Abstract:
A charged particle detection device has an active portion for configured to produce a signal in response secondary charged particles emitted from a sample landing on the active portion. The active portion is shaped to accommodate an expected asymmetric pattern of the secondary charged particles at a detector. This abstract is provided to comply with rules requiring an abstract that will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Description:
CLAIM OF PRIORITY 
       [0001]    This application is a nonprovisional of and claims the priority benefit of commonly owned, co-pending U.S. Provisional Patent Application No. 61/874,834, to John Gerling et al., filed Sep. 6, 2013, and entitled “ASYMMETRICAL DETECTOR DESIGN AND METHODOLOGY” the entire disclosures of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    Embodiments of the present invention relate to charged particle detection and detection devices, and more particularly, to an optimal detector layout design for secondary charged particle detectors in a charged particle system using multiple columns for line scans. 
       BACKGROUND OF THE INVENTION 
       [0003]    Secondary charged particles are emitted from a surface of the specimen to be examined when electron or ion source impinges on the surface with sufficient energy. Since the energy and/or the energy distribution of such secondary charged particles offers information as to the topography of the specimen, detectors are employed to detect the secondary charged particles and convert them to electrical signals used to generate images of the specimen. Scanning electron microscopes (SEMs) are generally provided with such a detection device for secondary electrons. 
         [0004]    Specifically in SEMs, an electron beam source generates a primary electron beam passing through a hole in the middle of a detection device. A variable electrostatic or magnetic field deflects the primary electron beam to scan it over a region of a specimen. When the primary beam strikes the specimen, secondary electrons are generated. Such particles have an energy which is significantly lower than that of the particles in the primary electron beam, e.g., 50 eV. Some of these secondary electrons pass back up through the electron optical column and interact with the primary beam deflection fields as they pass back through the optical column. Thereafter these secondary electrons are imaged onto the detection device. 
         [0005]    To collect as many of the secondary electrons as possible, conventional SEM systems use secondary electron detectors that are relatively large. However, since leakage current and capacitance of a detector (e.g., a photodiode) are proportional to the detector area (e.g., the area of the photodiode depletion zone), it is not desirable to have an excessive detector area. In addition, conventional secondary electron detectors are typically rotationally symmetric. However, while the detector may be rotationally symmetric, the pattern of electrons landing on the detector might not be symmetric. Secondary electrons traveling back up through the optical column tend to undergo rotation and deflection as a result of magnetic fields used in immersion lenses or the deflection by the optical column. The amount of rotation depends partly on the landing energy of the primary electrons. Higher energy electrons undergo less rotation since they spend less time in the magnetic field due to their relatively high velocities. 
         [0006]    Conventional detectors generally include a metal shield to cover up any exposed dielectric on the detectors to prevent charging that would produce a deflection field. For example, prior art SEM systems use a MEMS-type shield made of thin metal foil that is patterned (e.g., by laser) and bonded to the detector. The shield and the detectors are conventionally manufactured separately and are integrated afterwards. Thus, conventional detectors require additional process steps that confer additional cost and complexity of alignment or assembly. 
         [0007]    It is within this context that aspects of the present disclosure arise. 
       SUMMARY 
       [0008]    According to aspects of the present disclosure, a charged particle detector has an active portion configured to generate a signal in response to secondary charged particles emitted from a sample landing on the active portion. The active portion of the charged particle detector is shaped to accommodate an expected asymmetric distribution of the secondary charged particles at the detector. 
         [0009]    In some implementations, an electrically conductive layer deposited and/or formed on selected parts of the device other than the active portion. 
         [0010]    In some implementations the active portion of the charged particle detector is sector-shaped. 
         [0011]    In some implementation, the charged particle detector is a diode device having a junction and a depletion region. 
         [0012]    In some implementation, the charged particle detection device is a PN junction, PIN junction, CMOS detector, CCD, silicon-based/III-V detector, multi-channel plate, avalanche photodiode or Schottky diode. 
         [0013]    The charged particle detection device may include an aperture, e.g., in the middle or other location of the detection device. The aperture may be surrounded by an inactive area. The aperture and the inactive area may be sized to keep signal clipping losses of detection of charged particles to less than 1%. 
         [0014]    According to aspects of the present disclosure, a charged particle optical system comprises a charged particle optical column configured to collect charged particles from a sample and image the charged particles onto a detector. The detector includes active portion configured to produce a signal in response to a flux of the charged particles impinging on the active portion. The active portion is shaped to accommodate an expected asymmetrical pattern of the secondary charged particles at the detector. 
         [0015]    In some implementations, the system further includes a source configured to emit energetic particles that impinge on the sample. 
         [0016]    In some implementations, the charged particle optical system is a scanning electron microscope (SEM) system, wherein the system further includes an electron source configured to emit primary electrons, and wherein the charged particle optical column is configured to direct the primary electrons onto the sample. 
         [0017]    In some implementations, the detector is located between the electron source and an end of the charged particle optical column that is closest to the sample, wherein the detector includes an aperture configured to allow at least a portion of the primary electrons to pass through the detector towards the target. 
         [0018]    In some implementations, the aperture is surrounded by an inactive area, wherein the aperture and the inactive area are sized to keep signal losses due to clipping of detection of the secondary charged particles to less than 1%. 
         [0019]    In some implementations, the detector in the system further comprises a metallization layer on portions of the detector other than the active portion, wherein the metallization layer is formed as an integral part of the detector. 
         [0020]    In some implementations the detector in the system is a diode device having a junction and a depletion region. 
         [0021]    In some implementations, the primary optical column of the charged particle optical system has a source configured to emit energy beam that passes through the primary optical column before impinging on the sample. 
         [0022]    In some implementations, the detector is located between the energy source and an end of the optical column that is closest to the sample. In such implementations, the detector may include an aperture in the middle or other location of the detection device to permit the energy beam to pass through the detector. The aperture may be surrounded by an inactive area, wherein the aperture and the inactive area are sized to keep signal clipping losses of detection of charged particles to less than 1%. 
         [0023]    In some implementations, the charged particle optical system is a scanning electron microscope (SEM), a focused ion beam system, ultraviolet photoelectron spectroscopy system (UPS), an X-ray photoelectron spectroscopy (XPS) system, an auger electron spectroscopy (AES) system, and/or a Secondary Ion Mass Spectroscopy (SIMS) system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    Objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings in which: 
           [0025]      FIG. 1A  is a schematic diagram of an electron beam system adapted to include a detector according to an aspect of the present disclosure. 
           [0026]      FIG. 1B  is a block diagram of the system of  FIG. 1A . 
           [0027]      FIG. 1C  is a plan view diagram of a conventional secondary electron detection device. 
           [0028]      FIG. 2  is a plan view diagram of a secondary electron detection device according to an aspect of the present disclosure. 
           [0029]      FIG. 3  is a diagram of image plane for a line scan. 
           [0030]      FIG. 4  is a set of graphs showing scatter plots of secondary electron position on a detector according to an aspect of the present disclosure. 
           [0031]      FIG. 5  is a graph showing secondary electron capture as a function of the photodiode aperture radius/dead zone radius for a detector according to an aspect of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. The drawings show illustrations in accordance with examples of embodiments, which are also referred to herein as “examples”. The drawings are described in enough detail to enable those skilled in the art to practice the present subject matter. Because components of embodiments of the present invention can be positioned in a number of different orientations, directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. 
         [0033]    In this document, the terms “a” and “an” are used, as is common in patent documents, to include one or more than one. In this document, the term “or” is used to refer to a nonexclusive “or,” such that “A or B” includes “A but not B,” “B but not A,” and “A and B,” unless otherwise indicated. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. 
         [0034]      FIG. 1A  and  FIG. 1B  illustrate an example of a charged particle system  100  incorporating certain aspects of the present disclosure. In this non-limiting example, the system  100  is configured as a scanning electron microscope (SEM) having charged particle optical column  102  with an electron source  115 , beam optics  135 , a magnetic immersion lens  104 . The optical column  102  may be controlled by electronics  136 , referred to herein as a beam driver. The beam driver  136  may control the electron source  115 , beam optics  135  and immersion lens  104 . In this example, the beam optics  135  extract electrons from the source  115  and form them into a primary beam that travels in the direction of the target  101 . The immersion lens  104  focuses the primary beam into a narrow spot at the surface of the target. 
         [0035]    Electrons from the electron beam column  102  are focused onto a target surface  101 , which may be an integrated circuit wafer or a test wafer. The target  101  is supported by a stage  118 . The electrons may be scanned across the surface of the target  101 , e.g., by magnet deflecting fields provided by one or more scanning coils or electrostatic deflector plates  106 . In some implementations, the beam scanner driver  108  may provide current to deflector coils  106  via a beam scanner driver  108 . In other implementations, the beam scanner driver  108  may apply voltages to electrostatic deflector plates to scan the electron beam across the target  101 . Alternatively, the stage  118  may include a stage scanning mechanism  111  and stage scanner driver  119  configured to move the target along X-Y plane parallel to the surface of the target  101  in one or more directions relative to the optical column  102 . In some implementations the stage scanning mechanism  111  and stage scanner driver  119  may move the stage in one direction (e.g., the X direction) as the beam scanner driver  108  scans the beam in a different direction (e.g., the Y direction). Alternatively, the stage scanner driver  119  may drive the stage in both the X and Y directions relative to the optical column  102  to scan the beam across the target while the beam remains fixed relative to the optical column. 
         [0036]    Electrons striking the target  101  are either backscattered or initiate secondary emission. The electron beam column collects a portion of such backscattered or secondary electrons  117  that emerge from the surface of the target  101 . The collected electrons  117  travel back up through the electron beam column and impinge on a detector  110 , which generates a signal proportional to the amount of backscattering or secondary emission. The signal may be amplified by an amplifier  112 . The amplified signal and a signal from the beam scanner driver  108  and/or stage scanner driver  119  are combined by an image generator  114  to produce a high-contrast, magnified image of the surface of the target  101 . The images generated by the image generator  114  may be analyzed by the image analyzer  116 , e.g., to determine a measure of quality of the modified surface or shape and size of resulting formed structures. 
         [0037]    In alternative implementations, sources of energetic particles other than electrons (e.g., ions, neutrons, ultraviolet radiation, or X-rays) may be used as alternatives to the electron source  115 , depending on the nature of the system. In addition, the energetic particle source may be separate from and/or located outside of the charged particle optical column  102 . For example, in X-ray photoelectron spectroscopy (XPS) the primary energetic particles may be X-rays that initiate emission of secondary electrons from the target. In ultraviolet photoelectron spectroscopy (UPS) the primary energetic particles may be ultraviolet photons that similarly initiate emission of secondary electrons from the target. Also, in alternative implementations, other types of charged particles (e.g., positive or negative ions) may backscatter from or be emitted by the target and pass back up through the optical column  102  to impinge on the detector  110 . For example, in secondary ion mass spectroscopy (SIMS) the primary particles are energetic ions and the secondary charged particles are ionized atoms of the target material that are knocked off of the target as a result of energetic impact by the primary ions. 
         [0038]    Some charged particle systems include a charged particle energy analyzer (e.g., a cylindrical mirror analyzer, Bessel box, parallel plate analyzer) as part of the optical column  102  between the immersion lens  104  and the detector  110 . Such spectrometers are used for energy selection of secondary electrons, e.g., as in Auger electron spectroscopy (AES) for chemical analysis of the target  101 . Other systems include a mass spectrometer (e.g., a magnetic sector, RF quadrupole, or Wien filter to select secondary charged particles by mass, e.g., as in SIMS systems. 
         [0039]    By way of example, and not by way of limitation, images may be generated by driving the beam scanner in a raster pattern in which the primary beam scans across the sample  101  in one direction with the beam scanner driver  108  and beam scanner coils  106  (or deflector plates) and the detector signal as a function of beam position is converted into a line of the image as is well known in the art. At an end of the scan of the beam in one direction (e.g., the X-direction), the beam location may be adjusted by a small amount (e.g., an amount comparable to a size of the beam spot on the sample) in a different direction (e.g., the Y-direction) and another scan may be performed to generate another line of the image. By repeating this process an image of part of the sample may be generated. 
         [0040]    In alternative implementations, images may be generated by scanning the primary beam across the sample  101  in one direction (e.g., the X-direction) and converting the detector signal as a function of beam position into a line of the image. The stage scanner driver  119  and stage scanning mechanism may translate the sample  101  by a small amount in a different direction (e.g., the Y-direction) at the end of each line scan. 
         [0041]    Detector  110  may be a diode device with a junction and depletion region. By way of example and not by way of limitation, detector  110  can be a PN junction, a PIN junction. In alternative implementations, the detector  110  may be a CMOS detector (e.g., a charge coupled device (CCD)), silicon-based or III-V detector, multi-channel plate, photodiode array, avalanche photodiode and/or Schottky diode. 
         [0042]    In one example, the detector  110  is PN junction diode that includes a positively doped P region and a negatively doped N region. A depletion region, an area of neutral charge, exists between the P and N regions. When a photon enters the device, electrons in the crystalline structure become excited. If the energy of the photon is greater than the bandgap energy of the material, electrons will move into the conduction band crating holes in the valence band where the electrons were. These electron-hole pairs are created throughout the device. Those generated in the depletion region drift to their respective electrons. This results in a positive charge buildup in the P layer and a negative one in the N layer. The amount of charge is directly proportional to the amount of light falling on the detector. 
         [0043]    As noted above, conventional detectors have relatively large and symmetrical design for the active portion for collecting the electrons. According to aspects of the present disclosure, the detector  110  may have a layout design (as discussed below in connection with  FIG. 2 ) that may be optimized for use in a charged particle system that uses one or more columns for line scans while moving the target relative to the column  102  perpendicular to the scan direction. It should be noted that in addition to SEM systems, many other charged particle systems may employ the secondary charged particle detection device according to the present disclosure. Examples of systems may include systems configured to implement focused ion beam (FIB), ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and Secondary Ion Mass Spectroscopy (SIMS). 
         [0044]    As shown in the block diagram of  FIG. 1B , the image generator  114  and image analyzer may be part of a controller  120 . The controller  120  may be a self-contained microcontroller. Alternatively, the controller  120  may be a general purpose computer configured to include a central processor unit (CPU)  122 , memory  124  (e.g., RAM, DRAM, ROM, and the like) and well-known support circuits  128  such as power supplies  121 , input/output (I/O) functions  123 , clock  126 , cache  134 , and the like, coupled to a control system bus  130 . The memory  124  may contain instructions that the CPU  122  executes to facilitate the performance of the system  100 . The instructions in the memory  124  may be in the form of the program code  125 . The code  125  may control, e.g., the electron beam voltage and current produced by the source  115 , the focusing of the beam with the beam optics  135  and the immersion lens  104 , the scanning of the electron beam by the coils  106 , the scanning of the stage  118  by the stage scanner  111  and the formation of images with the signal from the detector  110  in a conventional fashion. The code  125  may also implement analysis of the images. 
         [0045]    The code  125  may conform to any one of a number of different programming languages such as Assembly, C++, JAVA or a number of other languages. The controller  120  may also include an optional mass storage device,  132 , e.g., CD-ROM hard disk and/or removable storage, flash memory, and the like, which may be coupled to the control system bus  130 . The controller  120  may optionally include a user interface  127 , such as a keyboard, mouse, or light pen, coupled to the CPU  122  to provide for the receipt of inputs from an operator (not shown). The controller  120  may also optionally include a display unit  129  to provide information to the operator in the form of graphical displays and/or alphanumeric characters under control of the processor unit  122 . The display unit  129  may be, e.g., a cathode ray tube (CRT) or flat screen monitor. 
         [0046]    The controller  120  may exchange signals with the imaging device scanner driver  108 , the e-beam driver  135  and the detector  110  or amplifier  112  through the I/O functions  123  in response to data and program code instructions stored and retrieved by the memory  124 . Depending on the configuration or selection of controller  120  the scanner driver  108  and detector  110  or amplifier  112  may interface with the I/O functions via conditioning circuits. The conditioning circuits may be implemented in hardware or software form, e.g., within code  125 . 
         [0047]    According to aspects of the present disclosure, the detector  110  is of unconventional design.  FIG. 1C  depicts a detector  1  of conventional design. The detector  1  is a PN junction diode with a central aperture  10 , an active portion  20  and a metal shield  30 . The active portion  20  is comprises four symmetrically arranged sector-shaped regions that surround the aperture  10 . The active portions  20  are electrically isolated by an insulator, e.g., an oxide. In particular, the insulator includes an oxide annulus  12  (shown in phantom) formed around the aperture  10  provides isolation of the detector  110  from leakage effects due to surface or edge states. The insulator, including the annulus  12 , is covered by the metal shield  30  to prevent charging. In this example, the aperture  10  is formed through the material of the detector and also through the metal shield  30 . The metal shield  30  is fabricated separately from the rest of the detector, e.g., using microelectromechancial systems (MEMS) processing. As noted above, the metal shield complicates assembly of the detector  1 . Portions of the shield  30  between the active portion sectors  20  can also cause signal clipping, particularly if the landing pattern of secondary electrons is asymmetric and significant numbers of secondary electrons would land on these portions of the shield. 
         [0048]      FIG. 2  shows a schematic layout of an improved detector  110  according to an aspect of the present disclosure. In this example, the detector  110  has an active portion  220  formed on a substrate  218 . A through-hole aperture  210  formed through the substrate  218 . A metallization area  230  covers certain electrically insulated (non-active) portions of the substrate  218 . In this example, the active portion  220  is an approximately sector-shaped region. The through-hole aperture  210  is provided to allow a primary electron beam (or other energetic beam, e.g., ion, neutron, x-ray, ultraviolet) to pass through the detector  110  on its way to a target. In this example, the aperture  210  is formed through the active portion  220  and is located at an axis of symmetry of the substrate  218 . In the illustrated example, the substrate  218  is square or rectangular in shape with a symmetry about an axis perpendicular to a plane of the substrate that runs through the center of the aperture  210 , which also happens to be the center of the substrate  218  in this example. The aperture  210  may be circular or any other suitable shape. In addition, the aperture  210  may be in the center of the detector  110  (e.g., on an axis of symmetry of the substrate  218  or other locations. In cases where the aperture  210  is off center, the primary beam may be deflected off center to go through the aperture and then deflected back in center to focus it on the sample. 
         [0049]    Since PN junctions for the active portion  220  cannot be made all the way to the edge of the aperture  210 , an inactive region (sometimes called a dead zone), which may result from an insulating (e.g., oxide) annulus  212 , typically exists around the aperture  210 . The aperture  210  and the dead zone would cause signal clipping for the secondary electron blobs that overlap them. Since the amount of clipping depends on the size of the aperture and the dead zone, the size of the aperture and the dead zone should be assessed and adjusted so that the signal loss is kept to 1% or less. One alternative solution to reduce the signal loss is to modify the scan pattern to keep the secondary electrons from landing in the dead zone or the aperture. 
         [0050]    The active portion  220  of detector  110  is the area that can capture secondary electrons emitted from the surface of a sample. The active portion  220  is shaped to accommodate an expected asymmetrical pattern of the secondary electrons at the detector location. In the example shown in  FIG. 2 , the substrate  218  is symmetric with respect to an axis through the aperture  210  and the active region  220  is asymmetric with respect to the axis. The asymmetric shape of the active region  220  is configured to accommodate an estimated axially asymmetrical distribution of the secondary particles at the detector  110  with respect to a beam axis of a charged particle beam optical system  100 . The expected pattern and location of the secondary electrons at the location of the detector  110  can be determined by computer simulation utilizing knowledge of the electron optic performance, e.g., deflection and rotation of electrons, in a charged particle system. For example, with the deflection conditions (e.g., rotation and deflection) determined for the optical system  100 , the positions of secondary electron at the plane of the detector  110  plane can be analyzed via a Matlab script as in  FIG. 4 . 
         [0051]      FIG. 4  shows an example of an estimated asymmetric pattern of secondary electrons landing on the active portion in an asymmetrical pattern in a line scan. From the Matlab output, the secondary electron positions can be analyzed as a function of scan position and the capture result can be analyzed as a function of the size of the dead zone/active portion as shown in  FIG. 5 . According to the simulation, the active portion  220  may be shaped to cover an expected area where the secondary electrons may land at the detector plane. With such an optimized design, the size of the active portion may be reduced, thereby improving leakage current and capacitance as well as the electrical performance and manufacturing yield. 
         [0052]    As an example,  FIG. 2  shows an active portion  220  in the shape of a sector, e.g., like a pie with a missing piece. In this example, the shape of the active portion  220  has been optimized for capturing the secondary electrons in a particular electron beam system for primary beam landing energies from 500 electron volts (eV) through 3 keV. The angles are chosen to correspond to the secondary electron positions after they have gone through a rotation and then a deflection as they travel back upwards through the optical column  102  to plane of the detector  110  for the different landing energies. The chosen angles are variable depending on the system behavior and can be fine-tuned given prior knowledge of the performance of the optical column  102 . It should be noted that the active portion  220  may be in any shape, angle, and/or size as long as it is shaped to accommodate the expected asymmetrical pattern of the secondary electrons at the detector location. 
         [0053]    In addition, an electrically conductive layer  230  is provided over portions of the surface of the device other than active portion  220  to prevent charging that would produce a deflection field. The electrically conductive layer  230  is either deposited or formed on selected parts of the surface of the detector which may be isolated from the active portion, e.g., by an insulating layer, such as an oxide. The electrically conductive layer  230  may thus be integrated into the detector  110  and can be manufactured as part of the integrated circuit processing that forms the detector. This simplifies, reduces, or eliminates issues of alignment and assembly of a separate conductive shield and detector. The metallization area  230  may also provide electrical contacts  250 . 
         [0054]    To illustrate the effects of beam rotation and the energy spread of secondary electrons it is useful to refer to  FIG. 3  and  FIG. 4  simultaneously.  FIG. 3  depicts an example image plane for a line scan with a landing energy of 500 eV at the target  101 . Three example points indicated at (−10,5), (0,5) and (10,5) correspond to three different locations where the primary beam lands on the target  101  during a line scan  320 . When secondary electrons from these three locations pass back up through the optical column, they are imaged onto the detector  110  as three different blobs along a detector scan  310  as shown in  FIG. 3  and  FIG. 4 . The detector scan  310  corresponds roughly to the line scan  320  but is rotated through an angle (104.18°) as shown in  FIG. 3 . It is noted that for a conventional detector with a symmetric active portion like the one shown in  FIG. 1C , a significant number of the secondary electrons are likely to land on parts of the metal shield  30  between adjacent active sectors  20 . This would result in signal clipping. 
         [0055]      FIG. 4  shows blob positions relative to a detector  110  in the form of a 1 mm diameter photodiode  400  with an aperture  410  having a 0.018 mm radius. Each blob represents secondary electrons resulting from primary electrons with 500 eV landing energy impinging on the target  101  at the three corresponding locations (−10,5), (0,5) and (10,5) on the target  101  shown in  FIG. 3 . As shown in  FIG. 4 , the three secondary electron blobs land in a roughly sector-shaped region. The secondary electrons land on the detector in blob-shaped patterns for a number of reasons. First, the secondary electrons, unlike backscattered electrons, have a nearly uniform angular distribution. Second, the secondary electrons have a much lower average kinetic energy than backscattered electrons, e.g., about 50 eV. Third, there is distribution of secondary electron kinetic energies. These factors tend to spread the landing locations of the secondary electrons over a larger area than the primary beam spot size at the target. 
         [0056]    In the example depicted in  FIG. 4 , a dead zone  412  is shown as a black annulus surrounding the aperture  410  out to a radius of 0.032 mm. According to aspects of the present disclosure, the size of the dead zone relative to the size of the aperture, and the size of the aperture relative to the size of the detector may be optimized.  FIG. 5  is a graph showing secondary electron capture as a function of the photodiode aperture radius and as a function of the dead zone radius with a landing energy of 500 eV and a primary image beam location of (0,5). The optimal diameters/sizes of the through-hole aperture and the dead zone can be determined based on graphs such as  FIG. 5  to achieve better capture result. 
         [0057]    Aspects of the present disclosure allow for charged particle detectors optimized for use in charged particle optical systems that use a line scan of a primary beam in conjunction with a translating target. The detector area can be made smaller and therefore leakage current and parasitic capacitance can be reduced. 
         [0058]    While the above includes a complete description of the preferred embodiment of the present invention, it is possible to use various alternatives, modifications and equivalents. Therefore, the scope of the present invention should be determined not with reference to the above description but should, instead, be determined with reference to the appended claims, along with their full scope of equivalents. 
         [0059]    The appended claims are not to be interpreted as including means-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase “means for.” Any element in a claim that does not explicitly state “means for” performing a specified function, is not to be interpreted as a “means” or “step” clause as specified in 35 USC §112, ¶6. In particular, the use of “step of” in the claims herein is not intended to invoke the provisions of 35 USC §112, ¶6.