Multi-beam system and multi-beam forming unit with reduced sensitivity to secondary radiation

Abstract

A multi-beam charged particle beam system and a method of operating a multi-beam charged particle beam system with higher accuracy are provided. A multi-beam forming unit having lower sensitivity to secondary electrons, scattered charged particles, and X-ray radiation is improved. Accordingly, a plurality of primary charged particle beamlets can be generated with high precision, and the multibeam forming unit has a longer lifetime. The system and method are suitable for improved sample inspection, such as wafer or mask inspection.

Description

Technical Field

[0001] The present invention relates to a multi-beam forming unit of a multi-beam charged particle imaging system having an array of microlenses or multipole elements. Background Art

[0002] WO 2005 / 024881 A2 discloses an electron microscope system that utilizes multiple electron beamlets to operate and scan an object to be inspected in parallel with multiple electron beamlets. Multiple beamlets for a multi-beam charged particle microscope are generated in a multi-beam generating unit. Multiple electron beamlets are generated by directing a primary electron beam to the multi-beam generating unit. The multi-beam forming unit includes a first porous element or filter plate having multiple openings. A portion of the electrons of the electron beam are incident on the filter plate and absorbed there, while another portion of the electron beam passes through the aperture opening of the filter plate. Electron beamlets are formed, and their cross-section is defined by the cross-section of the aperture opening. In addition, the multi-beam forming unit includes another porous array element that acts as a lens, deflector or stigmator on each electron beamlet. Downstream of the multi-beam generating unit, another electron optical element is configured to form a focus of the electron beamlet on the surface of the object or sample. The primary electron beamlets trigger secondary electrons or backscattered electrons as secondary electron beamlets emitted from the object, which are collected and imaged onto a detector. Each secondary beamlet is incident on a separate detector element so that the secondary electron intensity detected therewith provides information related to the sample at the position where the corresponding primary beamlet is incident on the sample. Multiple primary beamlets are systematically scanned over the surface of the sample and, similar to a scanning electron microscope, produce a microscopic image of the sample. The resolution of a scanning electron microscope is limited by the focal diameter of the primary beamlets incident on the object. Therefore, in a multi-beam electron microscope, all beamlets should form the same small focal point on the object.

[0003] It will be appreciated that the system and method described in detail in WO 2005 / 024881 using electrons as an example is generally very applicable to charged particles. Therefore, the object of the present invention is to provide a charged particle beam system that operates with multiple charged particle beams and can be used to achieve higher imaging performance, such as better resolution and narrower resolution range for each of the multiple beamlets.

[0004] Multi-beam charged particle microscopes usually use micro-optical array elements and macro elements in a charged particle projection system. The multi-beam generation unit includes elements for splitting, partially absorbing and affecting the charged particle beam. Thus, multiple charged particle beamlets in a predefined grating configuration are generated. The multi-beam generation unit includes micro-optical elements, such as filter plates, and additional porous elements, such as micro-optical deflection elements or multipole array elements. These array optical elements, for example multipole or multi-stigmator arrays or lens arrays, are arranged downstream of the filter plate. The array optical element has a plurality of holes, each hole having at least one electrode or coil for affecting each primary electron beamlet individually or in combination. The control architecture for the plurality of electrodes or coils of the array optical element includes several parallel microelectronic devices. The microelectronic device provides a plurality of predetermined voltages or currents to the plurality of electrodes or coils. It has been observed that during their operation, the performance of the array optical element drifts. There may be multiple reasons for the drift of the performance of the array optical element. Specific reasons may be residual charge and local damage, which may occur during the use of the array optical element.

[0005] The first cause of drift may be scattered or absorbed primary electrons. The second cause of drift may be secondary electrons, such as those generated at the filter plate. The third cause is secondary radiation, including X-ray radiation. Electrons or secondary radiation may be absorbed or scattered in the holes of the array optical element and may cause charging effects and local changes in the surface potential of the array optical element. It has also been observed that secondary radiation can cause damage to the array optical element. Other effects may be contamination caused by electrons, such as contamination of the holes of the array optical element.

[0006] It is therefore an object of the present invention to provide an improved multi-beam generator for a multi-beam charged particle system which has a reduced sensitivity to charging effects and damages.

[0007] WO 2021 / 180 365A1 discloses certain improvements in multi-beam grating units, such as multi-beam generating units and multi-beam deflector units of multi-beam charged particle microscopes. These improvements include the design, manufacture and adjustment of multi-beam grating units, including holes of specific shapes and sizes. These improvements enable higher precision multi-beam generation and multi-beam deflection or stigmation.

[0008] WO 2005 / 024 881A2 discloses a particle optical configuration. The particle optical configuration comprises a charged particle source for generating a charged particle beam; a porous plate arranged in a beam path of the charged particle beam, wherein the porous plate has a plurality of holes formed therein in a predetermined first array pattern, wherein a plurality of charged particle beamlets are formed downstream of the porous plate from the charged particle beam, and wherein a plurality of beam spots are formed in an image plane of the device by the plurality of beamlets, the plurality of beam spots being arranged in a second array pattern; and a particle optical element for manipulating the charged particle beam and / or the plurality of beamlets; wherein the first array pattern has a first pattern regularity in a first direction, and the second array pattern has a second pattern regularity in a second direction electronically optically corresponding to the first direction, and wherein the second regularity is higher than the first regularity.

[0009] US2003 / 0 209 673A is about an electro-optical system array with multiple electron lenses. The electro-optical system array includes an upper electrode, a middle electrode and a lower electrode arranged along the paths of multiple charged particle beams, wherein the upper electrode, the middle electrode and the lower electrode have multiple holes on the paths of the multiple charged particle beams; an upper shielding electrode inserted between the upper electrode and the middle electrode and having multiple shields corresponding to the corresponding paths of the charged particle beams; and a lower shielding electrode inserted between the lower electrode and the middle electrode and having multiple shields corresponding to the corresponding paths of the charged particle beams. Summary of the invention

[0010] The object of the present invention is solved by an improved architecture of a charged particle multi-beamlet generator of a multi-beam charged particle imaging system, which has reduced sensitivity to damage caused by charged and scattered charged particles, secondary electrons and secondary radiation.

[0011] This application claims priority to German Patent Application No. 10 2022 206314.7 filed on June 23, 2022, the entire disclosure of which is incorporated herein by reference.

[0012] These tasks are solved by the present invention, which is described by the claims of the invention and various specific embodiments. The present invention provides an improved multi-beam charged particle imaging system and an improved method for the operation of such a system. The multi-beam charged particle imaging system comprises a charged particle multi-beamlet generator for generating a plurality of primary charged particle beams. The multi-beam charged particle imaging system comprises an object irradiation system for focusing a plurality of primary charged particle beamlets at a plurality of irradiation positions on the surface of the object. During use, at each irradiation position on the surface of the object, secondary charged particles are generated, thereby forming a plurality of secondary beamlets. The multi-beam charged particle imaging system comprises a secondary electron imaging system for focusing a plurality of secondary beamlets and for forming a plurality of focal points of the secondary beamlets in an image plane. The multi-beam charged particle imaging system also comprises a detector arranged in the image plane.

[0013] The improved multi-beam system comprises at least one active array optical element and a control unit, the control unit being configured to control the active array optical element. The active array optical element comprises a plurality of J holes arranged in a grating structure, the holes being configured to transmit a first plurality of J primary charged particle beamlets through the active array optical element during use. The grating structure can be a hexagonal or rectangular grating of J holes, or the holes can be arranged in a series of rings. The active array optical element also comprises a plurality of electrodes, the electrodes comprising at least one electrode arranged in the periphery of each hole. The active array optical element can be a microlens array having a single annular electrode at each of the plurality of holes. The active array optical element can also be a multipole array comprising a plurality of multipole elements, wherein K electrodes are arranged on the periphery of each of the plurality of holes, and the number of electrodes K of each multipole element is two, four, six, eight or twelve.

[0014] In a first specific embodiment, an improved multi-beam system includes an improved charged particle multi-beamlet generator having a shielding porous plate. The shielding porous plate is arranged and configured to shield scattered charged particles and secondary radiation from hitting the active array optical element. The secondary radiation may be X-ray radiation or secondary electrons, which cause charging effects or damage at the active array optical element. In one example, the shielding porous plate is arranged at the beam entrance side of the active array optical element.

[0015] According to a first specific embodiment, an improved charged particle multi-beamlet generator is configured to generate a plurality of J primary charged particle beams during use. The charged particle multi-beamlet generator (300) according to the present invention comprises a multi-beam forming unit (305) having a plurality of array optical elements, which comprises a filter plate (304); a shielding porous plate (306); and a first active array optical element (307), which is arranged in the propagation direction of the primary charged particles. The filter plate (304) comprises a plurality of first holes (85.1), each of which has a first diameter D1, for generating a plurality of primary charged particle beamlets (3) during use. During use, a primary charged particle beam (309) impacts the filter plate (304). Most of the primary charged particles are absorbed by the filter plate (304), and the primary charged particles passing through the first hole (85.1) form a primary charged particle beamlet (3). The first active array optical element (307) comprises a plurality of third holes (85.3), each of which has a third diameter D3. At least one electrode (81, 82) is arranged near each third hole (85.3), and each electrode (81, 82) is arranged to affect the primary charged particle beamlet (3) individually during use. For example, the first active array optical element (307) can include a plurality of annular electrodes (82) configured to independently generate an electrostatic field for focusing each of the primary charged particle beamlets (3). For example, the first active array optical element (307) can include a plurality of multipole electrodes (81) configured to independently generate an electrostatic field for deflecting each of the primary charged particle beamlets (3) or for focusing or for correcting aberrations.

[0016] During use, some primary charged particles are scattered at the filter plate (304) and generate secondary electrons. According to a first specific embodiment of the present invention, the opening angle or acceptance angle α of the scattered charged particles or secondary electrons is reduced, reducing the charging or damage of the first active array optical element (307) and any other downstream array optical elements. Due to the limited acceptance angle or opening angle α, the amount of scattered charged particles or secondary electrons that can enter the portion of the porous stack below the filter plate (304) is reduced. The reduction of the opening angle α is achieved by shielding the porous plate (306) and the configuration geometry of the shielding porous plate (306) in the multi-beam forming unit (305). The shielding porous plate (306) is arranged between the filter plate (304) and the first active array optical element (307). The shielding porous plate (306) includes a plurality of second holes (85.2), each second hole having a second diameter D2.

[0017] The filter plate (304) has a first thickness L1. L1 is preferably maintained at a thin thickness below 20 μm, for example, L1 ≤ 10 μm. The shielding perforated plate (306) has a third thickness L3 and is disposed at a distance L2 downstream of the filter plate (304). In one example, the distance L2, the thickness L1, and the second diameter D2 define an opening angle α, where tan(α) = D2 / (L1 + L2). In one example, the distance L2, the thicknesses L1 and L3, and the second diameter D2 define an opening angle α, where tan(α) = D2 / (L1 + L2 + L3). According to the first example, the distance L2, the thickness L1 or L3, and the second diameter D2 are selected such that a reduced opening angle is formed, where tan(α) < 0.3, preferably tan(α) < 0.25. For example, the opening angle α is reduced by increasing the distance L2, such as L2 > 70 μm, for example, L2 = 70 μm, L2 = 80 μm, or L2 = 100 μm. For example, the opening angle α is reduced by increasing the thickness L3, such as L3 > 70 μm, for example, L3 = 100 μm or L3 = 120 μm. For example, the opening angle α is reduced by decreasing the diameter D2, such as D2 < 1.3x D1, for example, D2 <= 40 μm, for example, D2 = 38 μm. In one example, at least one of the thickness or the distance L2 or L3 is increased, and the diameter D2 is decreased. In one example, the sum of the thickness and the distance (L1 + L2 + L3) is selected to be more than 130 μm, for example, (L1 + L2 + L3) = 150 μm. In one example, the second diameter D2 is selected according to 1.1X D1 < D2 < 1.3X D1.

[0018] The third hole (85.3) has a third diameter D3, and D2 is selected to be less than D3. For example, D3 > 1.6x D1, but it is even possible to select D3 >= 1.8x D1. Thus, the active array optical element (307) is physically shielded by the shielding perforated plate (306), and the number of secondary electrons or scattered primary charged particles hitting the active array optical element (307) is even more effectively reduced. For example, D2 is selected in the range 0.625xD3 <= D2 <= 1.3x D1. For example, D2 = 1.3x D1 and D3 = 1.8x D1. For example, D2 = 1.2x D1 and D3 = 1.7x D1. For example, D2 = 1.1x D1 and D3 = 1.6x D1. For example, by achieving a ratio of approximately D2 / D3 <= 0.75, the electrodes (81, 82) of the active array optical element (307) are shielded by the shielding perforated plate (306), and the number of secondary electrons or scattered primary charged particles hitting the electrodes (81, 82) is effectively reduced.

[0019] The shielding perforated plate (306) may further have at least one absorption or metal layer (361) covering the beam inlet side of the shielding perforated plate (306). According to one example, the material of the absorption or metal layer (361) is from a group of materials including molybdenum, ruthenium, rhodium, palladium or silver, tungsten, rhenium, osmium, iridium, platinum or gold. This layer having a thickness of, for example, about 1 - 2 μm can provide sufficient stopping power for scattered charged particles and secondary electrons. The thickness of this layer can even be chosen to be thicker, for example greater than 10 μm or even greater than 20 μm, so that X - ray radiation is also effectively shielded.

[0020] The shielding perforated plate (306) can also be configured for improved reduction of scattered charged particles and secondary electrons. In a first example, at each of the second holes (85.2) of the shielding perforated plate (306), at least one baffle (369) is formed for absorbing scattered charged particles and secondary electrons. In a second example, the shielding perforated plate (306) is formed as a double - layer structure, and each of the plurality of holes (85.2) having a diameter D2 is formed in the first layer, and the thickness L3.1 of the first layer < L3. Thus, the scattering of charged particles or electrons in the second holes (85.2) is reduced. In a third example, each of the second holes (85.2) of the shielding perforated plate (306) is formed in a conical shape (365) such that the minimum hole diameter D2 is formed at the bottom or the beam exit side of the shielding perforated plate (306). The absorption layer (361) can also cover the conical aperture opening (85.2). In a fourth example, each of the plurality of second holes of the shielding perforated plate is formed in a conical shape such that the minimum hole diameter D2 is formed at the top or the beam inlet side of the shielding perforated plate. Thus, the surface area where contaminants may grow is reduced.

[0021] In one example, the primary multi - micro - beam forming unit (305) further includes another perforated plate formed as an absorption plate (371) between the filter plate (304) and the shielding perforated plate (306). In one example, the diameter D4 of the fourth hole (85.4) of the absorption plate (371, 371.1) is selected to be between the first diameter D1 and the third diameter D3, for example, D4 is selected in the range of 1.1x D1 < D4 <= D3.

[0022] The primary multi - micro - beam forming unit (305) may include additional perforated plates, including additional active array optical perforated plates and terminal perforated plates (310).

[0023] Due to the improvement of the first specific embodiment, the lifespan of the multi-small beam forming unit is increased. In addition, the charge or damage to the active array optical element (307) caused by scattered charged particles and secondary electrons is reduced. The second specific embodiment of the present invention further reduces the influence of scattered charged particles and secondary electrons. According to the second specific embodiment of the present invention, a charged particle multi-small beam generator (300) includes a multi-beam forming unit (305) having a filter plate (304) and a first array optical element (307). The charged particle multi-small beam generator (300) further includes a first absorber plate (371, 371.1) having a plurality of fourth holes (85.4) with a diameter of D4. The first absorber plate (371, 371.1) is disposed upstream of the filter plate (304). The filter plate (304) includes a plurality of first holes (85.1), each first hole having a first diameter D1 for generating a plurality of primary charged particle small beams (3) during use. In a first example, the diameter D4 of the fourth holes (85.4) is selected to be greater than the diameter D1 of the first holes (85.1). During use, the primary charged particle beam (309) first impinges on the first absorber plate (371, 371.1). Most of the primary charged particles are absorbed by the first absorber plate (371, 371.1), and the primary charged particles passing through the fourth holes (85.4) form a preformed charged particle small beam (312). The preformed charged particle small beam (312) impinges on the filter plate (304). A part of the preformed charged particle small beam (312) is absorbed by the filter plate (304), and the primary charged particles passing through the first holes (85.1) form a primary charged particle small beam (3). The first active array optical element (307) includes a plurality of third holes (85.3), each third hole having a third diameter D3. At least one electrode (81, 82) is disposed near each third hole (85.3), and each electrode (81, 82) is configured to individually affect the primary charged particle small beam (3) during use. For example, the first active array optical element (307) can include a plurality of annular electrodes (82) configured to independently generate an electrostatic field for focusing each primary charged particle small beam (3). For example, the first active array optical element (307) can include a plurality of multipole electrodes (81) configured to independently generate an electrostatic field for deflecting each of the primary charged particle small beams (3) or for focusing or for correcting aberration.

[0024] Due to the absorber plate (371, 371.1), the number of scattered charged particles and secondary electrons downstream of the filter plate (304) is effectively reduced. In one example, the diameter D4 of the fourth holes (85.4) of the absorber plate (371, 371.1) is selected to be between the first diameter D1 and the third diameter D3, for example, D4 is selected in the range of 1.1xD1 < D4 <= D3.

[0025] The X-ray induced radiation damage to the porous stack located below the absorber plate is further reduced by coating a thick metal layer (such as gold) that effectively shields X-ray radiation on the top side, bottom side or all surfaces of the absorber plate (371, 371.1), or by using a fully metal absorber plate (371, 371.1). For example, the absorber plate (371, 371.1) can be coated with a conductive layer thicker than, for example, 10 μm or even 20 μm. For example, the absorber plate (371, 371.1) can be made of a suitable metal or metal alloy, such as gold, tungsten or a gold alloy. In one example, the material for shielding the porous plate (306) is from a group of materials including molybdenum, ruthenium, rhodium, palladium or silver, tungsten, rhenium, osmium, iridium, platinum or gold. In one example, the conductive layer is formed of a material or material composition with a lower atomic mass number. Thus, the generation of secondary electrons is reduced. For example, the conductive layer (361) is a metal layer, a graphite layer or a doped semiconductor layer. Suitable low atomic mass number metals are aluminum, manganese, copper or silver.

[0026] In one example, the primary multi-beam forming unit (305) further includes a shielding porous plate (306) having a second hole (85.2) with a second diameter D2, the shielding porous plate (306) having a third thickness L3; where 1.1x D1 < D2 <= 1.5x D1. In one example, the primary multi-small beam forming unit (305) includes a second absorber plate (371.2) located between the filter plate (304) and the shielding porous plate (306). In one example, the diameter D5 of the fifth hole (85.5) of the absorber plate (371, 371.1) is selected between the first diameter D1 and the third diameter D3, for example, the range of D5 is selected within 1.1x D1 < D5 <= D3. The primary multi-small beam forming unit (305) can include additional porous plates, including additional active array optical porous plates and end porous plates (310).

[0027] In each of the shielding porous plate (306), the first absorber plate or the second absorber plate (371, 371.1, 371.2), each of the holes (85.2, 85.4, 85.5) can have at least one baffle (369). Each of the plurality of holes can be formed in a conical shape (365) such that the minimum hole diameter is formed at the bottom or the beam exit side of the corresponding hole (85.2, 85.4, 85.5). In an alternative example, each of the plurality of holes can be formed in a conical shape (365) such that the minimum hole diameter is formed at the upper part or the beam entrance side of the corresponding hole (85.2, 85.4, 85.5). For example, the absorber plate (371, 371.1, 371.2) can have at least one metal layer (361) at the upper side or the beam entrance side of the absorber plate (371, 371.1, 371.2).

[0028] The charged particle multi-beamlet generator (300) according to the second specific embodiment further comprises a primary charged particle source (301) and a collimating lens (303.1, 303.2) arranged upstream of the filter plate (304). According to a first example of the second specific embodiment, the absorption plate (371, 371.1) is arranged in the beam path of the collimated primary charged particle beam (309) generated by the collimating lens (303.1, 303.2). For example, the absorption plate (371, 371.1) is arranged between the collimating lens (303.1, 303.2) and the filter plate (304).

[0029] According to a second example of the second specific embodiment, an absorption plate (371, 371.1) is arranged in a diverging primary charged particle beam (309) between a primary charged particle source (301) and a collimating lens (303.1, 303.2). The charged particle multi-beamlet generator (300) can further include a collecting lens (315.1, 315.2), which is arranged between the primary charged particle source (301) and the absorption plate (371, 371.1). The absorption plate (371) has a plurality of fourth holes (85.4) arranged at a first pitch P1, which are arranged to generate a plurality of preformed beamlets (312) having the first pitch P1 during use. The first hole (85.1) of the filter plate (304) is arranged at a second pitch P2. The charged particle multi-beamlet generator (300) further comprises a control unit (830), which is configured to provide a first control signal to a first collecting lens (315, 315.2) during use to adjust the current of the plurality of primary charged particle beamlets (3), and is configured to provide a second control signal to a collimating lens (303.1, 303.2) to match the pitch P1 of the plurality of pre-formed beamlets (312) with the second pitch P2 of the filter plate (304), and to adjust the propagation angle of the plurality of pre-formed beamlets (312) to form a beam of parallel pre-formed beamlets (312). In a similar manner, an absorption plate (371, 371.1) can be arranged in a converging primary charged particle beam (309) between the primary charged particle source (301) and the collimating lens (303.1, 303.2).

[0030] According to one example, the absorption plate (371, 371.1, 371.2) comprises at least one layer, the material of which is from the material group comprising molybdenum, ruthenium, rhodium, palladium or silver, tungsten, rhenium, osmium, iridium, platinum or gold. Due to a thickness of, for example, about 50 μm to 300 μm, sufficient stopping power can be provided for scattered charged particles and X-rays. In one example, the absorption plate (371, 371.1, 371.2) has a conductive layer, which is formed by a material or material combination with a lower atomic mass number. Therefore, the generation of secondary electrons is reduced. For example, the conductive layer (361) is a metal layer, a graphite layer or a doped semiconductor layer. Suitable low atomic mass number metals are aluminum, manganese, copper or silver.

[0031] Due to the at least one absorption plate (371, 371.1, 371.2) according to the second specific embodiment, the influence of scattered primary charged particles and secondary electrons in the primary multi-beamlet forming unit (305) is further reduced. In addition, the influence of other secondary radiation such as X-ray radiation can be further reduced, and the life of the primary multi-beamlet forming unit (305) is increased. In addition, the charge or damage of the active array optical element (307) caused by X-rays, scattered charged particles and secondary electrons is reduced.

[0032] A third embodiment of the present invention provides a system and method configured to reduce the effects of scattered charged particles and secondary electrons. According to the third embodiment, an improved method for operating a multi-beam forming unit (305) of a multi-beam charged particle microscope (1) is provided. The method includes the steps of generating and applying a plurality of voltages to elements of the multi-beam forming unit (305), which are configured to reduce the effects of secondary electrons.

[0033] The plurality of voltages include a first voltage U1 provided to a filter plate (304). The filter plate (304) includes a plurality of first holes (85.1) for generating or transmitting a plurality of primary charged particle beamlets (3) during use. The plurality of voltages include a plurality of separate fourth voltages U4 provided to a plurality of electrodes (81, 82), the electrodes (81, 82) being arranged near a plurality of third holes (85.3) of an active array optical element (307), each electrode (81, 82) being arranged to generate an electric field for focusing, deflecting or shaping one of the primary charged particle beamlets (3). The plurality of voltages include a second voltage U2 provided to a shielding porous plate (306), the shielding porous plate being arranged between the filter plate (304) and the active array optical element (307). The plurality of voltages including the second voltage U2 are adjusted to achieve a repulsive force or an attractive force on secondary electrons (353), which are generated by the primary charged particle beam (309) at an intersection (317) with the filter plate (304). In general, a plurality of voltages U0, U1, U2, U3, U4 and U5 are selected to form a potential distribution G along the propagation direction of the primary charged particle beamlet (3) so that at least one of the following three examples occurs. In example A, a potential barrier (in the form of a potential step A1 or a potential maximum A2) is formed along the z-axis, which prevents low-energy secondary or scattered electrons from reaching the active array optical element (307). In example B, a potential distribution is designed so that the beam forming aperture or filter plate (304) is located in a potential well (Potential sink) B1 formed along the z-axis. In this case, secondary electrons or scattered electrons originating from the energy minimum of the well cannot escape the potential well along the z-axis and are effectively prevented from further penetrating into the elements downstream of the filter plate (304). In example C, voltages U0 and U1 are selected so that during use, an electric field is formed between the absorption plate 371 and the filter plate 304, which pulls the secondary electrons or scattered electrons into the negative z direction, away from the active array optical element (307).

[0034] In a first example, a first voltage U1 supplied to the filter plate (304) is selected to produce a sink for secondary electrons. For example, U1 is selected to be greater than U2. In a second example, a second voltage U2 supplied to the shielding aperture plate (306) is selected to produce a barrier for secondary electrons. For example, U2 is smaller than U1, for example, U2 is selected to be negative relative to the ground level U0, where U2 = U0-US. Primary charged particles typically have a large kinetic energy of about EK = 5-35 keV, corresponding to a voltage difference of UE = 5-35 kV. To effectively block secondary electrons, a shielding voltage US less than 0.3% of UE is sufficient. In one example, the shielding voltage US is about 100 V. At such a low voltage of US < 0.3% x UE, secondary electrons are effectively reduced, while primary charged particles are only slightly affected. In one example, the shielding voltage US is about 10 V. At such a low voltage of US < 0.03% x UE, secondary electrons are effectively reduced, while primary charged particles are only slightly affected. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will be better understood with reference to the accompanying drawings, in which:

[0036] Figure 1 A multi-beam imaging system is shown.

[0037] Figure 2 A diagram of a multi-beam forming unit.

[0038] Figure 3 An illustration of the generation of unwanted secondary radiation.

[0039] Figure 4 This is a diagram of the prior art.

[0040] Figure 5 is a diagram of a first example according to the first specific embodiment.

[0041] Figure 6 is a diagram of a second example according to the first specific embodiment.

[0042] Figure 7 Some examples of shielding aperture plates are shown.

[0043] Figure 8 is a diagram of a third example according to the first specific embodiment.

[0044] Fig. 9 is a diagram showing an example according to the second specific embodiment.

[0045] Fig.10 A first example according to the second specific embodiment is shown.

[0046] Fig.11 A second example according to the second specific embodiment is shown.

[0047] Fig.12 Another example according to the second embodiment is shown.

[0048] Fig.13 An example according to the third specific embodiment is shown.

[0049] Fig.14 Three examples A, B and C according to the third embodiment are shown.

[0050] Fig.15 The effect of an example according to the third embodiment is shown.

[0051] Fig.16 The effect of an example according to the third embodiment is shown.

[0052] Fig.17 The effect of an example according to the third embodiment is shown. DETAILED DESCRIPTION

[0053] In the following, identical reference numerals denote identical features, even if these are not explicitly mentioned in the text.

[0054] Figure 1 Schematic diagram of a multi-beam charged particle imaging system 1 (referred to as multi-beam system 1) according to a specific embodiment of the present invention. The multi-beam system 1 uses multiple charged particle beams to form an image of an object 7. The multi-beam system 1 generates multiple J primary electron beams 3, which impact the object 7 to be inspected to generate interaction products, such as secondary electrons, which are emitted from the object 7 and subsequently detected. The multi-beam system 1 is a scanning electron microscope (SEM) type, which uses multiple primary electron beams 3, which are incident at multiple locations on the surface of the object 7 and generate multiple primary electron beam focal points 5 separated from each other in space there. The object 7 to be inspected can be of any desired type, such as a semiconductor wafer or a semiconductor mask, and can include a configuration of miniaturized components. The surface 25 of the object 7 is configured in the object plane 101 of the objective lens 102 of the illumination system 100.

[0055] The diameter of the smallest beam spot or focus 5 shaped in the object plane 101 can be very small. Example values ​​for this diameter are below 5 nanometers, for example 4 nm, 3 nm or less. The focusing of the primary charged particle beamlet 3 for shaping the focus 5 is performed by the objective system 102. In this case, the objective system 102 can include a magnetic immersion lens. Other examples of focusing means are described in German patent application DE102020125534 B3, the entire contents of which are incorporated herein by reference.

[0056] The plurality of focal points 5 of the primary beam form a regular raster arrangement of incident positions, which is formed in the object plane 101. The number J of primary beamlets may be five, twenty-five or more. In practice, the number of beamlets J, and therefore the number of incident positions or focal points 5, may be chosen to be significantly larger, such as, for example, J=10 x 10, J=20 x 30 or J=100 x 100. Example values ​​for the pitch P between the incident positions are 1 micron, 10 microns or more, for example 40 microns. For simplicity, Figure 1 Only three primary beamlets 3.1, 3.2 and 3.3 with corresponding focusing points 5.1, 5.2 and 5.3 are shown in FIG.

[0057] The primary particles of the primary beamlet 3 that strike the object 7 generate interaction products, such as secondary electrons, backscattered electrons, or primary particles that undergo motion reversal for other reasons, that are emitted from the surface of the object 7. The interaction products are emitted from the surface of the object 7 and are shaped by the objective lens 102 to form a secondary electron beamlet 9. For simplicity, all interaction products are collectively referred to as secondary electrons herein, which form the secondary electron beamlet 9.

[0058] The multi-beam system 1 provides a detection beam path for guiding multiple secondary particle beamlets 9 to the secondary electron imaging system 200. The secondary electron imaging system 200 includes several electron optical lenses 205.1 to 205.5 for guiding the secondary particle beamlets 9 toward the spatially resolved particle detector 600. The detector 600 is configured in the image plane 225. The detector 600 includes multiple detection elements. The detection element can be, for example, a diode such as a PMD, or a CMOS detection element, which has an electron-to-light conversion element, or can be formed as a direct electron detection element. In one example, the detector 600 includes an electron-to-light conversion element (such as a scintillator plate), through which secondary electrons are converted into light; and multiple light detection elements.

[0059] The imaging using the secondary electron imaging system 200 is strongly magnified, so that both the grating pitch of the primary beam on the wafer surface and the size and shape of the focus of the primary beam are imaged in an enlarged manner. For example, the magnification is between 100x and 300x, so that 1 nm on the wafer surface is magnified and imaged to between 100nm and 300nm. In this process, the image field of a multi-beam system with a diameter of, for example, 100μm is magnified to about 30mm.

[0060] The primary particle beam 3 is generated in a beam generating device 300, which includes at least one particle source 301 (for example, an electron source), at least one collimating lens 303, a primary multi-beam forming unit 305 and a first field lens 308.1, and a second field lens 308.2. The particle source 301 generates at least one divergent particle beam 309, which is at least substantially collimated by at least one collimating lens 303 and irradiates the primary multi-beam forming unit 305. The primary multi-beam forming unit 305 includes at least one first porous plate or filter plate 304, which has a plurality of J openings formed therein in a first grating configuration. The particles of the illumination particle beam 309 pass through the J holes or openings of the filter plate 304 and form a plurality of J primary beamlets 3. The particles of the illumination beam 309 that hit the filter plate 304 are absorbed by the filter plate and have no effect on the formation of the primary beamlet 3. The primary multi-beamlet forming unit 305 typically has at least one further active porous plate 307, such as an array of lenses, an array of stigmators or an array of deflection elements.

[0061] Together with the field lens 308.1 and the second field lens 308.2, the primary multi-beamlet forming unit 305 focuses each of the primary beamlets 3 in such a way that a focus is formed in the intermediate image surface 321. Optionally, the beam focus and the intermediate image surface 321 may be virtual. The intermediate image surface 321 can be curved to pre-compensate for the field curvature of an imaging system arranged downstream of the intermediate image surface 321.

[0062] At least one field lens 103 and an objective lens 102 provide a first imaging particle optical unit for imaging a surface 321 formed with a beam focus onto an object plane 101 so that a focus 5 of a primary beamlet is formed there. Typically, a surface 25 of an object 7 is arranged in the object plane 101, and the focus 5 is correspondingly formed on the object surface 25. A plurality of primary beamlets 3 form an intersection 108, and a first scanning deflector 110 is arranged near the intersection 108. The first scanning deflector 110 is used to deflect a plurality of primary beamlets 3 together and synchronously so that a plurality of focal points 5 move simultaneously on the surface 25 of the object 7. The first scanning deflector 110 is driven by a scanning control unit 860 so that in an inspection operation mode, a plurality of two-dimensional image data of the surface 25 is acquired. Additionally, the multi-beam system 1 can also include another static deflector configured to adjust the positions of the plurality of primary beamlets 3.

[0063] The objective lens 102 and the projection lens 205 provide a secondary electron imaging system 200 for imaging the object plane 101 onto the detection plane 225. Thus, the objective lens 102 is a lens or lens system that is part of both the first and second particle optical units, while the field lenses 103, 307 and 308 belong only to the first particle optical unit 100 and the projection lens 205 belongs only to the secondary electron imaging system 200.

[0064] The beam splitter 400 is arranged in the beam path of the first particle optical unit 100 between the field lens 103 and the objective system 102. The beam splitter 400 is also part of the second optical unit in the beam path between the objective system 102 and the projection lens 205.

[0065] The first deflection scanner 110 is disposed in a primary electron beam path or a combined electron beam path. Figure 1 In the example shown, the secondary electron beamlet 9 transmits the first deflection scanner 110 in the opposite direction during use, and the scanning motion of the secondary beamlet 9 is partially compensated. Secondary electrons typically have different kinetic energy than primary electrons. Therefore, the scanning motion of the moving irradiation position is only partially compensated. In order to fully compensate for the scanning motion of the secondary electron beamlet 9, a second deflection scanner 222 is configured in the secondary electron beam path. The secondary electron imaging system 200 includes a second collective beam deflector 222, which is configured near the intersection of the secondary electron beamlets 9. The second collective beam deflector 222 operates synchronously with the first beam deflector 110, and in compensating for the beam deflection of the secondary electron beamlet 9, the focus 15 of the secondary beamlet 9 maintains a constant position on the detection plane 225.

[0066] The secondary electron imaging system 200 includes electron optical lenses 205.1 to 205.5 to adjust the focal plane of the focus 15 of the secondary electron beamlet 9. The electron optical lenses 205.1 to 205.5 can be implemented as magneto-optical elements, but are not limited to magneto-optical elements, and can also include electrostatic lens elements or stigmators. Using the electron optical lenses 205.1 to 205.5, the focal point 15 of the secondary electron beamlet 9 can be focused into the image plane 225 of the secondary electron imaging system 200. The secondary electron imaging system 200 includes multiple additional components, such as at least one of a porous array element, a deflector, or a replaceable aperture diaphragm. Together with the objective lens 102, the lens focuses the secondary beam 9 on the spatial resolution detector 600, and in the process compensates for the imaging ratio and distortion of the multiple secondary electron beamlets 9 caused by the magnetic lens, so that the third grating configuration of the focus 15 of the multiple secondary electron beamlets 9 remains constant on the detection plane 225. For example, the first magnetic lens 205.4 and the second magnetic lens 205.4 are designed in opposite order to each other and have opposite magnetic field directions. The Larmor rotation of the secondary electron beamlet 9 can be compensated by appropriately driving the magnetic lenses 205.4 and 205.5. The secondary electron imaging system 200 also has available correction elements, such as a porous plate 216.

[0067] Further information about such multi-beam particle beam systems and the components used therein, such as, for example, particle sources, multi-aperture plates and lenses, can be obtained from the international patent applications WO 2005 / 024881, WO 2007 / 028595, WO 2007 / 028596, WO2011 / 124352 and WO 2007 / 060017 and the German patent applications with publication numbers DE 10 2013 016 113 A1 and DE 10 2013 014976 A1, the contents of which are hereby incorporated by reference into the present application in their entirety.

[0068] The multi-beam charged particle imaging system 1 also includes a control system 800, which is configured to control the various particle optical components of the multi-particle beam system and to evaluate and analyze the signals obtained by the detector 600. In this case, the controller or controller system 800 can be composed of multiple separate computers or components. For example, the control unit 800 includes a control processor 880 and a control module 840 for controlling the electron optical elements of the secondary electron imaging system 200 and the object irradiation system 100. The control unit 800 is also connected to the control module 503 for supplying a voltage to the object 7, which is also referred to as an extraction voltage. Therefore, during use, an extraction field is generated between the objective lens 102 and the surface 25 of the object 7. During use, the extraction field decelerates the primary charged particles of the primary beamlet 3 before reaching the sample surface 25 and produces an additional focusing effect on multiple primary beamlets 3. At the same time, the extraction field is used to accelerate the secondary particles to leave the surface 25 of the object 7 during use.

[0069] Furthermore, the control unit 800 comprises a scanning control module 860. During the inspection operation mode, a plurality of focal spots 15 of the secondary electron beamlets are formed in the detection plane 225, and a plurality of signals are recorded during a scanning operation of the primary beamlet 3 over the surface 25 of the object 7. According to an embodiment of the present invention, the detector 600 comprises a plurality of groups of array detection elements, wherein there is a group of detection elements for each secondary electron beamlet 9. Each group of detection elements is configured to record an intensity signal of the assigned secondary electron beamlet 9. The plurality of intensity signals of the plurality of secondary electron beamlets 9 are transmitted to the image data acquisition unit 810, wherein the image data are processed and stored in the memory 890. The settings of the components of the multi-beam charged particle imaging system 1 are initially determined and stored in the memory 890 of the control unit 800 of the multi-beam charged particle imaging system 1.

[0070] The multi-beam charged particle imaging system 1 according to the first embodiment comprises a charged particle multi-beamlet generator 300 having a primary multi-beamlet forming unit 305 for generating a plurality of primary charged particle beamlets 3. The primary multi-beamlet forming unit 305 is shown in FIG. Figure 2In the propagation direction of the primary charged particles of the primary charged particle beam 309, the primary multi-beam forming unit 305 includes a filter plate 304, a second porous plate 306, an active array optical element 307 and an end porous plate 310. Each porous plate can also include a support area 333 of a larger thickness. The filter plate 304 is covered with a conductive coating 99, which is configured to absorb a major portion of the incident charged particles from the primary charged particle beam 309. Through a plurality of first holes 85.1, a plurality of primary charged particle beamlets 3.1 to 3.4 are formed. Each of the porous plates 304, 306, 307, 310 includes a plurality of holes 85.1 to 94. In Figure 2 In the diagram, only the hole 85.1 of the filter plate 304 and the one hole 94 of the terminal porous plate 310 are provided. The plurality of holes 85.1 to 94 of each of the porous plates 304, 306, 307, 3105 are arranged in the same grating configuration and pitch P2, and form a parallel sequence of holes, so that the collimated particle beamlets 3.1 to 3.4 can directly pass through each of the hole sequences. The primary multi-beamlet forming unit 305 also includes at least one first focusing lens electrode 308.1 and a plurality of spacers 83.1 to 83.3 and 86. The focusing lens electrode 308.1 is configured to generate an electrostatic immersion lens field 92 during use, which partially penetrates the terminal hole 94 of the terminal porous plate 310.

[0071] The active array optical element 307 and the end multi-aperture plate 310 have a plurality of electrodes 81 and 82, which are configured to individually and independently influence each primary charged particle beamlet 3.1 to 3.4. Therefore, the focus of the primary charged particle beamlets 3.1 to 3.4 is formed in an intermediate image plane 321, which is typically curved and can have a tilt component 323. More details about the primary multi-beam forming unit 305 are disclosed in the German patent application DE 102021208700.0 filed on August 10, 2021, which is incorporated herein by reference.

[0072] Figure 3 The filter plate 304 and the interaction of the filter plate 304 with the primary charged particle beam 309 are shown in more detail. The primary charged particles either transmit through the first aperture 85.1 and form a primary charged particle beamlet 3.1, or they are transported to the primary charged particle beamlet 3.1 at a plurality of intersection points 317 ( Figure 3Only some of the absorption coating 99 that impacts the filter plate 304 at (only some are shown) is depicted. Basically, different interaction products can be generated at each of the intersection points 317. In the first example, X-ray radiation (also known as bremsstrahlung) 351 is generated. This is depicted at the intersection point 317.1. In the second example, secondary electrons are generated, and the secondary electrons can leave the absorption coating and form a small beam of secondary electrons 353. In addition to secondary electrons and X-rays, a number of primary electrons can still pass through the filter plate 304 and form a transmitted electron beam. The primary charged particles may also be scattered at contaminant particles at scattering points 319, such as within the holes 85.1, and a small beam of scattered electrons 359 is generated. Therefore, downstream of the filter plate 304, not only are there primary charged particles that form the small beam of primary charged particles 3.1, but there can also be secondary radiation 351, secondary electrons 353, scattered charged particles 359, and transmitted scattered charged particles 355. This unwanted radiation and unwanted charged particles result in unwanted charging, contamination, and damage to the optical elements near the filter plate 304.

[0073] Figure 4 Illustrates the geometric characteristics of a typical primary multi-beamlet forming unit 305 according to the prior art. The filter plate 304 has an absorption layer 99, an electrode layer 98, and a plurality of holes 85.1 with a diameter of D1. The filter plate (304) has a first thickness L1. L1 is preferably maintained at a thin thickness below 20 μm, for example, L1 <= 10 μm. The filter plate 304 may even have a reduced thickness L1.1 at each of the plurality of holes 85.1. Therefore, the generation of scattered charged particles 359 within the holes 85.1 is reduced. However, the reduction in thickness increases the transmittance of the transmitted charged particles 355. The second perforated plate 306 has second holes 85.2, which have a larger diameter D2, where D2 > D1, and has a thickness of L3. A gap with a thickness of L2 is disposed between the filter plate 304 and the second perforated plate 306. The active array optical element 307 has third holes 85.3 and a thickness of L5. The third holes 85.3 have a diameter D3, where D3 < D2. A gap with a thickness of L2 is disposed between the second perforated plate 306 and the active array optical element 307. At each of the third holes 85.3, at least one electrode 81.1 to 81.8 is disposed, for example, eight electrodes 81.1 to 81.8 are disposed, through which the small beam of primary charged particles 3.1 can be affected during use (while in Figure 5Only two electrodes 81.1 and 81.5 are visible in the cross-section). Each electrode (81) is connected to a control unit (800) configured to supply a voltage to each electrode (81) for individually influencing each primary charged particle beamlet (3) during use. For example, the first active array optical element (307) can include a plurality of annular electrodes (82) configured to independently generate an electrostatic field for focusing each primary charged particle beamlet (3). For example, the first active array optical element (307) can include a plurality of multipole electrodes (81) configured to independently generate an electrostatic field for deflecting each of the primary charged particle beamlets (3) or for focusing or for correcting aberrations. The electrode layer 98 of the second perforated plate 306 or filter plate can be configured as counter-electrodes to form, for example, an Einzel lens. In designs of the prior art, the second diameter D2 of the second perforated plate 306 is chosen to be relatively large to avoid having a negative impact on the primary beamlet 3.1, where the third diameter D3 is chosen to be relatively small (D3 < D2) relative to the second diameter D2. As a result, the voltage supplied to electrodes 81.1 to 81.8 is reduced, which is required for generating the electrostatic field for influencing the primary beamlets 3 during use. Starting from the edge of the first aperture 85.1, an opening angle α is formed, with approximately tan(α) = D2 / (L1 + L2 + L3). The large opening angle α of the prior art has the following disadvantages: unwanted radiation and unwanted charged particles can impinge on the active array optical element 307 and have a parasitic effect on the electrostatic field generated by electrodes 81.1 to 81.8, thereby causing degradation of the focus generated by the primary multi-beamlet forming unit 305. For example, secondary electrons 353 can adhere to the upper surface of the active array optical element 307 and generate an additional electric field. Such parasitic charges will accumulate over time and gradually degrade the performance of the primary multi-beamlet forming unit 305.

[0074] Figure 5Illustrates a first specific embodiment of the present invention. According to the first example, the distance L2, the thicknesses L1 and L3, and the second diameter D2 are selected such that a reduced opening angle is formed, tan(α) < 0.3, preferably tan(α) < 0.25. By selecting the aperture diameter D2 relative to D3 such that D2 < D3, the reduced opening angle is achieved. In one example, D2 is selected in the range between 1.1X D1 and 1.3X D1. The third hole (85.3) has a third diameter D3, and D2 is selected to be less than D3. For example, D3 > 1.6x D1, but it is even possible to select D3 >= 1.8x D1. Thus, the active array optical element (307) is physically shielded by the second perforated plate (306), reducing the number of secondary electrons or scattered primary charged particles hitting the active array optical element (307). Therefore, according to the present invention, the second perforated plate (306) is also referred to as the shielding perforated plate (306). For example, D2 is selected in the range 0.625x D3 <= D2 <= 1.3x D1. For example, D2 = 1.3x D1, D3 = 1.8x D1. For example, D2 = 1.2x D1, D3 = 1.7x D1. For example, D2 = 1.1x D1, D3 = 1.6x D1. For example, by achieving a ratio of approximately D2 / D3 <= 0.75, the electrodes (81, 82) of the active array optical element (307) are shielded by the shielding perforated plate (306), and the number of secondary electrons or scattered primary charged particles hitting the electrodes (81, 82) is effectively reduced. For example, the opening angle α is reduced by reducing the diameter D2, such as D2 < 1.3x D1, for example D2 <= 40μm. As the diameter D2 of the shielding perforated plate (306) decreases, a reduction in the opening angle α is achieved, and more transmitted charged particles 355 are absorbed by the shielding perforated plate (306).

[0075] For example, the opening angle α is further reduced by increasing the distance L2, such as L2 > 70μm, for example L2 = 100μm. Figure 6 Illustrates an example where the distance L2 is increased. Thus, even the probability that the scattered charged particles 359 or the transmitted charged particles 355 and secondary electrons 353.1, 353.2 are absorbed at the shielding perforated plate (306) is increased, and they do not cause any harm at the shielding perforated plate (306). For example, the opening angle α is further reduced by increasing the thickness L3, such as L3 > 70μm, for example L3 = 120μm.

[0076] In one example, at least one of thickness or distance L2 or L3 is increased and diameter D2 is decreased. In one example, the sum of the thickness and distances (L1 + L2 + L3) is selected to be greater than 130 μm, for example (L1 + L2 + L3) = 150 μm. For example, to reduce the generation of scattered charged particles 359, the thickness of the filter plate 304 is selected as L1 = 10 μm, and the distances are selected as L2 = 20 μm, L3 = 120 μm. For example, the thickness of the filter plate 304 is selected as L1 = 10 μm, and the distances are selected as L2 = 70 μm, L3 = 70 μm.

[0077] The shielding perforated plate (306) may also have at least one absorption or metal layer (361) covering the beam inlet side of the shielding perforated plate (306). According to one example, the material of the absorption or metal layer (361) is from the group of materials comprising molybdenum, ruthenium, rhodium, palladium or silver, tungsten, rhenium, osmium, iridium, platinum or gold. Such a layer having a thickness of, for example, about 1 - 2 μm can provide sufficient stopping power for scattered charged particles 359 and secondary electrons 353. In another example, the shielding perforated plate (306) may also have at least one absorption layer or metal layer (361) covering the beam outlet side of the shielding perforated plate (306). In another example, the shielding perforated plate (306) is made of an absorption material, for example a material from the group containing molybdenum, ruthenium, rhodium, palladium or silver, tungsten, rhenium, osmium, iridium, platinum or gold or an alloy thereof.

[0078] According to another example of the first specific embodiment, the shielding perforated plate (306) can also be configured to improve the reduction of scattered charged particles 359 and secondary electrons 353. Figure 7 Illustrates several components for reducing scattered charged particles 359 and secondary electrons 353. In Figure 7 In the first example shown in a, at each of the second holes (85.2) of the shielding perforated plate (306), at least one baffle (369) for absorbing scattered charged particles and secondary particles is formed. The plurality of baffles 369 can be formed by, for example, a stack of a plurality of metal layers 361 and insulating layers 363 located on top of each other. The conductive metal layer 361 can be connected to the ground level. In Figure 7 In the second example shown in b, the shielding perforated plate (306) is formed with a double - layer structure, and each of the plurality of holes (85.2) having a diameter of D2 is formed in the first layer, the thickness L3.1 < L3. Thus, the scattering of charged particles or electrons in the second hole (85.2) is reduced. In the second example, since the thickness of the second hole 85.2 is reduced, the diameter D2 of the second hole can even be further reduced, for example D1 < D2 < 1.15x D1. In Figure 7In the third example shown in c, each of the second holes (85.2) of the shielding perforated plate (306) is formed to have a conical shape (365) such that the minimum hole diameter D2 is formed on the bottom side or the beam exit side of the shielding perforated plate (306). The absorption layer (361) may also cover the conical aperture opening (85.2). Thus, by having the minimum diameter D2 on the bottom side or the beam exit side of the shielding perforated plate (306), the opening angle α is further reduced to a minimum. Therefore, the protection or shielding of the shielding perforated plate (306) for the active array optical element (307) is improved.

[0079] In the fourth example (as shown in Figure 7 d), each of the second holes (85.2) of the shielding perforated plate (306) is formed to have a conical shape (365) such that the minimum hole diameter D2 is formed on the top side or the beam entrance side of the shielding perforated plate (306). Thus, similar to Figure 7 the second example shown in b, the cross-sectional area of the holes with scattered charged particles (359) or secondary electrons (353) is reduced, and the surface contamination caused by the scattered charged particles (359) or secondary electrons (353) is reduced. In the examples according to Figure 7 b or 7d, the opening angle α is formed such that approximately tan(α) = D2 / (L1 + L2) or tan(α) = D2 / (L1 + L2 + L3.1). To maintain a smaller opening angle, a larger distance L2 or a smaller diameter D2 may be required in these examples.

[0080] Figure 8 Another example according to the first specific embodiment is shown. In one example, the primary multi-small beam forming unit (305) further includes another perforated plate, which is formed as an absorption plate (371) between the filter plate (304) and the shielding perforated plate (306). The diameter D4 of the fourth hole (85.4) of the absorption plate (371, 371.1) is selected to be between the first diameter D1 and the third diameter D3. For example, the range of D4 is selected such that 1.1x D1 < D4 <= D3. The thickness of the absorption plate (371) is LX. The details of the absorption plate (370) are described in more detail in the second specific embodiment below.

[0081] The primary multi-small beam forming unit (305) may include additional perforated plates, which include an additional active array optical perforated plate and a terminal perforated plate (310).

[0082] According to the first specific embodiment of the present invention, the light receiving angle or the opening angle α of the transmitted charged particles 355, the scattered charged particles 359, or the secondary electrons 353 is reduced, and the charging, damage, or contamination of the first active array optical element (307) is reduced, and the lifespan of the primary multi-small beam forming unit 305 is increased.

[0083] Having an opening angle α

[0084] By the improvement according to the second specific embodiment of the present invention, the influence of scattered charged particles and secondary electrons is further reduced. Fig. 9 An example according to the second specific embodiment of the present invention is illustrated. Fig. 9 A multi-beam forming unit (305) having a filter plate (304) and a first active array optical element (307) is shown. The filter plate (304) includes a plurality of first holes (85.1), each first hole having a first diameter D1, for generating a plurality of primary charged particle beams (3) during use. The first active array optical element (307) includes a plurality of third holes (85.3), each third hole having a diameter D3, similar to the first active array optical element (307) described in the first specific embodiment of the present invention. The charged particle multi-beam generator (300) further includes a first absorption perforated plate (371) having a plurality of fourth holes (85.4) with a diameter of D4. In Fig. 9 the example, the first absorption perforated plate (371) (abbreviation: absorption plate 371) is disposed upstream of the filter plate (304). The diameter D4 of the fourth hole (85.4) is selected to be greater than the diameter D1 of the first hole (85.1). During use, the primary charged particle beam (309) first impinges on the first absorption plate (371). Most of the primary charged particles are absorbed by the first absorption plate (371), and the primary charged particles passing through the fourth hole (85.4) form a preformed charged particle beam (312). The preformed charged particle beam (312) impinges on the filter plate (304). Part of the preformed charged particle beam (312) is absorbed by the filter plate (304), and the primary charged particles passing through the first hole (85.1) form a primary charged particle beam (3).

[0085] In an example, the diameter D4 of the fourth hole (85.4) of the absorption plate (371) is selected to be between the first diameter D1 and the third diameter D3, for example, the range of D4 is selected to be within 1.1x D1 < D4 <= D3. Due to the absorption plate (371), the number of charged particles impinging on the filter plate 304 is reduced, and the transmitted charged particles 355 and secondary electrons 353 are instead generated at the absorption plate 371. Therefore, the number of transmitted charged particles 355 and secondary electrons 353 downstream of the filter plate (304) is effectively reduced.

[0086] In accordance with Fig. 9 the example, the multi-beam forming unit (305) further includes a shielding perforated plate (306) having a second hole (85.2) with a second diameter D2, the shielding perforated plate (306) having a third thickness L3; wherein 1.1x D1 < D2 <= 1.5xD1. In an example, the shielding perforated plate (306) within the multi-beam forming unit (305) is configured to reduce the opening angle α and is configured according to the first specific embodiment of the present invention.

[0087] Fig.10 A first example of a charged particle multi-beamlet generator (300) according to a second specific embodiment is shown. The charged particle multi-beamlet generator (300) includes a primary charged particle source (301) and a collimating lens (303.1, 303.2) arranged upstream of a filter plate (304). The collimating lenses (303.1, 303.2) can be formed as a pair of magnetic lenses 303.1 and 303.2, and can also include an electrostatic element, such as a deflection element 313. An absorption plate (371) is arranged in a parallel beam path of a collimated primary charged particle beam (309) downstream of the collimating lenses (303.1, 303.2). For example, the absorption plate (371) is arranged between the collimating lenses (303.1, 303.2) and the filter plate (304). The collimated primary charged particle beam (309) has a diameter DI on the incident side of the absorption plate (371). The absorption plate (371) generates during use a plurality of pre-formed beamlets (312) as parallel beamlets which impinge perpendicularly on the filter plate 304. Both the absorption plate 371 and the filter plate 304 have a plurality of holes at the same pitch P2.

[0088] Fig.11A second example of the second specific embodiment is shown. An absorption plate (371) is arranged in a diverging primary charged particle beam (309) between a primary charged particle source (301) and a collimating lens (303.1, 303.2). The charged particle multi-beamlet generator (300) of this example further comprises a collecting lens or a lens pair (315.1, 315.2), which is arranged between the primary charged particle source (301) and the absorption plate (371). The absorption plate (371) has a plurality of fourth holes (85.4) arranged at a first pitch P1, which are arranged to generate a plurality of preformed beamlets (312) having the first pitch P1 during use. The first hole (85.1) of the filter plate (304) is arranged at a second pitch P2. The charged particle multi-beamlet generator (300) further comprises a control unit (830) configured to provide a first control signal to the first light collecting lens (315.1, 315.2) during use to adjust the current of the plurality of primary charged particle beamlets (3). Thus, the light collecting angle of the primary charged particles collected from the primary charged particle source 301 is adjusted by the variable focal length of the first light collecting lens (315.1, 315.2). The light collecting lens pair (315.1, 315.2) can further comprise a first multipole element 313.1 for adjusting the average propagation direction and position of the primary charged particle beam 309 on the incident side of the absorption plate 371. The control unit (830) is configured to provide a second control signal to the collimating lens (303.1, 303.2) to match the pitch P1 of the plurality of pre-formed beamlets (312) with the second pitch P2 of the filter plate (304), and adjust the propagation angles of the plurality of pre-formed beamlets (312) to form a beam of parallel pre-formed beamlets (312). Therefore, the beam of parallel pre-formed beamlets (312) is adjusted to be parallel and perpendicular to the filter plate, and the primary charged particle beamlets 3 are able to pass through the plurality of holes in the primary multi-beamlet forming unit (305).

[0089] The control unit (830) can be part of the charged particle multi-beamlet generator (300) and connected to the control unit 800 of the multi-beamlet charged particle microscope system, or can be part of the control unit 800 of the multi-beamlet charged particle microscope system.

[0090] exist Fig.12In one illustrated example, a multi-small beam forming unit (305) includes a first absorber plate (371.1) according to the above example, and a second absorber plate (371.2) between the filter plate (304) and the shielding perforated plate (306). In one example, the diameter D5 of the fifth hole (85.5) of the first absorber plate (371.1) and the second absorber plate (371.2) is selected to be between the first diameter D1 and the third diameter D3. For example, the range of D5 is selected to be within 1.1x D1 < D5 <= D3. The multi-small beam forming unit (305) may include additional perforated plates, which include an additional active array optical perforated plate and a terminal perforated plate (310).

[0091] In each of the shielding perforated plate (306), the first absorber plate or the second absorber plate (371, 371.1, 371.2), each of the holes (85.2, 85.4, 85.5) can have at least one baffle (369). Each of the holes can be formed with a conical shape (365) such that the minimum hole diameter is formed on the beam entrance side or the beam exit side of the corresponding hole (85.2, 85.4, 85.5). At least one of the absorber plates (371, 371.1, 371.2), the shielding plate (306), and the filter plate (304) can have at least one conductive layer (361, 99) on the beam entrance side or the beam exit side of the plate (371, 371.1, 371.2, 304, 306).

[0092] According to one example, the material of the absorber perforated plate (371) is from a group of materials including molybdenum, ruthenium, rhodium, palladium or silver, tungsten, rhenium, osmium, iridium, platinum or gold. In one example, the thickness LX can be LX > 20 μm, for example LX = 30 μm or greater. Since the thickness LX is greater than the thickness of the filter plate L1, the stopping power of the transmitted charged particles 355 is increased, and the extinction of the X-rays generated at the intersection with the primary charged particles is increased. Due to the thickness, for example, about 50 μm to 300 μm, an almost complete stopping power for blocking more than 95% of the X-rays 351 can be provided. For example, for a 60-μm layer of gold, more than 95% of the X-rays will be absorbed. For example, less X-ray transmission can be achieved by using an absorber plate (371) made of tungsten. The absorber plate (371) can also have an absorption layer (361) for absorbing electrons or other charged particles. The absorption layer (99, 361) can be formed as, for example, a doped silicon or silicon oxide or graphite layer. Thus, the backscattering of charged particles is reduced.

[0093] Due to the at least one absorption plate (371, 371.1, 371.2) according to the second specific embodiment, the influence of scattered primary charged particles and secondary electrons in the primary multi-beamlet forming unit (305) is further reduced. In addition, the influence of other secondary radiation such as X-ray radiation can be further reduced, and the life of the primary multi-beamlet forming unit (305) is increased. In addition, the charging or damage of the active array optical element (307) caused by X-rays, scattered charged particles and secondary electrons is reduced.

[0094] A third embodiment of the present invention provides another system and method configured to reduce the effects of secondary electrons in particular. The secondary electrons 353 generated at the filter plate 304 or the absorption plate 371 typically have much lower kinetic energy than the primary charged particles. According to the third embodiment, an improved method for operating a multi-beam forming unit (305) of a multi-beam charged particle microscope (1) and a multi-beam charged particle microscope (1) are provided, wherein additional components are provided to reduce charging or damage to the active array optical element 307 of the primary multi-beam forming unit (305). Fig.13 A primary multi-beamlet forming unit (305) according to a third embodiment is shown. The primary multi-beamlet forming unit (305) includes a filter plate 304, a second or shielding porous plate 306, and an active array optical element (307). The active array optical element (307) includes a first or conductive layer 391, an insulating layer 392, and an electrode layer 393 including a plurality of electrodes (81, 82), a second insulating layer 394, and a base layer 395.

[0095] The filter plate (304) includes a plurality of first holes (85.1) for generating a plurality of primary charged particle beamlets (3) passing therethrough during use. The filter plate may include a conductive coating or an absorption coating 99. The active array optical element (307) includes a plurality of electrodes (81, 82) disposed near a plurality of third holes (85.3) of the active array optical element (307), each electrode being configured to generate an electric field for focusing, deflecting or shaping one of the primary charged particle beamlets (3). According to the first specific embodiment, the second porous plate 306 can be a shielding porous plate 306, which is configured and constructed to reduce the opening angle α. The primary multi-beam forming unit (305) according to the third specific embodiment can further include an absorption plate 371 of the second specific embodiment of the present invention. All elements are insulated from each other and electrically connected to a control unit 830. The control unit (830) is configured to provide a plurality of voltages to the elements of the multi-beam forming unit (305) to reduce the influence of secondary electrons according to the third specific embodiment.

[0096] The method comprises the steps of generating a plurality of voltages U4 by a control unit 830 and providing them to electrodes (81, 82) of an active array optical element (307). The voltage U4 is determined, generated and provided by the control unit 830, for example, based on the setting of a charged particle multi-beamlet generator (305), which is determined during calibration of the multi-beamlet charged particle microscope system (1) and stored in the memory of the control unit 800. The method also comprises the steps of generating a plurality of voltages by the control unit 830 and providing them to elements of a multi-beam forming unit (305). The plurality of voltages comprises a first voltage U1 provided to a filter plate (304). The plurality of voltages comprises a plurality of separate fourth voltages U4 provided to a plurality of electrodes (81, 82). The plurality of voltages comprises a second voltage U2 provided to a second or shielded porous plate (306), which is arranged between the filter plate (304) and the active array optical element (307). For example, the second voltage U2 is adjusted to achieve a repulsive force or an attractive force on secondary electrons (353) generated by the primary charged particle beam (309) at the intersection (317) with the filter plate (304). The amplitude of the first voltage U1 or the second voltage U2 is adjusted to the range of the kinetic energy of the secondary electrons 353 generated, for example, at the filter plate 304. Therefore, the amplitude of the first voltage U1 or the second voltage U2 is much smaller than the kinetic energy of the primary charged particles, corresponding to the voltage difference between the anode of the primary charged particle source 301 and the filter plate 304. The voltage U1 or U2 is selected and configured to form a potential energy well, the depth of which is adjusted to the range of the kinetic energy of the secondary electrons 353. The primary charged particles typically have a large kinetic energy of about EK=5-35 keV, corresponding to a voltage difference of UE=5-35 kV. The secondary electrons typically have a kinetic energy of less than 100 eV, for example less than 50 eV.

[0097] Typically, the plurality of voltages U0 , U1 , U2 , U3 , U4 , and U5 are selected such that at least one of the following three examples occurs. Fig.14 Three examples A, B and C are shown in FIG. In each example, the potential energy G corresponding to the voltage U0, U1, U2, U3, U4 and U5 is shown. The voltages U0, U1, U2, U3, U4 and U5 required to generate the potentials G0, G1, G2, G3, G4 and G5 are proportional to the negative value of the potential (U to -G).

[0098] exist Fig.14 The bottom of the schematic diagram shows the multi-well plate of the multi-beam forming unit, and the reference Fig.13 The potentials G0, G1, G2, G3, G4 and G5 along the z-axis through a well correspond to the multi-well plate sequence, wherein the corresponding voltages U0, U1, U2, U3, U4 and U5 are provided by the control unit 830.

[0099] In Example A, a potential barrier (in the form of a potential step A1 or a potential maximum A2) is formed along the z-axis, which prevents low energy secondary or scattered electrons from reaching the active array optical element (307).

[0100] In Example B, a potential distribution is designed so that the beam forming aperture or filter plate 304 is located in a potential well B1 formed along the z-axis. In this case, secondary electrons or scattered electrons originating from the energy minimum of the potential well cannot escape the potential well along the z-axis and are effectively prevented from further penetrating into the elements downstream of the filter plate (304), including the active array optical element (307). Fig.15 An example is shown in . A first positive voltage U1 supplied to the filter plate (304) is selected to generate a potential well B1 for secondary electrons. For example, U1 is selected to exceed the voltage U2 supplied to the second porous plate 306, where U1 = U2 + US, where US is less than 100V.

[0101] exist Fig.16 In the second example shown, a second voltage U2 is selected to be applied to the second or shielding porous plate (306) to create a potential well B2 for secondary electrons (see Fig.14 The potential G in ). For example, U2 is selected to exceed the third voltage U3 provided to the conductive first layer 391 of the active array optical element, where U2=U3+US, and US is lower than 100V. In one instance, both U1 and U2 exceed U3. To effectively block the secondary electrons 353, in both instances, it is sufficient that the shielding voltage US is less than 0.3% of UE. In one instance, the shielding voltage US is approximately 100V. At this low voltage of US<0.3% x UE, secondary electrons are effectively reduced, while primary charged particles are only slightly affected. Voltages U0, U3, and U5 can be set to ground level. In one instance, U1 and U2 are set to ground level, and U3 is set to a negative voltage between -100V and 0V. The ground level can be any reference level of the charged particle microscope.

[0102] In Example C, voltages U0 and U1 are selected so that during use, an electric field is formed between the absorption plate 371 and the filter plate 304, which pulls secondary electrons or scattered electrons into the negative z direction, away from the active array optical element (307) ( Fig.17 ).

[0103] It should be understood that combinations of A, B and C are also possible. It should be understood that in some examples, the absorbent plate 371 or the second porous plate 306 may be omitted.

[0104] Given the small distances L2 and L4 between the porous plates, the interaction volume of the field generated by the voltage difference between the filter plate 304, the second porous plate 306 and the first layer 391 of the active array optical element (307) is very small, so it will not significantly affect the high kinetic energy primary charged particles, while effectively preventing slow secondary electrons from reaching the active array optical element (307). Therefore, one source of charging and damage to the active array optical element (307) is effectively eliminated.

[0105] In the examples of the present invention and the claims, an array of electrostatic elements such as electrostatic microlenses or electrostatic multipole elements is described, to which a driving voltage is provided by at least one voltage supply unit. However, the active porous element can also be configured as a magnetodynamic element having a coil instead of an electrode. In these equivalent examples, a driving current is provided instead of the voltage U4 by at least one current source unit, which can, for example, include an application-specific integrated circuit (ASIC) or other equivalent microelectronic devices. Therefore, the coil, the driving current or the current supply unit is an equivalent component of the electrode, the driving voltage or the voltage supply unit, and the present invention can be applied to magnetodynamic array elements without difficulty.

[0106] The present invention is further described by the following items:

[0107] Item 1: A method for operating a multi-beam forming unit (305) of a multi-beam charged particle microscope (1), comprising the following steps:

[0108] - generating a primary charged particle beam (309);

[0109] - providing a first voltage U1 to a filter plate (304), the filter plate (304) comprising a plurality of holes (85) for forming and transmitting a plurality of primary charged particle beamlets (3) from the primary charged particle beam (309) during use, wherein the primary charged particle beam (309) generates secondary electrons (353) at an intersection point (317) of primary electrons of the primary charged particle beam (309) and the filter plate (304); or

[0110] - providing a plurality of individual fourth voltages U4 to a plurality of electrodes (81, 82) of the active array optical element (307), wherein the electrodes are arranged at a plurality of holes (85) of the active array optical element (307)

[0111] Nearby, each of the electrodes is configured to focus, deflect or shape one of the primary charged particle beamlets (3);

[0112] - providing at least one second voltage U2 to a second porous plate (306) disposed between the filter plate (304) and the active array optical element (307), or providing at least one absorption plate (371) disposed upstream of the filter plate (304) along the propagation direction of the primary charged particle beam (309);

[0113] Receive board voltage U0;

[0114] - adjusting at least one of the absorption plate voltage U0, the first voltage U1 or the second voltage U2 to prevent the secondary electrons (353) from intersecting the active array optical element (307) by realizing a potential barrier (A1, A2) or a potential well (B1, B2, C) for the secondary electrons (353).

[0115] Item 2: A method as described in Item 1, wherein the second voltage U2 is adjusted to be smaller than the first voltage U1, thereby realizing a potential barrier (A1, A2) or a potential well (B1) for the secondary electrons (353) upstream of the second porous plate (306).

[0116] Item 3: The method as described in Item 1, wherein the second voltage U2 is adjusted to be greater than the first voltage U1, thereby realizing a potential well (B2) for the secondary electrons (353) near the second porous plate (306).

[0117] Item 4: A method as described in any one of items 1 to 3, wherein the absorption plate voltage U0 is adjusted to be greater than the first voltage U1, thereby realizing a potential well (C) for the secondary electrons (353) upstream of the filter plate (304).

[0118] Item 5: The method of any one of items 1 to 4, wherein at least one of the absorption plate voltage U0, the first voltage U1, or the second voltage U2 is provided at a ground level or a reference level.

[0119] Item 6: The method as described in any one of Items 1 to 5 further comprises the step of providing a third voltage U3 to the first layer (391) of the active array optical element (307), wherein the third voltage U3 is equal to the first voltage U1 or the second voltage U2.

[0120] Item 7: The method as described in any one of Items 1 to 6 further comprises the step of providing a fifth voltage U5 to the fifth layer (395) of the active array optical element (307), wherein the fifth voltage U5 is equal to the first voltage U1 or the second voltage U2.

[0121] Item 8: A multi-beam charged particle beam microscope (1), comprising:

[0122] - a charged particle source (301) and at least one focusing lens (303.1, 303.2) for producing

[0123] generating a charged particle beam (309);

[0124] - a multi-beam forming unit (305), comprising:

[0125] a filter plate (304) having a plurality of holes (85) for forming a plurality of primary charged particle beamlets (3) from the primary charged particle beam (309);

[0126] - an active array optical element (307) having a plurality of electrodes (81, 82), the electrodes being arranged near a plurality of holes (85) of the active array optical element (307), each of the electrodes being arranged

[0127] One of focusing, deflecting or shaping the primary charged particle beamlet (3);

[0128] - at least one second porous plate (306) disposed between the filter plate (304) and the active array optical element (307), or at least one second porous plate (306) disposed along the propagation direction of the primary charged particle beam (309);

[0129] an absorption plate (371) disposed upwardly upstream of the filter plate (304);

[0130] - A control unit (830) configured to perform any of the methods described in items 1 to 7.

[0131] Item 9: A multi-beam charged particle beam microscope (1), comprising:

[0132] - a charged particle source (301) and at least one focusing lens (303.1, 303.2) for producing

[0133] generating and forming a primary charged particle beam (309);

[0134] - a multi-beam forming unit (305), comprising:

[0135] - a filter plate (304) having a plurality of holes (85.1) of diameter D1 for forming during use

[0136] into a plurality of primary charged particle beams (3);

[0137] - an active array optical element (307) having a plurality of apertures (85.3) of a third diameter D3, the active array optical element (307) being configured to focus, deflect or shape individually during use to

[0138] Less primary charged particle beam (3);

[0139] - at least one second porous plate (306) having holes (85.2) of a second diameter D2, the second porous plate (306) being arranged between the filter plate (304) and the active array optical element (307), or at least one absorption plate (371) having a plurality of holes (85.4) of a diameter D4, the absorption plate (371) being arranged upstream of the filter plate (304) along the propagation direction of the primary charged particle beam (309);

[0140] - a control unit (830) configured to adjust and provide at least a first voltage U1 to the filter plate (304), at least a second voltage U2 to the second porous plate (306) or at least an absorption plate voltage U0 to the absorption plate (371) during use, so as to prevent the secondary electrons (353) generated at the filter plate (304) during use by realizing a potential barrier (A1, A2) or a potential well (B1, B2, C) for the secondary electrons (353) upstream of the active array optical element (307).

[0141] Intersecting with the active array optical element (307).

[0142] Item 10: The multi-beam charged particle beam microscope (1) as described in Item 9, wherein

[0143] - the filter plate (304) has a first thickness L1<20 μm, preferably L1<=10 μm;

[0144] - the second porous plate (306) is arranged at a distance L2 from the filter plate (304), and

[0145] The distance L2, the thickness L1 and the second diameter D2 are calculated according to D2 / (L1+L2)<=

[0146] 0.3, preferably D2 / (L1+L2)<0.25, thereby improving the shielding of secondary electrons (353) or scattered primary electrons (355, 359) generated at the filter plate (304) during use.

[0147] Item 11: A multi-beam charged particle beam microscope (1) as described in Item 9 or 10, wherein

[0148] - the filter plate (304) has a first thickness L1<20 μm, preferably L1<=10 μm;

[0149] -The second porous plate (306) is arranged at a distance L2 from the filter plate (304) and has a third thickness L3, and wherein the distance L2, the thicknesses L1 and L3 and the second diameter D2 are selected according to D2 / (L1+L2+L3)<=0.3, preferably D2 / (L1+L2+L3)<0.25.

[0151] Item 12: The multi-beam charged particle beam microscope (1) as described in any one of Items 9 to 11, wherein D2 and D3 are selected according to D3 >= D2 > D1.

[0152] Item 13: The multi-beam charged particle beam microscope (1) as described in Item 12, wherein D2 is selected according to 1.1X D1 < D2 < 1.3X D1.

[0153] Item 14: The multi-beam charged particle beam microscope (1) as described in any one of Items 10 to 13, wherein (L1 + L2 + L3) > 130 μm, preferably > 150 μm.

[0154] Item 15: The multi-beam charged particle beam microscope (1) as described in any one of Items 9 to 14, wherein in each of the holes (85.2) of the second perforated plate (306), at least one baffle (369) is formed.

[0155] Item 16: The multi-beam charged particle beam microscope (1) as described in any one of Items 9 to 14, wherein in each of the holes (85.2) of the second perforated plate (306), a hole (85.2) having a diameter D2 and a thickness L3.1 < L3 is formed.

[0156] Item 17: The multi-beam charged particle beam microscope (1) as described in any one of Items 9 to 14, wherein in each of the holes (85.2) of the second perforated plate (306), a conical shape (365) is formed.

[0157] Item 18: The multi-beam charged particle beam microscope (1) as described in Item 17, wherein the minimum hole diameter D2 is formed on the bottom side or the beam exit side of the second perforated plate (306).

[0158] Item 19: The multi-beam charged particle beam microscope (1) as described in Item 17, wherein the minimum hole diameter D2 is formed on the upper side or the beam entrance side of the second perforated plate (306).

[0159] Item 20: The multi-beam charged particle beam microscope (1) as described in any one of Items 9 to 19, wherein the second perforated plate (306) has at least one metal layer (361) on the upper side or the beam entrance side.

[0160] Item 21: The multi-beam charged particle beam microscope (1) as described in any one of Items 9 to 20, wherein D4 is in the range of 1.1x D1 < D4 < D3.

[0161] Item 22: The multi-beam charged particle beam microscope (1) as described in any one of Items 9 to 21 further comprises a second absorption plate (371.2), wherein the second absorption plate (371.2) is arranged between the filter plate (304) and the shielding porous plate (306).

[0162] Item 23: The multi-beam charged particle beam microscope (1) as described in any one of Items 9 to 22, further comprising:

[0163] - a first light collecting lens (315.1, 315.2);

[0164] - the absorption plate (371) has a plurality of holes (85.4) arranged at a first pitch P1, configured to generate a plurality of pre-formed beamlets (312) having the first pitch P1 during use, the absorption plate (371) being arranged between the first collecting lens (315) and at least one collimating lens (303.1, 303.2),

[0165] the holes (85.1) of the filter plate (304) are arranged at a second pitch P2, which is different from the first pitch P1,

[0166] in

[0167] - the control unit (830) is configured to provide a first control signal to the first collecting lens (315.1, 315.2) during use to adjust the current of the plurality of primary charged particle beamlets (3), and is configured to provide a second control signal to the at least one collimating lens (303.1, 303.2) to match the first pitch P1 of the plurality of pre-formed beamlets (312) with the second pitch P2 of the filter plate (304) and adjust the propagation angle of the plurality of pre-formed beamlets (312),

[0168] To form parallel pre-shaped bundles (312).

[0169] Item 24: A multi-beam forming unit (305), comprising:

[0170] - a filter plate (304) having holes (85.1) of a first diameter D1, the filter plate (304) having

[0171] A first thickness L1;

[0172] a shielding perforated plate (306) having holes (85.2) of a second diameter D2, the shielding perforated plate (306) being arranged at a distance L2 from the filter plate (304) and having a third thickness L3;

[0173] - An active array optical element (307) having a plurality of electrodes (81, 82), the electrodes being disposed near a plurality of holes (85.3) having a third diameter D3, the active array optical element being disposed downstream of the shielded perforated plate (306),

[0174] wherein the distance L2, the thickness L1, and the second diameter D2 satisfy the following requirements: D2 / (L1 + L2) <= 0.3, preferably D2 / (L1 + L2) < 0.25.

[0175] Item 25: The multi-beam forming unit (305) according to Item 24, wherein the distance L2, the thickness L1 and L3, and the second diameter D2 are selected according to D2 / (L1 + L2) <= 0.3, preferably D2 / (L1 + L2) < 0.25.

[0176] Item 26: The multi-beam forming unit (305) according to Item 24 or 25, wherein D3 is selected according to D3 >= D2 > D1.

[0177] Item 27: The multi-beam forming unit (305) according to any one of Items 24 to 26, wherein D2 is selected according to 1.1XD1 < D2 < 1.3X D1.

[0178] Item 28: The multi-beam forming unit (305) according to any one of Items 24 to 27, wherein (L1 + L2 + L3) > 130 μm, preferably > 150 μm.

[0179] Item 29: The multi-beam forming unit (305) according to any one of Items 24 to 28, wherein at least one baffle (369) is formed in each of the holes (85.2) of the shielded perforated plate (306).

[0180] Item 30: The multi-beam forming unit (305) according to any one of Items 24 to 29, wherein a hole having a diameter D2 and a thickness of L3.1 < L3 is formed in each of the holes (85.2) of the shielded perforated plate (306).

[0181] Item 31: The multi-beam forming unit (305) according to any one of Items 24 to 30, wherein a conical shape (365) is formed in each of the holes (85.2) of the shielded perforated plate (306).

[0182] Item 32: The multi-beam forming unit (305) according to Item 31, wherein the minimum hole diameter D2 is formed on the bottom side or the beam exit side of the shielded perforated plate (306).

[0183] Item 33: The multi-beam forming unit (305) as described in Item 31, wherein the minimum hole diameter D2 is formed on the upper side or the beam entrance side of the shielding porous plate (306).

[0184] Item 34: A multi-beam forming unit (305) as described in any one of Items 24 to 33, wherein the shielding porous plate (306) has at least one conductive layer (361) on the upper side or the beam entrance side of the shielding porous plate (306).

[0185] Item 35: The multi-beam forming unit (305) of Item 34, wherein the at least one conductive layer (361) is one of a metal layer, a graphite layer, or a doped semiconductor layer.

[0186] Item 36: A multi-beam forming unit (305) as described in any one of Items 24 to 35, wherein the material of the shielding porous plate (306) is from the group of materials comprising molybdenum, ruthenium, rhodium, palladium or silver, tungsten, rhenium, osmium, iridium, platinum or gold.

[0187] Item 37: The multi-beam forming unit (305) according to any one of Items 24 to 36, further comprising a first absorption plate (371, 371.1) having a plurality of holes (85.4) with a diameter D4, wherein 1.1 x D1 <D4<D3。

[0188] Item 38: The multi-beam forming unit (305) as described in Item 37, wherein the first absorption plate (371, 371.1) is arranged between the filter plate (304) and the shielding porous plate (306).

[0189] Item 39: The multi-beam forming unit (305) as described in Item 37, wherein the first absorption plate (371, 371.1) is arranged upstream of the filter plate (304).

[0190] Item 40: The multi-beam forming unit (305) as described in any one of Items 24 to 39, further comprising a second absorption plate (371.2), wherein the second absorption plate (371.2) is arranged between the filter plate (304) and the shielding porous plate (306).

[0191] Item 41: A multi-beam forming unit (305), comprising:

[0192] - a filter plate (304) having holes (85.1) of a first diameter D1, the filter plate (304) having

[0193] A first thickness L1;

[0194] - a shielding perforated plate (306) having holes (85.2) of a second diameter D2, the shielding perforated plate (306)

[0195] The plate (306) has a third thickness L3;

[0196] - An active array optical element (307) having a plurality of electrodes (81, 82), the electrodes being disposed near a plurality of holes (85.3) having a diameter D3, the active array optical element (307)

[0197] has a thickness L5;

[0198] where 1.1x D1 < D2 <= 1.3x D1.

[0199] Item 42: The multi-beam forming unit (305) according to Item 41, wherein in each of the holes (85.2) of the shielded porous plate (306), a plurality of baffles (369) are formed.

[0200] Item 43: The multi-beam forming unit (305) according to Item 41 or 42, wherein in each of the holes (85.2) of the shielded porous plate (306), a hole having a diameter D2 and a thickness L3.1 < L3 is formed.

[0201] Item 44: The multi-beam forming unit (305) according to Item 41, wherein in each of the holes (85.2) of the shielded porous plate (306), a hole having a conical shape (365) is formed.

[0202] Item 45: The multi-beam forming unit (305) according to Item 44, wherein the minimum hole diameter D2 is formed on the bottom side or the beam exit side of the shielded porous plate (306).

[0203] Item 46: The multi-beam forming unit (305) according to Item 44, wherein the minimum hole diameter D2 is formed on the upper side or the beam entrance side of the shielded porous plate (306).

[0204] Item 47: The multi-beam forming unit (305) according to any one of Items 41 to 46, wherein the shielded porous plate (306) has at least one conductive layer (361) on the upper side or the beam entrance side of the shielded porous plate (306).

[0205] Item 48: The multi-beam forming unit (305) according to Item 47, wherein the at least one conductive layer (361) is one of a metal layer, a graphite layer, or a doped semiconductor layer.

[0206] Item 49: The multi-beam forming unit (305) according to any one of Items 41 to 46, wherein the material of the shielded porous plate (306) is from a material group including molybdenum, ruthenium, rhodium, palladium, or silver, tungsten, rhenium, osmium, iridium, platinum, or gold.

[0207] Item 50: The multi-beam forming unit (305) of any one of Items 41 to 49, further comprising a first absorption plate (371, 371.1) having a plurality of holes (85.4) with a diameter D4, wherein 1.1 x D1 <D4<D3。

[0208] Item 51: The multi-beam forming unit (305) of Item 50, wherein the first absorption plate (371, 371.1) is disposed between the filter plate (304) and the shielding porous plate (306).

[0209] Item 52: The multi-beam forming unit (305) of Item 50, wherein the first absorption plate (371, 371.1) is arranged upstream of the filter plate (304).

[0210] Item 53: The multi-beam forming unit (305) as described in Item 52 further includes a second absorption plate (371.2), wherein the second absorption plate (371.2) is arranged between the filter plate (304) and the shielding porous plate (306).

[0211] Item 54: A multi-beam forming unit (305), comprising:

[0212] - a filter plate (304) having holes (85.1) of a first diameter D1, the filter plate (304) having

[0213] A first thickness L1;

[0214] - an active array optical element (307) having a plurality of electrodes (81, 82), the electrodes being arranged near a plurality of holes (85.3) having a diameter D3, the active array optical element (307)

[0215] having a thickness L5;

[0216] - a first absorption plate (371, 371.1) having a plurality of holes (85) with a diameter D4, wherein

[0217] 1.1x D1 <D4<D3。

[0218] Item 55: The multi-beam forming unit (305) of Item 54, wherein the first absorption plate (371, 371.1) is disposed between the filter plate (304) and the first array optical element (306.2).

[0219] Item 56: The multi-beam forming unit (305) of Item 54, wherein the first absorption plate (371, 371.1) is arranged upstream of the filter plate (304).

[0220] Item 57: The multi-beam forming unit (305) as described in any one of Items 54 to 56, wherein a plurality of baffles (369) are formed in at least one of the holes (85.4) of the first absorption plate (371, 371.1).

[0221] Item 58: A multi-beam forming unit (305) as described in any one of Items 54 to 57, wherein in at least one of the holes (85.4) of the first absorption plate (371, 371.1), a hole having a diameter D4 is formed and having a thickness LX.1 <LX。

[0222] Item 59: The multi-beam forming unit (305) as described in any one of Items 54 to 68, wherein a hole (365) having a cone shape is formed in at least one of the holes (85.4) of the first absorption plate (371, 371.1).

[0223] Item 60: The multi-beam forming unit (305) of Item 59, wherein the minimum hole diameter D4 is formed on the bottom side or the beam exit side of the first absorption plate (371, 371.1).

[0224] Item 61: The multi-beam forming unit (305) as described in Item 59, wherein the minimum hole diameter D4 is formed on the upper side or the beam entrance side of the first absorption plate (371, 371.1).

[0225] Item 62: A multi-beam forming unit (305) as described in any one of Items 54 to 61, wherein the first absorption plate (371, 371.1) has at least one conductive layer (361) on the upper side or beam entrance side of the first absorption plate (371, 371.1).

[0226] Item 63: The multi-beam forming unit (305) of Item 62, wherein the at least one conductive layer (361) is one of a metal layer, a graphite layer, or a doped semiconductor layer.

[0227] Item 64: A multi-beam forming unit (305) as described in any one of Items 54 to 63, wherein the material of the first absorption plate (371, 371.1) is from the group of materials containing molybdenum, ruthenium, rhodium, palladium or silver, tungsten, rhenium, osmium, iridium, platinum or gold.

[0228] Item 65: The multi-beam forming unit (305) as described in any one of Items 56 to 64, further comprising a second absorption plate (371.2), wherein the second absorption plate (371.2) is arranged between the filter plate (304) and the first array optical element (306.2).

[0229] Item 66: A multi-beam charged particle microscope (1), comprising a multi-beam forming unit (305) as described in any one of Items 24 to 65.

[0230] Item 67: A multi-beam generation unit (300) for generating a plurality of primary charged particle beamlets (3), comprising:

[0231] - a charged particle source (301);

[0232] - a first collecting lens (315) for collecting and forming a primary charged particle beam (309);

[0233] - an absorbent plate (371) having a plurality of holes (85.4) arranged at a first pitch P1, configured to produce, during use, a plurality of preformed bundles (312) having this first pitch P1;

[0234] - a collimating lens (303);

[0235] - a multi-beam forming unit (305) having a filter plate (304) having

[0236] Holes (85.1) configured at a second pitch P2;

[0237] - a control unit (830),

[0238] in

[0239] - the control unit (830) is configured to provide a first control signal to the first collecting lens (315) during use to adjust the current of the plurality of primary charged particle beamlets (3), and

[0240] The invention is configured to provide a second control signal to the collimating lens (303) to match the first pitch P1 of the plurality of pre-formed beamlets (312) with the second pitch P2 of the filter plate (304), and to adjust the propagation angles of the plurality of pre-formed beamlets (312) to form parallel pre-formed beamlets (312).

[0241] Item 68: A multi-beam charged particle microscope (1), comprising a multi-beam generating unit (300) as described in Item 67.

[0242] Item 69: A multi-beam charged particle microscope (1), further comprising a multi-beam forming unit (305) as described in any one of Items 24 to 65.

[0243] The specific embodiments and examples described in the present invention can be combined with each other in whole or in part as long as no technical contradictions arise. The present invention is also not limited to specific specific embodiments, examples and combinations thereof, and variations of specific embodiments are also possible. For example, the material composition and structure of the shielding plate (306) or the absorption plate (371) can also be applied to the filter plate (304), and the filter plate can be made of a metal or a metal composition containing at least one metal, the metal being selected from the group consisting of molybdenum, ruthenium, rhodium, palladium or silver, tungsten, rhenium, osmium, iridium, platinum or gold. Therefore, the ability to stop X-rays is increased. The covering layer (99) or the filter plate (304) can be made of a conductive material of low atomic mass, and can be implemented as, for example, a graphite layer or a highly doped semiconductor layer, or a metal layer containing a metal of a lower atomic mass such as aluminum, manganese, copper or silver. Therefore, the generation of secondary electrons is reduced.

[0244] Although in principle reference is made to a wafer as an object, the invention is also applicable to other objects used in semiconductor manufacturing. For example, the object may also be a mask, such as a mask for EUV lithography, instead of a semiconductor wafer. Such masks are usually rectangular and have a significantly greater thickness than semiconductor wafers. However, the invention is not limited to objects used in semiconductor manufacturing, but is also applicable to general objects, including, for example, mineral probes or tissues. The invention is further described using a multi-beam system with a plurality of primary electron beamlets as an example, but other charged particles, such as helium ions, may also be used. A list of reference numerals is provided below:

[0245] 1 Multi-beam charged particle microscope system

[0246] 3. Primary charged particle beam

[0247] 5 Focusing point of a primary electron beam

[0248] 7 Objects

[0249] 9 Secondary electron beam

[0250] 15 Focusing point of secondary electron beam

[0251] 25 Wafer surface

[0252] 81 Multipolar Electrode

[0253] 82 Ring Electrode

[0254] 83 Spacer

[0255] 85 holes

[0256] 86 Spacer

[0257] 92 Electrostatic field (equipotential lines)

[0258] 94 end hole

[0259] 98 Layer of conductive material

[0260] 99 Absorption and Conductive Layer

[0261] 100 Object irradiation unit

[0262] 101 Object Plane

[0263] 102 Objective lens

[0264] 103 Field lens group

[0265] 108 First beam intersection

[0266] 110 Collect multi-beam raster scanner

[0267] 200 Secondary Electron Imaging System

[0268] 205 Electron Optical Components

[0269] 216 Multi-hole Corrector

[0270] 222 Second Deflection System

[0271] 225 Image plane

[0272] 261 Voltage supply line

[0273] 300 Charged Particle Multibeam Generator

[0274] 301 Charged Particle Source

[0275] 303 Collimating lens

[0276] 304 filter plate

[0277] 305 Multiple beam forming unit

[0278] 306 Shielding Perforated Plate

[0279] 307 Active Array Optical Element

[0280] 308 Field Lens

[0281] 309 Primary Electron Beam

[0282] 310 end porous plate

[0283] 311 Focusing point of a charged particle beam

[0284] 312 Preformed small bundles

[0285] 313 Beam Deflector

[0286] 315 light collecting lens

[0287] 317 intersection point

[0288] 319 Scattering Points

[0289] 321 Intermediate Image Surface

[0290] 323 Intermediate Image Tilt Component

[0291] 351 X-ray radiation

[0292] 353 Secondary Electrons

[0293] 355 Transmitted Charged Particles

[0294] 359 Scattered Charged Particles

[0295] 361 Conductive layer

[0296] 363 Insulation layer

[0297] 365 Slanted Edge

[0298] 367 Body structure

[0299] 369 Baffle

[0300] 371 Absorption Plate

[0301] 391 First Floor

[0302] 392 Second Floor

[0303] 393 Electrode layer

[0304] 394 Fourth Floor

[0305] 395 Fifth Floor

[0306] 400 beam splitter units

[0307] 500 Sample Stage

[0308] 503 Sample Voltage Source

[0309] 600 Detector

[0310] 800 Control Unit

[0311] 810 Imaging Control Module

[0312] 830 Multi-beam forming control unit

[0313] 860 Scanning Control Unit

[0314] 880 Control Processor

[0315] 890 Memory

Claims

1. A method for operating a multi-beam forming unit (305) of a multi-beam charged particle microscope (1), comprising the following steps: - generating a primary charged particle beam (309); - supplying a first voltage U1 to a filter plate (304), the filter plate (304) comprising a plurality of holes (85), for forming and transmitting a plurality of primary charged particle beamlets (3) from the primary charged particle beam (309) during use, wherein the primary charged particle beam (309) generates secondary electrons (353) at an intersection (317) of primary electrons of the primary charged particle beam (309) and the filter plate (304); or - providing a plurality of individual fourth voltages U4 to a plurality of electrodes (81, 82) of the active array optical element (307), wherein the electrodes are arranged at a plurality of holes (85) of the active array optical element (307) Nearby, each of the electrodes is configured to focus, deflect or shape one of the plurality of primary charged particle beamlets (3); - providing at least one second voltage U2 to a second porous plate (306) arranged between the filter plate (304) and the active array optical element (307), or providing at least one absorption plate voltage U0 to an absorption plate (371) arranged upstream of the filter plate (304) along the propagation direction of the primary charged particle beam (309); - adjusting at least one of the absorption plate voltage U0, the first voltage U1 or the second voltage U2 to prevent the secondary electrons (353) from intersecting the active array optical element (307) by realizing a potential barrier (A1, A2) or a potential well (B1, B2, C) for the secondary electrons (353).

2. The method of claim 1, wherein: The second voltage U2 is adjusted to be smaller than the first voltage U1, thereby realizing a potential barrier (A1, A2) or a potential well (B1) for the secondary electrons (353) upstream of the second porous plate (306).

3. The method of claim 1, wherein: The second voltage U2 is adjusted to be greater than the first voltage U1, thereby realizing a potential well (B2) for the secondary electrons (353) adjacent to the second porous plate (306).

4. The method according to any one of claims 1 to 3, wherein: The absorption plate voltage U0 is adjusted to be greater than the first voltage U1, thereby realizing a potential well (C) for the secondary electrons (353) upstream of the filter plate (304).

5. The method according to any one of claims 1 to 4, wherein: At least one of the absorption plate voltage U0, the first voltage U1 or the second voltage U2 is provided at a ground level or a reference level.

6. The method according to any one of claims 1 to 5, further comprising the step of providing a third voltage U3 to the first layer (391) of the active array optical element (307), wherein the third voltage U3 is equal to the first voltage U1 or the second voltage U2.

7. The method according to any one of claims 1 to 6, further comprising the step of providing a fifth voltage U5 to the fifth layer (395) of the active array optical element (307), wherein the fifth voltage U5 is equal to the first voltage U1 or the second voltage U2.

8. A multi-beam charged particle beam microscope (1), comprising: - a charged particle source (301) and at least one focusing lens (303.1, 303.2) for generating a primary charged particle beam (309); - a multi-beam forming unit (305), comprising: a filter plate (304) having a plurality of holes (85) for forming a plurality of primary charged particle beamlets (3) from the primary charged particle beam (309) during use; - an active array optical element (307) having a plurality of electrodes (81, 82), the electrodes being arranged near a plurality of apertures (85) of the active array optical element (307), each electrode being arranged to focus, deflect or shape one of the primary charged particle beamlets (3); - at least one second porous plate (306) arranged between the filter plate (304) and the active array optical element (307), or at least one absorption plate (371) arranged upstream of the filter plate (304) along the propagation direction of the primary charged particle beam (309); - A control unit (830) configured to perform any of the methods according to claims 1 to 7.

9. A multi-beam charged particle beam microscope (1), comprising: - a charged particle source (301) and at least one focusing lens (303.1, 303.2) for generating and forming a primary charged particle beam (309); - a multi-beam forming unit (305), comprising: - a filter plate (304) having a plurality of holes (85.1) of diameter D1 for forming a plurality of primary charged particle beamlets (3) during use; - an active array optical element (307) having a plurality of apertures (85.3) of a third diameter D3, the active array optical element (307) being configured to focus, deflect or shape at least one of the primary charged particle beamlets (3) individually during use; - at least one second porous plate (306) having holes (85.2) of a second diameter D2, the second porous plate (306) being arranged between the filter plate (304) and the active array optical element (307) or an absorption plate (371) having a plurality of holes (85.4) with a diameter D4, the absorption plate (371) being arranged upstream of the filter plate (304) along the propagation direction of the primary charged particle beam (309); - a control unit (830) configured to adjust and provide at least a first voltage U1 to the filter plate (304), at least a second voltage U2 to the second porous plate (306) or at least an absorption plate voltage U0 to the absorption plate (371) during use, so as to realize a potential barrier (A1, A2) or a potential well (B1, B2) for secondary electrons (353) upstream of the active array optical element (307) B2, C) to prevent the secondary electrons (353) generated at the filter plate (304) from intersecting with the active array optical element (307) during use.

10. The multi-beam charged particle beam microscope (1) according to claim 9, wherein - The filter plate (304) has a first thickness L1<20 μm, preferably L1<=10 μm. - The second perforated plate (306) is disposed at a distance L2 from the filter plate (304), and wherein the distance L2, the thickness L1, and the second diameter D2 are selected according to D2 / (L1 + L2) <= 0.3, preferably D2 / (L1 + L2) < 0.25, thereby improving the shielding of secondary electrons (353) or scattered primary electrons (355, 359) generated at the filter plate (304) during use.

11. The multi-beam charged particle beam microscope (1) according to claim 9 or 10, wherein - The filter plate (304) has a first thickness L1 < 20 μm, preferably L1 <= 10 μm. - The second perforated plate (306) is disposed at a distance L2 from the filter plate (304) and has a third thickness L3, and wherein the distance L2, the thicknesses L1 and L3, and the second diameter D2 are selected according to D2 / (L1 + L2 + L3) <= 0.3, preferably D2 / (L1 + L2 + L3) < 0.

25.

12. The multi-beam charged particle beam microscope (1) according to any one of claims 9 to 11, wherein: D2 and D3 are selected according to D3 >= D2 > D1.

13. The multi-beam charged particle beam microscope (1) according to claim 12, wherein: D2 is selected according to 1.1X D1 < D2 < 1.3XD1.

14. The multi-beam charged particle beam microscope (1) according to any one of claims 10 to 13, wherein: (L1 + L2 + L3) > 130 μm, preferably (L1 + L2 + L3) > 150 μm.

15. The multi-beam charged particle beam microscope (1) according to any one of claims 9 to 14, wherein: In each of the holes (85.2) of the second perforated plate (306), at least one baffle (369) is formed.

16. The multi-beam charged particle beam microscope (1) according to any one of claims 9 to 14, wherein: In each of the holes (85.2) of the second perforated plate (306), a hole (85.2) having a diameter D2 and a thickness L3.1 < L3 is formed.

17. The multi-beam charged particle beam microscope (1) according to any one of claims 9 to 14, wherein: In each of the holes (85.2) of the second perforated plate (306), a conical shape (365) is formed.

18. The multi-beam charged particle beam microscope (1) according to claim 17, wherein: The minimum hole diameter D2 is formed on the bottom side or the beam exit side of the second perforated plate (306).

19. The multi-beam charged particle beam microscope (1) according to claim 17, wherein: The minimum hole diameter D2 is formed on the upper side or the beam entrance side of the second perforated plate (306).

20. The multi-beam charged particle beam microscope (1) according to any one of claims 9 to 19, wherein: The second perforated plate (306) has at least one metal layer (361) on the upper side or the beam entrance side.

21. The multi-beam charged particle beam microscope (1) according to any one of claims 9 to 20, wherein: The D4 is in the range of 1.1xD1 < D4 < D3.

22. The multi-beam charged particle beam microscope (1) according to any one of claims 9 to 21, further comprising a second absorber plate (371.2), the second absorber plate (371.2) being disposed between the filter plate (304) and the shielding perforated plate (306).

23. The multi-beam charged particle beam microscope (1) according to any one of claims 9 to 22, further comprising: - First condenser lenses (315.1, 315.2); - The absorber plate (371) having a plurality of holes (85.4) arranged at a first pitch P1, configured to generate a plurality of preformed small beams (312) having the first pitch P1 during use, the absorber plate (371) being disposed between the first condenser lens (315) and at least one collimating lens (303.1, 303.2); - The holes (85.1) of the filter plate (304) are arranged at a second pitch P2, the second pitch P2 being different from the first pitch P1, wherein -The control unit (830) is configured to provide a first control signal to the first collecting lens (315.1, 315.2) during use to adjust the current of the multiple primary charged particle beamlets (3), and is configured to provide a second control signal to the at least one collimating lens (303.1, 303.2) to match the first pitch P1 of the multiple pre-formed beamlets (312) with the second pitch P2 of the filter plate (304), and adjust the propagation angles of the multiple pre-formed beamlets (312) to form parallel pre-formed beamlets (312).

Images