Patent Publication Number: US-11658004-B2

Title: Method for scanning a sample by a charged particle beam system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 16/730,875 filed Dec. 30, 2019, which claims priority of U.S. application 62/787,121 which was filed on Dec. 31, 2018, and U.S. application 62/943,695 which was filed on Dec. 4, 2019, all of which are incorporated herein by reference in their entireties. 
    
    
     FIELD 
     Apparatuses and methods consistent with the present disclosure relate generally to a scanning technique, and more particularly, to methods and systems for scanning a sample by a charged particle beam tool such as a scanning electron microscope (SEM). 
     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 SEM, can be employed. For inspection of fine structures, electron beam is preferred. Using electron beam for such inspection of a sample imposes a problem of charge accumulation in the sample. To solve the charge accumulation problem, technicians usually would sputter highly conductive material or thin film, such as gold thin film of a few nanometer thick, onto the sample surface for conducting the charge away from the scanned region of the sample. However, this approach would damage the originally designed device structure and would not allow the sample to be used as a device because the blanket-coated gold layer would short all circuits formed on the sample. Further improvements in the art are desired. 
     SUMMARY 
     According to some embodiments of the present disclosure, there is provided a method for scanning a sample by a charged particle beam tool, such as an electron beam tool. The method may comprise: providing the sample having a scanning area, wherein the sample is determined to have a plurality of unit areas; scanning a unit area of the plurality of unit areas; and blanking a first unit area adjacent to the scanned unit area. 
     The method may further comprise: determining whether any unit area on the sample remains to be scanned; in response to the determination that any unit area on the sample remains to be scanned, scanning a next unit area that is determined to be outside of a determined dissipation region associated with the scanned unit area; and blanking a second unit area adjacent to the scanned next unit area. The method may further comprise: blanking a third unit area adjacent to the blanked first unit area before scanning the next unit area. In the method, the blanked first unit area may include multiple unit areas. 
     In the method, the first blanked unit area may be adjacent to the scanned unit area in the X-direction. In the method, the first blanked unit area may be adjacent to the scanned unit area in the Y-direction. In the method, the scanned unit area may be a single pixel of a scanned image. In the method, the first blanked unit area may be a single pixel. In the method, the first blanked unit area may be multiple pixels. In the method, the scanned unit area may be a plurality of pixels of a scanned image. 
     In the method, blanking a first unit area adjacent to the scanned unit area may further comprise: applying a current to an electromagnetic blanker so that an electromagnetic field generated by the blanker deflects an electron beam of the electron beam tool such that the electron beam no longer reaches the sample. 
     In the method, blanking a first unit area adjacent to the scanned unit area may further comprise: moving a shutter to intercept a pathway of an electron beam of the electron beam tool such that the electron beam no longer reaches the sample. In the method, the scanning and the blanking may be determined based on a dissipation time for charge dissipation in the scanned unit area. In the method, the scanning and the blanking may be carried out on a predetermined pattern in the sample. 
     In the method, the predetermined pattern may he one of a line pattern parallel to the edges of the scanning area, a line pattern diagonal in the scanning area, or a circular pattern. In the method, the scanning and the blanking may be performed on the plurality of unit areas until all unit areas are scanned. 
     The method may further comprise: reconstructing an image of the sample using sub-images corresponding to the plurality of unit areas that have been scanned. In the method, the reconstructing may be performed by using at least one of interpolation, sparse sampling, or simulation. In the method, the plurality of unit areas of a scanning area may be organized in batches of unit areas provided in rows or columns and the scanned unit area and the blanked unit area may be in a first batch of unit areas. 
     In the method, after scanning and blanking unit areas in the first batch: blanking or skipping a second batch of unit areas that is adjacent to the first batch; and scanning and blanking unit areas in a third batch of unit areas that is at least a threshold distance from the first batch to mitigate charge induced distortion from scanned unit areas of the first batch. The method may further comprise: after a dissipation time threshold, returning to the first batch of unit areas to scan unit areas that have not been previously scanned to mitigate charge induced distortion from previously scanned unit areas of the first batch. 
     According to some embodiments of the present disclosure, there is provided a scanning electron microscope (SEM). The SEM may comprise: an electron source; a scanning deflector to scan an electron beam emitted from the electron source on a scanning area of a sample, wherein the sample is determined to have a plurality of unit areas; a blanker for blanking the electron beam such that the electron beam no longer reaches the sample; and a controller includes circuitry for controlling the scanning deflector and the blanker, wherein the controller is configured to scan a unit area of the plurality of unit areas; and blank a first unit area adjacent to the scanned unit area. 
     In the SEM, the controller may further configured to: determine whether any unit area on the sample remains to be scanned; in response to the determination that any unit area on the sample remains to be scanned, scan a next unit area that is determined to be outside of a determined dissipation region associated with the scanned unit area; and blank a second unit area adjacent to the scanned next unit area. 
     In the SEM, the controller may be further configured to: blank a third unit area adjacent to the blanked first unit area before scanning the next unit area. In the SEM, the blanked first unit area includes multiple unit areas. In the SEM, the first blanked unit area may be adjacent to the scanned unit area in the X-direction. In the SEM, the first blanked unit area may be adjacent to the scanned unit area in the Y-direction. In the SEM, the scanned unit area may be a single pixel of a scanned image. In the SEM, the first blanked unit area may be a single pixel. In the SEM, the first blanked unit area may be multiple pixels. In the SEM, the scanned unit area may be a plurality of pixels of a scanned image. 
     In the SEM, the blanker may be an electromagnetic blanker to which a current is applied so as to induce an electromagnetic field that deflects the electron beam of the SEM such that the electron beam no longer reaches the sample. In the SEM, the blanker may be a shutter configured to intercept a pathway of the electron beam of the SEM so as to perform the blanking. In the SEM, the blanker may blank for a time determined based on a dissipation time for charge dissipation. 
     In the SEM, the controller may include circuitry to determine a next unit area to scan, wherein the next unit area is at least a threshold distance from the scanned unit area and is selected to mitigate a charge induced distortion from the scanned unit area such that the blanked unit area separates the scanned unit area from the next unit area. In the SEM, the blanker may be configured to blank a predetermined pattern in the sample comprising any one of a line pattern parallel to edges of the scanning area, a line pattern diagonal in the scanning area to a direction, a circular pattern, or a random pattern. In the SEM, the blanker may be positioned between the electron source and the scanning deflector. 
     According to some embodiments of the present disclosure, there is provided a non-transitory computer readable medium that stores a set of instructions that is executable by at least one processor of a computer system to cause the computer system to perform a method for service processing, the method comprising: providing a sample having a scanning area, wherein the sample is determined to have a plurality of unit areas; scanning a unit area of the plurality of unit areas; and blanking a unit area adjacent to the scanned unit area. 
     In the non-transitory computer readable medium, the set of instructions that is executable by the at least one processor of a computer system to cause the computer system to further perform: determining whether any unit area on the sample remains to be scanned; in response to the determination that any unit area on the sample remains to be scanned, scanning a next unit area that is determined to be outside of a determined dissipation region associated with the scanned unit area; and blanking a unit area adjacent to the next unit area. In the non-transitory computer readable medium, wherein the scanned unit area is a single pixel or a plurality of pixels of a scanned image before a next unit area is scanned. 
     According to some embodiments of the present disclosure, there is provided a method for scanning a sample with a scanning electron microscope (SEM). The method may comprise: 
     scanning a first set of locations with the SEM, each location of the first set of locations being physically separated by at least a threshold distance; and scanning a second set of locations with the SEM a period of time after scanning the first set of locations, a location of the second set of locations being located within the threshold distance of a location of the first set of locations. In the method, the period of time enables charge resulted from the scanning the first set of locations to dissipate sufficiently so as to mitigate a charge induced distortion of a scan of a location within the threshold distance. In the method, each of the first set of locations may be arranged in diagonal to each other. In the method, each of the second set of locations may be arranged in diagonal to each other. 
    
    
     
       BRIEF DESCRIPTION OF FIGURES 
         FIG.  1    is a schematic diagram illustrating an exemplary electron beam inspection (EBI) system, consistent with some 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 (EBI) system of  FIG.  1   , consistent with some embodiments of the present disclosure. 
         FIG.  3    is a schematic diagram illustrating a top plan view of a reference sample with a rectangular scanning grid, consistent with some embodiments of the present disclosure. 
         FIGS.  4 A- 4 L  are schematic diagrams illustrating top plan views of the reference sample of  FIG.  3    undergoing an exemplary scanning process performed by the exemplary electron beam tool of  FIG.  2   , consistent with some embodiments of the present disclosure. 
         FIGS.  5 A- 5 C  are schematic diagrams illustrating top plan views of the reference sample of  FIG.  3    undergoing another exemplary scanning process performed by the exemplary electron beam tool of  FIG.  2   , consistent with some embodiments of the present disclosure. 
         FIGS.  6 A- 6 I  are schematic diagrams illustrating top plan views of the reference sample of  FIG.  3    undergoing another exemplary scanning process performed by the exemplary electron beam tool of  FIG.  2   , consistent with some embodiments of the present disclosure. 
         FIG.  7    is a flow chart illustrating an exemplary method of scanning and blanking a sample using a SEM, consistent with some 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 scanning electron microscope (SEM) for generation of a wafer image and defect detection, the disclosure is not so limited. Other types of microscopes such as transmission electron microscope (TEM) and scanning tunneling microscope (STM) be similarly applied. 
     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 1/1000 th  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%. 
     In various steps of the semiconductor manufacturing process, pattern defects can appear on at least one of a wafer, a chip, or a mask, which can cause a manufactured semiconductor device to fail, thereby reducing the yield to a great degree. As semiconductor device sizes continually become smaller and smaller (along with any defects), identifying defects becomes more challenging and costly. Currently, engineers in semiconductor manufacturing lines usually spend hours (and even sometimes days) to identify locations of small detects to minimize their impact on the final product. 
     Conventional optical inspection techniques are ineffective in inspecting small defects (e.g., nanometer scale defects). Advanced electron-beam inspection (EBI) tools, such as a scanning electron microscope (SEM) with high resolution and large depth-of-focus, have been developed to meet the need in the semiconductor industry. While SEM plays an important role in small defect detection for semiconductor wafers, using the electron beam for inspecting the semiconductor wafer involves depositing a charge on the sample (e.g. sample W in  FIG.  3   ) at a specific location (such as a unit area (or pixel) on the sample), e.g. pixel  1 A. This charge, however, can affect the imaging of subsequent adjacent pixels, e.g. pixels  1 B and  1 C, leading to a distortion in the imaging of the wafer W. Accordingly, this distortion can reduce the accuracy of the image, which can impact the ability to detect and analyze features on the image. 
     For example, as an e-beam scans across a sample (e.g., from left to right), charge begins to build up on the surface (e.g., on the surface of the sample or on the surface of a feature on the sample) on which the e-beam lands: As the charge builds up, an electric field also builds up, affecting the-trajectories of electrons that are emitted from the sample (e.g., secondary electrons, backscattered electron, etc.). This change in the trajectories of the emitted electrons affects the number of emitted electrons that are detected by a detector, resulting in a lower quality and less accurate SEM image. For example, charge can build up on a first pixel that is scanned, and the resulting electric field can affect electrons emitted from an adjacent pixel when the adjacent pixel is scanned, resulting in fewer electrons emitted from the adjacent pixel reaching a detector, and further resulting in a lower quality and less accurate image of the adjacent pixel. 
     The accumulated charge eventually dissipates; that is, the accumulated charge is conducted away from the scanned pixel after a sufficient amount of time. For example, in  FIG.  3   , pixels  1 A to  3 C appear in a row on a sample. Some embodiments of the present disclosure take this dissipation effect into account and provide a procedure to scan a unit area of the sample, e.g. pixel  1 A of sample W in  FIG.  3   , and blank a unit area, e.g. pixel  1 B, adjacent to the scanned unit area, e.g. pixel  1 A. The blanked unit area  1 B has a distance that falls within the charged area from the scanning of unit area IA, accordingly that unit area  1 B is not scanned at this time. Instead of scanning unit area  1 B, a unit area outside of the charged area (e.g., unit area  1 C) is scanned so that the dissipating charge would not affect the scanning. After the first round of scanning the sample, some pixels, e.g. pixels  1 A and  1 C, are scanned and some pixels, e.g. pixels  1 B and  2 A, are blanked. Then, in the subsequent scanning, the blanked pixels are scanned after charges associated with scanned pixels  1 A and  1 C have dissipated. Comparing with the conventional SEM continuous scanning, some of the disclosed embodiments are capable of generating improved accuracy results and information for examining the sample for fine structure and nanometer scale defects during production of high density integrated electronic devices such as computer processor, memory, and high-resolution sensor device such as digital camera sensor. 
     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   , a schematic diagram illustrating an exemplary electron beam inspection system, consistent with some embodiments of the present disclosure. As shown in  FIG.  1   , electron beam inspection system  100  includes a main chamber  101 , a load/lock chamber  102 , an electron beam tool  104 , an equipment front end module  106 , and a user interface  109 . Electron beam tool  104  is located within main chamber  101 . Equipment front end module  106  includes a first loading port  106   a  and a second loading port  106   b . Equipment front end module  106  may include additional loading port(s). First loading port  106   a  and second loading port  106   b  receive wafer cassettes that contain wafers (e.g., semiconductor wafers or wafers made of other material(s)) or samples to be inspected (wafers and samples are collectively referred to as “wafers” hereafter). One or more robot arms (not shown) in equipment front end module  106  transport the wafers to load/lock chamber  102 . Load/lock chamber  102  is connected to a load/lock vacuum pump system (not shown) which removes gas molecules in load/lock chamber  102  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  102  to main chamber  101 . Main chamber  101  is connected to a main chamber vacuum pump system (not shown) which removes gas molecules in main chamber  101  to reach a second pressure below the first pressure. After reaching the second pressure, the wafer is subject to inspection by electron beam tool  104  which is controlled by a user using the user interface  109 . 
     References are now made to  FIG.  2   , a schematic diagram illustrating an exemplary electron beam tool that can be a part of the exemplary electron beam tool  104  of  FIG.  1   , consistent with some embodiments of the present disclosure. As shown in  FIG.  2   , electron beam tool  104  includes a motorized stage  400 , and a wafer holder  402  supported by motorized stage  400  to hold a wafer  403  to be inspected. Wafer  403  may be referred to as a sample. Electron beam tool  104  further includes an objective lens assembly  404 , electron detector  406  (which includes electron sensor surfaces), an objective aperture  408 , a condenser lens  410 , a beam limit aperture  412 , a gun aperture  414 , a blanker  424 , an anode  416 , and a cathode  418 . Objective lens assembly  404 , in some embodiments, can include a modified swing objective retarding immersion lens (SORIL), which includes a pole piece  404   a , a control electrode  404   b , a deflector  404   c , and an exciting coil  404   d . Electron beam tool  104  may additionally include an energy dispersive X-ray spectrometer (EDS) detector (not shown) to characterize the materials on the wafer. 
     A primary electron beam  420  is emitted from cathode  418  by applying a voltage between anode  416  and cathode  418 . Primary electron beam  420  passes through blanker  424 , then passes through gun aperture  414  and beam limit aperture  412 , both of gun aperture  414  and beam limit aperture  412  can determine the size of electron beam entering condenser lens  410 , which resides below beam limit aperture  412 . Position of blanker  424  in electron beam tool  104  can be at any position between beam limit aperture  412  and sample wafer  403 , depending on the need for specific measurements. 
     Blanker  424  may be a shutter, an electromagnetic deflector, or a pure electrostatic deflector, among others. The shutter is mechanically moved or controlled by an electromagnetic field generated by e.g. electric current carrying coils to intercept primary electron beam  420  so that primary electron beam  420  cannot pass through blanker  424  and reach sample wafer  403 , in some embodiments. The electromagnetic deflector controls the deflection of primary electron beam  420  such that the electron beam  420  no longer reaches sample wafer  403  using a magnetic field generated by permanent magnet or electromagnet, in some embodiments. The pure electrostatic deflector controls the deflection of primary electron beam  420  such that the electron beam  420  no longer reaches sample wafer  403  using an electric field generated by opposite plates carrying opposite charges, in some embodiments. 
     Condenser lens  410  focuses primary electron beam  420  before the beam enters objective aperture  408  to set the size of primary electron beam  420  before entering objective lens assembly  404 . Deflector  404   c  deflects primary electron beam  420  to facilitate beam scanning on the wafer  403 . For example, in a scanning process, deflector  404   c  can be controlled to deflect primary electron beam  420  sequentially onto different locations of top surface of wafer  403  at different time points, to provide data for image reconstruction for different parts of wafer  403 . Moreover, deflector  404   c  can also he controlled to deflect primary electron beam  420  onto different sides of wafer  403  at a particular location, at different time points, to provide data for stereo image reconstruction of the wafer structure at that location. Further, in some embodiments, anode  416  and cathode  418  may be configured to generate multiple primary electron beams  420 , and electron beam tool  104  may include a plurality of deflectors  404   c  to project the multiple primary electron beams  420  to different parts/sides of wafer  403  at the same time, to provide data for image reconstruction for different parts of wafer  203 . 
     Exciting coil  404   d  and pole piece  404   a  generate a magnetic field that begins at one end of pole piece  404   a  and terminates at the other end of pole piece  404   a . A part of wafer  403  being scanned by primary electron beam  420  can be immersed in the magnetic field and can be electrically charged, which, in turn, creates an electric field. The electric field reduces the energy of impinging primary electron beam  420  near the surface of wafer  403  before it collides with wafer  403 . Control electrode  404   b , being electrically isolated from pole piece  404   a , controls an electric field on wafer  403  to prevent micro-arching of wafer  403  and to ensure proper beam focus. 
     A secondary electron beam  422  can be emitted from the part of wafer  403  upon receiving primary electron beam  420 . Secondary electron beam  422  can form a beam spot on a surface of a sensor of electron detector  406 . Electron detector  406  can generate a signal (e.g., a voltage, a current, etc.) that represents an intensity of the beam spot and provide the signal to a processing system (not shown). The intensity of secondary electron beam  422 , and the resultant beam spot, can vary according to the external or internal structure of wafer  403 . Moreover, as discussed above, primary electron beam  420  can be projected onto different locations of the top surface of wafer  403  to generate secondary electron beams  422  (and the resultant beam spot) of different intensities. Therefore, by mapping the intensities of the beam spots with the locations of wafer  403 , the processing system can reconstruct an image that reflects the internal or external structures of wafer  403 . Once a wafer image is acquired by electron beam tool  104 , the wafer image may be transmitted to computer system (not shown). 
       FIG.  3    is a schematic diagram illustrating a top plan view of a reference sample with a rectangular scanning grid, consistent with some embodiments of the present disclosure. In  FIG.  3   , in the top surface of the sample wafer W, a scanning area SA of the exemplary SEM of  FIG.  2    is a rectangular grid of scanning pattern of the exemplary SEM of  FIG.  2    is shown. The rectangular grid shown in  FIG.  3    is an 8×9 matrix rectangular grid having 8 rows and 9 columns of unit areas. The unit areas or pixels may cover a portion of a die or dies, and are designed for scanning and blanking purpose. Each of the unit areas or pixels has an exemplary area of 1 nm×1 nm. Each of the unit areas is labelled with a number and an alphabet, e.g. the unit area located at row  1  and column  1  is labelled  1 A. The unit area located at row  8  and column  9  is labelled  24 C. In this manner, all unit areas in the grid are labelled for convenience of describing the scanning pattern of the SEM. In other embodiments, the grid can be an m×n matrix rectangular grid, where m and n are natural numbers. Also, the shape of the grid can be rectangle, square, circle, ellipse, pentagon, hexagon, or any polygon. For a better coverage of the circular disc shaped sample W, the grid can have a circular shape. For explaining the scanning, a rectangular grid SA is used. 
     In  FIG.  4 A , during scanning the sample W, the SEM emits an electron beam that interacts with the first unit area  1 A of the scanning area or grid SA. During this scanning, the electron beam interacts with the unit area IA for a definite period of time and without or with minimally interacting with the surrounding area. During or after scanning, the charges accumulated on the unit area IA and any surrounding area dissipate, which involves the charges being conducted away from the charged region associated with unit area  1 A. The distance on the sample required for such conduction is dissipation distance L ( FIG.  4 B ). Distance L is a threshold distance between successively scanned unit areas and is selected to mitigate a charge induced distortion from previously scanned nearby unit area such that a blanked unit area separates the scanned unit area and a next unit area to be scanned by a distance equal to or greater than the threshold distance. Thus, after scanning the unit area  1 A, the next unit area to be scanned is located outside of a dissipation region located at or greater than a distance L from the scanned unit area  1 A, e.g., the next unit area to be scanned may not be located within the dissipation region circled by dotted line in  FIG.  4 B . The dissipation region is determined based on the intensity of the electron beam interacting with the unit area  1 A and the time duration for such interaction. That is, a greater dissipation region may occur when a higher electron beam intensity is used or when the electron beam interacts with the unit area over a longer time duration, resulting in a stronger electric field and an increased range in which the electric field may have a negative impact. 
     While it is preferred that the next unit area is located outside of the determined dissipation region to minimize any charge distortion, it is appreciated that some implementations may scan next unit areas that are not adjacent to the previously scanned unit area and that fall within the dissipation region. For example, referring to  FIG.  4 B , while unit area  7 A may have some charge/dissipation effects from the scanning of unit area  1 A, the effects may be determined as not being significant enough to cause consequential charge distortion. 
     Referring back to the scanning of sample W, the scanning and blanking can occur in organized batches of unit areas. The batch may be a set of unit areas in a row or a column. For example, in the embodiments described in  FIGS.  4 A- 4 L , each batch of unit areas corresponds to a different column. As illustrated, in situations where the batch is a column of unit areas, the scanning can start with unit area  1 A of a first batch and then down the column, after which unit areas  4 A and  7 A are blanked using a blanker (e.g., blanker  424  of  FIG.  2   ), so that the electron beam is deflected away from these unit areas. Then, the electron beam tool scans next unit area  10 A, which is separated from the scanned unit area  1 A by a distance greater than or equal to dissipation distance L. In this manner, after scanning the unit area  10 A, the electron beam tool blanks unit areas  13 A and  16 A ( FIG.  4 C ). Then, in  FIG.  4 C , the electron beam tool scans unit area  19 A. Since unit area  22 A is adjacent to the scanned unit area  19 A and the distance of separation is less than dissipation distance L, the unit area  22 A is blanked by the electron beam tool. 
     Then, in this way, a first round of scanning and blanking the first batch of unit areas in the first column is finished with some unit areas (i.e.,  1 A,  10 A, and  19 A) scanned and some unit areas ( 4 A,  7 A,  13 A,  16 A, and  22 A) blanked to allow the charged regions around unit areas  1 A,  10 A, and  19 A to dissipate. After the charge dissipates or substantially dissipates, the dissipation distance could be 0.1 to 5 μm, and the electron beam tool can later revisit the first batch one or more times to scan the blanked unit areas  4 A,  7 A,  13 A,  16 A, and  22 A so that the imaging information acquired from those unit areas are accurate and is not distorted by the electric field of the accumulated charges. 
     As shown in  FIG.  4 D , after scanning unit area  19 A, the electron beam tool scans unit area  2 A (which can be part of a second hatch of unit areas—in this case, the column of unit areas associated with unit area  2 A), which is outside of dissipation region associated with scanned unit area  1 A. As shown in  FIG.  4 D , unit areas  1 B and  1 C are located within dissipation region. Because they are still located in dissipation region, it is appreciated that the columns associated with unit areas  1 B and  1 C can he blanked or skipped altogether. 
     Moreover, while  FIG.  4 D  shows that dissipation region is relatively the same size as dissipation region of  FIG.  4 B , it is appreciated that the size of dissipation region and dissipation distance L may be affected by the elapsed time from the scanning of unit area  1 A. Accordingly, the electron beam tool may consider the elapsed time with respect to the dissipation region, when determining which unit area to scan next. To the extent that the dissipation region has been determined to become smaller so that charge has dissipated sufficiently enough from unit area  1 C, the electron beam tool can scan unit area  1 C and proceed down the column associated with unit area  1 C. 
     Referring back to  FIG.  4 D , while this figure shows that unit area  2 A is the next unit area to be scanned after the scanning of unit area  19 A, it is appreciated that any unit area outside of the dissipation regions associated with scanned unit areas  1 A,  10 A, and  19 A can be scanned. For example, unit areas  20 A or  23 A could be scanned after unit area  19 A as they are both outside of the dissipation region associated with unit area  19 A. Accordingly, the electron beam tool can blank and scan other unit areas in the column associated with unit areas  20 A or  23 A. 
     Using the same approach described above in  FIG.  4 B , in  FIG.  4 E , after scanning unit area  2 A of the second batch, the electron beam tool blanks unit areas  5 A and  8 A and scans the next unit area  11 A. Using the approach described above in  FIG.  4 C , as shown in  FIG.  4 F , after scanning unit area  11 A, the electron beam tool blanks unit areas  14 A and  17 A and scans unit area  20 A. After scanning unit area  20 A, the electron beam tool uses a similar approach described above in  FIG.  4 D . For example, as shown in  FIG.  4 G , the unit area  23 A is blanked and all the unit areas in columns associated with unit areas  2 B and  2 C are blanked or skipped, and the electron beam scans unit area  3 A of a third batch. In a manner similar to that described earlier, as shown in  FIG.  411   , after scanning unit area  3 A, the electron beam tool blanks unit areas  6 A and  9 A and then scans unit area  12 A. After scanning unit area  12 A, as shown in  FIG.  41   , the electron beam tool blanks unit areas  15 A and  18 A and then scans unit area  21 A. 
     After scanning unit area  21 A, unit area  24 A and all the unit areas in columns associated with unit areas  3 B and  3 C are within a range of distance L and may be either blanked or skipped. Then, after scanning unit area  21 A, as shown in  FIG.  4 J , the electron beam tool returns to the first batch of unit areas (in this case, the first column associated with unit area  1 A) to scan the un-scanned unit area  4 A, which is adjacent to previously scanned first unit area  1 A as the charge from unit area  1 A has dissipated enough over time to mitigate any threshold level of charge distortion for imaging unit area  4 A. 
     For the similar reason explained above, as shown in  FIG.  4 K  after scanning unit area  4 A in  FIG.  4 J , the electron beam tool blanks unit areas  7 A and  10 A, and the electron beam scans unit area  13 A ( FIG.  4 K ). This process continues, such that unit area  22 A is scanned, after which the electron beam tool scans unit areas  5 A,  14 A, and  23 A of the second batch and unit areas  6 A,  15 A, and  24 A of the third batch in order. Then, the electron beam tool can move back to the first column of unit areas and scan unit areas  7 A and  16 A of the first batch, after which the electron beam tool scans unit areas  8 A and  17 A of the second batch and unit areas  9 A and  18 A of the third batch. Upon completing the scanning of the A-columns associated with unit areas  1 A,  2 A, and  3 A, the scanning and blanking process can move to scan the B-columns (e.g., columns associated with unit areas  1 B,  2 B, and  3 B) in a manner similar to that described above with respect to  FIGS.  4 A- 4 K . After the unit—areas in the B-columns are scanned, the electron beam tool can then move to scan and blank the C-columns (e.g., columns associated with unit areas  1 C,  2 C, and  3 C), the completion of which is shown in  FIG.  4 L . In this way, the entire scanning area or grid SA is scanned. After completing the scanning, the information obtained are analyzed by the processor or controller of the SEM system with or without intervention of a user using the user interface  109  in  FIG.  1   . 
       FIGS.  5 A,  5 B, and  5 C  are schematic diagrams illustrating top plan views of the reference sample of  FIG.  3    undergoing different stages of scanning by the exemplary electron beam tool of  FIG.  2    by column-to-row scanning at a different dissipation distance L′ (i.e. L′# L), consistent with some embodiments of the present disclosure. Distance L′ is a distance greater than a threshold distance between successively scanned unit areas is selected to mitigate a charge induced distortion from previously scanned nearby unit area such that the blanked unit area separates the scanned said each unit area and a next unit area to be scanned by a distance greater than the threshold distance. In  FIG.  5 A , during scanning the sample W, the electron beam tool emits an electron beam, which interacts with the first unit area  1 A of the scanning area or grid SA. During this scanning, the electron beam interacts with most of the unit area  1 A or the entire unit area  1 A for a definite period of time. During or after scanning, the charges accumulated on the unit area  1 A begin to dissipate by being conducted away from the unit area of the sample W. The distance on the sample required for such conduction is dissipation distance L′ ( FIG.  5 B ). Thus, after scanning the unit area  1 A, the next unit area to be scanned may he located at or outside of distance L′ from the scanned unit area  1 A, that is, the next unit area to be scanned may not be located within the dissipation region annotated by dotted line in  FIG.  5 B . 
     As shown in  FIG.  5 B , after scanning unit area  1 A, the electron beam tool blanks unit areas  4 A,  7 A, and  10 A, by deflecting the electron beam away from these unit areas as each of these blanked unit areas fall within dissipation region of the dashed circle associated with dissipation distance L′. Then, the electron beam scans the next unit area  16 A, which is separated from the scanned unit area  1 A by dissipation distance L′. In this manner, after scanning the unit area  16 A, the unit areas  19 A and  22 A are blanked and all unit areas of columns  2  to  5  are either blanked or skipped ( FIG.  5 C ). 
     Then, the electron beam scans the next unit area  2 C. After scanning unit area  2 C, the electron beam tool blanks unit areas  5 C,  8 C,  11 C, and  14 C and scans unit area  17 C ( FIG.  5 C ). After scanning unit area  17 C, unit areas  20 C  23 C are blanked and all unit areas in columns  7  to  9  are all within a range of distance L′ and can be blanked or skipped, in which they can be scanned later. Then, the electron beam returns to the first column to continue to scan the next unit area (e.g., unit area  4 A). In this way, the first round of scanning the scanning area is completed by scanning unit areas IA,  16 A,  2 C, and  17 C. 
       FIGS.  6 A- 6 I , are schematic diagrams illustrating top plan views of the reference sample of  FIG.  3    undergoing different stages of scanning by the exemplary electron beam tool of  FIG.  2    by diagonal scanning at dissipation distance L, consistent with some embodiments of the present disclosure. In  FIG.  6 A , during scanning of the sample W, the electron beam tool emits an electron beam that interacts with the first unit area  1 A of the scanning area or grid SA. During this scanning, the electron beam interacts with most of the unit area  1 A or the entire unit area  1 A for a definite period of time. 
     During or after scanning, the charges accumulated on the unit area  1 A begin dissipating by being conducted away from the unit area of the sample W. The distance on the sample required for such conduction is dissipation distance L ( FIG.  6 B ). Thus, after scanning the unit area  1 A, the electron beam tool scans unit area  11 A, which is located outside of dissipation region. In a scanning fashion of starting from unit area  1 A and then diagonally to the bottom right corner of the grid SA, unit areas  4 B and  7 C are entirely or partially within the range of distance L from unit area  1 A and are blanked by a blanker (e.g., blanker  424  of  FIG.  2   ). Then, the electron beam scans the next unit area  11 A, which is separated from the scanned unit area  1 A by more than dissipation distance L. In this manner, after scanning the unit area  11 A, the electron beam tool blanks the unit areas  14 B and  17 C ( FIG.  6 C ). Then, the electron beam scans the next unit area  21 A. After scanning unit area  21 A, the electron beam tool blanks unit area  24 B and then scans unit area  2 A ( FIG.  6 D ). It is appreciated that between the blanking of unit area  24 B and the scanning of unit area  2 A, the electron beam tool can blank unit areas  1 B,  4 C,  8 A,  11 B,  14 C,  18 A,  2113 ,  24 C,  1 C,  5 A,  8 B,  11 C,  15 A,  18 B, and  21 C. 
     After scanning unit area  2 A, the electron beam tool blanks at least unit areas  5 B and  8 C as these unit areas&#39; fall within the range of distance L from unit area  2 A. Then, the electron beam scans unit area  12 A ( FIG.  6 E ). After the scanning of unit area  12 A, the electron beam tool can blank unit areas  2 B,  5 C,  9 A,  12 B,  15 C,  2 C,  6 A,  9 B, and  12 C or skip them altogether and proceed to the next unit area to scan. 
     Then, the electron beam scans unit area  3 A ( FIG.  6 F ). In  FIG.  6 G , after scanning unit area  3 A, the electron beam tool scans one of unit area  19 A ( FIG.  6 G ). It is appreciated that the electron beam tool can scan unit area  10 A instead of unit  19 A and then blank one or more unit areas that are diagonal from unit  10 A. 
     Referring to  FIG.  6 H , after scanning unit area  19 A, the electron beam tool can blank unit areas  22 B,  16 A,  19 B,  22 C,  13 A,  16 B, I 9 C, and  23 A because these unit areas are within the range of distance L and scanning these unit areas would result in distorted information. It is appreciated that instead of blanking these unit areas (i.e., unit areas  22 B,  16 A,  19 B,  22 C,  13 A,  16 B,  19 C, and  23 A), the electron beam tool can skip the units altogether before moving to scan the next unit area. Then, the electron beam tool scans unit area  10 A ( FIG.  6 H ). In the same manner as  FIG.  6 E , the electron beam tool blanks at least unit areas  13 B and  16 C before scanning at unit area  20 A ( FIG.  61   ). Thus, in the completion of the first round of scanning the scanning area SA, unit areas  1 A,  10 A,  19 A,  2 A,  11 A,  20 A,  3 A,  12 A, and  21 A are scanned while all other unit areas in the scanning area or grid SA are blanked (while some of the unit areas may be skipped altogether). The above embodiments show a rectangular grid. To one of ordinary skill in the art, the grid shape can be any shape including square, pentagon, hexagon, polygon, circle, ellipse, and a mixture of different shapes. 
     As described above, the plurality of unit areas of a scanning area can be organized in batches of unit areas provided in rows or columns, and the scanned unit area and the blanked unit area are in a first batch of unit areas. After scanning and blanking unit areas in the first batch, the electron beam tool blanks a second batch of unit areas that is adjacent to the first batch; and the electron beam tool scans and blanks unit areas in a third batch of unit areas that is not adjacent to the first batch and is at least a threshold distance from the first batch to mitigate charge induced distortion from scanned unit areas of the first batch. After scanning and blanking unit areas in the third hatch or after a dissipation time threshold, the electron beam tool returns to the first batch of unit areas to scan unit areas that have not been previously scanned to mitigate charge induced distortion from previously scanned unit areas of the first batch. In this way, the unit areas to be scanned and blanked can be flexibly controlled to suit different purposes (e.g. efficiency of scanning or time consumption, and image quality levels of the final image). 
     Alternately, the method includes scanning a first set of locations with the SEM. Each location of the first set of locations being physically separated by at least a threshold distance. The method further includes scanning a second set of locations with the SEM a period of time after scanning the first set of locations, in some embodiments. A location of the second set of locations is located within the threshold distance of a location of the first set of locations, in some embodiments. The period of time enables charge resulting from the scanning the first set of locations to dissipate sufficiently so as to mitigate a charge induced distortion of a scan of a location within the threshold distance. In some embodiments, each of the first set of locations are arranged in diagonal to each other. In some embodiments, each of the second set of locations are arranged in diagonal to each other. 
     References are now made to  FIG.  7    which is a flow chart illustrating an exemplary method of scanning a sample using a charged particle tool, consistent with some embodiments of the present disclosure. The method may be performed by a charged particle beam tool, such as an electron beam tool (e.g., electron beam tool  104  of  FIG.  2   ). 
     In step S 710 , a sample is provided in the electron beam tool. The sample (e.g., sample  403  of  FIG.  2    or sample W of  FIG.  3   ) includes a wafer made of silicon, silicon dioxide, germanium, and silicon germanium, with or without a pattern formed on it by any method including UV, DUV, and EUV photolithographic methods, among others. The sample may include regions having conducting, semiconducting, or insulating properties. Also, the sample may be processed by sputtering on it a layer of highly conductive material such as gold or silver or may not be processed. 
     Under the electron beam tool, the top surface of sample can be logically divided into numerous unit areas, such as pixels (e.g., as illustrated in  FIG.  3   ). Each of the unit areas is scanned by an electron beam of the electron-beam tool for a short period of time. In this example, the unit area or pixel is a 1 nm by 1 nm square region of the sample, but it is appreciated that the unit area may be a defined region of any size or any shape including rectangular, circular, or polygonal shape, among others. 
     In step S 720 , the electron beam tool scans one or more unit areas of the sample. During the scanning, the electron beam interacts with the material on the surface of the unit area of the sample. The more time that the electron beam interacts with the unit area, the more that charge buildup occurs at a region surrounding the unit area from that interaction. Optionally, in step S 720 , a time stamp associated with the scanning of the unit area can be provided, which may allow the electron beam tool to determine when to revisit the unit areas surrounding the scanned unit area in order to minimize the impact that the charge distortion from the previously scanned unit area may have on the surrounding unit areas. 
     The more charge buildup that occurs in the region surrounding the unit area, the longer it may take for the charge to dissipate from the region. Moreover, the type of sample material can affect the charge dissipation, as each type of sample material can have distance- and time-dissipation characteristics. These characteristics can vary based on the materials used. In some examples, the distance for conducting the accumulated charges away from the scanned unit area of the sample is about 0.1-5 μm and is called dissipation distance, and the time required for such effect is called dissipation time. 
     In step S 730 , the electron beam tool blanks a unit area adjacent to the scanned unit area of sample. Considering the dissipation distance and dissipation time required for conducting the accumulated charges away from the scanned unit area of the sample, the next region to be scanned would be located at a distance equal to or greater than the dissipation distance from the scanned unit area in step S 720 . To achieve the effect of not scanning the region between the scanned unit area in step S 720  and the next unit area to be scanned, the electron beam tool is equipped with a component called a blanker (e.g., blanker  424  of  FIG.  2   ). The blanker may be a shutter, electromagnetic field deflector, or pure electrostatic deflector, among others. The blanker can deflect the electron beam such that the electron beam no longer reaches the sample so that the region between the scanned unit area in step S 720  and the unit area to be scanned is not scanned by the electron beam. 
     As described above, it is appreciated that more than one unit area may be blanked (e.g., unit areas  4 A and  7 A after unit area IA has been scanned in  FIG.  4 B ). The number of blanked unit areas may depend on the amount of time that the electron beam interacts with the scanned unit area of step S 720 . The amount of time can affect the dissipation time and the dissipation distance, both of which can used to determine the blanking time and corresponding one or more blanking unit areas, respectively. That is, the time for blanking is determined by the dissipation time and the unit area for blanking is determined by the dissipation distance such that blanked distance is greater than the dissipation distance and the time for blanking is greater than the dissipation time. 
     At step S 750 , the electron beam tool determines whether there are any un-scanned unit areas in the sample. If, after the step S 730  of blanking a unit area, there is un-scanned unit area, the method proceeds to S 770 , in which the electron beam tool scans another unit area outside of the dissipation region associated with the previously scanned unit area (e.g., unit area scanned in step S 720 ). In this way, the scanning and blanking of unit areas can be repeated until the interested region of the sample is entirely scanned, at which point at step S 750 , the electron beam tool determines that there are no remaining un-scanned areas. Then, the process of scanning the sample ends at step S 760 . 
     Optionally, after step S 750 , the method further includes a process of providing an image of the sample by reconstructing the entire image using the sub-images generated using the various scanned unit area. To do so, the sequence of images may be mapped to the logical arrangement of the numerous unit areas and the order by which the numerous unit areas are scanned. For example, using  FIGS.  4 A- 4 J  as a reference, the first sub-image (sub-image associated with unit area  1 A) can be stitched together with the tenth sub-image (sub-image associated with unit area  4 A) using the scanning order of the unit areas as a reference. Also, the reconstructing is performed by using at least one of interpolation, sparse sampling or simulation. 
     The embodiments may further be described using the following clauses:
     1. A method for scanning a sample by a charged particle beam tool, comprising:
       providing the sample having a scanning area, wherein the sample is determined to have a plurality of unit areas;   scanning a unit area of the plurality of unit areas; and blanking a first unit area adjacent to the scanned unit area.   
       2. The method of clause 1, further comprising:
       determining whether any unit area on the sample remains to be scanned;   in response to the determination that any unit area on the sample remains to be scanned,
           scanning a next unit area that is more than a predetermined distance from the scanned unit area; and   blanking a second unit area adjacent to the scanned next unit area.   
           
       3. The method of clause 2, wherein the predetermined distance is based on a dissipation region associated with the scanned unit area.   4. The method of clause 2, further comprising blanking a third unit area adjacent to the blanked first unit area before scanning the next unit area.   5. The method of clause 1, wherein the blanked first unit area includes multiple unit areas.   6. The method of any one of clauses 1 to 5, wherein the first blanked unit area is adjacent to the scanned unit area in an X-direction.   7. The method of any one of clauses 1 to 5, wherein the first blanked unit area is adjacent to the scanned unit area in a Y-direction.   8. The method of clause 1, wherein the scanned unit area is a single pixel of a scanned image.   9. The method of clause 1, wherein the first blanked unit area is a single pixel.   10. The method of clause 1, wherein the first blanked unit area is multiple pixels.   11. The method of clause 1, wherein the scanned unit area is a plurality of pixels of a scanned image.   12. The method of any one of clauses 1 to 11, wherein blanking a first unit area adjacent to the scanned unit area further comprises:
       applying a current to an electromagnetic blanker so that an electromagnetic field generated by the blanker deflects a charged-particle beam of the charged-particle beam tool such that the charged-particle beam no longer reaches the sample.   
       13. The method of any one of clauses 1 to 11, wherein blanking a first unit area adjacent to the scanned unit area further comprises:
       moving a shutter to intercept a pathway of a charged-particle beam of the charged-particle beam tool such that the charged-particle beam no longer reaches the sample.   
       14. The method of any one of clauses 1 to 13, wherein the scanning and the blanking are determined based on a dissipation time for charge dissipation in the scanned unit area.   15. The method of any one of clauses 1 to 13, wherein the scanning and the blanking are carried out on a predetermined pattern in the sample.   16. The method of clause 15, wherein the predetermined pattern is one of a line pattern parallel to the edges of the scanning area, a line pattern diagonal in the scanning area, or a circular pattern.   17. The method of any one of clauses 1 to 15, wherein the scanning and the blanking are performed on the plurality of unit areas until all unit areas are scanned.   18. The method of clause 17, further comprising reconstructing an image of the sample using sub-images corresponding to the plurality of unit areas that have been scanned.   19. The method of clause 18, wherein the reconstructing is performed by using at least one of interpolation, sparse sampling, or simulation.   20. The method of any of one of clauses 1 to 19, wherein the plurality of unit areas of a scanning area are organized in batches of unit areas provided in rows or columns and wherein the scanned unit area and the blanked unit area are in a first batch of unit areas.   21. The method of clause 20, wherein after scanning and blanking unit areas in the first batch:
       blanking or skipping a second batch of unit areas that is adjacent to the first batch; and   scanning and blanking unit areas in a third batch of unit areas that is at least a threshold distance from the first hatch to mitigate charge induced distortion from scanned unit areas of the first batch.   
       22. The method of clause 20, further comprising after a dissipation time threshold, returning to the first batch of unit areas to scan unit areas that have not been previously scanned to mitigate charge induced distortion from previously scanned unit areas of the first batch.   23. A charged particle beam system comprising:
       a charged particle source;   a scanning deflector to scan a charged particle beam emitted from the charged particle source on a scanning area of a sample, wherein the sample is determined to have a plurality of unit areas;   a blanker for blanking the charged particle beam such that the charged particle beam no longer reaches the sample; and   a controller includes circuitry for controlling the scanning deflector and the blanker,   wherein the controller is configured to:
           scan a unit area of the plurality of unit areas; and   blank a first unit area adjacent to the scanned unit area.   
           
       24. The system of clause 23, wherein the controller is further configured to:
       determine whether any unit area on the sample remains to be scanned;   in response to the determination that any unit area on the sample remains to be scanned,
           scan a next unit area that is more than a predetermined distance from the scanned unit area; and   blank a second unit area adjacent to the scanned next unit area.   
           
       25. The system of clause 24, wherein the predetermined distance is based on a dissipation region associated with the scanned unit area.   26. The system of any one of clauses 24 and 25, wherein the controller is further configured to:
       blank a third unit area adjacent to the blanked first unit area before scanning the next unit area.   
       27. The system of clause 23, wherein the blanked first unit area includes multiple unit areas.   28. The system of any one of clauses 23 to 27, wherein the charged particle beam system is a scanning electron microscope (SEM).   29. The system of any one of clauses 23 to 28, wherein the charged particle beam is an electron beam.   30. The system of clauses 23 to 29, wherein the first blanked unit area is adjacent to the scanned unit area in an X-direction.   31. The system of clauses 23 to 29, wherein the first blanked unit area is adjacent to the scanned unit area in a Y-direction.   32. The system of clause 23, wherein the scanned unit area is a single pixel of a scanned image.   33. The system of clause 23, wherein the first blanked unit area is a single pixel.   34. The system of clause 23, wherein the first blanked unit area is multiple pixels.   35. The system of clause 23, wherein the scanned unit area is a plurality of pixels of a scanned image.   36. The system of any one of clauses 23 to 35, wherein the blanker is an electromagnetic blanker to which a current is applied so as to induce an electromagnetic field that deflects the charged particle beam of the SEM such that the charged particle beam no longer reaches the sample.   37. The system of any one of clauses 23 to 35, wherein the blanker is a shutter configured to intercept a pathway of the charged particle beam of the SEM so as to perform the blanking.   38. The system of any one of clauses 23 to 37, wherein the blanker is configured to blank for a time determined based on a dissipation time for charge dissipation.   39. The system of any one of clauses 23 to 37, wherein the controller includes circuitry to determine a next unit area to scan, wherein the next unit area is at least a threshold distance from the scanned unit area and is selected to mitigate a charge induced distortion from the scanned unit area such that the blanked unit area separates the scanned unit area from the next unit area.   40. The system of any one of clauses 23 to 39, wherein the blanker is configured to blank a predetermined pattern in the sample comprising any one of a line pattern parallel to edges of the scanning area, a line pattern diagonal in the scanning area to a direction, a circular pattern, or a random pattern.   41. The system of any one of clauses 23 to 40, wherein the blanker is positioned between the charged particle source and the scanning deflector.   42. A non-transitory computer readable medium that stores a set of instructions that is executable by at least one processor of a computer system to cause the computer system to perform a method for service processing, the method comprising:
       providing a sample having a scanning area, wherein the sample is determined to have a plurality of unit areas;   scanning a unit area of the plurality of unit areas with a charged particle beam; and blanking a unit area adjacent to the scanned unit area.   
       43. The non-transitory computer readable medium according to clause 42, wherein the set of instructions that is executable by the at least one processor of a computer system to cause the computer system to further perform:
       determining whether any unit area on the sample remains to be scanned;   
       

     in response to the determination that any unit area on the sample remains to be scanned,
         scanning with the charged particle beam a next unit area that is more than a predetermined distance from the scanned unit area; and   blanking a unit area adjacent to the next unit area.       44. The non-transitory computer readable medium according to clause 43, wherein the predetermined distance is based on a dissipation region associated with the scanned unit area.   45. The non-transitory computer readable medium according to clauses 42 to 44, wherein the scanned unit area is a single pixel or a plurality of pixels of a scanned image before a next unit area is scanned.   46. A method of scanning a sample by a charged particle beam system, the method comprising:
       scanning a first unit area of a first set of unit areas with a charged particle beam, each unit area of the first set of unit areas being separated by more than a predetermined distance; and   scanning a second unit area of a second set of unit areas a period of time after scanning the first unit area of the first set of unit areas, each unit area of the second set of unit areas being separated by more than the predetermined distance.   
       47. The method of clause 46, wherein the predetermined distance is based on a size of a dissipation region associated with a unit area.   48. The method of any one of clauses 46 to 47, wherein the period of time is based on a time to dissipate charge that results from the scanning of the first unit area.   

     It is appreciated that a controller of the electron beam tool could use software to control the functionality described above. For example, the controller may assist with the scanning and blanking of unit areas and the order by which the unit areas are scanned. Moreover, the controller can automatically adjust the order by which the unit areas are scanned and blanked based on the characteristics of the wafer and the length of time the electron beam interacts with the wafer. The controller may send instructions for scanning the wafer (such as scanning a wafer of  FIG.  7   ). The software may be stored on a non-transitory computer readable medium. 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 CD-ROM, any other optical data storage medium, any physical medium with patterns of holes, a RAM, a PROM, and EPROM, cloud storage, a FLASH-EPROM or any other flash memory, NVRAM, a cache, a register, any other memory chip or cartridge, and networked versions of the same. 
     It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of described embodiments may be made by those skilled in the art without departing from the scope as expressed in the following claims.