with one primary electron beam  10 . 
     It is preferable that the width of each stripe region  32  is set to a size similar to the y-direction size of the irradiation region  34  or a size reduced by the scan margin. In the example of  FIG. 13 , a case where the irradiation region  34  has the same size as the rectangular region  33  is shown. However, the invention is not limited thereto. The irradiation region  34  may be smaller than the rectangular region  33 . Alternatively, the irradiation region  34  may be larger than the rectangular region  33 . Then, each primary electron beam  10  forming the multiple primary electron beams  20  is emitted into the sub-irradiation region  29  where the beam itself is located, thereby scanning (scanning operation) the inside of the sub-irradiation region  29 . Then, after the end of the scanning of one sub-irradiation region  29 , the irradiation position is moved to the adjacent rectangular region  33  in the same stripe region  32  by collective deflection of all of the multiple primary electron beams  20  using the main deflector  208 . This operation is repeated to irradiate the inside of the stripe region  32  in order. After the end of the scanning of one stripe region  32 , the irradiation region  34  is moved to the next stripe region  32  by the movement of the stage  105  and/or collective deflection of all of the multiple primary electron beams  20  using the main deflector  208 . As described above, by emitting each primary electron beam  10 , the scanning operation for each sub-irradiation region  29  and the acquisition of a secondary electron image are performed. By combining the secondary electron images for the respective sub-irradiation regions  29 , a secondary electron image of the rectangular region  33 , a secondary electron image of the stripe region  32 , or a secondary electron image of the chip  332  is formed. In addition, when actually performing image comparison, the sub-irradiation region  29  in each rectangular region  33  is further divided into a plurality of frame regions  30 , and frame images  31  that are measurement images for the respective frame regions  30  are compared. In the example of  FIG. 13 , a case is shown in which the sub-irradiation region  29  scanned with one primary electron beam  10  is divided into four frame regions  30  that are formed by equally dividing the sub-irradiation region  29  in the x and y directions, for example. 
     Here, when the substrate  101  is irradiated with the multiple primary electron beams  20  while the stage  105  continuously moves, a tracking operation by collective deflection of the main deflector  208  is performed so that the irradiation position of the multiple primary electron beams  20  follows the movement of the stage  105 . Therefore, the emission positions of the multiple secondary electron beams  300  change from moment to moment with respect to the central axis of the trajectory of the multiple primary electron beams  20 . Similarly, when scanning the inside of the sub-irradiation region  29 , the emission position of each secondary electron beam changes from moment to moment in the sub-irradiation region  29 . For example, the deflector  226  collectively deflects the multiple secondary electron beams  300  so that each secondary electron beam whose emission position has changed is emitted into the corresponding detection region of the multi-detector  222 . Apart from the deflector  226 , it is also preferable to arrange an alignment coil or the like in the secondary electron optics to correct such an emission position change. 
     As described above, the image acquisition mechanism  150  performs the scanning operation for each stripe region  32 . As described above, the multiple primary electron beams  20  are emitted, and the multiple secondary electron beams  300  emitted from the substrate  101  due to the emission of the multiple primary electron beams  20  form an intermediate field in the deflector  218  and at the same time, are deflected by the deflector  218  and then detected by the multi-detector  222 . The detected multiple secondary electron beams  300  may include reflected electrons. Alternatively, the reflected electrons may diverge while moving through the secondary electron optics and may not reach the multi-detector  222 . Then, a secondary electron image based on the signal of the detected multiple secondary electron beams  300  is acquired. Specifically, detection data of the secondary electrons (measurement image data, secondary electron image data, or image data to be inspected) for each pixel in each sub-irradiation region  29  detected by the multi-detector  222  is output to the detection circuit  106  in the order of measurement. In the detection circuit  106 , analog detection data is converted into digital data by an A/D converter (not shown) and stored in the chip pattern memory  123 . Then, the obtained measurement image data is transmitted to the comparison circuit  108  together with information indicating each position from the position circuit  107 . 
     On the other hand, the reference image generation circuit  112  generates a reference image corresponding to the frame image  31  for each frame region  30  based on design data that is the basis of a plurality of figures formed on the substrate  101 . Specifically, the reference image generation circuit  112  operates as follows. First, design pattern data is read out from the storage device  109  through the control computer  110 , and each figure defined in the read design pattern data is converted into binary or multi-valued image data. 
     As described above, the figures defined in the design pattern data include, for example, a basic figure of a rectangle or a triangle. For example, figure data is stored in which the shape, size, position, and the like of each figure are defined by information such as the coordinates (x, y) at the reference position of the figure, the length of the side, and a figure code that serves as an identifier for identifying the figure type such as a rectangle or a triangle. 
     When the design pattern data that serves as the figure data is input to the reference image generation circuit  112 , the design pattern data is expanded into data for each figure, and the figure code, the figure dimension, and the like indicating the figure shape of the figure data are analyzed. Then, this is expanded into binary or multi-valued design pattern image data as a pattern arranged in a square having a grid with a predetermined quantization dimension as a unit, and is output. In other words, the design data is read, the occupancy rate of the figure in the design pattern is calculated for each square created by virtually dividing the inspection region into squares each having a predetermined dimension as a unit, and n-bit occupancy rate data is output. For example, it is preferable to set one square as one pixel. Then, assuming that one pixel has a resolution of 1/2 8  (=1/256), a small region of 1/256 is allocated to the region of the figure arranged in the pixel and the occupancy rate in the pixel is calculated. Then, 8-bit occupancy rate data is obtained. Such a square (inspection pixel) may be matched with each pixel of the measurement data. 
     Then, the reference image generation circuit  112  performs filtering processing on the design image data of the design pattern, which is the image data of the figure, by using a predetermined filter function. In this manner, the design image data whose image intensity (shade value) is image data on the design side of the digital value can be matched with image generation characteristics obtained by emission of the multiple primary electron beams  20 . The image data for each pixel of the generated reference image is output to the comparison circuit  108 . 
     The comparison circuit  108  aligns the frame image  31  (first image) serving as an image to be inspected and the reference image (second image) corresponding to the frame image in units of sub-pixels for each frame region  30 . For example, the alignment may be performed by the method of least squares. 
     Then, the comparison circuit  108  compares the frame image  31  (first image) with the reference image (second image). The comparison circuit  108  compares the frame image  31  (first image) with the reference image (second image) for each pixel  36  according to a predetermined determination condition. For example, the comparison circuit  108  determines whether or not there is a defect, such as a shape defect. For example, if the gradation value difference for each pixel  36  is larger than a determination threshold value Th, it is determined that there is a defect. Then, the comparison result is output. The comparison result may be output to the storage device  109 , the monitor  117 , or the memory  118 , or may be output from the printer  119 . 
     In addition to the die to database inspection described above, it is also preferable to perform a die to die inspection in which pieces of measurement image data obtained by imaging the same pattern at different locations on the same substrate are compared with each other. Alternatively, the inspection may be performed using only the self-measured image. 
       FIG. 14  is a configuration diagram showing the configuration of a pattern inspection apparatus according to a modification example of Embodiment 1.  FIG. 14  is the same as  FIG. 1  except that the electromagnetic lens  217  is arranged between the beam separator  214  and the deflector  218  with respect to the secondary electron trajectory. 
       FIG. 15  is a diagram showing an example of the trajectory of multiple secondary electron beams in the modification example of Embodiment 1. In  FIG. 15 , the multiple secondary electron beams  300  whose trajectory is bent in the focusing direction by the electromagnetic lens  207  (objective lens) to form the intermediate image plane  600  (imaging point) travel to the beam separator  214  while spreading. Then, the multiple secondary electron beams  300  are separated from the multiple primary electron beams  20  by the beam separator  214 , and travel to the electromagnetic lens  217  while spreading. Then, the trajectory of the multiple secondary electron beams in the divergence direction is bent in the focusing direction by the electromagnetic lens  217 . At that time, the electromagnetic lens  217  forms the intermediate image plane  601  (imaging point) at the deflection point of the deflector  218  with the multiple secondary electron beams. In this manner, as shown in  FIG. 15 , the beam diameter of each secondary electron beam can be reduced at the position of the deflection point in the deflector  218 . In the example of  FIG. 15 , the trajectory of the central secondary electron beam  301  of the multiple secondary electron beams  300  is shown. Thus, it is possible to suppress the aberration occurring in the deflector  218 . Therefore, the beam diameter can be reduced on the detection surface of the multi-detector  222  by the lens work of the electromagnetic lens  224  after the secondary electron beams pass through the deflector  218 , and an image can be formed on the detection surface of the multi-detector  222  in a state in which the secondary electron beams are separated. As a result, it is possible to detect the secondary electron beams individually. Therefore, the deflection point of the deflector  218  is conjugated to the surface of the substrate  101  and the detection surface of the multi-detector  222 . 
     As described above, according to Embodiment 1, it is possible to reduce the aberration occurring in the detection optical system and separate each secondary electron beam of the multiple secondary electron beams on the detection surface. Therefore, it is possible to reduce the pitch between beams. 
     In the above description, the series of “˜circuits” include a processing circuit, and the processing circuit includes an electric circuit, a computer, a processor, a circuit board, a quantum circuit, a semiconductor device, and the like. In addition, a common processing circuit (same processing circuit) may be used for the respective “˜circuits”. Alternatively, different processing circuits (separate processing circuits) may be used. A program for executing the processor and the like may be recorded on a record carrier body, such as a magnetic disk drive, a magnetic tape device, an FD, or a ROM (read only memory). For example, the position circuit  107 , the comparison circuit  108 , the reference image generation circuit  112 , and the like may be configured by at least one processing circuit described above. 
     The embodiment has been described above with reference to specific examples. However, the invention is not limited to these specific examples. For example, the electromagnetic lens  217  may be an electrostatic lens. 
     In addition, the description of parts that are not directly required for the description of the invention, such as the apparatus configuration or the control method, is omitted. However, the required apparatus configuration, control method, and the like can be appropriately selected and used. 
     In addition, all multi-electron beam image acquisition apparatuses and multi-electron beam image acquisition methods that include the elements of the invention and can be appropriately redesigned by those skilled in the art are included in the scope of the invention. 
     Additional advantages and modification will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.