Particle beam system having a multipole lens array for independently focusing multiple individual particle beams, its use, and related methods - Patents.com

Abstract

A particle beam system includes a multi-beam particle source configured to generate a plurality of charged individual particle beams (3), and a multipole lens arrangement (600) having at least one first multipole lens array (601) and at least one second multipole lens array (602), wherein the first multipole lens array (601) includes a plurality of individually adjustable first multipole lenses that generate a first quadrupole field (Q1) and is positioned in a particle beam path such that the individual particle beams (3) substantially pass through the first multipole lens array (601), and the second multipole lens array (602) generates a second quadrupole field (Q2). a multipole lens array (600) including a plurality of individually adjustable second multipole lenses for generating a first beam of light, the multipole lens array (601) being positioned in a particle beam path such that an individual particle beam (3) passing through the first multipole lens array (601) also substantially passes through the second multipole lens array (602); and a controller (10) configured to control the multipole lenses of the multipole lens array such that associated groups of multipole lenses of the multipole lens array, each passed by the same individual particle beam (3), collectively exert an individually adjustable focusing effect on each individual particle beam (3) passing therethrough.

Description

[Technical field]

[0001] The present invention relates to a particle beam system operating with multiple particle beams. [Background technology]

[0002] Similar to single-beam particle microscopes, multi-beam particle microscopes can be used to analyze objects on a microscopic scale. These particle microscopes can be used to record images of the object, for example representing its surface. In this way, for example the structure of the surface can be analyzed. Whereas in single-beam particle microscopes a single particle beam of charged particles, for example electrons, positrons, muons, ions, etc., is used to analyze the object, in multi-beam particle microscopes multiple particle beams are used for this purpose. As a result of simultaneously directing multiple particle beams, also called bundles, at the object's surface, the area of ​​the object's surface that can be scanned and analyzed in the same period of time is significantly larger than with single-beam particle microscopes.

[0003] US Pat. No. 5,399,633 discloses a multi-particle beam system in the form of an electron microscope system operating with a plurality of electron beams for scanning an object to be examined with a parallel electron beam bundle. The electron beam bundle is generated by directing an electron beam generated by an electron source onto a multi-aperture plate with a plurality of apertures. Some of the electrons of the electron beam enter the multi-aperture plate and are absorbed therein, while other parts of the beam pass through the apertures of the multi-aperture plate, so that the electron beam is shaped in the beam path downstream of each aperture, the cross section of which is defined by the cross section of the aperture. Furthermore, a suitably selected electric field is applied to the beam path upstream and / or downstream of the multi-aperture plate, so that each aperture of the multi-aperture plate acts as a lens for the electrons passing through it, thus having the effect of focusing the electron beam on a plane located away from the multi-aperture plate. The plane on which the focus of the electron beam is formed is imaged by a downstream optical unit onto the surface of the object to be examined, and the individual electron beams are focused as primary beams and enter the object. There, interaction products such as backscattered electrons or secondary electrons arising from the object are generated, which are shaped to form secondary beams and directed to a detector by a further optical unit. In the detector, each secondary beam is incident on a separate detector element, and the electron intensity detected by said detector element provides information about the object at the location where the corresponding primary beam is incident on the object. To produce an electron micrograph of the object in a manner customary for scanning electron microscopes, the primary beam bundle is systematically scanned over the surface of the object.

[0004] For the described multi-particle beam systems, high resolution and high throughput are very important for a sufficiently good practical use. In this case, it is desirable to significantly reduce the various types of imaging aberrations that arise. Especially for multi-particle beam systems, it is particularly important to reduce imaging aberrations away from the optical axis of the system, so that a high resolution can be achieved for all individual particle beams.

[0005] The more individual particle beams are used or the larger the size of the field of view (FOV) of a multi-particle beam system, the more important the field curvature imaging aberration becomes. In the case of field curvature, the focal points of individual particle beams positioned in a plane are imaged into a (convex) curved area. Thus, the image is not exactly formed over the entire object plane, and this imaging aberration is larger for individual particle beams positioned further away from the optical axis of the system.

[0006] The prior art has already disclosed the following approaches to reduce field curvature.

[0007] When the individual particle beams are generated by a multi-lens array, they pass through a multi-aperture device in which the circular apertures have different diameters (see US Pat. No. 5,399,313). In particular, the diameter d of the apertures increases with increasing distance from the optical axis of the system or with increasing distance from the central aperture. The larger the diameter, the lower the refractive power of the corresponding lens, and the longer the focal length of the individual particle beams. As a result, if the aperture diameter is appropriately selected, the focal point of the individual particle beams is located in a concavely curved region, so that the (convex) field curvature subsequently generated by further imaging can be compensated. However, the drawback is that this type of correction does not work without exchanging the multi-lens array if the working point of the particle beam system is changed.

[0008] Yet another approach to correcting the field curvature is to segment a multi-lens array and apply slightly different voltages to the lenses to set the focal length of individual particle beams, however this approach has limited accuracy or provides only an approximate solution.

[0009] Furthermore, in the German patent application with application number 102018007652.1, which was unpublished on the priority date of the present patent application, the applicant and more precisely its legal predecessor propose the use of a multi-lens array with a plurality of individually adjustable and focus-controllable particle lenses for correcting the field curvature. The disclosure of the German patent application 102018007652.1 is incorporated herein by reference in its entirety. Here, the particle lenses comprise ring electrodes. Alternatively, instead of ring electrodes, it is proposed to use azimuthally subdivided electrodes, such as quadrupoles or octopoles, precisely with the same voltage applied to all electrodes.

[0010] US Patent No. 5,399,633 discloses a multi-particle beam system with improved beam focusing. For this purpose, an astigmatic particle beam is generated by a quadrupole lens in a targeted manner and its image shape is analyzed, allowing conclusions to be drawn regarding the best focus settings for the astigmatism-free beam.

[0011] No. 5,399,633 discloses a particle beam system in which the astigmatism imparted to the particle beam can be tailored to suit the application, for which purpose multipole pairs are used which are arranged one after the other, in particular rotated azimuthally by 45° relative to each other.

[0012] US Pat. No. 5,999,333 discloses an electromagnetic field generator that generates a quadrupole field, which is useful for astigmatism compensation. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] International Publication No. 2005 / 024881 Brochure [Patent Document 2] U.S. Patent No. 7,554,094 [Patent Document 3] DE 10 2018 007 652 A1 [Patent Document 4] US Patent Application Publication No. 2015 / 0287568 [Patent Document 5] US Patent Application Publication No. 2017 / 0309449 [Patent Document 6] DE 10 2014 008 083 A1 Summary of the Invention [Problem to be solved by the invention]

[0014] It is an object of the present invention to provide an improved option of independent lensing or focusing settings for multiple individual particle beams in a multi-particle system. In particular, it is an object to provide independent lensing or focusing settings for multiple individual particle beams using low voltages. Further objects are to provide more efficient independent lensing for multiple individual particle beams, as well as focusing settings with greater optical power and shorter focal length.

[0015] It is yet another object of the invention to provide improved options for field curvature correction for multi-particle beam systems. This object is achieved by the independent patent claims. Advantageous embodiments of the invention are evident from the dependent patent claims.

[0016] This patent application claims priority to German patent application No. 10 2020 107 738.6, the entire disclosure of which is incorporated by reference into this patent application. [Means for solving the problem]

[0017] For the independent focusing of several individual particle beams, for example for field curvature correction, the present invention uses for the first time a multipole arrangement with at least two multipole arrays that are individually controllable and each generate a quadrupole field of a specific orientation. In principle, these quadrupole fields can consist of electric or magnetic quadrupole fields, or an electric-magnetic combination. However, in the case of several multipoles in a small space in a multipole array, only electric multipoles can be implemented well from a technical point of view, or only electric quadrupole fields can be easily generated. Therefore, in the following, only electric multipoles, multipole arrays, or multipole fields are considered. However, in principle, all statements can also be applied to magnetic or electric-magnetic embodiments.

[0018] In principle, the same particle-optical imaging as with individual lenses can be achieved by the quadrupole field.However, the implementation according to the invention has the advantage that it can be operated at significantly lower voltages, for example for the purpose of focusing several individual particle beams independently for the purpose of correcting field curvature.The combination of the quadrupole field with further multipole fields for further correction within the scope of individual beam guidance or for further correction of imaging aberrations is also possible in a simple manner.

[0019] Specifically, according to a first aspect, the present invention provides a particle beam system comprising: a multi-beam particle source configured to generate a plurality of charged individual particle beams; a multipole lens array having at least one first multipole lens array and at least one second multipole lens array; the first multipole lens array includes a plurality of individually adjustable first multipole lenses that generate a first quadrupole field, and is disposed in the particle beam path such that the individual particle beams substantially pass through the first multipole lens array; and the second multipole lens array includes a plurality of individually adjustable second multipole lenses that generate a second quadrupole field and is positioned in the particle beam path such that individual particle beams passing through the first multipole lens array also substantially pass through the second multipole lens array; A multipole lens array; a controller configured to control the multipole lenses of the multipole lens array such that associated groups of multipole lenses of the multipole lens array through which the same individual particle beam passes collectively exert an individually adjustable focusing effect on each individual particle beam passing therethrough; The present invention relates to a particle beam system comprising:

[0020] The charged particles can be, for example, electrons, positrons, muons or ions, or other charged particles. Preferably, the charged particles are electrons, for example generated using a thermal field emission source (TFE). However, other particle sources can also be used.

[0021] According to the invention, at least one particle source is provided, but also multiple particle sources can be provided. According to a preferred embodiment of the invention, the multiple particle source may in this case comprise at least one particle source configured to generate a charged particle beam and a multi-aperture plate having multiple apertures, more particularly circular apertures, arranged in the beam path of the particles such that at least a part of the particles pass through the apertures of the multi-aperture plate in the form of multiple individual particle beams.

[0022] The central idea of ​​the invention is realized by the provision of a specific multipole lens array and by its specific control. Multipole is understood to mean a dipole, a quadrupole, an octapole or a higher order multipole. Here, the multipole lens array comprises at least one first multipole lens array and at least one second multipole lens array. However, three, four, five, six or more multipole lens arrays can also be provided. In this case, the term array indicates that the multipole lens arrays are arranged successively, preferably directly successively, in the beam paths of the individual particle beams. However, other optical elements or components may be located between the various multipole lens arrays of the multipole lens array. What is important is that the desired focusing effect can be set by the controller using an array and not necessarily a single multipole lens array.

[0023] In principle, the individual multipole lenses of the multipole lens array can have the same structure within the same array. It is also possible that the multipole lens arrangement comprises several multipole lens arrays with the same structure. In this case, the apertures of the multipole lens array are preferably arranged regularly in the array. By way of example, the multipole lenses of the array can be arranged in a square or rectangular shape. However, it is preferred that the arrangement of the apertures of the array or the multipole lenses is hexagonal. That is, the individual particle beams are arranged according to a hexagonal structure (according to the general formula 3n(n-1)+1, n being a natural number) with, for example, 61 or 91 individual particle beams, which arrangement is also provided geometrically in the multipole lens array.

[0024] What is important here is that a first multipole lens array provides a number of individually adjustable first multipole lenses that generate first quadrupole fields. These quadrupole fields can be generated using quadrupole lenses. However, the generating multipole lenses can also be, for example, appropriately controlled octopoles. In this respect, the important aspect is not the structural configuration of the lenses, but the generation of the quadrupole fields by means of the lenses. It is also possible to superimpose one or more other fields, in particular multipole fields, on each of the quadrupole fields.

[0025] The first and second multipole lens arrays may be arranged directly in succession in the particle beam system, however, other multipole lens arrays or other optical components may also be arranged between the first and second multipole lens arrays.

[0026] It is possible that each of the first and second multipole lens arrays has the same number of multipole lenses. However, the number may be different. In a preferred case, an individual particle beam passes through all multipole lenses of the first multipole lens array and all multipole lenses of the second multipole lens array. Here, multipole lenses of multipole lens arrangements belonging to different multipole lens arrays can be combined into groups. Here, groups are formed by the multipole lenses of different multipole lens arrays through which the same individual particle beam passes respectively. Thus, the number of groups is in this case the same as the number of multipole lenses of each multipole lens array.

[0027] According to the invention, the controller is then configured to control the multipole lenses of the multipole lens array in such a way that the associated multipole lens groups of the multipole lens array, through which the same individual particle beams pass respectively, exert an individually adjustable focusing effect as a whole on each individual particle beam passing therethrough. Thus, with the multipole lens groups, one individual particle beam is individually influenced and focused respectively. The focusing of the individual particle beams is possible by passing the individual particle beams through two differently oriented quadrupole fields. It is known that in principle a similar focusing effect can be obtained by using two quadrupole fields as well as a single lens or a circular lens. In the case of focusing of axially parallel particle beams, the deviation from the optical axis Z is in principle reduced. Here, the influence of the quadrupole field on the particle or particle beam depends on the position from the optical axis along which the particle or particle beam travels or extends. Thus, if a single quadrupole field is used whose center is located on or extends along the optical axis, focusing may only be performed in a first direction (e.g., only correcting for deviations from the axis in the x direction or only correcting for deviations from the axis in the y direction). However, if a second quadrupole field is then also positioned on the optical axis of the system but subsequent to the first quadrupole field in a different orientation, it may also perform focusing in a second direction orthogonal to the first direction.

[0028] According to a preferred embodiment of the invention, the quadrupoles of the first quadrupole field and / or the quadrupoles of the second quadrupole field have orientations rotated by substantially 90° relative to one another and have substantially the same amplitude, where in the case of a quadrupole the rotation of 90° corresponds to a reversal of the voltage configuration on the electrodes of the quadrupole.

[0029] According to one variant of the invention, the orientation between the two quadrupoles is rotated by exactly 90°, i.e. in this case the quadrupoles are oriented as accurately as possible. However, it is possible that the orientation rotation is not exactly 90°, if there is a clear advantage in a deviation from 90°. By way of example, this is the case when there is a strong magnetic lens effect, for example a condenser lens system, in front of the multipole lens arrangement. The magnetic field of this magnetic lens then acts on the multipole lens arrangement, and the individual particle beams are subjected to a Larmor rotation in the magnetic field. The resulting errors can be corrected by rotating the orientation of the quadrupoles of the first and second quadrupole fields relative to each other.

[0030] The advantage of using sequentially arranged quadrupole fields compared to individual or circular lenses is that the voltages at the electrodes of the multipole lenses required for the focusing effect can be chosen to be significantly lower than when individual or circular lenses are used. At an exemplary beam energy of 10 keV, the typical absolute value of the voltage required for focusing is more than 1000V, for example -1250V. In contrast, when quadrupoles are used, the focusing voltage at the same beam energy is only about 50V. This is an overall advantage within the range of the power supplies to the multipole lenses.

[0031] According to yet another embodiment of the invention, the first and / or second multipole lens array comprises a quadrupole lens array. Thus, four electrostatic electrodes are provided per multipole lens, which preferably have the same configuration. Since preferably from a construction point of view, each of the two electrodes in a quadrupole should have exactly the same voltage, it is possible, for example, to supply the electrodes with the same polarity or voltage using the same voltage source. Thus, it is possible to mutually couple the opposing electrodes with respect to the power supply in order to generate a quadrupole field as pure as possible, with a minimum of parasitic dipole fields. Supplying the opposing electrodes with separate power supplies may result in such parasitic dipole fields with varying or noisy amplitudes due to fluctuations or noise of the individual power supplies. This concept of coupling electrodes of the same voltage applies equally to higher order multipoles.

[0032] According to yet another embodiment of the present invention, the multipole lens array includes a third multipole lens array, which includes a plurality of individually controllable third multipole lenses generating a third quadrupole field and is arranged in the particle beam path between the first and second multipole lens arrays such that an individual particle beam passing through the first multipole lens array also passes substantially through the third multipole lens array, and the controller is further configured to control the multipole lenses of the multipole lens arrays, through which the same individual particle beam passes respectively, in total to have an effect on each individual particle beam passing therethrough such that the imaging of the individual particle beam at the focal plane is substantially undistorted. Thus, the imaging quality can be further improved using this variant embodiment. If only two quadrupole fields are used, the desired focusing is in principle achieved only in a distorted way (a circular input beam is turned into an elliptical output beam), whereas if a total of three quadrupole fields are used, a distortion-free focusing can be achieved (a circular input beam is turned into a circular output beam). When transferring an expanded image field, the magnification in, for example, the x and y directions will be the same, but the observations on the image field are theoretical, since only the particle source is imaged.

[0033] Yet another criterion for distinction is the behavior of the multipole lenses when focusing without changing the excitation of the multipole. As an example, a parallel incoming particle beam is changed into a slightly divergent incoming particle beam, for example by reducing the refractive power of a condenser lens system located upstream of the multipole lens in the particle beam path. This leads to a displacement of the focal plane away from the quadrupole in both embodiments, i.e. in the case of two or three multilens arrays or multipole lens arrangements with two or three quadrupole fields. However, in the embodiment with two quadrupole fields, astigmatism occurs at the new focal plane, while in the embodiment with three quadrupole fields only distortion occurs.

[0034] With regard to the third multipole lens array and its configuration, what has already been described above with regard to the first and second multipole lens arrays applies.

[0035] According to the invention, when the first, second and third multipole lens arrays are used for focusing individual particle beams with correspondingly generated quadrupole fields, according to a preferred embodiment of the invention, the quadrupoles of the first and second multipole lens arrays have substantially the same orientation and substantially the same amplitude, while the quadrupoles of the third multipole lens array have an orientation rotated by approximately 90° with respect to the first and second quadrupoles, the amplitude of the third quadrupole being greater than the amplitude of each of the first and second quadrupoles, more particularly approximately twice the amplitude of each of the first and second quadrupoles. Alternatively, the increase in the effect of the third quadrupole can be achieved by doubling its length in the axial direction (or any combination thereof), while keeping the amplitude unchanged. Thus, the control of the power supplies of the multipole lens arrays is totally different in the case of three multipole lens arrays than in the case of only two multipole lens arrays. However, it still applies here that the effect on the individual particle beams can be obtained by suitable power supplies or by control of the same group of multipole lenses, i.e. the multipole lenses through which the same individual particle beams pass. Since it is advantageous from a manufacturing point of view, it is preferred that all multipoles of a multipole array have the same length. This applies to this and all other embodiments of the invention. Here, the length of a multipole (hereinafter also called the thickness of the multipole) is understood to mean its dimension in the direction of the multipole axis Z.

[0036] According to yet another embodiment of the invention, the multipole lens array comprises a fourth multipole lens array. In principle, what has already been explained with respect to the first, second and third multipole lens arrays in terms of construction also applies to this fourth multipole lens array. The fourth multipole lens array likewise comprises a plurality of individually adjustable fourth multipole lenses for generating a fourth quadrupole field. Here, the fourth multipole lens array is arranged in the particle beam path between the first and second multipole lens arrays such that an individual particle beam passing through the first multipole lens array also passes substantially through the fourth multipole lens array. Furthermore, the controller is configured to control the multipole lenses of the multipole lens array, i.e. the multipole lens array comprising the first, second, third and fourth multipole lens arrays in this case, such that the multipole lenses of the multipole lens array collectively exert, for each individual particle beam passing through a multipole lens of the multipole lens array, an effect of a substantially astigmatism-free imaging of the individual particle beam. Thus, the desired effect or desired imaging is still achieved for each individual particle beam by the associated multipole lens group through which the same individual particle beam passes. Thus, the imaging quality can be further improved by using a fourth multipole lens array or the fourth quadrupole field it generates. As in the embodiment with three quadrupoles, the imaging is aberration-free and distortion-free. However, in addition, during focusing with constant excitation of the quadrupole, the distortion is eliminated at the displaced focal plane. Thus, when four appropriately switched quadrupole fields are used, the imaging achieved in the axial distance becomes indistinguishable from the imaging of a linear approximation by a circular lens.

[0037] If a multipole lens arrangement with four multipole lens arrays is used for focusing, preferably the quadrupoles of the first and second multipole lens arrays have orientations rotated substantially by 90° relative to each other and have substantially the same amplitude, and the quadrupole orientation arrangement is alternating, the amplitudes of the third and fourth quadrupoles being greater than the amplitudes of the first and second quadrupoles, respectively, more particularly about three times the amplitudes of the first and second quadrupoles, respectively. For a beam energy of 10 keV, typical values ​​are ±22V for the outer quadrupole and ±66V for the inner quadrupole. Alternatively, it is possible to increase the amplitude of the outer quadrupole and shorten its axial length, for example, so that as a result the same power supply or at least the same structure of power supply can be used. Here too, the overall required focusing voltage is therefore significantly lower than that required for a single lens. Further details regarding the required voltages are explained in more detail below.

[0038] According to yet another embodiment of the present invention, the at least one multipole lens array comprises an octopole lens array, where the multipole lens array can be the first, second, third and / or fourth multipole lens array as described above or even another multipole lens array. It is important to note that the octopole lens array can also be used to generate a quadrupole field if the electrodes of the octopole lens are appropriately controlled. Furthermore, if there are eight electrodes on the octopole lens, two superimposed quadrupoles or a quadrupole field can also be generated with appropriate control. Thus, the orientation of the quadrupole field or the overall resulting quadrupole field can be changed using the octopole lens.

[0039] According to a preferred embodiment of the invention, the controller is configured to control the octopole lenses such that the electric field generated by the octopole electrodes results in a superposition of two quadrupole fields, which essentially results in a quadrupole field slightly rotated about the main axis of the individual particle beam with respect to one of the quadrupole fields, more particularly the stronger of the quadrupole fields. Again, in order to generate a particularly stable field, the electrodes of the octopole which should be energized with the same voltage can be supplied by a common voltage source.

[0040] According to a preferred embodiment of the invention, the controller is configured to control the multipole lenses such that the electric field generated by the multipole electrodes is a superposition of a quadrupole field and a dipole field, where the multipole lens can be, for example, an octapole lens. As already described, particles entering parallel to the quadrupole field are deflected towards or away from the axis. Particle beams centered on particle trajectories that enter the quadrupole field offset with respect to the geometric axis of the multipole are also deflected. With the correct selection of amplitudes and orientations, the superimposed dipole field can compensate for this deflection, and this superposition with respect to the quadrupole field results in a quadrupole field displaced from the geometric axis of a single multipole lens. Thus, the particle optical axis of the quadrupole field and the geometric axis of the multipole lens do not coincide.

[0041] If an additional dipole field is generated by only one quadrupole field, this results in a unidirectional deflection when the particle passes through the center of the multipole lens. In contrast, if a dipole field is generated in addition to the quadrupole field by two multipole lens arrays, a two-point deflection in two directions and therefore a parallel offset of the entire individual particle beam can be achieved upon passing through the multilens if the dipole fields are oriented anti-parallel to each other (the exact orientation depends on the presence of an external magnetic field, e.g. a condenser lens).

[0042] The above-mentioned superposition of quadrupole field and dipole field is successful both in the case of quadrupole lens and in the case of octopole lens or multipole lens with more poles.However, here, octopole lens is more advantageous than quadrupole lens, because the quadrupole field required according to the method can be electrically displaced and rotated.This also applies to multipole lens with more poles, but the technical cost is higher.

[0043] According to yet another embodiment of the invention, all electrodes of the octopole lenses of the octopole lens array have the same size and shape, which allows a particularly simple production of the octopole lens array.

[0044] Alternatively, however, at least some of the electrodes of the octopole lenses of the octopole lens array can have different sizes and / or shapes. The shape and size of the electrodes influence the electric field they generate. For example, if the electrodes generating the quadrupole field are large, the quadrupole field generated here will be dominant. In contrast, if the remaining electrodes arranged between them are small, they will generate a weaker electric field as a result of the shielding effect. Furthermore, for example, if the electrodes deviate from a circular shape, other electric field shapes can be generated as desired.

[0045] According to yet another embodiment of the present invention, at least one multipole lens array comprises a dipole lens array, where these are true dipole lenses, and not just dipole fields generated by higher order multipole lenses. This is in principle very much within the scope of the present patent application. When referring to a specific multipole lens, this multipole lens also has a corresponding number of electrodes. On the other hand, when referring to a field, this field can be generated by different types of multipole lenses depending on how the electrodes of the multipole lens are controlled.

[0046] According to yet another preferred embodiment of the invention, the multipole lens arrangement comprises a multipole lens array generating the following field arrangement: a quadrupole field - at least two dipole fields of different orientation with respect to each other, in particular two substantially anti-parallel dipole fields - quadrupole fields. With such an arrangement, the individual particle beams can be offset parallel to the optical axis between the paths of the two quadrupole fields.

[0047] According to an alternative embodiment of the present invention, the multipole lens arrangement includes a multipole lens array that produces the following field arrangement: A dipole field - a quadrupole field - yet another quadrupole field - yet another dipole field having a different orientation to the first dipole field, in particular a substantially anti-parallel orientation.

[0048] According to a preferred embodiment of the invention, the multi-beam particle source comprises at least one particle source configured to generate a charged particle beam and a multi-aperture plate having a plurality of apertures and arranged in the beam path of the particles such that at least a portion of the particles pass through the apertures in the form of a plurality of individual particle beams. The individual particle beams are thus first generated by the multi-aperture plate. Generally, the apertures of the multi-aperture plate are circular in order to correspond to the desired optimal beam diameter. However, according to another embodiment of the invention, it is also possible that at least some of the apertures of the multi-aperture plate, preferably all apertures except the aperture centrally located on the optical axis, have an elliptical cross section. If the size and orientation of the elliptical cross section of the apertures are appropriately selected, a subsequent asymmetry can be generated in the form of a distorted particle beam. If the individual particle beams pass through a central aperture of the multi-aperture plate, this central aperture expediently has a circular embodiment rather than an elliptical cross section. Overall, the ellipticity of the apertures of the multi-aperture plate increases the further away from the center of the multi-aperture plate or the central circular aperture of the multi-aperture plate. Considering the relationship between the centre of the ellipse and the centre of the multi-aperture plate, the major axis of the ellipse passing through the centre is perpendicular or parallel to the rays passing through the centre of the ellipse in a radial direction from the centre of the multi-aperture plate, or in other words, the minor axis of the ellipse is oriented radially from the centre of the multi-aperture plate or perpendicular to this direction.

[0049] Typical opening diameters of the apertures in the multi-aperture plate are d≦150 μm, in particular d≦50 μm and / or d≦10 μm.

[0050] According to yet another embodiment of the present invention, the particle beam system further comprises a circular lens array arranged in the particle beam path to substantially pass the individual particle beams passing through the multipole lens array, the focusing particle lenses of the circular lens array being not multipole lenses. Instead, they can be individual lenses, for example. Said circular lens array is already used in many particle beam systems, in particular in multibeam particle microscopes. When this circular lens array is combined with the multipole lens array according to the present invention, the field curvature of the existing system can be corrected. Moreover, the focusing effect caused by the multipole lens array in this case is relatively weak, since this arrangement only serves to correct the focal position and does not serve to focus the individual particle beams by itself. However, this would be possible as well.

[0051] According to yet another preferred embodiment of the invention, the circular lens array is arranged downstream of the multipole lens array in the particle beam path, and the system further comprises a condenser lens system arranged upstream of the multipole lens array in the particle beam path. Overall, this results in a condenser lens system-multipole lens array-circular lens array arrangement. The condenser lens system typically comprises one or more magnetic condenser lenses, the magnetic field of which still acts on the charged particles of the individual particle beam in the region of the multipole lens array. However, as already mentioned above, a suitably oriented quadrupole field of the multipole lens array allows the Larmor rotation that is also present as a result to be taken into account.

[0052] After the generation of the individual particle beams, i.e. after passing through a multi-aperture plate, which in this case can also be combined with a multipole lens array or a multilens array, the already mentioned imaging aberrations, in particular the unwanted field curvature, occur over the further course of the particle-optical beam path. According to the invention, the controller can then affect the individual particle beams in such a way that the focal point of the individual particle beams is located in a concave area. This concave arch can be selected to accurately compensate for the convex field curvature of all subsequent optical components of the imaging system. Thus, it is possible to achieve a precise and deep focal depth of the individual particle beams on the sample located in the object plane.

[0053] The above methods of using an ensemble of quadrupole fields to achieve focusing similar to that of a circular lens have in common: astigmatism occurs when the quadrupole fields deviate from their expected strength. This can be exploited to correct a further image aberration of the imaging system, the astigmatism of the tilted beam. In methods where the focal settings of the individual particle beams are set and thus the defocus (field curvature) which varies across the image field is corrected, it is also possible to correct the astigmatism which varies across the image field (tilted beam astigmatism) by adapting the strength and orientation of the individual quadrupole fields.

[0054] According to yet another embodiment of the invention, there is a combined power supply for the electrodes of the multipole lenses, which are supplied with the same voltage. As a result of this combined power supply, the dipole component of the electric field generated by the multipole lenses is more stable than in the case of separate power supplies for the electrodes. Furthermore, the arrangement of the wires for supplying the electrodes can be easier, since fewer wires need to be accommodated in a small space. Furthermore, the electrodes of the multipole lenses belonging to different multipole lens arrays, but preferably belonging to the same multipole lens group, are also jointly supplied by the same voltage source. This measure also makes it possible, firstly, to simplify the manufacture of the multipole lens arrays and, secondly, to generate more precise field shapes and particle beams with deflection angles that have only small variations or noise.

[0055] According to a preferred embodiment of the present invention, for beam energies of about 10 keV, the voltages applied to the electrodes of the multipole lens array are each less than 100 V. Thus, the applied voltages are very low compared to those applied in the case of individual lenses.

[0056] According to a second aspect of the invention, the invention relates to the use of a particle beam system as described above for field curvature correction. By means of a well-controlled multipole lens arrangement, it can be achieved here that the position of the focal point of an individual particle beam lies on a concave surface, as already explained in more detail above, and the curvature of this surface accurately compensates for the field curvature (convex form) occurring further downstream in the beam path. However, the particle beam system according to the invention can also be used for other purposes, for example within the scope of individual beam current adjustment.

[0057] According to a third aspect, the invention relates to the use of a particle beam system for correcting tilt astigmatism.

[0058] According to a fourth aspect of the invention, the invention relates to a multi-beam particle microscope comprising a particle beam system as described above. Here too there may be a field curvature correction of the multi-beam particle microscope with the particle beam system according to the invention.

[0059] According to a fifth aspect of the invention, the invention relates to a method for independently focusing a plurality of individual particle beams, e.g. for field curvature correction of a particle beam system as described above, comprising a step of individually setting focal lengths of the plurality of individual particle beams, in particular of all individual particle beams, by a multipole lens arrangement, wherein the adjustment is also performed such that the foci of the individual particle beams, in particular of all individual particle beams, are located on a concave surface having a curvature that compensates for the subsequent field curvature in the system, wherein the focal lengths can be set by control of the particle beam system.

[0060] The invention will be better understood with reference to the accompanying drawings. [Brief description of the drawings]

[0061] [Figure 1] 1 shows a schematic diagram of a multi-beam particle microscope. [Diagram 2] 1 illustrates diagrammatically the (weak) focusing of a charged particle beam by a circular lens or an Einzel lens. [Diagram 3] 1 illustrates a schematic of deflection of a charged particle beam by a quadrupole field. [Figure 4] 1 shows a schematic of the deflection of a charged particle beam by two quadrupole fields. [Diagram 5] FIG. 5 shows a schematic diagram of the detailed beam paths pertaining to the diagram of FIG. [Figure 6] 1 shows a schematic of the deflection of a charged particle beam by three quadrupole fields. [Figure 7] FIG. 7 shows a schematic diagram of the detailed beam paths pertaining to the diagram of FIG. 6. [Figure 8] 1 shows a schematic of the deflection of a charged particle beam by four quadrupole fields. [Figure 9] FIG. 9 shows a schematic diagram of the detailed beam paths pertaining to the diagram of FIG. [Figure 10] 1 shows a schematic diagram of a multipole lens array structure. [Figure 11] 1 illustrates a schematic of a multipole lens array arrangement of a multibeam particle microscope for field curvature correction. [Figure 12] 1 shows a schematic of a combination of a multi-aperture plate with an elliptical aperture and a multipole lens array. [Figure 13] 13 shows a schematic plan view of a multi-aperture plate having elliptical openings as shown in FIG. 12. [Figure 14] 1 shows a schematic representation of a portion of a multipole lens array having an octapole electrode arrangement. [Figure 15] 13A-13C show schematic excerpts of a multipole lens array with an alternative octopole electrode arrangement; [Figure 16] 1 shows a schematic of an excerpt of a multipole lens arrangement with a quadrupole and a dipole field. [Figure 17] 1 illustrates a schematic of a power supply for a multipole lens array. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0062] Fig. 1 is a schematic diagram of a particle beam system 1 in the form of a multi-beam particle microscope 1 using multiple particle beams. The particle beam system 1 generates multiple particle beams that are incident on an object to be examined in order to generate interaction products, e.g. secondary electrons, which arise from the object and are subsequently detected. The particle beam system 1 is of the Scanning Electron Microscope (SEM) type and uses multiple primary particle beams 3 that are incident on the surface of the object 7 at multiple positions 5 to generate multiple mutually spatially separated electron beam points or spots thereon. The object 7 to be examined can be of any desired type, e.g. a semiconductor wafer or a biological sample, and can include an arrangement of miniaturized elements, finely detailed extended structures, etc. The surface of the object 7 is arranged in a first plane 101 (object plane) of an objective lens 102 of the objective lens system 100.

[0063] The enlarged excerpt I1 of Fig. 1 shows a plan view of an object plane 101 with a square field 103 of 5 incidence positions formed in a first plane 101. In Fig. 1 the number of incidence positions is 25, forming a 5x5 field 103. The number of incidence positions, 25, is a number chosen for reasons of simplicity of illustration. In principle the number of beams, and therefore the number of incidence positions, can be chosen to be higher, for example 7x7 or 10x10, or significantly higher, for example 20x30, 100x100, etc.

[0064] In the illustrated embodiment, the field of view 103 of the entrance locations 5 is a substantially square field of view with a constant pitch P1 between adjacent entrance locations. Exemplary values ​​of the pitch P1 are 1 micrometer, 10 micrometers, and 40 micrometers. However, it is also possible for the field of view 103 to have other symmetries, such as hexagonal symmetry.

[0065] The diameter of the shaped beam spot at the first plane 101 can be small. Exemplary values ​​of said diameter are 1 nm, 5 nm, 10 nm, 100 nm and 200 nm. The focusing of the particle beam 3 to shape the beam spot 5 is performed by the objective lens system 100.

[0066] Primary particles incident on the object generate interaction products, e.g. secondary electrons, backscattered electrons or primary particles that have undergone a reversal of motion for other reasons, which originate from the surface of the object 7 or from the first plane 101. The interaction products originating from the surface of the object 7 are shaped by the objective lens 102 to form a secondary particle beam 9. The particle beam system 1 provides a particle beam path 11 which directs a number of secondary particle beams 9 to a detector system 200. The detector system 200 includes a particle optical unit having a projection lens 205 which directs the secondary particle beams 9 to a particle multi-detector 209.

[0067] Extract I2 of Fig. 1 shows a plan view of a plane 211 in which the individual detection areas of a particle multi-detector 209 are located, on which the secondary particle beam 9 is incident at positions 213. The incident positions 213 are placed in the field of view 217 with a regular pitch P2 relative to one another. Exemplary values ​​of the pitch P2 are 10 micrometers, 100 micrometers and 200 micrometers.

[0068] The primary particle beam 3 is generated in a beam generating device 300 comprising at least one particle source 301 (e.g. an electron source), at least one collimation lens 303, a multi-aperture device 305, and a field lens 307. The particle source 301 generates a diverging particle beam 309, which is collimated or at least substantially collimated by the collimation lens 303 to shape a beam 311 that illuminates the multi-aperture device 305.

[0069] Extract I3 of Fig. 1 shows a plan view of the aperture device 305. The aperture device 305 comprises a multi-aperture plate 313 in which a number of apertures or apertures 315 are formed. The centres 317 of the apertures 315 are arranged in a field of view 319 which is imaged in the field of view 103 formed by the beam spot 5 in the object plane 101. Exemplary values ​​of the pitch P3 between the centres 317 of the apertures 315 can be 5 micrometers, 100 micrometers and 200 micrometers. The diameter D of the apertures 315 is smaller than the pitch P3 between the centres of the apertures. Exemplary values ​​of the diameter D are 0.2 x P3, 0.4 x P3 and 0.8 x P3.

[0070] Particles of the illumination particle beam 311 pass through the aperture 315 to form the particle beam 3. Particles of the illumination beam 311 that impinge on the plate 313 are absorbed by the plate 313 and do not contribute to the formation of the particle beam 3.

[0071] By means of the applied electrostatic field, the multi-aperture device 305 focuses each of the particle beams 3 such that a beam focus 323 is formed in a plane 325. Alternatively, the beam focus 323 may be virtual. The diameter of the beam focus 323 may be, for example, 10 nanometers, 100 nanometers and 1 micrometer. The multi-aperture device 305 may then be supplemented with a multipole array according to the invention, as will be explained in more detail below.

[0072] The field lens 307 and the objective lens 102 provide a first imaging particle-optical unit for imaging a plane 325, in which the beam focus 323 is formed, onto a first plane 101, so that a field 103 of the incidence positions 5 or beam spots arise therein. If the surface of an object 7 is arranged in the first plane, then the beam spots are correspondingly formed on the object surface as well.

[0073] The objective lens 102 and the projection lens arrangement 205 provide a second imaging particle-optical unit for imaging the first plane 101 onto the detection plane 211. Thus, the objective lens 102 is a lens that is part of both the first and second particle-optical units, but the field lens 307 belongs only to the first particle-optical unit and the projection lens 205 belongs only to the second particle-optical unit.

[0074] A beam switch 400 is disposed in the beam path of the first particle-optical unit between the aperture device 305 and the objective system 100. The beam switch 400 is also part of a second optical unit in the beam path between the objective system 100 and the detector system 200.

[0075] Further information regarding such multi-beam particle beam systems and the components used therein, such as particle sources, aperture plates and lenses, can be obtained from International Patent Applications WO 2007 / 028595, WO 2007 / 028596, WO 2011 / 124352 and WO 2007 / 060017, as well as German Patent Applications No. 10 2013 016 113 and No. 10 2013 014 976, the disclosures of which are incorporated herein by reference in their entirety.

[0076] The multi-particle beam system further comprises a computer system 10 configured to control the individual particle-optical components of the multi-particle beam system and configured to evaluate and analyze the signals obtained by the multi-detector 209. In this case, the control may also include the control of the multipole lens array according to the invention. In this case, the computer system 10 may consist of several individual computers or components.

[0077] FIG. 2 shows a schematic representation of the (weak) focusing of a charged particle beam by a circular or Einzel lens. This should help to better understand the invention as described below. FIG. 2 shows an Einzel lens consisting of three plates 501, 502 and 503, each plate having a circular cross section and an aperture with an exemplary diameter of 0.3 mm in this case. In this case, the plates have an exemplary thickness of 0.5 mm each and are spaced about 1 mm apart (measured center to center). In this case, the optical axis Z of the particle beam system runs through the center of the apertures of the plates 501, 502 and 503. Here, the plates 501 and 503 are at the same potential. In relation to this potential, the plate 502 is at a negative potential of −1250 V. Furthermore, a beam energy of 10 keV is taken as the reference. FIG. 2 shows a charged particle beam 3, for example an electron beam, entering the device parallel to the axis. The beam is focused in the direction of the optical axis Z when passing through the Einzel lens consisting of plates 501, 502 and 503. The intersection with the optical axis is not shown in FIG. 2, but with the selected parameters of this example it is located at a distance of about 100 mm from the central electrode 502. In principle, halving the focusing voltage V results in a four times longer focal length. In terms of absolute values, a focusing voltage of -1250 V is of the order of about 1 kV. If such circular lenses are arranged in an array with a pitch of 1 mm or less, it is technically difficult to lead individual electric wires with sufficiently high insulation from many central electrodes to the power supply in this narrow space. However, the focal length of the individual particle beams 3 can in principle be set individually by changing the focusing voltage.

[0078] In contrast, FIG. 3 shows diagrammatically the deflection of a charged particle beam 3 through a quadrupole field Q1, which is a component of the first multipole lens array 601. In this case, the optical axis Z passes through the center of the quadrupole field Q1. Here, the charged particle beam 3 is shown extending through the quadrupole field Q1 parallel to the axis. The quadrupole lens generating the quadrupole field likewise has an aperture or circular bore with a diameter of 0.3 mm and a thickness (extending in the Z direction) of about 0.5 mm, to facilitate comparison with the individual lenses of FIG. 2. The charged particle beam, in this example an electron beam, passing through the quadrupole field Q1 parallel to the optical axis is again focused at a distance of about 100 mm from the quadrupole field Q1. This focusing is performed with the quadrupole field Q1, but only in one direction (split into directions x and y in the figure, both projected in the same axial direction in the plane of the figure). Thus, after passing through the quadrupole field Q1, the charged particle beam 3a defocused or virtually focused in the y direction is shown diagrammatically in FIG. 3 separately from the charged particle beam 3b focused in the x direction. However, again taking a beam energy of 10 keV as the reference, the focusing voltage required for one-way focusing is now only ±4.5 V. If the focusing voltage is halved, the focal length is only twice as long.

[0079] FIG. 4 shows a schematic of the deflection of a charged particle beam 3 by two quadrupole fields Q1 and Q2. The quadrupole fields Q1 and Q2 are generated using a first multipole lens array 601 and a second multipole lens array 602, respectively, only a part of which is shown in FIG. 4. Only the particle beam profile of a single individual particle beam 3 is shown. In this example, the two quadrupole fields Q1 and Q2 have the same structure, each with an aperture of 0.3 mm diameter, are spaced 1 mm apart from each other (measured center to center), and the multipole lenses generating the quadrupole fields Q1 and Q2 each have plates with a plate thickness of 0.5 mm. In the example shown, the quadrupoles Q1 of the first quadrupole field and the quadrupoles Q2 of the second quadrupole field have orientations rotated substantially by 90° relative to each other and have substantially the same amplitude. In the example shown, focusing of a 10 keV particle beam is obtained at a distance of 100 mm from the center of the first quadrupole Q1 using a focusing voltage of ±50 V. Now, if the focusing voltage is halved, the focal length becomes four times longer. Thus, a charged particle beam passing through the quadrupole array parallel to the axis will be focused in both the x and y directions by this arrangement.

[0080] FIG. 5 shows diagrammatically the detailed beam path belonging to the diagram of FIG. 4. The quadrupoles Q1 and Q2 are positioned along the optical axis Z. Here, a beam is shown with components 3a and 3b entering substantially parallel to the optical axis, said components being intended to show a deviation in the x and y directions. On passing through the quadrupole field Q1, the particle beam 3a is first defocused and a component of the particle beam 3b is focused. On passing through the quadrupole field Q2, the conditions are reversed, the particle beam 3a is now focused and the particle beam 3b is defocused. However, due to the large distance of the particle beam 3a from the axis, said particle beam is now focused more strongly than when it was previously defocused, and the corresponding or opposite applies to the particle beam 3b, so that both particle beams 3a and 3b are focused as a whole and meet at a focal point f on the optical axis Z. The particle beams 3c, 3d entering obliquely to the optical axis are likewise deflected in different ways on passing through the quadrupole fields Q1 and Q2. In a plane perpendicular to the optical axis Z through the focal point f, the particle beams have different distances from the axis, and for this reason imaging with the two quadrupole fields Q1 and Q2 results in an overall distorted image. Thus, imaging with the two quadrupole fields Q1 and Q2 allows focusing of beams 3a, 3b parallel to the axis, which extend to the focal point f at different angles due to distortion. However, it is possible to set the focal length for each individual particle beam 3 individually, as long as this imaging aberration is tolerated. If a circular particle beam is interrupted by a circular aperture of the multi-aperture plate 313 upstream of the quadrupole fields Q1 and Q2, an elliptical diverging particle beam is obtained downstream of the focal point f. On the other hand, if an elliptical particle beam is interrupted by an elliptical aperture of the multi-aperture plate 313 upstream of the quadrupole fields Q1 and Q2, a circular diverging particle beam is obtained downstream of the focal point f, if the eccentricity of the elliptical aperture is appropriately selected. Such a circular diverging particle beam is more suitable to be focused by the downstream objective lens system 100 to a very small spot 5 on the sample 7 than the elliptical diverging particle beam described above.

[0081] FIG. 6 shows a schematic representation of the deflection of a charged particle beam 3 by three quadrupole fields Q1, Q3, and Q2 generated by a first multipole lens array 601, a second multipole lens array 602, and a third multipole lens array 603, where the third multipole lens array 603 is arranged between the first multipole lens array 601 and the second multipole lens array 602. The multipole lens arrays 601, 602, and 603 are again shown only in an excerpt for a single individual particle beam 3. The exemplary illustration is again chosen for ease of comparison with the variant embodiment of FIGS. 3 to 5. Again, the three quadrupole fields Q1, Q2, and Q3 each have an aperture of 0.3 mm diameter, the plate thickness is also 0.5 mm, and the respective distances between the individual plates or multipole lens arrays 601, 603, and 602 are each 1 mm, measured center to center. To achieve focusing again at a distance of 100 mm from the centre of the central quadrupole Q3, for a beam energy of 10 keV, a focusing voltage of ±74 V is applied to the inner quadrupole Q3 and a voltage of ±37 V is applied to the two outer quadrupoles Q1 and Q2. Thus, in terms of absolute values, the inner quadrupoles are supplied with approximately twice as much voltage as the outer quadrupoles. Here, the polarity of the quadrupoles Q1, Q3 and Q2 alternates.

[0082] FIG. 7 shows a schematic representation of the detailed beam path belonging to the diagram of FIG. 6. Here, an improvement in the imaging quality is evident when using the described three quadrupole fields compared to the diagram of FIG. 5 and the case of only two quadrupole field arrangements. The particle beams 3a, 3b parallel to the axis are again focused with respect to the x- and y-direction displacements when passing through the quadrupole arrangement with the quadrupole fields Q1, Q3 and Q2 and intersect the optical axis Z at the focal point f. The particle beams 3c, 3d incident obliquely to the optical axis are similarly deflected when passing through the quadrupole arrangement Q1-Q3-Q2 and intersect at the intermediate image B, so that the image thus obtained is distortion-free. Thus, with a multipole lens arrangement with three quadrupole fields, it is possible to obtain an undistorted imaging at least at the intermediate image B. To obtain a circular diverging beam downstream of the focal point f, an elliptical aperture is not necessary in the multi-aperture plate that may be located upstream of the quadrupole fields Q1, Q2 and Q3, instead a circular aperture is sufficient.

[0083] FIG. 8 shows diagrammatically the deflection of a charged particle beam by four quadrupole fields Q1-Q4. To allow a proper comparison, each quadrupole Q1-Q4 again has an aperture diameter of 0.3 mm, the associated plates are 0.5 mm thick and are at a distance of 1 mm from each other (measured center to center). The particle beam incident parallel to the axis is focused at a distance of 100 mm from the center of the quadrupole Q4. Here, the polarity of the quadrupoles Q1, Q3, Q4 and Q2 is alternated, the quadrupoles Q1 and Q2 are applied with approximately the same voltage (amplitude) in terms of absolute value, and the quadrupoles Q3 and Q4 are similarly applied with approximately the same voltage (amplitude) in terms of absolute value. For a beam energy of 10 keV, the focusing voltages of the inner quadrupoles Q3 and Q4 in the selected example are ±66 V and the focusing voltages of the outer quadrupoles Q1 and Q2 are ±22 V. Again, halving the focusing voltage increases the focal length by a factor of four.

[0084] FIG. 9 shows diagrammatically the detailed beam paths belonging to the diagram of FIG. 8. The particle beams 3a, 3b incident parallel to the axis are focused at the same point at the same angle (i.e. coincide), and even the beams 3c and 3d incident obliquely to the axial direction coincide after passing through the arrangement of four quadrupoles Q1-Q4. Thus, each individual particle beam can be focused using the illustrated multipole lens arrangement without adapting the control of the multipole lens group. That is, by changing the excitation of, for example, the condenser lens system 303, it is possible to change with the multipole lens arrangement from axially parallel incident radiation to converging or diverging incident radiation, thereby displacing the relative positions of the intermediate image B and the focal point f without introducing distortions or astigmatism into the resulting image.

[0085] Since the imaging options using quadrupole fields have been described above based on a selection of various quadrupole or multipole arrays, the constructional setup of the multipole lens array 600 and its arrangement in a multibeam particle beam system, in particular in a multibeam particle microscope, for the purpose of independently focusing multiple individual particle beams, e.g. for field curvature correction, will now be described.

[0086] FIG. 10 shows a schematic structure of a multipole lens array 600. Here, the multipole lens array 600 includes a first multipole lens array 601, a second multipole lens array 602, a third multipole lens array 603, and a fourth multipole lens array 604. A fifth, sixth, seventh, or further multipole lens array may also be a component of the multipole lens array 600. In the illustrated case, the multipole lens arrays 601, 602, 603, and 604 each include a plate in which an aperture is arranged in which the multipole lenses M1i, M2i, M3i, and M4i are arranged. Here, the first multipole lens array includes multipole lenses M11, M12, and M13, which are illustrated by way of example. Since FIG. 10 shows a cross section of the multipole lens array 600, only some multipole lenses are illustrated by way of example. However, it is possible to arrange the multipole lenses M1i, M2i, M3i, M4i, and Mki in a square or rectangular shape, for example. However, the arrangement of the apertures or multipole lenses in the array is preferably hexagonal, i.e. the individual particle beams 3 are arranged according to a hexagonal structure with, for example, 61 or 91 individual particle beams (according to the general formula 3n(n-1)+1, n being a natural number), which arrangement is also provided geometrically in each multipole lens array 601, 602, 603, 604. The first, second, third, fourth and / or further multipole lens arrays 601, 602, 603, 604 can have an identical structure. However, it is also possible that the multipole lens arrays 601, 602, 603, 604 do not have the same structure or only partially have the same structure. By way of example, this may relate to the thickness of the plates forming the arrays 601, 602, 603, 604 (and thus to the length of the multipoles in the direction of the axis Z), but this may also apply to the configuration of the multipole lenses M1i, M2i, M3i and M4i. Additionally or alternatively, the distances of the multipoles in the array may be the same as one another (measured center to center), but may vary. In accordance with the invention, at least two of the illustrated multipole lens arrays generate quadrupole fields.In this case, with suitable field orientation and strength, it is possible to produce a focusing effect similar to that of an Einzel lens or a circular lens for a beam incident essentially parallel to the axis, i.e. from a slightly divergent beam to a slightly convergent beam. Further image aberrations can be corrected by using further multipole lenses. In this context, slightly convergent or slightly divergent means that the virtual source position of the incident particle beam is farther from the multipole in absolute terms than the focal point f, and as a result the multipole lens arrangement does not require either negative or too strong positive refractive powers. Negative refractive powers are difficult to achieve and would entail high voltage values ​​at the multipole electrodes, as would strong positive refractive powers.

[0087] Next, Fig. 11 shows a schematic arrangement of a multipole lens array 600 of a multibeam particle microscope 1 for field curvature correction. Here, the multibeam particle microscope 1 is only shown in an excerpt, and the entire detection area and the beam switch are not shown in Fig. 11. Furthermore, the illustrated beam paths are simplified, and by way of example, conventional crossovers of all individual particle beams 3 with respect to one another are not shown for clarity of the overall picture.

[0088] The multi-beam particle microscope shown in Fig. 11 comprises a particle source 301, for example a thermal field emission (TFE) source. In the illustrated example, an electron beam 3 is generated. The diverging particle beam is collimated using a collimation or condenser lens system 303. The particle beam, running substantially parallel to an optical axis O (not shown for clarity of the overview, but which does not necessarily have to coincide with the axis Z of the multipole lens array), then enters a multi-aperture plate 380, which should be considered as the starting point of the individual particle beam 3. The individual particle beam 3 thus generated then reaches a multipole lens array 600, which in the illustrated example comprises a first, a second and a third multipole lens array 601, 602 and 603. However, it would also be possible for there to be only two multipole lens arrays or more than four, for example four, five, six or more multipole lens arrays. However, according to the invention, at least two of the illustrated multipole arrays generate a quadrupole field. This allows for the overall focusing of the particle beam essentially parallel to the axis. After passing through the multipole lens array 600, the individual particle beam 3 passes through the circular lens array 385, which in this case does not contain multipole lenses, but instead immersion lenses which result from an electric field applied in particular globally to the end plates of the circular lens array 385 and which represent focusing particle lenses. The focusing power of the immersion lenses of the circular lens array 385 is usually stronger than that of the multipole lens array 600. However, this is also valid if the multipole lens array 600 only serves to correct the focal length in order to facilitate the correction of the field curvature. After passing through the circular lens array 385, the individual particle beam 3 is focused on a concavely curved surface 325, which is selected in such a way that the field curvature occurring on incidence on the sample 7 by the subsequent particle-optical imaging is just corrected. After passing through the field lens system 307 and the objective lens system 100, the charged particle beam 3 is planarly incident on the sample 7 at the incidence position 5 without any field curvature.

[0089] As an alternative to the location between the multi-aperture plate 380 and the circular lens array 385, the multipole lens array 600 can also be positioned upstream of the multi-aperture plate 380. This has the advantage that an elliptical incoming particle beam is automatically selected when only the two multipole lens arrays 601 and 602 are used with the circular aperture of the multi-aperture plate 380, said elliptical incoming particle beam having the necessary eccentricity to also generate a circular diverging particle beam 3 downstream of the focal point f. However, the multipole lens array 600 is completely illuminated by electrons, which may cause the insulating components therein to be charged, leading to poor imaging quality. However, the insulating components can be coated and charging can be prevented by using a further multi-aperture plate upstream of the multipole lens array 600. The aperture of this additional multi-aperture plate can be selected larger than the aperture of the multi-aperture plate 380, so that only the aperture of the multi-aperture plate 380 serves as the selection aperture.

[0090] Collimation or condenser lens systems 303 often make use of magnetic fields that induce Larmor rotation of the charged particles passing through the lens system, resulting in a helical motion profile of the particle trajectories with an overall angle of about 50° to 90°. The magnetic fields that cause the helical motion paths do not suddenly decay upstream of the multipole lens array 600, but instead the azimuthal angles of incidence of the particle trajectories are still possible. The excitation of the condenser lens system 303 should be advantageously selected so that the particle trajectories enter the multipole lens array 600 as parallel as possible, i.e., so that the polar angles of incidence are eliminated if possible. However, due to the spherical aberration of the condenser lens system 303, this is only successful in areas close to the optical axis O, for example, whereas in the edge regions of the multi-aperture plate 380 the particle beams are subsequently tilted towards the optical axis O. To take these situations into account, there are in particular the following options: 1. The multipole lenses are arranged in the multipole lens array 601, 602 etc. such that the optical axis of the multipole lens group is adapted to the angle of incidence of the particle beam. However, this is only valid for a specific configuration of the condenser lens system 303. This significantly limits the flexibility of the condenser lens system 303 in terms of adapting the particle current density. 2. A dipole field is used in the first multipole lens array 601 to make the obliquely incident particle beam reach the optical axis of the multipole lens group. A dipole field can also be used in the multipole lens array 602 to provide the necessary tilt for the remaining imaging system. The helical motion profile of the particle trajectories in the remaining particle beam in the presence of the residual magnetic field can then be taken into account using a suitably oriented quadrupole field. This increases the technical expenditure but increases the overall flexibility for the optimization of the whole system. 3. The azimuth angle of incidence. The residual magnetic field at the location of the multipole lens array 600 is reduced as much as possible, whether by a sufficient distance from the condenser lens system 303 or by an additional winding for compensation purposes. The design of the condenser lens system 303 is optimized for the smallest possible spherical aberration. These two measures do not lead to perfect results, but they mitigate the problem according to demand and also minimize the technical outlay. 4. Combination of 1~3.

[0091] Fig. 12 shows a schematic representation of yet another embodiment of the invention, which can be integrated into a multi-beam particle microscope 1 in a similar manner to Fig. 11. According to this variant of the invention, a multi-aperture plate 390 is provided, which generates individual particle beams 3 during the passage of apertures A1, A2, A3, Ai located therein upon the incidence of the particle beam. The multi-aperture plate 390 is combined with a multipole lens arrangement 600, which comprises a first multipole lens array 601 and a second multipole lens array 602. In the illustrated case, the lenses of the first multipole lens array 601 and the lenses of the second multipole lens array 602 are true quadrupole lenses Q11, Q12, Q13, Qi and Q21, Q22, Q23, Q2i, respectively. However, as an alternative, the quadrupole field can also be generated by a higher order multipole lens. It is of course possible to integrate further multipole lens arrays with quadrupole or other multipole fields into the illustrated variant. However, the cross section of the apertures A1, A2, A3 of the multi-aperture plate 390 is then decisive in this variant embodiment, since the apertures of the multi-aperture plate 390 have an elliptical cross section, the only exception in this case being an aperture that can be positioned centrally through which the optical axis O of the particle beam system extends. If the size and orientation of the elliptical cross section of the apertures is appropriately selected, it is possible to take into account the effects of subsequent imaging aberrations in the form of distortions. The resulting particle beam has a circular cross section rather than an elliptical cross section.

[0092] FIG. 13 shows a schematic plan view of the multi-aperture plate with elliptical apertures shown in FIG. 12. The central aperture A1 has a circular cross section and the optical axis O of the system passes through its center. The remaining apertures A2-A7 have an elliptical cross section. Overall, the ellipticity of the apertures of the multi-aperture plate 390 in this case increases with increasing distance from the center of the multi-aperture plate or from the central circular aperture A1 of the multi-aperture plate 390. Here, the orientation of the elliptical apertures in the illustrated example is as follows: If one considers the relationship between the center of the ellipse and the center of the multi-aperture plate 390, the major axis of the ellipse passing through the center is perpendicular to the ray passing through the center of the ellipse in a radial direction from the center of the multi-aperture plate 390. In other words, the minor axis of the ellipse is oriented in a radial direction from the center of the multi-aperture plate 390. It is self-evident that the multi-aperture plate 390 can have more apertures than the exemplary seven apertures A1-A7 shown. Instead, particularly in the hexagonal embodiment, apertures can be provided for all the individual particle beams present, as already mentioned many times above. Additionally, as described in the Summary section of this application, the orientation of the elliptical opening may differ from that shown.

[0093] Fig. 14 shows a schematic representation of an excerpt of a multipole lens array 601 with an octopole electrode arrangement. With this octopole electrode arrangement, a quadrupole field can be generated as well. In principle, only voltages U0=U4=Q and U2=U6=-Q are needed for this purpose. If further quadrupole fields, for example U1=U5=R and U3=U7=-R, are superimposed on this quadrupole field, the overall resulting quadrupole field can rotate around the optical axis Z. If the orientation of the quadrupole field due to an existing Larmor rotation or an existing magnetic field should be slightly changed, the voltage R is small compared to the voltage Q.

[0094] However, octopole electrodes allow much more variation in the application of the multipole field. For example, in order to compensate for tolerances, it is possible to laterally displace the desired quadrupole field, which can be achieved, for example, by applying a dipole field with U2=U6=0, U0=-U4=D and U1=-U3=-U5=U7=0.7D. Furthermore, it is of course possible to rotate this dipole field with different voltage distributions.

[0095] It is possible and advantageous to combine the counter electrodes and supply them with a single voltage source. This combination suppresses voltage deviations or differences and the resulting potentially unfavorable dipole fields. It is true in principle that charged particle beams, for example electron beams, react very sensitively to existing dipole fields, i.e. the voltage supplied to the multipole lenses must be very stable. It is therefore advantageous to use voltage sources which are already very stable in themselves. However, the maximum amplitude of the voltage sources can also be selected differently for the different electrodes. As an example, it is possible to use voltage sources with large maximum amplitudes for U0=U4 and U2=U6, and voltage sources with small maximum amplitudes for U1=-U3=-U5=U7. In principle, voltage sources with small maximum amplitudes have smaller absolute fluctuations or noise widths than voltage sources with large maximum amplitudes. It is still possible to generate sufficiently strong dipole fields at the electrodes U1, U3, U5 and U7 by omitting the dipole components of U0 and U4 (due to U0=U4). However, the absence of dipole components U0 and U4 results in a parasitic hexapole field along with the dipole field, which results in corresponding aberrations, however this may be tolerable for small amplitudes of the dipole field D. Additional dipole plates may also be used at other locations with voltage sources of smaller maximum amplitude, but appropriate space must also be provided for this purpose.

[0096] Alternatively, it is also possible to use a voltage source UQ with a larger maximum amplitude for both electrodes U0 and U4, and to add thereto two voltage sources UD0 and UD4 with the smallest maximum amplitude. In the most easily understandable case, the voltage sources UD0 and UD4 can be supplied galvanically isolated and simply connected in series (like a battery) to the voltage source UQ, UQ connected in series with UD0 supplies U0 and UQ connected in series with UD4 supplies U4. However, this process is extremely complex from a technical point of view and must be applied to all electrodes in the general case.

[0097] For a simpler technical implementation, the individual noise sources of the voltage source need to be analyzed. These are the reference source, a digitally adjustable voltage divider, one or usually several operational amplifiers, and a small number of resistors. Generally, most of the noise comes from the reference source and the voltage divider. In contrast, the noise of the resistors and the operational amplifiers is negligible if the resistors are selected small enough. As an example, a positive reference source URP of 10V is used. A further negative reference source URN of -10V is generated therefrom using an inverter, i.e. a 1:1 voltage divider and an operational amplifier. From these two voltages, for example, a quadrupole voltage UQCP is generated using a digitally adjustable voltage divider, and the inverted voltage UQCN is also generated immediately using an inverter. This is repeated with three further voltages, so that voltages UQCP=-UQCN, UQSP=-UQSN, UDXP=-UDXN, UDYP=-UDYN are obtained, all of which can be set within the range between URN and URP. Using a resistive network with downstream amplifiers, these voltages are then distributed among the electrodes of the octapole as follows:

number

[0098] As an example, if A=10 and B=1, it is possible to generate a quadrupole voltage with a large maximum amplitude and a bipole voltage with a small maximum amplitude. The noise of the digitally adjustable voltage divider rides on the quadrupole voltage with a large amplitude. However, the symmetrical feedthrough to the counter electrodes ensures that the particle beam position at the plane 325 is noise-free. In contrast, the noise of the digitally adjustable voltage divider rides on the bipole voltage relatively only, so that the particle beam position at the plane 325 is less noisy as a result of the bipole voltage having a small maximum amplitude. Since all output voltages are derived from the same reference voltage, the noise of the reference voltage is substantially cancelled. When the quadrupole voltage is maximally saturated, the symmetrical feedthrough to the counter electrodes again ensures that the particle beam position at the plane 325 is noise-free. When the bipole voltage is maximally saturated, the relative noise of the reference source propagates directly to the relative noise of the bipole voltage. However, since the bipole voltage has a small maximum amplitude, the absolute noise of the resulting beam position is similarly small.

[0099] FIG. 15 shows a schematic excerpt of a multipole lens array 601 with an alternative octopole electrode arrangement. The depicted electrodes with voltages U0 to U7 differ in size or shape. Some electrodes have a larger size compared to the diagram of FIG. 14, while others are smaller. By choosing the appropriate size and shape, a shielding effect occurs. Electrodes with reduced size have a weaker effect on the particle beam, even if supplied with a large maximum amplitude by the voltage source. It is possible to supply all electrodes with the same type of voltage source, but the effects shown are different. In particular, the generated quadrupole field can be varied with respect to its orientation. It is also possible to superimpose a quadrupole field on a weaker dipole field, but care must be taken that the required homogeneity of the field is nevertheless maintained.

[0100] The above-mentioned shielding principle can also be used in the direction along the optical axis Z. By using suitable manufacturing methods, it is possible to manufacture multipole arrays or multipole lenses in a layered structure in the Z direction. Here, most of these multipoles can be connected in the form of quadrupoles, preferably with counter electrodes coupled. Furthermore, some of the multipoles can be wired in the form of dipoles, with each electrode being individually controllable. It is also possible to connect octopoles in the form of dipoles, with adjacent electrodes coupled (however, this also results in a parasitic hexapole field). Overall, in this way, it is possible to manufacture stacks or arrays of very thin multipoles or multipole lenses, most of which have a quadrupole field generating a strong or main quadrupole field, preferably with counter electrodes coupled. Furthermore, it is also possible to wire the multipoles together in the form of dipoles in order to displace the relative position of the particle beam with respect to the optical axis, in particular to displace them in parallel, and it is also possible to provide octopoles in order to orient the resulting quadrupole field in a manner that is desired. It is also possible to use quadrupoles to generate a uniform dipole field. There are many different ways in which a multipole lens array can be used to provide a multipole lens arrangement.

[0101] 16 shows a schematic representation of a portion of a multipole lens array with a quadrupole field and a dipole field. The illustrated array includes a first multipole array 601 with a first quadrupole field, a second multipole lens array 602 with a first dipole field D1, a third multipole lens array 603 with a second dipole field D2, and a fourth multipole lens array 604 with a second quadrupole field Q2. Here, the two quadrupole fields Q1 and Q2 are oriented with respect to each other such that they have substantially 90° rotated orientations with respect to each other in the illustrated example and have substantially the same amplitude. The dipole fields D1 and D2 located between the two quadrupole fields Q1 and Q2 are aligned anti-parallel with respect to each other and have substantially the same amplitude so as to facilitate, in principle, a parallel offset of the particle beam 3 passing through the multipole lens array 600. Such a parallel offset allows the particle beam 3 to be guided through the center of all quadrupole fields even if the multipoles of the multipole lens array 604 are positioned offset from the optical axis due to manufacturing errors, as shown for example in FIG. 16. Another use of the two further dipole fields is to return a particle beam spiralled by an external magnetic field back to its optical axis in the first dipole field before passing through the multipole lens arrangement, and finally to return the spiralled particle beam to its original direction. An arrangement required for this purpose would be a first multipole lens array 601 with a first dipole field D1, a second multipole lens array 602 with a first quadrupole field Q1, a third multipole lens array 603 with a second quadrupole field Q2, and a fourth multipole lens array 604 with a second dipole field D2. Of course, it would also be possible to combine, for example, four dipole fields and two quadrupole fields in six multipole lens arrays.

[0102] Here, for a stable particle beam position in the plane 325, it is advantageous to cross-wire two multipoles, each excited in opposite directions as a dipole, and connect them together to a power supply. As a result, the noise in this power supply will only result in a parallel offset noise, and not an output angle noise. Since the plane 325 is far from the dipole relative to the distance of the dipole field, the output angle noise compared to the parallel offset noise will be a multiple of the noise level of the particle beam position in the plane 325. Such a cross-wired dipole doublet can be part of, for example, a multi-layered multipole lens array, and can be used especially when incorporating a dipole field together with a quadrupole field in a multipole lens has too many drawbacks.

[0103] FIG. 17 shows diagrammatically the power supply of the multipole lens array 601. A part of a plan view of the multipole lens array 601 is shown diagrammatically in FIG. 17. To generate a quadrupole field (and / or other multipole fields), an electromagnetic field generator 372 is assigned to each of the apertures 361, which exerts a quadrupole field on the beam 3 passing through this aperture 361. Each electromagnetic field generator 372 has eight electrodes 373, which are distributed circumferentially around the aperture 361 and are controlled by a controller 369. For this purpose, an electronic circuit 375 is arranged on the plate of the multipole lens array 601 in an area arranged away from the aperture 361, which generates adjustable voltages and supplies them to the electrodes 373 via electric wires 377. The controller 369 controls the electronic circuit 375 by means of a serial data connection 379 passing through a vacuum jacket 381 of the particle beam system. Here, a seal 382 is provided for sealing the lines of the serial data connection to the vacuum jacket 381. The electronic circuitry 375 generates voltages that are applied to the electrodes 373 via electrical lines 377 based on data received from the controller 369 via a serial data connection 379. The controller 369 can thus generate electric quadrupole fields (and / or other multipole fields) at each of the apertures 361, said fields being adjustable in terms of their strength and their orientation about the center of the aperture 361. Using these quadrupole fields (and / or other multipole fields), all of the particle beams 3 can be manipulated individually. The controller 369 sets the quadrupole fields of the multipole lens array 601 and the quadrupole fields (and / or other multipole fields) of one or more other multipole lens arrays 60i (not shown) such that the focal lengths of the individual particle beams 3 are individually selectable and thus, for example, the field curvature in a multi-beam particle beam system can be individually corrected for each individual particle beam.

[0104] To construct a layered multipole lens array system as described on the basis of Fig. 16, the multipole lens array 601 according to Fig. 17 can be constructed in sequence using photochemical methods known from semiconductor technology, resulting in the multipole lens arrangement 600 (for example MEMS technology). As an example, for more effective contact, through-holes can be arranged around the electrodes 373, said through-holes being connected by wires 377 to the electronic circuit 375 at the appropriate location or at the appropriate layer. Then, depending on the layer, the electrodes 373 can be connected to the corresponding multipole groups directly or by cross-wiring.

[0105] Using the same technique, it is possible to alternately connect 11 layers to a quadrupole group and 10 layers to a dipole group (without cross-wiring) in a stack of, for example, 21 layers of submultipole lens arrays to create, for example, multipole lens 601. In this multipole, it is possible to generate a strong quadrupole field that does not result in noisy particle beam positions in plane 325, and to superimpose on it a weak dipole field that does result in noisy particle beam positions in plane 325.

[0106] Further details regarding the manufacture of multi-lens arrays and voltage sources, which can also be applied to power supplies of multipole lens arrays, become apparent from German patent application No. 10 2020 106 801.8, which was unpublished on the priority date of this patent application, the disclosure of which is incorporated by reference in its entirety into this patent application.

[0107] With the multipole lens array according to the exemplary embodiment, independent lensing or focusing for the individual particle beams, for example for field curvature correction, can be achieved at lower voltages than when using lenses with ring electrodes. Although the exemplary embodiment describes the invention using the example of field curvature correction, the invention is not limited to field curvature correction. In another example, the focal length is significantly reduced, for example by more than 10%, preferably 20%, and the numerical aperture is significantly reduced, for example by more than 10%, preferably 20%, at lower voltages than with ring electrodes. Furthermore, the present invention allows independent stronger lensing or focusing at shorter focal lengths for the individual particle beams of the multiple particle beams, since the voltage for the multipole lens array is lower and thus there are less interaction effects, which occur especially in the case of the power supply of multiple multipole electrodes for the multiple individual particle beams. As an example, the multiple individual particle beams can include a plurality of individual particle beams, such as 100, 300, or more. Each individual particle beam of the multiple individual particle beams can be focused independently and individually, for example with a low voltage of less than 300V, more particularly less than 200V, or particularly preferably less than 100V, such that a first individual particle beam can be focused more strongly than an adjacent second individual particle beam. Using low voltages, even small voltage differences make it easier to adjust the focal length difference between adjacent individual particle beams. As an example, the focal length difference between the first and second individual particle beams can be greater than 10%, and the voltage difference between the multipole voltages of the first and second individual particle beams is less than 100V, preferably less than 50V, particularly preferably about 20V.

Claims

1. 1. A particle beam system comprising: a multi-beam particle source configured to generate a plurality of charged individual particle beams (3); a multipole lens arrangement (600) having at least one first multipole lens array (601) and at least one second multipole lens array (602); the first multipole lens array (601) includes a plurality of individually adjustable first multipole lenses that generate a first quadrupole field (Q1) and is arranged in a particle beam path such that the individual particle beams (3) substantially pass through the first multipole lens array (601); and the second multipole lens array (602) includes a plurality of individually adjustable second multipole lenses that generate a second quadrupole field (Q2) and is positioned in a particle beam path such that the individual particle beams (3) passing through the first multipole lens array (601) also substantially pass through the second multipole lens array (602); A multipole lens group is formed by an arrangement of multipole lenses belonging to different multipole lens arrays (601, 602) through which the same individual particle beam (3) passes, respectively. A multipole lens array (600); a controller (10) configured to control the generation of a first quadrupole field (Q1) in the first multipole lens array (601) and the generation of a second quadrupole field (Q2) in the second multipole lens array (602) for each of the multipole lens groups, such that an arrangement of multipole lenses in each multipole lens group exerts a focusing effect on each of the individual particle beams (3) passing through the different multipole lens arrays (601, 602) in a first direction (x) perpendicular to a principal axis (Z) of the individual particle beams (3) and in a second direction (y) perpendicular to the first direction (x) and the principal axis (Z); Equipped with 1. A particle beam system, comprising: a first multipole lens group having a first axis (Z) and a second axis (y) that are parallel to the first axis (Z), the first multipole lens group having a first axis (Z) and a second axis (y) that are parallel to the first axis (Z), the first axis (Z) and the second axis (y) of the first multipole lens group being focused together to meet at a focal point (f) on ... parallel to the first axis (Z), the second axis (y) and the second multipole lens group being parallel to the first axis (Z), the second axis (y) and the second multipole lens group being parallel to the first multipole lens group being focused together to meet at a focal point (f) on the first axis (Z), the second axis (y) and the second multipole lens group being parallel to the first multipole lens group being focused together

2. 2. The particle beam system of claim 1, wherein the quadrupoles of the first quadrupole field (Q1) and the quadrupoles of the second quadrupole field (Q2) have orientations rotated substantially by 90° relative to each other and / or have substantially the same amplitude.

3. 3. The particle beam system according to claim 1 or 2, wherein the first multipole lens array (601) and / or the second multipole lens array (602) comprises a quadrupole lens array.

4. A particle beam system according to any one of claims 1 to 3, The multipole lens array (600) includes a third multipole lens array (603); the third multipole lens array (603) includes a plurality of individually adjustable third multipole lenses generating a third quadrupole field (Q3), and is disposed in a particle beam path between the first multipole lens array (601) and the second multipole lens array (602) such that the individual particle beams (3) passing through the first multipole lens array (601) also substantially pass through the third multipole lens array (603); The controller (10) is further configured to control the multipole lenses of the multipole lens array through which each of the same individual particle beams (3) passes such that, as a whole, the multipole lenses have an effect on each of the individual particle beams (3) passing therethrough such that there is substantially no distortion in the imaging of the individual particle beams (3) at a focal plane (B).

5. 5. The particle beam system of claim 4, the quadrupoles of the first multipole lens array (601) and the second multipole lens array (602) have substantially the same orientation and substantially the same amplitude; A particle beam system, wherein the quadrupoles of the third multipole lens array (603) have an orientation rotated by approximately 90° relative to the first and second quadrupoles, and the amplitude of the third quadrupole is greater than the amplitude of the first and second quadrupoles, more specifically, approximately twice the amplitude of the first and second quadrupoles.

6. 6. A particle beam system according to claim 4 or 5, The multipole lens arrangement (600) includes a fourth multipole lens array (604); the fourth multipole lens array (604) includes a plurality of individually adjustable fourth multipole lenses for generating a fourth quadrupole field (Q4) and is disposed in a particle beam path between the first multipole lens array (601) and the second multipole lens array (602) such that the individual particle beams (3) passing through the first multipole lens array (601) also substantially pass through the fourth multipole lens array (603); and The controller (10) is configured to control the multipole lenses of the multipole lens array so that, as a whole, the multipole lenses have an effect on each of the individual particle beams (3) passing therethrough such that the imaging of the individual particle beams (3) is substantially undistorted.

7. 5. The particle beam system of claim 4, The multipole lens arrangement (600) includes a fourth multipole lens array (604); the fourth multipole lens array (604) includes a plurality of individually adjustable fourth multipole lenses for generating a fourth quadrupole field (Q4) and is disposed in a particle beam path between the first multipole lens array (601) and the second multipole lens array (602) such that the individual particle beams (3) passing through the first multipole lens array (601) also substantially pass through the fourth multipole lens array (603); and the controller (10) is configured to control the multipole lenses of the multipole lens array such that, as a whole, the multipole lenses have an effect on each of the individual particle beams (3) passing therethrough such that imaging of the individual particle beams (3) is substantially undistorted; the quadrupoles of the first multipole lens array (601) and the second multipole lens array (602) have orientations rotated by substantially 90° with respect to each other and have substantially the same amplitude; the quadrupoles of the third multipole lens array (603) and the fourth multipole lens array (604) have orientations rotated substantially by about 90° with respect to each other and have substantially the same amplitude; the arrangement of polarities of the quadrupoles is alternating; and A particle beam system wherein the amplitudes of the third and fourth quadrupoles are greater than the amplitudes of the first and second quadrupoles, respectively, and more particularly are approximately three times the amplitudes of the first and second quadrupoles, respectively.

8. The particle beam system according to any one of claims 1 to 7, wherein at least one multipole lens array (601, 602, 603, 604) comprises an octopole lens array.

9. 9. The particle beam system according to claim 8, wherein the controller (10) is configured to control the octapole lens such that an electric field generated by the octapole electrode results in a superposition of two quadrupole fields, the superposition resulting in a quadrupole field rotated about a principal axis (Z) of the individual particle beam (3) relative to one of the quadrupole fields, in particular the stronger of the quadrupole fields.

10. 10. The particle beam system according to claim 1, wherein the controller (10) is configured to control the multipole lenses such that an electric field generated by the multipole electrodes results in a superposition of a quadrupole field and at least one dipole field, the superposition with respect to the quadrupole field resulting in a quadrupole field displaced from a geometric axis of each of the multipole lenses.

11. A particle beam system according to any one of claims 8 to 10, wherein all electrodes of the octapole lenses of the octapole lens array have the same size and shape.

12. A particle beam system according to any one of claims 8 to 10, wherein at least some of the electrodes of the octopole lenses of the octopole lens array have different sizes and / or different shapes.

13. A particle beam system according to any one of the preceding claims, wherein at least one multipole lens array (601, 602, 603, 604) comprises a dipole lens array.

14. 14. The particle beam system of claim 13, wherein the multipole lens array (600) has the following field array: a dipole field - a quadrupole field - a further quadrupole field - a further dipole field having a different orientation to the first dipole field, in particular a substantially anti-parallel orientation. A particle beam system including a multipole lens array (601, 602, 603, 604) for generating

15. 14. The particle beam system of claim 13, wherein the multipole lens array (600) has the following field array: Quadrupole field (Q1) - at least two dipole fields (D1, D2) with mutually different orientations, in particular two substantially antiparallel dipole-quadrupole fields (Q2) A particle beam system including a multipole lens array (601, 602, 603, 604) for generating

16. 16. The particle beam system according to claim 1, wherein the multi-beam particle source comprises: at least one particle source (301) configured to generate a charged particle beam; a multi-aperture plate (380, 390) having a plurality of apertures (A1, A2, A3, A4, A5, A6, A7) and arranged in a particle beam path such that at least a portion of the particles pass through said apertures (A1, A2, A3, A4, A5, A6, A7) in the form of a plurality of individual particle beams (3); 2. A particle beam system comprising:

17. 17. The particle beam system of claim 16, wherein at least some of the apertures (A1, A2, A3, A4, A5, A6, A7) in the multi-aperture plate (390) have an elliptical cross-section.

18. A particle beam system according to any one of claims 1 to 17, a circular lens array (385) including a plurality of focusing particle lenses and arranged in a particle beam path to substantially pass the individual particle beams (3) passing through the multipole lens array (600); wherein the focusing particle lenses of the circular lens array (385) are not multipole lenses.

19. 20. The particle beam system of claim 18, wherein the circular lens array (385) is disposed downstream of the multipole lens arrangement (600) in a particle beam path, and the system further comprises: a condenser lens system (303) arranged upstream of said multipole lens array (600) in the particle beam path; The particle beam system further comprising:

20. 20. The particle beam system of claim 1, wherein the controller (10) effects the individual particle beam (3) such that a focal point (323) of the individual particle beam (3) is positioned in a concave region, the concave region being concave toward a downstream of the individual particle beam (3).

21. A particle beam system according to any one of the preceding claims, in which there is a combined power supply for the electrodes of the multipole lenses which are energised with the same voltage.

22. The particle beam system according to any one of claims 1 to 21, wherein the voltages applied to the electrodes of the multipole lens array (600) are less than 100V each for a beam energy of about 10 keV.

23. Use of a particle beam system according to any one of claims 1 to 22 for field curvature correction.

24. Use of a particle beam system according to any one of claims 1 to 22 for the correction of tilt astigmatism.

25. A multi-beam particle microscope (1) comprising a particle beam system according to any one of claims 1 to 22.

26. A method for correcting field curvature of a particle beam system according to any one of claims 1 to 22, comprising the steps of: setting the focal lengths of the plurality of individual particle beams (3), in particular of all of the particle beams, individually, by means of a multipole lens arrangement (600); The method includes:

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