Multi-beam charged particle microscope design with improved detection system for secondary electron imaging over a large range of primary electron impact energies

Abstract

A multi-beam charged particle system having a secondary electron imaging system configured to compensate for imaging or pupil aberrations over a wide range of primary charged particle impact energies and a method of operating the multi-beam charged particle system are provided. With the disclosed system and method, a systematic approach to compensating for imaging or pupil aberrations of a secondary electron imaging system is implemented. The invention is applicable to wafer inspection with a multi-beam charged particle system.

Description

Technical Field

[0001] This invention relates to a multi-beam charged particle microscope having an improved imaging system for imaging secondary electrons onto a detector, and a method of operating a multi-beam charged particle microscope with improved performance. Background Technology

[0002] WO 2005 / 024881 A2 discloses an electron microscopy system that utilizes multiple electron beams to perform parallel scanning of an object to be examined using clustered electron beams. Clustered primary charged particle beams are generated by guiding a primary charged particle beam onto a multi-beam forming unit comprising at least one porous plate with multiple openings. A portion of the electron beam is incident on and absorbed by the porous plate, while another portion is delivered through the multiple openings of the porous plate. Thus, an electron beam is formed in the beam path downstream of each opening, its profile defined by the profile of the corresponding opening. The multiple primary charged particle beams are focused onto the surface of the sample by an objective lens. Secondary electrons or backscattered electrons are emitted at the interaction volumes between the multiple focal points of the primary charged particle beams and the sample. Thus, the multiple secondary electron beams are emitted from the sample, focused, and imaged onto a detector. Each secondary beam is incident on a separate detector element or a set of detector elements, such that the intensity of the secondary electrons subsequently detected provides information about the sample surface at a location where a corresponding primary beam is incident on the sample. A small cluster is systematically scanned on the sample surface to produce an electron micrograph of the sample.

[0003] Generally, the imaging contrast of a multi-beam scanning electron microscope (MBS) depends on the signal generated by secondary electrons. This signal depends on the secondary electron (SE) yield of each primary electron and the geometric focusing efficiency of the electron microscope. The SE yield depends on the material properties and the kinetic energy of the primary electrons. The small beam of secondary electrons focused by the objective lens is then guided to the detector by the secondary electron imaging system. The imaging performance of the secondary electron imaging system is crucial to the imaging contrast. For example, the secondary electron imaging system forms multiple focal points for the secondary electron beam on the detector plane. Point aberrations can cause crosstalk between signals corresponding to individual secondary electron beams, and thus may lead to reduced signal contrast.

[0004] The signal and resolution of a multibeam scanning electron microscope also depend on the impact energy of the primary electron. In some cases, higher resolution can be achieved using lower impact energies. Typically, the impact energy of the primary electron is adjusted to meet the needs of the inspection task, for example, depending on the combination of materials to be examined or the charging characteristics of the sample. With different impact energies adjusted in, for example, the range from 100V to 2kV or even higher, the kinetic energy of the secondary electron also varies greatly.

[0005] Therefore, high performance requirements are placed on secondary electron imaging systems. Thus, a secondary electron imaging system with reduced crosstalk is needed. Therefore, a secondary electron imaging system with reduced aberrations is needed. Furthermore, an improved secondary electron imaging system with reduced aberrations based on the large kinetic energy of secondary electrons is also required.

[0006] Different mechanisms have been proposed to improve the imaging contrast of multibeam electron microscopes. US 11 049 686 BB, US 10 896 800 BB, US 10 811 215 B2, and WO 2021 239380 A1 describe configurations of several active electrostatic or magnetic dynamic elements within secondary electron imaging systems. However, these prior art systems do not describe the proper selection and adjustment of the active electrostatic or magnetic dynamic elements.

[0007] Generally, the components used for focus adjustment, image magnification, and image rotation within a secondary electronic imaging system are known in the prior art. For example, US 9 368 314 BB, US 7 601 972 BB, US 7 049 585 BB, US 6992 290 BB, US 2009 014 649 AA, or US 8362425 BB mention zoom lenses and rotation compensators in secondary electronic imaging systems. However, prior art, such as US 2016 / 0268096, only provides simplified sketches of secondary electronic imaging systems. These examples only provide the basic concept of a secondary electronic imaging system and do not simplify it to a practical design. Therefore, the prior art requires experts to design secondary electronic imaging systems through trial and error. Thus, proper guidance is needed on how to configure components and how many of these components are required to implement the specific requirements of a secondary electronic imaging system.

[0008] DE 10 2018 124 219 A1 and DE 10 2022 131 862 A1 provide further background information for this patent application. Summary of the Invention

[0009] This invention provides a multi-beam charged particle system and a method for operating the multi-beam charged particle system to acquire images with high image contrast. One objective of this invention is to achieve this through an improved system design of a secondary electron imaging system.

[0010] This patent application claims priority to German Patent Application No. 10 2023 211 672.3, filed on November 23, 2023, the entire disclosure of which is incorporated herein by reference.

[0011] An improved multi-beam charged particle beam system and an improved method of operating the system, according to embodiments, provide aberration compensation over a wide range of secondary electron kinetic energy within the secondary electron beam path. This wide range of secondary electron kinetic energy is related to the wide range of primary charged particle landing energy (LE). The primary charged particle landing energy (LE) typically varies over a wide range depending on the landing energy required for the inspection task. Landing energy can be used to adjust, for example, the resolution of the imaging task or the charging behavior of the sample. Different inspection tasks for semiconductor wafers may require different landing energies, thus altering the kinetic energy of the secondary electrons. At least the correct selection of the position of the first compensator is crucial for compensating for aberrations caused by electro-optical elements. Aberrations in multi-beam secondary electron imaging systems typically have a specific dependence on the field coordinates of the object plane. Therefore, these aberrations are described by aberration vector components, which are typically given by polynomial terms with low-order terms, such as constant aberrations, including axial astigmatism, pupil distortion (i.e., different pupil magnifications along x and y), field distortion (i.e., different field magnifications along x and y), quadratic field distortion (i.e., distortions with quadratic correlation along the x and y field coordinates), and linear field astigmatism (i.e., astigmatism linearly dependent along the x or y field coordinates). However, the present invention is not limited to these aberration vector components, but can also be applied to other aberration vector components.

[0012] Typically, aberrations are introduced by specific elements of a secondary electron imaging system, possessing specific characteristics of aberration vector components and compensable only by compensators with similar characteristics of the aberration vector components. According to an embodiment of the invention, this is achieved by placing the compensator at a position within the secondary electron beam path, having a similar ratio SAR between the diameter of a single secondary electron beam and the diameters of multiple secondary electron beams. The secondary electron beam path is affected by the kinetic energy of the secondary electrons and therefore depends on the impact energy of the primary electrons. In embodiments of the invention, at least two compensators or astigmatism reducers are applied, configured to jointly compensate for aberrations over a wide range of impact energies. Therefore, variations in the aberration vector introduced by specific electron optical elements can be compensated, even if the kinetic energy of the secondary electrons changes according to variations in the primary electron impact energy caused by voltage variations supplied to the sample or wafer. In one embodiment, the position of the compensator is selected based on different ratio SARs of the electron optical elements within the impact energy range. Using, for example, previously determined aberration vectors for the electron optical elements targeting aberrations, control of the secondary electron imaging system can be implemented during use within the impact energy range. By utilizing previously determined knowledge, such as the actuation effect of a compensator for a set of impact energies, control of the secondary electronic imaging system can be implemented during use within the impact energy range.

[0013] According to a first embodiment, a multi-beam charged particle system includes an object illumination unit configured to form multiple focal points of a plurality of primary charged particle beams in an object plane. The multi-beam charged particle system further includes a sample stage configured to hold the surface of an object in the object plane; and a voltage supply unit for providing a voltage VS to the sample, the voltage supply unit being configured to set a first impact energy LE1 of the primary charged particles of the plurality of primary charged particle beams. The multi-beam charged particle system further includes a detection unit. The detection unit forms at least a portion of a secondary electron imaging system configured to image the plurality of secondary electron beams along a secondary electron beam path onto a detector, the plurality of secondary electron beams being excited at multiple focal points on the object surface. The multi-beam charged particle system further includes a beam splitter for separating the plurality of primary charged particle beams from the plurality of secondary electron beams. The multi-beam charged particle system further includes: at least a first electron optical element disposed at a first position within the secondary electron imaging system, having a first ratio SAR1 of the beam diameter of a single secondary electron beam relative to the diameters of the plurality of secondary electron beams at a first impact energy LE1; and a first astigmatism reducer, the aberrations being caused by the first electron optical element. The first compensator is disposed at a second position within the secondary electron imaging system, having a second ratio SAR2 at the first impact energy LE1, wherein the second ratio SAR2 is the same as or deviates from the first ratio SAR1 by no more than 0.1.

[0014] The kinetic energy of the secondary electron depends on the selected impact energy LE1 of the primary electron. The secondary electron beam path within the secondary electron imaging system depends on the kinetic energy of the secondary electron, and therefore also on the selected impact energy LE1 of the primary electron. The aberrations introduced by the first electron optical element depend on the ratio SAR of the beam diameter of a single secondary electron beam relative to the diameters of multiple secondary electron beams at the location of the first electron optical element. The ratio SAR is different for each impact energy or kinetic energy of the secondary electron. Therefore, the aberrations introduced by the first electron optical element are different for each impact energy. According to the invention, at least a first compensator is configured at a location within the secondary electron beam path, and its ratio SAR is similar to that of the first electron optical element at the selected impact energy LE. Similarly, this means a maximum deviation of 0.1.

[0015] In one example, the first electron optical element is at least a portion of the beam splitter. The beam splitter may have separate components, including, for example, components within the primary and secondary electron beam paths, and components only within the secondary electron beam path. A portion of the beam splitter is typically an element that disrupts the rotational symmetry of the secondary electron beam path. Therefore, at least a portion of the beam splitter causes certain image and pupil aberrations specific to the field coordinates.

[0016] In one example, at least the first compensator or astigmatism corrector is a multipole element. Such a multipole element comprises a plurality of electrodes or coils arranged around the beam path for forming a non-uniform field distribution within the compensator. The number of electrodes or coils can be at least four, six, eight, or even more, such as twelve. Thus, various non-uniform field distributions can be adjusted. In one example, the non-uniform field distribution achieved by the compensator is described by an orthogonal set of non-uniform field distributions, for example by a polynomial expansion similar to a Zernike polynomial expansion. However, the compensator is not limited to a multipole element, but can be, for example, an electron optical lens element configured to be displaced or tilted within the secondary electron beam path.

[0017] In one example, the detection unit further includes an aperture stop disposed at the pupil plane of the secondary electron beam path at the first selected impact energy LE1. This aperture stop is used to uniformly filter the pupil or angular intensity distribution of each of the plurality of secondary electron beams.

[0018] In one example, the multi-beam charged particle system further includes a second compensator for aberrations within the secondary electron imaging system. In another example, the second compensator is positioned at a third location within the secondary electron imaging system, having a third ratio SAR3 at a first selected impact energy LE1, wherein at the location of the first compensator, this third ratio SAR3 differs from the second ratio SAR2. Therefore, two compensators with different ratios SAR2 and SAR3 are provided, thus having different effects on the imaging aberrations of the secondary electron imaging system at the first selected impact energy LE1. In one example, the first and second compensators are configured to jointly compensate for the aberrations of the first electron optical element at the first impact energy LE1. In yet another example, the first and second compensators are further configured to jointly compensate for the aberrations of the first electron optical element at a second impact energy LE2 or a primary charged particle, the second impact energy LE2 being different from the first impact energy LE1. For different second impact energies LE2, the ratios SAR1, SAR2, and SAR3 of each of the first electron optical element, the first compensator, and the second compensator differ from the ratios SAR1, SAR2, and SAR3 at the first impact energy LE1. However, by appropriately selecting the position of the first compensator, whose ratio SAR2 is at least similar to the ratio SAR1 of the first electro-optical element under the first impact energy LE1, and selecting the position of the second compensator, whose ratio SAR3 is at least similar to the ratio SAR1 of the first electro-optical element under the second impact energy LE2, aberration compensation can be performed over a wide range of impact energy LE.

[0019] In one example, the secondary electron beam path within the secondary electron imaging system further includes an intermediate image plane at the first impact energy LE1. The first compensator is positioned upstream of the intermediate image plane relative to the propagation direction of the secondary electrons, and the second compensator is positioned downstream of the intermediate image plane. In an alternative example, the first compensator is positioned upstream of the aperture stop relative to the propagation direction of the secondary electrons, and the second compensator is positioned downstream of the aperture stop within the secondary electron imaging system.

[0020] In one example, the multi-beam charged particle system further includes at least one correction lens within the secondary electron imaging system, configured to adjust the pupil plane at the aperture stop position using a second impact energy LE2 different from the first impact energy LE1. The pupil plane is defined as an intersecting plane, and its position within the secondary electron beam path typically depends on the kinetic energy of the secondary electrons or the impact energy LE of the primary electrons. Using the correction lens, the pupil plane can be adjusted at the aperture stop position, independent of the selected second impact energy LE.

[0021] According to a second embodiment, the multi-beam charged particle system includes an object illumination unit configured to form multiple focal points of a plurality of primary charged particle beams in an object plane. The multi-beam charged particle system further includes a sample stage configured to hold the surface of an object in the object plane. The multi-beam charged particle system further includes a voltage supply unit for providing a voltage VS to the sample, the voltage supply unit being configured to adjust the impact energy LE of the primary charged particles of the plurality of primary charged particle beams to a range between 100 eV or less and 2 keV or greater. The multi-beam charged particle system further includes a detection unit forming at least a portion of a secondary electron imaging system for imaging the plurality of secondary electron beams from the object surface onto a detector. Secondary electrons are excited and accelerated to kinetic energy at the plurality of focal points on the object surface, the kinetic energy depending on the selected impact energy LE. The multi-beam charged particle system further includes a beam splitter for separating the plurality of primary charged particle beams from the plurality of secondary electron beams. The multi-beam charged particle system further includes a first compensator and a second compensator configured to jointly compensate for aberrations in the electron optics of a secondary electron imaging system within the secondary electron kinetic energy range of the multiple secondary electron beams, which corresponds to the range of the impact energy LE of the primary charged particle. For example, the aberrations are caused by a portion of the beam splitter.

[0022] In one example, the multi-beam charged particle system further includes an aperture stop and at least one correction lens within a secondary electron imaging system. The correction lens is configured to adjust the pupil plane at a location of the aperture stop for each impact energy within the impact energy range LE of the primary charged particle beam.

[0023] In one example, the secondary electron beam path of the secondary electron imaging system is contained between the object plane and the image plane, wherein detectors are arranged in the order of a first pupil plane, an intermediate image plane, and a second pupil plane.

[0024] In one example, the first compensator is disposed in the secondary electron beam path between the first pupil plane and the intermediate image plane, and the second compensator is disposed in the secondary electron beam path between the intermediate image plane and the second pupil plane. In another example, the secondary electron imaging system further includes a third compensator. The third compensator may be disposed between the second pupil plane and the image plane of the secondary electron imaging system.

[0025] In another example, the first compensator is disposed in the secondary electron beam path between the first pupil plane and the second pupil plane, and the second compensator is disposed between the second pupil plane and the image plane of the secondary electron imaging system.

[0026] In one example, the multi-beam charged particle system includes a first electron optical element disposed at a first location within the secondary electron imaging system, having a first ratio SAR1 at a first impact energy LE1, where the diameter of a single secondary electron beam is relative to the diameters of the plurality of secondary electron beams. At least one of a first compensator or a second compensator is disposed at a second location within the secondary electron imaging system, having a second ratio SAR2 at the first impact energy LE1, wherein the second ratio SAR2 is the same as or deviates from the first ratio SAR1 by no more than 0.1. In one example, at least one of the compensators is a multipole element or an astigmatism reducer.

[0027] According to one embodiment, a method for operating a multi-beam charged particle system is provided. The method includes the steps of positioning an inspection point on a wafer within the field of view of the multi-beam charged particle system using a wafer stage, and providing a sample voltage VS to the wafer via a voltage supply unit to adjust a selected impact energy LES of a primary electron within an impact energy range. The method further includes the step of determining at least a first sensitivity matrix S(LES;1) of at least a first compensator, wherein f=1 for the selected impact energy LES. The method includes determining aberrations of a secondary electron imaging system at the selected impact energy LES and determining a first actuation of at least the first compensator at the selected impact energy LES to compensate for the aberrations. The method further includes applying the first actuation of at least the first compensator and performing an inspection task. Thus, aberration compensation is achieved, and the inspection task is performed using high imaging contrast.

[0028] In one instance, the determination of aberrations involves describing the aberrations using an aberration vector WR(LES). This aberration vector WR(LES) contains at least two pre-selected aberration vector components chosen from a group comprising normalized aberration vector components including axial astigmatism, pupil distortion, field distortion, second-order field distortion, and linear field astigmatism. Thus, for example, at least a portion of the aberrations of a portion of a beam splitter can be described.

[0029] In one example, the method includes determining a second sensitivity matrix S(LES; f=2) of the second compensator, where f=2 for a selected impact energy LES; and determining a second actuation of the second compensator at the selected impact energy LES.

[0030] In one instance, the step of determining the first and second actuation of the at least first and second compensators includes determining at least one actuation amplitude C(n,f) of a plurality of normalized actuation modes M(n) for each compensator.

[0031] In one instance, the step of determining the first and second actuations of at least the first and second compensators includes performing matrix equations. The optimization is performed, where the aberration vector is WR(LES), the actuation amplitude of the multiple normalized actuation modes M(n) of each compensator is C(n,f), the sensitivity matrix of each compensator with exponent f is S(LES; f), and a predetermined first weighting function is G(n,f).

[0032] In another instance, the steps of determining the first and second actuations of at least the first and second compensators involve performing optimization of the matrix equations, including minimizing the actuation amplitude C(n,f) of multiple normalized actuation modes M(n) for each compensator. In one instance, the optimization of the matrix equations is written as follows: The aberration vector is WR(LES), the actuation amplitude of the multiple normalized actuation modes M(n) of each compensator is C(n,f), the sensitivity matrix of each compensator is S(LES;f), a set of predetermined first weighting functions is G(n,f), and a second set of predetermined second weighting functions is T(n,f).

[0033] In one instance, the value of the first weighting function G(n,f) is set to 1.

[0034] In one instance, the first weighting function G(n,1) of the first compensator is set to the value G(n,1)>1, where f=1 for the first selected impact energy LES1 and G(n,1)=0 for the second impact energy LES2.

[0035] In one instance, the step of determining the sensitivity matrix S(LES;f) of the compensator includes determining the sensitivity matrix of the compensator based on a set of previously determined sensitivity matrices received from memory. S The sensitivity matrix S(LES;f) is determined using (LE(q);f). The previously determined sensitivity matrix... S (LE(q);f) is determined, for example, under a set of different impact energies LE (q=1...Q). In one instance, it is determined by interpolation for at least two different impact energies LE(q1) and LE(q2) from a previously determined sensitivity matrix. S (LE(q); f) is used to interpolate the sensitivity matrix S(LES; f) of the compensator.

[0036] In one instance, the method further includes the step of determining the aberrations of the secondary electron imaging system at a selected impact energy LES by using a monitoring system. In one instance, the aberrations of the secondary electron imaging system at the selected impact energy LES are determined based on at least two previously determined aberration vectors WR(Le(q)) received from a memory.

[0037] In one embodiment, a method for calibrating a compensator in a secondary electron imaging system is provided. This method enables calibration of a compensator in a multi-beam charged particle system within a range of impact energy LE. The method includes determining a set of N normalized actuation modes M (n=1...N) for the compensator. The normalized actuation modes M(n) can be derived, for example, from Zernike polynomial expansions. The method further includes determining an aberration vector WR of the secondary electron imaging system, wherein the aberration vector WR comprises at least K=2 normalized aberration vector components selected from a group of normalized aberration vector components, including axial astigmatism, pupil distortion, field distortion, secondary field distortion, and linear field astigmatism.

[0038] The method further includes the steps of individually applying each normalized actuation mode M(n) with an actuation amplitude C(n) at the compensator (264); and adjusting a first impact energy LE(1) from a set of impact energies LE(q) and determining the change in aberration vector dW under the first impact energy LE(1) caused by applying the actuation mode M(n) to the compensator. The method includes the steps of repeatedly adjusting the impact energy and determining the change in aberration dW for each impact energy LE(q) = (2...Q) and each normalized actuation mode M(n) in the set of impact energies. The method further includes the steps of determining, for each impact energy LE(q), a normalized sensitivity matrix S(k=1..K, n=1...N, LE(q)) of the K normalized aberration vector components of each normalized actuation mode M(n=1...N); and storing the multiple sensitivity matrices S(k=1..K, n=1...N, LE(q)) in memory for later use during the performance of an inspection task.

[0039] In one instance, the step of determining the aberration vector WR involves using a monitoring system without actuating the compensator to obtain at least K=2 normalized aberration vector components of a secondary electronic imaging system for each impact energy LE(q)=(2...Q) of the set of impact energies.

[0040] According to another embodiment, a multi-beam charged particle system is provided, comprising: an object illumination unit configured to form multiple focal points of a plurality of primary charged particle beams in an object plane; and a sample stage configured to hold the surface of an object in the object plane. The multi-beam charged particle system further includes a voltage supply unit for providing a voltage VS to the sample, the voltage supply unit being configured to set a selected impact energy LES of the primary charged particles of the plurality of primary charged particle beams within a range of impact energy LE. The multi-beam charged particle system further includes a detection unit forming at least a portion of a secondary electron imaging system for imaging the plurality of secondary electron beams along a secondary electron beam path onto a detector, the secondary electron beams being excited at multiple focal points on the object surface. The multi-beam charged particle system further includes a beam splitter for separating the plurality of primary charged particle beams from the plurality of secondary electron beams; and at least one first compensator for aberrations of the secondary electron imaging system. The multi-beam charged particle system further includes a control unit, the control unit including a control processing processor and a memory for storing software instructions. When executed by the control processing processor, the software instructions cause the multi-beam charged particle system to perform any of the aforementioned method steps.

[0041] In one example, the multi-beam charged particle system further includes a second aberration compensator configured within the secondary electron imaging system. In another example, the multi-beam charged particle system further includes a third aberration compensator configured within the secondary electron imaging system.

[0042] Through embodiments or examples of the present invention, a multi-beam charged particle system with improved image contrast and a method for operating the multi-beam charged particle system are provided. Therefore, the present invention allows for wafer inspection with higher precision and accuracy, including charging wafer samples. It should be understood that the present invention is not limited to the described embodiments and examples, but also includes combinations and variations of the described embodiments and examples. Attached Figure Description

[0043] The embodiments of the present invention will now be described in more detail with reference to the accompanying drawings, in which:

[0044] Figure 1 This is a schematic cross-sectional view of a multi-beam charged particle system 1.

[0045] Figure 2 Some details of the multi-beam charged particle system 1 are shown;

[0046] Figure 3 A detector 600 with an optical relay system is shown;

[0047] Figure 4a b shows a secondary electronic imaging system according to the prior art;

[0048] Figure 5a -c illustrates the first example of an improved secondary electron imaging system;

[0049] Figure 6a -c illustrates a second example of an improved secondary electron imaging system;

[0050] Figure 7a -c illustrates a third example of an improved secondary electron imaging system;

[0051] Figure 8a Figures 1 and 2b show a fourth example of an improved secondary electron imaging system;

[0052] Figure 9a b indicates the sub-aperture ratio SAR;

[0053] Figure 10 The fifth example of the improved secondary electron imaging system is shown;

[0054] Figure 11 This illustrates a method for determining the aberration vector components of a secondary electronic imaging system;

[0055] Figure 12The calibration method for the astigmatism reducer in a secondary electronic imaging system is shown.

[0056] Figure 13a -f indicates an example of a low-order actuation mode of the astigmatism canceller;

[0057] Figure 14a Figures 1 and 2 show further examples of the actuation modes of the astigmatism canceller;

[0058] Figure 15 The operation method of a multi-beam charged particle system is shown. Detailed Implementation

[0059] In the exemplary embodiments of the present invention described below, components with similar functions and structures are represented by similar or identical reference numerals whenever possible.

[0060] Some array elements (e.g., multiple primary charged particle bundles) are identified by reference numerals. According to this document, the same reference numerals may also identify a single element or an array element. Each primary charged particle bundle (3.1, 3.2, 3.3) is one of multiple primary charged particle bundles (3).

[0061] Figure 1 The schematic diagram illustrates the basic features and functions of the multi-beam charged particle system 1. It should be noted that the reference numerals used in the figure are chosen to denote their respective functions. The system shown is a multi-beam scanning electron microscope that uses multiple primary charged particle beams 3 to generate multiple primary charged particle spot 5 on the surface 25 of an object 7, such as a wafer or mask substrate located in the object plane 101 of the objective lens 102. For simplicity, only three primary charged particle beams 3.1 to 3.3 and three primary charged particle spot 5.1 to 5.3 are shown. The features and functions of the multi-beam charged particle system 1 can be implemented using electrons or other types of primary charged particles (such as ions, and particularly helium ions). Further details of the microscope system 1 are provided in International Patent Application WO 2022 / 262970 A1, which is incorporated herein by reference in its entirety.

[0062] The multi-beam charged particle system 1 includes an object irradiation unit 100, a detection unit 200, and a secondary electron beam splitter or beam splitter unit 400 for separating the secondary charged particle beam path 13 from the primary charged particle beam path 11. The object irradiation unit 100 includes a charged particle multi-beam generator 300 for generating multiple primary charged particle beams 3 and adjusting them to focus the multiple primary charged particle beams 3 onto the object plane 101, where the surface 25 of the object or wafer 7 is positioned in the object plane by a sample stage 500.

[0063] A primary beam generator 300 generates a plurality of small primary charged particle beams in an intermediate image surface 321. The primary beam generator 300 includes at least one primary charged particle (e.g., electron) source 301. The at least one primary charged particle source 301 emits a diverging primary charged particle beam, which is collimated by at least one collimating lens 303 to form a collimated or parallel primary charged particle beam 309. The collimating lens 303 is typically composed of one or more electrostatic or magnetic lenses, or a combination of electrostatic and magnetic lenses. The collimated primary charged particle beam 309 is incident on a primary multi-beam forming unit 305. The multi-beam forming unit 305 is explained, for example, in US 2019 / 0259575 and US 10.741.355 B1, both of which are incorporated herein by reference. The multi-beam forming unit 305 essentially comprises a first porous plate or filter plate 304 irradiated by the collimated primary charged particle beam 309. The first porous plate or filter 304 includes a plurality of apertures arranged in a grating configuration for generating a plurality of primary charged particle beams 3, which are generated by collimating the transmission of the primary charged particle beams 309 through the plurality of apertures. The multi-beam forming unit 305 includes at least one additional porous plate 306 located downstream of the first porous plate or filter 304 relative to the direction of electron movement in the primary charged particle beams 309. For example, the second porous plate 306 includes, for example, four or eight electrostatic elements for each of the plurality of apertures to, for example, individually deflect each of the plurality of beams. The multi-beam forming unit 305 is further configured with adjacent electrostatic field lenses 331, which in some instances are combined within the multi-beam forming unit 305. Each of the plurality of primary charged particle beams 3, combined with the second field lens 333, is focused in or near an intermediate image surface 321. The primary charged particle source 301 and each of the active porous plates 306 are controlled by a control unit 800.

[0064] Multiple focal points of the primary charged particle beam 3 passing through the intermediate image surface 321 are imaged onto the object plane 101 by the field lens group 103 and the objective lens 102, in which the surface 25 of the object 7 is positioned. A voltage is applied to the object by the sample voltage source 503, generating a decelerating electrostatic field between the objective lens 102 and the surface 25 of the object 7. Using the decelerating electrostatic field generated by the sample voltage source 503, the impact energy EL of the primary electron is adjusted to, for example, below 2keV, 1keV, below 800eV, below 500eV, below 300eV, or even smaller, such as 100eV. Figure 2More details of the generated decelerating electrostatic field are shown. A multi-aperture configuration 305 generates multiple primary charged particle beams 3 from a collimated electron beam 309. For simplicity, only three primary charged particle beams 3.1 to 3.3 are shown, but more, such as 60 or more, 90 or more, or even 300 or more, are possible. A beam tube 151 is positioned downstream of the multi-aperture configuration 305 and is connected to a voltage source having a first or tube voltage VT. From the inlet of the beam tube 151, the multiple primary charged particle beams 3 are at a constant kinetic energy ET until the outlet opening 153 of the beam tube 151. The kinetic energy ET of the primary charged particle beams 3 during their passage through the beam tube 151 is, for example, 20 keV, 30 keV, or greater.

[0065] Multiple primary charged particle beams 3 are imaged, with focal points 5.1 to 5.3 formed in the image plane 101 by the second field lens 333 and the field lens group 103, as well as by the objective lens 102. The objective lens 102 is a magnetic lens type with a coil 161 and a pole shoe 163 having a lower pole shoe section 165, forming an axial gap for the magnetic field. In use, a current I is supplied to the coil 161 to generate a focusing magnetic field (not shown). Other types of magnetic lenses may also be used, such as radially gap lenses for generating an immersion lens field, or magnetic lenses with multiple coils and pole shoes. Upstream of or partially integrated into the objective lens 102, a beam splitter 400 is configured to separate secondary electrons along the secondary electron beam path 13 to the detector unit 200. Below the lower pole shoe section 165, an electrode 133 is provided, which is connected to a voltage source to provide a second voltage VE to the electrode. In the example shown, the electrode 133 is configured as a single electrode. The voltage difference between VT and VE generates a first electric field 135, as shown. Figure 2The equipotential lines of the first electric field 135 are shown. The first electric field vector is almost parallel to the propagation direction of the primary charged particle beam 3 and generates a decelerating force on the primary charged particles. A sample voltage VL is provided to the sample mounting platform 505 via a sample voltage source 503 for holding and contacting the wafer 7 during use. A second electric field 137 is generated based on the voltage difference between VL and VE, which is almost parallel to the propagation direction of the primary charged particle beam 3 and generates a decelerating force on the primary charged particles. The third or sample voltage VL is adjusted such that the third kinetic energy or impact energy EL of the primary electron is adjusted to be below 2keV, 1keV, 800eV, below 300eV, or even below 100eV. At the surface 25 of the wafer 7, a first material composition 67 is disposed below the first group of primary charged particle beams 3.1 and 3.2, and a second material composition 69 is disposed below the second group of primary charged particle beams containing the primary charged particle beam 3.3. The first electric field 135 and the second electric field 137 together form a deceleration field to reduce the kinetic energy of the primary charged particle beam 3 before it impacts the sample surface 25 positioned in the image plane 101, thereby achieving high resolution. The first electric field 135 also forms an acceleration field on the secondary electrons extracted from the wafer 7. The second electric field 137 forms an extraction field for extracting and accelerating the secondary electrons from the wafer 7. Therefore, the second electric field 137 is also referred to as extraction field 137.

[0066] Figure 2 The example shown illustrates a multi-beam charged particle system 1 with two-stage deceleration fields 135 and 137 and an additional electrode 133. In another example, only a single deceleration or extraction field 137 is generated between the exit aperture 153 of the beam tube 151 and the sample 7 mounted on the sample platform 505. In this case, the exit aperture 153 of the beam tube 151 serves as the electrode 133 for extracting the field 137.

[0067] Figure 1 and Figure 2The object illumination system 100 of the multi-beam charged particle system 1 further includes a common multi-beam grating scanner 110 near the beam intersection 108, through which multiple charged particle beams 3 can be deflected along a scanning direction 143 perpendicular to the propagation direction of the charged particle beams. Throughout this example, the propagation direction of the primary beams is the positive z-direction. The objective lens 102 and the common multi-beam grating scanner 110 are centered on the optical axis (not shown) of the multi-beam charged particle system 1, which is perpendicular to the surface 25 of the wafer. Multiple primary charged particle beams 3 (forming multiple beam points 5 configured in a grating structure) are scanned synchronously on the surface 25 of the wafer. In one example, the grating structure of the focal points 5 of the multiple primary charged particle 3 is a hexagonal grating of about 100 or more primary charged particle beams 3, for example, J=91, J=100, or J=300 or more beams. The primary beam points 5 are spaced approximately 6 μm to 45 μm apart and have diameters less than 5 nm, such as 3 nm, 2 nm, or even smaller. In one example, the beam point size is approximately 3 nm, and the distance between two adjacent beam points is 8 μm. At each scan position of each of the primary beam points 5, multiple secondary electrons are generated to form multiple secondary electron beams with the same grating configuration as the primary beam point 5. The intensity of the secondary charged particle beams generated at each beam point 5 depends on the intensity of the impacting primary charged particle beam 3, the irradiation of the corresponding beam point 5, the arrangement of the material compositions 67, 69 and the object 7 under the beam point 5, and the charging state of the sample at the beam point 5. The multiple secondary charged particle beams are accelerated by the same electrostatic field between the objective lens 102 and the object surface 25 and focused by the objective lens 102, passing through the first common multi-beam grating scanner 110 in the opposite direction to the primary beam 3. The multiple secondary beams are deflected and scanned by the first common multi-beam grating scanner 110. Then, multiple secondary charged particle beams are guided by beam splitter unit 400 to follow secondary beam path 13 to reach detection unit 200. Multiple secondary electron beams travel in opposite directions from primary charged particle beam 3 with kinetic energy ES = ET - EL, and beam splitter unit 400 is configured to separate secondary beam path 11 from primary beam path by magnetic field or a combination of magnetic field and electrostatic field.

[0068] The detection unit 200 images secondary electron beams onto the image sensor 600 to form a plurality of secondary charged particle image points 15 on the image sensor. The detector or image sensor 600 includes a plurality of detector pixels or individual detectors. For each of the plurality of secondary charged particle image points 15, its intensity is detected separately, and the characteristics of the object surface 25 are detected at high throughput and high resolution for a large image patch of the object 7. For example, using a 10 x 10 beam grating with a spacing of 8 μm, an image patch of approximately 88 μm x 88 μm is generated by using a single image scan of a common multi-beam grating scanner 110, having an image resolution of, for example, 2 nm or less. The image patch is sampled using half the beam point size, so there are 8,000 pixels per image line for each beam, such that an image patch generated by 100 beams contains 6.4 gigapixels. The digital image data is collected by the control unit 800. The use of, for example, parallel processing of digital image data aggregation and the details of the processing are described in International Patent Application WO 2020 / 151904 A2 and U.S. Patent 9,536,702, which are incorporated herein by reference.

[0069] The detection unit 200 further includes at least one second raster scanner 222 connected to the scan control unit 860. The scan control unit 860 is configured to compensate for differences in the scan deflection power of the first scan deflector 110 in the common beam path, such that the positions of the plurality of secondary electron focal points 15 remain constant at the image sensor 600. The differences in the scan deflection power of the first scan deflector 110 arise from the difference between the kinetic energy ET of the primary electron and the kinetic energy ES of the secondary electron. The multi-beam charged particle system 1 may further include a selectively scalable monitoring system 230. Monitoring systems and methods for detecting the charging effect at such charged samples are described in patent applications WO 2022 / 248141 A1 and DE102022114923.4, which are therefore incorporated herein by reference in their entirety. The detection unit 200 is described in more detail below.

[0070] The image sensor 600 is configured with a sensing region array using a pattern equivalent to a grating configuration of secondary electron beams focused onto the image sensor 600 by the detection unit 200. This enables the detection of each individual secondary electron beam, independent of other secondary electron beams incident on the image sensor 600. Figure 1 The image sensor 600 shown may be an electron-sensitive detector array, such as a CMOS or CCD sensor. Such an electron-sensitive detector array may include electron-to-photon conversion units, such as scintillator elements or an array of scintillator elements. In another embodiment, the image sensor 600 may be configured as an electron-to-photon conversion unit or scintillator plate in the focal plane of a plurality of secondary electron particle image points 15. Figure 3 An example is shown. The image sensor 600 may further include a relay optics system comprising a condenser lens 605 and a zoom lens 611 for imaging at a secondary charged particle image point 15 on a dedicated photon detection element 623 and for guiding photons generated by the electron-to-photon conversion unit 602, such as multiple photomultiplier tubes or avalanche photodiodes. Such an image sensor is disclosed in US 9,536,702, which has been cited above and is incorporated herein by reference. The image sensor is further configured with a selectively scalable monitoring system 230, which includes a beam-splitting mirror 237, an imaging lens 235, and a high-resolution CMOS sensor 232.

[0071] During the acquisition of image blocks by scanning multiple primary charged particle beams 3, preferably, the sample stage 500 remains stationary, and after acquiring an image block, the sample stage 500 is moved to the next image block to be acquired. In an alternative embodiment, the sample stage 500 moves continuously along a second direction while acquiring images by scanning multiple primary charged particle beams 3 along a first direction using a common multi-beam grating scanner 110. The stage movement and stage position are monitored and controlled by sensors known in the art, such as laser interferometers, grating interferometers, confocal microlens arrays, or the like.

[0072] During image scanning, the control unit 800 is configured to trigger the image sensor 600 to detect multiple timely resolved intensity signals from multiple secondary electron beams at predetermined time intervals, and the digital image of the image block is accumulated and stitched together from all scanning positions of multiple primary charged particle beams 3.

[0073] The control unit 800 of the multi-beam charged particle system 1 further includes: an imaging control module 810 configured to receive a data stream from the image sensor 600 and generate a digital image of the surface of the sample 7 during operation; a secondary beam path control module 840 configured to control the detection unit 200; a primary beam path control module 830 configured to control the elements of the object irradiation unit 100; a stage control module 850 configured to control the stage positioning and alignment, and includes control of the sample voltage source 503; a scanning operation control module 860 configured to control the scanning operation through the first common multi-beam grating scanner 110 and the second deflection system 222; and a control processing processor 880 configured to perform sample inspection tasks and to control the modules 810, 820, 830, 840, 850, 860, and a memory 890 for storing software, instructions, and image data. The control processing processor 880 is further connected to an interface IX for exchanging data, instructions, software, or user interaction.

[0074] Figure 4 illustrates a secondary electron imaging system 250 according to the prior art, which includes an objective lens 102, a beam splitter 400, and a detection unit 200. The following components are arranged along the propagation axis ZS:

[0075] The surface 25 of object 7 in object plane 101 is at coordinate zs=0;

[0076] Objective lens 102;

[0077] Beam splitter 400 is located at coordinates zs=zb;

[0078] Astigmatism reducer 220 is located at coordinates zs=zm;

[0079] First Electron Optical Lens 205.1;

[0080] The second electro-optical lens 205.2 and the third electro-optical lens 205.3;

[0081] The image plane 225 of the detection unit 200 is configured with the detector 600.

[0082] Figure 4a The low-kinetic-energy beam trajectory of the secondary electrons ES is shown. Trajectory 281 shows the trajectory of the secondary electrons from the axial field point 5.i. Two trajectories 281.LX and 281.LY are shown. Due to astigmatism of the secondary electron imaging system 250, the trajectories along x and y are different. The third trajectory 283.L shows the trajectory of the secondary electrons departing from the sample surface 25 at the off-axial field point 5.o, which has an angle perpendicular to the wafer surface 25 or object plane 101.

[0083] At low kinetic energy ES1, within the secondary electron imaging system 250, a first low-energy cross or pupil plane 256l is formed at a distance zpl1, and an intermediate image plane 252 is formed at a distance zil. Furthermore, a second cross or pupil plane 258i is formed at a distance zp12.

[0084] Figure 4b The beam trajectory of the high kinetic energy ES of the secondary electrons is shown. The corresponding secondary electron trajectories are labeled 281.HX, 281.HY, and 283.H. At the high kinetic energy ES2, within the secondary electron imaging system 250, a first low-energy cross or pupil plane 256h is formed at a distance zph1, and a first intermediate image plane 254 is formed at a distance zih. Furthermore, a second cross or pupil plane 258h is formed at a distance zph2. Typically, each pupil plane or intermediate field plane 256, 252, 254, and 258 is at a different zs-position, depending on the kinetic energy of the secondary electrons, i.e., for example, zph2 < zpl1, or zil < zih, or zpl1 < zpl1. <zph1。

[0085] Astigmatism is a wavefront aberration corresponding to the formation of two vertically elliptical foci with an axial distance. Field distortion is given by different imaging scales of the imaging system along the x and y directions. The two aberrations are inherently related. Neither aberration exists in rotationally symmetric systems. However, the secondary electron imaging system 250 includes a beam splitter 400, which disrupts rotational symmetry. The purpose of the stigmator 220 is to correct axial astigmatism and field distortion. However, it has been shown that the stigmator 220 is insufficient to compensate for the axial astigmatism and field distortion caused by the different kinetic energies of the secondary electrons. Furthermore, it has also been demonstrated that an improperly placed stigmator 220 introduces higher-order aberrations.

[0086] Figure 5a Figures 5a through 5c show embodiments of the improved secondary electronic imaging system 250. The same reference numerals as in Figure 4 are used and are also referred to in Figure 4. Figure 5a The improved secondary electron imaging system 250 shows selected secondary electron trajectories 281 and 283 at the first low kinetic energy ES1 of the secondary electron. Figure 5b The improved secondary electron imaging system 250 shows selected secondary electron trajectories 281 and 283 at the second high kinetic energy ES2 of the secondary electrons. A first astigmatism reducer 264.1 is inserted at position zml and optically equivalent to beam splitter 400, instead of a single astigmatism reducer 220 at position zm. Beam splitter 400 is located at position zb. The optical position within the secondary electron optical system is described by the ratio of the effective diameter of a single secondary electron beam to the diameters of multiple secondary electron beams in SAR. This ratio is called sub-aperture ratio SAR, such as... Figure 5c As shown. At field planes 101, 225, or zi, SAR=0; at the intersection plane or pupil planes zp1, zp2, SAR=1. SAR continuously varies between SAR=0 and SAR=1. In the example of Figure 5, for low kinetic energy ES1, the SAR_B of beam splitter 400 is approximately SAR_B1=0.5, while for high kinetic energy ES2, the SAR_B of beam splitter 400 is approximately SAR_Bh=0.3. Imaging aberrations introduced at a specific SAR location can only be compensated at the same SAR location. In the first example, the first astigmatism corrector or compensator 264.1 is configured within the secondary electron imaging system 250 at a location where SAR is approximately equal to SAR_B1. However, considering the dependence of SAR_B on the kinetic energy of the secondary electron, it is impossible to compensate for axial astigmatism and field distortion in parallel for all kinetic energies of the secondary electron. In the second example, a second astigmatism corrector or compensator 264.2 is provided (see [link to example]). Figure 5a(Or 5b). By actuating the combined first astigmatism reducer 264.1 and the second astigmatism reducer 264.2, axial astigmatism and field distortion can be compensated within the range required by the secondary electron kinetic energy without introducing higher-order aberrations. In one example, the second astigmatism reducer or compensator 264.2 is positioned within the secondary electron imaging system 250 at a position where SAR is approximately equal to SAR_Bh. Therefore, by activating the combined first aberration compensator 264.1 and the second astigmatism reducer 264.2, compensation for aberrations introduced by the beam splitter 400 can be further improved, while reducing the introduction of higher-order aberrations.

[0087] Typically, only a portion or component of the beam splitter 400 causes aberrations in the secondary electron beam path. For example, as follows: Figure 10 In a more detailed description of the example, beam splitter 400 includes a beam splitter component 400.3 separately configured within the secondary electron beam path 13. This beam splitter component 400.3 can induce aberrations that depend on either the kinetic energy of the secondary electrons or the impact energy of the primary electrons.

[0088] Generally, according to the first embodiment, the secondary electron imaging system 250 includes at least one first astigmatism reducer 264.1 or 264.2 located at a position of an SAR with an equal sub-aperture ratio of the element, which is responsible for aberrations within the secondary electron imaging system 250, such as a beam splitter 400 at a position having a sub-aperture ratio SAR_B at a first selected kinetic energy of the secondary electron. If two SARs show a deviation of 15% or less (e.g., 10% or 5%), the first SAR is considered equal to the second SAR (e.g., SAR_B). In a multi-beam charged particle beam system 1 configured to image multiple secondary small beams 9, proper selection of the position of the astigmatism reducer 264 is more important; this is different in a single-beam system, where aberration compensation is typically performed on a single charged particle beam before scanning. On the other hand, in a multi-beam charged particle system, the components can introduce aberrations with specific field dependence for multiple small beams of charged particles (e.g., multiple small beams of secondary electrons 9); in order to compensate for the aberrations of the components with specific field dependence, it is preferable to place the astigmatism reducer 264 at an optically equivalent position with similar SAR.

[0089] In one example, the secondary electronic imaging system 250 further includes a second astigmatism corrector 264.2. Aberrations can be compensated within a desired range of secondary electronic kinetic energy through combined actuation of the first and second astigmatism correctors 264.1 and 264.2. In one example, the second astigmatism corrector 264.2 is located at the position of an element in an equal sub-aperture ratio SAR that causes aberrations within the secondary electronic imaging system 250.

[0090] In the example of Figure 5, the secondary charged particle beam path 13 within the secondary electron imaging system 250 further includes an intermediate image plane 252 at low kinetic energy and an intermediate image plane 254 at high kinetic energy of the secondary electrons. A first compensator 264.1 is positioned upstream of the intermediate image plane 252 or 254 relative to the propagation direction of the secondary electrons, and a second compensator 264.2 is positioned downstream of the intermediate image plane 252 or 254.

[0091] In the description, the terms "compensator" and "stigmator" are used. It should be noted that the compensator or stigmator according to the embodiments can be implemented as a conventional stigmator, which is typically implemented as a multipole element with at least four electrostatic poles for generating a non-uniform field distribution. Several examples are described below. However, the compensator or stigmator is not limited to a multipole element, but can also be implemented, for example, as an electron optical lens capable of displacement or tilting relative to the secondary electron beam path.

[0092] Figure 6a Figures 1 through 2 show the second embodiment. The same reference numerals as those in Figures 4 and 5 are used, and reference is also made to Figures 4 and 5. Figure 6a The improved secondary electron imaging system 250 shows selected secondary electron trajectories 281 and 283 at the first low kinetic energy ES1 of the secondary electron. Figure 6b The improved secondary electron imaging system 250 shows selected secondary electron trajectories 281 and 283 at the second high kinetic energy ES2 of the secondary electron. Figure 6c The sub-aperture ratio SAR of an improved secondary electron imaging system 250 for two selected kinetic energies ES1 and ES2 is shown. The secondary electron imaging system 250 according to a third embodiment further includes an aperture stop 284 located at the cross plane or pupil plane 258. Using the aperture stop 284, the image contrast is adjusted such that, for example, each secondary electron beam provides similar or identical image contrast. Such aperture stops are described in PCT / EP2023 / 025426, filed October 10, 2023, which is incorporated herein by reference in its entirety. However, the pupil position 258 is affected by the kinetic energy of the secondary electrons (see...). Figure 5a and 5b (The pupil plane coordinates are zp2 > zph2). In one example, the secondary electron imaging system 250 according to the second embodiment includes at least one electron optical lens element 211.1 or 211.2 located upstream of the filter plate or pupil plane 258. Using at least one electron optical lens element 211.1 or 211.2, the position zp2 of the pupil plane 258 is maintained at a constant position, independent of the kinetic energy of the secondary electrons. In one example, the secondary electron imaging system 250 according to the second embodiment includes at least two electron optical lens elements 211.1 and 211.2.

[0093] Axial astigmatism and field distortion are related to pupil aberration, which can lead to undesirable effects on the filtering operation of aperture stop 284. Pupil aberration is, for example, pupil distortion, corresponding to an elliptical pupil distribution. This type of pupil aberration can be different for each field point. Therefore, for example, the filtering operation of aperture stop 284 can be different for each of the plurality of secondary electron beams 9, resulting in different image contrasts for different secondary electron beams 9 or different field points 5. The improved secondary electron imaging system 250 according to the second embodiment includes at least a first astigmatism reducer 264.1 and a second astigmatism reducer 264.2 for compensating for axial astigmatism, field distortion, and pupil aberration. These aberrations can be introduced by beam splitter 400 and are at least partially compensated by the first astigmatism reducer 264.1 and the second astigmatism reducer 264.2. In one instance, at least one of the compensator or astigmatism canceller 264.1 or 264.2 is located at the SAR_B position of a component of the SAR beam splitter 400 that is similar to the selected secondary electronic kinetic energy.

[0094] Figure 7 illustrates the third embodiment. The same reference numerals as those in Figures 4, 5, and 6 are used, and reference is also made to the description of Figures 4 to 6. Figure 7a The improved secondary electron imaging system 250 shows selected secondary electron trajectories 281 and 283 at the first low kinetic energy ES1 of the secondary electron. Figure 7b The improved secondary electron imaging system 250 shows the trajectories 281 and 283 of a selected secondary electron at the second high kinetic energy ES2 of the secondary electron. Figure 7c This illustrates the sub-aperture ratio SAR of an improved secondary electron imaging system 250 for two selected kinetic energies ES1 and ES2 at different zs-coordinates. According to an example of the third embodiment, the second astigmatism reducer 264.2 is located downstream of the aperture filter 284 at coordinates zm2>zp2. According to the example shown in FIG. 7, the first astigmatism reducer 264.1 is configured upstream of the aperture stop 284. For example, the first astigmatism reducer 264.1 is configured between the first pupil plane 256 and the intermediate image plane at position zil or zih (see reference numerals 252 and 254 in FIG. 5). Therefore, the first astigmatism reducer 264.1 is used to compensate for pupil aberration, and the second astigmatism reducer 264.2 is used to compensate for residual axial astigmatism and field distortion. In one example, the second astigmatism reducer 264.2 is located at zs-coordinates zm2>zp2, where the SAR is analogous to the SAR_B of the component of the beam splitter 400 for the selected secondary electron kinetic energy.

[0095] Figure 8 illustrates another example according to the third embodiment. The same reference numerals as those in Figures 4 through 7 are used, and reference is also made to the description of Figures 4 through 7. Figure 8aThe improved secondary electron imaging system 250 shows selected secondary electron trajectories 281 and 283 at the first low kinetic energy ES1 of the secondary electron. Figure 8b The improved secondary electron imaging system 250 is shown with selected secondary electron trajectories 281 and 283 at the second high kinetic energy ES2 of the secondary electrons. In the example of FIG8, the secondary electron imaging system 250 further includes a third astigmatism reducer 264.3, at least one of which is configured downstream of the aperture filter 284. The compensation for axial astigmatism, field distortion, and pupil aberration can be further improved using at least three independent compensators or astigmatism reducers 264.1 to 264.3. In one example, at least one of the compensators 264.1 to 264.3 is positioned at a location similar to the SAR of the element causing the aberration. In another example, at least two of the compensators 264.1 to 264.3 are positioned at locations zm1, zm2, or zm2 that have similar SAR to the SAR of the element causing the aberration. In one example, all three compensators 264.1 to 264.3 are located at positions zm1, zm2, and zm3, which have elements causing aberrations in a SAR similar to those in a SAR. For example, the first astigmatism corrector 264.1 is disposed between the first pupil plane 256 and the intermediate image plane at position zil or zih (reference numerals 252 and 254, see Figure 5). The second astigmatism corrector 264.2 is disposed between the intermediate image plane (reference numerals 252 and 254 in Figure 5) and the second pupil plane 258.

[0096] Figure 9 shows the determination of the sub-aperture ratio SAR at two instances at the zs-position. Figure 9a An example of a smaller SAR with an axially oriented beam having a small effective diameter of 291.1 is shown near the field plane. The cluster diameter 295.1 of the multiple secondary electron beams 9 is determined by the maximum distance from the axis of the effective diameter of the secondary electron beam 293.1 at the peripheral field point 5.0. For smaller SARs, the secondary electron beams 291.1 and 293.1 may not overlap. Figure 9b An example with a large SAR and close to the pupil plane is shown, in which secondary electron beams 291.2 and 293.2 overlap each other. The effective diameter 291 or 293 of the secondary electron beam is defined by a filter stop 284, which can be positioned downstream of the corresponding zs-position.

[0097] Figure 10 Another example of one of the several embodiments is shown. Figure 1 , Figure 2 The same reference numerals are used as in Figures 4 through 8, and also refer to... Figure 1The descriptions in Figures 2 and 4 through 8 are provided. The multi-beam charged particle system 1 further includes a beam tube 151 comprising multiple beam tube segments 151.1 to 151.5. The beam splitter 400 includes a first beam splitter segment 400.1 disposed in the primary beam path 11; a third beam splitter segment 400.3 disposed in the secondary electron beam path 13; and a second beam splitter segment 400.2 disposed in both the primary beam path 11 and the secondary beam path 13 and configured to separate the secondary electron beam 9 from the primary charged particles. The detection unit 200 includes first to third electro-optical lenses 205.1 to 205.3, a deflection scanner 222, first and second electro-optical lens elements 211.1 and 211.2, a first compensator 220, and four astigmatism reducers 264.1 to 264.4. The pupil or aperture stop 284 is disposed within a common pupil plane 258 between the two tube sections 151.4 and 151.5, and is mounted, for example, on a support platform for adjustment or exchange. Figure 10 In this example, the first aberration compensator 264.1 and the second astigmatism corrector 264.2 are positioned upstream of the pupil plane 258, while the third astigmatism corrector 264.3 and the fourth astigmatism corrector 264.4 are positioned downstream of the pupil plane 258. Therefore, axial astigmatism, field distortion, and pupil aberration can be compensated individually, and higher-order residual aberrations can be minimized.

[0098] The detection unit 200 further includes an image sensor 600 connected to the imaging control module 810 and configured to receive image data during scanning operations. First to third electro-optical lenses 205.1 to 205.3, a deflection scanner 222, a first electro-optical lens element 211.1 and a second electro-optical lens element 211.2, a first compensator 220, and four astigmatism reducers 264.1 to 264.4 are connected to a secondary beam path control module 840. During use, the secondary beam path control module 840 is configured to provide individual control signals to the first to third electro-optical lenses 205.1 to 205.3, the deflection scanner 222, the first electro-optical lens element 211.1, and the second electro-optical lens element 211.2. The secondary beam path control module 840 is configured to generate individual control signals and provide them to the first to third electro-optical lenses to maintain the position and field rotation of the image plane 225 over a wide range of kinetic energies ES. Therefore, the allocation of individual detectors (e.g., detector 623) to individual secondary electron beams 9 is maintained over a large area of ​​the kinetic energy ES. The secondary beam path control module 840 is configured to generate and provide individual control signals to maintain the position of the common pupil plane 258. Therefore, field-invariant filtering operation of the aperture filter 284 can be implemented over a large area of ​​the kinetic energy ES. The secondary beam path control module 840 is also configured to generate individual control signals and provide them to the first astigmatism canceller 264.1 and the second astigmatism canceller 264.2 to minimize pupil aberrations within the common pupil plane 258 over a large area of ​​the kinetic energy ES. Therefore, for example, isotropic and field-invariant filtering operation of the aperture filter 284 can be implemented over a large area of ​​the kinetic energy ES. The secondary beam path control module 840 is further configured to generate individual control signals and provide them to the third astigmatism canceller 264.2 and the fourth astigmatism canceller 264.3. Therefore, field aberrations such as axial astigmatism due to field deformation are minimized within the image plane 225 over a large area of ​​the kinetic energy ES.

[0099] exist Figure 10In one example, at least one of the first electro-optic lens element 211.1 and the second electro-optic lens element 211.2 is configured as a fast electrostatic lens element. Such fast lens elements are disclosed in German patent application DE 102022213751.5, filed December 16, 2022, which is incorporated herein by reference. Using the fast lens element 211.1 or 211.2, rapid changes in the kinetic energy of secondary electrons caused by the charging effect of the sample 7 can be compensated during image scanning operations. The change in the kinetic energy of the secondary electrons caused by the charging effect of the sample 7 also alters aberrations of the multiple secondary electron beams 9, such as axial astigmatism, field distortion, or pupil aberration. By configuring the compensator or astigmatism reducer 264 as an electrostatic element comprising multiple electrodes, such as eight, ten, twelve, or more electrodes, aberrations of the multiple secondary electron beams 9 can be compensated during scanning operations when charge accumulates at the sample 7 and the kinetic energy of the secondary electrons changes.

[0100] The fourth to sixth embodiments provide examples of operating a multi-beam charged particle beam system 1 with an improved detection unit 200. In the fourth and second embodiments, a calibration method for the multi-beam charged particle beam system 1 and at least one astigmatism corrector 264 is provided. A control sensitivity is determined and stored in a memory. In the sixth embodiment, an inspection task is performed using the control sensitivity through the multi-beam charged particle beam system 1 with the improved detection unit 200.

[0101] In the fourth embodiment, a calibration method for a secondary electron imaging system is disclosed. Figure 11 An example of a calibration method for a secondary electron imaging system is shown.

[0102] In step C1, imaging or pupil aberration is determined for each of a sequence of impact energies LE(q). During the determination, for example, a monitoring system 230 is used.

[0103] During step C1, a sequence of impact energies LE(q) of the primary charged particles is determined. Each impact energy LE(q) of the primary charged particles (where q = 1...Q) corresponds to a specific kinetic energy ES(q) of the secondary electron and is adjusted, for example, by a sample voltage VL. This sequence of impact energies LE(q) can be selected as an energy sequence between 300 eV or less (e.g., 200 eV or 100 eV) and 1 keV or greater (e.g., 2 keV or 3 keV). This sequence can contain Q = two, three, four or more different impact energies LE(q), where q = 1...to Q.

[0104] The imaging or pupil aberration is expanded into an imaging difference vector WR. The aberration vector WR includes, for example, axial field astigmatism or astigmatism, which is a constant astigmatism in image plane 225; and pupil deformation, which describes the elliptical pupil shape in the intersecting or pupil plane 258. Further vector components may be:

[0105] - Field deformation, that is, the scale difference in different directions in the image plane 225;

[0106] - Secondary field distortion, that is, distortion that has a secondary correlation with the field coordinates in image plane 225; and

[0107] - Linear field astigmatism, that is, astigmatism that is linearly related to the field coordinates.

[0108] Other imaging or higher-order pupil aberrations are also possible.

[0109] Therefore, each aberration vector WR contains K vector components, where K=2 or greater, such as K=3, K=4, K=5 or greater. For example, the aberration vector for each impact energy LE(q) is given by the following equation:

[0110] (1)

[0111] Where wr1 represents axial astigmatism and wr2 represents pupil deformation at impact energy LE(q).

[0112] In step C2, the aberration vector WR(LE(q)) of the impact energy sequence is written into memory 890 for later use.

[0113] In a fifth embodiment, a method for calibrating at least one astigmatism corrector 264 is provided. An example of the calibration method is shown below. Figure 12 As shown. The method includes step C3 of selecting a set of normalized actuation or modes for the astigmatism canceller 264. Figure 13 illustrates an example of a set of normalized actuation or modes for the astigmatism canceller 264, using an astigmatism canceller containing eight electrodes 268 as an example. Figure 13 shows the N=6 mode according to orthogonal expansion, similar to the representation of tilt ( Figure 13a and 13b Z2 and Z3 in the middle), saddle shape (sometimes in Figure 13c and 13d In the middle, these are referred to as astigmatism Z5 and Z6) and third-order ripple ( Figure 13e and 13d The low-order Zernike polynomials (sometimes referred to as coma Z7 and Z8) are used. Each normalized actuation or mode M(n) is provided by a vector of eight specific voltages for each electrode 268, where

[0114] (2) .

[0115] However, the pattern is not limited to... Figure 13a -f has N=six modes. Figure 14a The diagram shows the high-order field distribution of an astigmatism reducer including eight electrodes 268 corresponding to higher-order astigmatism. By combining additional electrodes upstream and downstream of the astigmatism reducer 264, a rotationally symmetric low-order mode corresponding to defocus or Z4 can also be implemented. Figure 14b Further and higher modes are possible by using astigmatism erasers with other numbers of electrodes (e.g., six, ten, twelve or more electrodes).

[0116] In step C4, each normalized mode M(n), where n=1...N, is applied to the selected astigmatism reducer 64 during use. For each mode M(n) and each impact energy LE(q) of the impact energy sequence, the change in imaging or pupil aberration dW of the secondary electron imaging system 250 is determined. During the determination, for example, a monitoring system 230 is applied. Each change in imaging or pupil aberration expands the imaging difference vector dW, containing the aberration vector used in step C1. WR (LE(q)) are the same vector components, such as axial field astigmatism wr1 and pupil deformation wr2. For each normalized mode M(n), if the imaging or pupil aberration at a specific impact energy LE(q) is dw(k;LE(q)), the sensitivity S relative to changes in the vector components is typically determined by the following equation:

[0117] (3)

[0118] Where C(n) is the amplitude, through which the actuation mode M(n) is applied to the astigmatism reducer 264. For simplicity, a normalized actuation mode M(n) with C(n) = 1 is used.

[0119] Therefore, a sensitivity matrix of dimension (K;N) is determined for each impact energy LE(q). S Sensitivity matrix S Each component is described by applying the normalized actuation mode M(n) to the astigmatism deflector 264 to excite the vector component dw(k).

[0120] In one example, for each astigmatism canceller 264.1, 264.2, 264.3, 264.4, step C4 is repeated within sub-steps C4.1 to C4.F. For each astigmatism canceller 264.f with exponents f=1...F, a sensitivity is derived for each impact energy LE(q). S ,in

[0121] (4) .

[0122] It is worth noting that, typically, the response or sensitivity S(k,n;LE(q);f) of the astigmatism reducer 264.f relative to the actuation mode M(n) depends on the impact energy LE and therefore the kinetic energy of the secondary electrons. The sensitivity of the astigmatism reducer 264.f relative to the selected aberration vector component dw(k) depends on the aforementioned sub-aperture ratio SAR. For example, when SAR=1, no change in pupil distortion occurs. For example, when SAR=0, no field aberration occurs.

[0123] In selective step C5, a linear cross-check is performed. Within the linear range, for a linear combination of actuation modes M(n) applied to different astigmatism suppressors 264.f, the sensitivity S(k,n;LE(q);f) should be linear and will result in an aberration vector for each impact energy. W Linear combination:

[0124] (5)

[0125] In one example, in the selective step C5, the linear range cl(n;f) of the coefficients c(n;f) is determined for each mode M(n) applied to the astigmatism canceller 264.f. The linear range cl(n;f) is determined to be the maximum value of the coefficients c(n;f) with a deviation err below a critical value, for example, err < 50% of the demand specification or even less, such as err < 30% of the demand specification.

[0126] In step c6, the sensitivity matrix of each astigmatism canceller 264.f and each impact energy LE(q) of the impact energy sequence is... S (LE(q);f) and selectively determined constraints cl(n;f) are written into the memory 890 of the multi-beam charged particle beam system 1 for later use.

[0127] In the sixth embodiment, a method of operating the multi-beam charged particle system 1 is described. Figure 15 An example is shown. In step S1, an inspection task is received, for example, from an instruction file or using input. The inspection site on wafer 7 is positioned within the field of view of the multi-beam charged particle system 1 by the stage 500. The settings for the inspection task are selected, including selecting the impact energy LES of a single charged particle.

[0128] In step S2, the sensitivity matrix of at least the first astigmatism suppressor 264.1, 264.2, 264.3, or 264.4 of the selected impact energy LES is determined. S (LES; f=1...F). For example, the sensitivity matrix of the impact energy LES. S (LES;f=1) is based on a previously determined sensitivity matrix received from memory 890. SThe sensitivity matrix is ​​determined by (LE(q);f=1). In one instance, the sensitivity matrix is ​​selected from the impact energy sequence having the minimum difference between LE(q1) and LES. S (LE(q1);f=1). In another instance, the sensitivity matrix... S (LES;f) is a previously determined sensitivity matrix derived from at least two different impact energies LE(q) used during calibration. S (LE(q);f) is obtained by interpolation.

[0129] Generally, during step S2, the previously determined sensitivity matrix received from memory 890 is used... S (LE(q)) is used to determine the sensitivity matrix of multiple compensators or astigmatism cancellers 264.1, 264.2, 264.3, or 264.4. S (LES, f). The previously determined sensitivity matrix. S (LE(q), f) can be determined, for example, during calibration according to the fifth embodiment, as a sequence of impact energies LE (q=1…Q). For example, each sensitivity matrix at the selected impact energy LES. S (LES, f) represents at least two sensitivity matrices obtained by interpolation at different impact energies LE(q). S (LE(q), f) is determined.

[0130] In step S3, the aberrations of the secondary electron imaging system 250 at the selected impact energy LES are determined. The aberrations are described by an aberration vector WR, which has the characteristics of the aberration vector used in step C1. WR Or the vector components of the transformation vector dW used in C4. In one instance, the difference vector WR (LES) includes vector components of axial astigmatism wr1 and pupil deformation wr2. In one example, this is achieved by using at least two previously determined aberration vectors received from memory 890. WR (LE(q)) is used for interpolation to determine the aberration vector. WR (LES). In one instance, the aberration vector at the selected impact energy is determined during an inspection task using monitoring system 230. WR (LES).

[0131] In step S4, the actuation of at least one astigmatism canceller 264 is determined according to linear system theory. In this example, the actuation of F astigmatism cancellers 264.1 to 264.F is determined. For each astigmatism canceller 264.f = 1…F, the actuation amplitude C(n;f) of the normalized actuation mode M(n) is determined. As the normalized actuation mode M(n), the actuation mode selected in step C3 is applied. The actuation amplitude C(n;f) of each mode M(n) and each astigmatism canceller 264.f is determined by solving for the minimum aberration vector. WR The optimization problem of (LES) is determined as follows:

[0132] (6) .

[0133] In one instance, the solution to equation (6) is based on matrix inversion. In another instance, the solution to equation (6) is based on singular value decomposition (SVD).

[0134] However, in one instance, for a selected impact energy LES, the sensitivities of a pair of astigmatism cancellers 264.f1 and 264.f2 with respect to the aberration vector component wr(n) can be very similar, such that the solution to the optimization problem according to equation (6) leads to very high actuation amplitudes C(n;f1) and C(n;f2). For example, at the selected impact energy, the SAR of the two astigmatism cancellers 264.f1 and 264.f2 is very similar, with both exhibiting similar responses to the application of actuation mode M(n). For example, at the selected impact energy, the SAR of the two astigmatism cancellers 264.f1 and 264.f2 is different, with both exhibiting similar responses to the application of the first actuation mode M(n1) to the first astigmatism canceller 264.f1 and the application of the second actuation mode M(n2) to the second astigmatism canceller 264.f2. In such instances, the method according to the sixth embodiment includes further constraints. In one instance, the solution of equation (6) is based on a two-step method. In the first step S4.1, the sensitivities S(k,n1;LES;f1) and S(k,n2;LES;f2) of the astigmatism corrector for 264.f1 and 264.f2 are compared. If the sensitivity difference S(k,n2;LES;f2) - S(k,n1;LES;f1) with respect to the aberration vector component w(k) is lower than a predetermined critical value, according to equation (6), one actuation mode M(n1) or M(n2) of the astigmatism corrector 264.f1 or 264.f2 is discarded from the optimization problem. Generally, during step S4.1, a weighting function G(n;f) is determined by which a specific actuation mode M(n) of the selected astigmatism corrector 264.f is discarded by setting the weighting G(n,f) = 0. In the second step S4.2, the optimization problem is reduced by considering the weighting function G(n;f):

[0135] (7) .

[0136] For example, at the first selected impact energy LES1, the first astigmatism corrector 264.1 and the second astigmatism corrector 264.2 are used to compensate for the aberration WR(LES1), while the third astigmatism corrector 264.3 is not used and is completely discarded by the weighting function G(n,f=3)=0. For example, at the second selected impact energy LES2, the second astigmatism corrector 264.2 and the third astigmatism corrector 264.3 are used to compensate for the aberration WR(LES2), while the first astigmatism corrector 264.1 is not used and is completely discarded by the weighting function G(f=1)=0.

[0137] Further constraints may be applied during the optimization of equation (7), for example, the voltage range applied to the electrode 268 of the astigmatism reducer 264.f may be limited, or the linear range cl(n,f) may be limited. The linear range cl(n,f) may be determined according to step C5 of the fifth embodiment, or a predetermined linear range cl(n,f) may be received from the memory 890.

[0138] Therefore, the coefficients C(n,f) of the actuation mode M(n) are determined by the solution of equation (7).

[0139] In one example, the weighting coefficient C(n,f) of the actuation mode M(n) is introduced as an error function into the optimization problem; thus, large coefficients C(n,f) and large voltages V1 to V8 of the actuation mode M(n) are avoided. Therefore, the optimization problem can be written as:

[0140] (8) .

[0141] Using the second weighting function T(n;f), the linear range cl(n,f) can be solved. The additional term T(nf) is multiplied by the coefficient C(n,f) of the actuation mode M(n) to achieve Tychonov regularization. Therefore, the minimum coefficient C(n,f) of the actuation mode M(n) is determined by the solution of equation (8). In the examples of equation (8), the first weighting function G(n,f) is always set to G(n,f)=1.

[0142] In step S5, the generation coefficient C(n,f) of the actuation mode M(n) is applied to the corresponding astigmatism canceller 264.f and a check task is performed.

[0143] The selective step M can be performed in parallel with step S5. In step M, for example, an image of pupil aberration is determined by monitoring system 230. Using the actual image or pupil aberration, steps S3 and S4 are repeated during the image task, and the coefficients C(n,f) of the actuation mode M(n) are repeatedly optimized during the inspection task. Therefore, for example, the offset of the multi-beam charged particle system 1 or the changing surface charge during the inspection task are taken into account.

[0144] In step S6, the inspection results are written to the memory and further processed according to the inspection task. Based on the inspection results, the selective optimization coefficient C(n,f) of the actuation mode M(n) is analyzed and stored in the memory 890 for later use, for example, performing a similar inspection task at a similar inspection location.

[0145] The multi-beam charged particle system 1 includes a memory 890 and a control processing processor 880, wherein the memory 890 is configured to store software instructions that, when executed by the control processing processor 880, cause the multi-beam charged particle system 1 to perform at least one of the methods according to the fourth to sixth embodiments.

[0146] This invention may be described, for example, by the following terms:

[0147] Clause 1: A multi-beam charged particle beam system (1), comprising:

[0148] An object irradiation unit (100) is configured to form multiple focal points (5) of multiple primary charged particle beams (3) in an object plane (101);

[0149] A sample carrier stage (500) is configured to place the surface (25) of the object (7) in the object plane (101);

[0150] A voltage supply unit (503) is used to supply voltage VS to the sample (7), the voltage supply unit (503) being configured to set the first impact energy LE1 of the primary charged particles of a plurality of primary charged particle bundles (3);

[0151] A detection unit (200) that forms at least part of a secondary electron imaging system (250) for imaging a plurality of secondary electron beams (9) along a secondary electron beam path (13) onto a detector (600), the plurality of secondary electron beams being excited at the plurality of focal points (5) on the surface (25) of the object (7);

[0152] A beam splitter (400) is used to separate multiple primary charged particle beams (3) from multiple secondary electron beams (9);

[0153] A first electron optical element, which is arranged at a first position within a secondary electron imaging system (250), has a first ratio SAR1 of the beam diameter (293) of a single secondary electron beam (9) relative to the diameter (295) of the plurality of secondary electron beams (9) under a first impact energy LE1.

[0154] A first compensator for aberration (264.1, 264.2, 264.3), wherein the aberration is caused by the first electro-optical element, wherein the first compensator (264.1, 264.2, 264.3) is disposed at a second position within the secondary electronic imaging system (250), having a second ratio SAR2 under the first impact energy LE1, wherein the second ratio SAR2 is the same as the first ratio SAR1 or deviates from the first ratio SAR1 by no more than 0.1.

[0155] Clause 2: A multi-beam charged particle system (1) as described in Clause 1, wherein the first electron optical element is at least a portion of the beam splitter (400, 400.2, 400.3).

[0156] Clause 3: A multi-beam charged particle system (1) as described in Clause 1 or 2, wherein the first compensator (264.1, 264.2, 264.3) is a multipole element or an astigmatism suppressor.

[0157] Clause 4: A multi-beam charged particle beam system (1) as described in any one of Clauses 1 to 3, wherein the detection unit (200) further includes an aperture stop (284) disposed at the pupil plane (258) of the secondary electron beam path (13) of the first impact energy LE1.

[0158] Clause 5: The multi-beam charged particle beam system (1) as described in any one of Clauses 1 to 4 further includes a second aberration compensator (264.2, 264.3, 264.4).

[0159] Clause 6: A multi-beam charged particle system (1) as described in Clause 5, wherein the second compensator (264.1, 264.2, 264.3) is configured at a third position within a secondary electron imaging system (250) and has a third ratio SAR3 at the first impact energy LE1, wherein the third ratio SAR3 is different from the second ratio SAR2.

[0160] Clause 7: A multi-beam charged particle system (1) as described in Clause 5 or 6, wherein the first compensator (264.1, 264.2 or 264.3) and the second compensator (264.2, 264.3 or 264.4) are configured to jointly compensate for the aberrations of the first electro-optical element at the first impact energy LE1.

[0161] Clause 8: A multi-beam charged particle system (1) as described in any one of Clauses 5 to 7, wherein the first compensator (264.1, 264.2 or 264.3) and the second compensator (264.2, 264.3 or 264.4) are configured to jointly compensate for the aberration of the first electro-optical element at a second impact energy LE2 or a primary charged particle, wherein the second impact energy LE2 is different from the first impact energy LE1.

[0162] Clause 9: A multi-beam charged particle system (1) as described in any one of Clauses 5 to 8, wherein the secondary electron beam path (13) within the secondary electron imaging system (250) further includes an intermediate image plane (252, 254) at a first impact energy LE1, and wherein the first compensator (264.1, 264.2, 264.3) is disposed upstream of the intermediate image plane (252, 254) relative to the propagation direction of the secondary electrons, and the second compensator (264.2, 264.3, 264.4) is disposed downstream of the intermediate image plane (252, 254).

[0163] Clause 10: A multi-beam charged particle system (1) as described in any one of Clauses 5 to 8, wherein the first compensator (264.1, 264.2, 264.3) is disposed upstream of the aperture stop (284) relative to the direction of propagation of secondary electrons, and the second compensator (264.2, 264.3, 264.4) is disposed downstream of the aperture stop (284).

[0164] Clause 11: The multi-beam charged particle system (1) as described in any one of Clauses 4 to 10 further includes at least one correction lens (211.1, 211.2) configured to adjust the pupil plane (258) at a position of a second impact energy LE2 different from the first impact energy LE1 to the aperture stop (284).

[0165] Clause 12: A multi-beam charged particle system (1), comprising:

[0166] An object irradiation unit (100) is configured to form multiple focal points (5) of multiple primary charged particle beams (3) in an object plane (101);

[0167] A sample carrier stage (500) is configured to place the surface (25) of the object (7) in the object plane (101);

[0168] A voltage supply unit (503) is used to supply voltage VS to the sample (7) and is configured to adjust the impact energy LE of the primary charged particles of the multiple primary charged particle bundles (3) to a range between 100eV or less and 2keV or greater.

[0169] A detection unit (200) that forms at least part of a secondary electron imaging system (250) for imaging a plurality of secondary electron beams (9) along a secondary electron beam path (13) onto a detector (600), the secondary electron beams being excited at a plurality of focal points (5) on the surface (25) of the object (7);

[0170] A beam splitter (400) is used to separate multiple primary charged particle beams (3) from multiple secondary electron beams (9);

[0171] The first compensator (264.1, 264.2 or 264.3) and the second compensator (264.2, 264.3 or 264.4) are configured to jointly compensate for the aberrations of the electron optical elements of the secondary electron imaging system (250) within the range of secondary electron kinetic energy of a plurality of secondary electron beams (9), the range of secondary electron kinetic energy corresponding to the range of primary charged particle impact energy LE.

[0172] Clause 13: The multi-beam charged particle system (1) as described in Clause 12 further includes an aperture stop (284) and at least one correction lens (211.1, 211.2) configured to adjust the pupil plane (256, 258) at a position of the aperture stop (284) within the range of the impact energy LE of a single charged particle beam (3).

[0173] Clause 14: A multi-beam charged particle beam system (1) as described in Clause 12 or 13, wherein the secondary electron beam path (13) comprises, in sequence, a first pupil plane (256l, 256h), an intermediate image plane (252, 254) and a second pupil plane (258l, 258h, 258) at the first impact energy LE of the primary charged particle.

[0174] Clause 15: A multi-beam charged particle system (1) as described in Clause 14, wherein the first compensator (264.1, 264.2 or 264.3) is disposed in a secondary electron beam path (13) between the first pupil plane (256l, 256h) and the intermediate image plane (252, 254), and the second compensator (264.2, 264.3 or 264.4) is disposed in a secondary electron beam path (13) between the intermediate image plane (252, 254) and the second pupil plane (258l, 258h, 258).

[0175] Clause 16: The multi-beam charged particle system (1) as described in Clause 15 further includes a third compensator (264.3 or 264.4).

[0176] Clause 17: A multi-beam charged particle system (1) as described in Clause 16, wherein the third compensator (264.3 or 264.4) is disposed between the second pupil plane (258l, 258h, 258) and the image plane (225) of the secondary electron imaging system (250).

[0177] Clause 18: A multi-beam charged particle system (1) as described in Clause 14, wherein the first compensator (264.1, 264.2 or 264.3) is disposed in a secondary electron beam path (13) between the first pupil plane (256l, 256h) and the second pupil plane (258l, 258h, 258) and the second compensator (264.2, 264.3 or 264.4) is disposed in a secondary electron beam path (13) between the second pupil plane (258l, 258h, 258) and the image plane (225) of the secondary electron imaging system (250).

[0178] Clause 19: The multi-beam charged particle system (1) as described in any one of Clauses 12 to 18 further comprises:

[0179] A first electron optical element, disposed at a first position within the secondary electron imaging system (250), having at a first impact energy LE1 a first ratio SAR1 of the beam diameter (291) of a single secondary electron beam (9) relative to the diameters (293) of the plurality of secondary electron beams (9); and

[0180] At least one of the first compensator (264.1, 264.2, 264.3) and the second compensator (264.2, 264.3, 264.4) is disposed at a second position within the secondary electronic imaging system (250), having a second ratio SAR2 at the first impact energy LE1, wherein the second ratio SAR2 is the same as the first ratio SAR1 or deviates from the first ratio SAR1 by no more than 0.1.

[0181] Clause 20: A multi-beam charged particle beam system (1) as described in any one of Clauses 12 to 19, wherein at least one of the compensators (264.1 to 264.4) is a multipole element or an astigmatism reducer.

[0182] Clause 21: A method of operating a multi-beam charged particle beam system (1), comprising:

[0183] The inspection area on the wafer (7) is positioned in the field of view of the multi-beam charged particle system using the wafer carrier stage (500);

[0184] The sample voltage VS is supplied to the wafer (7) through the voltage supply unit (503) to adjust the selected impact energy LES of the primary electrons within the impact energy range;

[0185] Determine at least a first sensitivity matrix S(LES;1) for the at least first compensator (264.1, 264.2, 264.3, 264.4) of the selected impact energy LES;

[0186] Determine the aberrations of the secondary electron imaging system (250) at the selected impact energy LES;

[0187] Determine the first actuation of the at least first compensator (264.1, 264.2, 264.3, 264.4) at the selected impact energy LES to compensate for aberrations;

[0188] The first actuation of the at least first compensator (264.1, 264.2, 264.3, 264.4) is applied and the inspection task is performed.

[0189] Clause 22: The method as described in Clause 21, wherein determining the aberration includes describing the aberration by an aberration vector WR(LES) comprising at least two pre-selected aberration vectors selected from a group comprising normalized aberration vector components including: axial astigmatism, pupil distortion, field distortion, second-order field distortion, and linear field astigmatism.

[0190] Clause 23: The method of any one of Clauses 21 to 22 further comprises determining a second sensitivity matrix S (LES; f=2) for a second compensator (264.2, 264.3, 264.4) for a selected impact energy LES and determining a second actuation of the second compensator (264.2, 264.3, 264.4) at the selected impact energy LES.

[0191] Clause 24: The method as described in Clause 23, wherein determining the first actuation of at least the first and second compensators (264.1, 264.2, 264.3, 264.4) and the second actuation comprises determining at least one actuation amplitude C(n,f) of a plurality of normalized actuation modes M(n) of each compensator (264.1, 264.2, 264.3, 264.4).

[0192] Clause 25: The method as described in Clause 24, wherein determining the first actuation and the second actuation of at least the first and second compensators (264.1, 264.2, 264.3, 264.4) comprises executing matrix equations. The optimization is as follows: the aberration vector is WR(LES); the actuation amplitude of the multiple normalized actuation modes M(n) of each compensator is C(n,f), where f=1…F(264.1, 264.2, 264.3, 264.4); the sensitivity matrix of each compensator (264.1, 264.2, 264.3, 264.4) is S(LES; f); and a set of predetermined first weighting functions is G(n,f).

[0193] Clause 26: The method as described in Clause 24, wherein determining the first actuation and the second actuation of at least the first and second compensators (264.1, 264.2, 264.3, 264.4) comprises performing an optimization of the matrix equations, which includes minimizing the actuation amplitude C(n,f) of a plurality of normalized actuation modes M(n) of each compensator (264.1, 264.2, 264.3, 264.4).

[0194] Clause 27: The method described in Clause 26, wherein the optimization of the matrix equation is written as follows: The aberration vector is WR(LES), the actuation amplitude of the multiple normalized actuation modes M(n) of each compensator (264.1, 264.2, 264.3, 264.4) is C(n,f), the sensitivity matrix of each compensator (264.1, 264.2, 264.3, 264.4) is S(LES; f), a set of predetermined first weighting functions is G(n,f), and a second set of predetermined second weighting functions is T(n,f).

[0195] Clause 28: The method as described in any one of Clauses 24 to 27, wherein for the first selected impact energy LES1, the first weighting function G(n,f) of the first compensator (264.1, 264.2 or 264.3) is set to the value G(n,f)>1, and for the second impact energy LES2, G(n,f) is set to G(n,f)=0.

[0196] Clause 29: The method as described in any one of Clauses 21 to 28, wherein determining the sensitivity matrix S (LES;f) of the compensator (264.1, 264.2, 264.3, or 264.4) comprises a set of previously determined sensitivity matrices received from the memory (890). S (LE(q);f=1) is used to determine the sensitivity matrix S(LES;f).

[0197] Clause 30: The method as described in any one of Clauses 21 to 29, wherein the sensitivity matrix is ​​derived from a previously determined by interpolation at at least two different impact energies LE(q1) and LE(q2). SThe sensitivity matrix of the compensator (264.1, 264.2, 264.3, or 264.4) is obtained by interpolation using (LE(q); f). S (LES;f).

[0198] Clause 31: The method of any one of Clauses 21 to 30 further comprises determining the aberrations of the secondary electronic imaging system (250) at the selected impact energy LES by using the monitoring system (230).

[0199] Clause 32: The method as described in any one of Clauses 21 to 30, comprising determining the aberrations of the secondary electron imaging system (250) at the selected shock energy LES based on at least two previously determined aberration vectors WR(Le(q)) received from the memory (890).

[0200] Clause 33: A method for calibrating at least one compensator (264) of a secondary electron imaging system (250) of a multi-beam charged particle beam system (1) within the range of impact energy LE, comprising:

[0201] Determine a set of N normalized actuation modes M(n) for the compensator (264);

[0202] Determine the aberration vector WR of the secondary electronic imaging system (250), which contains at least K=2 normalized aberration vector components selected from groups of normalized aberration vector components, the groups including: axial astigmatism, pupil distortion, field distortion, secondary field distortion, and linear field astigmatism.

[0203] At the compensator (264), the actuation amplitude C(n) is applied individually to each normalized actuation mode M(n);

[0204] The first impact energy LE(1) is adjusted from a set of impact energies LE(q), and the change in aberration vector dW caused by applying the actuation mode M(n) to the compensator (264) under the first impact energy LE(1) is determined;

[0205] Repeatedly adjust the impact energy and determine the change in aberration dW for each impact energy LE(q)=(2…Q) and each normalized actuation mode M(n) in the set of impact energies;

[0206] Determine the sensitivity matrix S (k=1..K,n=1…N, LE(q)) of the K normalized aberration vector components of each normalized actuation mode M (n=1…N) for each impact energy LE(q);

[0207] Multiple sensitivity matrices S (k=1..K,n=1…N,LE(q)) are stored in memory (890).

[0208] Clause 34: The method described in Clause 33 further includes, without actuating the compensator (264), determining the aberration vector WR for each impact energy LE(q) = (2…Q) in the set of impact energies by using the monitoring system (230), the aberration vector WR containing at least K = 2 normalized aberration vector components of the secondary electronic imaging system (250).

[0209] Clause 35: A multi-beam charged particle system (1), comprising:

[0210] An object irradiation unit (100) is configured to form multiple focal points (5) of multiple primary charged particle beams (3) in an object plane (101);

[0211] A sample carrier stage (500) is configured to place the surface (25) of the object (7) in the object plane (101);

[0212] A voltage supply unit (503) is used to supply voltage VS to the sample (7) and is configured to set the selected impact energy LES of the primary charged particles of the plurality of primary charged particle bundles (3) within the range of impact energy LE;

[0213] A detection unit (200) that forms at least part of a secondary electron imaging system (250) for imaging a plurality of secondary electron beams (9) along a secondary electron beam path (13) onto a detector (600), the plurality of secondary electron beams (9) being excited at a plurality of focal points (5) on the surface (25) of the object (7);

[0214] A beam splitter (400) is used to separate the plurality of primary charged particle beams (3) from the plurality of secondary electron beams (9);

[0215] At least one first compensator (264.1, 264.2, 264.3) for aberrations is disposed within the secondary electronic imaging system (250);

[0216] The control unit (800) includes a control processing processor (880) and a memory (890) for storing software instructions that, when executed by the control processing processor (880), cause the multi-beam charged particle system (1) to perform the method as described in any one of clauses 21 to 34.

[0217] Clause 36: The multi-beam charged particle system (1) as described in Clause 35 further includes a second aberration compensator (264.2, 264.3, 264.4) configured within the secondary electron imaging system (250).

[0218] Clause 37: The multi-beam charged particle system (1) as described in Clause 36 further includes a third aberration compensator (264.3, 264.4) configured within the secondary electron imaging system (250).

[0219] However, the present invention is not limited to the foregoing embodiments or claims. These terms, embodiments, or examples may be combined with each other in whole or in part, and the embodiments and examples of the present invention cover various modifications known to those skilled in the art.

[0220] The following is a list of reference numerals.

[0221] 1. Multi-beam charged particle system

[0222] 3. One or more single-charged particle beams

[0223] 5. Primary charged particle beam point

[0224] 7. Objects or samples

[0225] 9 secondary electron beams are formed, creating multiple secondary electron beams.

[0226] 13 Secondary Electron Beam Path

[0227] 15 Secondary charged particle focus

[0228] 25. The surface of an object or sample

[0229] 67 First Material Composition

[0230] 69 Second Material Composition

[0231] 100 object illumination units

[0232] 101 Image plane

[0233] 102 Objective Lens

[0234] 103 field lens

[0235] 108 First beam intersection point

[0236] 110 Common Multibeam Raster Scanner

[0237] 133 electrode

[0238] 135 First Electric Field

[0239] 137 Second Electric Field

[0240] 151 Bundle Tube

[0241] 153 bundle outlet openings

[0242] 161 coil

[0243] 163 Extreme Boots

[0244] 165 Lower Pole Boot Section

[0245] 200 detection units

[0246] 205 Magnetic Dynamic Lens

[0247] 211 Correction Lens

[0248] 220 Multipole Corrector

[0249] 222 Second raster scanner

[0250] 225 Secondary Electron Image Plane

[0251] 230 Monitoring System

[0252] 232 High-resolution sensor

[0253] 235 Imaging Lens

[0254] 237 beam splitter mirror

[0255] 250 Secondary Electron Imaging System

[0256] 252 Low-energy intermediate image position

[0257] 254 High-energy intermediate image position

[0258] 256 First intersection or pupil position

[0259] 258 Second intersection or pupil position

[0260] 262 SAR through system

[0261] 264 Multipole Corrector

[0262] 266 Position of the multipole corrector

[0263] 268 electrode

[0264] 281 Axial point electronic trajectory

[0265] Electronic tracks of 283 field points

[0266] 284 aperture stop

[0267] Small beam at 291 axial field point

[0268] 293 Small clusters of peripheral field points

[0269] Coverage area of ​​more than 295 small bundles

[0270] 300 Charged Particle Multi-beam Generator

[0271] 301 Charged Particle Source

[0272] 303 Collimating Lens

[0273] 304 filter plate

[0274] 305 Single-phase multi-bundle forming unit

[0275] 306 perforated plate

[0276] 309 primary electron beam

[0277] 321 Intermediate image surface

[0278] 331 First Field Lens

[0279] 333 Second Field Lens

[0280] 400 beam splitter or beam splitter unit

[0281] 500 sample carrier platform

[0282] 503 Sample Voltage Source

[0283] 505 Sample Installation Platform

[0284] 600 Image Sensor

[0285] 602 Electron-to-Photon Conversion Unit

[0286] 605 Condensing Lens

[0287] 611 Zoom Lens

[0288] 623 Detection Element

[0289] 800 control unit

[0290] 810 Imaging Control Module

[0291] 820 sensor module

[0292] 830 Primary Beam Path Control Module

[0293] 840 Secondary Beam Path Control Module

[0294] 850 Platform Control Module

[0295] 860 Scan Control Unit

[0296] 880 Control Processor

[0297] 890 memory

Claims

1. A multi-beam charged particle beam system (1), comprising: An object illumination unit (100) is configured to form a plurality of primary bands in the object plane (101). Multiple focal points (5) of the small beam of electric particles (3); A sample carrier stage (500) is configured to place the surface (25) of the object (7) on the object plane. (101) in; A voltage supply unit (503) is used to provide a voltage VS to the object (7), the voltage supply unit (503) being configured to set the first impact energy LE1 of the primary charged particles of the plurality of primary charged particle bundles (3); A detection unit (200) that forms at least part of a secondary electron imaging system (250) for imaging a plurality of secondary electron beams (9) along a secondary electron beam path (13) onto a detector (600), the plurality of secondary electron beams being excited at the plurality of focal points (5) on the surface (25) of the object (7); A beam splitter (400) is used to split the plurality of primary charged particle beams (3) with the plurality of Secondary electron beam (9) separation; A first electron optical element, disposed at a first position within the secondary electron imaging system (250), has a first ratio SAR1 of the beam diameter (293) of a single secondary electron beam (9) relative to the diameter (295) of the plurality of secondary electron beams (9) under the first impact energy LE1. The first aberration compensator (264.1, 264.2, 264.3), wherein the aberration is compensated by the first... An electro-optical element causes this, wherein the first compensator (264.1, 264.2, 264.3) is disposed at a second position within the secondary electronic imaging system (250), having a second ratio SAR2 under the first impact energy LE1, wherein the second ratio SAR2 is the same as the first ratio SAR1 or deviates from the first ratio SAR1 by no more than 0.

1.

2. The multi-beam charged particle beam system (1) as claimed in claim 1, wherein the first electron optical element is at least a portion of the beam splitter (400, 400.2, 400.3).

3. The multi-beam charged particle beam system (1) as described in claim 1 or 2, wherein the first compensator (264.1, 264.2, 264.3) is a multipole element or an astigmatism reducer.

4. The multi-beam charged particle beam system (1) as claimed in any one of claims 1 to 3, wherein the detection unit (200) further comprises an aperture stop (284) disposed at the pupil plane (258) of the secondary electron beam path (13) under the first impact energy LE1.

5. The multi-beam charged particle beam system (1) as claimed in any one of claims 1 to 4, further comprising a second aberration compensator (264.2, 264.3, 264.4).

6. The multi-beam charged particle beam system (1) as claimed in claim 5, wherein the second compensator (264.1, 264.2, 264.3) is disposed at a third position within the secondary electron imaging system (250) and has a third ratio SAR3 at the first impact energy LE1, wherein the third ratio SAR3 is different from the second ratio SAR2.

7. The multi-beam charged particle system (1) as claimed in claim 5 or 6, wherein the first compensator (264.1, 264.2 or 264.3) and the second compensator (264.2, 264.3 or 264.4) are configured to jointly compensate for the aberrations of the first electro-optical element under the first impact energy LE1.

8. The multi-beam charged particle system (1) as claimed in any one of claims 5 to 7, wherein the first compensator (264.1, 264.2 or 264.3) and the second compensator (264.2, 264.3 or 264.4) are configured to jointly compensate for the aberrations of the first electro-optical element at the second impact energy LE2 of the primary charged particle, the second impact energy LE2 being different from the first impact energy LE1.

9. The multi-beam charged particle system (1) as claimed in any one of claims 5 to 8, wherein the secondary electron beam path (13) within the secondary electron imaging system (250) further comprises an intermediate image plane (252, 254) at the first impact energy LE1, and wherein the first compensator (264.1, 264.2, 264.3) is disposed upstream of the intermediate image plane (252, 254) relative to the propagation direction of the secondary electrons, and the second compensator (264.2, 264.3, 264.4) is disposed downstream of the intermediate image plane (252, 254).

10. The multi-beam charged particle system (1) according to any one of claims 5 to 8, wherein the first compensator (264.1, 264.2, 264.3) is disposed upstream of the aperture stop (284) relative to the propagation direction of the secondary electron, and the second compensator (264.2, 264.3, 264.4) is disposed downstream of the aperture stop (284).

11. The multi-beam charged particle beam system (1) according to any one of claims 4 to 10, further comprising at least one correction lens (211.1, 211.2) configured to adjust the pupil plane (258) at a position of the aperture stop (284) under a second impact energy LE2 different from the first impact energy LE1.

12. A multi-beam charged particle beam system (1), comprising: An object illumination unit (100) is configured to form a plurality of primary bands in the object plane (101). Multiple focal points (5) of the small beam of electric particles (3); A sample support stage (500) is configured to place the surface (25) of the object (7) on the object plane. (101) in; A voltage supply unit (503) is used to provide a voltage VS to the sample (7), the voltage supply unit (503) being configured to adjust the impact energy LE of the primary charged particles of the plurality of primary charged particle bundles (3) to a range between 100 eV or less and 2 keV or greater; A detection unit (200) that forms at least part of a secondary electron imaging system (250) for imaging a plurality of secondary electron beams (9) along a secondary electron beam path (13) onto a detector (600), the plurality of secondary electron beams being excited at the plurality of focal points (5) on the surface (25) of the object (7); A beam splitter (400) is used to split the plurality of primary charged particle beams (3) with the plurality of Secondary electron beam (9) separation; First compensator (264.1, 264.2, or 264.3) and second compensator (264.2, 264.3) Or 264.4), which is configured to jointly compensate for the aberrations of the electron optical elements of the secondary electron imaging system (250) within the kinetic energy range of the secondary electrons of the secondary electron beam (9), the kinetic energy range of the secondary electrons of the secondary electron beam (9) corresponding to the range of the impact energy LE of the primary charged particle.

13. The multi-beam charged particle beam system (1) as claimed in claim 12 further comprises: an aperture stop (284); and at least one correction lens (211.1, 211.2) configured to adjust the pupil plane (256, 258) at a position of the aperture stop (284) within the range of the impact energy LE of the primary charged particle beam (3).

14. The multi-beam charged particle beam system (1) as claimed in claim 12 or 13, wherein the secondary electron beam path (13) comprises, in sequence at the first impact energy LE of the primary charged particle, a first pupil plane (256l, 256h), an intermediate image plane (252, 254) and a second pupil plane (258l, 258h, 258).

15. The multi-beam charged particle system (1) as claimed in claim 14, wherein the first compensator (264.1, 264.2 or 264.3) is disposed in the secondary electron beam path (13) between the first pupil plane (256l, 256h) and the intermediate image plane (252, 254), and the second compensator (264.2, 264.3 or 264.4) is disposed in the secondary electron beam path (13) between the intermediate image plane (252, 254) and the second pupil plane (258l, 258h, 258).

16. The multi-beam charged particle beam system (1) as claimed in claim 15, further comprising a third compensator (264.3 or 264.4).

17. The multi-beam charged particle beam system (1) as claimed in claim 16, wherein the third compensator (264.3 or 264.4) is disposed between the second pupil plane (258l, 258h, 258) and the image plane (225) of the secondary electron imaging system (250).

18. The multi-beam charged particle system (1) as claimed in claim 14, wherein the first compensator (264.1, 264.2 or 264.3) is disposed in the secondary electron beam path (13) between the first pupil plane (256l, 256h) and the second pupil plane (258l, 258h, 258) and the second compensator (264.2, 264.3 or 264.4) is disposed in the secondary electron beam path (13) between the second pupil plane (258l, 258h, 258) and the image plane (225) of the secondary electron imaging system (250).

19. The multi-beam charged particle beam system (1) as described in any one of claims 12 to 18, further comprising: A first electron optical element, disposed at a first position within the secondary electron imaging system (250), having at a first impact energy LE1 a first ratio SAR1 of the beam diameter (291) of a single secondary electron beam (9) relative to the diameter (293) of the plurality of secondary electron beams (9); and At least one of the first compensator (264.1, 264.2, 264.3) and the second compensator (264.2, 264.3, 264.4) is disposed at a second position within the secondary electronic imaging system (250), having a second ratio SAR2 under the first impact energy LE1, wherein the second ratio SAR2 is the same as the first ratio SAR1 or deviates from the first ratio SAR1 by no more than 0.

1.

20. The multi-beam charged particle beam system (1) according to any one of claims 12 to 19, wherein at least one of the compensators (264.1 to 264.4) is a multipole element.

21. A method for operating a multi-beam charged particle beam system (1), comprising: The inspection area on the wafer (7) is positioned in the field of view of the multi-beam charged particle system (1) by means of the wafer carrier stage (500); The sample voltage VS is supplied to the wafer (7) through the voltage supply unit (503), and the first voltage is supplied to the wafer (7). The selected impact energy LES of the electron is adjusted within the impact energy range; Determine at least a first sensitivity matrix S(LES;1) for at least a first compensator (264.1, 264.2, 264.3, 264.4) of the selected impact energy LES; Determine the aberrations of the secondary electron imaging system (250) at the selected impact energy LES; Determine the first actuation of the at least first compensator (264.1, 264.2, 264.3, 264.4) at the selected impact energy LES to compensate for aberrations; The first actuation of the at least first compensator (264.1, 264.2, 264.3, 264.4) is applied and the inspection task is performed.

22. The method of claim 21, wherein determining the aberration comprises describing the aberration by an aberration vector WR(LES), the aberration vector WR(LES) comprising at least two preselected aberration vector components selected from a group of normalized aberration vector components, the group including axial astigmatism, pupil distortion, field distortion, second-order field distortion, and linear field astigmatism.

23. The method of any one of claims 21 to 22, further comprising determining a second sensitivity matrix S (LES; f=2) for a second compensator (264.2, 264.3, 264.4) for the selected impact energy LES and determining a second actuation of the second compensator (264.2, 264.3, 264.4) at the selected impact energy LES.

24. The method of claim 23, wherein determining the first actuation and the second actuation of the at least first and second compensators (264.1, 264.2, 264.3, 264.4) comprises determining at least one actuation amplitude C(n,f) of a plurality of normalized actuation modes M(n) of each compensator (264.1, 264.2, 264.3, 264.4).

25. The method of claim 24, wherein determining the first actuation and the second actuation of the at least first compensator and the second compensator (264.1, 264.2, 264.3, 264.4) comprises executing matrix equations. Optimization, The aberration vector is WR(LES); the actuation amplitude of the multiple normalized actuation modes M(n) of each compensator is C(n,f), where f=1...F (264.1, 264.2, 264.3, 264.4); the sensitivity matrix of each compensator (264.1, 264.2, 264.3, 264.4) is S(LES;f); and a predetermined first weighting function is G(n,f).

26. The method of claim 24, wherein determining the first actuation and the second actuation of the at least first compensator and the second compensator (264.1, 264.2, 264.3, 264.4) comprises performing an optimization of the matrix equations, which includes minimizing the actuation amplitude C(n,f) of a plurality of normalized actuation modes M(n) of each compensator (264.1, 264.2, 264.3, 264.4).

27. The method of claim 26, wherein the optimized matrix equation is written as: ， in, The aberration vector is WR(LES); the actuation amplitude of the multiple normalized actuation modes M(n) of each compensator (264.1, 264.2, 264.3, 264.4) is C(n,f); the sensitivity matrix of each compensator (264.1, 264.2, 264.3, 264.4) is S(LES; f); a set of predetermined first weighting functions is G(n,f); and a second set of predetermined second weighting functions is T(n,f).

28. The method of any one of claims 24 to 27, wherein for the first selected impact energy LES1, the first weighting function G(n,f) of the first compensator (264.1, 264.2 or 264.3) is set to the value G(n,f)>1, and for the second impact energy LES2, it is set to G(n,f)=0.

29. The method of any one of claims 21 to 28, wherein determining the sensitivity matrix S(LES;f) of the compensator (264.1, 264.2, 264.3 or 264.4) comprises a set of previously determined sensitivity matrices received from the memory (890). S (LE(q);f=1) is used to determine the sensitivity matrix S(LES;f).

30. The method of any one of claims 21 to 29, wherein the sensitivity matrix is ​​derived from at least two different impact energies LE(q1) and LE(q2) previously determined by interpolation. S The sensitivity matrix of the compensator (264.1, 264.2, 264.3, or 264.4) is obtained by interpolation using (LE(q);f). S (LES;f).

31. The method of any one of claims 21 to 30, further comprising determining the aberrations of the secondary electron imaging system (250) at the selected impact energy LES by using a monitoring system (230).

32. The method of any one of claims 21 to 30, comprising determining the aberrations of the secondary electron imaging system (250) at the selected impact energy LES based on at least two previously determined aberration vectors WR(Le(q)) received from the memory (890).

33. A multi-beam charged particle beam system (1), comprising: An object irradiation unit (100) is configured to form multiple focal points (5) of multiple primary charged particle beams (3) in an object plane (101); A sample carrier stage (500) is configured to place the surface (25) of the object (7) in the object plane (101); A voltage supply unit (503) is used to supply a voltage VS to the sample (7), the voltage supply unit (503) being configured to set the selected impact energy LES of the primary charged particles of the plurality of primary charged particle bundles (3) within the range of impact energy LE; A detection unit (200) that forms at least part of a secondary electron imaging system (250) for imaging a plurality of secondary electron beams (9) along a secondary electron beam path (13) onto a detector (600), the plurality of secondary electron beams being excited on the surface (25) of the object (7) at the plurality of focal points (5); A beam splitter (400) is used to separate the plurality of primary charged particle beams (3) from the plurality of secondary electron beams (9); At least one first compensator (264.1, 264.2, 264.3) for aberrations is configured within the secondary electronic imaging system (250); A control unit (800) includes: a control processing processor (880); and a memory (890) for storing software instructions that, when executed by the control processing processor (880), cause the multi-beam charged particle system to perform the method as described in any one of claims 21 to 32.

34. The multi-beam charged particle system (1) as claimed in claim 33 further includes a second aberration compensator (264.2, 264.3, 264.4) disposed within the secondary electron imaging system (250).

35. The multi-beam charged particle system (1) as claimed in claim 34 further includes a third aberration compensator (264.3, 264.4) disposed within the secondary electron imaging system (250).

Images