Abstract:
A method of operating a charged particle beam system, the method comprises extracting a particle beam from a source; performing a first accelerating of the particles of the beam; forming a plurality of particle beamlets from the beam after the performing of the first accelerating; performing a second accelerating of the particles of the beamlets; performing a first decelerating of the particles of the beamlets after the performing of the second accelerating; deflecting the beamlets in a direction oriented transverse to a direction of propagation of the particles of the beamlets after the performing of the first decelerating; performing a second decelerating of the particles of the beamlets after the deflecting of the beamlets; and allowing the particles of the beamlets to be incident on an object surface after the performing of the second decelerating.

Description:
FIELD 
       [0001]    The present disclosure relates to charged particle beam systems and methods of operating charged particle beam systems in which a plurality of particle beamlets are directed onto an object surface. 
       BACKGROUND 
       [0002]    A conventional charged particle beam system in which a plurality of particle beamlets is directed onto an object is known from WO 2005/024881. The system is an electron microscope in which a plurality of primary electron beamlets are focused in parallel to form an array of primary electron beam spots on the object. Secondary electrons generated by the primary electrons and emanating from respective primary electron beam spots are received by a charged particle imaging optics to form a corresponding array of secondary electron beamlets which are supplied to an electron detection system having an array of detection elements such that each secondary electron beamlet is incident on a separate detection element. Detection signals generated from the detection elements are indicative of properties of the object at those locations where the primary electron beam spots are formed. 
         [0003]    By scanning the array of primary electron beam spots across the object surface, it is possible to obtain an electron microscopic image of the object. It is desirable to obtain images at a high resolution and a high throughput. For this purpose it is desirable to achieve small primary electron beam spots on the object and to be able to scan the primary electron beam spots rapidly across the object surface. 
         [0004]    Additional prior art is disclosed in U.S. Pat. No. 7,960,697 B2. 
       SUMMARY 
       [0005]    The present invention has been accomplished taking the above problems into consideration. 
         [0006]    Embodiments of the invention provide a method of operating a charged particle system, wherein the method comprises: extracting a particle beam from a source; performing a first accelerating of the particles of the beam; forming a plurality of particle beamlets from the beam after the performing of the first accelerating; performing a second accelerating of the particles of the beamlets; performing a first decelerating of the particles of the beamlets after the performing of the second accelerating; deflecting the beamlets in a direction oriented transverse to a direction of propagation of the particles of the beamlets after the performing of the first decelerating; performing a second decelerating of the particles of the beamlets after the deflecting of the beamlets; and allowing the particles of the beamlets to be incident on an object surface after the performing of the second decelerating. 
         [0007]    Other embodiments of the invention provide a method of operating a charged particle system, wherein the method comprises: extracting a particle beam from a source; performing a first accelerating of the particles of the beam; forming a plurality of particle beamlets from the beam after the performing of the first accelerating; performing a first decelerating of the particles of the beamlets; performing a second accelerating of the particles of the beamlets after the performing of the first decelerating; deflecting the beamlets in a direction oriented transverse to a direction of propagation of the particles of the beamlets after the performing of the first decelerating; performing a second decelerating of the particles of the beamlets after the deflecting of the beamlets; and allowing the particles of the beamlets to be incident on an object surface after the performing of the second decelerating. 
         [0008]    Further embodiments of the invention provide a method of operating a charged particle system, wherein the method comprises: extracting a particle beam from a source; performing a first accelerating of the particles of the beam; performing a second accelerating of the particles of the beam after performing the first accelerating; performing a first decelerating of the particles of the beam after the performing of the second accelerating; forming a plurality of particle beamlets from the beam after the performing of the first decelerating; deflecting the beamlets in a direction oriented transverse to a direction of propagation of the particles of the beamlets; performing a second decelerating of the particles of the beamlets after the deflecting of the beamlets; and allowing the particles of the beamlets to be incident on an object surface after the performing of the second decelerating. 
         [0009]    Still further embodiments of the invention provide a method of operating a charged particle system, wherein the method comprises: extracting a particle beam from a source; performing a first accelerating of the particles of the beam; performing a first decelerating of the particles of the beam after performing the first accelerating; performing a second accelerating of the particles of the beam after the performing of the first decelerating; forming a plurality of particle beamlets from the beam after the performing of the second accelerating; deflecting the beamlets in a direction oriented transverse to a direction of propagation of the particles of the beamlets; performing a second decelerating of the particles of the beamlets after the deflecting of the beamlets; and allowing the particles of the beamlets to be incident on an object surface after the performing of the second decelerating. 
         [0010]    The accelerating and decelerating can be achieved by distributing a plurality of electrodes along a path of the beam and the beamlets, respectively, wherein suitably selected voltages are supplied to the electrodes such that electric fields are generated between adjacent electrodes. The particles are accelerated and decelerated, respectively, by these electric fields. The electrodes may have a configuration of a plate oriented transverse to the direction of the beam and the beamlets, respectively, wherein the plate is provided with an aperture allowing the particles to traverse the electrode. 
         [0011]    The plurality of particle beamlets can be formed, for example, by a plate oriented transverse to the beam direction such that the beam is incident on the plate. A plurality of apertures are formed in the plate such that particles of the beam traversing the apertures form the plurality of beamlets downstream of the plate. 
         [0012]    The deflecting of the beamlets is performed in order to scan the locations of incidence of the beamlets on the object surface across the surface. 
         [0013]    According to some embodiments, the deflecting is achieved by operating a magnetic deflector generating time-varying deflection fields by supplying time-varying electric currents to coils generating the magnetic fields. 
         [0014]    According to other exemplary embodiments, the deflection is achieved by electrostatic deflectors generating time-varying electric deflection fields, wherein time-varying electric voltages are supplied to electrodes of the deflector. Since the deflection is performed after the performing of the first decelerating of the particles, the kinetic energy of the particles is relatively low such that electrostatic deflectors can be successfully used for achieving a desired amount of deflection. Electrostatic deflectors have an advantage over magnetic deflectors in that the generated deflection fields can be readily changed at very high rates, allowing for rapid scanning of the beamlets across the object surface. 
         [0015]    The second decelerating of the particles is performed in order to adjust a kinetic energy at which the particles are incident on the object surface. Typically, this kinetic energy changes from application to application and is sufficiently low to avoid damages of the object during the irradiation with the particle beamlets, or to improve a contrast of a detected image. For example, the kinetic energy with which the electrons are incident on the object surface can be adjusted to operate at the neutral point of the electron yield at which, on the average, each incident electron causes one electron to leave the object surface such that a significant charging of the object surface does not occur. However, the particles travel at significantly higher kinetic energy through the particle beam system before the second decelerating is performed. The higher kinetic energies reduce the total time necessary for the particles to traverse the system such that the Coulomb interaction between the particles does not unnecessarily increase a diameter of the particle beam spots formed on the object surface. A high spatial resolution can be achieved, accordingly. 
         [0016]    Further embodiments of the present invention provide a charged particle beam system comprising: a particle beam source configured to generate a particle beam wherein the particle beam source includes a particle emitter; a first electrode downstream of the particle beam source; a multi-aperture plate downstream of the first electrode; a second electrode downstream of the multi-aperture plate; a third electrode downstream of the multi-aperture plate; a deflector downstream of the third electrode; an objective lens downstream of the deflector; a fourth electrode downstream of the deflector; and an object mount configured to mount an object such that a surface of the object is located downstream of the objective lens; a voltage supply configured to maintain the particle emitter at a first voltage; the first electrode and/or the multi-aperture plate at a second voltage; the second electrode at a third voltage; the third electrode at a fourth voltage; the fourth electrode at a fifth voltage; and object mount at a sixth voltage; wherein an absolute value of a first difference between the first voltage and the second voltage is greater than a first voltage amount; an absolute value of a second difference between the second voltage and the third voltage is greater than the first voltage amount; an absolute value of a third difference between the third voltage and the fourth voltage is greater than the first voltage amount; an absolute value of a fourth difference between the fourth voltage and the fifth voltage or the sixth voltage is greater than the first voltage amount; the first difference and the second difference have a same sign; the third difference and the fourth difference have a same sign; and the first difference and the third difference have opposite signs. 
         [0017]    Other embodiments of the present invention provide a charged particle beam system comprising: a particle beam source configured to generate a particle beam wherein the particle beam source includes a particle emitter; a first electrode downstream of the particle beam source; a multi-aperture plate downstream of the first electrode; a second electrode downstream of the multi-aperture plate; a third electrode downstream of the multi-aperture plate; a deflector downstream of the third electrode; an objective lens downstream of the deflector; a fourth electrode downstream of the deflector; and an object mount configured to mount an object such that a surface of the object is located downstream of the objective lens; a voltage supply configured to maintain the particle emitter at a first voltage; the first electrode and/or the multi-aperture plate at a second voltage; the second electrode at a third voltage; the third electrode at a fourth voltage; the fourth electrode at a fifth voltage; and object mount at a sixth voltage; wherein an absolute value of a first difference between the first voltage and the second voltage is greater than a first voltage amount; an absolute value of a second difference between the second voltage and the third voltage is greater than the first voltage amount; an absolute value of a third difference between the third voltage and the fourth voltage is greater than the first voltage amount; an absolute value of a fourth difference between the fourth voltage and the fifth voltage or the sixth voltage is greater than the first voltage amount; the first difference and the third difference have a same sign; the second difference and the fourth difference have a same sign; and the first difference and the second difference have opposite signs. 
         [0018]    Further embodiments of the present invention provide a charged particle beam system comprising: a particle beam source configured to generate a particle beam wherein the particle beam source includes a particle emitter; a first electrode downstream of the particle beam source; a second electrode downstream of the first electrode; a third electrode downstream of the second electrode; a multi-aperture plate downstream of the third electrode; a deflector downstream of the third electrode; an objective lens downstream of the deflector; a fourth electrode downstream of the deflector; and an object mount configured to mount an object such that a surface of the object is located downstream of the objective lens; a voltage supply configured to maintain the particle emitter at a first voltage; the first electrode and/or the second electrode at a second voltage; the third electrode at a third voltage; the multi-aperture plate at a fourth voltage; the fourth electrode at a fifth voltage; and object mount at a sixth voltage; wherein an absolute value of a first difference between the first voltage and the second voltage is greater than a first voltage amount; an absolute value of a second difference between the second voltage and the third voltage is greater than the first voltage amount; an absolute value of a third difference between the third voltage and the fourth voltage is greater than the first voltage amount; an absolute value of a fourth difference between the fourth voltage and the fifth voltage or the sixth voltage is greater than the first voltage amount; the first difference and the second difference have a same sign; the third difference and the fourth difference have a same sign; and the first difference and the third difference have opposite signs. 
         [0019]    Still further embodiments of the present invention provide a charged particle beam system comprising: a particle beam source configured to generate a particle beam wherein the particle beam source includes a particle emitter; a first electrode downstream of the particle beam source; a second electrode downstream of the first electrode; a multi-aperture plate downstream of the second electrode; a deflector downstream of the third electrode; an objective lens downstream of the deflector; a third electrode downstream of the deflector; and an object mount configured to mount an object such that a surface of the object is located downstream of the objective lens; a voltage supply configured to maintain the particle emitter at a first voltage; the first electrode at a second voltage; the second electrode at a third voltage; the multi-aperture plate at a fourth voltage; the third electrode at a fifth voltage; and object mount at a sixth voltage; wherein an absolute value of a first difference between the first voltage and the second voltage is greater than a first voltage amount; an absolute value of a second difference between the second voltage and the third voltage is greater than the first voltage amount; an absolute value of a third difference between the third voltage and the fourth voltage is greater than the first voltage amount; an absolute value of a fourth difference between the fourth voltage and the fifth voltage or the sixth voltage is greater than the first voltage amount; the first difference and the third difference have a same sign; the second difference and the fourth difference have a same sign; and the first difference and the second difference have opposite signs. 
         [0020]    The first voltage difference between the particle emitter and the first electrode is selected such that the particles are accelerated. When the particles are electrons, the particle emitter is commonly referred to as a cathode, and the voltage applied to the cathode is lower than the voltage applied to the first electrode, which is then commonly referred to as an anode. 
         [0021]    The second voltage difference between the voltage applied to the first electrode and the voltage applied to the second electrode is selected such that the particles are accelerated. The third voltage difference between the voltage applied to the second electrode and the voltage applied to the third electrode is selected such that the particles are decelerated, and the fourth voltage difference between the voltage applied to the third electrode and the voltage applied to the fourth electrode is selected such that the particles are decelerated. A voltage difference between the particle emitter and the object mount determines the landing energy of the particles, i.e. the kinetic energy at which the particles are incident on the object surface. 
         [0022]    Absolute values of the first, second, third and fourth voltage differences can be greater than 10 kV, greater than 20 kV or greater than 30 kV. 
         [0023]    Similarly, the first and second accelerating of the particles and the first and second decelerating of the particles can increase, or decrease, respectively, the kinetic energy of the particles by more than 10 keV, more than 20 keV or more than 30 keV. 
         [0024]    According to some embodiments, the method further comprises performing a first converging of the beam before the deflecting. Since the particle beam extracted from the particle beam source is generally a diverging beam, the first converging may reduce a distance between adjacent particle beam spots on the object surface. 
         [0025]    According to exemplary embodiments, the first converging is performed before forming of the plurality of beamlets. According to alternative exemplary embodiments, the first converging is performed after forming of the plurality of beamlets. 
         [0026]    According to further exemplary embodiments, the first converging is performed before the deflecting. 
         [0027]    According to further embodiments, the converging is performed such that a crossover of the beamlets is formed. Such crossover is a location or region along the beam path where the particle beamlets intersect an optical axis of the system. 
         [0028]    According to some embodiments herein, the crossover is formed after the first decelerating and before the second decelerating. 
         [0029]    According to further embodiments herein, the method further comprises performing a second converging of the beamlet after the crossover is formed and before the performing of the second decelerating. The first and second converging can be performed such that images of the particle emitter of the source are generated on the substrate surface, resulting in small particle beam spots on the substrate surface. 
         [0030]    The first and second converging can be achieved by focusing lenses arranged along the particle beam path. According to some embodiments, the focusing lenses are magnetic lenses generating focusing magnetic fields. 
         [0031]    According to some embodiments, the system comprises a first focusing lens downstream of the beam source and upstream of the deflector. According to some embodiments herein, the first focusing lens is positioned upstream of the multi-aperture plate. 
         [0032]    According to some embodiments, the method comprises performing a third accelerating of the particles of the beamlets before the crossover is formed. Such third accelerating reduces the traveling time of the particles for traversing the crossover such that an increase of the particle beam spots on the object surface is avoided or significantly reduced. 
         [0033]    In some embodiments, a third decelerating is performed after forming of the crossover, such that the kinetic energy of the particles is already reduced before the second converging is performed. 
         [0034]    The third accelerating and the third decelerating may change the kinetic energy of the particles by more than 10 keV, more than 20 keV or more than 30 keV. 
         [0035]    According to some embodiments, the forming of the plurality of beamlets includes generating of beamlet foci. The beamlet foci are images of a particle emitter of the source, and the these images can be further imaged onto the substrate surface, resulting in small beam spots formed on the substrate surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]    The forgoing as well as other advantageous features of the disclosure will be more apparent from the following detailed description of exemplary embodiments with reference to the accompanying drawings. It is noted that not all possible embodiments necessarily exhibit each and every, or any, of the advantages identified herein. 
           [0037]      FIG. 1  schematically illustrates basic features and functions of a charged particle beam system; 
           [0038]      FIG. 2  schematically illustrates particle beam paths in a charged particle beam system according to a first embodiment; 
           [0039]      FIG. 3  schematically illustrates particle beam paths in a charged particle beam system according to a second embodiment; 
           [0040]      FIG. 4  schematically illustrates particle beam paths in a charged particle beam system according to a third embodiment; 
           [0041]      FIG. 5  schematically illustrates particle beam paths in a charged particle beam system according to a fourth embodiment; 
           [0042]      FIG. 6  schematically illustrates particle beam paths in a charged particle beam system according to a fifth embodiment; and 
           [0043]      FIG. 7  schematically illustrates particle beam paths in a charged particle beam system according to a sixth embodiment. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0044]    In the exemplary embodiments described below, components that are alike in function and structure are designated as far as possible by alike reference numerals. Therefore, to understand the features of the individual components of a specific embodiment, the descriptions of other embodiments and of the summary of the disclosure should be referred to. 
         [0045]      FIG. 1  is a schematic diagram symbolically illustrating basic functions and features of an inspection system using a plurality of particle beamlets. The inspection system generates a plurality of primary electron beamlets which are incident on a substrate to be inspected to produce secondary electrons emanating from the substrate which are subsequently detected. The inspection system  1  is of a scanning electron microscope type (SEM) using a plurality of primary electron beamlets  3  for generating primary electron beam spots  5  on a surface of the substrate  7  to be inspected. The inspected substrate  7  can be of any type and may comprise, for example, a semiconductor wafer, a biological sample and an arrangement of miniaturized features of other types. The surface of the substrate  7  is arranged in an object plane  101  of an objective lens  102  of an objective lens system  100 . 
         [0046]    Insert I 1  of  FIG. 1  shows an elevational view of the object plane  101  with a regular rectangular array  103  of primary electron beam spots  5  formed thereon. In  FIG. 1  a number of 25 primary electron beam spots are arranged as a 5×5-array  103 . This number of 25 primary electron beam spots is a low number chosen for ease of illustration in the schematic diagram of  FIG. 1 . In practice, the number of primary electron beam spots may be chosen substantially higher, such as 20×30, 100×100 and others. 
         [0047]    In the illustrated embodiment, the array  103  of primary electron beam spots  5  is a substantially regular rectangular array with a substantially constant pitch p 1  between adjacent beam spots. Exemplary values of P 1  can be greater than 1 μm, greater than 10 μm, greater than 20 μm or even greater than 50 μm. It is however also possible that the array  103  is a distorted regular array having different pitches in different directions, and the array may also have other symmetries, such as a hexagonal symmetry. 
         [0048]    A diameter of the primary electron beam spots formed in the object plane  101  can be small. Exemplary values of such diameter are 1 nm to 5 nm, but they can also be as large as 100 nm or even 200 nm. The focusing of the primary electron beamlets  3  to form the primary electron beam spots  5  is performed by the objective lens system  100 . 
         [0049]    The primary electrons incident on the substrate  7  at the beam spots  5  produce secondary electrons emanating from the surface of the substrate  7 . The secondary electrons emanating from the surface of the substrate  7  are received by the objective lens  102  to form secondary electron beamlets  9 . The inspection system  1  provides a secondary electron beam path  11  for supplying the plurality of secondary electron beamlets  9  to a charged particle detection system  200 . The detection system  200  comprises a projection lens arrangement  205  for directing the secondary electron beamlets  9  towards a detector  207 . The detector is a detector having plural detection elements and may comprise a CCD detector, a CMOS detector, a scintillator detector, a micro-channel plate, an array of PIN-diodes, Avalange photodiodes (APD), and others and suitable combinations thereof. 
         [0050]    Insert I 2  of  FIG. 1  shows an elevational view of the detector  207 , wherein secondary electron beam spots  213  are formed on individual detection elements  215  which are arranged as an array  217  having a regular pitch p 2 . Exemplary values of the pitch p 2  are 10 μm, 100 μm and 200 μm. 
         [0051]    The primary electron beamlets  3  are generated by a beamlet generation system  300  comprising at least one electron source  301 , at least one collimating lens  303 , a multi-aperture plate arrangement  305  and a field lens  307 . 
         [0052]    The electron source  301  generates a diverging electron beam  309  which is collimated by collimating lens  303  to form a beam  311  illuminating the multi-aperture arrangement  305 . 
         [0053]    Insert I 3  of  FIG. 1  shows an elevational view of the multi-aperture arrangement  305 . The multi-aperture arrangement  305  comprises a multi-aperture plate  313  having a plurality of apertures  315  formed therein. Centers  317  of the apertures  315  are arranged in a pattern  319  corresponding to the pattern  103  of the primary electron beam spots  5  formed in the object plane  101 . A pitch p 3  of array  103  may have exemplary values of 5 μm, 100 μm and 200 μm. Diameters D of the apertures  315  are less than the pitch p 3 . Exemplary values of the diameters D are 0.2·p 3 , 0.4·p 3  and 0.8·p 3 . 
         [0054]    Electrons of the illuminating beam  311  traversing the apertures  315  form the primary electron beamlets  3 . Electrons of illuminating beam  311  impinging on the plate  313  are intercepted by the plate and do not contribute to forming the primary electron beamlets  3 . 
         [0055]    Moreover, the multi-aperture arrangement  305  focuses the individual electron beamlets  3  such that foci  323  are generated in a plane  325 . Insert I 4  of  FIG. 1  shows an elevational view of plane  325  with foci  323  arranged in a pattern  327 . A pitch p 4  of pattern  327  may be equal to or different from the pitch p 3  of pattern  319  of the multi-aperture plate  313 . A diameter of the foci  323  may have exemplary values of 10 nm, 100 nm and 1 μm. 
         [0056]    The field lens  307  and the objective lens  102  provide an imaging system for imaging the plane  325  onto the object plane  101  to form the array  103  of primary electron beam spots  5  on the surface of the substrate  7 . 
         [0057]    A beam splitter system  400  is provided in the primary electron beam path  13  in-between the beam generating system  300  and the objective lens system  100 . The beam splitter system  400  is also part of the secondary electron beam path  11  such that the beam splitter system  400  is located in-between the objective lens system  100  and the detection system  200 . 
         [0058]    Background information relating to such beamlet inspection system and charged particle components used therein, such as charged particle sources, multi-aperture plates and lenses may be obtained from WO 2005/024881, WO 2007/028595, WO 2007/028596 and WO 2007/060017 wherein the full disclosure of these applications is incorporated herein by reference. 
         [0059]      FIG. 2  is a schematic illustration of a charged particle beam system  1   a  in which a plurality of charged particle beamlets  3   a  are directed onto a surface of an object  7   a  mounted on an object mount  8 . In the illustration of  FIG. 2 , the number of particle beamlets  3   a  is three. This low number has been chosen for illustration purposes only, and the number of particle beamlets used in practice can be significantly higher, as already mentioned above. Moreover, the diameter of the beamlets is exaggerated relative to the length of the total beam path between a charged particle source  301   a  and the surface of the object  7   a.    
         [0060]    The particle beam source  301   a  comprises a particle beam emitter  331  which is also referred to as a cathode, since the particles emitted from the particle emitter  331  are electrons. The particle beam source  301   a  comprises at least one connector  333  connecting the emitter  331  to a controller  11  of the system  1   a . The controller  11  supplies a heating current and other necessary signals to the emitter  331  and maintains the emitter  331  at a predefined electric potential by supplying a first voltage V 1  to the emitter  331 . 
         [0061]    The beam source  301   a  further comprises an extractor electrode  335  connected via a connector  337  to the controller  11 . The controller  11  maintains the extractor electrode  335  at a suitable voltage relative to the voltage V 1  of the emitter  331  such that a diverging particle beam  309   a  is extracted from the emitter  331 . 
         [0062]    A first electrode  339  is located downstream of the particle source  301   a  along a beam path of the particle beam  309   a . The first electrode  339  is configured as a plate oriented orthogonal to an optical axis  340  along which the particle beam  309   a  propagates. The plate has a circular aperture centered on the optical axis  340  and traversed by the beam  309   a . The first electrode  339  is connected via a connector  341  with the controller  11  which supplies a second voltage V 2  to the first electrode. 
         [0063]    A voltage difference between the first voltage V 1  and the second voltage V 2  and a voltage difference between the voltage applied to the extractor  335  and the second voltage V 2  are selected such that the particles of the particle beam  309   a  are accelerated after the extraction from the particle source  301   a . Two arrows between the electrodes  335  and  339  in  FIG. 2  represent an accelerating electric field E 1  generated between the electrodes  335  and  339  and which accelerates the particles. A focusing condenser lens  303   a  is located downstream of the first electrode  339 . The condenser lens  303   a  can be a magnetic lens which is energized by the controller such that the diverging beam  309  is converged to form a parallel beam  311   a.    
         [0064]    A multi-aperture plate  313   a  is positioned downstream of the condenser lens  303   a . The multi-aperture plate  313   a  has a plurality of apertures which are traversed by the particles of the beam  311   a  such that particle beamlets are generated downstream of the multi-aperture plate  313   a . The multi-aperture plate  313   a  is connected, via a connector  315 , to the controller  11 , and the controller  11  maintains the multi-aperture plate  313  at a suitable voltage. In the present example, this voltage is equal to the second voltage V 2  applied to the first electrode  339 , such that no accelerating or decelerating electric fields are generated between the electrode  339  and the multi-aperture plate  313   a , and the kinetic energy at which that particles of the beam  311   a  are incident on the multi-aperture plate  313   a  is the kinetic energy to which the particles have been accelerated after traversing the electric field E 1 . 
         [0065]    A second electrode  343  is positioned downstream of the multi-aperture plate  313   a . The second electrode  343  is configured similar to the first electrode  339  and is formed of a plate having a circular aperture centered at the optical axis  340  and of a size such that all beamlets formed by the multi-aperture plate  313  can traverse the aperture. The second electrode  343  is connected, via a connector  345 , to the controller  11  and maintained by the controller at a third voltage V 3 . The third voltage V 3  is selected such that an accelerating electric field E 2  is generated between the multi-aperture plate  313   a  and the second electrode  343 . The electric field E 2  generated downstream and adjacent to the apertures of the multi-aperture plate accelerates the particles of the beamlets having traversed the apertures of the multi-aperture plate  313   a  and has a function of focusing the particle beamlets having traversed the multiple apertures such that beamlet foci  323   a  are formed downstream of the multi-aperture plate  313   a.    
         [0066]    A third electrode  347  is positioned downstream of the second electrode  343 . The third electrode  347  is formed of a plate having an aperture traversed by the beamlets  3   a  and is connected to the controller  11  via a connector  349 . The controller  11  maintains the third electrode  347  at a fourth voltage V 4  selected such that a decelerating electric field E 3  is generated between the second electrode  343  and the third electrode  347 . The electric field E 3  decelerates the particles of the beamlets such that their kinetic energies are significantly reduced. Further, the electric field E 3  produced between the second and third electrodes  343  and  347  has a function of a diverging particle optical lens, such that adjacent beamlet foci  323   a  have a greater distance from each other than adjacent centers of the apertures of the multi-aperture plate  313   a . In the present example, the voltage V 4  is 0 V such that the third electrode  347  is at ground potential. However, other voltages can be applied to the third electrode  347  in order to generate a decelerating electric field E 3  upstream of the third electrode  347 . The ground potential is the potential of major components of the system, such as a vacuum vessel enclosing the particle beam path. The ground potential at this portion of the beam path provides advantages regarding the mechanical design since insulators are not required, and it provides advantages for the electrostatic scanning system. 
         [0067]    A focusing lens  307   a  is positioned downstream of the third electrode  347 . The focusing lens  303   a  can be a magnetic lens. The focusing lens  307   a  has a function of a field lens and converges the particle beamlets such that a crossover of the bundle of the particle beamlets  3   a  is formed in a region  352  downstream of the field lens  307   a . In the present example, the field lens  307   a  is positioned upstream of the beamlet foci  323   a . However, the beamlet foci  323   a  can also be formed upstream of the field lens  307   a  or within the field lens. The beamlet foci  323   a  can be even formed upstream of the third electrode  347 . 
         [0068]    A deflector arrangement  353  is located downstream of the field lens  307   a . The deflector  353  has a function of deflecting the particle beamlets  3   a  such that the locations of incidence  5   a  of the beamlets  3   a  on the surface of the object  7   a  can be changed. The deflector arrangement  353  comprises a first deflector  354  and a second deflector  355  positioned downstream of the first deflector  354 . The deflector arrangement  353  comprises two deflectors  354  and  355  to be able to simultaneously adjust the position of the location of incidence of the beamlets on the object surface and the landing angle of the beamlets on the object surface. Each of the deflectors  354 ,  355  comprises plural pairs of electrodes positioned on opposite sides of the optical axis  340 . The electrodes are connected, via respective connectors  356 , to the controller  11 . The controller  11  can apply different voltages to the electrode pairs such that deflecting electric fields oriented orthogonal to the optical axis  340  are generated between the pairs of electrodes. Time-varying voltages can be applied to the deflectors  354 ,  355  in order to scan the array of particle beam spots  5   a  across the surface of the object  7   a.    
         [0069]    A focusing objective lens  102   a  is located downstream of the crossover  352  and has a function of focusing the particle beamlets  3   a  onto the surface of the object  7   a  such that small beam spots  5   a  are generated on the object surface. 
         [0070]    A further electrode  359  is positioned upstream of the surface of the object and has an aperture traversed by the particle beamlets  3   a . The electrode  359  can be integrated with components of the objective lens  102   a . For example, a pole piece of the objective lens may form the electrode  359 . However, it is also possible to provide the electrode  359  as a separate element. The fourth electrode  359  is connected, via a connector  361  to the controller  11 . The controller supplies a fifth voltage V 5  to the fourth electrode  359  such that a decelerating electric field E 4  is generated upstream of the fourth electrode  359 . The decelerating electric field E 4  is generated between the fourth electrode  359  and a further electrode  363  positioned upstream of the fourth electrode  359  and connected, via a connector  365 , to the controller  11 . The controller  11  supplies a voltage to the further electrode  363  selected such that the field generated between the electrodes  363  and  359  is decelerating to the particles of the beamlets  3   a . In the present example, the voltage applied to the further electrode  363  is the fourth voltage V 4  also applied to the third electrode  347 , such that the particles are maintained at a constant kinetic energy when they traverse the field lens  351 , the deflector  353 , the crossover  352  and a beam splitter  400   a  illustrated in more detail below. 
         [0071]    The further electrode  363  can be integrated with components of the objective lens  102   a . For example, pole pieces of the objective lens  102   a  can provide the further electrode  363 . However, it is also possible that the further electrode  363  is provided by an element separate from the objective lens  102   a.    
         [0072]    The object mount  8  is connected, via a connector  367 , to the controller  11 , and the controller  11  supplies a sixth voltage V 6  to the object mount  8 . The inspected object  7   a  is electrically connected to the object mount  8  and has a sufficient conductivity such that also the surface of the object  7   a  is maintained substantially at the voltage V 6 . The difference between the sixth voltage V 6  and the first voltage V 1  at which the particle emitter is maintained substantially determines the landing energy of the particles on the object  7   a , i.e. the kinetic energy at which the particles are incident on the surface of the object  7   a . In this context, it is to be noted that the landing energy is further influenced by charges locally accumulated on the object surface. In some embodiments, the sixth voltage V 6  is selected such that it is equal to the fifth voltage V 5  of the fourth electrode  359  positioned upstream of the object surface, such that the particles are not further accelerated or decelerated between the fourth electrode  359  and the object  7   a.    
         [0073]    The particles of the particle beamlets  3   a  incident on the object  7   a  at the beam spots  5   a  generate secondary particles, such as backscattered electrons and secondary electrons, which emanate from the object surface. These secondary particles may traverse the fourth electrode  359  and are then accelerated in the electric field E 4  such that they gain a significant amount of energy in order to traverse the objective lens  102   a . A beam  11   a  formed from the secondary particles is then separated from the beamlets  13   a  of the primary particles in a beam splitter  400   a . The beam splitter  400   a  directs the secondary particles towards a detector arrangement  200   a  including one detection element  215   a  for each primary particle beam spot  5   a.    
         [0074]    Various voltages can be supplied to the emitter  331 , the first electrode  339 , the second electrode  343 , the third electrode  347  and the fourth electrode  359  such that the electric field E 1  provided upstream of the multi-aperture plate  313   a  is accelerating, the electric field E 2  provided downstream of the multi-aperture plate  313   a , i.e. the forming of the plurality of beamlets, is accelerating to the particles, and the electric field E 3  provided downstream of the accelerating electric field E 2  is decelerating and the electric field E 4  provided downstream of the deflector arrangement  353  and after the deflecting of the particles is decelerating to the particles. According to one example, the voltage V 1  applied to the emitter  331  is a negative high voltage HV, the voltage V 2  applied to the first electrode  339  is 0 V, i.e. ground potential, the voltage V 3  applied to the second electrode  343  is a positive high voltage HV, the voltage V 4  applied to the third electrode  347  is 0 V, i.e. ground potential, and the voltage V 5  applied to the fourth electrode  359  is the negative high voltage HV, wherein the voltage V 6  applied to the object mount  8  can be also the negative high voltage HV or suitably higher in order to adjust the landing energy of the particles on the object surface to a desired value. 
         [0075]    The high voltage HV can be, for example, 10 kV, 20 kV or 30 kV. 
         [0076]      FIG. 3  is a schematic illustration of a further charged particle beam system  1   b  in which a plurality of charged particle beamlets  3   b  are directed onto a surface of an object  7   b  mounted on an object mount  8   b . The charged particle beam system  1   b  has a configuration similar to the configuration of the system illustrated with reference to  FIG. 2  above. For example, a divergent particle beam  309   b  is extracted from the particle source  301   b  and accelerated by an electric field E 1  generated between an extractor electrode  335   b  and a first electrode  339   b . The divergent beam  309   b  is converged by a focusing condenser lens  303   b . While the converged beam downstream of the first focusing or condenser lens was a parallel beam in the embodiment illustrated with reference to  FIG. 2  above, the converged beam  311   b  of the present example is a converging beam incident on a multi-aperture plate  313   b  provided for forming a plurality of particle beamlets. The particles of the particle beamlets are accelerated by an electric field E 2  provided between the multi-aperture plate  313   b  and a second electrode  343   b , such that beamlet foci  323   b  are generated downstream of the second electrode  343   b . A decelerating electric field E 3  is provided between the second electrode  343   b  and a third electrode  347   b  subsequent to the accelerating field E 2 . After the deceleration in the electric field E 3 , the particle beamlets traverse a deflector arrangement  353   b , form a crossover  352   b  and are converged in a focusing objective lens  102   b  such that beam spots  5   b  are formed on the surface of the object  7   b  from the particle beamlets  3   b . Further, a decelerating electric field E 4  is provided upstream of the object surface between a fourth electrode  359   b  and a further electrode  363   b.    
         [0077]    The system  1   b  differs from the system illustrated with reference to  FIG. 2  above in that a field lens is not provided in a region where the beamlet foci  323   b  are formed. However, the condenser lens  303   b  is energized such that the particle beam  311   b  from which the plurality of beamlets are formed is a converging beam such that the crossover  352   b  is formed downstream of the beamlet foci  323   b.    
         [0078]    The system  1   b  further differs from the system illustrated with reference to  FIG. 2  above in that a fifth electrode  371  is located downstream of the deflector arrangement  353   b  and upstream of the crossover  352   b . The fifth electrode  371  has an aperture traversed by the particle beamlets and is connected, via a connector  373 , to a controller  11   b , which supplies a seventh voltage V 7  to the fifth electrode  371 . The seventh voltage V 7  is selected such that an accelerating electric field E 5  is generated upstream of the fifth electrode  371  in order to accelerate the particles of the beamlets such that they traverse the region of the crossover  352   b  in a shorter time for avoiding an increase of the beam spots  5   b  formed on the object surface due to Coulomb interaction. The accelerating electric field E 5  is generated between the fifth electrode  371  and a further electrode  375  provided upstream of the fifth electrode  371 . The further electrode  375  is connected, via a connector  377 , to the controller  11   b . A suitable voltage can be supplied to the further electrode  375  such that the electric field E 5  generated between the further electrode  375  and the fifth electrode  371  is accelerating to the particles. In the present example, the voltage supplied to the further electrode  375  is equal to the fourth voltage V 4  supplied to the third electrode  347   b  provided upstream of the deflector arrangement  353   b . As in the previous example, the voltage V 4  can be 0 V, i.e. ground potential, such that the deflector arrangement  353   b  can be operated at ground potential, enabling the use of an electrostatic scan deflector not requiring a static high voltage offset added to the dynamic scan voltage. It is then advantageous to embody the deflector arrangement  353   b  as an electrostatic deflector in which deflecting electric fields are generated by electrodes  354   b ,  355   b  located at opposite sides of the optical axis  340   b.    
         [0079]    This advantage does not only apply to the embodiment shown in  FIG. 3  with a convergent beam at the multi-aperture plate but to the same extent also applies to embodiments with parallel beam paths or divergent beam paths at the multi-aperture plate as shown in  FIGS. 2 and 4 . 
         [0080]    The voltage V 1  applied to the particle emitter  331   b , the voltage V 2  applied to the first electrode  339   b , the third voltage V 3  applied to the second electrode  343   b , the fourth voltage V 4  applied to the third electrode  347   b , the fifth voltage V 5  applied to the fourth electrode  359   b  and the sixth voltage V 6  applied to the object mount  8   b  can be selected as illustrated above with reference to  FIG. 2 . 
         [0081]      FIG. 4  is a schematic illustration of a further charged particle beam system  1   c  in which a plurality of charged particle beamlets  3   c  are directed onto a surface of an object  7   c  mounted on an object mount  8   c . The charged particle beam system  1   c  has a configuration similar to the configuration of the system illustrated with reference to  FIG. 3  above. In particular, a divergent particle beam  309   c  is extracted from the particle source  301   c  and accelerated by an electric field E 1  generated between an extractor electrode  335   c  of the particle source  301   c  and a first electrode  339   c . While the divergent beam extracted from the source is converged by a condenser lens before the plurality of particle beamlets are formed in the example illustrated with reference to  FIG. 3  above, it is the divergent beam  309   c  extracted from the source  301   c  which is incident on a multi-aperture plate  313   c  in order to form the plurality of particle beamlets in the system  1   c . Since the beam  309   c  incident on the multi-aperture plate  313   c  is a divergent beam, the particle beamlets formed downstream of the multi-aperture plate  313   c  also diverge from each other. A focusing condenser lens  303   c  is positioned downstream of the multi-aperture plate  313   c  such that the particle beamlets converge relative to each other downstream of the condenser lens  303   c  and form a crossover  352   c  before they are focused by an objective lens  102   c  to form beam spots  5   c  or a surface of an object  7   c.    
         [0082]    A second electrode  343   c  is positioned downstream of the multi-aperture plate  313   c  and supplied with a voltage V 3  such that an accelerating electric field E 2  is provided to the particles downstream of the multi-aperture plate  313   c  such that beamlet foci  323   c  are formed downstream of the multi-aperture plate  313   c.    
         [0083]    A third electrode  347   c  is supplied with a voltage V 4  selected such that a decelerating electric field E 3  is provided to the particles subsequent to the accelerating electric field E 2 . As in the previous example, the voltage V 4  can be 0 V, i.e. ground potential, such that the condenser lens  303   c  and a deflector arrangement  353   c  can be operated at ground potential. 
         [0084]    A fourth electrode  359   c  supplied with a fifth voltage V 5  is provided upstream of the object  7   c  for generating a decelerating electric field E 4 . 
         [0085]    Similar to the example illustrated with reference to  FIG. 3  above, a fifth electrode  371   c  is provided downstream of the deflector  353   c  for generating an accelerating electric field E 5  such that the particles traverse the crossover in a shorter time. 
         [0086]    While there is only one decelerating electric field E 4  provided upstream of the object in the embodiment illustrated with reference to  FIG. 3  above, a further decelerating electric field E 6  is generated in the system  1   c  downstream of the crossover  352   c  and upstream of a objective lens  102   c . The sixth electric field is generated between a sixth electrode  381  located upstream of the objective lens  102   c  and connected, via a connector  383  to a controller  11   c , and a further electrode  385  connected, via a connector  387  to the controller  11   c  and supplied with a suitable voltage. The voltage supplied to the further electrode  385  can be the same voltage as voltage V 7  supplied to the fifth electrode  371   c , such that the particles are not accelerated or decelerated while traversing the crossover  352   c . However, other voltages can be supplied to the further electrode  385 . The voltage V 8  can be 0 V, i.e. ground potential, such that the objective lens  102   c  can be operated at ground potential. 
         [0087]    The other voltages V 1 , V 2 , V 3 , V 4 , V 5 , V 6  and V 7  supplied to the various electrodes of system  1   c  can be selected similarly as illustrated above with reference to  FIGS. 2 and 3 . 
         [0088]    In the embodiment shown in  FIG. 2 , the crossover  352  of the bundle of beamlets is generated in a region upstream of the beam splitter  400   a . However, the crossover can also be generated within or downstream of the beam splitter  400   a.    
         [0089]      FIG. 5  is a schematic illustration of a further charged particle beam system  1   d  in which a plurality of charged particle beamlets  3   d  are focused on a surface of an object  7   d . The charged particle beam system  1   d  has a configuration similar to the systems illustrated with reference to  FIGS. 2 to 4  above. In particular, a particle emitter  313   d  of a particle beam source  301   d  is maintained at a first voltage V 1 , and a diverging particle beam  309   d  is extracted from the emitter  331   d  using an extractor electrode  335   d . A first electrode  339   d  is located downstream of the particle source  301   d  and maintained at a voltage V 2  such that an accelerating electric field E 1  is generated between the extractor electrode  335   d  and the first electrode  339   d . A condenser lens  303   d , which can be a magnetic lens, is positioned downstream of the first electrode  339   d  and converges the diverging beam  309   d  such that a parallel beam  311   d  is formed. 
         [0090]    A multi-aperture plate  313   d  is positioned within the beam  311   d  such that a plurality of charged particle beamlets  3   d  are formed downstream of the multi-aperture plate  313   d . A second electrode  343   d  is positioned downstream of the multi-aperture plate  313   d . The second electrode  343   d  has an aperture traversed by the plurality of beamlets  3   d  and is maintained at an electric potential V 3  such that a decelerating electric field E 2  is generated between the multi-aperture plate  313   d  and the second electrode  343   d . In the illustrated example, the multi-aperture plate  313   d  is maintained at the same electric potential V 2  as the first aperture plate  339   d . However, other voltages can be applied to the second electrode  313   d  via the terminal  314   d  in order to generate the decelerating electric field E 2  between the multi-aperture plate  313   d  and the second electrode  343   d . The decelerating electric field E 2  generated at the downstream side of the multi-aperture plate  313   d  has an effect such that the apertures of the multi-aperture plate  313   d  have a function of diverging lenses on the beamlets  3   d  such that diverging particle beamlets  3   d  are formed from the incident parallel beam  311   d  downstream of the multi-aperture plate  313   d.    
         [0091]    A third aperture plate  347   d  traversed by the bundle of the particle beamlets  3   d  is positioned downstream of the second aperture plate  343   d . The third aperture plate  347   d  is maintained at an electric potential V 4  selected such that an accelerating electric field E 3  is generated between the second aperture plate  343   d  and the third aperture plate  347   d . The accelerating field E 3  has a focusing function on the particle beamlets such that the bundle of the beamlets  3   d  forms a crossover  351   d  and such that the individual diverging beamlets  3   d  are converged such that beamlet foci  323   d  are formed downstream of the third aperture plate  347   d.    
         [0092]    A focusing lens  307   d , which can be a magnetic lens, is positioned downstream of the crossover  351   d  in order to reduce a divergence of the bundle of the beamlets  3   d  downstream of the crossover  351   d . In the present example, the focusing lens  307   d  has a focusing power selected such that the beamlets  3   d  propagate parallel to each other downstream of lens  307   d.    
         [0093]    The beamlet foci  323   d  are imaged onto the surface of the object  7   d  positioned in an object plane  101   d  using a further focusing lens  308   d  and an objective lens  102   d . The focusing lens  308   d  and the objective lens  102   d  can be magnetic lenses. 
         [0094]    A further aperture plate  363   d  and a fourth aperture plate  359   d  are positioned upstream of the object plane  101   d . The fourth aperture plate  359   d  is maintained at a voltage V 5  and the further aperture plate  363   d  is maintained at a suitable voltage selected such that a decelerating electric field E 4  is generated between the further aperture plate  363   d  and the fourth aperture plate  359   d . In the present example, the voltage applied to the further electrode  363   d  is equal to the voltage V 4  applied to the third aperture plate  347   d . However, the further electrode  363   d  can be maintained at under suitable voltages such that the decelerating electric field E 4  is generated between the aperture plate  363   d  and  359   d.    
         [0095]    A further crossover  352   d  of the bundle of the particle beamlets  3   d  is formed between the lenses  308  and  102   d . A deflector arrangement  353   d  is positioned between the lens  308  and the crossover  352   d . However, the deflector arrangement  353   d  can also be located at other positions between the second aperture plate  347   d  and the object surface  101   d . Moreover, the focusing power of the lenses  307   d  and  308  can be combined into one focusing lens. 
         [0096]    The voltage V 1  can be a negative high voltage, the voltage V 3  can be a negative high voltage, the voltage V 6  can be negative high voltage, and the voltages V 2 , V 4  and V 5  can be voltages close to ground voltage, such that the beam deflector arrangement  353   d  can be operated close to or at ground voltage. In the illustrated embodiment, the following voltages are selected: V 1 =−30 kV, V 2 =0 kV, V 3 =−20 kV, V 4 =0 kV and V 6 =−29 kV, wherein the voltage V 5  is selected such that it is equal to V 6  or such that at least a small decelerating field is generated between the aperture plate  359   d  and the object  7   d . It is also possible to omit the further aperture plate  363   d  and to select the voltage V 5  such that the decelerating electric field E 4  is generated between the fourth aperture plate  359   d  and the object  7   d.    
         [0097]      FIG. 6  is a schematic illustration of a further charged particle beam system  1   e  in which a plurality of charged particle beamlets  3   e  are directed onto a surface of an object  7   e . The charged particle beam system be has a configuration similar to the systems illustrated with reference to  FIGS. 2 to 5  above. For example, a divergent particle beam  309   e  is extracted from a particle source  301   e  and accelerated by an electric field E 1  generated between an extractor electrode  335   e  and a first electrode  339   e . A second electrode provided by a second single-aperture plate  343   e  is positioned in the beam path of the divergent beam  309   e . A third electrode or aperture plate  347   e  is positioned downstream of the second aperture plate  343   e . The third aperture plate  347   e  is maintained at an electric potential V 3  selected such that an accelerating field E 2  is generated between the electrodes  343   e  and  347   e . The electric voltage supplied to the second aperture plate  343   e  via a terminal  345   e  can be equal to the voltage V 2 , or it can be different from the voltage V 2 . The accelerating field E 2  has a focusing function on the diverging beam  309   e  such that a converging beam  311   e  is formed. Additional focusing lenses, such as magnetic focusing lenses, can be positioned between the first and second aperture plates  339   e ,  343   e  in order to provide additional focusing power on the diverging beam  309   e.    
         [0098]    A multi-aperture plate  313   e  is positioned downstream of the third aperture plate  347   e  and maintained at an electric potential V 4  such that a decelerating electric field E 3  is generated between the third aperture plate  347   e  and the multi-aperture plate  313   e . The decelerating electric field E 3  has a function of a diverging lens on the converging beam  311   e  such that a parallel beam  312   e  is formed which is incident on the multi-aperture plate  313   e . The apertures provided in the multi-aperture plate  313   e  allow the particle beamlets  3   e  to pass through the multi-aperture plate  313   e . The decelerating electric field E 3  generated on the upstream side of the multi-aperture plate  313   e  has a result that the apertures of the multi-aperture plate  313   e  perform a focusing function on the particle beamlets  3   e  generated from the incident parallel beam  312   e , such that beamlet foci  323   e  are formed downstream of the multi-aperture plate  313   e . The beamlet foci  323   e  are imaged onto the surface of the object  7   e  positioned at the object plane  101   e . The components shown in  FIG. 6  for this purpose have a similar configuration to the corresponding components of the embodiments illustrated with reference to  FIGS. 2 to 5  above and will not be further illustrated in detail here. Reference should be made to the preceding specification, accordingly. It is to be noted that a decelerating field E 4  is generated upstream of the object  7   e  between two electrodes  363   e  and  359   e  or between an electrode and the object  7   e  itself. 
         [0099]    The voltage V 1  can be a negative high voltage, the voltage V 2  can be close to or equal to ground potential, the voltage V 3  can be a positive high voltage, the voltage V 4  can be close to or equal to ground potential, and the voltage V 6  can be a negative high voltage. In the present example, the following voltages are selected: V 1 =−30 kV, V 2 =0 kV, V 3 =+20 kV, V 4 =0 kV and V 6 =−29 kV. 
         [0100]      FIG. 7  is a schematic illustration of a further charged particle beam system  1   f  in which a plurality of charged particle beamlets  3   f  are directed onto a surface of an object  7   f  mounted on an object mount  8   f . The charged particle beam system if has a configuration similar to the systems illustrated with reference to  FIGS. 2 to 6  above. For example, a divergent particle beam  309   f  is extracted from a particle source  301   f  and accelerated by an electric field E 1  generated between an extractor electrode  335   f  and a first electrode provided by a single-aperture plate  339   f . For this purpose, a particle emitter  331   f  of the particle source  301   f  is maintained at an electric potential V 1 , and the first aperture plate  339   f  is maintained at a potential V 2 . A second aperture plate  343   f  is positioned downstream of the first aperture plate  339   f  and maintained at a voltage V 3  selected such that a decelerating electric field E 2  is generated between the first and second electrodes  339   f  and  343   f . A multi-aperture plate  313   f  is positioned downstream of the second aperture plate  343   f  and maintained at an electric potential V 4  selected such that an accelerating electric field E 3  is generated between the single-aperture plate  343   f  and the multi-aperture plate  313   f . The decelerating electric field E 2  generated on the upstream side of the second aperture plate  343   f  and the accelerating electric field E 3  provided on the downstream side of the second aperture plate  343   f  result in that a focusing lens function is provided on the diverging beam  309   f . This focusing function  309   f  converges the diverging beam  309   f  such that a parallel beam  311   f  is formed. The parallel beam  311   f  is incident on the multi-aperture plate  313   f . The accelerating electric field E 3  provided on the upstream side of the multi-aperture plate  313   f  results in that a diverging lens function is provided to each of the particle beamlets  3   f  traversing the apertures of the multi-aperture plate  313   f . Therefore, the particle beamlets  3   f  generated from the incident beam  311   f  are diverging particle beamlets  3   f . At positions downstream of the multi-aperture plate  313   f , the particle beamlets  3   f  appear to originate from virtual beamlet foci  323   f  positioned upstream of the multi-aperture plate  313   f  as indicated by dotted lines in  FIG. 7 . The virtual beamlet foci  323   f  are imaged onto the surface of the object  7   f  positioned in an object plane  101   f  using imaging optics configured similar to the imaging optics illustrated with reference to  FIGS. 2 to 6  above. It is to be noted that a decelerating electric field E 4  is provided upstream of the object  7   f , wherein the decelerating electric field E 4  can be generated between electrodes  363   f  and  359   f  as shown in  FIG. 7 , or between an electrode and the object  7   f  itself. Moreover, a deflector arrangement  353   f  can be positioned at a suitable location along the beam path between the virtual beamlet foci  323   f  and the object surface  101   f.    
         [0101]    The voltage V 1  can be a negative high voltage, the voltage V 2  can be close to or equal to ground potential, the voltage V 3  can be a negative high voltage, the voltage V 4  can be close to or equal to ground potential, and the voltage V 6  can be a negative high voltage. In the present example, the following voltages are selected: V 1 =−30 kV, V 2 =0 kV, V 3 =−20 kV, V 4 =0 kV and V 6 =−29 kV. 
         [0102]    In the particular embodiments illustrated above, it is to be noted that some of the electrodes are maintained at ground potential while the Figures indicate separate terminals connected to the controller to maintain the respective electrodes at desired voltages. It is apparent that, if the desired voltages are 0 kV, separate terminals connected to the controller can be omitted and that the electrodes maintained at ground potential may have a suitable connection to ground. 
         [0103]    While the disclosure has been described with respect to certain exemplary embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments of the disclosure set forth herein are intended to be illustrative and not limiting in any way. Various changes may be made without departing from the spirit and scope of the present disclosure as defined in the following claims.