Multi-beam particle microscope operating with a wide range of landing energies

Abstract

A multi-beam particle microscope with reduced aberrations in the secondary particle optical beam path is disclosed. The solution is applicable to a wide range of landing energies up to several keV. One measure to achieve this aim is an architectural approach with an improved design of the entire projection path, and particularly an improved positioning of a first projection lens in the secondary particle optical beam path, wherein the first projection lens is an installation space consuming magnetic lens. A filling factor in the first projection lens has been identified as a leading source for remaining aberrations in the secondary particle optical beam path when operating the multi-beam particle microscope over a wide range of landing energies. Another measure is the performance enhancement of the beam splitter arrangement itself in the secondary particle optical beam path. Several designs of the beam splitter arrangement and design rule for reducing aberrations when operating the multi-beam particle microscope over a wide range of landing energies are disclosed.

Description

[0001] Multi-beam particle microscope operating with a wide range of landing energies

[0002] Field of the invention

[0003] The invention relates to a multi-beam particle microscope which operates with a wide range of landing energies. The multi-beam particle microscope comprises an improved projection system and / or an improved beam splitter arrangement. The beam splitter arrangement comprises a magnet arrangement for separating a primary particle-optical beam path and a secondary particle-optical beam path.

[0004] Prior art

[0005] With the continuous development of ever smaller and ever more complex microstructures such as semiconductor components, there is a need to further develop and optimize planar production techniques and inspection systems for producing and inspecting small dimensions of the microstructures. By way of example, the development and production of the semiconductor components requires monitoring of the design of test wafers, and the planar production techniques require process optimization for a reliable production with a high throughput. Moreover, there have been recent demands for an analysis of semiconductor wafers for reverse engineering and for a customer-specific, individual configuration of semiconductor components. Therefore, there is a need for inspection means which can be used with a high throughput for examining the microstructures on wafers with a high accuracy.

[0006] Typical silicon wafers used in the production of semiconductor components have diameters of up to 300 mm. Each wafer is divided into 30 to 60 repeating regions ("dies") with a size of up to 800 mm2. A semiconductor apparatus comprises a plurality of semiconductor structures, which are produced in layers on a surface of the wafer by planar integration techniques. Semiconductor wafers typically have a plane surface on account of the production processes. The structure size of the integrated semiconductor structures in this case extends from a few pm to the critical dimensions (CD) of 5 nm, with the structure sizes becoming even smaller in the near future; in future, structure sizes or critical dimensions (CD) are expected to be less than 3 nm, for example 2 nm, or even under 1 nm. In the case of the aforementioned small structure sizes, defects in the size of the critical dimensions must be identified quickly in a very large area. For several applications, the specification requirement regarding the accuracy of a measurement provided by inspection equipment is even higher, for example by a factor of two or one order of magnitude. By way of example, a width of a semiconductor feature must be measured with an accuracy of below 1 nm, for example 0.3 nm or even less, and a relative position of semiconductor structures must be determined with an overlay accuracy of below 1 nm, for example 0.3 nm or even less.

[0007] The MSEM, a multi-beam scanning electron microscope, is a relatively new development in the field of charged particle systems (charged particle microscopes, CPMs). By way of example, a multi-beam scanning electron microscope is disclosed in US 7 244 949 B2 and in US 2019 / 0355544 A1. In the case of a multi-beam electron microscope or MSEM, a sample is irradiated simultaneously with a plurality of individual electron beams, which are arranged in a field or raster. By way of example, 4 to 10 000 individual electron beams can be provided as primary radiation, with each individual electron beam being separated from an adjacent individual electron beam by a pitch of 1 to 200 micrometres. By way of example, an MSEM has approximately 100 separate individual electron beams ("beamlets"), which are arranged for example in a hexagonal raster, with the individual electron beams being separated by a pitch of approximately 10 pm. The plurality of charged individual particle beams (primary beams) are focused on a surface of a sample to be examined by way of a common objective lens. By way of example, the sample can be a semiconductor wafer which is secured to a wafer holder mounted on a movable stage. During the illumination of the wafer surface with the charged primary individual particle beams, interaction products, for example secondary electrons or backscattered electrons, emanate from the surface of the wafer. Their start points correspond to those locations on the sample on which the plurality of primary individual particle beams are focused in each case. The amount and the energy of the interaction products depend on the material composition and the topography of the wafer surface. The interaction products form a plurality of secondary individual particle beams (secondary beams), which are collected by the common objective lens and which are incident on a detector arranged in a detection plane as a result of a projection imaging system of the multi-beam inspection system. The detector comprises a plurality of detection regions, each of which comprises a plurality of detection pixels, and the detector captures an intensity distribution for each of the secondary individual particle beams. An image field of, for example, 100 pm x 100 pm is obtained in the process.

[0008] The multi-beam electron microscope of the prior art comprises a sequence of electrostatic and magnetic elements. At least some of the electrostatic and magnetic elements are adjustable in order to adapt the focus position and the stigmation of the plurality of charged individual particle beams. The multi-beam system with charged particles of the prior art moreover comprises at least one cross-over plane of the primary or the secondary charged individual particle beams. Moreover, the system of the prior art comprises detection systems to make the adjustment easier. The multi-beam particle microscope of the prior art comprises at least one beam deflector ("deflection scanner") for collective scanning of a region of the sample surface by means of the plurality of primary individual particle beams in order to obtain an image field of the sample surface.

[0009] What is known as a beam splitter (or alternatively as a beam separator or beam divider) is used to separate the particle-optical beam path of the primary beams from the particle-optical beam path of the secondary beams. In this case, separation is implemented by means of special arrangements of magnetic fields and / or electrostatic fields, for example by means of a Wien filter.

[0010] Imaging aberrations arise quite generally as a result of using particle-optical components. Aberrations within the scope of particle-optical imaging, which need to be corrected where possible, also arise when a beam splitter is used. Ideally, imaging aberrations should be avoided or corrected for all individual particle beams. The corrections normally become ever more important as image fields become ever more extensive within the scope of the particle- optical imaging. An image field can be particularly extensive in the case of multi-beam particle microscopes which operate with a plurality of individual particle beams (multi-image field, so- called mFOV).

[0011] To correct aberrations due to beam splitters of multi-beam particle microscopes, EP 1 668662 B1 discloses the provision of a further magnetic sector field in the primary path upstream of the actual separating magnetic sector field. Aberrations in the secondary path are corrected by up to three further magnetic sector fields in the secondary path.

[0012] US 9,153,413 B2 discloses a further beam splitter for multi-beam particle microscopes, in the case of which there is a correction of beam splitter-induced aberrations. The beam splitter operates according to the Wien filter principle. To correct aberrations, alignments or skews of individual particle beams are respectively corrected singly or individually by means of multideflector arrays following the passage through the beam splitter.

[0013] DE 10 2022 120 496 A1 discloses a particle-optical arrangement, in particular a multi-beam particle microscope, with a magnet arrangement for separating a primary and a secondary particle-optical beam path. The magnet arrangement has: a first magnetic field region through which the primary particle-optical beam path and the second particle-optical beam path pass, for the separation of the primary particle-optical beam path and the secondary particle-optical beam path from one another; a second magnetic field region arranged in the primary particle- optical beam path and not arranged in the secondary particle-optical beam path, the second magnetic field region being arranged upstream of the first magnetic field region in relation to the primary particle-optical beam path and the first magnetic field region and the second magnetic field region substantially deflecting the primary particle-optical beam path in different directions; a third magnetic field region arranged in the primary particle-optical beam path and not arranged in the secondary particle-optical beam path, the third magnetic field region being arranged upstream of the second magnetic field region in relation to the primary particle-optical beam path and the first and the third magnetic field region substantially deflecting the primary particle-optical beam path in the same direction. An entrance direction of the primary particle- optical beam path into the third magnetic field region and an exit direction of the primary particle-optical beam path from the first magnetic field region are parallel to one another and without an offset.

[0014] With increasing demands on the resolution of multi-beam particle microscopes, there are also increasing demands on corrections of aberrations. Thus, there is a need for improvement overall in the context of the correction of beam splitter-induced imaging aberrations.

[0015] DE 102023 120 127 A1 - which was not yet published on the priority date of the present patent application - discloses an improved beam splitter suited for a multi-beam particle microscope, the full disclosure of which is incorporated in the present patent application by reference. The application discloses an arrangement of two magnetic sectors in the primary beam path, wherein a so-called first sector or splitting sector through which the primary particle-optical beam path and the secondary particle-optical beam path pass, for the separation of the primary particle-optical beam path and the secondary particle-optical beam path from one another, has a specific orientation. More precisely, each magnetic sector has an entrance region for the primary particle-optical beam path with an entrance inclination and an exit region for the primary particle-optical beam path with an exit inclination, wherein the entrance inclination is defined as the angle by which the alignment of the entrance region deviates from the normal to the optical axis of the primary particle-optical beam path, and wherein the exit inclination is defined as the angle by which the alignment of the exit region deviates from the normal to the optical axis of the primary particle-optical beam path. In DE 102023 120 127 A1 it is disclosed that said exit inclination deliberately deviates from 0°. This measure contributes to a further significant reduction of aberrations induced by the beam splitter arrangement in the primary particle-optical beam path. Furthermore, it is disclosed that a beam splitter arrangement in the secondary particle-optical beam path, after passing through the first magnetic field region, has at least six further magnetic field regions and / or quadrupole fields which are set up in order to precisely couple the particle-optical axis in the secondary beam path with respect to offset and angle into a subsequent projection optics when the energy of secondary particles varies, whose path forms the second particle-optical beam path, and additionally enable paraxial stigmatic, paraxial distortion-free and paraxial dispersion-free imaging. Further details of the beam splitter arrangement in the secondary particle optical beam path are not disclosed.

[0016] Therefore, there is a further demand to also further reduce beam splitter induced aberrations occurring in the secondary particle-optical beam path.

[0017] EP 1 668662 B1 discloses a beam splitter arrangement in the secondary particle optical beam path. Said beam splitter arrangement comprises four magnetic sectors in the secondary particle optical beam path followed by a quadrupole lens. The beam splitter arrangement is in first order stigmatic, in first order distortion free, and in first order dispersion corrected in the secondary particle optical beam path for one setting of the landing energy LE of the primary electrons on the object. There is a further demand for a beam splitter arrangement that allows for respective corrections at more than just one landing energy.

[0018] EP 1 668 662 B1 discloses a typical range of landing energies between OeV and about 100eV on the object. However, it is aimed to operate a multi-beam particle microscope with higher landing energies since an optimum landing energy depends on the nature of the sample / the object. However, if the landing energy is high, the kinetic energy of secondary particles emanating from the object becomes low and aberrations in the secondary particle optical beam path are generally enhanced. Therefore, operating a multi-beam particle microscope with higher landing energies and still allowing for a very good correction of aberrations in the second particle optical beam path is a general task.

[0019] The cited landing energy range that is currently available is not sufficient to perform specific defect inspection and / or metrology tasks. If, e.g., physical defect inspection on a EUV photoresist layer shall be performed, rather low landing energies in the range from 50eV to 500eV are beneficial to improve contrast and to reduce CD shrinkage. If, on the other hand, overlay metrology of buried layers or imaging of deep trenches and contact holes shall be accomplished, high landing energies in the range from 3keV to 30keV can be useful. Description of the invention

[0020] It is an object to provide an improved multi-beam particle microscope which can operate over a large range of landing energies and can still provide a very good correction of aberrations in the secondary particle optical beam path.

[0021] It is another object of the present invention to further reduce beam splitter-induced aberrations in the secondary particle-optical beam path of a multi-beam particle microscope.

[0022] The object is achieved by the subject matter of the independent patent claims.

[0023] Advantageous embodiments of the invention are evident from the dependent patent claims.

[0024] The present patent application claims the priority of German patent application No. 10 2024 108 091.4 filed on 21 March 2024, the disclosure of which in the full scope thereof is incorporated in the present patent application by reference.

[0025] The performance of the mentioned state-of-the-art projection system in multi-beam-particle microscopes prevents accessing the described extended range of LEs, especially the higher LEs, for several reasons, two of them being:

[0026] - To avoid cross-talk between neighbouring detectors, the blur and distortion of the projected signal / secondary electron spots has to be sufficiently small which is currently not the case at high landing energies LE (a typical limit of the blur spot radius plus the maximal distortion being approximately 80% of the radius of the detector circle which is attributed for detection of each individual signal electron beamlet).

[0027] - To limit contrast anisotropy, excessive ellipticity of the beamlet crossover cross-section at the plane in which the contrast aperture is put needs to be avoided (typical ellipticity limit of 0.1).

[0028] The inventors have further investigated the above-mentioned problems and have identified two solution strategies which are sometimes conflicting. The first solution strategy is most concerned about optimizing the complete projection system performance (architectural approach) while the second solution strategy puts optimization of the intrinsic beam splitter performance at its centre (component-based approach).

[0029] The first approach is motivated by the finding that the projection system performance, especially at higher landing energies, is not necessarily mainly limited by the intrinsic beam splitter performance, but by the aberrations of one or several of the projection system lenses (PLs) which are positioned in relation to the secondary particle optical beam path after the beam splitter arrangement according to the prior art. It is a basic idea that it can be beneficial to lower the requirements on the beam splitter performance if, in this way, the aberrations of the performance-limiting projection lens system can be significantly reduced.

[0030] The second approach is motivated by the rationale that a well-corrected beam splitter design, first, contributes only few aberrations to the total projection system by itself, and second, delivers signal electron beamlets with only few aberrations to the following electron-optical elements in the projection system, thus helping in avoiding consequential errors.

[0031] The present invention covers solutions according to both approaches as identified above.

[0032] According to the first approach, it has been found out that the so-called filling factor of the very first projection lens in the projection lens system becomes a decisive influence on aberrations when working with increasing landing energies. In more detail, for increasing landing energies, the energy of the secondary particle / signal electrons gets smaller and smaller such that the focusing by the objective lens increases. The focusing of the objective lens is fix because of an optimum operation of the primary particle beam path and cannot be changed for the secondary particles. Therefore, the first intermediate image of the secondary particles / signal electron beamlets moves increasingly close to the sample / the object. Consequently, the multi- field-of-view (mFOV) radius inside the first projection lens increases for high landing energies LE. This increases the filling factor inside the first projection lens which in turn leads to an accumulation of large aberrations in the first projection lens and thus in the subsequent particle optical path.

[0033] Having identified the importance of the filling factor in the first projection lens for suppression of aberrations, the filling factor is reduced according to a first aspect of the present invention. In more detail, according to a first aspect of the invention, the latter relates to a multi-beam particle microscope, comprising: a multi-beam particle generator, which is configured to generate a first field of a plurality of charged first individual particle beams; a first particle-optical unit with a primary particle-optical beam path, configured to image the generated first individual particle beams onto an object plane such that the first individual particle beams impinge an object at incidence locations, which form a second field; a detection unit with a plurality of detection regions which form a third field; a second particle-optical unit with a secondary particle-optical beam path, configured to image second individual particle beams, which emanate from the incidence locations in the second field, onto the third field of the detection regions of the detection system; a magnetic and / or electrostatic objective lens system, through which both the first and the second individual particle beams pass; a beam splitter arrangement which is arranged in the primary particle-optical beam path between the multi-beam generator and the objective lens and which is arranged in the secondary particle-optical beam path between the objective lens system and the detection unit; and a controller configured to control the multi-beam particle microscope and to control a landing energy of the first individual particle beams on the object; wherein the beam splitter arrangement comprises the following features: at least a first magnetic sector, the first magnetic sector being configured for providing a homogeneous magnetic field through which during use the primary particle-optical beam path and the secondary particle-optical beam path pass, and being configured for the separation of the primary particle-optical beam path and the secondary particle-optical beam path from one another; wherein each magnetic sector has an entrance region for the secondary particle-optical beam path with an entrance inclination and an exit region for the secondary particle-optical beam path with an exit inclination, wherein the entrance inclination is defined as the angle by which the alignment of the entrance region deviates from the normal to the optical axis of the secondary particle-optical beam path, and wherein the exit inclination is defined as the angle by which the alignment of the exit region deviates from the normal to the optical axis of the secondary particle-optical beam path; wherein the entrance inclination of the first magnetic sector deviates from 0°; wherein the secondary particle optical beam path comprises a first cross-over of the second individual particle beams corresponding to a focal plane of the objective lens system and a second cross-over of the second individual particle beams which is arranged between the beam splitter arrangement and the detection unit and which can be arranged during use level with a contrast aperture; and wherein the second particle-optical unit comprises a projection lens system with a first projection lens which is a magnetic lens, the first projection lens being arranged in relation to the secondary particle optical beam path after the first cross-over and before the second crossover; the projection lens system being configured for imaging the second individual particle beams onto the third field and the first projection lens being configured for focussing the plurality of second individual particle beams on the second cross-over; wherein the controller is configured for controlling the first projection lens for focussing the plurality of second individual particle beams on the second cross-over depending on the landing energy; and wherein the first projection lens is arranged so close to the first cross-over that a filling factor PL1 of the first projection lens is set to PL1 < 15%, in particular PL1 < 10% or PL1 < 5%, wherein the filling factor PL1 is defined as the ratio between a maximum radius Rmax of the plurality of second individual particle beams altogether within the first projection lens and an inner radius Ri of an opening of the first projection lens through which opening the second individual particle beams pass, thus PL1= Rmax / Ri.

[0034] In other words, the first projection lens which is a magnetic lens typically has a pole shoe with a central bore hole which has an inner radius Ri. The second individual particle beams must pass through said bore hole or opening and must keep a certain distance to the inner walls not to pick-up too many aberrations. The area of the plurality of the second individual particle beams altogether corresponds to the field of view FOV inside the first projection lens. However, it is in principle also possible that the first projection lens and possibly other lenses of a projection lens system is / are electrostatic lens(es).

[0035] The landing energy can be in the range from zero up to several keV, for example 3keV, 5keV, 10keV, 15keV, 20keV, 25keV or 30keV.

[0036] The magnetic sectors themselves can be formed in a manner known per se. They are designed in particular to form homogeneous magnetic fields, with the direction of the magnetic field being oriented orthogonal to the movement direction of the individual particle beams. By way of example, the magnetic sectors can each be formed by two spaced apart slabs of magnetizable material, each with milled depressions into which current conductors or coils have been inserted. However, other embodiments are also possible.

[0037] The second cross-over is during use of the multi-beam particle microscope arranged level with a contrast aperture. Said contrast aperture allows filtering the second individual particle beams emanating from the object with respect to their starting angles from the object.

[0038] The first individual charged particle beams can be, for example, electrons, positrons, muons or ions or other charged particles. The second individual charged particle beams can be mirror particles of the first individual charged particle beams; they can be secondary electrons or backscattered electrons. In principle, the particle-optical arrangement is therefore flexibly usable. The terms primary particle-optical beam path and secondary particle-optical beam path are used as conventional in the art. However, attention is drawn here to the fact that the primary particle-optical beam path, just like the secondary particle-optical beam path, describes the paths of the plurality of first or second individual particle beams. For simplification, it may however naturally be - depending on context - that the terms primary particle-optical beam path and secondary particle-optical beam path only reference an individual particle beam, moving along the optical axis of the system, or the central beam.

[0039] According to a preferred embodiment, the beam splitter arrangement further comprises a second magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the second magnetic sector being arranged downstream of the first magnetic sector in relation to the secondary particle-optical beam path and being configured for providing a homogeneous magnetic field for deflecting the second individual particle beams. The beam splitter arrangement further comprises a third magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the third magnetic sector being arranged downstream of the second magnetic sector in relation to the secondary particle-optical beam path and being configured for providing a homogeneous magnetic field. The first projection lens is arranged between the first magnetic sector and the second magnetic sector; and the controller is configured to control the second magnetic sector and the third magnetic sector depending on the landing energy. With this radical approach and the first projection lens being very close to the object / the sample, the filling factor PL1 inside the first projection lens can be reduced very efficiently. The second and third magnetic sectors can be used for further corrections in the secondary particle optical beam path.

[0040] According to a preferred embodiment, the controller is configured for controlling the second magnetic sector and the third magnetic sector to adjust a tilt and an offset of the particle optical axis within the projection lens system. For example, coupling into a second projection lens can be corrected with respect to a tilt and an offset. The second magnetic sector can be used to adjust a tilt and the third magnetic sector can be used to adjust an offset or vice versa.

[0041] According to a preferred embodiment, the beam splitter arrangement further comprises at least one multipole arrangement arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the multipole arrangement being arranged downstream of the first magnetic sector in relation to the secondary particle-optical beam path. The first projection lens is arranged in the direction of the secondary particle optical beam path after the first magnetic sector and before the multipole arrangement. The controller is configured to control the multipole arrangement depending on the landing energy.

[0042] According to a preferred embodiment, the controller is configured to control the at least one multipole arrangement to additionally enable paraxial stigmatic, paraxial distortion-free and / or paraxial dispersion-free imaging on the detection plane.

[0043] According to a preferred embodiment, the beam splitter arrangement further comprises a second magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the second magnetic sector being arranged downstream of the first magnetic sector in relation to the secondary particle-optical beam path and being configured for providing a homogeneous magnetic field for deflecting the second individual particle beams. The first projection lens is arranged in relation to the secondary particle optical beam path directly after the second magnetic sector. The controller is configured for controlling the second magnetic sector depending on the landing energy. Controlling the second magnetic sector and thus adjusting its magnetic field offers one optimization parameter before the second individual particle beams enter the first projection lens. According to a preferred embodiment, the controller is configured control the second magnetic sector to adjust a tilt or an offset of the secondary particle optical axis before the plurality of second individual particle beams enters the first projection lens.

[0044] According to an alternative embodiment, the beam splitter arrangement comprises a last magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path and being configured for providing a homogeneous magnetic field, the last magnetic sector being arranged in relation to the secondary particle- optical beam path as the last magnetic sector of the beam splitter arrangement before the first projection lens. The last magnetic sector can be for example a third magnetic sector or a fourth magnetic sector. The beam splitter arrangement further comprises an isolation trench configured for decoupling of the magnetic field of the last magnetic sector and the magnetic field of the first projection lens. An exit inclination of the last magnetic sector is smaller than 15°, in particular smaller than 10° or 5°. This has the advantage that the isolation trench can be provided in a space saving manner. This in turn allows to position the first projection lens closer to the sample and therefore reduces its filling factor. A filling factor can be reduced to about 8% by this measure. According to a preferred embodiment, the isolation trench is basically rectangular. A rectangular trench needs less installation space than a triangular isolation trench and can be used in case the exit inclination of the last magnetic sector is small enough.

[0045] According to a preferred embodiment, the secondary particle optical beam path further comprises a collimation lens which is arranged in relation to the secondary particle optical beam path after the first magnetic sector and before the first projection lens. The controller is configured for controlling the collimation lens depending on the landing energy. The provision of the collimation lens contributes to a reduction of the FOV radius inside the first projection lens and thus decreases its filling factor PL1 . The collimation lens can for example be switched on at high landing energies, but can stay be switched off at low landing energies.

[0046] According to a preferred embodiment, a focal length f_col of the collimation lens is in the range 20mm < f_col < 500mm, preferably in the range 50mm < f_col < 150mm.

[0047] According to a preferred embodiment the collimation lens is an electrostatic lens. An electrostatic lens needs less installation space than a magnetic lens and is therefore advantageous for positioning the first projection lens rather close to the sample.

[0048] According to a preferred embodiment, the strength of the magnetic field M 1 in the first magnetic sector and the strength of the magnetic field M2 in the second magnetic sector is similar, thus 0,8 < M1 / M2 < 1 ,2 and in particular identical.

[0049] According to a preferred embodiment, the beam splitter arrangement further comprises a second magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the second magnetic sector being arranged downstream of the first magnetic sector in relation to the secondary particle-optical beam path and being configured for providing a homogeneous magnetic field for further deflecting the second individual particle beams in the same direction as in the first magnetic sector. A total deflection angle a in the secondary particle optical beam path, about which the secondary particle optical beam path is deflected by the beam splitter arrangement is described by the following relation: a > 40°, in particular a > 41° or a > 42°. This large deflection angle a is a decisive parameter for creating installation space in the second particle optical beam path. More installation space allows for installation of a bigger first projection lens which is a magnetic lens. If the first projection lens can be made bigger, its opening can be made bigger and thus the filling factor PL1 can be reduced and less aberrations will be picked up inside the first projection lens. According to a preferred embodiment, the strength of the magnetic field M 1 in the first magnetic sector and the strength of the magnetic field M2 in the second magnetic sector is different and one of the following relations holds:

[0050] (i) M1 / M2 > 2,0, in particular M1 / M2 > 2,5 or M1 / M2 > 3,0; or

[0051] (ii) M2 / M1 > 2,0, in particular M2 / M1 > 2,5 or M2 / M1 > 3,0.

[0052] Therefore, an increase of aberrations being picked up in the beam splitter arrangement is accepted at least for one magnetic sector which provides a comparatively strong magnetic field. However, this is more than counterbalanced by the reduced aberrations picked up in the first projection lens. This is a rather general finding which can be transferred to other embodiments and aspects of the invention as well, for example to embodiments having more than two magnetic sectors in the secondary particle optical beam path and also to embodiments in which the two different magnetic sectors are configured to deflect the secondary particle beams substantially in different directions.

[0053] According to a second aspect of the present invention, the latter relates to a multi-beam particle microscope, comprising a multi-beam particle generator, which is configured to generate a first field of a plurality of charged first individual particle beams; a first particle-optical unit with a primary particle-optical beam path, configured to image the generated first individual particle beams onto an object plane such that the first individual particle beams impinge an object at incidence locations, which form a second field; a detection unit with a plurality of detection regions which form a third field; a second particle-optical unit with a secondary particle-optical beam path, configured to image second individual particle beams, which emanate from the incidence locations in the second field, onto the third field of the detection regions of the detection system; a magnetic and / or electrostatic objective lens system, through which both the first and the second individual particle beams pass; a beam splitter arrangement which is arranged in the primary particle-optical beam path between the multi-beam generator and the objective lens and which is arranged in the secondary particle-optical beam path between the objective lens system and the detection unit; and a controller configured to control the multi-beam particle microscope and to control a landing energy of the first individual particle beams on the object; wherein the beam splitter arrangement comprises the following features: a first magnetic sector, the first magnetic sector being configured for providing a homogeneous magnetic field through which during use the primary particle-optical beam path and the secondary particle-optical beam path pass, and being configured for the separation of the primary particle-optical beam path and the secondary particle-optical beam path from one another; wherein each magnetic sector has an entrance region for the secondary particle-optical beam path with an entrance inclination and an exit region for the secondary particle-optical beam path with an exit inclination, wherein the entrance inclination is defined as the angle by which the alignment of the entrance region deviates from the normal to the optical axis of the secondary particle-optical beam path, and wherein the exit inclination is defined as the angle by which the alignment of the exit region deviates from the normal to the optical axis of the secondary particle-optical beam path; wherein the entrance inclination of the first magnetic sector deliberately deviates from 0°; wherein the beam splitter arrangement further comprises a maximum of five further components, wherein a component can either be a further magnetic sector or a multipole arrangement, the further components providing a maximum of five degrees of freedom for further adjusting imaging in the secondary particle optical beam path; wherein the secondary particle optical beam path comprises a first cross-over of the second individual particle beams corresponding to a focal plane of the objective lens system and a second cross-over of the second individual particle beams which is arranged between the beam splitter arrangement and the detection unit and which can be arranged during use level with a contrast aperture; and wherein the second particle-optical unit comprises a projection lens system with a first projection lens, the projection lens system being configured for imaging the second individual particle beams onto the third field, and the first projection lens being arranged in relation to the secondary particle optical beam path after the first cross-over and before the second crossover and the first projection lens being configured for focussing the plurality of second individual particle beams on the second cross-over; wherein the controller is configured for controlling the first projection lens for focussing the plurality of second individual particle beams on the second cross-over depending on the landing energy; and wherein the controller is configured for controlling the further components depending on the landing energy to at least adjust an axial fundamental ray height ratio xa / ya between the axial fundamental rays in x-direction and in y-direction inside the first projection lens such that the following relation holds:

[0054] (1 - xa / ya) < 15%, in particular (1 - xa / ya) < 10% or (1 - xa / ya) < 5%.

[0055] In general, reducing the FOV anisotropy in x-direction and in y-direction inside the first projection lens reduces an ellipticity in the second cross-over. However, if less than five magnetic sectors or multipoles are applied as further correction components in front of the first projection lens, the imaging of the beam splitter arrangement can never be perfectly stigmatic for all landing energies, but only one or two aspects of the in-total four beam splitter astigmatism components can be corrected for all landing energies. Hence, the question arises which of these astigmatism components should be compensated best. To achieve small crossover ellipticities, it turns out to be advantageous to aim for small FOV-anisotropy inside the first projection lens, e.g., by targeting comparable heights of the axial fundamental rays in x- and y-direction inside the first projection lens.

[0056] According to a third aspect of the invention, the latter relates to a multi-beam particle microscope, comprising a multi-beam particle generator, which is configured to generate a first field of a plurality of charged first individual particle beams; a first particle-optical unit with a primary particle-optical beam path, configured to image the generated first individual particle beams onto an object plane such that the first individual particle beams impinge an object at incidence locations, which form a second field; a detection unit with a plurality of detection regions which form a third field; a second particle-optical unit with a secondary particle-optical beam path, configured to image second individual particle beams, which emanate from the incidence locations in the second field, onto the third field of the detection regions of the detection system; a magnetic and / or electrostatic objective lens system, through which both the first and the second individual particle beams pass; a beam splitter arrangement which is arranged in the primary particle-optical beam path between the multi-beam generator and the objective lens and which is arranged in the secondary particle-optical beam path between the objective lens system and the detection unit; and a controller configured to control the multi-beam particle microscope and to control a landing energy of the first individual particle beams on the object; wherein the beam splitter arrangement comprises at least a first magnetic sector, the first magnetic sector being configured for providing a homogeneous magnetic field through which during use the primary particle-optical beam path and the secondary particle-optical beam path pass, and being configured for the separation of the primary particle-optical beam path and the secondary particle-optical beam path from one another, wherein each magnetic sector of the beam splitter arrangement has an entrance region for the secondary particle-optical beam path with an entrance inclination and an exit region for the secondary particle-optical beam path with an exit inclination, wherein the entrance inclination is defined as the angle by which the alignment of the entrance region deviates from the normal to the optical axis of the secondary particle-optical beam path, and wherein the exit inclination is defined as the angle by which the alignment of the exit region deviates from the normal to the optical axis of the secondary particle-optical beam path; and wherein the entrance inclination of the first magnetic sector deliberately deviates from 0°; wherein the beam splitter arrangement comprises a dispersion free plane in the secondary particle optical beam path, the z-position of the dispersion free plane being fix by design of the beam splitter arrangement; wherein the secondary particle optical beam path comprises a first cross-over of the second individual particle beams corresponding to a focal plane of the objective lens system, the objective lens system further having an objective lens system image plane arranged in relation to the secondary particle optical beam path after the first cross-over; and wherein the second particle optical unit comprises an adjustment means configured for adjusting a z-position of the objective lens system image plane; wherein the controller is configured for controlling the adjustment means depending on the landing energy in such a way that the adjusted z-position of the objective lens system image plane matches the fix z-position of the dispersion free plane of the beam splitter arrangement.

[0057] This solution is contrary to the known approach to understand the z-position of the objective lens system image plane as fix and to adjust for example a magnetic sector of the beam splitter arrangement to adjust the dispersion free plane such that it matches with the fix objective lens system image plane. The contrary approach according to the present invention can be realized in several different ways.

[0058] According to a preferred embodiment, the adjustment means comprises an adjustment lens which is arranged in relation to the secondary particle optical beam path after the first magnetic sector. The adjustment lens acts on the second individual particle beams, only. The largest refractive power of this adjustment lens is needed for the smallest landing energy / small landing energies.

[0059] According to a preferred embodiment, the controller is configured to control the landing energy for values between and including a minimum landing energy LEmin and a maximum landing energy LEmax; and the controller is configured to control the adjustment lens between and including zero and a maximum adjustment value. The controller is configured to control the adjustment lens with the maximum adjustment value when the minimum landing energy LEmin is set by the controller. According to a preferred embodiment, the adjustment lens is configured to have a maximum refractive power RP of RP > 20 / m. However, smaller or bigger values are also possible.

[0060] According to another preferred embodiment, the objective lens system comprises a two-part objective lens and the adjustment means is realized by the two-part objective lens, the two parts of the objective lens system are configured to be controllable independently from one another. The control is configured to control the two-part objective lens to keep the position of its image plane in the primary particle optical beam path and the control is configured to control the two-part objective lens to adjust the position of its image plane in the secondary particle optical beam path. In brief, this effect of the two-part objective lens can be understood by the fact that a two-part objective lens is equivalent to a replacement lens arranged at a variable position and having a variable strength.

[0061] According to a fourth aspect of the invention, the latter relates to a multi-beam particle microscope, comprising a multi-beam particle generator, which is configured to generate a first field of a plurality of charged first individual particle beams; a first particle-optical unit with a primary particle-optical beam path, configured to image the generated first individual particle beams onto an object plane such that the first individual particle beams impinge an object at incidence locations, which form a second field; a detection unit with a plurality of detection regions which form a third field; a second particle-optical unit with a secondary particle-optical beam path, configured to image second individual particle beams, which emanate from the incidence locations in the second field, onto the third field of the detection regions of the detection system; a magnetic and / or electrostatic objective lens system, through which both the first and the second individual particle beams pass; a beam splitter arrangement which is arranged in the primary particle-optical beam path between the multi-beam generator and the objective lens and which is arranged in the secondary particle-optical beam path between the objective lens system and the detection unit; and a controller configured to control the multi-beam particle microscope and to control a landing energy of the first individual particle beams on the object; wherein the beam splitter arrangement comprises a first magnetic sector, the first magnetic sector being configured for providing a homogeneous magnetic field through which during use the primary particle-optical beam path and the secondary particle-optical beam path pass, and being configured for the separation of the primary particle-optical beam path and the secondary particle-optical beam path from one another; and a dispersion correction sector, the dispersion correction sector being configured for providing a homogenous magnetic field through which during use the secondary particle optical beam path passes and the primary particle optical beam path does not pass; wherein the beam splitter arrangement comprises a dispersion free plane in the secondary particle optical beam path, the position of the dispersion free plane being adjustable by controlling the dispersion correction sector; wherein each magnetic sector of the beam splitter arrangement has an entrance region for the secondary particle-optical beam path with an entrance inclination and an exit region for the secondary particle-optical beam path with an exit inclination, wherein the entrance inclination is defined as the angle by which the alignment of the entrance region deviates from the normal to the optical axis of the secondary particle-optical beam path, and wherein the exit inclination is defined as the angle by which the alignment of the exit region deviates from the normal to the optical axis of the secondary particle-optical beam path; and wherein the entrance inclination of the first magnetic sector deliberately deviates from 0°; wherein the secondary particle optical beam path comprises a first cross-over of the second individual particle beams corresponding to a focal plane of the objective lens system, the objective lens system further having an objective lens system image plane arranged in relation to the secondary particle optical beam path after the first cross-over; and wherein the controller is configured for controlling the dispersion correction sector depending on the landing energy to match the position of the dispersion free plane of the beam splitter arrangement with the position of the objective lens system image plane.

[0062] According to a fifth aspect of the invention, the latter relates to a multi-beam particle microscope, comprising a multi-beam particle generator, which is configured to generate a first field of a plurality of charged first individual particle beams; a first particle-optical unit with a primary particle-optical beam path, configured to image the generated first individual particle beams onto an object plane such that the first individual particle beams impinge an object at incidence locations, which form a second field; a detection unit with a plurality of detection regions which form a third field; a second particle-optical unit with a secondary particle-optical beam path, configured to image second individual particle beams, which emanate from the incidence locations in the second field, onto the third field of the detection regions of the detection system; a magnetic and / or electrostatic objective lens system, through which both the first and the second individual particle beams pass; a beam splitter arrangement which is arranged in the primary particle-optical beam path between the multi-beam generator and the objective lens and which is arranged in the secondary particle-optical beam path between the objective lens system and the detection unit; and a controller configured to control the multi-beam particle microscope and to control a landing energy of the first individual particle beams on the object; wherein the beam splitter arrangement comprises a first magnetic sector, the first magnetic sector being configured for providing a homogeneous magnetic field through which during use the primary particle-optical beam path and the secondary particle-optical beam path pass, and being configured for the separation of the primary particle-optical beam path and the secondary particle-optical beam path from one another; a second magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the second magnetic sector being arranged downstream of the first magnetic sector in relation to the secondary particle-optical beam path and being configured for providing a homogeneous magnetic field for deflecting the second individual particle beams, and a third magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the third magnetic sector being arranged downstream of the second magnetic sector in relation to the secondary particle- optical beam path and being configured for providing a homogeneous magnetic field; wherein each magnetic sector of the beam splitter arrangement has an entrance region for the secondary particle-optical beam path with an entrance inclination and an exit region for the secondary particle-optical beam path with an exit inclination, wherein the entrance inclination is defined as the angle by which the alignment of the entrance region deviates from the normal to the optical axis of the secondary particle-optical beam path, and wherein the exit inclination is defined as the angle by which the alignment of the exit region deviates from the normal to the optical axis of the secondary particle-optical beam path; and wherein the entrance inclination of the first magnetic sector deliberately deviates from 0°; and wherein the beam splitter arrangement does not comprise a dispersion correction sector or other dispersion correction means for controlling a position of a dispersion free plane in the secondary particle optical beam path depending on the landing energy LE; wherein the secondary particle optical beam path comprises a first cross-over of the second individual particle beams corresponding to a focal plane of the objective lens system, the objective lens system further having an objective lens system image plane arranged in relation to the secondary particle optical beam path after the first cross-over; and wherein the controller is configured for controlling the landing energy LE in a range LEmin < LE < LEmax, and wherein the beam splitter arrangement is designed in such a way that for a landing energy LE_ave = (LEmax-LEmin) / 2 the z-position z1 of the dispersion free plane of the beam splitter arrangement matches with the z-position z2 of the objective system lens image plane within + / -5%, thus 0,95 < |(z1-z2) / z2| < 1 ,05.

[0063] The idea behind this solution is as follows: It has been found out that beam splitter aberrations for landing energies up to several keV are strongly dominated by the first-degree dispersion (Ck term). It is hence fruitful to aim for dispersion reduction in order to decrease the total beams splitter aberrations. If no dedicated magnetic sector is available for dispersion-correction at all landing energies but the dispersion correction can only be made for one reference LE_ref via choosing a suitable beam splitter / magnet arrangement design, then this choice should be made optimally. The beam splitter aberrations exhibit a minimum at the minimum position of the dispersion curve. This minimum comes about the following way: each beam splitter design features a specific plane in which the dispersion vanishes, the so-called dispersion-free plane. The image plane position after the objective lens and the beam splitter strongly varies with the landing energy, being high above the sample for small landing energies at which the secondary particles / signal electrons have a large energy, and being much closer to the sample for high landing energies, with the exact positions depending on the refractive power of the respective objective lens and beam splitter. Now, there exists one landing energy at which the image plane after the objective lens and the beam splitter crosses the dispersion-free plane and at this landing energy LE_ref, the minimum of the beam splitter dispersion occurs. Consequently, if the beam splitter shall be used over a specific range of landing energies, the goal is to optimize the beam splitter design such that the dispersion-free plane lies at such a position that the dispersion minimum approximately occurs in the middle of the targeted LE range. In this case the dispersion at the two edges of the LE range is the same and thus the smallest possible maximum dispersion value that can occur in the whole landing energy range is reached.

[0064] According to a sixth aspect of the invention, the latter relates to a multi-beam particle microscope, comprising a multi-beam particle generator, which is configured to generate a first field of a plurality of charged first individual particle beams; a first particle-optical unit with a primary particle-optical beam path, configured to image the generated first individual particle beams onto an object plane such that the first individual particle beams impinge an object at incidence locations, which form a second field; a detection unit with a plurality of detection regions which form a third field; a second particle-optical unit with a secondary particle-optical beam path, configured to image second individual particle beams, which emanate from the incidence locations in the second field, onto the third field of the detection regions of the detection system; a magnetic and / or electrostatic objective lens system, through which both the first and the second individual particle beams pass; a beam splitter arrangement which is arranged in the primary particle-optical beam path between the multi-beam generator and the objective lens and which is arranged in the secondary particle-optical beam path between the objective lens system and the detection unit; and a controller configured to control the multi-beam particle microscope and to control a landing energy of the first individual particle beams on the object; wherein the beam splitter arrangement comprises a first magnetic sector, the first magnetic sector being configured for providing a homogeneous magnetic field M1 through which during use the primary particle-optical beam path and the secondary particle-optical beam path pass, and being configured for the separation of the primary particle-optical beam path and the secondary particle-optical beam path from one another; a second magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the second magnetic sector being arranged downstream of the first magnetic sector in relation to the secondary particle-optical beam path and being configured for providing a homogeneous magnetic field M2 for deflecting the second individual particle beams, and a third magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the third magnetic sector being arranged downstream of the second magnetic sector in relation to the secondary particle- optical beam path and being configured for providing a homogeneous magnetic field M3; a fourth magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the fourth magnetic sector being arranged downstream of the third magnetic sector in relation to the secondary particle-optical beam path and being configured for providing a homogeneous magnetic field M4; wherein each magnetic sector of the beam splitter arrangement has an entrance region for the secondary particle-optical beam path with an entrance inclination and an exit region for the secondary particle-optical beam path with an exit inclination, wherein the entrance inclination is defined as the angle by which the alignment of the entrance region deviates from the normal to the optical axis of the secondary particle-optical beam path, and wherein the exit inclination is defined as the angle by which the alignment of the exit region deviates from the normal to the optical axis of the secondary particle-optical beam path; and wherein the entrance inclination of the first magnetic sector deliberately deviates from 0°; and wherein a first drift region which is substantially free from magnetic fields is provided between the first magnetic sector and the second magnetic sector; wherein the first magnetic sector comprises two plates which are arranged parallel to one another and which have a plate distance D1 , wherein during use the homogeneous magnetic field M1 is generated between the two plates; wherein the entrance region of the first magnetic sector is linear and comprises a width W11 and wherein the exit region of the first magnetic sector is linear and comprises a width W12, and wherein for a ratio R11 = W11 / D1 the following relation holds: R11 > 2,0, in particular R11 > 3,0 or R11 > 3,5; wherein for a ratio R12 = W12 I D1 the following relation holds: R12 > 2,0, in particular R12 > 3,0 or R12 > 3,5; and wherein the second magnetic sector comprises two plates which are arranged parallel to one another and which have a plate distance D2, wherein during use the homogeneous magnetic field M2 is generated between the two plates; wherein the entrance region of the second magnetic sector is linear and comprises a width W21 and wherein the exit region of the second magnetic sector is linear and comprises a width W22, and wherein for a ratio R21 = W21 I D2 the following relation holds: R21 > 2,0, in particular R21 > 3,0 or R21 > 3,5; and / or wherein for a ratio R22 = W22 I D2 the following relation holds: R22 > 2,0, in particular R22 > 3,0 or R22 > 3,5.

[0065] The above ratios R11 , R12, R21 and R22 contribute to the further reduction of aberrations. This applies in particular to the image field tilt and image field astigmatism. The linear entrance / exit area for the particle-optical beam path is located between the two plates and is often referred to as a trench. It would therefore be advantageous to make the widths W11 , W12, W21 , W22 of the trenches as large as possible. However, this is only structurally possible or sensible to a limited extent if further magnetic sectors of the primary particle-optical beam path are to be arranged. These could collide with the magnetic sectors of the secondary particle-optical beam path. The other option for achieving the above ratio is to keep the distances D1 , D2 between the two plates as small as possible, for example D1 < 20mm or D1 < 15mm or D1< 10mm and / or D2 < 20mm or D2 < 15mm or D2 < 20mm.

[0066] According to a preferred embodiment, the third magnetic sector comprises two plates which are arranged parallel to one another and which have a plate distance D3, wherein during use the homogeneous magnetic field M3 is generated between the two plates. The entrance region of the third magnetic sector is linear and comprises a width W31 and the exit region of the third magnetic sector is linear and comprises a width W32. Then, for a ratio R31 = W31 I D3 the following relation holds: R31 > 2,0, preferably R31 > 3,0 or R31 > 3,5; and / or wherein for a ratio R32 = W32 I D2 the following relation holds: R32 > 2,0, preferably R32 > 3,0 or R32 > 3,5.

[0067] According to a preferred embodiment the fourth magnetic sector comprises two plates which are arranged parallel to one another and which have a plate distance D4, wherein during use the homogeneous magnetic field M4 is generated between the two plates. The entrance region of the fourth magnetic sector is linear and comprises a width W41 and the exit region of the third magnetic sector is linear and comprises a width W42. Then, for a ratio R41 = W41 I D4 the following relation holds: R41 > 2,0, preferably R41 > 3,0 or R41 > 3,5; and / or for a ratio R42 = W42 I D4 the following relation holds: R42 > 2,0, preferably R42 > 3,0 or R42 > 3,5.

[0068] According to a preferred embodiment, the exit inclination of the first magnetic sector is limited to q < 35°, preferably q < 25° or most preferably q < 15°.

[0069] According to a preferred embodiment, the entrance inclination of the second magnetic sector is limited to q21 < 35°, preferably q21 < 25° or most preferably q21 < 15°. This reduces aberrations.

[0070] According to a seventh aspect of the invention, the latter relates to a multi-beam particle microscope, comprising a multi-beam particle generator, which is configured to generate a first field of a plurality of charged first individual particle beams; a first particle-optical unit with a primary particle-optical beam path, configured to image the generated first individual particle beams onto an object plane such that the first individual particle beams impinge an object at incidence locations, which form a second field; a detection unit with a plurality of detection regions which form a third field; a second particle-optical unit with a secondary particle-optical beam path, configured to image second individual particle beams, which emanate from the incidence locations in the second field, onto the third field of the detection regions of the detection system; a magnetic and / or electrostatic objective lens system, through which both the first and the second individual particle beams pass; a beam splitter arrangement which is arranged in the primary particle-optical beam path between the multi-beam generator and the objective lens and which is arranged in the secondary particle-optical beam path between the objective lens system and the detection unit; and a controller configured to control the multi-beam particle microscope and to control a landing energy of the first individual particle beams on the object; wherein the beam splitter arrangement comprises a first magnetic sector, the first magnetic sector being configured for providing a homogeneous magnetic field M1 through which during use the primary particle-optical beam path and the secondary particle-optical beam path pass, and being configured for the separation of the primary particle-optical beam path and the secondary particle-optical beam path from one another; a second magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the second magnetic sector being arranged downstream of the first magnetic sector in relation to the secondary particle-optical beam path and being configured for providing a homogeneous magnetic field M2 for deflecting the second individual particle beams; a third magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the third magnetic sector being arranged downstream of the second magnetic sector in relation to the secondary particle- optical beam path and being configured for providing a homogeneous magnetic field M3; a fourth magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the fourth magnetic sector being arranged downstream of the third magnetic sector in relation to the secondary particle-optical beam path and being configured for providing a homogeneous magnetic field M4; wherein each magnetic sector of the beam splitter arrangement has an entrance region for the secondary particle-optical beam path with an entrance inclination and an exit region for the secondary particle-optical beam path with an exit inclination, wherein the entrance inclination is defined as the angle by which the alignment of the entrance region deviates from the normal to the optical axis of the secondary particle-optical beam path, and wherein the exit inclination is defined as the angle by which the alignment of the exit region deviates from the normal to the optical axis of the secondary particle-optical beam path; and wherein the entrance inclination of the first magnetic sector deliberately deviates from 0°; and wherein a first drift region which is substantially free from magnetic fields is provided between the first magnetic sector and the second magnetic sector; wherein the second, third and fourth magnetic sectors are arranged directly in succession without a drift region between neighboured magnetic sectors, and therefore the exit region of the second magnetic sector corresponds to the entrance region of the third magnetic sector, the exit region of the third magnetic sector corresponds to the entrance region of the fourth magnetic sector; wherein the entrance region of the second magnetic sector, the entrance region of the third magnetic sector, the entrance region of the fourth magnetic sector and the exit region of the fourth magnetic sector are linear and have in their theoretical prolongation a common intersection point or several intersection points within an intersection circle with a minimum diameter d, wherein all intersection points of the prolongations with each other are situated in said intersection circle, wherein the exit region of the second magnetic sector is linear and has a width W22; and wherein the following relation holds for the diameter d and the width WD22: d < WD22, in particular d < 0,5*WD22.

[0071] This embodiment describes a rather fan-like design and therefore arrangement of the second, third and fourth magnet sector. This fan-like design contributes to balance and equalize the widths of the linear entrance regions and exit regions. Very short entrance regions and / or exit regions can be avoided. This measure in turn contributes to a reduction of aberrations, in particular rather strong field astigmatism.

[0072] According to a preferred embodiment, the following relation holds for the diameter d of the intersection circle: d<10mm, preferably d<5mm or d < 3mm. This is in the order of magnitude of a trench width.

[0073] According to an eighth aspect of the present invention, the latter relates to a multi-beam particle microscope, comprising: a multi-beam particle generator, which is configured to generate a first field of a plurality of charged first individual particle beams; a first particle-optical unit with a primary particle-optical beam path, configured to image the generated first individual particle beams onto an object plane such that the first individual particle beams impinge an object at incidence locations, which form a second field; a detection unit with a plurality of detection regions which form a third field; a second particle-optical unit with a secondary particle-optical beam path, configured to image second individual particle beams, which emanate from the incidence locations in the second field, onto the third field of the detection regions of the detection system; a magnetic and / or electrostatic objective lens system, through which both the first and the second individual particle beams pass; a beam splitter arrangement which is arranged in the primary particle-optical beam path between the multi-beam generator and the objective lens and which is arranged in the secondary particle-optical beam path between the objective lens system and the detection unit; and a controller configured to control the multi-beam particle microscope and to control a landing energy of the first individual particle beams on the object; wherein the beam splitter arrangement comprises a magnet arrangement consisting of a first magnetic sector, a second magnetic sector and a third magnetic sector, the first magnetic sector being configured for providing a homogeneous magnetic field M1 through which during use the primary particle-optical beam path and the secondary particle-optical beam path pass, and being configured for the separation of the primary particle-optical beam path and the secondary particle-optical beam path from one another; the second magnetic sector being arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the second magnetic sector being arranged downstream of the first magnetic sector in relation to the secondary particle-optical beam path and being configured for providing a homogeneous magnetic field M2 for deflecting the second individual particle beams; the third magnetic sector being arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the third magnetic sector being arranged downstream of the second magnetic sector in relation to the secondary particle- optical beam path and being configured for providing a homogeneous magnetic field M3; wherein each magnetic sector of the magnet arrangement has an entrance region for the secondary particle-optical beam path with an entrance inclination and an exit region for the secondary particle-optical beam path with an exit inclination, wherein the entrance inclination is defined as the angle by which the alignment of the entrance region deviates from the normal to the optical axis of the secondary particle-optical beam path, and wherein the exit inclination is defined as the angle by which the alignment of the exit region deviates from the normal to the optical axis of the secondary particle-optical beam path; and wherein the entrance inclination of the first magnetic sector deliberately deviates from 0°; and wherein a first drift region which is substantially free from magnetic fields is provided between the first magnetic sector and the second magnetic sector; and wherein a second drift region which is substantially free from magnetic fields is provided between the second magnetic sector and the third magnetic sector; wherein the controller is configured for controlling the landing energy LE in a range LEmin < LE < LEmax; wherein the design of the second magnetic sector is configured for optimum astigmatism and dispersion correction at a low landing energy LEJow and wherein the design of the third magnetic sector is configured for optimum astigmatism and dispersion correction at a high landing energy LE_high; OR wherein the design of the second magnetic sector is configured for optimum astigmatism and dispersion correction at a high landing energy LE_high and wherein the design of the third magnetic sector is configured for optimum astigmatism and dispersion correction at a low landing energy LEJow, with LEmin < LEJow < LE_high < LEmax.

[0074] For the intrinsic beam splitter performance, it can be advantageous to choose beam splitter designs / magnet arrangement designs with gaps between the consecutive magnetic sectors since this offers more geometrical degrees of freedom (contrary to the fan-like design-rule explained above). Considering a design consisting of 3 magnet sectors in the secondary particle optical beam path with drift regions between consecutive magnet sectors, this provides enough degrees of freedom to achieve astigmatism and dispersion correction at two landing energies. The geometrical parameters of the first magnetic sector could, for example, be used for astigmatism and dispersion correction at a low landing energy within the targeted wide landing energy range while astigmatism and dispersion compensation at a high landing anergy could be achieved via the geometrical parameters of the second sectors, thus yielding a “W’~ shaped landing energy dependence of the intrinsic beam splitter aberrations and hence smaller maximum aberration values than for the “V”-shaped curve when astigmatism and dispersion is only corrected at a single landing energy.

[0075] According to a preferred embodiment, the controller is configured for switching off the second magnetic sector or the third magnetic sector when the controller sets the landing energy LE to LE_high or LEJow.

[0076] According to a preferred embodiment, the design parameters of the second magnetic sector are geometrical parameters and comprise or consist of the following: length of the first drift region, entrance inclination, exit inclination, distance between the entrance region and the exit region. In contrast thereto, the strength of a magnetic field in a magnetic sector is not a geometrical design parameter.

[0077] According to a preferred embodiment, the design parameters of the third magnetic sector are geometrical parameters and comprise or consist of the following: length of the second drift region, entrance inclination, exit inclination, distance between the entrance region and the exit region.

[0078] The above-described aspects and embodiments of the invention can be combined with one another in full or in part, provided that no technical contradictions arise as a result.

[0079] The invention will be understood even better with reference to the accompanying figures, in which:

[0080] Fig. 1: schematically shows a multi-beam particle microscope;

[0081] Fig. 2: schematically shows a multi-beam particle microscope with a beam splitter or magnet arrangement according to the prior art;

[0082] Fig. 3: schematically shows a beam splitter or magnet arrangement;

[0083] Fig. 4: schematically shows beam splitter arrangement;

[0084] Fig. 5: schematically shows a splitting sector and its arrangement in the first and second particle optical beam paths;

[0085] Fig. 6: schematically illustrates the problem of an increased filling factor inside the first projection lens when varying a landing energy LE over a large range;

[0086] Fig. 7: schematically illustrates the definition of the filling factor PL1 ;

[0087] Fig. 8: schematically illustrates the position of the first projection lens in the secondary particle optical beam path;

[0088] Fig. 9: schematically shows a beam splitter arrangement;

[0089] Fig. 10: schematically shows a beam splitter arrangement;

[0090] Fig. 11 : schematically shows a beam splitter arrangement;

[0091] Fig. 12: schematically shows a beam splitter arrangement;

[0092] Fig. 13: schematically illustrates the dependence of aberrations from the landing energy;

[0093] Fig. 14: schematically shows geometric relationships of the first magnetic sector;

[0094] Fig. 15: schematically shows geometric relationships of the second magnetic sector;

[0095] Fig. 16: schematically shows geometric relationships of the third magnetic sector;

[0096] Fig. 17: schematically shows geometric relationships of the fourth magnetic sector;

[0097] Fig. 18: schematically illustrates a fan-like beam splitter arrangement; and

[0098] Fig. 19: schematically illustrates a beam splitter arrangement.

[0099] Fig. 1 schematically shows a multi-beam particle microscope 1. The multi-beam particle microscope 1 comprises a beam generating apparatus 300 with a particle source 301, for example an electron source. A divergent particle beam 309 is collimated by a sequence of condenser lenses 303.1 and 303.2, and strikes a multi-aperture arrangement 305. The multi- aperture arrangement 305 comprises a plurality of multi-aperture plates 306 and a field lens 308. A plurality of individual particle beams 3 or individual electron beams 3 is generated by the multi-aperture arrangement. Midpoints of apertures in the multi-aperture plate arrangement are arranged in a field which is imaged onto a further field formed by beam spots 5 in the object plane 101. The pitch between midpoints of apertures of a multi-aperture plate 306 can be 5 pm, 100 pm and 200 pm, for example. The diameters D of the apertures are smaller than the pitch of the midpoints of the apertures, examples of the diameters are 0.2-times, 0.4-times and 0.8- times the pitches between the midpoints of the apertures.

[0100] The multi-aperture arrangement 305 and the field lens 307 are configured to generate a multiplicity of focal points 323 of primary beams 3 in a raster arrangement on a surface 325. The surface 325 need not be a plane surface but can be a spherically curved surface in order to account for field curvature of the subsequent particle-optical system.

[0101] The multi-beam particle microscope 1 further comprises a system of electromagnetic lenses 103 and an objective lens 102, which image the beam foci 323 with reduced size from the intermediate image surface 325 into the object plane 101. In between, the first individual particle beams 3 pass through the beam splitter 400 and a collective beam deflection system 500, by means of which the plurality of first individual particle beams 3 are deflected when in operation and the image field is scanned. The first individual particle beams 3 incident in the object plane 101 for example form a substantially regular field, wherein pitches between adjacent incidence locations 5 can be 1 pm, 10 pm or 40 pm, for example. By way of example, the field formed by the incidence locations 5 may have a rectangular or hexagonal symmetry.

[0102] The object 7 to be examined can be of any desired type, for example a semiconductor wafer or a biological sample, and can comprise an arrangement of miniaturized elements or the like. The surface 15 of the object 7 is arranged in the object plane 101 of the objective lens 102. The objective lens 102 may comprise one or more electron-optical lenses. By way of example, this may be a magnetic objective lens and / or an electrostatic objective lens.

[0103] The primary particles 3 incident on the object 7 generate interaction products, for example secondary electrons, backscattered electrons or primary particles which have experienced a reversal of movement for other reasons, and these interaction products emanate from the surface of the object 7 or from the first plane 101 or object plane 101 . The interaction products emanating from the surface 15 of the object 7 are shaped by the objective lens 102 to form secondary particle beams 9. In the process, the secondary beams 9 pass through the beam splitter 400 after the objective lens 102 and are supplied to a projection system 200. The projection system 200 comprises an imaging system 205 with a plurality of projection lenses, for example magnetic projection lenses 206, 208 und 210, a contrast aperture 214 positioned in the second cross-over 212 allowing to filter the secondary particle beams 9 with respect to their starting angles from the object 7, a collective beam deflector (anti-scan) 222 and a multiparticle detector 209. Incidence locations of the second individual particle beams 9 on detection regions of the multi-particle detector 209 are located in a third field with a regular pitch from one another. Exemplary values are 10 pm, 100 pm and 200 pm.

[0104] The multi-beam particle microscope 1 further has a computer system or control unit 10, which in turn may be made of one part or many parts and which is designed both to control the individual particle-optical components of the multi-beam particle microscope 1 and to evaluate and analyse the signals obtained by the multi-detector 209 or detection unit 209.

[0105] There also exist means for varying a landing energy LE which with the primary particle beams 3 impinge the object 7. This can be achieved for example by providing a respective voltage to the object 7 or its holder 600, or by varying a deceleration voltage provided to an electrode (not shown) arranged between the objective lens 102 and the object 7. Varying the landing energy LE can be controlled by the controller 10.

[0106] Further information relating to such multi-beam particle beam systems or multi-beam particle microscopes 1 and components used therein, such as, for instance, particle sources, multiaperture plates and lenses, can be obtained from the international patent applications WO 2005 / 024881 A2, WO 2007 / 028595 A2, WO 2007 / 028596 A1 , WO 2011 / 124352 A1 and WO 2007 / 060017 A2 and the German patent applications DE 102013016 113 A1 and DE 102013 014 976 A1 , the full disclosure of which is incorporated in the present application by reference.

[0107] Fig. 2 schematically shows a sectional illustration of a multi-beam particle microscope 1 with a beam splitter arrangement 400 according to the prior art. Special aspects of the known beam splitter arrangement 400 are explained here. In the multi-beam particle microscope 1 depicted in Fig. 2, a particle beam which is emitted by a particle source 301 passes through a magnetooptic condenser lens system 303 and subsequently strikes the multi-aperture arrangement 305. The latter serves as a multi-beam particle generator, and individual particle beams 3 emanating from the multi-aperture arrangement 305 thereupon pass through a magneto-optic field lens system 307 and subsequently enter the magneto-optic beam splitter arrangement 400. The depicted beam splitter arrangement 400 comprises a beam tube arrangement 490, which has a Y-shaped embodiment and comprises three limbs 461 , 462 and 463 in the example shown. Here, in addition to two flat, interconnected structures for holding the magnetic sectors or magnetic field regions 410, 430, the beam splitter 400 includes the two magnetic sectors or magnetic field regions 410 and 430 which are contained in, or secured to, said structures. After passing through the beam splitter 400, the first particle beams 3 pass through a scan deflector 500 and, thereupon, the particle-optical objective lens 102, before the primary particle beams 3 are incident on the surface 15 of an object 7, in this case a semiconductor wafer with HV structures. In this case, HV structures denote the predominantly horizontal or vertical profile of semiconductor structures. In this case, the semiconductor wafer 7 is positioned by a displacement stage 600 below the objective lens 102. As a result of the incidence of the first individual particle beams 3, secondary particles or second individual particle beams 9 are released from the object 7. After emerging from the object 7, the second individual particle beams 9 initially pass through the particle-optical objective lens 102 and subsequently pass through the scan deflector 500 and then the beam splitter 400 arrangement. From the beam splitter arrangement 400, the second individual particle beams 9 emerge from the limb 462, pass through a projection lens system 205 (illustrated in much-simplified fashion), pass through an electrostatic element 260, the so-called anti-scan, and then impinge a particle- optical detection unit 209. The computer system 10 or the control unit 10, serving to control particle-optical components and other constituent parts of the multi-beam particle microscope 1 according to Fig. 2, is not depicted in Fig. 2 in order to keep things simple.

[0108] From the beam splitter 400 according to the prior art, it is clear that the provision of a beam tube arrangement 490 offers advantages for the shown structure and for the necessary evacuation of the surroundings of the first and second particle-optical beam path 13 and 11 , respectively, within the beam splitter 400. However, it is also evident that the first particle- optical beam path 13 cannot pass through the beam splitter 400 when the beam splitter 400 is in the switched off state, and instead strikes the walls of the beam tube arrangement 490. This makes the adjustment of the multi-beam particle microscope 1 more difficult since a contribution of the beam splitter 400 to a possible maladjustment cannot be examined separately.

[0109] Fig. 3 schematically shows a beam splitter arrangement 400 according to the prior art and the occurrence of a field inclination. In the example shown, the magnet arrangement 400 comprises a first magnetic sector410 and a second magnetic sector 430, the magnetic fields of which are oriented in the opposite sense to one another, and a primary particle-optical beam path 13 travels through both of these magnetic sectors. Moreover, three further magnetic sectors 450, 460 and 470 are provided in the example shown. The secondary particle-optical beam path 11 extends through the first magnetic sector 410 and through these additional magnetic sectors regions 450, 460 and 470. The magnetic field in the magnetic sector 450 is oriented in the same direction as the magnetic field in the magnetic sector 410, with the result that the curvature of the second particle-optical beam path 11 is without a change of curvature in these magnetic field regions 410, 450.

[0110] The beam splitter arrangement 400 shown in Fig. 3 is not of an aligned optical axes type: Instead, there is a skew angle p between the optical axis Z of the first particle-optical beam path 13 and the axis A, which corresponds to the optical axis of the objective lens 102 or the continuation thereof. A right angle is set between a lower edge of the first magnetic sector 410 and the axis A, which is an intuitive arrangement because of the symmetry between the first and second particle optical paths 13, 11.

[0111] The angle y is the so-called splitting angle, which provides a measure for the separation of the primary particle-optical beam path 13 from the second particle-optical beam path 11 within the magnetic sector 410. This angle must not be chosen to be too small, otherwise there might not be sufficient installation space available for the arrangement of magnetic sectors 450, 460 and 470 in the secondary particle-optical beam path 11.

[0112] Imaging aberrations of the first particle-optical beam path 13 may be largely corrected and the imaging can be substantially stigmatic to first order and substantially distortion-free to first order. However, there are ever greater demands on the resolution within the scope of ever more accurate measurement tasks for multi-beam particle microscopes 1 and it turned out that a field inclination cf of the beam splitter 400 depicted in Fig. 3 often makes up the majority of the remaining residual aberration. In Fig. 3, this field inclination cf has not been plotted true to scale. First individual particle beams 3 impinge the object 7 or the object plane 101 at slightly different heights, wherein the location of the minimum particle beam diameter is considered to be the focus in this case. The individual particle beam 3 located exactly on the optical axis A has a focal position exactly on the object plane 101 , the first individual particle beam 3 arranged to the left thereof has a focal position arranged just in front of the object plane 101 and the first individual particle beam 3 arranged to the right of the axis A has a focal position slightly below the object plane 101. The coming together of the field inclination cf is explained substantially by slightly different path lengths traversed by the plurality of the first individual particle beams 3 within the magnet arrangement 400.

[0113] Fig. 4 schematically an improved beam splitter arrangement 400. Said beam splitter arrangement 400 basically differs from the beam splitter arrangement shown in Fig. 3 with respect to the arrangement of the first magnetic sector 410: The orientation of its linear bottom region (which corresponds to the exit region for the primary particle beams 3 as well as to the entrance region for the secondary particle beams 9) is inclined with respect to the normal of the optical axis Z. By means of the exit inclination, which deviates from 0°, it is possible to reduce aberrations of the beam splitter arrangement 400 significantly further in the primary particle optical beam path 13. If the beam splittee arrangement 400 is integrated into a multibeam particle microscope 1 as a beam switch 400, this leads to the situation that an extension of the particle-optical axis A of the objective lens 102 does not orthogonally intersect the exit region of the first magnetic sector of the magnet arrangement. It is therefore surprising that aberrations picked up in the beam splitter arrangement 400 and therefore occurring in the multi-beam particle microscope 1 are significantly reduced with such a geometric arrangement.

[0114] In particular, it is possible to reduce a beam-switch-induced image field tilt and a beam-switch- induced image field astigmatism by a factor of about 6 compared to a beam splitter arrangement in which the exit tilt o1 of the first magnetic sector 410 is 0° or in a multi-beam particle microscope 1 in which an extension of the particle-optical axis A of the objective lens 102 orthogonally intersects the exit region of the first magnetic sector 410. For example, an image field tilt 5 in an object plane 101 can be reduced to 6 < 0.05°, preferably 5 < 0.04° - without using or requiring an additional active corrector such as a multi-stigmator arrangement. In addition, the exit inclination o1=r|11 0 can also significantly improve the resolution of a multibeam particle microscope 1 , namely by a factor of about 1.5 to 2. All other aberrations of second order or higher are also small or remain small in total. Further details are described in undisclosed German patent application No. 10 2023 120 127.1 , the disclosure of which in the full scope thereof is incorporated in the present patent application by reference.

[0115] Fig. 5 is an enlarged view of the first magnetic sector 410 and shows geometric conditions of its arrangement in more detail. According to the depicted embodiment (not true to scale), the exit inclination q12 of the first magnetic sector 410 is limited to q12 < 35°, preferably q12 < 25° or most preferably q12 < 15°. Furthermore, an entrance inclination q12 of the second magnetic sector 450 (not shown) is limited to q21 < 35°, preferably q21 < 25° or most preferably q21 < 15°. This reduces aberrations.

[0116] The terms primary particle-optical beam path 13 and secondary particle-optical beam path 11 are used as is customary in technical terminology. However, it should be noted at this point that the primary particle-optical beam path 13, like the secondary particle-optical beam path 11 , describes the paths of the plurality of first or second individual particle beams 3, 9. For simplification purposes, however, the terms primary particle-optical beam path 13 or secondary particle-optical beam path 11 can of course - depending on the context - only be used to refer to a single particle beam 3, 9 that moves along the particle-optical axis Z of the system or the central beam. The central beam corresponds to the middle (i.e. central) single particle beam 3, 9 of the bundle of single particle beams 3, 9. The direction of the particle-optical axis Z when entering or leaving a magnetic sector is defined by the direction of the central beam, which is preferably identical to the central beam of all individual particle beams of the beam bundle.

[0117] According to an example, the following relation applies to the exit inclination o1 of the first magnetic sector: |o1 | > 0.5°, preferably |o1 | > 1°, |o1 | > 3° or |o1 | > 5°. At the same time, |q11 > 0.5°, preferably |q11| > 1°, |q111 > 3° or |q111 > 5° hold for the entrance inclination of the second particle optical beam path. The exit inclination o1 I the entrance inclination q11 is therefore a "real" inclination and greater than this inclination would be merely due to inaccuracies during adjustment. The sign or direction of the inclination depends on the specific design of the magnet arrangement and the charge of the primary particle beams used.

[0118] According to a further example, the following relation applies to the exit inclination o of the first magnetic sector: 0°< |o1 | < 10°, preferably 1° < |o1 | < 9° or most preferably 3° < |o1 | < 7°. Limiting the exit slope o of the primary particle optical beam path to a maximum value can be useful because the geometric conditions of the second particle-optical beam path 11 must also be taken into account. It is possible that a limited exit slope o1 helps to limit the pick-up of aberrations in the secondary particle-optical beam path 11 when traveling through the first magnetic sector 410. However, this depends on the specific design of a secondary path 11 .

[0119] As already explained above, the existing beam splitter arrangements 400 operate rather well with low aberrations when the corresponding multi-beam particle microscopes 1 are operated at one fixed landing energy LE. However, as explained above, varying the landing energy LE enhances aberrations. This is particularly true for big variations and very high landing energies.

[0120] It has been found out that the so-called filling factor of the very first projection lens in the projection lens system becomes a decisive influence on aberrations when working with highly increasing landing energies. In more detail, for increasing landing energies, the energy of the secondary particle / signal electrons gets smaller and smaller such that the focusing effect by the objective lens 102 increases. The focusing of the objective lens cannot be freely changed, but is in principle fix because of an optimum operation of the primary particle beam path. Therefore, the first intermediate image of the secondary particles / signal electron beamlets moves increasingly close to the sample / the object 7. Consequently, the multi-field-of-view (mFOV) radius inside the first projection lens 205a increases for high landing energies LE. This increases the filling factor inside the first projection lens 205a which in turn leads to an accumulation of large aberrations in the first projection lens 205a and thus in the subsequent particle optical path.

[0121] Fig. 6 schematically illustrates the problem of increased filling factor inside the first projection lens 205a when varying a landing energy LE over a large range. The secondary particle beam path 13 is depicted in a very simplified way for different landing energies which are 50eV, 500eV and 5keV. The respective intermediate images indicated by a star in Fig. 6 move closer to the objective lens 102 with increasing landing energy LE. Assuming a fix position of a first projection lens 205a arranged subsequently to a beam splitter arrangement 400, the height of a-rays in the first projection lens 205 dramatically increases, and thus the filling factor PL1 inside the first projection lens 205a increases.

[0122] Fig. 7 illustrates the definition of the filling factor PL1 : The filling factor PL1 is defined as the ratio between a maximum radius Rmax of the plurality of second individual particle beams 9 altogether within the first projection lens 205a and an inner radius Ri of an opening 213 of the first projection lens 205a through which opening 213 second individual particle beams 9 pass. Therefore, PL1= Rmax / Ri. The maximum radius Rmax corresponds to the multi-field-of view (mFOV) inside the first projection lens 205a The first projection lens 205a is a magnetic lens. Therefore, the opening 213 corresponds to the borehole of the magnetic lens 205a.

[0123] Fig. 8 schematically illustrates the position of the first projection lens 205a in the secondary particle optical beam path 11 . The plurality of second individual particle beams 9 start from the object 7 (not shown) and pass through the objective lens 102 where they get focussed. In Fig. 8, two exemplary second individual particle beams 9a and 9c are depicted. They cross each other in the first cross-over 215 of the secondary particle optical beam path 11. Subsequently, they pass through the beam splitter arrangement 400 and then travers a first projection lens 205a which is a magnetic lens in the example shown. The lens 205a is arranged in front of a contrast aperture 214 which is arranged at a second cross-over 212 in the secondary particle optical beam path 11. The first projection lens 205a focusses (or contributes to focussing) the second individual particle beams 9a, 9c on the second cross-over 212. If another magnetic projection lens (not depicted in Fig. 8) is provided after the beam splitter arrangement 400, but in front of the second cross-over 212, the magnetic projection lens arranged closest to the objective lens 102 is the first projection lens according to the present invention. In other words, the very first magnetic lens of the projection system 205 through which the second individual particle beams 9a, 9c travel, is the first projection lens according to the invention. In the example shown in Fig. 8, two further projection lenses 205b and 205c are provided, however, they are arranged after the second cross-over 212. In the example shown, the projection lens 205b can be used to adjust a focus on a detection system 209, the lens 205c can be used to adjust a magnification on the detection system 209.

[0124] Therefore, the multi-beam particle microscope 1 according to the present invention comprises a multi-beam particle generator 5, which is configured to generate a first field of a plurality of charged first individual particle beams 3. It further comprises a first particle-optical unit with a primary particle-optical beam path 13, configured to image the generated first individual particle beams 3 onto an object plane 101 such that the first individual particle beams 3 impinge an object 7 at incidence locations 5, which form a second field. The multi-beam particle microscope 1 comprises a detection unit 209 with a plurality of detection regions which form a third field and a second particle-optical unit with a secondary particle-optical beam path 11 , configured to image second individual particle beams9, which emanate from the incidence locations 5 in the second field, onto the third field of the detection regions of the detection system 209. The multi-beam particle microscope 1 further comprises a magnetic and / or electrostatic objective lens system 102, through which both the first and the second individual particle beams 3, 9 pass and a beam splitter arrangement 400 which is arranged in the primary particle-optical beam path 13 between the multi-beam generator 5 and the objective lens 102 and which is arranged in the secondary particle-optical beam path 11 between the objective lens system 102 and the detection unit 209. A controller 10 is configured to control the multibeam particle microscope 1 and to control a landing energy LE of the first individual particle beams 3 on the object 7. The beam splitter arrangement 400 comprises at least a first magnetic sector 410 in the secondary particle optical beam path 11 , the first magnetic sector 410 being configured for providing a homogeneous magnetic field through which during use the primary particle-optical beam path 13 and the secondary particle optical beam path 11 pass. The first magnetic sector 410 is configured for the separation of the primary particle-optical beam path 13 and the secondary particle-optical beam path 11 from one another. The entrance inclination 11 of the first magnetic sector 410 deviates from 0°. The secondary particle optical beam path 11 comprises a first cross-over 215 (see Fig. 8) of the second individual particle beams 9 corresponding to a focal plane of the objective lens system 102 and a second cross-over 212 of the second individual particle beams 9 which is arranged between the beam splitter arrangement 400 and the detection unit 209. Preferably, a contrast aperture 214 is arranged at the second cross-over 212. The second particle-optical unit comprises a projection lens system 205 with a first projection lens 205a, the first projection lens 205a being arranged in relation to the secondary particle optical beam path 11 after the first cross-over 215 and before the second cross-over 212; the projection lens system 205 being configured for imaging the second individual particle beams 9 onto the third field and the first projection lens 205a being configured for focussing the plurality of second individual particle beams 9 on the second cross-over 212. The controller 10 is configured for controlling the first projection lens 205a for focussing the plurality of second individual particle beams 9 on the second cross-over 212 depending on the landing energy LE. The first projection lens 205a is arranged so close to the first cross-over 215 that a filling factor PL1 of the first projection lens 205a can be set to PL1 < 15%, in particular PL1 < 10% or PL1 < 5%, wherein the filling factor PL1 is defined as mentioned above.

[0125] The respective landing energies LE of the first individual particle beams can be in the range from zero up to several keV, for example 3keV, 5keV, 10keV, 15keV, 20keV, 25keV or 30keV.

[0126] The magnetic sector 410 (as well as further magnetic sectors, if present) can be formed in a manner known per se. They are designed in particular to form homogeneous magnetic fields, with the direction of the magnetic field being oriented orthogonal to the movement direction of the individual particle beams. By way of example, the magnetic sectors can each be formed by two spaced apart plates of magnetizable material, each with milled depressions into which current conductors or coils have been inserted. However, other embodiments are also possible.

[0127] Fig. 9 schematically shows a beam splitter arrangement 400 according to the present invention. The beam splitter arrangement 400 is compatible with the multi-beam particle microscope shown in Fig. 1. According to Fig. 9, the beam splitter arrangement 400 further comprises a second magnetic sector 450 arranged in the secondary particle-optical beam path 11 and not arranged in the primary particle-optical beam path 13. The second magnetic sector 450 is arranged downstream of the first magnetic sector 410 in relation to the secondary particle-optical beam path 11 and being configured for providing a homogeneous magnetic field for deflecting the second individual particle beams 9. The beam splitter arrangement further comprises a third magnetic sector 460 arranged in the secondary particle-optical beam path 11 and not arranged in the primary particle-optical beam path 13, the third magnetic sector 460 being arranged downstream of the second magnetic sector 450 in relation to the secondary particle-optical beam path and being configured for providing a homogeneous magnetic field. The first projection lens 205a is arranged between the first magnetic sector 410 and the second magnetic sector 450; and the controller 10 is configured to control the second magnetic sector 450 and the third magnetic sector 460 depending on the landing energy. With this radical approach and the first projection lens 205a being very close to the object 7 / the sample 7, the filling factor PL1 inside the first projection lens 205a can be reduced very efficiently. The second and third magnetic sectors 450, 460 can be used for further corrections in the secondary particle optical beam path 11 . According to a preferred embodiment, the controller 10 is configured for controlling the second magnetic sector 450 and the third magnetic sector 460 to adjust a tilt and an offset of the particle optical axis Z within the projection lens system 205. For example, coupling into a second projection lens 205b can be corrected with respect to a tilt and an offset. The second magnetic sector 450 can be used to adjust a tilt and the third magnetic sector 460 can be used to adjust an offset or vice versa.

[0128] According to a preferred embodiment, the beam splitter arrangement 400 further comprises at least one multipole arrangement (not depicted in Fig. 9) arranged in the secondary particle- optical beam path 11 and not arranged in the primary particle-optical beam path, the multipole arrangement being arranged downstream of the first magnetic sector 410 in relation to the secondary particle-optical beam path. The first projection lens 205a is arranged in the direction of the secondary particle optical beam path 11 after the first magnetic sector 410 and before the multipole arrangement. The controller 10 is configured to control the multipole arrangement depending on the landing energy. According to a preferred embodiment, the controller 10 is configured to control the at least one multipole arrangement to additionally enable paraxial stigmatic, paraxial distortion-free and / or paraxial dispersion-free imaging on the detection plane.

[0129] Fig. 10 schematically shows a beam splitter arrangement 400 according to the present invention. The beam splitter arrangement 400 is also compatible with the multi-beam particle microscope shown in Fig. 1. According to this embodiment, the beam splitter arrangement 400 further comprises a second magnetic sector 450 arranged in the secondary particle-optical beam path 11 and not arranged in the primary particle-optical beam path13, the second magnetic sector being 450 arranged downstream of the first magnetic sector 410 in relation to the secondary particle-optical beam path 11 and being configured for providing a homogeneous magnetic field for deflecting the second individual particle 9 beams, in the example shown in the same direction as in the first magnetic sector 410. The first projection lens 205a is arranged in relation to the secondary particle optical beam path 11 directly after the second magnetic sector 450, which means that there are no further particle optical elements arranged in between. The controller 10 is configured for controlling the second magnetic sector 450 depending on the landing energy. Controlling the second magnetic sector 450 and thus adjusting its magnetic field offers one optimization parameter before the second individual particle beams 9 enter the first projection lens 205a. According to a preferred embodiment, the controller 10 is configured control the second magnetic sector 205a to adjust a tilt or an offset of the secondary particle optical axis Z before the plurality of second individual particle beams 9 enters the first projection lens 205a.

[0130] Fig. 11 schematically shows an alternative embodiment. The beam splitter arrangement 400 is also compatible with the multi-beam particle microscope shown in Fig. 1. The beam splitter arrangement 400 comprises a last magnetic sector 470 arranged in the secondary particle- optical beam path 11 and not arranged in the primary particle-optical beam path 13 and being configured for providing a homogeneous magnetic field, the last magnetic sector 470 being arranged in relation to the secondary particle-optical beam path 11 as the last magnetic sector 470 of the beam splitter arrangement 400 before the first projection lens 205a. The last magnetic sector can be a fourth magnetic sector as in the shown embodiment, but this is not mandatory. The beam splitter arrangement 400 further comprises an isolation trench 480 configured for decoupling of the magnetic field of the last magnetic sector 470 and the magnetic field of the first projection lens 205a. An exit inclination qiast of the last magnetic sector 470 is smaller than 15°, in particular smaller than 10° or 5°. This has the advantage that the isolation trench 480 can be provided in a space saving manner. This in turn allows to position the first projection lens closer to the sample and therefore reduces its filling factor. A filling factor can be reduced to about 8% by this measure. According to the shown embodiment, the isolation trench 480 is basically rectangular. A rectangular isolation trench 480 needs less installation space than a triangular isolation trench (see Fig. 4) and can be used in case the exit inclination qiast of the last magnetic sector 470 is small enough.

[0131] Fig. 12 schematically shows a beam splitter arrangement 400 according to the present invention. The beam splitter arrangement 400 is also compatible with the multi-beam particle microscope shown in Fig. 1. According to the depicted embodiment, the secondary particle optical beam path 11 further comprises a collimation lens 204 which is arranged in relation to the secondary particle optical beam path 11 after the first magnetic sector 410 and before the first projection lens 205a. The controller 10 is configured for controlling the collimation lens 204 depending on the landing energy. The provision of the collimation lens 204 contributes to a reduction of the FOV radius inside the first projection lens 205 and thus decreases its filling factor PL1. The collimation lens 204 can for example be switched on at high landing energies, but can stay switched off at low landing energies. The collimation lens 204 is preferably an electrostatic lens. An electrostatic lens needs less installation space than a magnetic lens and is therefore advantageous for positioning the first projection lens 205a rather close to the sample 7. According to an example, a focal length f_col of the collimation lens 204 is in the range 50mm < f_col < 150mm. According to a preferred embodiment, the strength of the magnetic field M1 in the first magnetic sector 410 and the strength of the magnetic field M2 in the second magnetic sector 450 is similar, thus 0,8 < M1 / M2 < 1 ,2.

[0132] According to an alternative embodiment, the beam splitter arrangement 400 further comprises a second magnetic sector 450 arranged in the secondary particle-optical beam path 11 and not arranged in the primary particle-optical beam path 13, the second magnetic sector 450 being arranged downstream of the first magnetic sector 410 in relation to the secondary particle-optical beam path 11 and being configured for providing a homogeneous magnetic field for further deflecting the second individual particle beams in the same direction as in the first magnetic sector. A total deflection angle a in the secondary particle optical beam path 11 , about which the secondary particle optical beam path 11 is deflected by the beam splitter arrangement 400 is described by the following relation: a > 40°, in particular a > 41° or a > 42°. This large deflection angle can be a decisive parameter for creating installation space in the second particle optical beam path 11. More installation space allows for the installation of a bigger first projection lens 205a which is preferably a magnetic lens and thus need lots of space. If the first projection lens can be made bigger, its opening / bore hole 213 can be made bigger and thus the filling factor PL1 can be reduced and less aberrations will be picked up inside the first projection lens 205a. According to an example, the strength of the magnetic field M1 in the first magnetic sector 410 and the strength of the magnetic field M2 in the second magnetic sector 450 is different and one of the following relations holds:

[0133] (i) M1 / M2 > 2,0, preferably M1 / M2 > 2,5 or M1 / M2 > 3,0; or

[0134] (ii) M2 / M1 > 2,0, preferably M2 / M1 > 2,5 or M2 / M1 > 3,0.

[0135] Therefore, an increase of aberrations being picked up in the beam splitter arrangement 400 is accepted at least for one magnetic sector which provides a comparatively strong magnetic field. However, this is more than counterbalanced by the reduced aberrations picked up in the first projection lens 205a.

[0136] According to an alternative embodiment of the present invention, the beam splitter arrangement 400 further comprises a maximum of five further components, wherein a component can either be a further magnetic sector 450, 460, 470 or a multipole arrangement, the further components providing a maximum of five degrees of freedom for further adjusting imaging in the secondary particle optical beam path. The controller 10 is configured for controlling the further components depending on the landing energy to at least adjust an axial fundamental ray height ratio xa / ya between the axial fundamental rays in x-direction and in y- direction inside the first projection lens 205a such that the following relation holds: (1 - xa / ya) < 15%, in particular (1 - xa / ya) < 10% or (1 - xa / ya) < 5%. In general, reducing the FOV anisotropy in x-direction and in y-direction inside the first projection lens 205a reduces an ellipticity in the second cross-over 212. However, if less than five magnetic sectors or multipoles are applied as further correction components in front of the first projection lens 205a, the imaging of the beam splitter arrangement 400 can never be perfectly stigmatic for all landing energies, but only one or two aspects of the in-total four beam splitter astigmatism components can be corrected for all landing energies. Hence, the question arises which of these astigmatism components should be compensated best. To achieve small cross-over ellipticities, it turns out to be advantageous to aim for small FOV-anisotropy inside the first projection lens 205a, e.g., by targeting comparable heights of the axial fundamental rays in x- and y-direction inside the first projection lens 205a.

[0137] According to a further embedment, the beam splitter arrangement 400 comprises a dispersion free plane in the secondary particle optical beam path 11 , the z-position of the dispersion free plane being fix by design of the beam splitter arrangement 400. The second particle optical unit comprises an adjustment means configured for adjusting a z-position of the objective lens system image plane. The controller 10 is configured for controlling the adjustment means depending on the landing energy in such a way that the adjusted z-position of the objective lens system image plane matches the fix z-position of the dispersion free plane of the beam splitter arrangement. This solution is contrary to the known approach to understand the z- position of the objective lens system image plane as fix and to adjust for example a magnetic sector of the beam splitter arrangement 400 to adjust the dispersion free plane such that it matches with the fix objective lens system image plane. The contrary approach according to the present invention can be realized in several different ways:

[0138] According to a preferred embodiment, the adjustment means comprises an adjustment lens which is arranged in relation to the secondary particle optical beam path after the first magnetic sector. The adjustment lens acts on the second individual particle beams, only. The largest refractive power of this adjustment lens is needed for the smallest landing energy / small landing energies. The adjustment lens can be arranged like the collimation lens already depicted in Fig. 12.

[0139] The, the controller 10 can for example be configured to control the landing energy for values between and including a minimum landing energy LEmin and a maximum landing energy LEmax; and the controller 10 is configured to control the adjustment lens 204 between and including zero and a maximum adjustment value. The controller 10 is configured to control the adjustment lens 204 with the maximum adjustment value when the minimum landing energy LEmin is set by the controller. According to an example, the adjustment lens 204 is configured to have a maximum refractive power RP of RP > 15 / m. However, smaller or bigger values are also possible, for example RP > 20 / m.

[0140] According to an alternative embodiment, the objective lens system 102 comprises a two-part objective lens and the adjustment means is realized by the two-part objective lens 102, the two parts of the objective lens system 102 are configured to be controllable independently from one another. The control is configured to control the two-part objective lens to keep the position of its image plane in the primary particle optical beam path and the control is configured to control the two-part objective lens to adjust the position of its image plane in the secondary particle optical beam path. In brief, this effect of the two-part objective lens 102 can be understood by the fact that a two-part objective lens 102 is equivalent to a replacement lens arranged at a variable position and having a variable strength.

[0141] According to a further embodiment, the beam splitter arrangement 400 further comprises a dispersion correction sector, the dispersion correction sector being configured for providing a homogenous magnetic field through which during use the secondary particle optical beam path 11 passes and the primary particle optical beam path 13 does not pass. The beam splitter arrangement 400 comprises a dispersion free plane in the secondary particle optical beam path 11 , the position of the dispersion free plane being adjustable by controlling the dispersion correction sector. The entrance inclination of the first magnetic sector 410 deliberately deviates from 0°. The controller 10 is configured for controlling the dispersion correction sector depending on the landing energy to match the position of the dispersion free plane of the beam splitter arrangement with the position of the objective lens system image plane.

[0142] According to an alternative embodiment, the beam splitter arrangement 400 does not comprise a dispersion correction sector or other dispersion correction means for controlling a position of a dispersion free plane in the secondary particle optical beam path 11 depending on the landing energy LE. The controller 10 is configured for controlling the landing energy LE in a range LEmin < LE < Lemax. The beam splitter arrangement 400 is designed in such a way that for a landing energy LE_ave = (LEmax-LEmin) / 2 the z-position z1 of the dispersion free plane of the beam splitter arrangement matches with the z-position z2 of the objective system lens image plane within + / -5%, thus 0,95 < |(z1-z2) / z2| < 1 ,05. The idea behind this solution is as follows: It has been found out that beam splitter aberrations for landing energies up to several keV are strongly dominated by the first-degree dispersion (Ck term). It is hence fruitful to aim for dispersion reduction in order to decrease the total beams splitter aberrations. If no dedicated magnetic sector is available for dispersion-correction at all landing energies, but the dispersion correction can only be made for one reference LE_ref via choosing a suitable beam splitter 400 / magnet arrangement design, then this choice should be made optimally. The beam splitter aberrations exhibit a minimum at the minimum position of the dispersion curve. This minimum comes about the following way: Each beam splitter design features a specific plane in which the dispersion vanishes, the so-called dispersion-free plane. The image plane position after the objective lens 102 and the beam splitter 400 strongly varies with the landing energy LE, being high above the sample 7 for small landing energies at which the secondary particles / signal electrons have a large energy, and being much closer to the sample 7 for high landing energies, with the exact positions depending on the refractive power of the respective objective lens 102 and beam splitter 400. Now, there exists one landing energy LEopt at which the image plane after the objective lens and the beam splitter crosses the dispersion-free plane. At this landing energy LEopt, the minimum of the beam splitter dispersion occurs. Consequently, if the beam splitter 400 shall be used over a specific range of landing energies, the goal is to optimize the beam splitter design such that the dispersion-free plane lies at such a position that the dispersion minimum approximately occurs in the middle of the targeted LE range. In this case the dispersion at the two edges of the LE range is the same and thus the smallest possible maximum dispersion value that can occur in the whole landing energy range is reached.

[0143] Fig. 13 illustrates the above-described adjustment solution: Fig. 13 a schematically shows the aberrations depending on the landing energy LE without the specific adaptations according to the present invention. The curve basically shows a V-shape. However, the curve is not symmetric with respect to the landing energy LEopt at which the dispersion vanishes. The aberrations are quite low in the range LEmin < LE < LE1. However, in the range LE1 < LE < LEmax, the aberrations increase drastically. Therefore, over the entire range LEmin < LE < LEmax, the aberrations differ a lot, namely from 0 up to a2 in the example shown.

[0144] Fig. 13b shows the situation, in which the beam splitter design 400 is designed such that the dispersion-free plane lies at such a position that the dispersion minimum approximately occurs in the middle of the targeted LE range. In other words, the minimum dispersion is reached at the landing energy LEopt which situated by design of the beam splitter 400 approximately in the middle between the minimum landing energy LEmin and the maximum landing energy LEmax. Therefore, over the entire range LEmin < LE < LEmax, the aberrations differ less, namely from 0 up to a1 or aT in the example shown.

[0145] Fig. 14 to Fig. 17 illustrate parameters of influence for suppressing aberrations in the second particle optical beam path 11. More precisely, it has been found for magnetic sectors 410, 450, 460, 470 that the ratios between a width W of a linear entrance or exit region and a distance D between the two plates forming the respective magnetic sector 410, 450, 460, 470 have a decisive influence on suppressing aberrations.

[0146] Fig. 14 schematically shows geometric relationships of the first magnetic sector 410, which can further contribute to the reduction of aberrations as independent control parameters: Shown in Figure 14a is the entry region of the first magnetic sector 410, with the particle-optical axis Z pointing into the paper plane in the example shown. The first magnetic sector 410 has two mutually parallel plates 411 , 412, which in the example shown have a distance D1 between them. The spaced-apart plates 411 , 412 can be made of magnetizable material and recesses can be milled into the plates 411 , 412 into which current conductors or coils are inserted. However, other embodiments for the two mutually parallel plates 411 , 412 are also possible. The entrance region of the first magnetic sector 410 is linear and has a width W11. Thus, in principle, the entire entrance region or trench is linear and the width W11 can be defined at all. It has now been found that a ratio of trench width W11 to plate spacing D1 has advantages if the following relation for the ratio R11 = W11 / D1 is fulfilled: R11 > 2.0, preferably R11 > 3.0 or R11 > 3.5. In this case, aberrations can be reduced even further. The same applies to the ratio R12 = W12 I D1 , where W12 denotes the width of the exit region of the first magnetic sector 410, which is shown in Figure 14b. Here too, there are advantages in terms of aberration reduction if the following ratio applies: R12 > 2.0, preferably R12 > 3.0 or R12 > 3.5.

[0147] Fig. 15 schematically shows geometric relationships of the second magnetic field region 450, which can further contribute to the reduction of aberrations as independent control parameters: Shown in Figure 15a is the entry region of the second magnetic sector 450, with the particle- optical axis Z pointing into the paper plane in the example shown. The second magnetic sector 450 has two mutually parallel plates 451 , 452, which in the example shown have a distance D2 between them. The spaced-apart plates 451 , 452 can be made of magnetizable material and recesses can be milled into the plates 451 , 452 into which current conductors or coils are inserted. However, other embodiments for the two mutually parallel plates 451 , 452 are also possible. The entrance region of the second magnetic sector 450 is linear and has a width W21. Thus, in principle, the entire entrance region or trench is linear and the width W21 can be defined at all. It has now been found that a ratio of trench width W21 to plate spacing D2 has advantages if the following relation for the ratio R21 = W21 I D2 is fulfilled: R21 > 2.0, preferably R21 > 3.0 or R21 > 3.5. In this case, aberrations can be reduced even further. The same applies to the ratio R22 = W22 I D2, where W22 denotes the width of the exit region of the second magnetic sector 450, which is shown in Figure 15b. Here too, there are advantages in terms of aberration reduction if the following ratio applies: R22 > 2.0, preferably R22 > 3.0 or R22 > 3.5. Fig. 16 schematically shows geometric relationships of the third magnetic sector 460, which can further contribute to the reduction of aberrations as independent control parameters: Shown in Figure 16a is the entry region of the third magnetic sector 460, with the particle- optical axis Z pointing into the paper plane in the example shown. The third magnetic sector 460 has two mutually parallel plates 467, 468, which in the example shown have a distance D3 between them. The spaced-apart plates 467, 468 can be made of magnetizable material and recesses can be milled into the plates 467, 468 into which current conductors or coils are inserted. However, other embodiments for the two mutually parallel plates 467, 468 are also possible. The entrance region of the third magnetic sector 460 is linear and has a width W31. Thus, in principle, the entire entrance region or trench is linear and the width W31 can be defined at all. It has now been found that a ratio of trench width W31 to plate spacing D3 has advantages if the following relation for the ratio R31 = W31 1 D3 is fulfilled: R31 > 2.0, preferably R31 > 3.0 or R31 > 3.5. In this case, aberrations can be reduced even further. The same applies to the ratio R32 = W321 D3, where W32 denotes the width of the exit region of the third magnetic sector 460, which is shown in Figure 16b. Here too, there are advantages in terms of aberration reduction if the following ratio applies: R32 > 2.0, preferably R32 > 3.0 or R32 > 3.5.

[0148] Fig. 17 schematically shows geometric relationships of the fourth magnetic sector 470, which can further contribute to the reduction of aberrations as independent control parameters: Shown in Figure 17a is the entry region of the fourth magnetic sector 470, with the particle- optical axis Z pointing into the paper plane in the example shown. The fourth magnetic sector 470 has two mutually parallel plates 471 , 472, which in the example shown have a distance D4 between them. The spaced-apart plates 471 , 472 can be made of magnetizable material and recesses can be milled into the plates 471 , 472 into which current conductors or coils are inserted. However, other embodiments for the two mutually parallel plates 471 , 472 are also possible. The entrance region of the fourth magnetic sector 470 is linear and has a width W41. Thus, in principle, the entire entrance region or trench is linear and the width W41 can be defined at all. It has now been found that a ratio of trench width W41 to plate spacing D4 has advantages if the following relation for the ratio R41 = W41 1 D4 is fulfilled: R41 > 2.0, preferably R41 > 3.0 or R41 > 3.5. In this case, aberrations can be reduced even further. The same applies to the ratio R42 = W42 I D4, where W42 denotes the width of the exit region of the fourth magnetic sector 470, which is shown in Figure 17b. Here too, there are advantages in terms of aberration reduction if the following ratio applies: R42 > 2.0, preferably R42 > 3.0 or R42 > 3.5. Fig. 18 illustrates a further embodiment of a beam splitter arrangement 400. This embodiment describes a rather fan-like design and therefore arrangement of the second, third and fourth magnet sector 450, 460, 470. This fan-like design contributes to balance and equalize the widths of the linear entrance regions and exit regions. Very short entrance regions and / or exit regions can be avoided. This measure in turn contributes to a reduction of aberrations, in particular rather strong field astigmatism.

[0149] In more detail, the beam splitter arrangement 400 comprises a first magnetic sector 410, the first magnetic sector 410 being configured for providing a homogeneous magnetic field M1 through which during use the primary particle-optical beam path 13 and the secondary particle- optical beam path 11 pass, and being configured for the separation of the primary particle- optical beam path 13 and the secondary particle-optical beam path 11 from one another. The entrance inclination q11 of the first magnetic sector 410 deliberately deviates from 0°.

[0150] Furthermore, the beam splitter arrangement 400 comprises a second magnetic sector 450 arranged in the secondary particle-optical beam path 11 and not arranged in the primary particle-optical beam path 13, the second magnetic sector 450 being arranged downstream of the first magnetic sector 410 in relation to the secondary particle-optical beam path 13 and being configured for providing a homogeneous magnetic field M2 for deflecting the second individual particle beams 9. A first drift region which is substantially free from magnetic fields is provided between the first magnetic sector 410 and the second magnetic sector 450.

[0151] The beam splitter arrangement 400 further comprises a third magnetic sector 460 arranged in the secondary particle-optical beam path 11 and not arranged in the primary particle-optical beam path 13, the third magnetic sector 460 being arranged downstream of the second magnetic sector 450 in relation to the secondary particle-optical beam path 11 and being configured for providing a homogeneous magnetic field M3. The beam splitter arrangement 400 further comprises a fourth magnetic sector 470 arranged in the secondary particle-optical beam path 11 and not arranged in the primary particle-optical beam path 13, the fourth magnetic sector 470 being arranged downstream of the third magnetic sector 460 in relation to the secondary particle-optical beam path 11 and being configured for providing a homogeneous magnetic field M4.

[0152] The second, third and fourth magnetic sectors 450, 460, 470 are arranged directly in succession without a drift region between neighboured magnetic sectors, and therefore the exit region of the second magnetic sector 450 corresponds to the entrance region of the third magnetic sector 460, the exit region of the third magnetic sector 460 corresponds to the entrance region of the fourth magnetic sector 470. In the example shown the entrance region of the second magnetic sector 450, the entrance region of the third magnetic sector 460, the entrance region of the fourth magnetic sector 470 and the exit region of the fourth magnetic sector 470 are linear and have in their theoretical prolongation several intersection points within an intersection circle 479 with a minimum diameter d. All intersection points of the prolongations with each other are situated in said intersection circle. Two intersection point P1 and P2 are the intersection points with the maximum distance between each possible pair of two intersection points. The points P1 and P2 are thus arranged on the intersection circle 479. The exit region W22 of the second magnetic sector 460 is linear and has a width W22.The following relation holds for the diameter d and the width WD22: d < WD22, in particular d < 0,5*WD22. According to an example, the following relation holds for the diameter d of the intersection circle 479: d<10mm, preferably d<5mm or d < 3mm. This is in the order of magnitude of a trench width or less.

[0153] Fig. 19 schematically shows another embodiment of the invention, wherein the magnet arrangement of beam splitter arrangement 400 consist of three magnetic sectors 410, 450, 460, only. The first magnetic sector 410 is configured for providing a homogeneous magnetic field M1 through which during use the primary particle-optical beam path 13 and the secondary particle-optical beam path 11 pass, and it is configured for the separation of the primary particle-optical beam path 13 and the secondary particle-optical beam path 11 from one another.

[0154] The second magnetic sector 450 is arranged in the secondary particle-optical beam path 11 and not arranged in the primary particle-optical beam path 13, the second magnetic sector 450 being arranged downstream of the first magnetic sector 410 n relation to the secondary particle-optical beam path 11 and being configured for providing a homogeneous magnetic field M2 for deflecting the second individual particle beams 9 410.

[0155] The third magnetic sector 460 is arranged in the secondary particle-optical beam path 11 and not arranged in the primary particle-optical beam path 13, the third magnetic sector 460 being arranged downstream of the second magnetic sector 450 in relation to the secondary particle- optical beam path 11 and being configured for providing a homogeneous magnetic field M3.

[0156] The entrance inclination q 11 of the first magnetic sector 410 deliberately deviates from 0° and a first drift region 453 which is substantially free from magnetic fields is provided between the first magnetic sector 410 and the second magnetic sector 450. Furthermore, a second drift region 473 which is substantially free from magnetic fields is provided between the second magnetic sector 450 and the third magnetic sector 460.

[0157] The controller 10 is configured for controlling the landing energy LE in a range LEmin < LE < LEmax. According to this embodiment, the design of the second magnetic sector 450 is configured for optimum astigmatism and dispersion correction at a low landing energy LEJow and the design of the third magnetic sector 460 is configured for optimum astigmatism and dispersion correction at a high landing energy LE_high or vice versa, with LEmin < LEJow < LE_high < LEmax.

[0158] According to a preferred embodiment, the controller 10 is configured for switching off the second magnetic sector 450 or the third magnetic sector 460 when the controller 10 sets the landing energy LE to LE_high or LEJow.

[0159] For the intrinsic beam splitter performance, it can be advantageous to choose beam splitter designs / magnet arrangement designs 400 with gaps / drift regions 453, 463 between the consecutive magnetic sectors since this offers more geometrical degrees of freedom (contrary to the fan-like design-rule explained above with respect to Fig. 18). Considering a design consisting of three magnet sectors in the secondary particle optical beam path with drift regions between consecutive magnet sectors, this provides enough degrees of freedom to achieve astigmatism and dispersion correction at two landing energies. The geometrical parameters of the first magnetic sector could, for example, be used for astigmatism and dispersion correction at a low landing energy within the targeted wide landing energy range while astigmatism and dispersion compensation at a high landing anergy could be achieved via the geometrical parameters of the second sectors, thus yielding a “W’-shaped landing energy dependence of the intrinsic beam splitter aberrations and hence smaller maximum aberration values than for the “V”-shaped curve when astigmatism and dispersion are only corrected at a single landing energy.

[0160] According to a preferred embodiment, the design parameters of the second magnetic sector 450 are geometrical parameters and comprise or consist of the following: length of the first drift region 453, entrance inclination q21 , exit inclination q22, distance between the entrance region and the exit region. In contrast thereto, the strength of a magnetic field in a magnetic sector is not a geometrical design parameter.

[0161] According to a preferred embodiment, the design parameters of the third magnetic sector 460 are geometrical parameters and comprise or consist of the following: length of the second drift region 463, entrance inclination q31 , exit inclination q32, distance between the entrance region and the exit region.

[0162] The above-described aspects and embodiments of the invention can be combined with one another in full or in part, provided that no technical contradictions arise as a result.

[0163] In many embodiments of the beam splitter arrangement 400 as described above in the figures, details of the beam splitter arrangement with respect to the first particle optical beam path are also disclosed. However, it is noted that the beam splitter arrangement 400 as described for the secondary particle optical 11 beam path also functions in combination with other beam splitter arrangements in the primary particle optical beam path. Details of the primary particle optical beam path are shown as exemplary illustrations, only.

[0164] It is also possible to adapt the disclosed embodiments to a beam splitter arrangement with a first magnetic sector 410 arranged in both the first and the second particle optical beam paths 13, 11 which lower trench G11 is orthogonal to the prolongation of the optical axis A of the objective lens system 102, thus q11=0.

[0165] Furthermore, it is noted that the figures presented are not true to scale, but are used for illustrative purposes, only.

[0166] A multi-beam particle microscope 1 with reduced aberrations in the secondary particle optical beam path 11 is disclosed. The solution is applicable to a wide range of landing energies LE up to several keV. One measure to achieve this aim is an architectural approach with an improved design of the entire projection path, and particularly an improved positioning of a first projection lens 205a in the secondary particle optical beam path 11 , wherein the first projection lens 205 is an installation space consuming magnetic lens. A filling factor in the first projection lens 205a has been identified as a leading source for remaining aberrations in the secondary particle optical beam path 11 when operating the multi-beam particle microscope 1 over a wide range of landing energies LE. Another measure is the performance enhancement of the beam splitter arrangement 400 itself in the secondary particle optical beam path 11 . Several designs of the beam splitter arrangement 400 and design rules for reducing aberrations when operating the multi-beam particle microscope 1 over a wide range of landing energies LE are disclosed.

[0167] List of reference signs

[0168] 1 Multi-beam particle microscope

[0169] 3 Primary particle beams (individual particle beams) Beam spots, incidence locations

[0170] Object, sample

[0171] Secondary particle beams

[0172] Computer system, controller

[0173] Secondary particle-optical beam path

[0174] Primary particle-optical beam path

[0175] Sample surface

[0176] Object plane

[0177] Objective lens

[0178] Axis

[0179] Detector system

[0180] Collimation lens

[0181] Projection lens system

[0182] Projection lens

[0183] Projection lens

[0184] Detection system, particle multi-detector, detection unit

[0185] Projection lens

[0186] Second cross-over

[0187] Opening

[0188] Contrast aperture

[0189] Cross-over

[0190] Anti-scan

[0191] Beam generating apparatus

[0192] Particle source

[0193] Collimation lens system

[0194] Multi-aperture arrangement

[0195] Micro-optics

[0196] Field lens

[0197] Field lens

[0198] Diverging particle beam

[0199] Beam foci

[0200] Intermediate image plane

[0201] Beam splitter, magnet arrangement

[0202] Drift region

[0203] Magnetic sector

[0204] Plate

[0205] Plate 430 Magnetic sector 450 Magnetic sector 451 Plate 452 Plate 453 Drift region 460 Magnetic sector 461 Limb of the beam tube arrangement 462 Limb of the beam tube arrangement 463 Limb of the beam tube arrangement

[0206] 466 Branching point 467 Plate 468 Plate 470 Magnetic sector 471 Plate 472 Plate 473 Drift region 479 Intersection circle 480 Isolation trench

[0207] 490 Beam tube arrangement 500 Scan deflector 600 Displacement stage or positioning device A Axis of objective lens, prolongation of said axis d diameter of intersection circle Di Distance between plates P Skew angle Y Splitting angle 6 Field inclination angle o Exit angle

[0208] Entrance angle nu exit angle, entrance angle (secondary path) PI Intersection point

[0209] P2 Intersection point Wij Width of entrance regions I exit regions G11 Trench G12 Trench S1 Arc length S2 Arc length

Claims

Patent claims1. A multi-beam particle microscope, comprising a multi-beam particle generator, which is configured to generate a first field of a plurality of charged first individual particle beams; a first particle-optical unit with a primary particle-optical beam path, configured to image the generated first individual particle beams onto an object plane such that the first individual particle beams impinge an object at incidence locations, which form a second field; a detection unit with a plurality of detection regions which form a third field; a second particle-optical unit with a secondary particle-optical beam path, configured to image second individual particle beams, which emanate from the incidence locations in the second field, onto the third field of the detection regions of the detection system; a magnetic and / or electrostatic objective lens system, through which both the first and the second individual particle beams pass; a beam splitter arrangement which is arranged in the primary particle-optical beam path between the multi-beam generator and the objective lens and which is arranged in the secondary particle-optical beam path between the objective lens system and the detection unit; and a controller configured to control the multi-beam particle microscope and to control a landing energy of the first individual particle beams on the object; wherein the beam splitter arrangement comprises the following features: at least a first magnetic sector, the first magnetic sector being configured for providing a homogeneous magnetic field through which during use the primary particle- optical beam path and the secondary particle-optical beam path pass, and being configured for the separation of the primary particle-optical beam path and the secondary particle-optical beam path from one another; wherein each magnetic sector has an entrance region for the secondary particle-optical beam path with an entrance inclination and an exit region for the secondary particle-optical beam path with an exit inclination, wherein the entrance inclination is defined as the angle by which the alignment of the entrance region deviates from the normal to the optical axis of the secondary particle-optical beam path, and wherein the exit inclination is defined as the angle by which the alignment of the exit region deviates from the normal to the optical axis of the secondary particle-optical beam path; wherein the entrance inclination of the first magnetic sector deviates from 0°; wherein the secondary particle optical beam path comprises a first cross-over of the second individual particle beams corresponding to a focal plane of the objective lens systemand a second cross-over of the second individual particle beams which is arranged between the beam splitter arrangement and the detection unit and which can be arranged during use level with a contrast aperture; wherein the second particle-optical unit comprises a projection lens system with a first projection lens which is a magnetic lens, the first projection lens being arranged in relation to the secondary particle optical beam path after the first cross-over and before the second crossover; the projection lens system being configured for imaging the second individual particle beams onto the third field and the first projection lens being configured for focussing the plurality of second individual particle beams on the second cross-over; wherein the controller is configured for controlling the first projection lens for focussing the plurality of second individual particle beams on the second cross-over depending on the landing energy; and wherein the first projection lens is arranged so close to the first cross-over that a filling factor PL1 of the first projection lens is set to PL1 < 15%, in particular PL1 < 10% or PL1 < 5%, wherein the filling factor PL1 is defined as the ratio between a maximum radius Rmax of the plurality of second individual particle beams altogether within the first projection lens and an inner radius Ri of an opening of the first projection lens through which opening the second individual particle beams pass, thus PL1= Rmax / Ri.

2. The multi-beam particle microscope according to claim 1 , wherein the beam splitter arrangement further comprises a second magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the second magnetic sector being arranged downstream of the first magnetic sector in relation to the secondary particle-optical beam path and being configured for providing a homogeneous magnetic field for deflecting the second individual particle beams, and a third magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the third magnetic sector being arranged downstream of the second magnetic sector in relation to the secondary particle- optical beam path and being configured for providing a homogeneous magnetic field; and wherein the first projection lens is arranged between the first magnetic sector and the second magnetic sector; and wherein the controller is configured to control the second magnetic sector and the third magnetic sector depending on the landing energy.

3. The multi-beam particle microscope according to claim 2,wherein the controller is configured for controlling the second magnetic sector and the second magnetic sector to adjust a tilt and an offset of the particle optical axis within the projection lens system.

4. The multi-beam particle microscope according to claim 3, wherein the beam splitter arrangement further comprises at least one multipole arrangement arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the multipole arrangement being arranged downstream of the first magnetic sector in relation to the secondary particle-optical beam path; wherein the first projection lens is arranged in the direction of the secondary particle optical beam path after the first magnetic sector and before the multipole arrangement; and wherein the controller is configured to control the multipole arrangement depending on the landing energy.

5. The multi-beam particle microscope according to claim 4, wherein the controller is configured to control the at least one multipole arrangement to additionally enable paraxial stigmatic, paraxial distortion-free and / or paraxial dispersion-free imaging on the detection plane.

6. The multi-beam particle microscope of claim 1 , wherein the beam splitter arrangement further comprises a second magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle- optical beam path, the second magnetic sector being arranged downstream of the first magnetic sector in relation to the secondary particle-optical beam path and being configured for providing a homogeneous magnetic field for deflecting the second individual particle beams, wherein the first projection lens is arranged in relation to the secondary particle optical beam path directly after the second magnetic sector; and wherein the controller is configured for controlling the second magnetic sector depending on the landing energy.

7. The multi-beam particle microscope according to claim 6, wherein the controller is configured control the second magnetic sector to adjust a tilt or an offset of the secondary particle optical axis defined by the plurality of second individual particle beams before entering the first projection lens.

8. The multi-beam particle microscope according to claim 1 , wherein the beam splitter arrangement further comprises: a last magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path and being configured for providing a homogeneous magnetic field, the last magnetic sector being arranged in relation to the secondary particle-optical beam path as the last magnetic sector of the beam splitter arrangement before the first projection lens; and an isolation trench configured for decoupling of the magnetic field of the last magnetic sector and the magnetic field of the first projection lens, wherein an exit inclination qiast of the last magnetic sector is smaller than 15°, in particular smaller than 10° or 5°.

9. The multi-beam particle microscope according to claim 8, wherein the isolation trench is basically rectangular.

10. The multi-beam particle microscope according to claim 1 , wherein the secondary particle optical beam path further comprises a collimation lens which is arranged in relation to the secondary particle optical beam path after the first magnetic sector and before the first projection lens, and wherein the controller is configured for controlling the collimation lens depending on the landing energy.

11. The multi-beam particle microscope according to claim 10, wherein a focal length f_col of the collimation lens is in the range 20mm < f_col < 500mm, in particular in the range 50mm < f_col < 150mm.

12. The multi-beam particle microscope according to claim 10 or 11 , wherein the collimation lens is an electrostatic lens.

13. The multi-beam particle microscope according to claim 2 or 6, wherein the strength of the magnetic field M1 in the first magnetic sector and the strength of the magnetic field M2 in the second magnetic sector is similar, thus 0,8 < M1 / M2 < 1 ,2 and in particular identical.

14. The multi-beam particle microscope according to claim 1 , wherein the beam splitter arrangement further comprises a second magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the second magnetic sector being arranged downstream of the first magnetic sector in relation to the secondary particle-optical beam path and being configured for providing a homogeneous magnetic field for further deflecting the second individual particle beams in the same direction as in the first magnetic sector, wherein for a total deflection angle a in the secondary particle optical beam path, about which the secondary particle optical beam path is deflected by the beam splitter arrangement, the following relation holds: a > 40°, in particular a > 41 ° or a > 42°15. The multi-beam particle microscope according to claim 14, wherein the strength of the magnetic field M1 in the first magnetic sector and the strength of the magnetic field M2 in the second magnetic sector is different and wherein one of the following relations holds:(i) M1 / M2 > 2,0, in particular M1 / M2 > 2,5 or M1 / M2 > 3,0; or(ii) M2 / M1 > 2,0, in particular M2 / M1 > 2,5 or M2 / M1 > 3,0.

16. A multi-beam particle microscope, comprising a multi-beam particle generator, which is configured to generate a first field of a plurality of charged first individual particle beams; a first particle-optical unit with a primary particle-optical beam path, configured to image the generated first individual particle beams onto an object plane such that the first individual particle beams impinge an object at incidence locations, which form a second field; a detection unit with a plurality of detection regions which form a third field; a second particle-optical unit with a secondary particle-optical beam path, configured to image second individual particle beams, which emanate from the incidence locations in the second field, onto the third field of the detection regions of the detection system; a magnetic and / or electrostatic objective lens system, through which both the first and the second individual particle beams pass; a beam splitter arrangement which is arranged in the primary particle-optical beam path between the multi-beam generator and the objective lens and which is arranged in the secondary particle-optical beam path between the objective lens system and the detection unit; and a controller configured to control the multi-beam particle microscope and to control a landing energy of the first individual particle beams on the object; wherein the beam splitter arrangement comprises the following features: a first magnetic sector, the first magnetic sector being configured for providing a homogeneous magnetic field through which during use the primary particle-optical beam path and the secondary particle-optical beam path pass, and being configuredfor the separation of the primary particle-optical beam path and the secondary particle- optical beam path from one another; wherein each magnetic sector has an entrance region for the secondary particle-optical beam path with an entrance inclination and an exit region for the secondary particle-optical beam path with an exit inclination, wherein the entrance inclination is defined as the angle by which the alignment of the entrance region deviates from the normal to the optical axis of the secondary particle-optical beam path, and wherein the exit inclination is defined as the angle by which the alignment of the exit region deviates from the normal to the optical axis of the secondary particle-optical beam path; wherein the entrance inclination of the first magnetic sector deliberately deviates from 0°; wherein the beam splitter arrangement further comprises a maximum of five further components, wherein a component can either be a further magnetic sector or a multipole arrangement, the further components providing a maximum of five degrees of freedom for further adjusting imaging in the secondary particle optical beam path; wherein the secondary particle optical beam path comprises a first cross-over of the second individual particle beams corresponding to a focal plane of the objective lens system and a second cross-over of the second individual particle beams which is arranged between the beam splitter arrangement and the detection unit and which can be arranged during use level with a contrast aperture; and wherein the second particle-optical unit comprises a projection lens system with a first projection lens, the projection lens system being configured for imaging the second individual particle beams onto the third field, and the first projection lens being arranged in relation to the secondary particle optical beam path after the first cross-over and before the second crossover and the first projection lens being configured for focussing the plurality of second individual particle beams on the second cross-over; wherein the controller is configured for controlling the first projection lens for focussing the plurality of second individual particle beams on the second cross-over depending on the landing energy; and wherein the controller is configured for controlling the further components depending on the landing energy to at least adjust an axial fundamental ray height ratio xa / ya between the axial fundamental rays in x-direction and in y-direction inside the first projection lens such that the following relation holds:(1 - xa / ya) < 15%, in particular (1 - xa / ya) < 10% or (1 - xa / ya) < 5%.

17. A multi-beam particle microscope, comprisinga multi-beam particle generator, which is configured to generate a first field of a plurality of charged first individual particle beams; a first particle-optical unit with a primary particle-optical beam path, configured to image the generated first individual particle beams onto an object plane such that the first individual particle beams impinge an object at incidence locations, which form a second field; a detection unit with a plurality of detection regions which form a third field; a second particle-optical unit with a secondary particle-optical beam path, configured to image second individual particle beams, which emanate from the incidence locations in the second field, onto the third field of the detection regions of the detection system; a magnetic and / or electrostatic objective lens system, through which both the first and the second individual particle beams pass; a beam splitter arrangement which is arranged in the primary particle-optical beam path between the multi-beam generator and the objective lens and which is arranged in the secondary particle-optical beam path between the objective lens system and the detection unit; and a controller configured to control the multi-beam particle microscope and to control a landing energy of the first individual particle beams on the object; wherein the beam splitter arrangement comprises at least a first magnetic sector, the first magnetic sector being configured for providing a homogeneous magnetic field through which during use the primary particle-optical beam path and the secondary particle-optical beam path pass, and being configured for the separation of the primary particle-optical beam path and the secondary particle-optical beam path from one another, wherein each magnetic sector of the beam splitter arrangement has an entrance region for the secondary particle-optical beam path with an entrance inclination and an exit region for the secondary particle-optical beam path with an exit inclination, wherein the entrance inclination is defined as the angle by which the alignment of the entrance region deviates from the normal to the optical axis of the secondary particle-optical beam path, and wherein the exit inclination is defined as the angle by which the alignment of the exit region deviates from the normal to the optical axis of the secondary particle-optical beam path; and wherein the entrance inclination of the first magnetic sector deliberately deviates from 0°; wherein the beam splitter arrangement comprises a dispersion free plane in the secondary particle optical beam path, the z-position of the dispersion free plane being fix by design of the beam splitter arrangement; wherein the secondary particle optical beam path comprises a first cross-over of the second individual particle beams corresponding to a focal plane of the objective lens system,the objective lens system further having an objective lens system image plane arranged in relation to the secondary particle optical beam path after the first cross-over; and wherein the second particle optical unit comprises an adjustment means configured for adjusting a z-position of the objective lens system image plane; wherein the controller is configured for controlling the adjustment means depending on the landing energy in such a way that the adjusted z-position of the objective lens system image plane matches the fix z-position of the dispersion free plane of the beam splitter arrangement.

18. The multi-beam particle microscope according to claim 17, wherein the adjustment means comprises an adjustment lens which is arranged in relation to the secondary particle optical beam path after the first magnetic sector.

19. The multi-beam particle microscope according to claim 18, wherein the controller is configured to control the landing energy for values between and including a minimum landing energy LEmin and a maximum landing energy LEmax; and wherein the controller is configured to control the adjustment lens between and including zero and a maximum adjustment value; wherein the controller is configured to control the adjustment lens with the maximum adjustment value when the minimum landing energy LEmin is set by the controller.

20. The multi-beam particle microscope according to claim 18 or 19, wherein the adjustment lens is configured to have a maximum refractive power RP of RP > 15 / m.

21. The multi-beam particle microscope according to claim 17, wherein the objective lens system comprises a two-part objective lens; wherein the adjustment means is realized by the two-part objective lens, the two parts of the objective lens system are configured to be controllable independently from one another; wherein the control is configured to control the two-part objective lens to keep the position of its image plane in the primary particle optical beam path; and wherein the control is configured to control the two-part objective lens to adjust the position of its image plane in the secondary particle optical beam path.

22. A multi-beam particle microscope, comprising a multi-beam particle generator, which is configured to generate a first field of a plurality of charged first individual particle beams;a first particle-optical unit with a primary particle-optical beam path, configured to image the generated first individual particle beams onto an object plane such that the first individual particle beams impinge an object at incidence locations, which form a second field; a detection unit with a plurality of detection regions which form a third field; a second particle-optical unit with a secondary particle-optical beam path, configured to image second individual particle beams, which emanate from the incidence locations in the second field, onto the third field of the detection regions of the detection system; a magnetic and / or electrostatic objective lens system, through which both the first and the second individual particle beams pass; a beam splitter arrangement which is arranged in the primary particle-optical beam path between the multi-beam generator and the objective lens and which is arranged in the secondary particle-optical beam path between the objective lens system and the detection unit; and a controller configured to control the multi-beam particle microscope and to control a landing energy of the first individual particle beams on the object; wherein the beam splitter arrangement comprises a first magnetic sector, the first magnetic sector being configured for providing a homogeneous magnetic field through which during use the primary particle-optical beam path and the secondary particle-optical beam path pass, and being configured for the separation of the primary particle-optical beam path and the secondary particle-optical beam path from one another; and a dispersion correction sector, the dispersion correction sector being configured for providing a homogenous magnetic field through which during use the secondary particle optical beam path passes and the primary particle optical beam path does not pass; wherein the beam splitter arrangement comprises a dispersion free plane in the secondary particle optical beam path, the position of the dispersion free plane being adjustable by controlling the dispersion correction sector; wherein each magnetic sector of the beam splitter arrangement has an entrance region for the secondary particle-optical beam path with an entrance inclination and an exit region for the secondary particle-optical beam path with an exit inclination, wherein the entrance inclination is defined as the angle by which the alignment of the entrance region deviates from the normal to the optical axis of the secondary particle-optical beam path, and wherein the exit inclination is defined as the angle by which the alignment of the exit region deviates from the normal to the optical axis of the secondary particle-optical beam path; and wherein the entrance inclination of the first magnetic sector deliberately deviates from 0°;wherein the secondary particle optical beam path comprises a first cross-over of the second individual particle beams corresponding to a focal plane of the objective lens system, the objective lens system further having an objective lens system image plane arranged in relation to the secondary particle optical beam path after the first cross-over; and wherein the controller is configured for controlling the dispersion correction sector depending on the landing energy to match the position of the dispersion free plane of the beam splitter arrangement with the position of the objective lens system image plane.

23. A multi-beam particle microscope, comprising a multi-beam particle generator, which is configured to generate a first field of a plurality of charged first individual particle beams; a first particle-optical unit with a primary particle-optical beam path, configured to image the generated first individual particle beams onto an object plane such that the first individual particle beams impinge an object at incidence locations, which form a second field; a detection unit with a plurality of detection regions which form a third field; a second particle-optical unit with a secondary particle-optical beam path, configured to image second individual particle beams, which emanate from the incidence locations in the second field, onto the third field of the detection regions of the detection system; a magnetic and / or electrostatic objective lens system, through which both the first and the second individual particle beams pass; a beam splitter arrangement which is arranged in the primary particle-optical beam path between the multi-beam generator and the objective lens and which is arranged in the secondary particle-optical beam path between the objective lens system and the detection unit; and a controller configured to control the multi-beam particle microscope and to control a landing energy of the first individual particle beams on the object; wherein the beam splitter arrangement comprises a first magnetic sector, the first magnetic sector being configured for providing a homogeneous magnetic field through which during use the primary particle-optical beam path and the secondary particle-optical beam path pass, and being configured for the separation of the primary particle-optical beam path and the secondary particle-optical beam path from one another; a second magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the second magnetic sector being arranged downstream of the first magnetic sector in relation to the secondary particle-optical beam path and being configured for providing a homogeneous magnetic field for deflecting the second individual particle beams, anda third magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the third magnetic sector being arranged downstream of the second magnetic sector in relation to the secondary particle- optical beam path and being configured for providing a homogeneous magnetic field; wherein each magnetic sector of the beam splitter arrangement has an entrance region for the secondary particle-optical beam path with an entrance inclination and an exit region for the secondary particle-optical beam path with an exit inclination, wherein the entrance inclination is defined as the angle by which the alignment of the entrance region deviates from the normal to the optical axis of the secondary particle-optical beam path, and wherein the exit inclination is defined as the angle by which the alignment of the exit region deviates from the normal to the optical axis of the secondary particle-optical beam path; and wherein the entrance inclination of the first magnetic sector deliberately deviates from 0°; and wherein the beam splitter arrangement does not comprise a dispersion correction sector or other dispersion correction means for controlling a position of a dispersion free plane in the secondary particle optical beam path depending on the landing energy LE; wherein the secondary particle optical beam path comprises a first cross-over of the second individual particle beams corresponding to a focal plane of the objective lens system, the objective lens system further having an objective lens system image plane arranged in relation to the secondary particle optical beam path after the first cross-over; and wherein the controller is configured for controlling the landing energy LE in a range LEmin < LE < LEmax, and wherein the beam splitter arrangement is designed in such a way that for a landing energy LE_ave = (LEmax-LEmin) / 2 the z-position z1 of the dispersion free plane of the beam splitter arrangement matches with the z-position z2 of the objective system lens image plane within + / -5%, thus 0,95 < |(z1-z2) / z2| < 1 ,05.

24. A multi-beam particle microscope, comprising a multi-beam particle generator, which is configured to generate a first field of a plurality of charged first individual particle beams; a first particle-optical unit with a primary particle-optical beam path, configured to image the generated first individual particle beams onto an object plane such that the first individual particle beams impinge an object at incidence locations, which form a second field; a detection unit with a plurality of detection regions which form a third field; a second particle-optical unit with a secondary particle-optical beam path, configured to image second individual particle beams, which emanate from the incidence locations in the second field, onto the third field of the detection regions of the detection system;a magnetic and / or electrostatic objective lens system, through which both the first and the second individual particle beams pass; a beam splitter arrangement which is arranged in the primary particle-optical beam path between the multi-beam generator and the objective lens and which is arranged in the secondary particle-optical beam path between the objective lens system and the detection unit; and a controller configured to control the multi-beam particle microscope and to control a landing energy of the first individual particle beams on the object; wherein the beam splitter arrangement comprises a first magnetic sector, the first magnetic sector being configured for providing a homogeneous magnetic field M1 through which during use the primary particle-optical beam path and the secondary particle-optical beam path pass, and being configured for the separation of the primary particle-optical beam path and the secondary particle-optical beam path from one another; a second magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the second magnetic sector being arranged downstream of the first magnetic sector in relation to the secondary particle-optical beam path and being configured for providing a homogeneous magnetic field M2 for deflecting the second individual particle beams, and a third magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the third magnetic sector being arranged downstream of the second magnetic sector in relation to the secondary particle- optical beam path and being configured for providing a homogeneous magnetic field M3; a fourth magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the fourth magnetic sector being arranged downstream of the third magnetic sector in relation to the secondary particle-optical beam path and being configured for providing a homogeneous magnetic field M4; wherein each magnetic sector of the beam splitter arrangement has an entrance region for the secondary particle-optical beam path with an entrance inclination and an exit region for the secondary particle-optical beam path with an exit inclination, wherein the entrance inclination is defined as the angle by which the alignment of the entrance region deviates from the normal to the optical axis of the secondary particle-optical beam path, and wherein the exit inclination is defined as the angle by which the alignment of the exit region deviates from the normal to the optical axis of the secondary particle-optical beam path; and wherein the entrance inclination of the first magnetic sector deliberately deviates from 0°; andwherein a first drift region which is substantially free from magnetic fields is provided between the first magnetic sector and the second magnetic sector; wherein the first magnetic sector comprises two plates which are arranged parallel to one another and which have a plate distance D1 , wherein during use the homogeneous magnetic field M1 is generated between the two plates; wherein the entrance region of the first magnetic sector is linear and comprises a width W11 and wherein the exit region of the first magnetic sector is linear and comprises a width W12, and wherein for a ratio R11 = W11 / D1 the following relation holds: R11 > 2,0, in particular R11 > 3,0 or R11 > 3,5; wherein for a ratio R12 = W12 I D1 the following relation holds: R12 > 2,0, in particular R12 > 3,0 or R12 > 3,5; and wherein the second magnetic sector comprises two plates which are arranged parallel to one another and which have a plate distance D2, wherein during use the homogeneous magnetic field M2 is generated between the two plates; wherein the entrance region of the second magnetic sector is linear and comprises a width W21 and wherein the exit region of the second magnetic sector is linear and comprises a width W22, and wherein for a ratio R21 = W21 I D2 the following relation holds: R21 > 2,0, in particular R21 > 3,0 or R21 > 3,5; and / or wherein for a ratio R22 = W22 1 D2 the following relation holds: R22 > 2,0, in particular R22 > 3,0 or R22 > 3,5.

25. The multi-beam particle microscope according to claim 24, wherein the third magnetic sector comprises two plates which are arranged parallel to one another and which have a plate distance D3, wherein during use the homogeneous magnetic field M3 is generated between the two plates; wherein the entrance region of the third magnetic sector is linear and comprises a width W31 and wherein the exit region of the third magnetic sector is linear and comprises a width W32, and wherein for a ratio R31 = W31 I D3 the following relation holds: R31 > 2,0, in particular R31 > 3,0 or R31 > 3,5; and / or wherein for a ratio R32 = W32 I D2 the following relation holds: R32 > 2,0, in particular R32 > 3,0 or R32 > 3,5.

26. The multi-beam particle microscope according to claim 24 or 25, wherein the fourth magnetic sector comprises two plates which are arranged parallel to one another and which have a plate distance D4, wherein during use the homogeneous magnetic field M4 is generated between the two plates; wherein the entrance region of the fourth magnetic sector is linear and comprises a width W41 and wherein the exit region of the third magnetic sector is linear and comprises a width W42, and wherein for a ratio R41 = W41 I D4 the following relation holds: R41 > 2,0, in particular R41 > 3,0 or R41 > 3,5; and / or whereinfor a ratio R42 = W42 I D4 the following relation holds: R42 > 2,0, in particular R42 > 3,0 or R42 > 3,5.

27. The multi-beam particle microscope according to any one of claims 24 to 26, wherein the exit inclination of the first magnetic sector is limited to q12 < 35°, preferably q12 < 25° or most preferably q < 15°.

28. The multi-beam particle microscope according to any one of claims 24 to 27, wherein the entrance inclination of the second magnetic sector is limited to q21 < 35°, preferably q21 < 25° or most preferably q21 < 15°.

29. A multi-beam particle microscope, comprising a multi-beam particle generator, which is configured to generate a first field of a plurality of charged first individual particle beams; a first particle-optical unit with a primary particle-optical beam path, configured to image the generated first individual particle beams onto an object plane such that the first individual particle beams impinge an object at incidence locations, which form a second field; a detection unit with a plurality of detection regions which form a third field; a second particle-optical unit with a secondary particle-optical beam path, configured to image second individual particle beams, which emanate from the incidence locations in the second field, onto the third field of the detection regions of the detection system; a magnetic and / or electrostatic objective lens system, through which both the first and the second individual particle beams pass; a beam splitter arrangement which is arranged in the primary particle-optical beam path between the multi-beam generator and the objective lens and which is arranged in the secondary particle-optical beam path between the objective lens system and the detection unit; and a controller configured to control the multi-beam particle microscope and to control a landing energy of the first individual particle beams on the object; wherein the beam splitter arrangement comprises a first magnetic sector, the first magnetic sector being configured for providing a homogeneous magnetic field M1 through which during use the primary particle-optical beam path and the secondary particle-optical beam path pass, and being configured for the separation of the primary particle-optical beam path and the secondary particle-optical beam path from one another; a second magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the second magnetic sector beingarranged downstream of the first magnetic sector in relation to the secondary particle-optical beam path and being configured for providing a homogeneous magnetic field M2 for deflecting the second individual particle beams; a third magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the third magnetic sector being arranged downstream of the second magnetic sector in relation to the secondary particle- optical beam path and being configured for providing a homogeneous magnetic field M3; a fourth magnetic sector arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the fourth magnetic sector being arranged downstream of the third magnetic sector in relation to the secondary particle-optical beam path and being configured for providing a homogeneous magnetic field M4; wherein each magnetic sector of the beam splitter arrangement has an entrance region for the secondary particle-optical beam path with an entrance inclination and an exit region for the secondary particle-optical beam path with an exit inclination, wherein the entrance inclination is defined as the angle by which the alignment of the entrance region deviates from the normal to the optical axis of the secondary particle-optical beam path, and wherein the exit inclination is defined as the angle by which the alignment of the exit region deviates from the normal to the optical axis of the secondary particle-optical beam path; and wherein the entrance inclination of the first magnetic sector deliberately deviates from 0°; and wherein a first drift region which is substantially free from magnetic fields is provided between the first magnetic sector and the second magnetic sector; wherein the second, third and fourth magnetic sectors are arranged directly in succession without a drift region between neighbored magnetic sectors, and therefore the exit region of the second magnetic sector corresponds to the entrance region of the third magnetic sector, the exit region of the third magnetic sector corresponds to the entrance region of the fourth magnetic sector; wherein the entrance region of the second magnetic sector, the entrance region of the third magnetic sector, the entrance region of the fourth magnetic sector and the exit region of the fourth magnetic sector are linear and have in their theoretical prolongation an intersection point or an intersection circle with a minimum diameter d, wherein all intersections of the prolongations with each other are situated in said intersection circle, wherein the exit region of the second magnetic sector is linear and has a width W22; and wherein the following relation holds for the diameter d and the width WD22: d < WD22, in particular d < 0,5*WD22.

30. The multi-beam particle microscope according to claim 29, wherein d<10mm, in particular d<5mm or d < 3mm.

31. A multi-beam particle microscope, comprising a multi-beam particle generator, which is configured to generate a first field of a plurality of charged first individual particle beams; a first particle-optical unit with a primary particle-optical beam path, configured to image the generated first individual particle beams onto an object plane such that the first individual particle beams impinge an object at incidence locations, which form a second field; a detection unit with a plurality of detection regions which form a third field; a second particle-optical unit with a secondary particle-optical beam path, configured to image second individual particle beams, which emanate from the incidence locations in the second field, onto the third field of the detection regions of the detection system; a magnetic and / or electrostatic objective lens system, through which both the first and the second individual particle beams pass; a beam splitter arrangement which is arranged in the primary particle-optical beam path between the multi-beam generator and the objective lens and which is arranged in the secondary particle-optical beam path between the objective lens system and the detection unit; and a controller configured to control the multi-beam particle microscope and to control a landing energy of the first individual particle beams on the object; wherein the beam splitter arrangement comprises a magnet arrangement consisting of a first magnetic sector, a second magnetic sector and a third magnetic sector, the first magnetic sector being configured for providing a homogeneous magnetic field M1 through which during use the primary particle-optical beam path and the secondary particle-optical beam path pass, and being configured for the separation of the primary particle-optical beam path and the secondary particle-optical beam path from one another; the second magnetic sector being arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the second magnetic sector being arranged downstream of the first magnetic sector in relation to the secondary particle-optical beam path and being configured for providing a homogeneous magnetic field M2 for deflecting the second individual particle beams; the third magnetic sector being arranged in the secondary particle-optical beam path and not arranged in the primary particle-optical beam path, the third magnetic sector being arranged downstream of the second magnetic sector in relation to the secondary particle- optical beam path and being configured for providing a homogeneous magnetic field M3;wherein each magnetic sector of the magnet arrangement has an entrance region for the secondary particle-optical beam path with an entrance inclination and an exit region for the secondary particle-optical beam path with an exit inclination, wherein the entrance inclination is defined as the angle by which the alignment of the entrance region deviates from the normal to the optical axis of the secondary particle-optical beam path, and wherein the exit inclination is defined as the angle by which the alignment of the exit region deviates from the normal to the optical axis of the secondary particle-optical beam path; and wherein the entrance inclination of the first magnetic sector deliberately deviates from 0°; and wherein a first drift region which is substantially free from magnetic fields is provided between the first magnetic sector and the second magnetic sector; and wherein a second drift region which is substantially free from magnetic fields is provided between the second magnetic sector and the third magnetic sector; wherein the controller is configured for controlling the landing energy LE in a range LEmin < LE < LEmax; wherein the design of the second magnetic sector is configured for optimum astigmatism and dispersion correction at a low landing energy LEJow and wherein the design of the third magnetic sector is configured for optimum astigmatism and dispersion correction at a high landing energy LE_high; OR wherein the design of the second magnetic sector is configured for optimum astigmatism and dispersion correction at a high landing energy LE_high and wherein the design of the third magnetic sector is configured for optimum astigmatism and dispersion correction at a low landing energy LEJow, with LEmin < LEJow < LE_high < LEmax.

32. The multi-beam particle microscope according to claim 31 , wherein the controller is configured for switching off the second magnetic sector or the third magnetic sector when the controller sets the landing energy LE to LE_high or LEJow.

33. The multi-beam particle microscope according to claim 31 or 32, wherein the design parameters of the second magnetic sector are geometrical parameters and comprise or consist of the following: length of the first drift region, entrance inclination, exit inclination, distance between the entrance region and the exit region.

34. The multi-beam particle microscope according to claim 31 or 32,wherein the design parameters of the third magnetic sector are geometrical parameters and comprise or consist of the following: length of the second drift region, entrance inclination, exit inclination, distance between the entrance region and the exit region.

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