Patent Publication Number: US-2023154723-A1

Title: Systems and methods for real time stereo imaging using multiple electron beams

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of U.S. application 62/787,098 which was filed on Dec. 31, 2018, and which is incorporated herein in its entirety by reference. 
    
    
     TECHNICAL FIELD 
     The embodiments provided herein disclose a charged-particle beam inspection system, and more particularly systems and methods of real-time stereo imaging of structures of a sample using multiple charged-particle beams. 
     BACKGROUND 
     In manufacturing processes of integrated circuits (ICs), unfinished or finished circuit components are inspected to ensure that they are manufactured according to design and are free of defects. Inspection systems utilizing optical microscopes or charged particle (e.g., electron) beam microscopes, such as a scanning electron microscope (SEM) can be employed. IC components are manufactured by placing multiple layers onto one another to build the IC. Accordingly, it is necessary to be able to inspect the three-dimensional structure of the IC components as they are manufactured for defects. 
     Moving stages that secure the IC chip in place can be used to allow a charged-particle beam to capture images of different sides of structures of an IC chip, but these methods are slow and prone to error. Some related art systems adjust a single beam to attempt to inspect sides of structures of the IC chip, but these systems that use a single beam suffer from aberrations from manipulation of the charged-particle beam particularly when trying to image IC components at larger angles that provide better inspection images. 
     Accordingly, methods and systems for creating large-angle, stereo or three-dimensional inspection images of IC chips in real time are desired. 
     SUMMARY 
     Embodiments consistent with the disclosure herein include methods and a multi-beam apparatus configured to emit multiple charged-particle beams for imaging a top of and a side of a structure of a sample, the apparatus including: a deflector array including a first deflector and configured to receive a first charged-particle beam and a second charged-particle beam; a blocking plate configured to block one of the first charged-particle beam and the second charged-particle beam; and a controller having circuitry and configured to change the configuration of the apparatus to transition between a first mode and a second mode. The first mode and the second mode can be configured wherein: in the first mode, the deflector array is configured to direct the second charged-particle beam to image the top of the structure, and the blocking plate is configured to block the first charged-particle beam; and in the second mode, the first deflector is configured to deflect the first charged-particle beam to image the side of the structure, and the blocking plate is configured to block the second charged-particle beam. 
     In another embodiment the methods and apparatus include an objective lens that can be an electrostatic lens, a magnetic lens, or a combination of both. In some embodiments, the objective lens is a moveable objective lens. 
     In yet additional embodiments, the methods and apparatus include a condenser lens that can be an electrostatic lens, a magnetic lens, or a combination of both. The condenser lens can be movable and rotatable to axially align with any of the at least three charged-particle beams. 
     In some embodiments, the first charged-particle beam and second charged-particle beam are focused using separate objective lenses and in some embodiments the apparatus of the first charged-particle beam and second charged-particle beam are focused using separate condenser lenses 
     In yet another embodiment the methods and apparatus include a deflector array that includes a second deflector configured to deflect the second charged-particle beam into the blocking plate when operating the first mode. In some embodiments, the deflector array is configured to receive a third charged-particle beam and includes a third deflector configured to deflect the third charged-particle beam into the blocking plate when operating in either the first or second modes. 
     In yet another embodiment of the methods and apparatus, The controller is configured to change the configuration of the apparatus to transitions between the first mode, the second mode, and a third mode, wherein in the third mode, the third deflector is configured to direct the third charged-particle beam to image a side different from the side of the structure, and the blocking plate is configured to block the first and second charged-particle beams. 
     In yet additional embodiments of the methods and apparatus, the controller is further configured to acquire an image from each portion of the structure and combine the acquired images into a stereo image of the structure. 
     Embodiments consistent with the present disclosure further include a scanning electron microscope (SEM) system, comprising: a charged particle source for providing charged particles to enable a plurality of beamlets, a first beamlet being an axial beam configured to perpendicularly impact a structure of a sample; a plurality of deflectors, wherein a subset of the deflectors are configured to deflect a subset of the beamlets to cause each of the subset of beamlets to impact the structure at a tilt relative to the axial beam; and a plurality of condensers, wherein each of a subset of the condensers has an axis tilted to coincide with a path of one of the subset of beamlets. 
     In some embodiments the SEM system, further comprises a Moving Objective Lens (MOL) that can be configured to shift the focusing field of the objective lens. In some embodiments, the MOL is configured to shift the focusing field of the objective lens to coincide, at different times, with each of the beamlets. 
     In yet another embodiment, the SEM system includes an objective lens that is one of an electrostatic lens, a magnetic lens, or both. In some embodiments, each of the condensers of the SEM system is an electrostatic lens, a magnetic lens, or both. 
     In yet another embodiment, the SEM system further comprises a controller having circuitry and configured to process images based on the plurality of beamlets to enable a real time display of a three-dimensional representation of the structure. 
     In some embodiments of the SEM system, each of the subset of deflectors is configured to deflect a different beamlet of the subset of beamlets to cause each beamlet of the subset of beamlets to impact the structure at a different tilt relative to the axial beam. 
     In yet another embodiment, the SEM system further includes a blocking mechanism configured to prevent all but one of the beamlets from impacting the structure. 
    
    
     
       BRIEF DESCRIPTION OF FIGURES 
         FIG.  1    is a schematic diagram illustrating an exemplary electron beam inspection (EBI) system, consistent with embodiments of the present disclosure. 
         FIG.  2    is a schematic diagram illustrating an exemplary electron beam tool that can be a part of the exemplary electron beam inspection system of  FIG.  1   , consistent with embodiments of the present disclosure. 
         FIGS.  3 A- 3 C  are schematic diagrams illustrating an exemplary electron beam tool that can be a part of the exemplary electron beam inspection system of  FIG.  1   , consistent with embodiments of the present disclosure. 
         FIG.  4    illustrates a cross-section view of an exemplary lens structure of a charged-particle beam system, consistent with embodiments of the present disclosure. 
         FIG.  5    is a process flow chart of an exemplary method of real-time stereo imaging using multiple electron beams, consistent with embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings in which the same numbers in different drawings represent the same or similar elements unless otherwise represented. The implementations set forth in the following description of exemplary embodiments do not represent all implementations consistent with the invention. Instead, they are merely examples of apparatuses and methods consistent with aspects related to the invention as recited in the appended claims. For example, although some embodiments are described in the context of utilizing electron beams, the disclosure is not so limited. Other types of charged particle beams may be similarly applied. Furthermore, other imaging systems may be used, such as optical imaging, photo detection, x-ray detection, etc. 
     The enhanced computing power of electronic devices, while reducing the physical size of the devices, can be accomplished by significantly increasing the packing density of circuit components such as, transistors, capacitors, diodes, etc. on an IC chip. For example, in a smart phone, an IC chip (which is the size of a thumbnail) may include over 2 billion transistors, the size of each transistor being less than 1/1000th of a human hair. Not surprisingly, semiconductor IC manufacturing is a complex process, with hundreds of individual steps. Errors in even one step have the potential to dramatically affect the functioning of the final product. Even one “killer defect” can cause device failure. The goal of the manufacturing process is to improve the overall yield of the process. For example, for a 50-step process to get 75% yield, each individual step must have a yield greater than 99.4%, and if the individual step yield is 95%, the overall process yield drops to 7%. 
     While high process yield is desirable in an IC chip manufacturing facility, it is also essential to maintain a high wafer throughput, defined as the number of wafers processed per hour. High process yields, and high wafer throughput can be impacted by the presence of defects, especially when operator intervention is involved. Thus, detection and identification of micro and nano-sized defects by inspection tools (such as, a SEM) may be essential for maintaining high yields and low cost. Moreover, as IC chips are manufactured, multiple layers are placed on top of each other during the manufacturing process. Accordingly, it is also important to be able to inspect the three-dimensional structure of the IC chip in an efficient manner to that can maintain high process yields and high wafer throughput. 
     In a charged-particle beam imaging or inspection system, such as, for example, a SEM, the charged-particle beam may be focused on the wafer to produce an image of the layout for the IC chip. As more and more layers are deposited onto the IC chip, charged-particle beams focused on the sides of structures of the IC chip can provide a three-dimensional view of the components on the IC chip for inspection. To accomplish this, the charged-particle beam can be directed at the IC chip at an angle that is relative to a line perpendicular to the surface of the chip. 
     But directing a charged-particle at such an angle can be accomplished in different ways. Some methods use a single charged-particle beam and rotate the stage that holds the IC chip so that the beam can image side walls of structures of the IC chip as the stage rotates. However, this method is slow and requires complex mechanical movement and adjustment of the stage which prevents the use of this method for real-time inspection. Other systems include deflecting a single-charged particle beam to illuminate the sides of structures an IC chip. But these methods only work for small inspection angles and provide significantly degraded results as the inspection angle increases. None of the present systems provide for real time stereo or three-dimensional imaging while also providing effective imaging resolution at larger imaging angles (e.g., over 30). 
     To meet the need for high resolution, three-dimensional imaging at larger imaging angles and in real-time, the charged-particle beam system can utilize multiple particle beams for imaging the different parts of the IC chip. For example, different charged-particle beams can be used to image the top, left, right, front, and back of the IC chip or structures on the IC chip. Images for these various portions of the IC chip can be taken rapidly in sequence and combined to create the three-dimensional image. Because of the speed at which the system can take and combine the different images, the system can still operate in real time for the purposes of IC chip inspection even when imaging each surface of the IC chip sequentially. By operating in real time, the feedback produced by the inspection system can be captured and processed without slowing the manufacturing process and reducing wafer throughput. 
     A first charged-particle beam can be emitted directly toward the IC chip as shown in  FIG.  3 A  by electron beam  305 . This particle beam can pass through a condenser lens and through an optical lens that focuses the charged particle beam on the top of the chip providing a top-down view of the IC chip. Additional charged-particle beams can be emitted by the inspection tool. These beams can be initially angled away from the IC chip as shown by the electron beams  303  and  307  in  FIGS.  3 A- 3 C . Deflectors can then deflect the charged-particle beams back toward the IC chip. The charged-particle beams can pass through both a condenser lens and an objective lens that focus the charged-particle beam onto a side of structures of the IC chip as shown in  FIGS.  3 B and  3 C . 
     The condenser lens can be moved and rotated to align axially with the charged-particle beam it is focusing, as shown in  FIGS.  3 A- 3 C . This alignment eliminates the introduction of off-axis aberration from the condenser lens. In some instances, instead of moving, the condenser lens can include separate lenses—one for each charged-particle beam that is oriented to axially align with that particular beam, using, for example, the lens structure shown in  FIG.  4   . The objective lens can also move side to side so that the center of the objective lens can align with the charged-particle it is focusing. By aligning the center of the objective lens with the charged-particle beam, inspection system can reduce the amount of off-axis aberration introduced by the objective lens. As with the condenser lens, in some instances multiple objective lenses can be used with each one being axially aligned with one of the charged-particle beams to prevent off-axis aberration. 
     Because multiple charged-particle beams illuminating the IC chip at the same time would distort the acquired image, a blocking plate and deflectors can be used to block all but one of the charged-particle beams at any point in time. In this way, an inspection tool can use a sequence of configurations (e.g., a sequence of each of the configurations shown in  FIGS.  3 A,  3 B, and  3 C ) to capture sequential images of the IC chip. After capturing the first image, the inspection tool can adjust the configuration to capture the next image. This process can continue until the inspection tool has captured all the necessary images for creating the three-dimensional image of the IC chip. For the example configuration shown in  FIGS.  3 A- 3 C , the inspection tool can sequentially capture three images of the IC chip—one image of the top of the IC chip and an image of each of two opposite sides of structures of the IC chip. These images can then be combined to create the three-dimensional image of the IC chip. 
     The inspection tool can utilize electrostatic or magnetic condenser and objective lenses to focus the electron beam. Additionally, separate lenses can be used to eliminate the time necessary to move and position the lenses each time a different charged-particle beam is used for imaging. The response time of the deflectors and the lenses are fast enough that the sequence of images needed for the inspection of the IC chip can be captured in real time in order to maintain high wafer throughput. 
     Relative dimensions of components in drawings may be exaggerated for clarity. Within the following description of drawings, the same or like reference numbers refer to the same or like components or entities, and only the differences with respect to the individual embodiments are described. 
     As used herein, unless specifically stated otherwise, the term “or” encompasses all possible combinations, except where infeasible. For example, if it is stated that a database may include A or B, then, unless specifically stated otherwise or infeasible, the database may include A, or B, or A and B. As a second example, if it is stated that a database may include A, B, or C, then, unless specifically stated otherwise or infeasible, the database may include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C. 
     Reference is now made to  FIG.  1   , which illustrates an exemplary electron beam inspection system consistent with embodiments of the present disclosure. Although the present disclosure refers to an electron beam inspection system, it is understood that the present disclosure can apply more generally to charged-particle beam inspection systems and the use description of electron beams is exemplary. In some embodiments, electron beam inspection system is an electron beam inspection (EBI) system  100 . In some embodiments, electron beam inspection as shown in  FIG.  1   , electron beam inspection system  1  includes a main chamber  10 , a load/lock chamber  20 , a charged-particle beam tool  100 , and an equipment front end module (EFEM)  30 . Electron beam tool  100  is located within main chamber  10 . 
     EFEM  30  includes a first loading port  30   a  and a second loading port  30   b . EFEM  30  may include additional loading port(s). First loading port  30   a  and second loading port  30   b  receive wafer front opening unified pods (FOUPs) that contain wafers (e.g., semiconductor wafers or wafers made of other material(s)) or samples to be inspected (a sample can be a wafer or other component, or can be a portion of the wafer or the other component, and the terms sample and wafer can both refer to a same component, can refer to different portions of a same component, or can refer to different components). One or more robot arms (not shown) in EFEM  30  transport the wafers to load/lock chamber  20 . 
     Load/lock chamber  20  is connected to a load/lock vacuum pump system (not shown), which removes gas molecules in load/lock chamber  20  to reach a first pressure below the atmospheric pressure. After reaching the first pressure, one or more robot arms (not shown) transport the wafer from load/lock chamber  20  to main chamber  10 . Main chamber  10  is connected to a main chamber vacuum pump system (not shown), which removes gas molecules in main chamber  10  to reach a second pressure below the first pressure. After reaching the second pressure, the wafer is subject to inspection by electron beam tool  100 . While the present disclosure provides examples of main chamber  10  housing an electron beam inspection system, it should be noted that aspects of the disclosure in their broadest sense, are not limited to a chamber housing an electron beam inspection system. Rather, it is appreciated that the foregoing principles may be applied to other chambers as well. 
     A controller  50  is electronically connected to electron beam tool  100 . Controller  50  may be a computer configured to execute various controls of the electron beam inspection system. Controller  50  may also include a processing circuitry configured to execute various signal and image processing functions. While controller  50  is shown in  FIG.  1    as being outside of the structure that includes main chamber  10 , load lock chamber  20 , and EFEM  30 , it is appreciated that controller  50  may be part of the structure. While the present disclosure provides examples of main chamber  10  housing an electron beam inspection tool  100 , it should be noted that aspects of the disclosure in their broadest sense are not limited to a chamber housing an electron beam inspection tool. Rather, it is appreciated that the foregoing principles may also be applied to other tools that operate under the second pressure. 
     Reference is now made to  FIG.  2   , which illustrates a schematic diagram illustrating an exemplary electron beam tool or, in some embodiments, an electron-beam tool, that can be a part of the exemplary electron beam inspection system  1  of  FIG.  1   , consistent with embodiments of the present disclosure. Electron beam tool  100  (also referred to herein as apparatus  100 ) comprises an electron beam source  101 , a gun aperture plate  171  with a gun aperture  103 , a condenser lens  110 , a source conversion unit  120 , a primary projection optical system  130 , a sample stage (not shown in  FIG.  2   ), a secondary optical system  150 , and an electron detection device  140 . Primary projection optical system  130  can comprise an objective lens  131 . Electron detection device  140  can comprise a plurality of detection elements  140 _ 1 ,  140 _ 2 , and  140 _ 3 . Beam separator  160  and deflection scanning unit  132  can be placed inside primary projection optical system  130 . It may be appreciated that other commonly known components of apparatus  100  may be added/omitted as appropriate. 
     Electron source  101 , gun aperture plate  171 , condenser lens  110 , source conversion unit  120 , beam separator  160 , deflection scanning unit  132 , and primary projection optical system  130  can be aligned with a primary optical axis  100 _ 1  of apparatus  100 . Secondary optical system  150  and electron detection device  140  can be aligned with a secondary optical axis  150 _ 1  of apparatus  100 . 
     Electron source  101  can comprise a cathode, an extractor or an anode, wherein primary electrons can be emitted from the cathode and extracted or accelerated to form a primary electron beam  102  that forms a crossover (virtual or real)  101   s . Primary electron beam  102  can be visualized as being emitted from crossover  101   s.    
     Source conversion unit  120  can comprise an image-forming element array (not shown in  FIG.  2   ). The image-forming element array can comprise a plurality of micro-deflectors or micro-lenses to form a plurality of parallel images (virtual or real) of crossover  101   s  with a plurality of beamlets of primary electron beam  102 .  FIG.  2    shows three beamlets  102 _ 1 ,  102 _ 2 , and  102 _ 3  as an example, and it is appreciated that the source conversion unit  120  can handle any number of beamlets. Controller  50  of  FIG.  1    may be connected to various parts of charged particle beam inspection system  100  of  FIG.  1   , such as source conversion unit  120 , electron detection device  140 , primary projection optical system  130 , or a motorized stage (not shown). In some embodiments, as explained in further details below, controller  50  may perform various image and signal processing functions. Controller  50  may also generate various control signals to govern operations of the charged particle beam inspection system. 
     Condenser lens  110  can focus primary electron beam  102 . The electric currents of beamlets  102 _ 1 ,  102 _ 2 , and  102 _ 3  downstream of source conversion unit  120  can be varied by adjusting the focusing power of condenser lens  110  or by changing the radial sizes of the corresponding beam-limit apertures within the beam-limit aperture array. Objective lens  131  can focus beamlets  102 _ 1 ,  102 _ 2 , and  102 _ 3  onto a sample  190  for inspection and can form three probe spots  102 _ 1   s ,  102 _ 2   s , and  102 _ 3   s  on surface of sample  190 . Gun aperture plate  171  can block off peripheral electrons of primary electron beam  102  not in use to reduce Coulomb effect. The Coulomb effect can enlarge the size of each of probe spots  102 _ 1   s ,  102 _ 2   s , and  102 _ 3   s , and therefore deteriorate inspection resolution. 
     Beam separator  160  can be a beam separator of Wien filter type comprising an electrostatic deflector generating an electrostatic dipole field μl and a magnetic dipole field B 1  (both of which are not shown in  FIG.  2   ). If they are applied, the force exerted by electrostatic dipole field μl on an electron of beamlets  102 _ 1 ,  102 _ 2 , and  102 _ 3  is equal in magnitude and opposite in direction to the force exerted on the electron by magnetic dipole field B 1 . Beamlets  102 _ 1 ,  102 _ 2 , and  102 _ 3  can therefore pass straight through beam separator  160  with zero deflection angles. 
     Deflection scanning unit  132  can deflect beamlets  102 _ 1 ,  102 _ 2 , and  102 _ 3  to scan probe spots  102 _ 1   s ,  102 _ 2   s , and  102 _ 3   s  over three small scanned areas in a section of the surface of sample  190 . In response to incidence of beamlets  102 _ 1 ,  102 _ 2 , and  102 _ 3  at probe spots  102 _ 1   s ,  102 _ 2   s , and  102 _ 3   s , three secondary electron beams  102 _ 1   se ,  102 _ 2   se , and  102 _ 3   se  can be emitted from sample  190 . Each of secondary electron beams  102 _ 1   se ,  102 _ 2   se , and  102 _ 3   se  can comprise electron beams with a distribution of energies including secondary electrons (energies ≤50 eV), and backscattered electrons (energies between 50 eV and landing energies of beamlets  102 _ 1 ,  102 _ 2 , and  102 _ 3 ). Beam separator  160  can direct secondary charged-particle beams  102 _ 1   se ,  102 _ 2   se , and  102 _ 3   se  towards secondary optical system  150 . Secondary optical system  150  can focus secondary electron beams  102 _ 1   se ,  102 _ 2   se , and  102 _ 3   se  onto detection elements  140 _ 1 ,  140 _ 2 , and  140 _ 3  of electron detection device  140 . Detection elements  140 _ 1 ,  140 _ 2 , and  140 _ 3  can detect corresponding secondary electron beams  102 _ 1   se ,  102 _ 2   se , and  102 _ 3   se  and generate corresponding signals, which are sent to controller  50  or a signal processing system (not shown), e.g. to construct images of the corresponding scanned areas of sample  190 . 
     In some embodiments, detection elements  140 _ 1 ,  140 _ 2 , and  140 _ 3  detect corresponding secondary electron beams  102 _ 1   se ,  102 _ 2   se , and  102 _ 3   se , respectively, and generate corresponding intensity signal outputs (not shown) to an image processing system (e.g., controller  50 ). In some embodiments, each detection element  140 _ 1 ,  140 _ 2 , and  140 _ 3  may comprise one or more pixels. The intensity signal output of a detection element may be a sum of signals generated by all the pixels within the detection element. 
     In some embodiments, controller  50  may comprise image processing system that includes an image acquirer (not shown), a storage (not shown). The image acquirer may comprise one or more processors. For example, the image acquirer may comprise a computer, server, mainframe host, terminals, personal computer, any kind of mobile computing devices, and the like, or a combination thereof. The image acquirer may be communicatively coupled to electron detection device  140  through a medium such as an electrical conductor, optical fiber cable, portable storage media, IR, Bluetooth, internet, wireless network, wireless radio, among others, or a combination thereof. In some embodiments, the image acquirer may receive a signal from electron detection device  140  and may construct an image. The image acquirer may thus acquire images of sample  190 . The image acquirer may also perform various post-processing functions, such as generating contours, superimposing indicators on an acquired image, and the like. The image acquirer may be configured to perform adjustments of brightness and contrast, etc. of acquired images. In some embodiments, the storage may be a storage medium such as a hard disk, flash drive, cloud storage, random access memory (RAM), other types of computer readable memory, and the like. The storage may be coupled with the image acquirer and may be used for saving scanned raw image data as original images, and post-processed images. 
     In some embodiments, the image acquirer may acquire one or more images of a sample based on an imaging signal received from electron detection device  140 . An imaging signal may correspond to a scanning operation for conducting charged particle imaging. An acquired image may be a single image comprising a plurality of imaging areas. The single image may be stored in the storage. The single image may be an original image that may be divided into a plurality of regions. Each of the regions may comprise one imaging area containing a feature of sample  190 . The acquired images may comprise multiple images of a single imaging area of sample  190  sampled multiple times over a time sequence. The multiple images may be stored in the storage. In some embodiments, controller  50  may be configured to perform image processing steps with the multiple images of the same location of sample  190 . 
     In some embodiments, controller  50  may include measurement circuitries (e.g., analog-to-digital converters) to obtain a distribution of the detected secondary electrons. The electron distribution data collected during a detection time window, in combination with corresponding scan path data of primary electron beam  102  incident on the wafer surface, can be used to reconstruct images of the wafer structures under inspection. The reconstructed images can be used to reveal various features of the internal or external structures of sample  190 , and thereby can be used to reveal any defects that may exist in the wafer. 
     Reference is now made to  FIGS.  3 A- 3 C , which are schematic diagrams of an exemplary electron beam tool  300  that can use multiple charged-particle beams for stereo or three-dimensional imaging of a sample, e.g. a wafer. Each of  FIGS.  3 A,  3 B, and  3 C  show electron beam tool in a different state. In some embodiments, electron beam tool  300  can be EBI tool  100  of  FIG.  2   . Electron beam tool  300  includes electron source  301  that can emit electron beams  303 ,  305 , and  307 . Electron beams can pass through aperture array  310  that focuses the beams toward deflectors  313 ,  315 , and  317 . In some embodiments, electron beam source  301  can emit a single electron beam and further include a deflector to deflect the single electron beam along the path shown by electron beams  303 ,  305 , and  307 . 
     Deflectors  313 ,  315 , and  317  can direct electron beams in different directions. In some embodiments any of deflectors  313 ,  315 , and  317  can direct a corresponding electron beam (e.g., electron beam  303 ,  305 , or  307 ) into blocking plate  320 . Blocking plate  320  can block one or more of the electron beams  303 ,  305 , and  307 . In some embodiments, blocking plate  320  is moveable (e.g., via controller  50  of  FIG.  1   ) and can be moved to block different electron beams  303 ,  305 , and  307  at different times. In some embodiments, blocking plate  320  is designed so that only one of electron beam  303 ,  305 , and  307  can be unblocked at a time. 
     Electron beam tool  300  can further include condenser lens  330 . Condenser lens  330  can be condenser lens  110  of  FIG.  2   . Condenser lens  330  can focus any of electron beams  303 ,  305 , and  307 . As shown in  FIGS.  3 A,  3 B, and  3 C , condenser lens  330  can move from side to side and can rotate to properly align with any of electron beams  303 ,  305 , and  307  that are not blocked by blocking plate  320 . In some embodiments, condenser lens  330  can include multiple condenser lenses. In these embodiments, each electron beam (e.g., electron beam  303 ,  305 , and  307 ) uses a separate, fixed-position condenser lens. For example, this structure is shown in  FIG.  4   . 
     In some embodiments, the central beam  305  that passes through condenser lens  330  of  FIG.  3 A  is an axial beam that is manipulated, such as by electron source  301  or deflector  315 , to impact sample  360  substantially perpendicularly. The left beam  303  that passes through left condenser lens  330  of  FIG.  3 C  and the right beam  307  that passes through condenser lens  330  of  FIG.  3 B  are manipulated or deflected, such as by electron source  301  or deflectors  313  or  317 , to cause the beams to impact sample  360  at a tilt relative to the axial beam. In some embodiments, the tilt is equal to or greater than three degrees relative to the axial beam, to enable improved imaging of the side walls of a structure on sample  360 . In other embodiments, the tilt is equal to or greater than five degrees relative to the axial beam, also to enable improved imaging of the side walls of a structure on sample  360 . Further, in some embodiments a subset of the condenser lenses are tilted relative to the axial beam to coincide with a corresponding one of the tilted beamlets. For example, the left condenser lens  330  is tilted to coincide with the path of left beam  330  of  FIG.  3 C  and the right condenser lens  330  is tilted to coincide with the path of right beam  330  of  FIG.  3 B . 
       FIG.  4    is a schematic diagram of an exemplary lens  400 . Lens  400  can be a magnetic lens, electrostatic lens, or a combination of the two. Lens  400  can use deflectors lens elements  440 A- 440 C to direct an electron beam. Lens  400  can be used as, for example, condenser lens  330  of  FIGS.  3 A- 3 C  and objective lens  340  of  FIGS.  3 A- 3 C  and described in more detail below. Lens  400  can include channels  410 ,  420 , and  430 , through which an electron beam (e.g., electron beam  303 ,  305 , or  307 ) can pass. As the electron beam passes through one of channels  410 ,  420 , and  430 , lens elements  440 A- 440 C can focus the electron beam. The lens elements can create a lens structure or effect like that shown as effective lenses  443 ,  445 , and  447 . The structure of lens  400  can be used for condenser lens  330 , describe above in relation to  FIGS.  3 A- 3 C , and can be used for objective lens  340 , described in more detail below in relation to  FIGS.  3 A- 3 C . 
     Referring back to  FIGS.  3 A- 3 C , electron beams  303 ,  305 , and  307  can pass through condenser lens  330  to objective lens  340 . Objective lens  340  can focus any of electron beams  303 ,  305 , and  307  on the sample  360  on a wafer. In some embodiments, electron beam tool  300  can include deflectors  350  to correct off-axis aberrations that can occur from electron beams  303 ,  305 , and  307  not being axially aligned with objective lens  340 . Deflectors  350  can be magnetic deflectors, electrostatic deflectors, or a combination of both technologies. Deflectors  350  can shift the focusing field of objective lens  340  (e.g., using Moving Objective Lens (“MOL”) technology). Accordingly, objective lens  340  is moveable, and moving the objective lens ensures that each electron beam goes through the center of objective lens  340  (as shown through each of  FIGS.  3 A- 3 C ), leading to smaller aberrations even for large tilting angles. 
     In some embodiments, objective lens  340  can be multiple objective lenses. In these embodiments, each of the objective lenses of objective lens  340  can be axially aligned with one of electron beams  303 ,  305 , and  307 , thereby minimizing off-axis aberrations from being introduced. As described above, objective lens  340  can use the structure of lens  400  described in reference to  FIG.  4    above. After being focused by objective lens  340 , electron beams  303 ,  305 , and  307  can illuminate sample  360  on the wafer, which can allow electron beam tool  300  to generate an image of the sample. 
     As described above,  FIGS.  3 A- 3 C  illustrate exemplary electron beam tool  300 . Although  FIGS.  3 A- 3 C  illustrate the same components, each can demonstrate a particular configuration of electron beam tool  300  and each configuration is described in more detail below. During operation, only one configuration, (e.g., a configuration shown in  FIG.  3 A,  3 B , or  3 C) can be active at a time. Electron beam tool  300  can move through the configurations shown in  FIGS.  3 A- 3 C  sequentially to allow imaging of the top and sides of structures of sample  360  on the wafer. It is appreciated that a specific sequence of configurations is not necessary, only that each of the configurations occur in the sequence to allow electron beam tool  300  to generate a stereo or three-dimensional image of sample  360 . 
     Reference is now made to  FIG.  3 A , which is an exemplary configuration of electron beam tool  300 . In the configuration shown in  FIG.  3 A , electron beam tool  300  can image the top of sample  360  on a wafer. In the configuration of  FIG.  3 A , blocking plate  320  can be positioned to block electron beams  303  and  307 . Deflectors  313  and  317  can also direct or deflect electron beams  303  and  307 , respectively, into blocking plate  320 . As used herein, directing an electron beam can mean making minor changes to the path of an electron beam. In some embodiments deflecting an electron beam can mean causing a larger change in the direction of an electron beam. Moreover, directing an electron beam can be the same as deflecting an electron beam. Electron beam  305  can pass through deflector  315  that can direct electron beam  305  past blocking plate  320  to condenser  330 . Condenser  330  can focus electron beam  305  through objective lens  340 . As described above, condenser  330 , objective lens  340 , and deflectors  350  can work in conjunction (e.g., via controller  50  of  FIG.  1   ) to direct electron beam  305  to sample  360  on the wafer. In this configuration, electron beam  305  can intersect the top of sample  360 , producing an image of the top of sample  360 . 
     Reference is now made to  FIG.  3 B , which is an exemplary configuration of electron beam tool  300 . In the configuration shown in  FIG.  3 B , electron beam tool  300  can image one side wall of structures of sample  360  on a wafer. In the configuration of  FIG.  3 B , blocking plate  320  can be positioned to block electron beams  303  and  305 . Deflectors  313  and  315  can also direct electron beams  303  and  305 , respectively, into blocking plate  320 . Electron beam  307  can pass through deflector  317 , that can direct electron beam  307  past blocking plate  320  to condenser  330 . Condenser  330  can focus electron beam  307  through objective lens  340 , which has been shifted to the right (e.g., to be centered on line  377 ) from its original location (e.g., centered on line  373 ) to allow beam  307  to go through the center of objective lens  340 , thereby minimizing aberrations. As described above condenser  330 , objective lens  340 , and deflectors  350  can work in conjunction to direct electron beam  307  to sample wafer  360 . In this configuration, electron beam  307  can intersect the side walls of structures of sample  360  producing an image of the side walls of the structures. The configuration shown in  FIG.  3 B  can direct the electron beam at large angles that can provide increased resolution for the imaging of the side walls of structures of sample  360  while also limited aberration produced by the condenser lens  330  and objective lens  340 . 
     Reference is now made to  FIG.  3 C , which is an exemplary configuration of electron beam tool  300 . In the configuration shown in  FIG.  3 C , electron beam tool  300  can image a side wall of a structure of sample  360  on a wafer. In the configuration of  FIG.  3 C , blocking plate  320  can be positioned to block electron beams  305  and  307 . Deflectors  315  and  317  can also direct electron beams  305  and  307 , respectively, into blocking plate  320 . Electron beam  303  can pass through deflector  313  that can direct electron beam  303  past blocking plate  320  to condenser  330 . Condenser  330  can focus electron beam  303  through objective lens  340 , which has been shifted to the left (e.g., to be centered on line  377 ) from its original location (e.g., centered on line  373 ) to allow beam  303  to go through the center of objective lens  340 , thereby minimizing aberrations. As described above condenser  330 , objective lens  340 , and deflectors  350  can work in conjunction to direct electron beam  303  to sample wafer  360 . In this configuration, electron beam  303  can intersect the side walls of structures of sample wafer  360 , producing an image of the side walls of the structures. The configuration shown in  FIG.  3 B  can direct the electron beam at large angles that can provide increased resolution for the imaging of the side walls of structures of sample  360 , while also limiting aberration produced by the condenser lens  330  and objective lens  340 . Moreover, the configuration shown in  FIG.  3 C  can produce an image of the opposite side of that shown in the configuration of  FIG.  3 B . 
     Electron beam tool  300 , using the three configurations shown in reference to  FIGS.  3 A- 3 C  can, in sequence, produce images of the top and two sides of structures of sample  360 . Using these images, EBI system  100  can construct a stereo or three-dimensional image of sample  360  that can show the three-dimensional structure of sample  360 . 
     Reference is now made to  FIG.  5   , which illustrates a flowchart of an exemplary method for real-time stereo imaging using multiple electron beams A controller (e.g. controller  50  of  FIG.  1   ) may be programmed to implement one or more blocks of the flowchart of  FIG.  5   . The controller may be coupled with a charged-particle beam apparatus (e.g., EBI tool  100  of  FIG.  2   ). The controller may control operations of the charged-particle beam apparatus. 
     In a step S 101 , the method can begin. At step S 102 , the charged-particle beam apparatus can generate a first, second, and third charged-particle beams (e.g., electron beams  303 ,  305 , and  307  of  FIGS.  3 A- 3 C ) using, for example, electron beam source  301  of  FIGS.  3 A- 3 C . The three charged-particle beams can be directed in different directions. In some embodiments, the three charged-particle beams are emitted parallel to each other. In some embodiments, the three charged-particle beams are generated independently of each other. In other embodiments, the three charged-particle beams can come from a single beam. In these embodiments, each single beam can be directed using a deflector to generate three beams, one of which can be active at any point in time. 
     In step S 103 , the method can use a blocking plate, e.g., blocking plate  320  of  FIGS.  3 A- 3 C , to block the first and third charged-particle beams. In embodiments where the three charged-particle beams are generated from a single particle beam and a deflector, as described above, only the second charged-particle beam can be active instead of requiring a blocking plate. Blocking the first and third charged-particle beams can produce a configuration like that shown in  FIG.  3 A  where the second charged-particle beam (e.g., electron beam  305  of  FIG.  3 A ) reaches the sample (e.g., sample  360  of  FIG.  3 A ). 
     In step S 104 , the second charged-particle beam can image the top of the sample wafer. The second charged-particle beam (e.g., electron beam  305  of  FIG.  3 A ) can pass through a condenser (e.g., condenser  330  of  FIG.  3 A ) to focus the charged-particle beam on an objective lens (e.g., objective lens  340  of  FIG.  3 A ) that can focus the charged-particle beam on the sample wafer. The image of the top of the sample wafer illuminated by the second charged-particle beam can be acquired by the charged-particle beam apparatus. 
     In step S 105 , after acquiring the image of the top of the sample wafer, the charged-particle beam apparatus can block the first and second charged-particle beams (e.g., electron beams  303  and  305  of  FIG.  3 B ) and allow the third charged-particle beam (e.g., electron beam  307  of  FIG.  3 B ) to pass as shown in the configuration of  FIG.  3 B . In some embodiment, the blocking plate (e.g., blocking plate  320  of  FIG.  3 B ) can be repositioned to block the first and second charged-particle beams and to allow the third charged-particle beam to pass. In some embodiments, one or more deflectors (e.g., deflectors  313  and  315  of  FIG.  3 B ) can deflect the first and second charged-particle beams into the blocking plate. The third charged-particle beam can be emitted at an angle away from sample wafer to a deflector (e.g., deflector  317  of  FIG.  3 B ). 
     In step S 106 , a deflector (e.g., deflector  317  of  FIG.  3 B ) can deflect the third charged-particle beam (e.g., electron beam  307  of  FIG.  3 B ) at an angle toward the side walls of structures of the sample. The third charged-particle beam (e.g., electron beam  307  of  FIG.  3 B ) can pass through a condenser (e.g., condenser  330  of  FIG.  3 B ) to focus the charged-particle beam on an objective lens (e.g., objective lens  340  of  FIG.  3 B ) that can focus the charged-particle beam on the sample. In some embodiments, the condenser lens can be repositioned and angled to be axially aligned with the third charged-particle beam. In other embodiments, a separate condenser lens from that used for the second charged-particle beam can be used. As explained earlier, the objective lens can be moveable as shown in  FIGS.  3 A- 3 C  or fixed as shown in  FIG.  4   . For example, the objective lens can be positioned (e.g., by deflectors  350  of  FIG.  3 B ) to reduce off-axis aberrations created by the intersection of the third charged-particle beam and the objective lens. In other embodiments (e.g., the embodiment of  FIG.  4   ), a separate objective lens from that used for the second charged particle beam can be used that is axially aligned with the third charged particle beam to reduce any aberration. The image of the side walls of structures of the sample illuminated by the third charged-particle beam can be acquired by the charged-particle beam apparatus. 
     In step S 107 , the third charged particle beam can image the side walls of structures of the sample wafer. The third charged-particle beam (e.g., electron beam  307  of  FIG.  3 B ) can be deflected by a deflector (e.g., deflector  317  of  FIG.  3 B ) and pass through a condenser (e.g., condenser  330  of  FIG.  3 B ) to focus the charged-particle beam on an objective lens (e.g., objective lens  340  of  FIG.  3 B ) that can focus the charged-particle beam on the sample wafer. The image of the side walls of structures of the sample illuminated by the third charged-particle beam can be acquired by the charged-particle beam apparatus. 
     In step S 108 , after acquiring the image of the side walls of the structures of the sample, the charged-particle beam apparatus can block the second and third charged-particle beams (e.g., electron beams  305  and  307  of  FIG.  3 C ) and allow the first charged-particle beam (e.g. electron beam  303 ) to pass as shown in the configuration shown in  FIG.  3 C , In some embodiments, the blocking plate (e.g., blocking plate  320  of  FIG.  3 C ) can be repositioned to block the second and third charged-particle beams and can allow the first charged-particle beam to pass. In some embodiments, one or more deflectors (e.g., deflectors  315  and  317  of  FIG.  3 C ) can deflect the first and second charged-particle beams into the blocking plate. The first charged-particle beam can be emitted at an angle away from the sample to a deflector (e.g., deflector  313  of  FIG.  3 C ). 
     In step S 109 , a deflector (e.g., deflector  313  of  FIG.  3 C ) can deflect the first charged-particle beam (e.g., electron beam  303  of  FIG.  3 F ) at an angle toward the other side wall of structures of the sample that were not previously imaged. The first charged-particle beam (e.g., electron beam  303  of  FIG.  3 C ) can pass through a condenser (e.g., condenser  330  of  FIG.  3 C ) to focus the charged-particle beam on an objective lens (e.g., objective lens  340  of  FIG.  3 C ) that can focus the charged-particle beam on the sample wafer. In some embodiments, the condenser can be repositioned and angled to be axially aligned with the first charged-particle beam. In other embodiments, a separate condenser lens from that used for the second and third charged-particle beam can be used. In some embodiments the objective lens can be positioned (e.g., by deflectors  350  of  FIG.  3 C ) to reduce off-axis aberrations created by the intersection of the first charged-particle beam and the objective lens. In other embodiments a separate objective lens from that used for the second and third charged particle beam can be used that is axially aligned with the first charged particle beam to reduce any aberration. The image of the side wall of the structures of the sample wafer, not already imaged, illuminated by the first charged-particle beam can be acquired by the charged-particle beam apparatus. 
     In step S 110 , the first charged particle beam can image the other side wall of the structures of the sample. The first charged-particle beam (e.g., electron beam  303  of  FIG.  3 C ) can be deflected by a deflector (e.g., deflector  313  of  FIG.  3 C ) and pass through a condenser (e.g., condenser  330  of  FIG.  3 C ) to focus the charged-particle beam on an objective lens (e.g., objective lens  340  of  FIG.  3 C ) that can focus the charged-particle beam on the sample. The image of the side wall of the structures of the sample illuminated by the first charged-particle beam can be acquired by the charged-particle beam apparatus. 
     The process can end in step S 111  and the charged particle beam apparatus (e.g., EBI tool  100  of  FIG.  2   ) can construct a three-dimensional or stereo image of the sample using the image of the top and two sides of the structures of the sample. It is appreciated that the specific order in which the top and two sides of the structures of the sample are imaged is not important and can be done in any sequential order. The previously described process is one exemplary order for creating a three-dimensional or stereo image of sample wafer. It is also appreciated that reference in the present disclosure to structures of the sample can include both a single structure or multiple structures. 
     The embodiments may further be described using the following clauses: 
     1. A multi-beam apparatus configured to emit multiple charged-particle beams for imaging two sides of a structure of a sample, the apparatus comprising: 
     a deflector array including a first deflector and configured to receive a first charged-particle beam and a second charged-particle beam; 
     a blocking plate configured to block one of the first charged-particle beams and the second charged-particle beam; and 
     a controller having circuitry and configured to change the configuration of the apparatus to transition between a first mode and a second mode, wherein:
         in the first mode:
           the deflector array is configured to deflect the second charged-particle beam to image a first side of the structure, and   the blocking plate is configured to block the first charged-particle beam, and   
           in the second mode:
           the first deflector is configured to deflect the first charged-particle beam to image a second side of the structure, and   the blocking plate is configured to block the second charged-particle beam.
 
2. A multi-beam apparatus configured to emit multiple charged-particle beams for imaging a top of and a side of a structure of a sample, the apparatus comprising:
   
               

     a deflector array including a first deflector and configured to receive a first charged-particle beam and a second charged-particle beam; 
     a blocking plate configured to block one of the first charged-particle beams and the second charged-particle beam; and 
     a controller having circuitry and configured to change the configuration of the apparatus to transition between a first mode and a second mode, wherein:
         in the first mode:   the deflector array is configured to direct the second charged-particle beam to image the top of the structure, and       

     the blocking plate is configured to block the first charged-particle beam, and
         in the second mode:       

     the first deflector is configured to deflect the first charged-particle beam to image the side of the structure, and 
     the blocking plate is configured to block the second charged-particle beam. 
     3. The apparatus of any one of clauses 1 and 2, further comprising an objective lens.
 
4. The apparatus of clause 3, wherein the objective lens is one of an electrostatic lens or a magnetic lens.
 
5. The apparatus of clause 3 wherein the objective lens is a combination of a magnetic lens and an electrostatic lens.
 
6. The apparatus of any one of clauses 3-5 wherein the objective lens is a moveable objective lens.
 
7. The apparatus of any one of clauses 2-6, wherein the direction of the second charged-particle beam by the deflector array includes a deflection of the second charged-particle beam.
 
8. The apparatus of any of clauses 1-7, further comprising a condenser lens.
 
9. The apparatus of clause 8, wherein the condenser lens is an electrostatic lens.
 
10. The apparatus of clause 8, wherein the condenser lens is a magnetic lens.
 
11. The apparatus of clause 8 wherein the condenser lens is a combination of a magnetic lens and an electrostatic lens.
 
12. The apparatus of any one of clauses 8-11 wherein the condenser lens is movable and rotatable to axially align with the first charged-particle beam or the second charged-particle beam.
 
13. The apparatus of any one of clauses 1-12 wherein each of the first charged-particle beam and second charged-particle beam are focused using separate objective lenses.
 
14. The apparatus of any one of clauses 1-13 wherein each of the first charged-particle beam and second charged-particle beam are focused using separate condenser lenses.
 
15. The apparatus of any one of clauses 1-14 wherein the deflector array includes a second deflector configured to deflect the second charged-particle beam into the blocking plate when operating the first mode.
 
16. The apparatus of any one of clauses 2-15, wherein the deflector array is configured to receive a third charged-particle beam and includes a third deflector configured to deflect the third charged-particle beam into the blocking plate when operating in either the first or second modes.
 
17. The apparatus of clause 15, wherein the controller is configured to change the configuration of the apparatus to transitions between the first mode, the second mode, and a third mode, wherein
 
     in the third mode,
         the third deflector is configured to direct the third charged-particle beam to image a second side different from the side of the structure, and       

     the blocking plate is configured to block the first and second charged-particle beams. 
     18. The apparatus of clause 1, wherein: 
     the deflector array is configured to receive a third charged-particle beam and includes a third deflector configured to deflect the third charged-particle beam into the blocking plate when operating in either the first or second modes; and 
     the controller is configured to change the configuration of the apparatus to transitions between the first mode, the second mode, and a third mode, wherein
         in the third mode,       

     the third deflector is configured to direct the third charged-particle beam to image a top of the structure, and 
     the blocking plate is configured to block the first and second charged-particle beams. 
     19. The apparatus of any one of clauses 1-18, wherein the controller is further configured to: acquire an image from each portion of the structure;
 
combine the acquired images into a stereo image of the structure.
 
20. A method for imaging two sides of a structure of a sample using a charged-particle beam tool, the method comprising:
 
     transitioning to a first mode, the transition comprising: 
     deflecting, using a deflector array, a second charged-particle beam to a first side of the structure; 
     blocking, using a blocking plate, the first charged-particle beam. 
     imaging the first side of the structure; and 
     transitioning to a second mode, the transition comprising: 
     deflecting, using a first deflector of the deflector array, the first charged-particle beam to a second side of the structure; 
     blocking, using the blocking plate, the second charged-particle beam; and 
     imaging the side of the structure. 
     21. A method for imaging a top of and a side of a structure of a sample using a charged-particle beam tool, the method comprising: 
     transitioning to a first mode, the transition comprising: 
     directing, using a deflector array, a second charged-particle beam to the top of the structure; 
     blocking, using a blocking plate, the first charged-particle beam. 
     imaging the top of the structure; and 
     transitioning to a second mode, the transition comprising: 
     deflecting, using a first deflector of the deflecting array, the first charged-particle beam to the side of the structure; 
     blocking, using the blocking plate, the second charged-particle beam; and 
     imaging the side of the structure. 
     22. The method of any one of clauses 20 and 21, further comprising: 
     focusing the second charged-particle beam on a portion of the structure using a condenser lens. 
     23. The method of any one of clauses 20-22, further comprising focusing the second charged-particle beam on a portion of the structure using an objective lens.
 
24. The method of any one of clauses 20-23, further comprising focusing the first charged-particle beam on a portion of the structure using a condenser lens.
 
25. The method of any one of clauses 20-24, further comprising focusing the second charged-particle beam on a portion of the sample using an objective lens.
 
26. The method of any one of clauses 20-25, further comprising moving the condensing lens to be aligned with the second charged-particle beam.
 
27. The method of any one of clauses 20-26, further comprising rotating the condensing lens to be axially aligned with the second charged-particle beam.
 
28. The method of any one of clauses 20-27, further comprising moving the condensing lens to be aligned with the first charged-particle beam.
 
29. The method of any one of clauses 20-25 and 28, further comprising rotating the condensing lens to be axially aligned with the first charged-particle beam.
 
30. The method of any one of clauses 20-29, further comprising moving the objective lens to be aligned with the second charged-particle beam.
 
31. The method of any one of clauses 20-30, further comprising moving the objective lens to be aligned with the first charged-particle beam.
 
32. The method of any one of clauses 20-31, wherein blocking the second charged-particle beam further comprises deflecting the second charged-particle beam to the blocking plate.
 
33. The method of any one of clauses 20-32, wherein blocking the first charged particle beam further comprises deflecting the first charged-particle beam to the blocking plate.
 
34. The method of any one of clauses 21-33, further comprising:
 
     transitioning to a third mode, the transition comprising: 
     deflecting, using a deflector array, a third charged-particle beam to a second side of the structure; 
     blocking, using a blocking plate, the first charged-particle beam and the second charged-particle beam; 
     imaging the second side of the structure. 
     35. The method of clause 20, further comprising: 
     transitioning to a third mode, the transition comprising: 
     deflecting, using a deflector array, a third charged-particle beam to a top of the structure; 
     blocking, using a blocking plate, the first charged-particle beam and the second charged-particle beam; 
     imaging the top of the structure. 
     36. The method of any one of clauses 20-35, further comprising: 
     combining images from imaging into a stereo image of the structure. 
     37. A non-transitory computer readable medium storing a set of instructions that is executable by one or more processors of a system to cause the system to perform a method comprising: 
     transitioning to a first mode, the transition comprising: 
     deflecting, using a deflector array, a second charged-particle beam to a first side of a structure of a sample; 
     blocking, using a blocking plate, the first charged-particle beam. 
     imaging the first side of the structure; and 
     transitioning to a second mode, the transition comprising; and 
     deflecting, using a first deflector of the deflector array, the first charged-particle beam to a second side of the structure; 
     blocking, using the blocking plate, the second charged-particle beam; and 
     imaging the second side of the structure. 
     38. A non-transitory computer readable medium storing a set of instructions that is executable by one or more processors of a system to cause the system to perform a method comprising: 
     transitioning to a first mode, the transition comprising: 
     directing, using a deflector array, a second charged-particle beam to a top of a structure of a sample; 
     blocking, using a blocking plate, the first charged-particle beam. 
     imaging the top of the structure; and 
     transitioning to a second mode, the transition comprising; and 
     deflecting, using a first deflector of the deflector array, the first charged-particle beam to a side of the structure; 
     blocking, using the blocking plate, the second charged-particle beam; and 
     imaging the side of the structure. 
     39. The computer readable medium of any one of clauses 37 and 38, wherein the set of instructions that is executable by one or more processors of a system to cause the system to further perform: 
     focusing the second charged-particle beam on a portion of the structure using a condenser lens. 
     40. The computer readable medium of any one of clauses 37-39, wherein the set of instructions that is executable by one or more processors of a system to cause the system to further perform focusing the second charged-particle beam on a portion of the structure using an objective lens.
 
41. The computer readable medium of any one of clauses 37-40, wherein the set of instructions that is executable by one or more processors of a system to cause the system to further perform focusing the first charged-particle beam on a portion of the structure using a condenser lens.
 
42. The computer readable medium of any one of clauses 37-41, wherein the set of instructions that is executable by one or more processors of a system to cause the system to further perform focusing the second charged-particle beam on a portion of the structure using an objective lens.
 
43. The computer readable medium of any one of clauses 37-42, wherein the set of instructions that is executable by one or more processors of a system to cause the system to further perform moving the condensing lens to be aligned with the second charged-particle beam.
 
44. The computer readable medium of any one of clauses 37-43, wherein the set of instructions that is executable by one or more processors of a system to cause the system to further perform rotating the condensing lens to be axially aligned with the second charged-particle beam.
 
45. The computer readable medium of any one of clauses 37-44, wherein the set of instructions that is executable by one or more processors of a system to cause the system to further perform moving the condensing lens to be aligned with the first charged-particle beam.
 
46. The computer readable medium of any one of clauses 37-42 and 45, wherein the set of instructions that is executable by one or more processors of a system to cause the system to further perform rotating the condensing lens to be axially aligned with the first charged-particle beam.
 
47. The computer readable medium of any one of clauses 37-46, wherein the set of instructions that is executable by one or more processors of a system to cause the system to further perform moving the objective lens to be aligned with the second charged-particle beam.
 
48. The computer readable medium of any one of clauses 37-47, wherein the set of instructions that is executable by one or more processors of a system to cause the system to further perform moving the objective lens to be aligned with the first charged-particle beam.
 
49. The computer readable medium of any one of clauses 37-48, wherein blocking the second charged-particle beam further comprises deflecting the second charged-particle beam to the blocking plate.
 
50. The computer readable medium of any one of clauses 37-49, wherein blocking the first charged particle beam further comprises deflecting the first charged-particle beam to the blocking plate.
 
51. The computer readable medium of any one of clauses 38-50, wherein the set of instructions that is executable by one or more processors of a system to cause the system to further perform:
 
     transitioning to a third mode, the transition comprising: 
     using a deflector array, deflect a third charged-particle beam to a second side of the structure; 
     using a blocking plate, blocking the first charged-particle beam and the second charged-particle beam; 
     imaging the second side of the structure. 
     52. The computer readable medium of clause 37, wherein the set of instructions that is executable by one or more processors of a system to cause the system to further perform: 
     transitioning to a third mode, the transition comprising: 
     using a deflector array, deflect a third charged-particle beam to a top of the structure; 
     using a blocking plate, blocking the first charged-particle beam and the second charged-particle beam; 
     imaging the top of the structure. 
     53. The computer readable medium of any one of clauses 37-52, wherein the set of instructions that is executable by one or more processors of a system to cause the system to further perform: 
     combining images from imaging into a stereo image of the structure. 
     54. A scanning electron microscope (SEM) system, comprising: 
     a charged particle source for providing charged particles to enable a plurality of beamlets, a first beamlet being an axial beam manipulated to impact a sample substantially perpendicularly; 
     a plurality of deflectors, wherein a subset of the deflectors are configured to deflect a subset of the beamlets to cause each of the subset of beamlets to impact the sample at a tilt relative to the axial beam; and 
     a plurality of condensers, wherein each of a subset of the condensers has an axis tilted to coincide with a path of a different one of the subset of beamlets. 
     55. The SEM system of clause 54, wherein the sample includes one or more structures.
 
56. The SEM system of any one of clauses 54 and 55, wherein the first beamlet is further configured to, based on the impact with the sample, image the top of the one or more structures.
 
57. The SEM system of any one of clauses 54-56, wherein each of the subset of beamlets is further configured to, based on impact with the sample, image a side of the one or more structures.
 
58. The SEM system of any one of clauses 54-57, wherein the sample is a wafer and the one or more structures are components of an integrated circuit manufactured on the wafer.
 
59. The SEM system of any one of clauses 54-58, further comprising:
 
     a Moving Objective Lens (MOL) that can be configured to shift the focusing field of the objective lens. 
     60. The SEM system of clause 59, wherein the MOL is configured to shift the focusing field of the objective lens to coincide, at different times, with each of the beamlets.
 
61. The SEM of any one of clauses 54-60, wherein the objective lens is one of an electrostatic lens, a magnetic lens, or both.
 
62. The SEM system of any one of clauses 54-61, wherein the first beamlet has a path that is straight and perpendicular to the sample.
 
63. The SEM system of any one of clauses 54-62, wherein each of the condensers is an electrostatic lens, a magnetic lens, or both.
 
64. The SEM system of any one of clauses 54-63, further comprising:
 
     a controller having circuitry and configured to process images based on the plurality of beamlets to enable a real time display of a three dimensional representation of the sample. 
     65. The SEM system of any one of clauses 54-64, wherein each of the subset of deflectors is configured to deflect a different beamlet of the subset of beamlets to cause each beamlet of the subset of beamlets to impact the sample at a different tilt relative to the axial beam.
 
66. The SEM system of any one of clauses 54-65, further comprising a blocking mechanism configured to prevent all but one of the beamlets from impacting the sample.
 
67. The SEM system of any one of clauses 54-66, wherein the tilt relative to the axial beam is greater than or equal to three degrees.
 
68. The SEM system of any one of clauses 54-66, wherein the tilt relative to the axial beam is greater than or equal to five degrees.
 
     A non-transitory computer readable medium may be provided that stores instructions for a processor that can be part of, for example EBI tool  100  of  FIG.  2   , to carry out thermal sensing, flow sensing, image inspection, image acquisition, stage positioning, beam focusing, electric field adjustment, cleaning, hardening, heat treatment, material removal, and polishing, etc. Common forms of non-transitory media include, for example, a floppy disk, a flexible disk, hard disk, solid state drive, magnetic tape, or any other magnetic data storage medium, a Compact Disc Read Only Memory (CD-ROM), any other optical data storage medium, any physical medium with patterns of holes, a Random Access Memory (RAM), a Programmable Read Only Memory (PROM), and Erasable Programmable Read Only Memory (EPROM), a FLASH-EPROM or any other flash memory, Non-Volatile Random Access Memory (NVRAM), cloud storage, a cache, a register, any other memory chip or cartridge, and networked versions of the same. 
     The block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer hardware or software products according to various exemplary embodiments of the present disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical functions. It should be understood that in some alternative implementations, functions indicated in a block may occur out of the order noted in the figures. For example, two blocks shown in succession may be executed or implemented substantially concurrently, or two blocks may sometimes be executed in reverse order, depending upon the functionality involved. Some blocks may also be omitted. It should also be understood that each block of the block diagrams, and combination of the blocks, may be implemented by special purpose hardware-based systems that perform the specified functions or acts, or by combinations of special purpose hardware and computer instructions. 
     It will be appreciated that the embodiments of the present disclosure are not limited to the exact construction that has been described above and illustrated in the accompanying drawings, and that various modifications and changes may be made without departing from the scope thereof. The present disclosure has been described in connection with various embodiments, other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims. 
     The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made as described without departing from the scope of the claims set out below.