Multibeam particle beam system and method for operating a multibeam particle beam system

Abstract

Disclosed is a multi-beam particle microscope equipped with an improved micro-optical unit that generates a number of individual beams. The improved micro-optical unit includes means for setting and maintaining the unchanging imaging characteristics of the number of individual beams. The improved micro-optical unit includes, in one example, at least one measuring device used to detect changes in the length, distance, contamination, or degradation of the components of the micro-optical unit during operation. The multi-beam particle microscope includes a control unit that determines the impact of changes in the length, distance, contamination, or degradation of the components on at least one individual beam. The multi-beam particle microscope also includes a compensation element that compensates for the impact on at least one individual beam. Depending on the method of operating the multi-beam particle microscope, the remaining service life of the multi-beam particle microscope that meets the requirements for wafer inspection is also determined.

Description

Technical Field

[0001] The present invention relates to a multi-beam particle beam system. More particularly, the present invention relates to a multi-beam particle microscope having a control unit that guarantees imaging characteristics of a multi-beam particle microscope during operation, and a related method for operating the multi-beam particle microscope.

Background Art

[0002] As smaller and more complex microstructures such as semiconductor components are continuously developed, there is a need to further develop and optimize planar production techniques and inspection systems for inspecting microstructures of small dimensions. Therefore, in order to scrutinize microstructures on a wafer with high precision, inspection means that can be used with high throughput are required.

[0003] A typical silicon wafer used in the production of semiconductor components has a diameter of up to 300 mm. Each wafer is subdivided into repetitive regions (“dies”). A semiconductor device comprises a plurality of semiconductor structures created in layers on the surface of the wafer by planar integration techniques. A semiconductor wafer typically has a flat surface by virtue of the production process. The structure size of the integrated semiconductor structures ranges in this case from a critical dimension (CD) of several μm to 5 nm, and in the near future the structure size will become even smaller. The structure size or critical dimension (CD) is expected to be less than 3 nm in the future, for example 2 nm, or even less than 1 nm. In some applications, the specification requirements regarding the measurement accuracy achieved by inspection equipment are even higher, for example twice as high or one order of magnitude higher. As an example, the width of a semiconductor feature has to be measured with an accuracy of less than 1 nm, for example 0.3 nm or less, and the relative position of semiconductor structures has to be specified with an overlay accuracy of less than 1 nm, for example 0.3 nm or less.

[0004] Multibeam electron microscopes (MSEMs) are a relatively new development in the field of charged particle systems (charged particle beam microscopes, CPMs). Multibeam electron microscopes are disclosed, for example, in U.S. Patent No. 7,244,949 and U.S. Patent Application Publication No. 2019 / 0355544. In the case of a multibeam electron microscope, i.e., an MSEM, the sample is simultaneously irradiated with a number of individual electron beams arranged in a field or raster. For example, 4 to 10,000 individual electron beams can be supplied as primary radiation, and each individual electron beam is separated from adjacent individual electron beams by a distance of 1 to 200 micrometers. An MSEM, for example, has about 100 separated individual electron beams ("beamlets"), which are arranged in a hexagonal raster, for example, and are separated at a distance of about 10 μm. The number of individual charged particle beams (primary beams) are focused onto the surface of the sample being examined by a common objective lens. The sample could be, for example, a semiconductor wafer securely fastened in a wafer chuck mounted on a movable stage. When the wafer surface is irradiated with a charged primary discrete particle beam, interaction products, such as secondary electrons or backscattered electrons, are emitted from the wafer surface. The starting points of the interaction products all coincide with locations on the sample where a large number of primary discrete particle beams are focused. The amount and energy of the interaction products vary depending on the material composition and the surface shape of the wafer. The interaction products form multiple secondary discrete particle beams (secondary beams), which are collected by a common objective lens and imaged onto a detector placed on the detection surface by the projection imaging system of a multibeam electron microscope. The detector comprises multiple detection regions, each with multiple detection pixels, and the detector acquires the intensity distribution of each of the secondary discrete particle beams. In this process, an image plane of, for example, 100 μm × 100 μm is obtained.

[0005] Conventional multibeam electron microscopes comprise a series of electrostatic and magnetic elements. At least some of the electrostatic and magnetic elements are adjustable to match the focal position and stigmation of multiple charged individual particle beams. Conventional multibeam systems with charged particles further comprise at least one crossover plane of primary or secondary charged individual particle beams. Conventional systems further comprise a detection system to facilitate adjustment. Conventional multibeam electron microscopes comprise at least one beam deflector ("deflection scanner") for scanning a region of the sample surface using multiple primary individual particle beams in a single pass to obtain an image plane of the sample surface.

[0006] In conventional multibeam electron microscopes, a first multi-aperture plate or filter plate having a number of first apertures in a first raster array is used to generate a number of individual beams. These individual beams then pass through a further multi-aperture plate, for example, a second multi-aperture plate having a second aperture comprising an array of active electrostatic elements. The first aperture is ideally circular and generates a number of ideal individual beams. Each individual beam ideally passes through its assigned second aperture, centered on the geometric center of the second aperture. In a typical example, in addition to the first and second multi-aperture plates, there is a further multi-aperture plate having an additional aperture.

[0007] Multi-aperture plates may deform or degrade during the operation of a multi-beam microscope. This can result in effects such as at least one individual beam no longer passing through the center of the second aperture of the second multi-aperture plate.

[0008] This can have the effect that, for example, at least one individual beam will no longer pass through the center of the electrostatic field generated in the second aperture. Furthermore, the electrostatic field generated in the second aperture may be disturbed by degradation or contamination. The electrostatic field generated in the second aperture during operation may also be disturbed by increased roughness. Contamination may generate creepage currents that can disturb measurement or control signals.

[0009] International Patent Application No. 2023001401 discloses the possibility of placing a detector on a first multi-aperture plate to measure the absorbed beam current of an incident charged particle beam, which can be used, for example, to control the source current. However, this measured beam current cannot provide any information about the state of the multi-aperture plate. On the contrary, disturbances on the multi-aperture plate that occur during operation may be superimposed on the absorbed beam current, thereby interfering with the measurement of the absorbed beam current and potentially leading to incorrect control of the source current.

[0010] In summary, a problem that arises during the operation of multi-beam microscopes, which have high resolution and precision requirements, is that disturbances occurring during operation can affect many individual beams, making the predetermined method for generating individual beams more difficult. This can, for example, lead to individual beams deviating from their predetermined position in the raster array or from their predetermined shape. [Overview of the project]

[0011] An object of the present invention is therefore to provide an improved multibeam particle microscope suitable for the high resolution and accuracy requirements when performing wafer inspection work. A further object of the present invention is therefore to provide a method for operating a multibeam microscope that is capable of meeting the high resolution and accuracy requirements of wafer inspection work during operation.

[0012] This objective is achieved by the subject matter of the independent claim. Advantageous embodiments of the present invention are evident from the dependent claims.

[0013] This patent application claims priority to German Patent Application No. 102023202582.5, filed on 22 March 2023, the entire scope of its disclosure is incorporated into this patent application by reference.

[0014] In a first exemplary embodiment, an improved multibeam particle microscope is disclosed. The improved multibeam particle microscope includes a device for detecting the properties of at least one multi-aperture plate during operation of the multibeam particle microscope for performing wafer inspection tasks. The improved multibeam particle microscope also includes a control device designed to identify a predictive adverse impact on system performance from a single property.

[0015] A multi-beam system comprises a particle source that generates a particle beam and a micro-optical unit that includes at least one multi-aperture plate or filter plate for generating a number of individual beams. The multi-beam system also includes a beam splitter and objective lens that generate a number of focus points on the image plane. The need for multiple focus points on the image plane is increasing in relation to achieving image quality for a number of individual beams in wafer inspection operations.

[0016] In a multibeam particle microscope, numerous individual beams are generated using a first multi-aperture plate, such as a filter plate, which has numerous first apertures in a first raster array. The numerous individual beams generated in a fixedly defined raster array using the filter plate are actuated by lenses or an array of multipole elements. The action on at least one individual beam includes at least deflection, focusing, or aberration compensation. The first aperture is ideally circular or elliptical, generating numerous ideal individual beams.

[0017] Multiple individual beams then pass through further multi-aperture plates, such as a second multi-aperture plate. For example, the second aperture of the second multi-aperture plate, which comprises an array of active electrostatic or magneto-dynamic elements, is provided with a second raster array, and the first and second raster arrays are mapped to each other by similarity transformation. Ideally, each individual beam passes through its assigned second aperture, centered on the geometric center of the second aperture. In a typical example, the first and second multi-aperture plates are complemented by further multi-aperture plates, each having apertures of further raster arrays that are mathematically similar to the first raster array.

[0018] In one example, the second raster array is identical to the first raster array, and numerous individual beams pass parallel to the filter plate and the second multi-aperture plate or further multi-aperture plates. In a further example, the filter plate with numerous apertures of the first raster array is located at the position of the diffuse electron beam, and the second raster array of the second multi-aperture plate coincides with the stretched first raster array. In a further example, the magnetic field is located between the filter plate and the second multi-aperture plate, and the second raster array is revealed from the first raster array by spiral similarity. In all cases, each individual beam passes through the second aperture at its assigned location, centered, for example, on the geometric center of the assigned second aperture.

[0019] Multi-aperture plates may deform, become contaminated, or degrade during the operation of a multi-beam microscope. The multi-beam particle microscope according to the first embodiment therefore includes a measuring device for identifying deformation, contamination, or degradation of at least one multi-aperture plate. The measuring device may include a strain sensor or interdigital structure for detecting changes in length, a capacitive sensor for detecting changes in distance, and / or an ammeter for detecting leakage current. The strain sensor can be designed as an optical strain sensor, such as a fiber Bragg grating sensor. The strain sensor can be designed as a strain gauge. It is also possible to provide a device for determining the temperature distribution across the entire multi-aperture plate. Deformation of the multi-aperture plate can be estimated from the temperature distribution.

[0020] Deformation may include lateral deformation or bending or twisting of the multi-aperture plate in the beam direction. Deformation may also include deformation of the load-bearing structure of the multi-aperture plate, for example, due to a temperature gradient. Deformation of the load-bearing structure may lead to deformation of the multi-aperture plate, or a change in position or tilt of the multi-aperture plate. Deformation may be permanent or reversible.

[0021] Degradation may include changes in resistivity due to, for example, radiation-induced material modification or thermal diffusion. Degradation may also include changes in the current or voltage bearing capacity of the printed circuit board. Furthermore, surface roughness may be modified as a result of degradation or contamination.

[0022] A multibeam system according to a first exemplary embodiment comprises a control unit connected to at least one measuring device on a multi-aperture plate. The measuring device supplies a measurement signal to the control unit during operation, and the control unit is configured to identify a change in shape, contamination, or degradation of at least one multi-aperture plate from the measurement signal during operation. The control unit is further designed to identify the impact of the change in shape, contamination, or degradation of at least one multi-aperture plate on at least one individual beam.

[0023] By indirectly identifying the impact on at least one individual beam, it becomes possible to eliminate the time-consuming measurement of the imaging characteristics of each individual beam. It is possible to estimate the impact on at least one operating individual beam, and consequently its imaging characteristics, from shape changes, contamination, or degradation of at least one multi-aperture plate, without interrupting wafer inspection operations. Therefore, it is possible to reliably meet the imaging characteristics requirements of wafer inspection operations while increasing throughput.

[0024] The effects resulting from changes in shape, contamination, or degradation of the multi-aperture plate may be identified in advance. Deformation of the multi-aperture plate may result in, for example, at least one individual beam no longer passing through the center of the aperture of the multi-aperture plate. For example, deformation of the first multi-aperture plate or filter plate may result in a number of individual beams being generated in a first raster array that is already shifted, and at least one individual beam no longer passing through the center of the second aperture of the second multi-aperture plate. For example, deformation may exist in the second multi-aperture plate, resulting in at least one individual beam no longer passing through the center of the second aperture of the second multi-aperture plate.

[0025] This results in, for example, the effect that at least one individual beam no longer passes through the center of the electrostatic field generated in the second aperture. This effect may, for example, in addition to the lens effect of the electrostatic lens field, bring about an undesirable deflection effect on the individual beam. In the case of a multipole stigmator, this effect may, for example, generate undesirable aberrations in the individual beam. In the case of a deflector, the individual beam is moved outside the linear field region, which may result in an undesirable different deflection of the individual beam.

[0026] The electrostatic field generated in the aperture may also be disturbed by deterioration or contamination that changes over time. The electrostatic field that changes in the aperture during operation may also be disturbed by increased roughness.

[0027] Such effects that change over time, and the undesirable effects of this influence on the imaging characteristics of the individual beam, are detected by an improved multi-beam particle microscope. The multi-beam particle microscope according to an embodiment thus comprises a control unit configured to identify an undesirable influence on the characteristics of at least one individual beam from deformation, contamination, or deterioration of the multi-aperture plate. According to an embodiment, the control unit is also configured to make a prediction regarding whether the inspection operation can continue to be performed while meeting a predetermined requirement and how much longer it can be performed, based on the undesirable influence on the characteristics of at least one individual beam. This prediction can be used, for example, to identify the need for maintenance inspection, cleaning, recalibration, or replacement of at least one multi-aperture plate.

[0028] The improved multi-beam particle microscope, in one example, further comprises means for compensating for harmful actions or influences on at least one individual beam. The multi-beam system, in one example, further comprises at least one active multi-aperture plate acting on a number of individual beams.

[0029] The control device is designed to generate a correction signal that is used to control means for compensating for adverse effects based on prediction of adverse effects on imaging characteristics. The compensation element is designed to at least partially compensate for the effects on at least one individual beam, and the control unit is configured to determine a control signal for the compensation element and supply the control signal to the compensation element.

[0030] The multi-beam particle microscope according to an embodiment comprises means for compensating for undesirable effects. Such means may include elements of a second multi-aperture plate, and for example, electrostatic elements of the second multi-aperture plate are variously controlled to compensate for beam offsets of individual beams. Such means may further comprise an additional multi-aperture plate, for example, a deflector array for compensating for undesirable beam deflections, or a stigmator array for compensating for undesirable aberrations. Undesirable aberrations may also include changes in the cross-sectional area of an individual beam in a plane parallel to the image plane.

[0031] The compensation element, in one example, comprises an active multi-aperture plate comprising an array made of multipole elements. The control device, in one example, is further designed to identify a prediction of the service life, capable of operating the multi-beam system according to requirements of inspection work.

[0032] The multibeam system, in one example, also includes a movable measuring means for inspecting at least one aperture of a multi-aperture plate, and a positioning element for positioning the movable measuring means. This can further improve the detection of, for example, contamination or roughness on the inner surface of the aperture. The multibeam system may further include a cleaning chamber and a positioning device for positioning at least one multi-aperture plate within the cleaning chamber. The cleaning chamber includes a cleaning apparatus, such as a plasma source for plasma cleaning or a heating element for heat treatment. The cleaning chamber may also be provided for replacing the multi-aperture plate. At least one measuring means for inspecting at least one aperture of the multi-aperture plate can be placed within the cleaning chamber. This allows for, for example, the detection of contamination or roughness on the inner surface of the aperture.

[0033] Multibeam systems are generally particularly susceptible to deformation of the filter plate used to generate numerous individual beams through multiple apertures. The apertures may be elliptical relative to the incident electron beam, for example, due to the deformation of the filter plate. In exemplary embodiments, the multiple aperture openings in the filter plate of a multibeam system are designed with an elliptical cross-sectional shape, the ellipse being designed according to the subsequent beam deflection of each individual beam such that each individual beam has the same circular cross-sectional area in a plane parallel to the image plane. In this example, due to the deformation of the filter plate, the apertures may be shaped differently from the desired ellipse relative to the incident electron beam. The compensation element, in one example, comprises two active multi-aperture plates to at least partially compensate for the impact on at least one individual beam, and the control unit is designed to ensure that, during operation, each individual beam maintains a circular cross-sectional area in a plane parallel to the image plane.

[0034] In a second embodiment, a method for operating a multi-beam system is disclosed that can meet high resolution and accuracy requirements for wafer inspection operations during operation. This method includes detecting at least one characteristic of at least one multi-aperture plate during operation. This method also includes predicting adverse effects on system performance based on the one characteristic. While performing wafer inspection operations using a number of individual beams, measurement signals are acquired from a measuring device connected to at least one multi-aperture plate of the micro-optical unit. This method includes determining the type of current load on the multi-aperture plate from the measurement signals, the type of load including longitudinal elongation, deformation, contamination, or degradation of at least one multi-aperture plate. This method includes identifying the effect of the type of current load on the imaging characteristics of at least one individual beam. The effect may be a deviation in the desired beam direction, a deviation in the desired beam position, or beam aberration of the individual beam. Beam aberration may be, for example, astigmatism or coma aberration. Beam aberration refers to a possible deviation from a circular shape in the cross-sectional area of ​​at least one individual beam in a plane parallel to the image plane. Acquisition, determination, and specific steps may be repeated during the inspection process. Determining the current load diagram may involve model-based analysis or finite element analysis. The measured signals and their respective current load diagrams can be saved.

[0035] This method, in one example, also includes identifying measures to compensate for the impact on at least one individual beam. In that case, this method includes deriving at least one control signal to at least one compensation element that at least partially compensates for the impact on the imaging characteristics of at least one individual beam, and supplying at least one control signal to at least one compensation element.

[0036] In one example, this method includes, as a further step, introducing a measuring means for inspecting at least one aperture of at least one multi-aperture plate and detecting contamination, misalignment, or roughness within at least one aperture.

[0037] This method, in one example, also includes identifying a predicted service life. In this case, the method also includes deriving the remaining service life of the multi-beam system from at least one load diagram, and ensuring that the operation of the multi-beam system meets the requirements for the imaging characteristics of the numerous individual beams within its service life. This method also includes initiating maintenance, cleaning, or replacement of at least one multi-aperture plate. For this purpose, a further step may be provided to move at least one multi-aperture plate or micro-optical unit into a cleaning chamber. Maintenance may include mechanical processing, for example, correcting deformation or positional changes of the multi-aperture plate by a microactuator.

[0038] The method steps of the second embodiment make it possible to ensure that the operation of the multibeam system reliably meets the requirements of wafer inspection work over a longer period of time. The method steps of the second embodiment can be used to predict and control the maintenance, inspection, or replacement of components of the micro-optical unit. This reliably extends the uptime of the multibeam system. The method steps of the second embodiment make it possible to ensure uniformity and isotropy of the imaging characteristics of a number of individual beams, even during high-throughput operation.

[0039] In a third embodiment, a multi-beam system is provided that ensures uniformity and isotropy of the imaging characteristics of a number of individual beams, even during high-throughput operation. The multi-beam system according to the third embodiment comprises a micro-optical unit having a filter plate with multiple apertures for generating a number of individual beams. The multi-beam system also comprises an objective lens that creates multiple focal points of the number of individual beams on the image plane during operation, and a beam splitter that deflects the number of individual beams by a deflection angle greater than 0°. The deflection angle may range, for example, from 3° to 20°, preferably from 4° to 10°. The first filter plate has a number of apertures having an elliptical cross-sectional shape, and the elliptical shape of the apertures is designed according to the subsequent beam deflection of each individual beam such that each individual beam has the same circular cross-sectional area in a plane parallel to the image plane. This ensures uniformity of isotropy of the imaging characteristics of each individual beam on the image plane. The elliptical cross-sectional shape can be designed to compensate for the effect of the beam splitter's deflection angle on the cross-sectional area of ​​multiple individual beams in a plane parallel to the image plane. The multi-beam system may also include at least one active multi-aperture plate, which comprises multiple deflectors that deflect each individual beam axially by a predetermined angle. Each aperture, in this case, has an individual elliptical cross-sectional shape to compensate for the effect of the predetermined deflection of each of the at least one active multi-aperture plate. In one example, the diameter of the aperture having an elliptical cross-sectional shape further has a parameter that depends on the position of the individual beam to compensate for or maintain image shell error (Petzval field curvature) and image plane inclination.

[0040] In one example of a third embodiment, the filter plate or at least one active multi-aperture plate includes a usable measuring device that supplies a measurement signal to a control unit of the multibeam system. The control unit is configured to identify, from the measurement signal, any deformation, contamination, or degradation of the filter plate or at least one active multi-aperture plate during operation. The measuring device may include at least one of the following measuring means: a strain sensor or interdigital structure for detecting changes in length, a capacitive sensor for detecting changes in distance, and / or an ammeter for detecting leakage current. The strain sensor can be designed as an optical strain sensor, such as a fiber Bragg grating sensor. In one example, the multibeam system also includes at least one compensation element that at least partially compensates for the effects of deformation, contamination, or degradation of the filter plate or at least one active multi-aperture plate. The control unit is designed to determine and supply a control signal to the compensation element from the deformation, contamination, or degradation. The compensation element may include an active multi-aperture plate comprising an array of multipole elements. The multibeam system may further include a cleaning chamber and a positioning device for positioning a filter plate or at least one active multi-aperture plate within the cleaning chamber.

[0041] In one embodiment of the present invention, a measuring device that generates a measurement signal for identifying contamination or degradation of at least one multi-aperture plate comprises a differential ammeter DI. The differential ammeter DI is used to measure the difference between the current flowing toward the active multi-aperture plate and the current flowing toward the active multi-aperture plate. The leakage current resulting from contamination or degradation can be estimated by the deviation of the current difference from a predetermined target value.

[0042] In one embodiment of the present invention, a micro-optical unit comprises an electrically conductive radiating layer positioned between two multi-aperture plates, the radiating layer being insulated from adjacent multi-aperture plates by an insulator. For example, the first multi-aperture plate may be a filter plate, and the second multi-aperture plate may be an active multi-aperture plate. The conductive radiating layer is grounded. Therefore, leakage current from the first or second multi-aperture plate is radiated through the conductive radiating layer. Thus, current measurements of particle currents absorbed by the filter plate are not inaccurately performed, for example, by leakage current. Thus, control of the active multi-aperture plate is not inaccurately performed, for example, by leakage current. The conductive radiating layer may further be grounded via an ammeter so that the resulting leakage current can be measured.

[0043] Various embodiments and aspects of the present invention can be combined with one another, either whole or in part, as long as no technical inconsistencies result.

[0044] The present invention will be better understood with reference to the attached figures. [Brief explanation of the drawing]

[0045] [Figure 1] This is a diagram showing a multibeam system. [Figure 2] This figure shows further examples of components in a multibeam system. [Figure 3a] This figure shows the design of a beam forming apparatus comprising a filter plate and at least one active multi-aperture plate. [Figure 3b] This figure shows the design of a beam forming apparatus comprising a filter plate and at least one active multi-aperture plate. [Figure 3c]This figure shows the design of a beam forming apparatus comprising a filter plate and at least one active multi-aperture plate. [Figure 4a] This figure shows the deformation of a multi-aperture plate during operation. [Figure 4b] This figure shows the deformation of a multi-aperture plate during operation. [Figure 4c] This figure shows the surface current during operation and the means for measuring the surface current. [Figure 4d] This figure shows the creepage current during operation and the means for measuring the creepage current. [Figure 4e] This diagram shows the means for measuring surface current. [Figure 4f] This diagram shows the means for measuring surface current. [Figure 5a] This figure shows an example of a measurement means for determining the deformation of a multi-aperture plate. [Figure 5b] This figure shows an example of a measurement means for determining the deformation of a multi-aperture plate. [Figure 5c] This figure shows an example of a measurement means for determining the deformation of a multi-aperture plate. [Figure 5d] This figure shows an example of a measurement means for determining the deformation of a multi-aperture plate. [Figure 6] This figure shows an example of a measuring device for inspecting an aperture. [Figure 7] This diagram shows an example of the arrangement, including inspection, cleaning, and replacement locations. [Figure 8a] This figure shows examples of effects caused by deformation of a multi-aperture plate. [Figure 8b] This figure shows examples of effects caused by deformation of a multi-aperture plate. [Figure 8c] This figure shows examples of effects caused by deformation of a multi-aperture plate. [Figure 8d] This figure shows examples of effects caused by deformation of a multi-aperture plate. [Figure 9a]This figure shows an example of a means to compensate for the effects caused by deformation of a multi-aperture plate. [Figure 9b] This figure shows an example of a means to compensate for the effects caused by deformation of a multi-aperture plate. [Figure 9c] This figure shows an example of a means to compensate for the effects caused by deformation of a multi-aperture plate. [Figure 9d] This figure shows an example of a means to compensate for the effects caused by deformation of a multi-aperture plate. [Figure 10] This diagram shows the method steps for operating a multibeam system. [Modes for carrying out the invention]

[0046] Figure 1 schematically shows a multibeam particle microscope 1. The multibeam particle microscope 1, also referred to below as a multibeam system 1, comprises a beam generator 300 equipped with a particle source 301, such as an electron source, for generating charged particles. A diffuse particle beam 309 is collimated by a series of focusing lenses 303.1 and 303.2 and collides with a multi-aperture array 305. The multi-aperture array 305 comprises a plurality of multi-aperture plates 306 and field lenses 308. The multi-aperture array 305 (also referred to as a micro-optical unit 305) generates a number of individual particle beams 3 or individual electron beams 3. The aperture centers of the micro-optical unit 305 are positioned in a raster array in a first field, which is imaged onto a further raster array formed by beam spots 5 on the object surface 101. The distance between the center points of the beam spots 5 on the object surface 101 can be, for example, 5 μm, 10 μm, or 100 μm. The aperture spacing in a multi-aperture plate is, for example, 100 μm. The aperture diameter D is shorter than the distance between the aperture centers, and in the example of diameter, it is 0.2 times, 0.4 times, and 0.8 times the distance between the aperture centers.

[0047] The micro-optical unit 305 and the field lens 307 are configured to generate a raster array of multiple focal points 323 of the primary beam 3 on the intermediate image plane 325. The plane 325 does not need to be planar and can rather be spherically curved to account for the image field curvature of the subsequent particle optical system.

[0048] The multibeam particle microscope 1 further comprises a system of electromagnetic lenses 103 and objective lenses 102, which image a reduced-size beam focus 323 from the intermediate image plane 325 onto the object plane 101. The first individual particle beam 3 passes between the intermediate image plane 325 and the object plane 101 through a beam splitter 400 and a first collective beam deflector or scanner 500, which are used to deflect multiple first individual particle beams 3 during operation and scan the image plane. The first individual particle beam 3 incident on the object plane 101 forms, for example, a substantially equilateral and equiangular field. The field formed at the incident location 5 may have, for example, rectangular or hexagonal symmetry.

[0049] The object 7 being examined may be any desired type of object, such as a semiconductor wafer, a lithography mask, or a biological sample, and may comprise an array of miniaturized elements. The surface 15 of the object 7 is positioned on the object surface 101 of the objective lens 102. The objective lens 102 may include one or more electro-optical lenses. The objective lens 102 may, for example, be a magnetic objective lens and / or an electrostatic objective lens. The object 7, such as a wafer, is positioned on a moving device or stage 600 such that its surface 15 is on the image plane 101. The surface 15 is aligned perpendicular to the optical axis 105 of the objective lens 102, and it is preferable that a number of individual beams 3 are incident on the object substantially perpendicular to the surface 15 and therefore parallel to the optical axis 105.

[0050] Primary particles of the individual beam 3 incident on the object 7 generate interaction products, such as secondary electrons, backscattered electrons, or primary particles that have moved backward for other reasons. These interaction products are emitted from the surface of the object 7 or from the first plane 101 or the object surface 101. The interaction products emitted from the surface 15 of the object 7 are shaped by the objective lens 102 to form a secondary particle beam 9. In this process, the secondary beam 9 passes through a beam splitter 400 located downstream of the objective lens 102 and is supplied to the projection system 200. The projection system 200 comprises an imaging system with a plurality of electrostatic or magnetic lenses 210.1-210.3, a contrast aperture 222, and a multi-particle detector 209. The incident locations 215 of the second individual particle beam 9 on the detection area of ​​the multi-particle detector 209 are arranged at regular intervals in the third field. Exemplary values ​​are 10 μm, 100 μm, and 200 μm. The projection system further includes a second bulk deflector or scanner 220 used to maintain the incidence location 215 of the second individual particle beam 9 on the multi-particle detector 209 in a fixed position.

[0051] The multibeam particle microscope 1 can be implemented as an integrated unit or in a multi-part configuration and further comprises a computer system or control unit 10 designed to control the individual particle optical components of the multibeam particle microscope 1, as well as to evaluate and analyze the signals obtained by the multi-detector 209 or detection unit 209.

[0052] Further information relating to such multi-beam particle beam systems or multi-beam particle microscopes 1, as well as components used therein, such as particle sources, multi-aperture plates, and lenses, can be obtained from International Patent Applications 2005 / 024881, 2007 / 028595, 2007 / 028596, 2011 / 124352, and 2007 / 060017, as well as German Patent Applications 102013016113 and 102013014976A1, the disclosures thereof fully incorporated into this application by reference.

[0053] The multi-beam system 1 is subject to more stringent requirements, particularly in wafer inspection. For example, the resolution of each subimage captured using each individual particle beam should be identical within a strict tolerance range, for example, better than 3.5 nm, better than 3.0 nm, or even better. The resolution should be independent of direction, for example; that is, the resolution in the x-direction should differ from the resolution in the y-direction by no more than 5%. In this regard, the so-called HV difference is also mentioned. Furthermore, the position of the individual beam spot 5 should be very stable so that the relative positions of the individual subimages are held stably, eliminating the need to correct the offset of many subimages by complex calculations. These stringent requirements lead, firstly, to high requirements regarding the design of the micro-optical unit, and secondly, to high requirements during the operation of the micro-optical unit. The multi-beam system 1 according to embodiments of the present invention is designed to meet these high requirements even during operation. For example, the micro-optical unit 305 is designed to meet these high requirements. For example, the micro-optical unit 305 includes a device for monitoring the micro-optical unit during operation. For example, the micro-optical unit 305 includes means for compensating for effects that occur during operation. The micro-optical unit 305 comprises a series of at least one filter plate 304 and a further multi-aperture plate 306. The micro-optical unit 305 may be designed as an aberration correction unit for a multi-beam particle microscope 1 according to the present invention.

[0054] Figure 2 shows a further embodiment of the beam generator 300. Downstream of the electron source 301 are a first aperture 311 and a first multi-aperture plate or first filter plate 304.1 having a plurality of first apertures. The incident electron beam 309 is partially absorbed by the first filter plate 304.1. Primary particles passing through the plurality of first apertures form a plurality of primary beams or individual particle beams 3. A collimation lens or focusing lens 303 and a further multi-aperture plate follow the first filter plate 304.1. The further multi-aperture plate comprises a second filter plate 304.2, a first active array element 306.1, a second active array element 306.2, and a third active array element 306.3. The second filter plate 304.2 and active array elements 306.1-306.3 form a micro-optical unit 305. The field lens 307 and other components of the multi-beam system 1 follow the micro-optical unit 305; for other components of the multi-beam system 1, please refer to Figure 1 and the related description. The multiple primary beams are deflected by the beam splitter 400 by a deflection angle 109 in the direction of the optical axis 105 of the objective lens 102. The deflection angle 109 can be 3° to 20°, preferably 4° to 10°. However, smaller or larger deflection angles 109 are also possible.

[0055] In particular, wafer inspection requires high standards for the isotropy and uniformity of resolution in the imaging of multiple particle beams. Isotropy of resolution means that the resolution in the x-direction is less than, for example, 5% different from the resolution in the y-direction perpendicular to the x-direction. This deviation is even smaller, preferably less than, for example, 3%. Furthermore, the resolution of the first individual beam should be less than, and preferably less than, 5%, different from the resolution of the second individual beam. Such isotropy and invariance of resolution is achieved when the beam cross-section 115 at the pupil plane 117 is circular and has the same diameter for all beams. Thus, the (actual or virtual) beam cross-sections 113 of all individual beams 3 are identical and circular in a plane 111 parallel to the image plane.

[0056] Each active array element 306.1-306.2 may have at least one to, for example, eight or twelve electrodes in each aperture, so that individual effects can be set for each individual beam by the applied voltage during operation, such effects include, for example, lensing effects by circular electrodes, or deflection effects or beam correction (sometimes called stigmeter effects) by multipolar electrodes.

[0057] Details of an exemplary micro-optical unit 305 are illustrated in detail in Figure 3a. For simplification, only one aperture 85.11 for generating individual beams is depicted. The electron beam 309 is emitted from the electron source 301 and filtered by the first aperture 85.11 of the first filter plate 304.1, resulting in the formation of the i-th individual beam 3.i downstream of the first filter plate 304.1. In this case, the beam cross-section 89.i of the individual beam 3.i matches the aperture shape of aperture 85.11. The individual beam 3.i then passes through the aperture 86.i of the first active array element 306.1, which is designed in this case as a deflector. Voltages applied to two electrodes 87.1 and 87.5 generate an electric field that has a deflection effect on the individual beam 3.i and aligns the individual beam 3.i parallel to the z' axis. In this example, individual beam 3.i has a slightly elliptical beam cross-section 91 after deflection. To meet the high demands of the wafer inspection multi-beam system 1, the beam cross-section 91 must have a predetermined shape downstream of the micro-optical unit 305. To obtain a predetermined elliptical beam cross-section 91, the aperture shape of the first beam-forming aperture 85.11 must have an elliptical design. To obtain an elliptical beam cross-section 91 for each individual beam 3.j (j=1~J), each aperture shape of each first beam-forming aperture 85.j must have a separate design.

[0058] Figure 3c shows a plan view of the first filter plate 304.1, which has a number of elliptical apertures 85.11, 85.12, and 85.21 having various diameters and designed to produce the aforementioned effect, where similar beam cross-sections 91 are produced after each individual beam is individually deflected by at least the first active element 306.1, and the intermediate image of the source spreads over a curved surface 321.

[0059] Due to the requirement for uniform resolution across all individual beams, all beam cross-sections (113, 115) of each individual beam must have the same diameter in the plane 111 parallel to the pupil plane 117 or image plane 101 (see Figure 2). Due to the requirement for isotropy of resolution described above, the beam cross-section of each individual beam must be circular in the plane 111 parallel to the image plane 101. The effect of the deflection angle 109 of the beam splitter 400 has an effect on the beam cross-section of each individual beam, similar to the beam deflection effect by electrodes 87.1 and 87.5 described in Figure 3a. To make this effect available, each first aperture 85 is further slightly elliptical in the direction of the beam deflection of the beam splitter 400. In Figure 3c, the elliptical shape of aperture 85.0 is depicted in a highly exaggerated manner for illustrative purposes. This elliptical shape is equally superimposed for all apertures 85 in the x-direction, depending on the deflection direction of the beam splitter 400. For example, various aperture shapes of the first aperture of the first filter plate can be designed by tracing the beam backward from the image plane 101.

[0060] Here, it is clear that the position and shape of apertures 85, 86, and other apertures must be precisely determined and manufactured in advance, as even slight deviations can quickly become noticeable astigmatism, resulting in aberrations, inaccurate beam deflection angles, or non-circular beam cross-sections. Furthermore, contamination within the apertures can also lead to beam shape deviations. In this regard, deviations occurring during production can often be compensated for, for example, by proper calibration of the deflection angle of the active element 306.1. However, some deviations occur only during operation. Such deviations may include lateral deformation, beam-direction bending or twisting of the multi-aperture plate. Deformations may also include deformation of the load-bearing structure of the multi-aperture plate, for example, due to temperature gradients. Deformation of the load-bearing structure may lead to deformation of the multi-aperture plate, or a change in position or tilt of the multi-aperture plate. Deformations may be permanent or reversible.

[0061] Several examples are shown in Figure 4. Figure 4a shows the case where the film of the multi-aperture plate 306 is fixedly positioned by a fixed connection point 1307. Such a fixed connection point 1307 occurs, for example, when multiple multi-aperture plates 304, 306 are stacked on top of each other and firmly connected to one another. The multi-aperture plate 306a has the desired shape (dashed line) when cold. The multi-aperture plate 306 is heated during operation, and the shape 306b bends due to the fixed mounting point (solid line). In this case, the bend is depicted as a substantially spherical bend, but depending on the fixed connection point 1307, more complex bends and more complex undulations may occur in the film of the multi-aperture plates 304, 306.

[0062] Figure 4b shows a similar case where the multi-aperture plate 306 is mounted with high degrees of freedom at at least one high-degree-of-freedom mounting point 1309. In this case, the multi-aperture plate 306 expands in volume as a result of heating. However, the multi-aperture plate 306 does not necessarily have to bend due to heating; instead, it may extend in length from the fixed mounting point 1307. Thus, aperture displacement occurs (not shown here). From both cases, it is clear that the diameter and position of the aperture, and even the tilt angle as in the case of the fixed mounting point 1307, may change during operation. Furthermore, a temperature gradient may occur, leading to further changes in the shape of the aperture. Some of these changes are reversible, while others remain as permanent deformation of the film of the multi-aperture plate 306.

[0063] In addition to deformation, further deviations may occur in the characteristics of the micro-optical unit 305 during operation. These deviations may be caused by contamination or degradation and may affect individual beams. Degradation may include changes in resistivity due to, for example, radiation-induced material modification or thermal diffusion. Degradation may also include changes in the current-to-voltage or current-to-voltage capability of the printed circuit board. Furthermore, surface roughness may be modified as a result of degradation or contamination.

[0064] An example is shown in Figure 4c. In this example, the micro-optical unit 305 has a stacked structure. The film layer 382 of the first filter plate 304 facing the incident electron beam 309 absorbs most of the incident primary particles and is therefore electrically grounded. For example, the outflowing current IA can be measured to control the current of the source 301 using the measurement of the outflowing current IA. The first filter plate 304 is connected to another multi-aperture plate 306 separated by an insulating layer 380, for example, via a wide range of fixed connection points 1307. The insulating layer 380 may be made of silicon dioxide, for example. During operation, carbon deposits, for example, that form a contamination layer 313, accumulate inside the insulating layer 380 facing the individual beams 3.1 to 3.4. Through the contamination layer 313, leakage current or creepage current 1311a is generated, leading to charging of the first active multi-aperture plate 306.1. This charging results in a change in the electric field intensity at the aperture of the first active multi-aperture plate 306.1, and consequently, a change in the influence of at least one active element on the individual beam 3.1.

[0065] Furthermore, the insulating layer 380 deteriorates. As a result, the insulating layer 380 may lose its insulating effect after relatively long-term use and become conductive, which may lead to further leakage current 1311b, resulting in further charging of the first active multi-aperture plate 306.1 during operation.

[0066] Generally, several factors can overlap to cause displacement during operation. For example, mechanical deformation may be compounded by temperature changes. Mechanical deformation may occur permanently or as irreversible deformation resulting from the combined effects of temperature gradients during operation.

[0067] Accordingly, according to one embodiment of the present invention, at least one measuring device 1601 is provided which is mounted on at least one multi-aperture plate 304, 306 and can be used to monitor the deformation of the film of the multi-aperture plate 304, 306 in operation. Figures 3a and 3b show an example in which a first measuring device 1601.1 is mounted on a first filter plate 304.1 and a second measuring device 1601.4 is mounted on an active multi-aperture plate 306.1. Multiple measuring devices 1601 may also be arranged on at least one multi-aperture plate to detect load diagrams or deformations. Figure 3b shows an example in which three measuring devices 1601.1 to 1601.3 are mounted on the first filter plate 304.1 (only two of which are visible in the cross-sectional image). Unlike Figure 3a, in Figure 3b the incident electron beam is collimated by the focusing lens 303, so that the electron beam is incident on the filter plate 304.1 substantially perpendicularly. Each individual beam 3.i is individually deflected by the active multi-aperture plate 306.1. For a further explanation of Figure 3b, please refer to the explanation of Figure 3a.

[0068] Figure 5 shows several examples of the measuring device 1601. Figure 5a shows the arrangement of three strain gauges 1611.1 to 1611.3 as a first example of the measuring device 1601.a. Multiple strain gauges arranged in different directions make it possible to independently determine length elongation in various directions. Such strain gauges may be based on the piezoresistive effect, for example. The strain gauges can further be designed as optical strain gauges or optical strain sensors, such as fiber Bragg grating sensors. Such optical strain gauges are advantageous because they do not cause undesirable interactions with the electron beam. Figure 5b shows a capacitive sensor 1613 between two adjacent multi-aperture plates 306.1 and 306.2 as a second example of the measuring device 1601.b. Figure 5c shows an interdigital structure 1615, which is a strain sensor, as a third example of the measuring device 1601.c. The measuring device 1601 may further include a temperature sensor or a resistance measuring unit. Furthermore, leakage currents resulting from contamination or degradation can also be measured, for example. Such a measuring device is shown in Figure 4c. The creepage current 1311 leading to the charging of the active multi-aperture plate 306.1 can be dissipated, at least partially, via the ammeter 1617. The creepage current IL can be measured using such a measuring device 1601 in the form of an ammeter 1617.

[0069] However, creepage currents are not limited to the flow from the first multi-aperture plate 304 to the active multi-aperture plate 306.1 and can impair the function of the active multi-aperture plate 306.1. The electrodes of the active multi-aperture plate 306.1 are charged in a focused manner during operation, for example, to generate an electric field that deflects or focuses. The electrodes can be charged by applying a voltage through the DAC. To set or maintain the voltage, a current flows between the control unit 10 and the active multi-aperture plate 306.1 through the DAC. However, in this case, creepage currents and leakage currents 1311c and 1311d are also conducted from the active multi-aperture plate 306.1 to the first multi-aperture plate 304, where they may overlap with the current measurement of the outflow current IA. Therefore, for example, current control of the particle source 301 is incorrect because the control signal (ideally given by the outflow current IA which is proportional to the absorbed particle current) is already incorrect. For example, surface currents and leakage currents from multiple electrodes or all electrodes may overlap, resulting in a considerably large total current as surface current and leakage current, which may be orders of magnitude larger than the current flowing through or from individual electrodes.

[0070] Figure 4d shows a further example of the embodiment. The multi-aperture array or micro-optical unit 305 of this embodiment includes a further conductive plate 361 that forms a radiating layer between the first multi-aperture plate 304 and the active multi-aperture plate 306.1. The creepage currents 1311a and 1311b from the first multi-aperture plate 304, and the creepage currents 1311c and 1311d from the active multi-aperture plate 306.1, first flow to this radiating layer 361, which has, for example, a low-resistance connection to ground. The creepage currents IL can be measured using an ammeter 1617 at this connection without impairing the current measurement IA from which the radiating layer 361 is the source or the function of the active components of the active multi-aperture plate 306.1.

[0071] Figure 4e shows a further embodiment of indirect creepage current measurement. In the example of Figure 4e, the current supplied to the active multi-aperture plate 306 is compared with the current flowing out of the active multi-aperture plate 306. The electrodes of the multi-aperture plate 306 are controlled by a multi-channel DAC, where one DAC channel controls, for example, one electrode (or multiple electrodes, optionally). The DAC is supplied with a power supply voltage that provides power or current for the output voltage. In ideal conditions, the sum of all currents entering or leaving the DAC is very small, for example, zero. Therefore, the sum of the currents at all DAC outputs is also reflected in the supply lines and summed in the supply lines to form the current required inside the DAC. Thus, in ideal conditions, i.e., without contamination or damage to the system, the difference between the supplied current and the conducted current out should match a predetermined difference, which can be verified, for example, by calibration. Any deviation from this difference indicates leakage current or creepage current due to damage to or contamination of the micro-optical unit 305. Figure 4e shows an example of a micro-optical unit 305, including part of the control unit 10. The control unit first detects a source current IA from the first multi-aperture plate 304. The control unit is further connected to a venting layer 361 for the purpose of detecting leakage current IL. The control unit 10 is further connected to an active multi-aperture plate 306 via a DAC (digital-to-analog converter). The control unit 10 and the DAC are designed to generate predetermined individual voltage values ​​at each of the numerous electrodes of the active multi-aperture plate 306. The control unit also has a current source DC for generating voltage. The voltage supplied to the DAC is generated by a voltage regulator UR. The current 391 supplied to the system of the voltage regulator, ASIC, and active multi-aperture plate 306, and the current 393 flowing out of the same system, are measured by a differential ammeter DI(1601). The typical current required to control the DAC or active multi-aperture plate 306 is around a few mA to 100 mA.Under ideal conditions, a differential current in the range of several nA to several μA is expected. The differential current under ideal conditions is measured and stored as a predetermined differential current. The differential current measured by the differential ammeter DI during operation is compared to the predetermined differential current, and the deviation from the predetermined differential current, along with the leakage current IL measured in the radiating layer 361, is analyzed by the signal processor 820. As a result, the current of the source in the control unit 810 can be adjusted, and the control of the active multi-aperture plate 306 can be corrected. As a further result, cleaning or replacement of the micro-optical unit 305 can be triggered. Thus, the differential ammeter DI is another example of a measuring device 1601 for monitoring or detecting the condition of the micro-optical unit 305.

[0072] Figure 4e also illustrates an example of a device (1701) for controlling an active multi-aperture plate (306), comprising a power supply DC, a differential ammeter DI, a voltage regulator UR, and an ASIC, where the power supply DC, the differential ammeter DI, and the voltage regulator UR may be located outside the vacuum isolation wall 550. Measuring the current difference between the current flowing into the DAC and the current flowing out of the DAC is advantageous because the overall current is larger, and therefore the measurement is easier or can be performed with lower resolution. This is advantageous because, in contrast to per-electrode current measurement, only one measurement channel is required outside the vacuum chamber with the isolation wall 550.

[0073] Figure 4f shows an example of a differential ammeter DI. The current 391 that becomes available from the power supply or voltage source in the direction of the voltage regulator UR is measured across the resistor R / shunt, just as the current 393 that flows back from the voltage regulator UR. The current measurement is performed by measuring the voltage drop across a known resistor R / shunt, which is amplified by a differential amplifier 891. The currents 391 and 393 conducted to and returned through the resistor R / shunt are compared by another differential amplifier 891, and the analog signals are fed to an analog-to-digital converter (ADC). The digital results of the differential measurement are fed to a signal processor 820.

[0074] Figure 5d shows a further example of an active multi-aperture plate 306 having a plurality of apertures 86, each comprising a plurality of electrodes 87 that form a multipole element for individual particle beams. The plurality of elements of the active multi-aperture plate 306 are simply drawn in isolation, with only some of them labeled with reference numerals. The active multi-aperture plate 306 is made of an insulator 380, for example, silicon dioxide. Each of the eight electrodes 87 of each multipole element is made of a conductive material, for example, doped silicon. The electrodes are insulated from each other, i.e., separated from each other by gaps or an insulator. Each electrode 87 of the multipole element is connected to a control unit 10 via a feed line 83. The feed line 83 can be generated on the surface of the multi-aperture plate 306, for example, by lithography, and can be made of a metal, for example, aluminum. The control unit 10 is configured to act on each of the plurality of individual beams during operation, for example, to deflect or change the shape of the individual beams. In addition, eight strain sensors 1611.1 to 1611.8 are positioned on the surface of the active multi-aperture plate 306 to detect local expansion of the multi-aperture plate 306 at multiple locations and in multiple directions. The strain sensors 1611.1 to 1611.8 are connected to the control unit 10 by signal connectors 1619.1 to 1619.8. The strain sensors 1611.1 to 1611.8 may also be made of doped silicon, for example, and can therefore be pre-formed during production by a microsystems technology type deposition and structuring process. A further advantage of doped silicon is that it can be used for both strain measurement and temperature measurement. By comparing signals from multiple strain sensors 1611.2a and 1611.2b of different lengths, it is possible to determine expansion and temperature simultaneously and independently.

[0075] Figure 6 shows a further example of the measuring device 1601. The measuring device 1601 consists of an optical measuring device, which can be used to identify, for example, contamination or roughness within apertures 85 and 86 of multi-aperture plates 304 and 306. For simplification, each cross-sectional image depicts only three apertures per multi-aperture plate. The measuring device 1601 consists of an endoscope 1631 equipped with a CMOS sensor 1633 that can move in the direction 1635 across individual apertures 85 and 86 of multi-aperture plates 304 and 306 using a moving device (not shown here). This makes it possible to detect contamination or degradation within apertures 85 and 86 during operation of the multi-beam system 1, during inspection pauses, for example, during wafer changes.

[0076] Figure 7 shows a further example of the measuring device 1601. The measuring device 1601 consists of at least one optical measuring device 1633.1, 1633.2 located within the inspection chamber 1647. The micro-optical unit 305 is moved from the operating position 1641 to the inspection position 1643, for example, by a mounted moving device 1637, when the inspection is paused. The multibeam microscope 1 may also be equipped with two micro-optical units 305a, 305b, where, during operation, the first micro-optical unit 305a operates at the operating position 1641 and the second micro-optical unit is at the inspection position 1643, using optical measuring devices 1639.1, 1639.2 to examine for contamination. In the illustrated example, the inspection chamber 1647 is separated from the vacuum chamber 135 by a valve 1649, and the inspection chamber 1647 simultaneously functions as a cleaning chamber from which contamination can be removed by a cleaning process (plasma cleaning, heat treatment). For this purpose, a further step may be provided in which at least one multi-aperture plate or micro-optical unit is moved to a cleaning chamber. Furthermore, heat treatment or mechanical treatment may be performed at the maintenance or cleaning position, and deformation or positional changes of the multi-aperture plates 304, 306 can be corrected during the treatment, for example, by a microactuator or localized infrared irradiation.

[0077] Generally, it is possible to combine multiple different measuring devices. For example, a measuring device can consist of a group of sensors including a temperature sensor, a strain sensor, a leakage current measuring sensor, an optical measuring device, and an optical endoscope.

[0078] To enable improved separation of mechanical and thermal strains from each other, a reference element may be provided in the measuring device, which is positioned so as not to be subjected to any load, i.e., held in a manner that does not subject it to any force or moment. For example, based on the reference element, mechanical strain or positional changes can be separated from thermal strains.

[0079] Figure 8 shows several examples of loads and effects. In detail, each figure shows only one aperture of each multi-aperture plate. Figure 8a shows the ideal case of lensing effect at the first aperture 86.1 of the active multi-aperture plate 306.3. Figure 8b shows the case where aperture 86.1 is moved laterally by dx as a result of volume expansion of the multi-aperture plate 306.3. The individual beam 3.i no longer incident on the center of the electrostatic lens field and is deflected laterally by an angle dt. Figure 8c shows the case where the multi-aperture plate 306.3 is deformed. In this case, aperture 86.1 can be tilted by a local tilt angle dr with respect to the incident individual beam, and as a result the tilt causes aberrations in the individual beam 3.i, such as astigmatism or coma. Therefore, the diameter of the image point increases to a diameter da.

[0080] Figure 8d shows further loading on the first filter plate 304.1 of the micro-optical unit 305 described in Figure 3a. In the example of Figure 8d, the filter plate 304.1 is deformed or bent by heating, similar to that depicted in the active multi-aperture plate 306 in Figure 4a. Therefore, the aperture 85.11 of the deformed filter plate 304.1 is tilted by a rotation angle dr with respect to the z' axis. The tilt or rotation of the aperture 85.11 results in a change in the cross-sectional shape of the aperture 85.11 with respect to the incident electron beam 309, and the cross-section of the individual particle beam 3.i after passing through the aperture 85.11 has a shape 89b.i that is deviated from the target shape 89a.i. Therefore, the individual particle beam has an individual shape 91b.i that is deviated from the target shape 91a after deflection by the first active multi-aperture plate 306.1. Due to the deformation of the filter plate 304.1, the local inclination angle dr at each aperture 85 of the filter plate 304.1 is different, so each cross section 91b.j of each individual beam 3.j (for J individual beams, j=1 to J) is also slightly different, and each individual beam may have slightly different directional anisotropy, which can lead to differences in resolution in different directions, for example.

[0081] According to an embodiment of the present invention, the multi-beam system 1 includes a control unit 10 that acquires a number of measurement signals from a measuring device 1601 and thereby identifies deformation of at least one multi-aperture plate 304, 306. The impact on a number of individual beams 3, as in the example of Figure 8, can be identified from the deformation thus identified. This impact can be compared with the accuracy requirements of the multi-beam system 1. Based on this impact, it is possible to predict how long the multi-aperture plates 304, 306 can continue to operate within the accuracy requirements of the multi-beam system 1.

[0082] According to embodiments of the present invention, the multibeam system 1 comprises a control unit 10 and at least one means for compensating for the effects of deformation of at least one multi-aperture plate 304, 306. An active multi-aperture plate 306 can be such means. Figure 9a shows an example. In this example, the active multi-aperture plate 306.3 for generating a lens field is equipped with eight electrodes 87.1 to 87.8, rather than just one ring electrode 87 (Figure 9a is a plan view of aperture 86.1). During operation, the same voltages V1 to V8 are supplied to all eight electrodes to produce a lens effect. If deformation that would result in aberration is detected, as shown in Figure 8c, the voltages V1 to V8 are modified accordingly to compensate for, for example, astigmatism (Figure 9b).

[0083] Figure 9c shows a further example. At least one additional active multi-aperture plate 306.5, 306.7 may be provided as a means of compensating for the effects of deformation of at least one active multi-aperture plate 304, 306. In the example of Figure 9c, two additional active multi-aperture plates 306.5 and 306.7 are provided, and the two active multi-aperture plates are designed as a multi-pole deflector with electrode arrays at each aperture, as shown in Figure 9a. The electrodes are controlled by a control unit to compensate for beam offset, for example (shown in Figure 8b).

[0084] Figure 9d shows a further example of compensating for the effects caused by the local tilt angle dr of the filter plate 304. The individual beams 3.i generated at aperture 85 of the filter plate 304 have an undesirable elliptical cross-sectional shape due to the local tilt angle dr, which is a result of deformation due to heating. This elliptical shape can be compensated for by the anamorphic electrostatic lensing effect of the multi-aperture plates 306.5 and 306.7, which are designed as multi-pole array elements, so that the beam cross-sections of each individual beam 3.j in the plane parallel to the image plane 101 are identical and circular or isotropic, as required for isotropic resolution.

[0085] In this way, the measuring means 1601 makes it possible to determine the impact on a number of individual beams 3.j in operation without even an additional measuring system. The means for compensating for the impact makes it possible to at least partially compensate for this impact. Thus, it is possible to ensure that the multi-beam system 1 operates to meet the requirements over a relatively long period of time. In particular, it is possible to increase throughput by making a larger beam current of the electron source 301 available, for example. An increase in beam current leads to a larger thermal load, particularly on the first filter plate 304, resulting in increased volume expansion and deformation, which have adverse effects on the first filter plate 304, as depicted in Figure 8d.

[0086] Figure 10 shows how to operate the multibeam system 1. In the first step S1 during the operation of the multibeam system 1, this method includes acquiring measurement data from at least one measuring means 1601. Step S1 includes, for example, acquiring any of three independent measurement data items from any of the three measuring means 1601.1 to 1601.3 of at least one multi-aperture plate 304 or 306. Step S1 includes acquiring measurement data from measuring means such as a temperature sensor, optical strain sensor, strain gauge, capacitive sensor, or ammeter. Step S1 includes acquiring measurement data from measuring means such as an endoscope 1631 or optical inspection system 1639. Step S1 includes, for example, detection of creepage current IL using an ammeter 1617 (see Figures 4c and 4d). Step S1 includes, for example, detection of differential current using a differential ammeter DI (see Figures 4e and 4f).

[0087] In step S2, the measurement data is converted to digital values, filtered, and compared with calibration values. Filtering may include, for example, time averaging. In one example, the deformation of at least one multi-aperture plate 304, 306 is determined from the filtered measurement data. This deformation determination can be performed based on a model or, for example, by simplified finite element analysis.

[0088] Furthermore, contamination or degradation of the multi-aperture plates 304, 306, or the insulating layer 380 between the multi-aperture plates 304 and 306 can be estimated from the filtered measurement data.

[0089] In step S3, the effects on a number of individual beams are determined. These effects may include the displacement of a single individual beam and the aberration of a single individual beam. Aberrations may result from, for example, a change in the filtering effect of the first aperture 85.11 of the filter plate 304.1 with respect to the beam cross-section 87.1, or from passing through an inclined lens field. Beam offset may result from deformation of the active multi-aperture plate 306.1 designed as a beam deflector, or from passing through a lens field that is laterally offset, for example. Lensing effects may be reduced or increased by the charging of the multi-aperture plate by creepage currents. These cumulative effects on a number of individual beams are compared with requirements for the multi-beam system 1, such as requirements for resolution or requirements for superposition accuracy (so-called superposition requirements).

[0090] In step S4, compensation for this effect is determined and set. For this purpose, a control signal to a predetermined effect compensation means is determined and supplied to the effect compensation means. This means may be, for example, an additional active multi-aperture plate 306, or an active multi-aperture plate 306 with a modified design. The action of the effect compensation means can be identified in advance during calibration and stored in the control unit 10 of the multi-beam system 1. Using this action as a starting point, the effect compensation is calculated and performed.

[0091] In step S5, the remaining service life of the multibeam system 1 is estimated. As described above, permanent deformation or degradation may occur. In other cases, deformation or contamination may continuously increase during operation. Permanent deformation and continuous increase in deformation make the effects more pronounced. For example, if the effects exceed a predetermined size, compensation by step S4 is no longer possible, for example, because the adjustment range of the compensation means is being utilized to its maximum extent, or because higher-order aberrations have already occurred and it is impossible to compensate for them, and therefore the requirements for the multibeam system 1 can no longer be met. The allowable adjustment range of the compensation means and the maximum allowable higher-order aberrations can be determined in advance. In step S5, the remaining service life is calculated from the actual state of the multibeam system 1 and any further expected changes. These changes may be predicted by model-based simulation or by linear extrapolation of the history of the deformation state.

[0092] Next, in step S6, maintenance, component replacement, or recalibration of the multibeam system 1 is performed. Maintenance may include, for example, heat treatment of the multi-aperture plates 304 and 306. Heat treatment may, for example, eliminate permanent deformation at least partially. Contamination can be removed by plasma treatment. In the case of component replacement, a deformed or deteriorated element 305 of the micro-optical unit can be replaced with a new element 305 of the micro-optical unit. Some effects of deformation can be eliminated within the scope of recalibration.

[0093] The present invention can be described by the following clauses. Article 1 - A particle source (301) that generates a particle beam (309), - A micro-optical unit (305) comprising at least one multi-aperture plate (304, 306), - A beam splitter (400) and objective lens (102) that generate a number of focal points (5) on the image plane (101), - Control unit (10), - A measuring device (1601) connected to at least one multi-aperture plate (304, 306) and supplying a measurement signal to the control unit (10) A multibeam system (1) comprising the above, wherein the control unit (10) is configured to detect, during operation, a change in shape, contamination, or deterioration of at least one multi-aperture plate (304, 306) from a measurement signal. Article 2 A multibeam system (1) according to Clause 1, wherein at least one multi-aperture plate (304, 306) comprises a filter plate (304) for generating a number of individual beams (3) from a particle beam (309). Article 3 A multibeam system (1) according to Clause 1 or 2, comprising a micro-optical unit (305) and an active multi-aperture plate (306, 306.1, 306.2, 306.3) acting on a number of individual beams (3). Article 4 A multibeam system (1) according to any one of Clauses 1 to 3, wherein the measuring device (1601) comprises at least one of the following measuring means: a strain sensor (1611), an interdigital structure (1615) for detecting changes in length, and an ammeter (1617) for detecting leakage current (1311). Article 5 The multibeam system (1) according to Clause 4, wherein the strain sensor (1611) is formed as an optical strain sensor, for example as a fiber Bragg grating sensor. Article 6 A multibeam system (1) according to Clause 4, wherein at least one strain sensor (1611) or interdigital structure (1615) is formed on a filter plate (304) or on an active multi-aperture plate (306, 306.1, 306.2, 306.3). Article 7 A multibeam system (1) according to any one of clauses 4 to 6, further comprising a micro-optical unit (305) that dissipates leakage current (1311) via an ammeter (1617) for detecting leakage current (1311). Article 8 A multibeam system (1) as described in any one of Clauses 1 to 7, wherein the measuring device (1601) further comprises a differential ammeter DI for detecting leakage current (1311), the differential ammeter DI being designed to detect the difference between the current (391) flowing into the active multi-aperture plate (306) and the current (393) flowing out of the active multi-aperture plate (306). Article 9 A multibeam system (1) as described in any one of Clauses 1 to 8, wherein the control unit (10) is further designed to identify the impact on at least one individual beam (3) from deformation, contamination, or degradation of at least one multi-aperture plate (304, 306). Clause 10 The multibeam system (1) according to Clause 9, further comprising at least one compensating element that at least partially compensates for an effect on at least one individual beam (3), wherein a control unit (10) is designed to determine and supply a control signal to the compensating element. Article 11 A multibeam system (1) according to Clause 10, wherein at least one compensation element comprises an active multi-aperture plate (306.3, 306.5, 306.7) having an array of multipole elements (315). Article 12 A multibeam system (1) according to any one of clauses 1 to 8, further comprising a movable measuring means (1631) and a positioning element (1635) for positioning the movable measuring means (1631) for inspecting at least one aperture (85, 86) of a multi-aperture plate (304, 306). Article 13 A multibeam system (1) according to any one of clauses 1 to 12, further comprising a cleaning chamber (1647) and a positioning device (1643) for positioning at least one component of a micro-optical unit (305) within the cleaning chamber (1647). Article 14 A multibeam system (1) according to Clause 13, wherein at least one measuring means (1651) for inspecting at least one aperture (85, 86) of a multi-aperture plate (304, 306) is located within a cleaning chamber (1647). Article 15 A multibeam system (1) according to any one of clauses 1 to 14, wherein the first filter plate (304) has a number of elliptical aperture openings (85), and the elliptical shape of the aperture openings is designed according to the subsequent beam deflection of each individual beam (3) such that each individual beam has the same circular cross-sectional area (113) in a plane (111) parallel to the image plane (101). Article 16 A multibeam system (1) according to Clause 15, comprising at least one compensation element comprising two active multi-aperture plates (306.5, 306.7) for at least partially compensating for the effect on at least one individual beam (3.i), and a control unit (10) is designed so that during operation, at least one individual beam (3.i) has a circular cross-sectional area (113) in a plane (111) parallel to the image plane (101). Article 17 A method for operating a multibeam system (1), wherein the method uses a number of individual beams (3) to perform inspection work on a wafer (7), - A step of acquiring a measurement signal from a measuring device (1601) connected to at least one multi-aperture plate (304, 306) or radiating layer (361) of the micro-optical unit (305), - A step of determining the type of current load from the measurement signal, wherein the type of load includes elongation, deformation, contamination, or degradation of the length of at least one multi-aperture plate (304, 306), - A step of identifying the effect of the type of current load on the imaging characteristics of at least one individual beam (3.i) and Methods that include... Article 18 The method according to Clause 17, wherein the step of identifying the impact includes identifying a cross-sectional area (113) of at least one individual beam (3.i) in a plane (111) parallel to the image plane (101). Article 19 The method described in Clause 17 or 18, wherein the steps of obtaining, determining, and identifying are repeated during the inspection work. Article 20 The method used to determine the current load diagram, including model-based analysis or finite element analysis, as described in any one of clauses 17 to 19. Article 21 The method according to any one of the clauses 17 to 20, further comprising the step of saving the measurement signal and the current load diagram. Article 22 - A step of deriving at least one control signal to at least one compensation element (306.3, 306.5, 306.7) in order to at least partially compensate for the effect on the imaging characteristics of at least one individual beam (3.i), - The step of supplying at least one control signal to at least one compensation element (306.3, 306.5, 306.7) and The method described in any one of the clauses 17 to 21, further including the method described in any one of the clauses 17 to 21. Article 23 - A step of introducing measuring means (1631) for inspecting at least one aperture (85, 86) of at least one multi-aperture plate (304, 306), - A step of detecting contamination, deformation, or roughness within at least one aperture (85, 86) and The method described in any one of the clauses 17 to 22, further including the method described in any one of the clauses 17 to 22. Article 24 - A step of deriving the remaining service life of a multi-beam system (1) that satisfies requirements regarding the imaging characteristics of a number of individual beams (3) from at least one load diagram, - A step to initiate maintenance, cleaning, or replacement of at least one multi-aperture plate (304, 306) of the micro-optical unit (305) and The method described in any one of the clauses 17 to 23, further including the method described in any one of the clauses 17 to 23. Article 25 The method according to clause 24, further comprising the step of moving at least one multi-aperture plate (304, 306) or micro-optical unit (305) into a cleaning chamber (1647). Article 26 - A micro-optical unit (305) comprising a filter plate (304) having multiple apertures (85) for generating multiple individual beams (3), - An objective lens (102) that generates a number of focal points (5) of a number of individual beams (3) on the image plane (101), - A beam splitter (400) that deflects multiple individual beams (3) by a deflection angle (10⁹) greater than 0° and A multibeam system (1) comprising a first filter plate (304) having a number of apertures (85) having an elliptical cross-sectional shape, wherein the elliptical shape of the apertures is designed according to the subsequent beam deflection of each individual beam (3) such that each individual beam has the same circular cross-sectional area (113) in a plane (111) parallel to the image plane (101). Article 27 The multibeam system (1) according to Clause 26, wherein the elliptical cross-sectional shape of each of the numerous apertures (85) of the filter plate (304) is designed to compensate for the effect of the deflection angle (109) of the beam splitter (400) on each individual beam (3), so that each individual beam (3) has a circular cross-sectional area (113) in a plane (111) parallel to the image plane (101). Article 28 A multibeam system (1) as described in Clause 26 or 27, further comprising at least one active multi-aperture plate (306, 306.1, 306.2, 306.3, 306.5, 306.7). Article 29 A multibeam system (1) according to Clause 28, comprising at least one active multi-aperture plate (306.1) with a number of deflectors designed to individually deflect each individual beam in the axial direction, and at least one aperture (85) of a filter plate (304) having an individual elliptical cross-sectional shape to compensate for the effects of the deflection of at least one active multi-aperture plate (306.1). Article 30 A multibeam system (1) according to Clause 28 or 29, wherein at least one active multi-aperture plate (306.1) comprises a plurality of deflectors designed to individually deflect each individual beam in the axial direction, and at least one aperture (85) of the filter plate (304) has an individual elliptical cross-sectional shape such that each individual beam (3) has a circular cross-sectional area (113) in a plane (111) parallel to the image plane (101), in order to compensate for the effect of the deflection angle (109) of the beam splitter (400) and the effect of the deflection of at least one active multi-aperture plate (306.1) on each individual beam (3). Article 31 A multibeam system (1) according to any one of clauses 26 to 30, wherein the diameter of the aperture (85) having an elliptical cross-sectional shape further has a parameter that depends on the position of the individual beams in order to compensate for image shell error and image plane inclination. Article 32 A multibeam system (1) as described in any one of clauses 26 to 31, wherein at least one filter plate (304) or at least one active multi-aperture plate (306, 306.1, 306.2, 306.3, 306.5, 306.7) is connected to a measuring device (1601) that supplies a measurement signal to a control unit (10) of the multibeam system (1), and the control unit (10) is configured to identify any change in shape, contamination, or degradation of the at least one filter plate (304) or at least one active multi-aperture plate (306, 306.1, 306.2, 306.3, 306.5, 306.7) from the measurement signal during operation. Article 33 A multibeam system (1) according to any one of clauses 26 to 32, further comprising a micro-optical unit (305) and a conductive diffusing layer (361) for dissipating leakage current (1311). Article 34 A multibeam system (1) according to any one of clauses 32 and 33, wherein the measuring device (1601) comprises at least one of the following measuring means: a strain sensor (1611) or interdigital structure (1615) for detecting a change in length, a capacitive sensor (1613) for detecting a change in distance, and an ammeter (1617) or differential ammeter DI for detecting leakage current. Article 35 A multibeam system (1) according to any one of clauses 32 to 34, further comprising at least one compensating element (306.3, 306.5, 306.7) that at least partially compensates for the effects of shape change, contamination, or degradation of at least one filter plate (304) or at least one active multi-aperture plate (306, 306.1, 306.2, 306.3, 306.5, 306.7), wherein a control unit (10) is designed to determine and supply a control signal to the compensating element (306.3, 306.5, 306.7) from shape change, contamination, or degradation. Article 36 A multibeam system (1) as described in Clause 35, comprising an active multi-aperture plate (306.3, 306.5, 306.7) having an array of multi-pole elements as a compensating element. Article 37 A multibeam system (1) according to any one of clauses 26 to 36, further comprising a cleaning chamber (1647) and a positioning device (1643) for positioning at least one filter plate (304) or at least one active multi-aperture plate (306, 306.1, 306.2, 306.3, 306.5, 306.7) within the cleaning chamber (1647). Article 38 A device (1701) for controlling an active multi-aperture plate (306) for a multi-beam particle beam system (1), wherein the active multi-aperture plate (306) comprises a number of electrodes (87) arranged in a number of apertures (86), and the device (1701) is designed to supply voltages to each electrode (87) that act individually on the individual particle beams (3) of the multi-beam particle beam system (1) during operation, and the device (1701) is equipped with a differential ammeter DI that detects the difference between the current (391) flowing through the active multi-aperture plate (306) and the current (393) flowing out of the active multi-aperture plate (306). Article 39 A micro-optical unit (305) for generating or acting on a number of individual particle beams (3) of a multi-beam particle beam system (1), wherein the micro-optical unit (305) comprises a first multi-aperture plate or filter plate (304), an active multi-aperture plate (306) having a number of electrodes (87), and a conductive radiating layer (361) between the filter plate (304) and the active multi-aperture plate (306), wherein all plates (304, 306, 361) are separated from each other by an insulator (380), and the conductive radiating layer (361) is grounded to radiate leakage current (1311). Article 40 A micro-optical unit (305) according to Clause 39, wherein a conductive dissipation layer (361) is further grounded via an ammeter (1617) for measuring leakage current (1311).

[0094] However, the present invention is not limited to these provisions, and combinations or modifications of these provisions are equally possible and incorporated.

[0095] (Explanation of symbols) 1. Multibeam particle microscope or multibeam system 3. Individual particle beam or multiple individual particle beam 5 Beam Spot 7. Object, for example, wafer 9. Secondary particle beam or multiple secondary particle beams 10 Control Unit 15. Surface of the object 83 Power line 85 Aperture of the filter plate 86 Aperture of Active Array Elements 87 Electrode 89 Beam section downstream of the first aperture 91 Beam cross section after deflection 101 Object surface 102 Objective lens 103 Electromagnetic Lens 105 Optical axis of the objective lens 109 Beam deflection angle of the primary beam by the beam splitter 111 A plane parallel to the image plane 101 113 Beam section 115 Pupil distribution 117 Pupil plane 131 Beam tube 135 Vacuum Chamber 200 Projection Systems 209 Particle detectors 210 Electromagnetic Lens 215 Secondary beam injection location 220 Second Coordinated Deflector 222 Contrast Aperture 300 Beam Generation Devices 301 Particle source 303 Focusing lens 304 Filter Plate 305 Multi-aperture array or micro-optical unit 306 Multi-aperture plate or active array element 307 Field Lens 308 Field Lens 309 Particle beam 311 aperture 313 Contaminated layer 315 Multipolar elements 323 Focus point 325 Intermediate image plane 361 Radiation layer 380 Insulator 382 Membrane 391 Inflow current 393 Outflow current 400 Beam Splitter 500 Beam deflection systems or scanners 550 Vacuum Enclosure Wall 891 Differential Amplifier 1307 Fixed connection point 1309 Support points with a high degree of freedom 1311 Leakage current 1601 Measuring device 1611 Strain Gauge 1613 Capacitive Sensor 1615 Interdigital Structure 1617 Ammeter 1619 Electrical signal connection section 1631 Movable measuring means 1633 Camera Sensor 1635 Positioning device 1637 Positioning device 1639 Optical Inspection System 1641 Operating position 1643 Inspection and maintenance locations 1647 Cleaning Chamber 1649 Air block 1651 Measuring means 1701 Device for controlling an active multi-aperture plate

Claims

1. - A particle source (301) that generates a particle beam (309), - A micro-optical unit (305) comprising at least one multi-aperture plate (304, 306), - A beam splitter (400) and objective lens (102) that generate a number of focal points (5) on the image plane (101), - Control unit (10), - A measuring device (1601) connected to at least one of the multi-aperture plates (304, 306) and supplying a measurement signal to the control unit (10) A multibeam system (1) comprising the control unit (10) configured to detect, during operation, a change in shape, contamination, or deterioration of at least one multi-aperture plate (304, 306) from the measurement signal.

2. The multibeam system (1) according to claim 1, wherein the at least one multi-aperture plate (304, 306) comprises a filter plate (304) for generating a number of individual beams (3) from the particle beam (309).

3. The multibeam system (1) according to claim 1 or 2, wherein the micro-optical unit (305) comprises active multi-aperture plates (306, 306.1, 306.2, 306.3) that act on the numerous individual beams (3).

4. The multibeam system (1) according to any one of claims 1 to 3, wherein the measuring device (1601) comprises at least one of the following measuring means: a strain sensor (1611), an interdigital structure (1615) for detecting changes in length, and an ammeter (1617) for detecting leakage current (1311).

5. The multibeam system (1) according to claim 4, wherein the strain sensor (1611) is formed as an optical strain sensor, for example as a fiber Bragg grating sensor.

6. The multibeam system (1) according to claim 4 or 5, wherein at least one strain sensor (1611) or interdigital structure (1615) is formed on a filter plate (304) or on an active multi-aperture plate (306, 306.1, 306.2, 306.3).

7. The multibeam system (1) according to any one of claims 4 to 6, wherein the micro-optical unit (305) further comprises a conductive radiating layer (361) that radiates the leakage current (1311) via the ammeter (1617) in order to detect the leakage current (1311).

8. The multibeam system (1) according to any one of claims 1 to 7, wherein the measuring device (1601) further comprises a differential ammeter DI for detecting the leakage current (1311), and the differential ammeter DI is designed to detect the difference between the current (391) flowing to the active multi-aperture plate (306) and the current (393) flowing from the active multi-aperture plate (306).

9. The multibeam system (1) according to any one of claims 1 to 8, wherein the control unit (10) is further designed to identify the impact on at least one individual beam (3) from the shape change, contamination, or degradation of the at least one multi-aperture plate (304, 306).

10. The multibeam system (1) according to claim 9, further comprising at least one compensating element for at least partially compensating for the effect on at least one individual beam (3), wherein the control unit (10) is designed to determine and supply a control signal to the compensating element.

11. The multibeam system (1) according to claim 10, wherein the at least one compensation element comprises an active multi-aperture plate (306.3, 306.5, 306.7) having an array of multipole elements (315).

12. A multibeam system (1) according to any one of claims 1 to 8, further comprising a movable measuring means (1631) and a positioning element (1635) for positioning the movable measuring means (1631) for inspecting at least one aperture (85, 86) of a multi-aperture plate (304, 306).

13. The multibeam system (1) according to any one of claims 1 to 12, further comprising a cleaning chamber (1647) and a positioning device (1643) for positioning at least one component of the micro-optical unit (305) within the cleaning chamber (1647).

14. The multibeam system (1) according to claim 13, wherein at least one measuring means (1651) for inspecting at least one aperture (85, 86) of a multi-aperture plate (304, 306) is located within the cleaning chamber (1647).

15. The multibeam system (1) according to any one of claims 1 to 14, wherein the first filter plate (304) has a number of elliptical aperture openings (85), and the elliptical shape of the aperture openings is designed according to the subsequent beam deflection of each individual beam (3) such that each individual beam has the same circular cross-sectional area (113) in a plane (111) parallel to the image plane (101).

16. The multibeam system (1) according to claim 15, wherein the at least one compensation element comprises two active multi-aperture plates (306.5, 306.7) for at least partially compensating for the effect on at least one individual beam (3.i), and the control unit (10) is designed so that during operation the at least one individual beam (3.i) has a circular cross-sectional area (113) in a plane (111) parallel to the image plane (101).

17. A method for operating a multibeam system (1), wherein the method performs a wafer (7) inspection using a number of individual beams (3), - A step of acquiring a measurement signal from a measuring device (1601) connected to at least one multi-aperture plate (304, 306) or radiating layer (361) of the micro-optical unit (305), - A step of determining the type of current load from the measurement signal, wherein the type of load includes elongation, deformation, contamination, or deterioration of the length of at least one multi-aperture plate (304, 306), - A step of identifying the effect of the type of current load on the imaging characteristics of at least one individual beam (3.i) Methods that include...

18. The method according to claim 17, wherein the step of identifying the influence includes identifying a cross-sectional area (113) of at least one individual beam (3.i) in a plane (111) parallel to the image plane (101).

19. The method according to claim 17 or 18, wherein the steps of acquiring, determining, and identifying are repeatedly performed during the inspection operation.

20. The method according to any one of claims 17 to 19, wherein the determination of the current load diagram includes model-based analysis or finite element analysis.

21. The method according to any one of claims 17 to 20, further comprising the step of saving the measurement signal and the current load diagram.

22. - A step of deriving at least one control signal to at least one compensation element (306.3, 306.5, 306.7) in order to at least partially compensate for the effect of the at least one individual beam (3.i) on the imaging characteristics, - The step of supplying the at least one control signal to the at least one compensation element (306.3, 306.5, 306.7) and The method according to any one of claims 17 to 21, further comprising:

23. - A step of introducing measuring means (1631) for inspecting at least one aperture (85, 86) of at least one multi-aperture plate (304, 306), - A step of detecting contamination, deformation, or roughness within at least one aperture (85, 86) and The method according to any one of claims 17 to 22, further comprising:

24. - A step of deriving the remaining service life of the multi-beam system (1) that satisfies the requirements for the imaging characteristics of the numerous individual beams (3) from at least one load diagram, - A step of starting maintenance, inspection, cleaning, or replacement of at least one multi-aperture plate (304, 306) of the micro-optical unit (305) and The method according to any one of claims 17 to 23, further comprising:

25. The method according to claim 24, further comprising the step of moving the at least one multi-aperture plate (304, 306) or the micro-optical unit (305) into a cleaning chamber (1647).

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