Multibeam systems and multibeam generation units with reduced susceptibility to drift and damage

Abstract

A multi-beam generating unit of a multi-beam charged particle imaging system is disclosed that has reduced susceptibility to drift and extended lifetime. Drift due to X-ray irradiation and thermal load is minimized by at least one combination of shielding elements, cooling members, or improved methods for operating the active multi-aperture element. The lifetime is further improved by annealing methods of the active multi-aperture element or the microelectronic device that forms, for example, the voltage supply unit.

Description

Technical Field

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

Background Art

[0002] International Publication No. 2005 / 024881 discloses an electron microscope system that operates using multiple electron beamlets to scan an object under inspection in parallel with multiple electron beamlets. The multiple beamlets of the multibeam charged particle microscope are generated in a multibeam generation unit. The multiple electron beamlets are generated by directing a primary electron beam onto the multibeam generation unit. The multibeam generation unit comprises a first multi-aperture element having multiple apertures. One portion of the electrons of the electron beam enters the multi-aperture element and is absorbed there, while another portion of the beam passes through the apertures of the multi-aperture element, thereby forming electron beamlets downstream of each aperture whose cross-section is defined by the cross-section of the aperture. Furthermore, appropriately selected electric fields provided to the beam paths upstream and / or downstream of the multi-aperture element cause each aperture within the multi-aperture element to act as a lens for the electron beamlets passing through the apertures, resulting in each electron beamlet being focused into a surface located at a certain distance from the multi-aperture element. The surface on which the electron beamlet focus is formed is imaged onto the surface of the object or sample being inspected by a downstream optical system. The primary electron beamlet triggers secondary or backscattered electrons to be generated from the object as secondary electron beamlets, which are collected and imaged onto a detector. Each secondary beamlet is incident on a separate detector element, and the resulting detected secondary electron intensity provides information about the sample at the location where the corresponding primary beamlet is incident on the sample. Multiple primary beamlets are systematically scanned across the surface of the sample to produce an electron microscope image of the sample, as is typical for a scanning electron microscope. The resolution of a scanning electron microscope is limited by the focal diameter of the primary beamlets incident on the object. As a result, in a multi-beam electron microscope, all beamlets form the same small focus on the object.

[0003] The systems and methods illustrated in great detail in the example of electrons in International Publication No. 2005 / 024881 are generally very well applicable to charged particles. Therefore, the present invention aims to propose 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 a narrower range of resolution for each of the multiple beamlets.

[0004] Multibeam charged particle microscopes typically use both micro-optical array elements and macroscopic elements in their charged particle projection system. The multibeam generation unit comprises elements for splitting, partially absorbing, and influencing the beam of charged particles. As a result, multiple beamlets of charged particles are generated in a given raster configuration. The multibeam generation unit includes a first multi-aperture element, further multi-aperture elements, and micro-optical elements such as micro-optical deflection elements or multi-pole array elements.

[0005] A multibeam generation unit includes a first multi-aperture element having multiple apertures. A primary electron beamlet collides with the first multi-aperture element, and some electrons pass through the apertures, forming multiple beamlets. However, most are absorbed at the surface of the first multi-aperture element. On the other hand, multiple primary charged particle beamlets are formed from electrons passing through the apertures. For this task, an array optical element, such as a multipole or multistigmeter array or lens array, is placed downstream of the first multi-aperture element. The array optical element has multiple apertures, each aperture having at least one electrode or coil to individually or cooperatively influence each primary electron beamlet. During their operation, it has been observed that the multistigmeter array or lens array is subject to performance drift of the array optical element.

[0006] There can be several reasons for performance drift in array optical elements. One specific reason is driver drift in the array optical element. For example, a multistigmeter array with multiple beamlets, approximately 100 beamlets, may have 8 or 12 electrodes per beamlet, resulting in a total of over 1000 electrodes, which need to be individually controlled by multiple voltage source units, which can be formed by microelectronic devices. Thus, the control architecture for multiple multipole electrodes in an array optical element involves several microelectronic devices in parallel. These microelectronic devices provide multiple predetermined voltages to multiple electrodes or predetermined currents to multiple coils. Voltage or current drift can result from thermal drift, charging effects of microelectronic devices, or localized damage generated, for example, by X-ray radiation. The drift can be irreversible damage and can lead to failure of the electrode drivers in the multipole element.

[0007] The primary cause of drift in microelectronic devices may be the scattering or absorption of primary electrons. A small fraction of the colliding electrons are absorbed or scattered within an aperture, for example, at an electrode, resulting in charging effects and localized voltage changes.

[0008] A second reason for drift may be secondary radiation generated by primary electrons absorbed in the first multi-aperture element. Secondary radiation includes secondary electrons and electromagnetic radiation, including X-rays or gamma radiation. Typically, a microelectronic device for controlling a voltage source unit or array optical element is placed near or around the array optical element and may be penetrated by or absorbed by secondary radiation. It has been observed that secondary radiation generates a charging effect and ultimately causes damage to the microelectronic device.

[0009] A third reason for drift could be the power driving individual microelectronic devices, which can result in high thermal loads.

[0010] Secondary radiation is absorbed to a small extent in the absorption layer or the bulk material of the first multi-aperture element. U.S. Patent Application Publication 2019 / 0051494 proposes adding an additional second multi-aperture element. However, a second multi-aperture element of sufficient thickness would need to have multiple apertures for the multiple primary charged beamlets generated by the first multi-aperture element. A thicker plate increases the amount of scattered charged particles, negatively impacting the multiple primary beamlets generated in the first multi-aperture element. In modern designs of beam generators with numerous primary beamlets, multiple multi-aperture elements cannot be given sufficient thickness to adequately block all generated X-rays. In addition, secondary radiation is undirected and generated in all directions, including the multiple apertures. Therefore, X-rays can pass through the second multi-aperture element and still cause charging effects on the first multi-aperture element and downstream electro-optical elements of the second multi-aperture element. Furthermore, drift in microelectronic devices can also be generated for the other reasons mentioned above.

[0011] U.S. Patent Application Publication No. 2017 / 0133194 discloses a particle beam system comprising: a particle source; a first multi-aperture plate having a plurality of openings formed downstream by a particle beam; a second multi-aperture plate having a plurality of openings into which the particle beam enters; an aperture plate having an opening into which all particles that also enter the openings of the first and second multi-aperture plates enter; a third multi-aperture plate having a plurality of field generators, each providing a dipole field or quadrupole field for the beam, each having an opening into which the particle beam enters; and a controller for supplying potential to the multi-aperture plates and aperture plates such that the second openings in the second multi-aperture plate each act as lenses for the particle beam 3, supplying tunable excitation to the field generators. The controller itself is located outside the vacuum enclosure of the system. The controller is connected via a data link to electronic circuits for generating tunable voltages supplied to the field generators or electrodes. The data link is guided through a seal within the vacuum enclosure. Therefore, the electronic circuitry is located inside the vacuum chamber and is not shielded from secondary radiation, for example, from X-rays generated inside the vacuum chamber.

[0012] Therefore, an object of the present invention is to provide an improved beam generator for a multi-beam charged particle system in which the effects of drift, such as thermal drift of the charging effect, are reduced. A further object of the present invention is to provide an improved driver for the improved beam generator for a multi-beam charged particle system in which the effects of drift or damage are reduced. A further object of the present invention is to provide an improved method for operating the improved beam generator for a multi-beam charged particle system in which the effects of drift, such as thermal drift of the charging effect, are reduced. Another further object of the present invention is to provide improved shielding of secondary radiation, such as X-rays. [Overview of the project]

[0013] The object of the present invention is solved by an improved architecture for a multibeam generation unit of a multibeam charged particle imaging system that is less susceptible to drift and has an extended lifetime. The improved architecture minimizes drift caused by X-ray irradiation and thermal load through a combination of at least one member from the group including shielding elements, cooling members, or improved methods for operating active multi-aperture elements. Lifetime is further improved by an annealing method for active multi-aperture elements or microelectronic devices forming, for example, a voltage source unit.

[0014] This patent application claims priority to German Patent Application Publication No. 10 2022 201 005.1, filed on 31 January 2022, and the entire contents of said patent document are incorporated into this patent application by reference.

[0015] In a first embodiment, an improved multi-beam system is provided having a plurality of J primary charged particle beamlets, configured for an improved method of operating an active multi-aperture element. The improved multi-beam system comprises at least one active multi-aperture element and a control unit configured to control the active multi-aperture element. The active multi-aperture element comprises a plurality of J apertures arranged in a raster configuration, the apertures configured to transmit the first plurality of J primary charged particle beamlets through the active multi-aperture element during use. The raster configuration can be a hexagonal or rectangular raster consisting of the J apertures, or the apertures can be arranged in a series of circular rings. The active multi-aperture element further comprises a plurality of electrodes, each comprising at least one electrode arranged around each of the apertures. According to the first embodiment, the plurality of electrodes comprises at least a first electrode group and a second electrode group. The improved multibeam system further comprises a first voltage source unit configured to provide multiple voltages to a first electrode group during use, and a second voltage source unit configured to provide multiple voltages to a second electrode group during use. The first and second voltage source units may be part of an active multi-aperture element. The first and second voltage source units are connected to a control unit. The control unit is configured to control the multiple voltages provided to the first and second electrode groups by the first and second voltage source units during use. Control can be achieved, for example, via an image quality monitor or a voltage drift monitor. In the latter example, the improved multibeam system further comprises a monitoring device connected to at least the first voltage source unit. The monitoring device can monitor the drift of the first voltage source unit during use.

[0016] The control unit is further configured to compensate for drift of at least the first voltage source unit during use. In one example, the control unit is configured to compensate for drift of the first voltage source unit during use by a compensation control signal provided to the second voltage source unit.

[0017] The first electrode group and the second electrode group can be arranged in different angular divisions of the raster configuration of multiple J apertures. In an alternative example, the first electrode group and the second electrode group can be arranged in different radial divisions of the raster configuration.

[0018] An active multi-aperture element can be a microlens array having a single ring electrode at each of the multiple apertures. An active multi-aperture element can also be a multipole array having multiple multipole elements having K electrodes arranged around each of the multiple apertures, where the number of electrodes K in each multipole element is 2, 4, 6, 8, or 12.

[0019] According to a further example of the first embodiment, the improved multi-beam system further comprises a shielding member. The shielding member is positioned and configured to shield secondary radiation from hitting the first and second voltage source units. Secondary radiation can be X-ray radiation or secondary electrons, which result in charging effects or damage to the voltage source units. In one example, the first shielding member is positioned on the beam inlet side of the primary multi-beamlet forming unit and is configured to have a large aperture. The charged particle beam from the particle beam source is filtered by the large aperture to produce a beam having a raster-like diameter and shape. This reduces the secondary radiation generated within the multi-aperture plate of the primary multi-beamlet forming unit. Furthermore, the large aperture allows the first shielding member to be configured with a material composition of sufficient thickness, including a high-density material, to prevent secondary radiation generated within the first shielding member from penetrating the lower primary multi-beamlet forming unit.

[0020] In one example, the active multi-aperture element comprises an outer or peripheral zone in which at least a first voltage source unit and a second voltage source unit are arranged, and an inner or film zone having a plurality of J openings. In this example, a second shielding member can be provided between the outer or peripheral zone and the film zone.

[0021] In a further example, at least a first voltage source unit is positioned in the space between a plurality of J openings, and the shielding member is formed as a cap covering the first voltage source unit.

[0022] According to a further example of the first embodiment, an active multi-aperture element for a multi-beam system is provided. The active multi-aperture element comprises a base plate having an inner film zone having a plurality of J apertures arranged in a raster configuration. Thereafter, the active multi-aperture element is configured to transmit a plurality of J primary charged particle beamlets during use. The active multi-aperture element further comprises a plurality of J multipole elements, each multipole element having one aperture from the plurality of J apertures, each multipole element having K electrodes, and each multipole element being configured to influence one of the primary charged particle beamlets.

[0023] The active multi-aperture element further comprises a plurality of L voltage source units, which are arranged on a base plate. In this example, each of the K electrodes of a single multipole element is connected to only one of the plurality of L voltage source units. For example, a first plurality of J multipole elements includes at least a first multipole element group and a second multipole element group. The electrodes of the first multipole element group are connected to a first voltage source unit, and the second multipole element group is connected to a second voltage source unit. The first and second multipole element groups can be arranged within different annular or ring sections of the raster configuration, or within various angular sections of the raster configuration. One example of an active multi-aperture element includes a second group of J multi-pole elements positioned downstream of a first group of multi-pole elements, each multi-pole element having a plurality of K2 electrodes, and each of the K2 electrodes of one of the second group of J multi-pole elements is connected to only one of a plurality of L voltage source units. In a further example, each of the K1 electrodes of one of the first group of J multi-pole elements and each of the K2 electrodes of the corresponding multi-pole elements in the second group of J multi-pole elements are connected to the same voltage source unit.

[0024] In a second embodiment, an improved multibeam system is provided having at least one shielding or cooling member. The primary multibeamlet forming unit of the multibeam system comprises an active multi-aperture element. The active multi-aperture element comprises a plurality of J apertures arranged in a raster configuration, configured to transmit a first plurality of J primary charged particle beamlets through the active multi-aperture element during use. The active multi-aperture element further comprises a plurality of electrodes, each having at least one electrode positioned around each aperture, and at least a first voltage source unit configured to provide a plurality of voltages to a group of electrodes among the plurality of electrodes. The primary multibeamlet forming unit of the multibeam system according to the second embodiment further comprises at least a shielding member provided to shield secondary radiation from striking the first voltage source unit.

[0025] In one example, the first shielding member is positioned on the beam inlet side of the primary multi-beamlet forming unit and is configured to have a large opening. The large opening allows the first shielding member to be constructed with a material composition of sufficient thickness, including a high-density material, so that secondary radiation generated within the first shielding member cannot penetrate into the primary multi-beamlet forming unit below.

[0026] In one example, the active multi-aperture element comprises an outer or peripheral zone in which at least a first voltage source unit and a second voltage source unit are arranged, and an inner or film zone having a plurality of J openings. In this example, a second shielding member can be provided between the outer or peripheral zone and the film zone. According to this example, the first voltage source unit is arranged adjacent to the plurality of J openings, and the second shielding member is arranged between the plurality of J openings and the first voltage source unit. Such a second shielding member can be elongated parallel to the propagation direction of the primary charged particle beamlet.

[0027] The primary multi-beamlet forming unit according to the second embodiment can further include a cooling member configured to reduce the thermal drift of the first voltage source unit. The cooling member can be connected to a heat sink outside the vacuum chamber of the multi-beam system.

[0028] The shielding member can be provided in contact with the first voltage source unit. In such an example, the shielding member can be the same as the cooling member. In one example, the first voltage source unit is arranged between a plurality of J openings, and the shielding member is attached to the first voltage source unit and can be configured as a cap or platelet covering the first voltage source unit.

[0029] According to one example, the shielding member includes a material from a first group of materials including molybdenum, ruthenium, rhodium, palladium, or silver. Such a shielding member is preferably configured to have a thickness D exceeding 1 mm. Thereby, it is possible to absorb more than 80% of the secondary emission.

[0030] According to a further example, the shielding member includes a material from a second group of materials including tungsten, rhenium, osmium, iridium, platinum, gold, or lead. Such a shielding member can be given a smaller thickness, for example, about 100 μm or more. Thereby, it is possible to absorb more than 80% of the secondary emission. In both examples, the shielding member can be connected to the ground level, and as a result, any charging of the shielding layer is prevented.

[0031] In a third embodiment of the present invention, a method of extending the life of an active multi-aperture element is provided. According to the third embodiment, such a method of operating a multi-beam array element is a) performing a series of inspection tasks and monitoring the voltage drift or imaging performance of the active multi-aperture element; b) The step of triggering an annealing step of an active multi-aperture element when voltage drift or image performance exceeds a predetermined threshold.

[0032] The annealing step includes at least one of processing the voltage source unit of the active multi-aperture element with pulses of voltage VG, or thermal annealing at a temperature above 200°C, preferably above 250°C.

[0033] The annealing step may further include processing of the film zone of the active multi-aperture element by pulses of voltage VG, thermal annealing at a temperature above 250°C, or low-energy plasma processing.

[0034] Secondary radiation can induce localized charging effects within the film zone or voltage source unit. Pulsing the voltage VG reduces these localized charging effects. Localized damage can be generated by X-ray radiation, for example, at the interface between the silicon layer and the silicon oxide layer, or in structures within the film zone or voltage source unit. At least some of the localized damage can be repaired by thermal or plasma annealing steps. However, damage will accumulate even with repeated annealing steps. Therefore, this method can further monitor the dose of secondary radiation, the number or frequency of annealing steps, and predict the end of life of the voltage source unit or active multi-aperture element.

[0035] In a fourth embodiment, an improved method for operating an active multi-aperture element is provided. The method for operating an active multi-aperture element of a multi-beam charged particle microscope is as follows: a) A calibration step of determining a plurality of digital control signals for controlling at least a first voltage source unit and a second voltage source unit, wherein the first voltage source unit and the second voltage source unit are configured to provide a plurality of voltages to at least a first electrode group and a second electrode group among a plurality of electrodes of an active multi-aperture element, and in one example, the electrodes or plurality of electrodes form a plurality of multi-pole elements, and the steps of determining a plurality of digital control signals b) A step of performing a series of inspection tasks, c) Monitoring imaging performance by an image quality monitor of a multibeam charged particle microscope, or monitoring voltage drift of at least a first voltage source unit, d) A step of triggering a voltage correction step when imaging performance or voltage drift exceeds a predetermined threshold, e) A step of determining a set of compensating digital control signals for controlling at least a second voltage source unit during the voltage correction step, f) the step of providing a compensating digital control signal to at least a second voltage source unit.

[0036] According to this method, drift in the first voltage source unit is compensated by providing a corrected signal to the second voltage source unit. Thus, drift in the first voltage source unit is compensated by the second voltage source unit by providing a corrected voltage. According to the fourth embodiment, the set of compensating digital control signals is determined according to at least the voltage drift of the first voltage source unit.

[0037] According to the solutions provided by embodiments of the present invention or any combination thereof, the drift of the voltage source unit is effectively reduced by a shielding member or a cooling member. This minimizes damage to the multi-aperture element and voltage source unit due to X-ray radiation. A voltage monitor can be further provided for the multi-beam system. According to the improved operating method and the multi-beam system configured to perform the improved method, the effects of voltage drift of the voltage source unit can be reduced. This allows for a longer lifespan for the active multi-aperture plate.

[0038] The annealing method described above can at least partially reduce or recover localized charging and localized defects, thereby extending the lifespan of the multi-aperture element or voltage source unit. Consequently, the uptime of the multi-beam charged particle microscope is increased, and service or maintenance, including the replacement of expensive components, is reduced.

[0039] In the examples of this disclosure and 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 source unit. However, active multi-aperture elements can also be configured as magnetodynamic elements having coils instead of electrodes. In these equivalent examples, the driving current is provided by at least one current source unit, which may comprise, for example, an ASIC or other equivalent microelectronic device. Thus, coils, driving current, or current source units are equivalent means to electrodes, driving voltage, or voltage source units, and the present invention can be readily applied to magnetodynamic array elements.

[0040] Please understand that the present invention is not limited to these embodiments and examples, but also includes combinations and variations of these embodiments and examples.

[0041] Embodiments of this disclosure will be described in more detail with reference to the drawings. [Brief explanation of the drawing]

[0042] [Figure 1] This is a schematic cross-sectional view of a multi-beam charged particle system for wafer inspection according to the first embodiment. [Figure 2] This figure shows a multibeamforming unit 305 with an improved drive architecture. [Figure 3] This is a top view of the multi-pole array element 306.2. [Figure 4] This figure shows one section of the multi-pole array element 306.2 in Figure 3. [Figure 5] This figure shows one section of the alternative multi-pole array element 306.2. [Figure 6] This is a top view of a further example of the multi-pole array element 306.2. [Figure 7] This figure shows a multi-beam forming unit 305 having a shielding member 93. [Figure 8] This figure shows a further example of the multi-pole array element 390. [Figure 9] This figure shows a method for extending the lifespan of a multi-pole array element and operating it. [Figure 10] This figure shows the spot aberration induced by the global voltage offset of individual voltage source units. [Figure 11] This figure shows a method for operating a multi-pole array element while reducing the effects of voltage drift. [Figure 12] This figure shows a multi-aperture element formed as a microlens array with multiple ring electrodes. [Figure 13] This figure shows the vacuum compartment receiving thermal or plasma annealing in the primary multi-beamlet formation unit 305. [Figure 14] This figure shows a further example of a multi-beam forming unit 305 having a shielding member 93. [Modes for carrying out the invention]

[0043] In the exemplary embodiments of the present invention described below, components having similar function and structure are indicated by the same or identical reference numerals where possible. The multi-beam raster unit in this example is described in an irradiation beam path where charged particles propagate in the positive z direction, with the z direction pointing downwards. However, the multi-beam raster unit can also be applied in an imaging beam path where a secondary charged particle beamlet propagates in the negative z direction in the coordinate system of Figure 1. Still, consecutive multi-aperture elements are arranged sequentially in the direction of propagation of the transmitted charged particle beam or beamlet. The beam inlet side or top side is understood to be the first surface or side of the element in the direction of the transmitted charged particle beam or beamlet, and the bottom side or beam exit side is understood to be the last surface or side of the element in the direction of the transmitted charged particle beam or beamlet.

[0044] Figure 1 is a schematic representation illustrating the basic features and functions of a multi-beam charged particle microscope system 1 according to an embodiment of the present invention. Note that the symbols used in the drawing have been selected to symbolize their respective functionalities. The type of system illustrated is a multi-beam scanning electron microscope (MSEM or Multi-SEM) that uses multiple primary electron beamlets 3 to generate multiple primary charged particle beam spots 5 on the surface 25 of an object 7, such as a wafer, with its upper surface 25 located within the objective plane 101 of the objective lens 102. For simplicity, only five primary charged particle beamlets 3 and five primary charged particle beam spots 5 are shown. The features and functions of the multi-beamlet charged particle microscope system 1 can be implemented using electrons, or other types of primary charged particles such as ions and especially helium ions. Further details of the microscope system 1 are given in German Patent Application Publication No. 102020209833.6, filed on August 5, 2020, which is incorporated herein by reference in its entirety.

[0045] The microscope system 1 comprises an object irradiation unit 100, a detection unit 200, and a beam splitter unit 400 for separating the secondary charged particle beam path 11 from the primary charged particle beam path 13. The object irradiation unit 100 includes a charged particle multi-beam generator 300 for generating multiple primary charged particle beamlets 3, and is adapted to focus the multiple primary charged particle beamlets 3 within an objective plane 101 where the surface 25 of the wafer 7 is positioned by the sample stage 500.

[0046] The primary beam generator 300 generates multiple primary charged particle beamlet spots 311 within an intermediate image plane 321, which is typically a spherically curved surface. The positions of the multiple focal points (311) of the multiple primary charged particle beamlets (3) are generated and adjusted within the intermediate image plane (321) by the multibeam generator unit (305) to pre-compensate for the image plane curvature and tilt of the elements of the object irradiation unit (100) downstream of the multibeam generator unit 305.

[0047] The primary beamlet generator 300 includes a primary charged particle source 301, such as electrons. The primary charged particle source 301 emits a diverging primary charged particle beam, which is collimated by at least one collimating lens 303 to form a collimated or parallel primary charged particle beam 309. The collimating lens 303 is typically composed of one or more electrostatic or magnetic lenses, or a combination of electrostatic and magnetic lenses. The collimated primary charged particle beam is incident on a primary multibeam forming unit 305. The multibeam forming unit 305 essentially comprises a first multi-aperture element or filter plate 304 irradiated by the collimated primary charged particle beam 309. The first multi-aperture element or filter plate 304 has multiple apertures, which are arranged in a raster configuration to generate multiple primary charged particle beamlets 3, which are produced when the collimated primary charged particle beam 309 passes through the multiple apertures. The multi-beamlet forming unit 305 in this example comprises two active multi-aperture elements 306.1 to 306.2 located downstream of the first multi-aperture or filter plate 304 with respect to the direction of electron movement in the beam 309. For example, the first active multi-aperture element 306.1 functions as a microlens array comprising multiple ring electrodes, each ring electrode set to a defined potential such that the focal positions of multiple primary beamlets 3 are adjusted within the intermediate image plane 321. The second active multi-aperture element 306.2 is configured as a deflector of a multi-pole array and comprises, for example, two, four, or eight electrostatic elements for each of the multiple apertures to individually deflect each of the multiple beamlets. The multi-beamlet forming unit 305 according to some embodiments is configured to have a termination multi-aperture element (310). The multi-beamlet forming unit 305 is further configured with an adjacent electrostatic field lens 307, which in some examples is combined with the multi-beamlet forming unit 305. Together with an optional second field lens 308, multiple primary charged particle beamlets (3) are focused within or near the intermediate image plane 321.

[0048] Further active multi-aperture elements can be positioned within or near the intermediate image plane 321, configured as beam steering multi-aperture elements 390, which have multiple apertures with electrostatic elements, such as deflectors, in order to individually manipulate the propagation direction of each of the multiple charged particle beamlets 3. The apertures of the beam steering multi-aperture elements 390 are configured to have a larger diameter to allow multiple primary charged particle beamlets 3 to pass through, even when the focal spot 311 of the primary charged particle beamlet 3 is located on the curved intermediate image plane 321. The primary charged particle source 301, the active multi-aperture elements 306, and the beam steering multi-aperture elements 390 are controlled by a primary beamlet control module 830 connected to a control unit 800.

[0049] Multiple focal points of the primary charged particle beamlet 3 passing through the intermediate image plane 321 are imaged within the image plane 101 on which the surface 25 of the wafer 7 is positioned by the field lens group 103 and the objective lens 102. A decelerating electrostatic field is generated between the objective lens 102 and the wafer surface by applying a voltage to the wafer by the sample voltage supply source (503). The object irradiation system 100 further comprises a focusing multibeam raster scanner 110 adjacent to the first beam crossover 108, which can deflect the multiple charged particle beamlets 3 in a direction perpendicular to the propagation direction of the charged particle beamlets. Throughout this example, the propagation direction of the primary beamlets is in the positive z direction. The objective lens 102 and the focusing multibeam raster scanner 110 are centered on the optical axis 105 of the multibeam charged particle system 1, which is perpendicular to the wafer surface 25. Multiple primary charged particle beamlets 3 forming multiple beam spots 5 arranged in a raster configuration are scanned synchronously across the wafer surface 25. In one example, the raster configuration of the focal spot 5 of multiple N primary charged particles 3 is a hexagonal raster of approximately 100 or more primary charged particle beamlets 3, such as beamlets with N=91, N=100, or N=approximately 300. The primary beam spots 5 have a distance of approximately 6 μm to 15 μm and a diameter of less than 5 nm, such as 3 nm, 2 nm, or even less. In one example, the beam spot size is approximately 1.5 nm, and the distance between two adjacent beam spots is 8 μm. At each scanning position of each of the multiple primary beam spots 5, multiple secondary electrons are generated, forming multiple secondary electron beamlets 9 with the same raster configuration as the primary beam spots 5. The intensity of the secondary charged particle beamlets 9 generated at each beam spot 5 depends on the intensity of the colliding primary charged particle beamlets 3 irradiating the corresponding spot 5, the material composition and topology of the object 7 below the beam spot 5, and the charging conditions of the sample at the beam spot 5. The secondary charged particle beamlet 9 is accelerated by the electrostatic field generated by the sample charging unit 503 between the sample 7 and the objective lens 102.Multiple secondary charged particle beamlets 9 are accelerated by an electrostatic field between the objective lens 102 and the wafer surface 25, collected by the objective lens 102, and pass through the first focusing multi-beam raster scanner 110 in the opposite direction to the primary beamlet 3. The multiple secondary beamlets 9 are scanned and deflected by the first focusing multi-beam raster scanner 110. The multiple secondary charged particle beamlets 9 are then guided by the beam splitter unit 400 to follow the secondary beam path 11 of the detection unit 200. The multiple secondary electron beamlets 9 are traveling in the opposite direction to the primary charged particle beamlet 3, and the beam splitter unit 400 is typically configured to separate the secondary beam path 11 from the primary beam path 13 by a magnetic field or a combination of a magnetic field and an electrostatic field. Optionally, additional magnetic correction elements 420 are present in the primary and secondary beam paths.

[0050] Microscope system 1 includes a vacuum chamber 31 for maintaining a vacuum environment for the charged particle beam. The vacuum chamber 31 is shown in a very schematic manner. Part of the vacuum chamber 31 can be formed by beam tubes around multiple primary or secondary charged particle beamlets. Other functional elements of the charged particle optics can be located outside the vacuum chamber 31.

[0051] The detection unit 200 images the secondary electron beamlet 9 onto the image sensor 207, where it forms multiple secondary charged particle image spots 15. The detector or image sensor 207 includes multiple detection pixels or individual detectors. For each of the multiple secondary charged particle beam spots 15, the intensity is detected separately, and the material composition of the wafer surface 25 is detected with high throughput and high resolution in large image patches of the wafer. For example, a raster of 10 × 10 beamlets with an 8 μm pitch generates an image patch of approximately 88 μm × 88 μm in a single image scan by the focused multi-beam raster scanner 110 with an image resolution of, for example, 2 nm or less. The image patch is sampled by half the beam spot size, and therefore has 8000 pixels per image line for each beamlet, resulting in an image patch generated by 100 beamlets containing 6.4 gigapixels. Digital image data is collected by the control unit 800. Details of digital image data acquisition and processing using parallel processing, for example, are described in German Patent Application Publication No. 102019000470.1 and U.S. Patent No. 9,536,702, which are incorporated herein by reference.

[0052] The projection system 205 further comprises at least a second focusing raster scanner 222 connected to a scanning and imaging control unit 820. The control unit 800 and the imaging control unit 820 are configured to compensate for residuals in the positions of multiple focal points 15 of multiple secondary electron beamlets 9 so that the positions of the multiple secondary electron focal spots 15 are kept constant in the image sensor 207.

[0053] The projection system 205 of the detection unit 200 comprises further electrostatic or magnetic lenses 208, 209, 210 and a second crossover 212 of a plurality of secondary electron beamlets 9 on which the aperture 214 is located. In one example, the aperture 214 further comprises a detector (not shown) connected to an imaging control unit 820. The imaging control unit 820 is further connected to at least one electrostatic lens 206 and a third deflection unit 218. The projection system 205 may further comprise at least a first multi-aperture corrector 220 connected to a control unit 800 or the imaging control unit 820, having apertures and electrodes for individually affecting each of the plurality of secondary electron beamlets 9, and an optional further active element 216.

[0054] The image sensor 207 consists of an array of detection regions in a pattern that conforms to the raster arrangement configuration of secondary electron beamlets 9 focused onto the image sensor 207 by the projection lens 205. This makes it possible to detect each individual secondary electron beamlet independently of other secondary electron beamlets incident on the image sensor 207. The image sensor can also serve as an image quality monitor for the multi-beam charged particle microscope 1. The image sensor 207 shown in Figure 1 can be an electron-sensitive detector array such as a CMOS or CCD sensor. Such an electron-sensitive detector array can include an electron-photon conversion unit, such as a scintillator element or an array of scintillator elements. In another embodiment, the image sensor 207 can be configured as an electron-photon conversion unit or scintillator plate arranged within the focal plane of multiple secondary electron particle image spots 15. In this embodiment, the image sensor 207 may further comprise a relay optical system for imaging and guiding photons generated by an electron-photon conversion unit at a secondary charged particle image spot 15 on a dedicated photon detection element, such as a plurality of photomultiplier tubes or avalanche photodiodes (not shown). Such an image sensor is disclosed in U.S. Patent No. 9,536,702, which is cited and incorporated by reference above. In one example, the relay optical system further comprises a beam splitter for splitting the light and guiding it to a first slow photodetector and a second fast photodetector. The second fast photodetector is comprised of an array of photodiodes, such as avalanche photodiodes, which are fast enough to resolve the image signals of a plurality of secondary electron beamlets 9 according to the scanning speed of a plurality of primary charged particle beamlets 3. The first slow photodetector is preferably a CMOS or CCD sensor that provides high-resolution sensor data signals, serving as an image quality monitor for the multi-beam charged particle microscope 1.

[0055] While acquiring image patches by scanning multiple primary charged particle beamlets 3, the stage 500 is preferably not moved, and after acquiring an image patch, the stage 500 moves to the next image patch to be acquired. In an alternative embodiment, the stage 500 is continuously moved in a second direction while an image is being acquired by scanning multiple primary charged particle beamlets 3 in a first direction by a focused multi-beam raster scanner 110. Stage movement and stage position are monitored and controlled by sensors known in the art, such as laser interferometers, grating interferometers, and confocal microlens arrays.

[0056] According to one embodiment of the present invention, multiple electrical signals are generated, converted into digital image data, and processed by a control unit 800. During image scanning, the control unit 800 is configured to trigger the image sensor 207 to detect multiple timely resolved intensity signals from multiple secondary electron beamlets 9 at predetermined time intervals, and digital images of image patches from all scanning positions of multiple primary charged particle beamlets 3 are accumulated and stitched together.

[0057] The multibeam generation unit 305 is described, for example, in U.S. Patent Application No. 16 / 277.572, U.S. Patent Publication No. 2019 / 0259575, and U.S. Patent Application No. 16 / 266.842, filed on 4 February 2019, both of which are incorporated herein by reference. Further details of the multibeam generation unit 305, which is insensitive to fabrication errors and scattering, are disclosed in PCT / EP2021 / 025095, filed on 3 September 2021, which is incorporated herein by reference.

[0058] To enhance the performance of the multi-beam charged particle microscope during use, each of the multiple charged particle beamlets is individually controlled, for example, by individual focusing correction using multiple individually controlled ring electrodes of a microlens array 306.1, or multiple individually controlled electrodes of a stigmeter or multipole array element 306.2. Individual control of the voltages of the multiple electrodes is provided by a programmable control element. A first embodiment of the present invention of an improved control architecture for generating and controlling multiple voltages is shown in Figure 2. A primary multi-beamlet forming unit 305, comprising multi-aperture elements 304, 306, and 310, each having a parallel-arranged film in a film zone 199 and a support structure in a support zone 197, is mounted on a carrier or support substrate 271 having additional functions of a support substrate. In this example, the primary multi-beamlet forming unit 305 comprises three active multi-aperture elements 306, including a microlens array element 306.1 and a multipole array element 306.2, each having multiple electrodes arranged in each aperture 85. Further active multi-aperture elements 306.3 can be, for example, second multi-pole array elements. At least two ASICs 261.1 and 261.2 are mounted on a support substrate 271. For example, the ASICs form a voltage source unit for multiple electrodes of the active multi-aperture element. The ASICs or voltage source units may be provided for the ring electrodes of the microlens array 306.1 and the electrodes of the multi-pole array element 306.2. The electrodes are connected to the voltage source unit 261 by low-voltage wiring connections 257.1 and 257.2. The ASICs are controlled by digital signals via digital signal lines 267.1 and 267.2 and receive power from a power source (not shown) via low-voltage supply lines 269.1 and 269.2. In this example, only J=25 apertures (85) in film zone 199, as well as only two ASICs 261.1 and 261.2, are shown. The number of J openings 85 can be made larger, for example, J=91, J=100 or more, for example, J=1000.The number of electrodes in each multipole element can be, for example, 6, 8, or 12 electrodes in each aperture, and the total number of electrodes can easily exceed 500, for example, more than 700, or even more, for example, J=1000, so that a multipole array element has up to 12000 electrodes. In addition, individual voltages are supplied to multiple J ring electrodes of the active multi-aperture element 306.1 that forms a microlens array. Therefore, the number of ASICs can also be significantly larger than 2, for example, 6, 8, or even up to about 100 ASICs may be required. The ASICs form, for example, multiple digital-to-analog converters (DACs) for supplying analog voltages to the electrodes, with one DAC for each electrode. In one example, a multi-beam raster unit 305 with multiple J=91 beamlets requires at least 728 individual DACs and 728 individual wiring connections 257 to 728 electrodes.

[0059] Figure 2a shows a cross-section through an example of a primary multi-beamlet forming unit 305 according to the first embodiment. The primary multi-beamlet forming unit 305 comprises a filter plate 304 and several active multi-aperture elements 306.1 to 306.3 having different functions. The primary multi-beamlet forming unit 305 further comprises a terminal multi-aperture element 310. A primary electron beam 309 is incident at the beam inlet or upper side 74. Multiple primary electron beamlets 3 are emitted from the primary multi-beamlet forming unit 305 at the bottom side or beam exit side 76. Each of the multi-aperture elements 304, 306 and 310 comprises an inner film zone 199 having multiple apertures 85 arranged in a raster configuration of the multiple primary electron beamlets 3 generated by the primary multi-beamlet forming unit 305. Each multi-aperture element 304, 306, and 310 further comprises a support zone 197, thereby positionally aligned and mounted to one another. The primary multi-beamlet forming unit 305 further comprises a carrier element 271 to which the support zone 197 of at least one multi-aperture element is attached. Multiple voltage source units, including ASICs 262.1 and 262.2, are arranged on the carrier element. Microelectronic devices such as the ASIC devices 262.1 and 262.2 generate and provide the multiple voltages required for the multiple electrodes of the active multi-aperture array element.

[0060] Figure 2b shows a top view of the primary multi-beamlet forming unit 305 in the positive z direction. The same elements are labeled by the same reference numerals. To control multiple electrodes individually, the electrodes are connected by wiring connections 257 to microelectronic devices such as ASIC devices 262.1 and 262.2. Additional wiring can be provided for shielding and absorption layers or sensors. High voltage is provided by an external controller using connections 251 to the multi-aperture elements or 253 to the ASIC 261. High voltage connections 251 and 253 can be electrically shielded by a coaxial shielding casing 255. The electrodes require drive voltages with differences of several orders of magnitude, for example, between 10V and up to 1kV. For example, a multi-lens array 306.1 requires J voltage wirings to provide approximately 200V to each of the ring electrodes of the lens array (not shown). A multi-pole array 306.2 for beam correction and deflection requires, for example, J × 8 voltage wirings to provide approximately a few volts with very low noise. The voltage is supplied by ASICs 261.1 and 261.2 (only two shown) located in a vacuum, via a digital interface to the array control unit 840. The array control unit 840 is an element of the primary beam path control module 830, configured to control the active multi-aperture elements 306.1-306.3.

[0061] The routing of the signal and voltage sources is obtained via UHV flanges (not shown). In one example, the ASICs or voltage source units 261.1 and 261.2 are further connected to a voltage drift monitor 835 that controls at least representative voltages or voltage control outputs 263.1 and 263.2 of the ASICs, respectively. The voltage drift monitor 835 is connected to an array control unit 840. The array control unit 840 is configured to evaluate the voltage control outputs 263.1 and 263.2 and to compensate for drift of the first voltage source unit or ASIC 261.1, for example, by calculating digital control signals provided to the first voltage source unit 261.1 or the second voltage source unit 261.2. The array control unit 840 is further connected to the image performance sensor 860, which provides input to the array control unit 840 to determine the digital control signals that are provided to the ASICs 261.1 and 261.2 via digital signal lines 267.1 and 267.2. For example, the astigmatism of individual beamlets is determined, and corresponding corrections for astigmatism are derived to compensate for the astigmatism by the multipole elements corresponding to each beamlet. The architecture given above enables precise and reliable control of the multipole array elements. Further details are described below.

[0062] Figure 3 shows an example of an active multi-aperture element formed as a multipole array 306.2 having multiple J apertures 85 arranged in a hexagonal raster configuration. The raster configuration is rotated with respect to the x and y axes, thereby pre-compensating for the rotation of the magnetodynamic objective lens 102 and other magnetic lenses. In each of the multiple apertures, eight electrodes 81 are arranged to form a multipole element 87. In this example, only J=61 apertures with J=61 multipole elements 87 are shown. The multipole array 306.1 is composed of eight sections 273.1 to 273.8 by section boundaries 275. Each section contains electrode groups 83.1 to 83.8. The divisional boundaries are shown in Figure 4 in the example of a multipole element 87 in aperture 85.59, where electrodes 81.1-81.4 and 81.8 are members of the third electrode group 83.3, and electrodes 81.5-81.2 are members of the fourth electrode group 83.4. For simplicity, only a single aperture and a single multipole element 87 are shown. In one example, electrode 81 in section 273 forms a first electrode group connected to the first voltage source unit 261.3. Electrodes in section 261.4 form a second electrode group connected to the voltage source unit 261.4. Thus, global drift in the voltage source unit 261.3 can be compensated by applying a local compensating voltage offset to the electrode in aperture 85.59 of the second electrode group in section 273.4. This maintains the relative voltage difference between the eight electrodes 81.1-81.8, allowing the multipole element 87 to operate in the expected predetermined manner. Figure 5 shows another example in which the divisions are selected such that, in this example, the electrodes of multipole element 87 in aperture 85.59 belong to and are connected to only one voltage source unit 261.3. In this example, the global drift of voltage source unit 261.3 does not affect the relative voltage difference between the eight electrodes 81.1-81.8, and multipole element 87 operates in the expected predetermined manner. However, voltage source unit 261 may also have local voltage drift and may be composed of multiple microelectronic subunits, such as in a multicore architecture. In other examples, the divisions are not formed as angular divisions.

[0063] According to the example in Figure 5, the multibeam array element 306.2 of the multibeam system (1) includes an inner film zone 199 having multiple J apertures 85 arranged in a raster configuration, which is configured to transmit multiple J primary charged particle beamlets 3 during use. The multibeam array element 306.2 further includes multiple J multipole elements (87), each multipole element (87) having one of the multiple J apertures (85), each multipole element having multiple K1 electrodes (81.1~81.K), and each multipole element (87) is configured to affect one of the primary charged particle beamlets (3). The multibeam array element 306.2 further includes multiple L voltage source units, and each of the K electrodes (81.1~81.K) of one multipole element (87) is connected to only one of the multiple L voltage source units 261. In one example, multiple L voltage source units (261) are arranged on a base plate (271) surrounding a raster configuration of multiple J openings (85).

[0064] An example having annular sections 273.1 to 273.5 is shown in Figure 6. The selection of annular sections is advantageous when one task of the multipole array element 306.2 is to contribute to the focusing capability of the primary multibeamlet formation unit 305, as well as to compensate for image plane curvature and image plane tilt of the multibeam charged particle microscope system 1. By assigning the multipole element 87 to different ring sections, the corresponding voltage source units of the corresponding electrode groups are driven by similar power. The first electrode group of the first section 273.1 is driven by a higher voltage to achieve, for example, stronger focusing capability, while the fifth electrode group of the fifth section 273.5 is driven by a lower voltage on average. Thus, the fifth electrode group is less affected by, for example, the thermal drift of the first voltage source unit 261.1 of the first electrode group.

[0065] The performance of the multipole array element 306.2 is sensitive to drift of the voltage source unit 261. The voltage source unit 261 may exhibit voltage drift over time or accumulate different voltage offsets over time. Furthermore, inaccurate voltages generated for the multipole array element 306.2 may result from local or global damage to the voltage source unit 261. For example, secondary radiation, such as X-ray radiation, may be one source of different offset voltages or damage. According to a second embodiment of the present invention, the effects of secondary radiation are reduced by a shielding member. An example is shown in Figure 7. In Figure 7, a thick absorber or first shielding member 93.1 is provided on the inlet side 74 of the filter plate 304. The first shielding member 93.1 has an aperture 91 configured to restrict the primary beam 309 to the area necessary to irradiate the raster of the aperture 85. In one example, the aperture 91 has a conical shape with a diameter increasing in the z direction. This minimizes the scattering of the primary electron beam 309 inside the aperture 91. The cross-section of the aperture 91 can be composed of a hexagonal region having a diameter of, for example, about 1 mm or more, according to the region of the raster configuration. Thus, the first shielding member 93.1 having a large aperture 91 can be given a large thickness. This effectively prevents secondary radiation 901.1 generated upstream of the first shielding plate 93.1 from reaching the voltage source unit 261, thereby reducing voltage drift or damage. Furthermore, the transmission of secondary radiation 901.2 generated in the first shielding member 93.1 is reduced. The first shielding member 93.1 is made of a highly conductive material and is connected to the ground level. This avoids charging, including local surface charge, of the first shielding member 93.1.

[0066] The beam diameter of the primary charged particle beam 309.1 is effectively reduced to a filtered primary beam 309.2 having the size and area of ​​the raster of aperture 85 by aperture 91 having the size and area of ​​aperture 85. This reduces to a minimum the number of electrons absorbed or the generation of secondary radiation in the filter plate 304. The first multi-aperture element or filter plate 304 comprises an absorption layer made of a high-density, highly conductive material. The absorption layer is connected to ground level. Most of the primary charged particles in the filtered beam 309.2 are absorbed, and the corresponding charges are dissipated to ground level. However, some primary electrons are still scattered in the filter plate 304, and some secondary radiation 901.3 may still be generated in the filter plate 304. Secondary radiation 901.3, such as X-rays or secondary electrons, may be emitted in any direction. In particular, X-rays can penetrate the thin-film zone 199 and support element 197 of the active multi-aperture element 306, potentially affecting the voltage source unit 261 and causing damage or charge drift. In one example, further damage or drift to the voltage source unit 261 is avoided. In this example, the primary multi-beamlet forming unit 305 is provided with a second shielding member 93.2, which is placed between the multi-aperture elements 304, 306, and 310 and the voltage source element 261. This effectively prevents secondary radiation 901.3 generated within the multi-aperture elements 304, 306, and 310 from reaching the voltage source unit 261, thereby reducing voltage drift or damage to the voltage source unit 261. In one example, the shielding member 93.2 is placed around the multi-aperture elements 304, 306, and 310, surrounding them.

[0067] The primary multi-beamlet forming unit 305 can be configured to have at least a first shielding member 93.1, a second shielding member 93.2, or a combination of both. In a further example shown in Figure 7, further damage or drift to the voltage source unit 261 is avoided. In this example, the primary multi-beamlet forming unit 305 is provided with a third shielding member 93.3, which is positioned below the multi-aperture elements 304, 306, and 310 and the voltage source element 261. This effectively prevents secondary radiation 901.4 generated by the electro-optical elements downstream of the primary multi-beamlet forming unit 305 from reaching the voltage source unit 261, further reducing voltage drift or damage to the voltage source unit 261. Although only one voltage source unit 261 is shown in Figure 7, several voltage source units 261.1 to 261.N can be arranged around the active multi-aperture array elements 306.1 to 306.3 as described above.

[0068] Secondary radiation in the form of X-ray emission 901 can generate space charge or localized charging effects within the semiconductor. These charging effects can accumulate over time and affect the performance of microelectronic devices such as transistors or the capacitance of a DAC. Therefore, charging effects are a source of voltage drift. The X-ray emission 901 can also be absorbed, generating heat. Changes in the operating temperature of the voltage source unit 261 are a further source of voltage drift. However, even with the shielding member 93, the operating temperature of the voltage source unit 261 is generally affected by its operating conditions, such as the current required to charge the electrodes to the required voltage. Since the voltage source unit 261 is located inside the vacuum chamber, cooling via thermal convection is not possible. Therefore, in one example, the voltage source unit 261 in Figure 7 is physically connected to a cooling member 97. The cooling member 97 can be connected to a heat sink outside the vacuum chamber 31 (see Figure 1, not shown in Figure 7). This allows for control of the temperature of the voltage source unit 261 and minimizes temperature-induced voltage drift. In one example, the cooling member 97 and the shielding member 93 are identical and formed as a single component.

[0069] The effect of the shielding element 93 is typically explained by the absorption coefficient μ of the secondary radiation in question. The attenuation is typically explained by the Lambert-Beer law using the following equation: I = I0exp(-μD) In the formula, D is the thickness. Measured absorption coefficients μ of the X-ray energy spectrum produced by 30 keV electron irradiation are, for example, 1.1 / mm for aluminum, 14.2 / mm for iron, and 17.5 / mm for copper. However, the resulting X-ray spectrum depends on the electron energy and, for example, the material composition of the filter plate 304. Generally, it is advantageous to use high-density paramagnetic or diamagnetic materials, such as a first group of materials consisting of, for example, molybdenum, ruthenium, rhodium, palladium, or silver (atomic numbers 42, 44-47), or a second group of materials consisting of, for example, tungsten, rhenium, osmium, iridium, platinum, gold, or lead (atomic numbers 74-79 and 82). On the other hand, other materials such as silicon or aluminum are not suitable for blocking X-ray radiation. Typically, multi-aperture elements are formed by microstructuring of silicon or silicon compounds. With typical multi-aperture elements 304, 306, and 310 having thicknesses less than 200 μm, less than 10% of the secondary radiation is absorbed within each multi-aperture element. Even with a thick coating of gold, for example, 5 μm thick, more than 70% of the secondary radiation is transmitted. Therefore, even thick coatings or films are not sufficient to effectively shield the secondary radiation. Such thick coatings would also cause stress bending or deformation of the film zones, and are therefore not feasible.

[0070] According to the second embodiment, the attenuation of secondary radiation and, therefore, the prevention of charging effects or damage to the voltage source unit are achieved by shielding members 93.1 to 93.3. For example, a first shielding member 93.1 having a large aperture 91 with a diameter of about 1.1 mm and an area due to the raster of the primary beamlet 3 can be made of a material with sufficient thickness, sufficient absorbency and high conductivity. For example, a shielding member with a thickness of about D=1 mm, made from one of the materials of the first or second material group, achieves sufficient attenuation of secondary radiation down to a ratio of 10E-5 or less. A second shielding member 93.2 is placed between the multi-aperture elements (304, 306 and 310) and the voltage source unit 261. A second shielding member 93.2 with a thickness of about D=1 mm, made from one of the materials of the first or second material group, achieves sufficient attenuation of secondary radiation down to a ratio of 10E-5 or less.

[0071] The shielding member 93 may also be provided by a thick support layer, for example, 2 mm thick, made from aluminum or silicon, which may include, for example, a layer of a second group of materials having a thickness of about 200 μm, or a layer of a first group of materials having a thickness of about 300 μm. Of course, other thicker materials are also possible, such as copper or zirconium, or any combination thereof. To increase conductivity and reduce surface charge, the shielding member 93 may also be provided with a conductive surface coating, for example, a layer made from copper, gold, or lead.

[0072] Figure 8 shows a further example of a shielding member 93.4. In some applications, the spacing between individual apertures 85 or multi-aperture elements is large enough to allow microelectronic devices, such as voltage source units 261, to be placed directly between the apertures or directly structured. In Figure 1, an example is given with a multi-pole array element 390 configured as a beam steering multi-aperture element. Such an element can correct the telecentricity characteristics of multiple primary charged particle beamlets. In such an example, a shielding member 93.4 made from a material of the second group of materials allows the shielding member 93.4 to be positioned as a capping plate directly above each voltage source unit. With the materials of the second group and a thickness of shielding member 93.4 of about 100 μm or more, suppression of more than 99% is achieved. Figure 8a shows an xy cross-section of a multi-pole array 390 having multiple apertures, including apertures labeled 85.1 to 85.8. Between the apertures 85.i are several small voltage source units 261.1-261.7, formed as microelectronic devices, which act as DACs to supply the corresponding voltages to the electrodes 81 of the multipole element 87. Several wiring connections 257 between the voltage source units 261.i and the electrodes 81 are shown. Further signal lines 267 and voltage lines 269 of the present invention are not shown in Figure 2. Figure 8b shows a cross section along line AB with two apertures 85.5 and 85.8. The electrodes 81.54 and 81.88 of the third group are connected to the voltage source unit 261.3 by connections 257.34 and 257.38. Electrode 81.58 is of the second group of electrodes, connected to the voltage source unit 261.2 via line 257.28. The voltage source unit 261.3 is covered by a shielding member 93.4, which is formed as a cap or plate made from a material of the second group, such as tungsten, platinum, or lead, having a thickness of approximately 100 μm or more. The shielding member 93.4 is configured to cover the voltage source unit 261.3 from the inlet side of the primary charged particle beamlets 3.5 and 3.8.As a result, over 99% of the secondary radiation 901.3 from the filter plate 304 (see Figure 7) is absorbed, minimizing the charge damage to the voltage source unit 261.3. Of course, additional shielding material can be placed on the back to avoid damage from secondary radiation 901.4 generated downstream of the multi-pole array 390.

[0073] Figure 14 shows a further example of the shielding member 93.4. Figure 14 is similar to Figure 7, and Figure 7 is used for its description. Similar to the example in Figure 7, the voltage source units 261 are arranged around the multi-aperture elements 304, 306, and 310. In the example in Figure 14, the shielding member 93.4 is provided to cover the voltage source units 261 as a covering plate or cap directly above each voltage source unit 261. Each cap may cover one or more voltage source units 261, and each cap may have an extension in the z direction for mounting the cap on a carrier or support substrate 271, providing shielding between the primary charged particle beamlets 3. This avoids direct contact between the voltage source units 261 and the shielding member 93.4.

[0074] Throughout these examples, the substrate 271 is shown as a single support substrate for supporting the voltage source unit 261 and at least one multi-aperture plate 306. Of course, it is also possible, for example, for the multi-aperture plate 306 to be mounted on the first support substrate 271, and the voltage source unit 261 to be mounted on a second support substrate which is mechanically separated from the first support substrate 271 and electrically connected to the first support substrate by flexible connections similar to the wiring connection 257.

[0075] According to an example of the second embodiment, damage or charge accumulation in the microelectronic circuits of a voltage source unit induced by secondary radiation is reduced to a minimum. This significantly reduces the contribution to voltage drift. According to a third embodiment of the present invention, a further reduction of voltage drift induced by charge accumulation is provided. The function of a microelectronic semiconductor structure in the presence of secondary radiation such as secondary electron radiation and X-rays is affected by charging effects, including, for example, the accumulation of positive space charge in silicon oxide or surface charging effects at interfaces. Some charging effects can be reduced or balanced by applying pulses of a negative voltage-VG. Therefore, according to the first example of the third embodiment, a method is provided for balancing or restoring the charging effects of a voltage source unit by applying pulses of a negative voltage-VG to the voltage source unit. However, some charging effects and damage are not reversible by the application of voltage pulses. However, some of these charging effects or damage are reversible by heating the microelectronic device to a temperature above 250°C. Such heating over several minutes can reduce or completely anneal many charging effects or localized damage of the voltage source unit. According to a second example of the third embodiment, the multi-aperture elements 304, 306, 310, or 390 or the voltage source unit 261 are treated by a voltage pulse and thermal annealing process to reduce charging effects or damage. Thermal annealing can be achieved by a resistance heater or by external heating, for example, by IR laser irradiation. Figure 9 illustrates the method. In the first step M, a series of inspection tasks are performed by the multi-beam charged particle microscope 1 according to the first embodiment. In step D, the control unit interrupts the measurement and optionally initiates step A of the annealing procedure. After completing the annealing procedure, the control unit triggers the continuation of the measurement by the next inspection task. The interruption of the inspection task in step D can be triggered by various parameters. According to the first example, the imaging performance index of the multi-beam charged particle microscope 1 is monitored.If a deviation in beam quality due to a malfunction of the active multi-aperture element 306 is detected, a trigger signal is generated to initiate annealing process A. According to the second example, a typical voltage output is measured by the voltage drift monitor 835 (see Figure 2). If the voltage drift exceeds a predetermined threshold, a trigger signal is generated to initiate annealing process A. According to the third example, the trigger signal is generated by model-based control. The estimated voltage drift over time or the cumulative irradiation dose is calculated, and a trigger signal is generated when the estimated voltage drift over time or the cumulative irradiation dose exceeds a predetermined threshold. The annealing procedure in step A may include a negative voltage pulse applied to the voltage source unit 261, thermal annealing, or a combination of both.

[0076] The lifespan of the voltage source unit can be extended by the method according to the third embodiment. In an optional step C, the success of the annealing process is determined. Irreversible damage accumulates over time due to the service life or increasing irradiation dose of the voltage source unit, gradually reducing the performance of the voltage source unit. After a certain level of damage is reached, even after repeated annealing, a replacement step R may be triggered to replace the multibeamforming unit 305 or the active multi-aperture element 390.

[0077] The multipole array according to this embodiment can have more than 488 electrodes (see Figure 3). By increasing the number of beamlets J and making the correction of each individual beamlet more precise, for example, by a multipole element 87 having 12 electrodes, the number of electrodes to which individual voltages are supplied can be increased well beyond 1000 in a single multipole array 306.2. In advanced multi-beam charged particle microscopes, two or more multipole arrays may be required. In one example, two multipole arrays are required to achieve deflection and angle correction of multiple primary beamlets. In a further example, four or five multipole arrays are required to achieve the individual focusing capability of each beamlet. Therefore, a very large number of individual voltages must be generated, controlled, and supplied for multiple electrodes. According to a fourth embodiment, a method is provided for operating multiple electrodes of an active multi-aperture element such as a multipole array or microlens array with at least two voltage source units. In one example, an octupole array is controlled using multiple voltage source units, such as ASICs that form an array of DACs, each having 128 DAC channels. Due to routing constraints, some octupoles are controlled by two or more ASICs (see Figures 3 and 4). In such an example, the voltage offset or voltage drift of the first ASIC affects the beam quality or beam deflection. An example is shown in Figure 10. Figure 10 shows the effect of a global voltage offset of one voltage source, as can be measured by an image quality monitor of the multi-beam charged particle system 1. In this example, the voltage source unit 261.4 of the electrodes in section 83.4 has an offset. Since all electrodes are given a constant global voltage offset, the beam spot 5.n by all electrodes of the corresponding multipole elements supplied by the same voltage source unit 261.4 shows no deviation whatsoever. However, a focal spot 5.k or 5.m with a corresponding multipole element, powered by at least two different voltage source units, exhibits astigmatic behavior and / or deflection due to voltage offset.The offset voltage of the voltage source unit 261 can be determined from the position and influence of the deflection or beam shape of spot 5.1...J. The primary electron spot 5.1...J can be measured directly using the mirror imaging method, or the beam aberration can be determined from the image acquisition of a calibration test sample.

[0078] In the example shown in Figure 4, the first electrode groups 81.1-81.4 and 81.8 are controlled by the first voltage source unit 261.3, and the second electrode groups 81.5-81.7 are controlled by the second voltage source unit 261.4. In this example, the voltage offset of the first voltage source unit 261.3 introduces the beam tilt. The beam tilt can be compensated for by the equivalent voltage offset of electrodes 81.5-81.7 of the second electrode group. This method is not limited to just two voltage source units and two corresponding aperture groups. A multi-beamforming unit may require six, eight, ten, or even more voltage source units. An example is also shown in Figure 8, where smaller voltage source units with fewer DAC channels are used. Here, for example, an array of 10x10 apertures could utilize 50 voltage source units with 50 electrode groups.

[0079] The method according to the fourth embodiment is described in detail with reference to Figure 11. In the first step CM, a digital control signal for controlling the voltage source unit is determined. This determination can be performed, for example, during the calibration step of the multibeam charged particle microscope 1, and the imaging performance is optimized by optimized control parameters of the multibeam charged particle microscope 1, which include an optimized digital control signal for controlling the voltage source unit for the operation of the active multi-aperture element 306, including a multipole array 306.2 or 390. During the performance of a series of inspection tasks in step M, the performance is repeatedly monitored in step PM. If the performance parameters exceed a predetermined threshold, the voltage correction step VC is triggered. In the first example, the monitoring step is performed by an image quality monitor. The image quality monitor monitors the imaging performance. In particular, if a reduction in imaging performance is detected for beamlets corresponding to multipole elements 87 that are powered by at least two voltage source units, the voltage correction step is triggered. In the second example, the monitoring step utilizes a signal generated by a voltage drift monitor 835 (see Figure 2). For example, if the representative voltage generated by the first voltage source unit deviates from a predetermined voltage by an amount exceeding a predetermined threshold, a voltage compensation step is triggered, and a constant voltage offset is determined and generated for the electrodes of the second multi-pole element group, for example. The predetermined threshold can be, for example, 1V, 0.5V, or even less. The corresponding digital control signal for controlling the second voltage source unit is then modified to achieve a compensating digital control signal. This ensures that the second voltage source unit adds a constant voltage offset value to the required electrodes of the second electrode group. This maintains the imaging performance of the multi-beam charged particle microscope 1, even if individual voltage source units experience different voltage drifts.

[0080] Figure 12 shows an example of an active multi-aperture element 306.1 having multiple ring electrodes 81 that form multiple microlenses during use. In this example, the ring electrodes are grouped into four sections 83.1 to 83.4. The voltage supplied during use is configured to adjust the focal positions of multiple primary beamlets 3 within the curved intermediate image plane 321. This compensates for the image plane curvature of the object irradiation unit 100. The voltage is supplied to each group or electrode of the sections by separate voltage source units 261.1 to 261.4. A typical voltage is 100V, but higher voltages up to 200V are possible. Therefore, the voltage source units of the microlenses are even more sensitive to thermal drift. Here, for example, if an individual voltage source unit 261.3 is affected by drift due to, for example, X-ray radiation or thermal drift, the focus 311 or primary charged particle beamlet 3 corresponding to section 83.3 has a certain offset from the intermediate image plane 321 and is out of focus at the objective plane 101 of the multi-beam charged particle microscope 1. The voltage drift of the voltage source unit 261.3 can be detected by either the voltage monitor 835 or the imaging quality monitor. The beamlet corresponding to section 83.3 provides lower resolution during imaging, and this resolution can be determined, for example, by the image quality monitor. For example, the voltage drift of the voltage source unit 261.3 can be compensated by providing a modified control signal to the voltage source unit 261.3 or voltage source units 261.1, 261.2 and 261.4 by the method described in the fourth embodiment. This maintains the focusing of the multiple primary beamlets on a single focus plane. If this focal plane deviates from the image plane 101, the focal plane can be adjusted by further lens elements of the multi-beam charged particle beam system 1.

[0081] Due to X-ray radiation, not only the voltage source unit or ASIC261 but also the active multi-aperture element 306 of the primary multi-beamlet forming unit 305 can accumulate localized damage, including localized charging effects. The film zone 199 of the multi-aperture element is formed by doped silicon having characteristics such as being made from an insulating layer and silicon dioxide. The interconnection between the electrodes and the voltage source unit or ASIC261 can be formed by a metal layer. Therefore, for example, X-ray radiation can cause localized intersurface defects between silicon and silicon dioxide, which can cause localized charging effects, affecting the electric field generated by the electrodes and, therefore, the performance of the active element. At least a large portion of the defects or localized charging effects can be annealed by thermal or plasma annealing. Figure 13 shows a further example of annealing operation. Figure 13 is similar to Figure 7, for which Figure 7 is referred. In addition to Figure 7, shielding plates 93.1 and 93.3 further act as vacuum valves having slides 281.1 and 281.2. In Figure 13, both valves are shown in the open position, but both valves can be closed by the movable slides 281.1 and 281.2. This allows for the creation of closed and isolated vacuum compartments of the primary multi-beamlet forming unit 305. The required annealing temperature of approximately 250°C or higher can be achieved, for example, by infrared irradiation by the irradiation device 285. In one example, annealing is achieved at approximately 0.1 mbar by a low-energy gas plasma, such as a hydrogen plasma or nitrogen plasma. The plasma may be operated by a plasma generator 283, for example, at a frequency of 13.56 MHz and a low power of approximately 10-20 W. By either or both methods, local defects can be at least partially recovered, and the lifetime of the multi-aperture element can be extended.

[0082] According to the solutions provided by embodiments of the present invention, the drift of the voltage source unit 261 can be effectively reduced by the shielding member 93, the cooling member 97, or by an improved operating method of the voltage source unit 261, including the application of an optional voltage monitor 835. It is also possible to implement a combination of the shielding member 93 and the cooling member 97 with an improved operating method of the active multi-aperture element. This reduces the effects of voltage drift and minimizes damage to the multi-aperture element and voltage source unit due to X-ray radiation. This extends the lifespan of the voltage source unit or active multi-aperture element, for example. The annealing method described above can at least partially reduce or recover localized charging and localized defects, thereby extending the lifespan of the multi-aperture element or voltage source unit. Thus, the uptime of the multi-beam charged particle microscope is increased, and service or maintenance, including the replacement of expensive parts, is reduced. [Explanation of Symbols]

[0083] 1. Multi-beamlet charged particle microscope system 3. Primary charged particle beamlets, or multiple primary charged particle beamlets 5. Primary charged particle beam spot 7. Object or water 9. Secondary electron beamlets that form multiple secondary electron beamlets 11. Secondary electron beam path 13. Primary beam path 15 Secondary charged particle image spots 25 Wafer surface 31 Vacuum Chamber 74 Beam inlet or upper side 76 Bottom side or beam emission side 81 Multipolar electrode 83 Electrode Group 85 Aperture 87 Multi-pole element 91 Large opening 93 Shielding member 97 Cooling components 100 Object Irradiation Units 101 Objective surface 102 Objective lens 103 Field Lens Group 105 Optical axis of a multi-beamlet charged particle microscope system 108 First Beam Crossover 110 Focused Multibeam Raster Scanner 197 Support Zone 199 Membrane Zone 200 detection units 205 Projection System 206 Electrostatic Lens 207 Image Sensor 208 Imaging Lens 209 Imaging lens 210 Imaging lens 212 The Second Crossover 214 Aperture filter 216 Active elements 218 The Third Deflection System 220 Multi-Aperture Corrector 222 Second Deflection System 251 High-voltage wiring connections 253 Ground wire 255 Coaxial shielding and insulation 257 Low-voltage wiring connections 261 Voltage Source Unit 263 Voltage-controlled output 267 Digital signal line 269 ​​Low-voltage supply line 271 Career Elements 273 classification 275 Division boundary 281 Vacuum valve slider 283 Plasma Generator 285 Infrared source 300 Charged Particle Multibeamlet Generator 301 Charged Particle Source 303 Collimating Lens 304 Filter Plate 305 Primary multi-beamlet formation unit 306 Active multi-aperture element 307 First field lens 308 Second field lens 309 Primary electron beam 310 Terminated Multi-Aperture Element 311 Primary electron beamlet spot 321 Intermediate image plane 390 Active or beam steering multi-aperture elements 400 Beam Splitter Unit 420 Correction Elements 500 sample stages 503 Sample voltage supply source 800 Control Unit 820 Imaging Control Module 830 Primary beam path control module 835 Voltage Drift Monitor 840 Array Control Unit 860 Image Performance Sensor 901 Secondary radiation

Claims

1. A multibeam system (1) having active multi-aperture elements (306, 390) and a control unit (840) configured to control the active multi-aperture elements (306, 390), wherein the active multi-aperture elements (306, 390) - A plurality of J apertures (85) arranged in a raster configuration are configured to transmit a first plurality of J primary charged particle beamlets (3) through the active multi-aperture elements (306, 390) during use, - A plurality of electrodes (81) comprising at least one electrode (81) arranged around each of the openings (85), wherein the plurality of electrodes (81) includes a first electrode group (83.1) and a second electrode group (83.2), - A first voltage source unit (261.1) is configured to provide multiple voltages to the first electrode group (83.1) during use, - A second voltage source unit (261.2) is configured to provide multiple voltages to the second electrode group (83.2) during use. Equipped with, - The first voltage source unit (261.1) and the second voltage source unit (261.2) are connected to the control unit (840), The control unit (840) is configured to control, during use, a plurality of voltages supplied to the first electrode group (83.1) and the second electrode group (83.2) by the first voltage source unit (261.1) and the second voltage source unit (261.2), The control unit (840) is further configured to compensate for the drift of the first voltage source unit (261.1) during use, in a multibeam system (1).

2. The multibeam system (1) according to claim 1, wherein the control unit (840) is configured to compensate for the drift of the first voltage source unit (261.1) during use by a compensation control signal provided to the second voltage source unit (261.2).

3. The multibeam system (1) according to claim 1 or 2, wherein the first electrode group (83.1) and the second electrode group (83.2) are arranged in different angular divisions (273.1 to 273.8) of the raster configuration.

4. The multibeam system (1) according to claim 1 or 2, wherein the first electrode group (83.1) and the second electrode group (83.2) are arranged in different radial sections (273.1 to 273.5) of the raster configuration.

5. The multibeam system (1) according to claim 1 or 2, further comprising a monitoring device (835) connected to at least the first voltage source unit (261.1) and configured to monitor the drift of the first voltage source unit (261.1).

6. The multibeam system (1) according to claim 1 or 2, wherein the active multi-aperture element (306, 390) is a microlens array (306.1) having a ring electrode (81) in each of the plurality of apertures 85.

7. The multibeam system (1) according to claim 1 or 2, wherein the active multi-aperture element (306, 390) is a multi-pole array (306.2) comprising a plurality of multi-pole elements (87) each having K electrodes (81.1 to 81.K) in each of the plurality of apertures 85, and the number K of electrodes of each multi-pole element (87) is 2, 4, 6, 8, or 12.

8. The multibeam system (1) according to claim 1 or 2, further comprising a shielding member (93) provided for shielding secondary radiation from hitting the first voltage source unit (261.1) and the second voltage source unit (261.2).

9. The shielding member (93) is provided between the first voltage source unit (261.1) and the second voltage source unit (261.2) of the active multi-aperture element (306, 390) and the film zone (199), and comprises the plurality of J apertures (85), according to claim 8, multi-beam system (1).

10. The multibeam system (1) according to claim 8, wherein the first voltage source unit (261.1) is arranged between the plurality of J openings (85), and the shielding member (93.4) ​​is formed as a cap covering the first voltage source unit (261.1).

11. A method for operating the active multi-aperture element (306.2, 390) of a multi-beam charged particle microscope (1), - A step of determining a plurality of digital control signals for controlling at least a first voltage source unit and a second voltage source unit (261, 261.3, 261.4) configured to provide a plurality of voltages to at least a first electrode group and a second electrode group (83, 83.1, 83.2) among a plurality of electrodes (81.1 to 81.K) of a plurality of multi-pole elements (87), in the calibration step, - Steps to perform a series of inspection tasks, - A step of monitoring the imaging performance of the multi-beam charged particle microscope (1) or the voltage drift of at least the first voltage source unit (261.3), - A step of triggering a voltage correction step when the imaging performance or the voltage drift exceeds a predetermined threshold, - A step of determining a set of compensating digital control signals for controlling at least the second voltage source unit (261.4), - The step of providing the compensated digital control signal to at least the second voltage source unit (261.4) and Methods that include...

12. The method according to claim 11, wherein the set of compensating digital control signals is determined according to the voltage drift of at least the first voltage source unit (261.3).

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