Method for passively aligning a particle-optical component for a functional unit of a particle beam system, in particular of a pole shoe for a magnetic lens, method for equipping a particle beam system with the functional unit, in particular a magnetic lens, and particle beam system

Abstract

The invention relates to a method for passively aligning a pole shoe for a magnetic lens of a particle beam system, including the following steps: providing a reference pole shoe with a predefined minimum magnetic homogeneity in a measuring device; releasably arranging the pole shoe to be aligned relative to the reference pole shoe in a predefined reference position and thereby assembling a magnetic lens in the measuring device; exciting the magnetic lens in the measuring device; measuring characteristics of the magnetic field generated by the magnetic lens; determining a deviation of the characteristics of the generated magnetic field from corresponding characteristics of a predefined reference magnetic field; and mechanically modifying the pole shoe on the basis of the ascertained deviation in order to adapt the magnetic field that can be generated by the magnetic lens.

Description

[0001] Method for passively aligning a particle-optical component for a functional unit of a particle beam system, in particular of a pole shoe for a magnetic lens, method for equipping a particle beam system with the functional unit, in particular a magnetic lens, and particle beam system

[0002] Field of the invention

[0003] The invention relates to a particle beam system in general and to multiple particle beam systems operating with a multiplicity of individual charged particle beams in particular. Specifically, the invention relates to a method for passively aligning a particle-optical component for a functional unit of a particle beam system, to a method for equipping a particle beam system with the functional unit, and to a particle beam system. For example, the functional unit may be a magnetic lens.

[0004] Prior art

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

[0006] Typical silicon wafers used in the production of semiconductor components have diameters of up to 300 mm. Each wafer is divided into several ten to several hundred repeating regions ("dies") with a size of up to 800 mm2. A semiconductor device comprises a plurality of semiconductor structures, which are produced in layers on a surface of the wafer by planar integration techniques. Semiconductor wafers typically have a plane surface on account of the production processes. The feature size of the integrated semiconductor structures in this case extends from a few pm to the critical dimensions (CD) of a few nanometres, and the feature sizes will become even smaller in the near future; the expectation is that in future the feature sizes or critical dimensions (CD) will correspond to the 3 nm, 2 nm or even smaller technology nodes of the International Technology Roadmap for Semiconductors (ITRS). In the case of the aforementioned small feature sizes, defects of the order of the critical dimensions must be identified quickly over a very large area. For multiple applications, the specification requirement regarding the accuracy of a measurement provided by an inspection device is even higher, for example by a factor of two or one order of magnitude. For instance, a width of a semiconductor feature must be measured with an accuracy better than 1 nm, for example 0.3 nm or even less, and a relative position of semiconductor structures must be determined with an overlay accuracy better than 1 nm, for example 0.3 nm or even less.

[0007] The mSEM, a multi-beam scanning electron microscope, is a relatively new development in the field of charged particle systems (charged particle microscopes, CPMs). For instance, a multi-beam scanning electron microscope is disclosed in US 7 244 949 B2 and in US 2019 / 0355544 A1. In the case of a multi-beam electron microscope or mSEM, a sample is irradiated simultaneously by a multiplicity of individual electron beams arranged in a field or grid. For instance, 4 to 10 000 individual electron beams may be provided as primary radiation, with each individual electron beam being separated from an adjacent individual electron beam by a pitch of 1 to 200 micrometres. For example, an mSEM has approximately 100 separate individual electron beams ("beamlets"), which are arranged for example in a hexagonal grid, with the individual electron beams being separated by a pitch of approximately 10 pm. The multiplicity of individual charged particle beams (primary beams) are focused on a surface of a sample to be examined by way of a common objective lens. For example, the sample can be a semiconductor wafer that is secured to a wafer holder mounted on a movable stage. When the wafer surface is illuminated by the primary individual charged particle beams, interaction products, for example secondary electrons or backscattered electrons, emanate from the surface of the wafer. Their start points correspond to those locations on the sample on which the multiplicity of primary individual particle beams are focused in each case. The amount and the energy of the interaction products depend on the material composition and the topography of the wafer surface. The interaction products form multiple secondary individual particle beams (secondary beams), which are collected by the common objective lens and, by virtue of a projection imaging system of the multi-beam inspection system, are incident on a detector arranged in a detection plane. The detector comprises a plurality of detection regions, each of which comprises multiple detection pixels, and the detector captures an intensity distribution for each of the secondary individual particle beams. An image field of 100 pm x 100 pm, for example, is obtained in the process. The multi-beam electron microscope of the prior art comprises a sequence of electrostatic and magnetic elements. At least some of the electrostatic and magnetic elements are adjustable in order to adapt the focus position and the stigmation of the multiplicity of individual charged particle beams. The state-of-the-art multi-beam system with charged particles moreover comprises at least one crossover plane of the primary or the secondary individual charged particle beams. Moreover, the state-of-the-art system comprises detection systems to facilitate the adjustment. The state-of-the-art multi-beam particle microscope comprises at least one beam deflector (deflection scanner) for collective scanning of a region of the sample surface by means of the multiplicity of primary individual particle beams in order to obtain an image field of the sample surface.

[0008] What is known as a beam splitter (or alternatively beam separator or beam divider) is used to separate the particle-optical beam path of the primary beams from the particle-optical beam path of the secondary beams. Separation is effected by means of specific arrangements of magnetic fields and / or electrostatic fields, for example by means of a Wien filter.

[0009] An alignment of the multi-beam electron microscope, or more generally of a multi-beam particle microscope, is of great importance for precision applications. One aspect of the alignment is the alignment of magnetic lenses of the system. These magnetic lenses can be in particular so-called global magnetic lenses, where substantially all of the charged particles or all of the individual charged particle beams pass through these global magnetic lenses in equal measure. These lenses must therefore be aligned particularly accurately. Moreover, the fact is that, on account of the geometric dimensions of such a magnetic lens, the magnetic field generated in the lens cannot be deduced exactly. To put it another way, the magnetic fields of lenses manufactured identically within the scope of the manufacturing accuracy may indeed be measurably different from one another, which is why an individual lens alignment is necessary. The reason for this lies in inhomogeneities in the magnetic material: Magnetic materials are not perfectly homogeneous but have grain boundaries. If the magnetic materials are not homogeneous, or if a different type of material inhomogeneity has arisen, then it is possible that the magnetic flux at the end of the pole shoe does not emerge completely homogeneous from a pole shoe end. The magnetic field generated in a pole shoe opening therefore often does not exhibit perfect round symmetry or is often not tolerance-aberration- free.

[0010] For this reason, inter alia, magnetic lenses for multi-beam particle beam systems are mechanically aligned. In principle, the upper pole shoe of the magnetic lens and the lower pole shoe of the magnetic lens are mechanically aligned with each other in the process. The upper pole shoe (also called Linsentopf in German) with a coil arranged therein and the lower pole shoe (also called Linsendeckel in German) are separately movable or mechanically alignable, especially in an alignment plane perpendicular to the particle-optical axis Z. The pole shoes are subsequently fixed.

[0011] In accordance with the prior art, the magnetic lenses in a multi-beam particle microscope are often aligned purely mechanically, with experienced technicians performing the alignment of the magnetic lenses manually. Such an alignment is time-consuming and performed while observing a multi-beam particle microscope image at the same time. Screws on the exterior of the multi-beam particle microscope or the housing thereof are adjusted in order to align the magnetic lenses. The alignment and subsequent fixing of the magnetic lenses are normally carried out during the commissioning of the multi-beam particle microscope in production; afterwards, the alignment normally remains unchanged and is carried out on site at the customer's premises only after module exchange or magnetic lens exchange. Such an exchange may be necessary, for example, due to mechanical damage or a voltage flashover, especially in the case of objective lenses. In this case, the renewed alignment following an exchange, on site at the customer's premises, is more difficult since at the customer's premises the multi-beam particle microscope is often incorporated in a production facility and the associated process chain. Long and expensive outage times in a production facility may therefore occur, which need to be avoided.

[0012] DE 10 2022 114 098 A1 discloses an improved alignment for magnetic lenses in a multi-beam particle microscope. For this purpose, an electrically controllable mechanical alignment and fixing means with an actuator system is provided for at least one in particular global alignable magnetic lens, said means being configured to mechanically align and mechanically fix a position of the at least one alignable magnetic lens in the particle-optical beam path in a plane orthogonal to the optical axis of the multi-beam particle microscope, and provision is made for a controller configured to electrically control the electrically controllable mechanical alignment and fixing means. But this improved alignment is also associated with an expenditure - albeit lesser expenditure - of time.

[0013] US 2015 / 0021476 A1 discloses a magnetic lens for focusing a beam of charged particle. For better adjustment or more precise generation of a magnetic field, instead of a pole shoe opening, a pole shoe waist is provided from which a magnetic field emerges. US 2015 / 0060662 A1 discloses the integration of two inspection units in one system, which can operate at different resolutions. For this purpose, a special design of objective lenses or objective lens arrays is provided, which are multi-axial in design.

[0014] DE 199 52 169 A1 discloses a specially designed magnetic lens. It comprises special arrangements of an inner lens pole and an outer lens pole, which each have different aperture diameters and are aligned with each other in the best possible way.

[0015] JP H02 - 204 953 A discloses a standard objective lens.

[0016] DE 11 2017 007 063 T5 shows a lens system with a combination of a magnetic lens and an electrostatic lens. The electrostatic lens is arranged as a control electrode formed between a distal end portion of a first pole piece and a distal end portion of a second pole piece. It allows control of an electric field formed between the sample and the distal end portion.

[0017] US 2007 / 0023673A1 refers to problems in the adjustment of magnetic lenses and in particular to difficulties in connection with soldering technology and its effects on the optical properties of particle optical elements. The document proposes a design approach or design measures in which a field-generating element is arranged in a vacuum-tight container. The container is sealed vacuum-tight by welding, soldering, or brazing.

[0018] Description of the invention

[0019] The problem addressed by the present invention therefore is that of enabling a faster alignment of magnetic lenses for particle beam systems and in particular for multi-beam particle beam systems. The exchange of magnetic lenses in a particle beam system, and in particular in a multi-beam particle beam system, should be simplified and performable faster than it is now.

[0020] The problem is solved by the subject matter of the independent claims. Dependent patent claims are directed to advantageous embodiments of the invention.

[0021] The present patent application claims the priority of the German patent application No. 102024 128 202.9 filed on 30 September 2024, the disclosure of which in the full scope thereof is incorporated in the present patent application by reference.

[0022] A basic concept of the invention is that of replacing the active mechanical alignment of a magnetic lens during or after an installation of the magnetic lens in a particle beam system with a passive alignment. During active alignment, the two pole shoes of a magnetic lens are moved relative to each other within an alignment plane. In a passive alignment, however, the relative orientation of the two pole shoes in the installation situation or operating position is already fixed and predetermined highly precisely, for example by means of a highly precise fit. This saves valuable time. Instead of an active alignment in the system itself, the alignment is carried out passively in advance of an installation using a reference standard or a reference pole shoe in a measuring stand. In particular, material-removing methods may be used at a joining surface of the pole shoe and / or in the region of a pole shoe opening of the pole shoe for the precise positioning and orientation of a magnetic axis of the magnetic lens. The idea of the invention can in principle also be transferred to other functional units of a particle beam system and, in particular, of a multiple particle beam system.

[0023] According to a first aspect of the invention, the latter relates to a method for passively aligning a pole shoe for a magnetic lens of a particle beam system, including the following steps: providing a reference pole shoe with a predefined minimum magnetic homogeneity in a measuring device; releasably arranging the pole shoe to be aligned relative to the reference pole shoe in a predefined reference position and thereby assembling a magnetic lens in the measuring device; exciting the magnetic lens in the measuring device; measuring characteristics of the magnetic field generated by the magnetic lens; determining a deviation of the characteristics of the generated magnetic field from corresponding characteristics of a predefined reference magnetic field; mechanically modifying the pole shoe on the basis of the ascertained deviation in order to adapt the magnetic field that can be generated by the magnetic lens.

[0024] As already explained above, a passive alignment is understood to mean an alignment of two pole shoes of a magnetic lens relative to each other, with no relative movement of the two pole shoes with respect to each other taking place within an alignment plane. The magnetic lens can be any desired magnetic lens, for example an objective lens, a condenser lens, a field lens or a projection lens. The particle beam system may likewise be of any desired type, in principle. By preference, it is a multi-beam particle beam system but other configurations are also possible.

[0025] The magnetic lens is composed of two pole shoes, in this case the reference pole shoe and the pole shoe to be aligned. Self-evidently, the magnetic lens may comprise further constituent parts, for example the winding arranged therein. The magnetic lens is the functional unit that needs to be passively aligned.

[0026] The reference pole shoe has a predefined minimum magnetic homogeneity. The reference pole shoe therefore represents a reference standard. Normally, this reference pole shoe will be manufactured with a certain amount of effort and also tested accordingly so that it can actually perform its function as a reference.

[0027] The measuring device is a device for measuring the functionality of the magnetic lens. It therefore contains those means that, as a minimum, are required to examine or test the function of the assembled magnetic lens. For example, the measuring device may comprise a particle source and in particular a multi-beam particle source. It may comprise a particle optics unit in addition to the magnetic lens. The measuring device moreover may comprise a sample stage and a test sample, which is arranged on the sample stage with its surface in the object plane of a magnetic lens, a deflection system having a control electronics unit, and a detection system for detecting secondary particles. Furthermore, the measuring device may comprise an evaluation unit, for example a computer system. What holds true fundamentally is that the measuring device is as simple as possible but nevertheless allows highly precise testing of the functionality of the magnetic lens. The measuring device may also be formed integrally with the reference pole shoe. This means that the reference pole shoe is fixedly and permanently arranged in the measuring device and need not be initially inserted into the measuring device for the method for passively aligning a pole shoe. The fixed arrangement of the reference pole shoe in the measuring device eliminates possible sources of error during test operation.

[0028] The pole shoe to be aligned is releasably arranged in a predefined reference position relative to the reference pole shoe. Releasability is important because all that matters within the measuring device is the testing or establishment of a proper functionality of the functional unit made of pole shoe to be aligned and reference pole shoe. Subsequently, the pole shoe passively aligned in this way should be insertable directly in a particle beam system. For example, the releasable arrangement can be implemented by screwing.

[0029] The magnetic lens assembled thus can now be tested. To do this, the magnetic lens is initially excited within the measuring device. Then, characteristics of the magnetic field generated by means of the magnetic lens are measured, and deviations of the characteristics of the generated magnetic field from corresponding characteristics of a predefined reference magnetic field are determined. On the basis of the ascertained deviation, there is a mechanical modification of the pole shoe in order to adapt the magnetic field that can be produced by the magnetic lens. In concrete terms, for example, the following procedure may be implemented:

[0030] 1) The properties of the magnetic lens when transmitting particles are investigated by recording an image of a reference sample in a raster-type scanning method.

[0031] 2) This image is examined for geometric properties, e.g. distortion. Should the reference magnetic field be present in the real magnetic lens as well, this image would have certain properties that are known in advance or would correspond to a reference image with distortion.

[0032] 3) In addition, the excitation of the magnetic lens can be changed, and the changes in certain properties of the image are measured in the process. These properties may be a distortion, rotation, a change in magnification, or a displacement, or any other property.

[0033] 4) From the various evaluations of the images, the difference between the axis of the electron beam and the magnetic axis, for example, can then be determined by means of calculation methods and, for example, be minimized iteratively by displacing and / or tilting the pole shoes with respect to each other. Possible characteristics of the generated magnetic field for example are the position and / or the orientation of a magnetic axis of the magnetic lens or the magnetic field generated therewith. The characteristics need not be measured directly, but these characteristics may instead be inferred on the basis of imaging properties, as described above. However, it is also conceivable in principle to directly measure characteristics of the magnetic field generated by means of the magnetic lens.

[0034] The ascertained characteristics of the generated magnetic field are compared with corresponding characteristics of a predefined reference magnetic field, and a deviation between the measured or ascertained characteristics and the corresponding characteristics of the predefined reference magnetic field is determined. For example, a reference magnetic field may be defined by the position and / or orientation of the magnetic axis of the magnetic lens. A further possible characteristic of a generated magnetic field is a round symmetry of the generated magnetic field perpendicular to the axis. In principle, a roundness of the generated magnetic field can be measured as well and can also be adjusted in a targeted manner by means of a mechanical modification of the pole shoe.

[0035] Thereupon the pole shoe is mechanically modified on the basis of the ascertained deviation in order to adapt the magnetic field that can be generated by the magnetic lens. The actual passive alignment is implemented in this method step by means of a mechanical modification to the pole shoe. The mechanical modification allows modification of the magnetic field generated by the magnetic lens overall, so that the characteristics of said magnetic field correspond to those of the predefined reference magnetic field. In order for this mechanical modification to be successful, it is necessary to arrange the pole shoe to be aligned relative to the reference pole shoe in the predefined reference position. Thus, the desired modification of the magnetic field that can be generated by means of the magnetic lens can be realized by means of a targeted mechanical modification of the pole shoe. In this case, the pole shoe is preferably not modified mechanically within the measuring device or a chamber associated with the measuring arrangement. Instead, what is preferably the case is that the pole shoe to be aligned is initially released and then moved into a further chamber for mechanical modification or processing. This protects the measuring device having the reference pole shoe that is sensitive as a matter of principle.

[0036] According to a preferred embodiment of the invention, the method further includes the following step: at least partly annealing the pole shoe in order to homogenize its magnetic properties. A mechanical modification of the pole shoe may in turn cause the occurrence of magnetic inhomogeneities within the pole shoe, for example on account of deformations or stresses. Annealing the pole shoe or at least a part of the pole shoe therefore contributes to the (re- )homogenization of its magnetic properties. Annealing may be implemented in a separate chamber.

[0037] According to a preferred embodiment of the invention, the pole shoe to be aligned and the reference pole shoe are connectable or connected to each other by way of at least one fit. In this context, a fit is understood within the usual definition taken from engineering. A fit therefore refers to the dimensional relationship between two parts that should fit together without reworking. In most cases, these parts have the same contour at the joining point, once as an inner shape, once as an outer shape. Such a fit allows the pole shoe to be aligned to be arranged relative to the reference pole shoe in the predefined reference position.

[0038] According to a preferred embodiment of the invention, the at least one fit has an accuracy of 100 pm, advantageously of 10 pm and most advantageously of 1 pm.

[0039] The provision of more than one fit, for example two, three, four, five or six fits, is possible.

[0040] According to a preferred embodiment of the invention, the mechanical modification of the pole shoe comprises a material-removing method. Examples of such material-removing methods include machining methods, for example turning and / or milling.

[0041] Bending methods also represent alternative methods for the mechanical modification of the pole shoe. According to a preferred embodiment of the invention, the pole shoe has an opening, which is penetrated by charged particles during the operation of the magnetic lens. In this context, the opening of the pole shoe to be aligned has a position and a shape. In this embodiment, the position and / or shape of the opening of the pole shoe is modified when the pole shoe is mechanically modified for the purpose of passively aligning the pole shoe. For example, the centre of the circular opening may be used as the position of the opening in the case of a circular opening. The shape of the opening may also differ from circular, for example be elliptical or an intermediate form between circle and ellipse. In that case, too, it is possible to define a position of this shape, for example by way of the position of the left edge of the opening or, in the case of an ellipse, by the position of one of its foci. A position and / or an orientation (angle) of the magnetic axis of the magnetic lens and / or a round symmetry of the magnetic field can be adjusted by modifying the opening shape and / or opening position of the pole shoe to be aligned.

[0042] According to a preferred embodiment of the invention, the pole shoe to be aligned has a pole shoe joining surface, and the reference pole shoe has a reference pole shoe joining surface. The pole shoe joining surface and the reference pole shoe joining surface correspond to each other. This correspondence may be direct or indirect. In any case, the pole shoe joining surface and the reference pole shoe joining surface correspond to each other in terms of their shape. According to this embodiment variant of the invention, the pole shoe joining surface is modified when the pole shoe is mechanically modified. This creates a new pole shoe joining surface, which in turn corresponds to the reference pole shoe joining surface. Thus, the pole shoe to be aligned and the reference pole shoe fit perfectly to each other, even after the mechanical modification of the pole shoe.

[0043] For example, a tilt between the pole shoe and the reference pole shoe can be adjusted by mechanically modifying the pole shoe joining surface and thereby producing a new pole shoe joining surface. What therefore holds true according to a preferred embodiment of the invention is that in order to adjust a tilt between the pole shoe and the reference pole shoe, the pole shoe joining surface is asymmetrically removed such that this leads to the formation of a new pole shoe joining surface which also corresponds to the reference pole shoe joining surface. For example, an asymmetric removal is an oblique removal of a pole shoe joining surface that was formerly straight or aligned to be straight. By contrast, only the height of the pole shoe would be reduced in the case of a symmetric removal, but this type of removal would otherwise have no influence on the symmetry. According to a further preferred embodiment of the invention, the pole shoe joining surface and the reference pole shoe joining surface have a flange-like form and in particular are screwed to each other. This allows a comprehensibly precise and simple connection between the pole shoe joining surface and the reference pole shoe joining surface.

[0044] According to a further preferred embodiment of the invention, the method furthermore includes the following step: arranging a spacer or distance compensation piece, in particular a spacer ring, between the mechanically modified pole shoe joining surface and the reference pole shoe joining surface. The arrangement of a spacer is an example of the pole shoe joining surface and the reference pole shoe joining surface corresponding only indirectly to each other. The arrangement or use of a spacer may be rendered necessary by virtue of the mechanical modification of the pole shoe being achieved quite predominantly by means of material removal. This allows the length of the pole shoe along its main axis to be reduced, especially if material is repeatedly removed for the purpose of a passive alignment. The spacer may be provided to compensate for this.

[0045] According to a preferred embodiment of the invention, the reference position between the pole shoe to be aligned and the reference pole shoe is defined by means of a reference marking. By preference, this reference marking is visible in the circumferential direction of the magnetic lens. However, a reference position may also be defined differently, for example by means of a notch or by means of one or more aforementioned fits.

[0046] According to a further preferred embodiment of the invention, the reference marking is formed as a stop of a kinematic mount and, during mechanical modification of the pole shoe, the pole shoe is modified in the region of the reference marking, or the region that rests against the stop is modified, such that a or the position of a or the opening of the pole shoe is modified. Ultimately, the mechanical modification of the pole shoe results in a relative displacement of the pole shoe with respect to the reference pole shoe. However, the contact position between the pole shoe and the reference pole shoe is still precisely defined.

[0047] According to a preferred embodiment of the invention, the determination of characteristics of the generated magnetic field in the measuring device includes recording an image of a test sample and subjecting this image to an image evaluation method.

[0048] According to a preferred embodiment of the invention, the determination of characteristics of the generated magnetic field in the measuring device includes recording multiple images of the test sample, each for different excitations of the magnetic lens, and subjecting each image to the image evaluation method, wherein the various images are moreover compared with one another in the image evaluation method.

[0049] According to a further preferred embodiment of the invention, the method furthermore includes the following step: providing a lookup table that links deviations of magnetic fields from a reference magnetic field to measures for the mechanical modification of the pole shoe; wherein the mechanical modification of the pole shoe is carried out on the basis of the lookup table. For example, if referencing is performed in relation to the position and / or the orientation or inclination of the magnetic axis of the magnetic lens, such a lookup table may contain information regarding the measure that, in the ideal case, causes an appropriate correction in the event of a positional deviation and / or inclination deviation. This makes it possible to perform the mechanical modification of the pole shoe in a very targeted manner.

[0050] According to a preferred embodiment of the invention, the generated magnetic field is characterized in relation to a position of its magnetic axis, wherein the position of the magnetic axis is characterized by means of a positional deviation from a reference point and / or by means of a tilt relative to a reference axis of the reference magnetic field.

[0051] According to a further preferred embodiment of the invention, the positional deviation of the magnetic axis and / or the tilt of the magnetic axis is linked to a measure for the mechanical modification of the pole shoe which brings about a displacement of the position of the opening of the pole shoe on the pole shoe. The required nature or implementation of mechanical modification of the pole shoe for correcting for the positional deviation and / or tilt is thus specified exactly in that case.

[0052] According to a preferred embodiment of the invention, the generated magnetic field is characterized in relation to its round symmetry. Such a round symmetry is of great relevance to many applications in the field of particle optics.

[0053] According to a preferred embodiment of the invention, a deviation of the magnetic field from the round symmetry is linked to a measure for material removal in the region of the opening of the pole shoe which brings about a change in the ellipticity of the opening.

[0054] According to a further preferred embodiment of the invention, a tilt of the magnetic axis is linked to a measure for the mechanical modification of the pole shoe which brings about a tilt of the pole shoe relative to the reference pole shoe. For example, this may be the above-described asymmetric removal of the joining surface of the pole shoe. Alternatively, it is also possible to bend a pole shoe joining surface using a bending method.

[0055] The above-described characteristics and their deviations from corresponding characteristics of a predefined reference magnetic field should be understood to be merely exemplary and not an exhaustive list.

[0056] According to a further preferred embodiment of the invention, the method furthermore includes the following step: testing the mechanically modified pole shoe in the test device. Testing the mechanically modified pole shoe in the test device is intended to ensure that the mechanical modification of the pole shoe also has the desired effect. If necessary, further reworking must be carried out. The testing preferably comprises the steps of releasable arrangement, operation or excitation of the magnetic lens in the measuring device, renewed measurement of characteristics of the magnetic field generated by means of the magnetic lens and renewed determination of a deviation of the characteristics of the generated magnetic field from corresponding characteristics of a predefined reference magnetic field.

[0057] According to a preferred embodiment of the invention, the method is carried out repeatedly until a threshold value is undershot when determining the deviation of the characteristics of the generated magnetic field from corresponding characteristics of the predefined reference magnetic field. The magnetic field may be considered to be tolerance aberration-free in that case. The threshold value itself may be ascertained in advance from extensive tolerance calculations.

[0058] On the basis of the method according to the invention, the passively aligned pole shoe can now be used directly in a correspondingly constructed particle beam system; no further mechanical alignment of the pole shoe in the particle beam system itself is required.

[0059] According to a further aspect of the invention, the latter relates to a method for equipping a particle beam system with a magnetic lens, including the following steps: providing a first pole shoe by applying the method as described above in multiple embodiment variants; arranging the first pole shoe in the particle beam system; providing a second pole shoe by applying the method as described above in multiple embodiment variants; and releasably arranging the second pole shoe relative to the first pole shoe in the predefined reference position and thereby assembling the magnetic lens in the particle beam system. The method for equipping a particle beam system with a magnetic lens is based on the idea that the two pole shoes installed therein have each been passively aligned in advance, to be precise with respect to a reference pole shoe or reference standard in each case. In this case, the first pole shoe can be an upper pole shoe, and the second pole shoe can be a lower pole shoe, or vice versa. It is important that in advance of equipping a particle beam system with a reference pole shoe, the respective (first or second) pole shoe to be aligned has been passively pre-aligned.

[0060] In the case of a particle beam system constructed thus and having a magnetic lens assembled as described above, it is easily possible to simply replace one of the pole shoes with only a very short interruption in operation. For example, a damaged pole shoe can be removed and replaced by another pole shoe, which in turn has already been passively aligned in advance in an appropriately equipped measuring device. In this way, a great deal of time can be saved when aligning a particle beam system.

[0061] In principle, the magnetic lens may be any desired magnetic lens. By preference, the magnetic lens is an objective lens. This objective lens may be damaged by external influences, e.g. by contact with a surface in the sample space, or a voltage flashover in the sample space. Specifically, it is the lower pole shoe of the objective lens that needs to be replaced in that case.

[0062] However, the magnetic lens may also be a condenser lens, a field lens, a projection lens or else any other type of magnetic lens.

[0063] Otherwise, reference is made to the explanations given in conjunction with the first aspect of the invention.

[0064] According to a third aspect of the invention, the latter relates to a particle beam system which has been equipped in accordance with the described method for equipping a particle beam system with a magnetic lens. Furthermore, the descriptions already provided in the context of the first aspect of the invention and of the second aspect of the invention apply.

[0065] According to a preferred embodiment of the invention, the particle beam system comprises an element of the following list: a SEM, a TEM, a STEM, a SEM-STEM, a dual particle beam system, a multi-beam particle microscope, a mask repair system, a LEEM, a PEEM. In this context, this list should not be construed as exhaustive. The above-described aspects and embodiments of the invention may be combined with one another in full or in part, provided that this does not result in any technical contradictions.

[0066] As already indicated above, the idea of the invention for passively aligning a pole shoe for a magnetic lens may in principle also be transferred to other functional units of a particle beam system and in particular of a multiple particle beam system. Precise particle-optical orientation of elements of a functional unit may also be necessary for other functional units. Centring tasks for functional units in a particle beam system are particularly common in this context. A passive alignment may replace the previous mechanical alignment, which is based on relative movements within an alignment plane, or even enable an alignment of a functional unit for the first time.

[0067] According to a fourth aspect of the invention, the latter consequently relates to a method for passively aligning a particle-optical element for a functional unit of a particle beam system, including the following steps: providing a reference element with a reference joining surface in a measuring device; providing the particle-optical element with an element joining surface that corresponds to the reference joining surface; releasably arranging the particle-optical element to be aligned relative to the reference element in a predefined reference position and thereby assembling a functional unit for a particle beam system in the measuring device; operating the functional unit in the measuring device; measuring particle-optical characteristics of the functional unit; determining a deviation of the measured particle-optical characteristics of the functional unit from corresponding characteristics of a predefined reference functional unit; and mechanically modifying the particle-optical element by means of a material-removing method on the basis of the ascertained deviation for adapting the functional unit.

[0068] According to a preferred embodiment of the invention, the assembled functional unit comprises exactly two elements, namely the reference element and the particle-optical element to be aligned. However, it is also possible that the functional unit in turn is a constituent part of a larger functional unit. For example, it is possible that a particle-optical element to be aligned passively comprises a first element joining surface, which corresponds to a first reference joining surface, and a second element joining surface, which corresponds to a second reference joining surface. What preferably holds true in this case is that a separate measuring device for testing or measuring the functional unit or partial functional unit is provided in each case for the (partial) functional units.

[0069] According to a preferred embodiment of the invention, the element joining surface is mechanically modified during the mechanical modification of the particle-optical element, whereby a new element joining surface which also corresponds directly or indirectly to the reference joining surface is formed. According to a preferred embodiment of the invention, material of an element joining surface is removed asymmetrically with respect to a main axis of the particle-optical element to be aligned. This allows a tilt between the reference element and the particle-optical element to be aligned to be adjusted in a targeted manner.

[0070] According to a preferred embodiment of the invention, the mechanical modification of the particle-optical element comprises a machining method, in particular turning and / or milling.

[0071] According to a preferred embodiment of the invention, the particle-optical element to be aligned and the reference element are connected to each other by way of at least one fit. This allows the realization of a very precise arrangement of the particle-optical element relative to the reference element.

[0072] According to a preferred embodiment of the invention, the fit has an accuracy of 100 pm, preferably of 10 pm or most preferably of 1 pm.

[0073] According to a preferred embodiment of the invention, the element joining surface and the reference joining surface have a flange-like form and in particular are screwed to each other. This allows a particularly simple and precise arrangement of the particle-optical element and the reference element to each other.

[0074] According to a further preferred embodiment of the invention, the method furthermore includes the following step: arranging a spacer, in particular a spacer ring, between the mechanically modified element joining surface and the reference joining surface. This takes into account the fact that, in practical terms, the mechanical modification of the element joining surface can only be a removal. This is particularly relevant if the method according to the invention is carried out repeatedly and / or iteratively, and a material loss is comparatively large. It may be necessary to provide a spacer in that case. According to a preferred embodiment of the invention, the particle-optical characteristics of the functional unit describe a centring and / or an orientation of an electrostatic field generated by means of the functional unit. In other words, it is possible to describe a position and / or inclination of the electrostatic field. For example, the position and orientation of an electrostatic axis can be described. The latter may be characterized by a position in a specific plane and by an inclination of the axis relative to this plane.

[0075] According to a further preferred embodiment of the invention, the particle-optical characteristics of the functional unit describe a centring and / or an orientation of a magnetic field generated by means of the functional unit. For example, the magnetic axis may be described in terms of position and inclination.

[0076] According to a preferred embodiment of the invention, the functional unit comprises an element from the following list: an electrostatic lens, an electrostatic deflection system, an electrostatic stigmation system, an electrostatic multipole system of higher order, a magnetic lens, a magnetic deflection system, a magnetic stigmation system, a magnetic multipole system of higher order, an aperture arrangement having a plurality of apertures, a Wien filter, a beam splitter. In this context, this list should not be construed as exhaustive.

[0077] What is common to all functional units is the fact that a measurement of particle-optical properties is carried out in the measuring device in which the passive alignment of a particle- optical element for the functional unit of a particle beam system is performed. This is not purely a mechanical measurement. In this respect, the method for passive alignment is not a purely mechanical solution to any (desired) alignment problem. Instead, the passive alignment is closely linked to the function of the functional unit of the particle beam system, and the proper function of a functional unit in the particle beam system is measured. The method for passive alignment of a particle-optical element for a functional unit of a particle beam system is thus a specific method which not only replaces a conventional, active mechanical alignment but may often also be superior over the latter with regard to the achievable result. This is due to the fact that some alignment errors precisely do not emerge on account of manufacturing inaccuracies but are also due to other sources of error that are not measurable or at least not easily measurable from a mechanical point of view, such as inhomogeneities, mechanical stresses, etc. If necessary, the particle-optical element for the functional unit may also be annealed following the passive alignment by means of material removal.

[0078] According to a preferred embodiment of the invention, the method is carried out in cascadelike fashion for a plurality of particle-optical elements, wherein the particle-optical elements from the second particle-optical element onward are in each case assembled in cascade-like fashion to form an augmented new particle-optical element, for which the method is carried out in each case. As a result, it is possible to mount on each other and passively align different particle-optical elements in sequence. The cascade thus starts with a first particle-optical element, which has been passively aligned. The first particle-optical element is followed by a second particle-optical element, which is mounted on and fitted to the first particle-optical element. A third particle-optical element follows this or this overall unit made up of the first and the second particle-optical element, etc. In this context, the particle-optical elements may be of different physical types. In this respect, different structural units of a particle beam system may be successively mounted on each other and fitted together.

[0079] Furthermore, all the statements given in the context of the method for passively aligning a pole shoe for a magnetic lens of a particle beam system also apply figuratively to the described method for passively aligning a particle-optical element for a functional unit of a particle beam system.

[0080] Once again, the described exemplary embodiments and variants according to the fourth aspect of the invention may be combined with one another in full or in part, provided that no technical contradictions arise as a result.

[0081] According to a fifth aspect of the invention, the latter relates to a method for equipping a particle beam system with a functional unit, including the following steps: providing a first particle-optical element of the functional unit by applying the method for passively aligning a particle-optical element for a functional unit of a particle beam system, as described above in multiple embodiment variants; arranging the first particle-optical element in the particle beam system; providing a second particle-optical element by applying the method for passively aligning a particle-optical element for a functional unit of a particle beam system, as described above in multiple embodiment variants; and releasably arranging the second particle-optical element relative to the first particle-optical element in the predefined reference position and thereby assembling the functional unit in the particle beam system.

[0082] Thus, a basic concept of this aspect of the invention, too, is that of already having passively aligned the installable particle-optical elements on the basis of reference elements, rendering the active mechanical alignment in relation to the functional unit superfluous within the particle beam system. A particle beam system can thus be equipped much faster. The same applies to the case where a functional unit or a particle-optical element of a functional unit needs to be replaced. This is also possible very quickly and without long downtimes of the particle beam system.

[0083] According to a sixth aspect of the invention, the latter relates to a particle beam system, wherein the particle beam system has been equipped in accordance with the above-described method for equipping a particle beam system with a functional unit, as described above.

[0084] According to a preferred embodiment of the invention, the particle beam system comprises an element of the following list: a SEM, a TEM, a STEM, a SEM-STEM, a dual particle beam system, a multi-beam particle microscope, a mask repair system, a LEEM, a PEEM. In this context, the aforementioned list should not be construed as exhaustive.

[0085] The above-described aspects and embodiment variants of the invention may be combined with one another in full or in part, provided that this does not result in any technical contradictions.

[0086] The invention will be understood even better with reference to the accompanying figures, in which:

[0087] Fig. 1 : schematically shows a particle beam system in the form of a multi-beam particle microscope;

[0088] Fig. 2: schematically shows aspects of a mechanical alignment of a magnetic lens;

[0089] Fig. 3: schematically shows aspects of a mechanical alignment of a magnetic lens;

[0090] Fig. 4: schematically shows aspects of a mechanical alignment of a magnetic lens;

[0091] Fig. 5: schematically shows aspects of a passive alignment of a magnetic lens;

[0092] Fig. 6: schematically shows aspects of a passive alignment of a magnetic lens;

[0093] Fig. 7: schematically shows a plan view of a passively aligned pole shoe;

[0094] Fig. 8: schematically shows a perspective illustration of joining surfaces of a reference pole shoe and of a pole shoe to be aligned;

[0095] Fig. 9: schematically shows a perspective illustration of joining surfaces of a reference pole shoe and of a pole shoe to be aligned;

[0096] Fig. 10: schematically shows a sectional view of a reference pole shoe and a pole shoe to be aligned with fits;

[0097] Fig. 11 : schematically shows a sectional view of fits of a pole shoe to be aligned with a reference pole shoe;

[0098] Fig. 12: schematically shows a plan view of a reference pole shoe with fits or screw connections; Fig. 13: schematically shows a measuring device for testing pole shoes to be aligned;

[0099] Fig. 14: schematically shows the measuring device from Figure 13 during operation;

[0100] Fig. 15: schematically shows a method for passively aligning a pole shoe for a magnetic lens of a particle beam system;

[0101] Fig. 16: schematically shows a method for equipping a particle beam system with a magnetic lens;

[0102] Fig. 17: schematically shows a method for replacing a pole shoe of a magnetic lens in a particle beam system;

[0103] Fig. 18: schematically shows a method for passively aligning a particle-optical element for a functional unit of a particle beam system; and

[0104] Fig. 19: schematically shows a method for equipping a particle beam system with a functional unit.

[0105] Fig. 1 schematically shows a multiple particle beam system 1 in the form of a multi-beam particle microscope 1. The multi-beam particle microscope 1 comprises a beam-generating apparatus 300 having a particle source, for example an electron source. By means of the beam-generating apparatus 300, charged particles or electrons are generated for example by means of thermal field emission. The emitted charged particles form a divergent particle beam 309, and the latter is collimated by a sequence of condenser lenses 303.1 and 303.2 and incident on a multi-beam particle generator 305 having a multi-aperture arrangement. The multi-beam particle generator 305 comprises multiple multi-aperture plates 304, 306 and a field lens 307. The multi-beam particle generator 305 generates a multiplicity of individual particle beams 3 or individual electron beams 3, which are arranged in a field, which is imaged onto a further field formed by beam spots 5 in the object plane 101. The pitch between centre points of apertures in a multi-aperture plate 306 can be for example 5 pm, 100 pm and 200 pm. The diameters D of the apertures are smaller than the pitch between the centre points of the apertures; examples of the diameters are 0.2 times, 0.4 times and 0.8 times the pitches between the centre points of the apertures.

[0106] The multi-aperture arrangement 305 and the field lens 308 are configured to generate a multiplicity of focal points 323 of primary beams 3 in a grid arrangement on a surface 321 . The surface 321 need not be a plane surface but rather can be a spherically curved surface in order to account for an image field curvature of the subsequent particle-optical system.

[0107] The multi-beam particle microscope 1 furthermore comprises a system of electromagnetic lenses 103 and an objective lens 102, which image the beam foci 323 from the intermediate image surface 321 into the object plane 101 with reduced size. In between, the individual first particle beams 3 pass through the beam splitter 400 and a collective beam deflection system 500, by means of which the multiplicity of individual first particle beams 3 are deflected during operation and the image field is scanned. The individual first particle beams 3 incident in the object plane 101 form for example a substantially regular field, wherein pitches between adjacent incidence locations 5 can be for example 1 pm, 10 pm or 40 pm. The field formed by the incidence locations 5 can have a rectangular or hexagonal symmetry, for example.

[0108] The object 7 to be examined may be of any desired type, for example a semiconductor wafer or a biological sample, and may comprise an arrangement of miniaturized elements or the like. The surface 15 of the object 7 is arranged in the object plane 101 of the objective lens 102. The objective lens 102 may comprise one or more electron-optical lenses. For example, it may be a magnetic objective lens and / or an electrostatic objective lens.

[0109] The primary particles 3 incident on the object 7 generate interaction products, for example secondary electrons, backscattered electrons or primary particles, which have experienced a reversal of movement for other reasons, and these interaction products emanate from the surface of the object 7 or from the first plane 101 or object plane 101 . The interaction products emanating from the surface 15 of the object 7 are shaped by the objective lens 102 to form secondary particle beams 9. In the process, the secondary beams 9 pass through the beam splitter 400 downstream of the objective lens 102 and are supplied to a projection system 200. The projection system 200 comprises an imaging system 205 with projection lenses 206, 208 and 210, a contrast stop 214 and a multi-particle detector 207. Incidence locations 25 of the second individual particle beams 9 on detection regions of the multi-particle detector 207 are located with a regular pitch in a third field. Exemplary values are 10 pm, 100 pm and 200 pm.

[0110] The multi-beam particle microscope 1 furthermore comprises a computer system or control unit or controller 10, which in turn can be embodied integrally or in multipartite fashion and which is designed both to control the individual particle-optical components of the multi-beam particle microscope 1 and to evaluate and analyse the signals obtained by the multi-detector 207 or detection unit.

[0111] The particle-optical functional unit according to the invention which has been passively aligned, for instance a magnetic lens and in particular an objective lens 102, may be integrated into the multiple particle beam system 1 shown in Fig. 1. However, the functional unit may also be integrated into any other particle beam system 1. Further information relating to such multi-beam particle beam systems or multi-beam particle microscopes 1 and component parts used therein, such as, for instance, particle sources, multi-aperture plate and lenses, can be obtained from the international patent applications WO 2005 / 024881 A2, WO 2007 / 028595 A2, WO 2007 / 028596 A1 , WO 2011 / 124352 A1 and WO 2007 / 060017 A2 and the German patent applications DE 102013016 113 A1 and DE 102013 014 976 A1 , the disclosure of which is incorporated in this patent application in full by reference.

[0112] Figure 2 schematically shows aspects of a mechanical alignment of a magnetic lens 700. The magnetic lens 700 comprises an upper pole shoe 701 and a lower pole shoe 702. A winding 703 that is excitable for the purpose of generating a magnetic field is arranged within the magnetic lens 700. During the operation of the magnetic lens 700, a charged particle beam or multiple charged particle beams enter(s) the magnetic lens 700 through the opening 706 in the upper pole shoe 701 and leave(s) said magnetic lens through the opening 707 in the lower pole shoe 702. The charged particles or the charged particle beam(s) pass(es) through the magnetic field of the magnetic lens 700 in the process. At the openings 706, 707, the magnetic field of the magnetic lens 700 emerges from the pole shoes 701 , 702 with a defined form. By way of example, some field lines 708 are plotted in Figure 2a. A section along the sectional plane C is shown in Fig. 2b: Ideally, the magnetic field generated by means of the magnetic lens 700 is round symmetric, as depicted in Figure 2b by way of the equipotential lines 708a. The particle-optical axis Z runs centrally through the magnetic field, and the equipotential lines 708a are arranged in a circle around the particle-optical axis Z.

[0113] The upper pole shoe 701 and the lower pole shoe 702 are movable relative to each other so as to be able to align the magnetic lens 700: In the example shown, the lower pole shoe 702 is displaceable in the x-direction. The same usually also applies to a displacement in the y- direction (not depicted explicitly in Figure 2). A mechanical adjustment element 704 that works against a spring or against an abutment 705 is provided for the mechanical displacement. Overall, the lower pole shoe 702 is thus movable in an alignment plane (xy-plane) that is oriented orthogonal to the particle-optical axis Z. This is the alignment known from the prior art.

[0114] Figure 2 shows the ideal case of an alignment situation: The magnetic lens 700 has been manufactured perfectly and contains no inhomogeneities within grain boundaries within the pole shoes. What holds true in this ideal case is that the particle-optical axis Z corresponds to the geometric axis A of the magnetic lens. Furthermore, the upper pole shoe 701 and the lower pole shoe 702 are exactly oriented with respect to each other, i.e. the opening 706 of the upper pole shoe and the opening 707 of the lower pole shoe 702 are also located exactly above each other.

[0115] By contrast, Figure 3 shows a possible real case: Although the pole shoe 702 has been produced exactly within the specified manufacturing accuracies, two inhomogeneities 709, for example, are present within the pole shoe 702 and influence the magnetic flux in the pole shoe 702. This influence is depicted schematically in Figure 3. This may result in a slight modification to the magnetic field lines 708 shown in Figure 3a. For example, the axis Z of the magnetic field that can be generated by means of the magnetic lens 700 might not correspond with the geometric axis A of the magnetic lens 700.

[0116] The magnetic lens 700 depicted in Figure 3 therefore requires a further alignment: This is illustrated schematically in Figure 4. Over the course of the alignment, the lower pole shoe 702 was mechanically displaced by the amount d in the x-direction, to the left in the example shown. The spring 705 has been compressed slightly by means of the mechanical adjustment element 704, and the position of the lower pole shoe 702 is subsequently fixed (not shown). The tilt of the particle-optical axis Z has been corrected by the mechanical alignment on account of the relative displacement of the upper pole shoe 701 and the lower pole shoe 702; the particle- optical axis Z or the axis of the magnetic field now runs exactly vertically or in the z-direction. By contrast, the geometric axis A is inclined with respect to the z-direction. However, it is not the geometric axis A but the orientation of the particle-optical axis Z that is decisive for an alignment.

[0117] However, the above-described active mechanical alignment is relatively time-consuming. The alignment of a magnetic lens 700 that might be installed in a particle beam system 1 , and in a multi-beam particle microscope in particular, is time-consuming. Therefore, a replacement of a pole shoe of the magnetic lens 700 should be avoided where possible, or the alignment time should be kept short, if this magnetic lens 700 has been installed in a particle beam system. This can be achieved by the passive alignment according to the present invention:

[0118] Figures 5 and 6 show the principle of passive alignment according to the invention for a magnetic lens 700: Unlike in the conventional mechanical alignment described in conjunction with Figures 2 to 4, the two pole shoes 720, 721 of the magnetic lens 700 are releasably connected to each other in a predefined reference position. A relevant connection element 722 is depicted schematically in Figure 5. Moreover, according to the invention, work is performed with a reference standard or a reference pole shoe 720. This reference pole shoe 720 has a predefined minimum magnetic homogeneity. In other words, the reference pole shoe 720 has been produced to the greatest possible perfection and, for example, has been additionally analysed. The pole shoe 720 thus has very small inhomogeneities, which would deform the magnetic flux emanating from the pole shoe 720 with minimal errors.

[0119] By contrast, the lower pole shoe 721 is a conventional pole shoe that has been produced within manufacturing tolerances by means of the usual manufacturing methods but nevertheless has the above-described inhomogeneities 709, and this disadvantageously influences the emergence of the magnetic flux from the opening 707 of the pole shoe 721.

[0120] The position and orientation of the magnetic axis Z of the magnetic lens 700 can be ascertained on the basis of measurements, for example within a measuring device 900. The magnetic axis Z is tilted relative to the geometric axis A, or the magnetic axis Z is not oriented in the z- di recti on.

[0121] The pole shoe 721 to be aligned can be mechanically modified on the basis of an analysis of characteristics of the magnetic field generated by means of the magnetic lens 700 in a measuring device 900. In the example shown, the region 723 of the pole shoe 721 to be aligned in the region of the pole shoe opening 707 was modified; material was removed from there in the example shown, for example by turning and / or milling. A reassembly of the reference pole shoe 720 with the mechanically modified pole shoe 721 and subsequent operation of the magnetic lens 700, and a measurement and analysis of characteristics of the generated magnetic field, shows a correspondence of the particle-optical axis Z with the geometric axis A.

[0122] A mechanical modification of the pole shoe 721 to be aligned may be performed firstly in the region of the pole shoe opening 707 and secondly in the region of the joining surface 731 with the reference pole shoe 720.

[0123] Figure 7 schematically shows several examples of a passively aligned pole shoe 721 in a top view of the pole shoe 721 : Specifically, Figure 7a shows an initial situation, wherein the opening 707 is arranged concentrically within the exterior 724 of the pole shoe 721. Following a mechanical modification, the pole shoe opening 707 of Figure 7b is enlarged on the one hand and displaced laterally in the x-direction on the other hand. The xy-coordinate system shown in Figure 7 serves here to better elucidate these circumstances. In Figure 7c, the opening 707 is still arranged concentrically within the exterior 724 of the pole shoe 721 , but the opening 707 has been enlarged in comparison with the situation shown in Figure 7a. Finally, the shape of the opening 707 is no longer circular but elliptical in Figure 7d. Furthermore, this elliptical opening 707 could still be displaced within the xy-plane such that the centre of the ellipse would no longer lie on the coordinate origin of the xy-coordinate system.

[0124] Figure 7 thus shows that there are many options for mechanically modifying the pole shoe 721 to be aligned, which serve to position and orient the magnetic field of the magnetic lens 700 (angle or tilt correction) that was generated by the interplay between the reference pole shoe 720 and the pole shoe 721 to be aligned.

[0125] Figures 8 and 9 schematically illustrate a further option for mechanically modifying, over the course of passive alignment according to the invention, the pole shoe 721 to be aligned. Figure 8 schematically shows the reference pole shoe 720 and its pole shoe opening 706 and the pole shoe 721 to be aligned and its pole shoe opening 707. In Figure 8, the two pole shoes 720, 721 are depicted in a manner spaced apart from each other. The surface 731 of the lower pole shoe 721 that runs around the pole shoe opening 707 on the outside is visible in the perspective illustration. This surface 731 represents the pole shoe joining surface 731 , which corresponds to the corresponding reference pole shoe joining surface 730 of the reference pole shoe 720. In the example shown, the reference pole shoe joining surface 730 thus corresponds to the underside of the reference pole shoe 720; only the edge region of the reference pole shoe joining surface 730 can be identified in Figure 8. The pole shoe opening 707 and the pole shoe joining surface 731 are spaced apart from each other, and so a mechanical modification of the pole shoe joining surface 731 has no influence on the pole shoe opening 707 or its magnetic homogeneity; thus, annealing of the pole shoe 721 after mechanical processing may be omitted.

[0126] The two pole shoes 721 , 720 are joined at the pole shoe joining surface 731 and the reference pole shoe joining surface 730. This joining or interconnecting is also indicated in Figure 8 by the two arrows pointing upwards. The reference pole shoe 720 and the pole shoe 721 to be aligned are releasably arranged against each other in a predefined reference position. This means that the position and orientation of the reference pole shoe 720 and the pole shoe 721 to be aligned are fixed. For referencing purposes, a reference marking 732 is shown in Figure 8, but this should be understood to be merely exemplary.

[0127] According to an exemplary embodiment of the invention, the pole shoe 721 to be aligned is now modified mechanically by means of a mechanical modification of the pole shoe joining surface 731. Removal of the latter may be performed asymmetrically, especially in relation to the geometric axis A. A new pole shoe joining surface 731 is created, which is inclined relative to the original pole shoe joining surface 731 and hence also relative to the corresponding reference pole shoe joining surface 730. This is depicted schematically and with much exaggeration in Figure 9. The different lengths of the arrows in Figure 9 are intended to additionally illustrate the slight tilting of the pole shoe 721 to be aligned, when the latter is joined to the reference pole shoe 720. Naturally, this tilt of the pole shoe 721 to be aligned has an influence on the magnetic field that can be formed by an assembled magnetic lens 700, comprising the reference pole shoe 720 and the pole shoe 721 to be aligned, during the operation of said magnetic lens. The magnetic axis Z may be tilted, or a previously existing tilting may be corrected.

[0128] In Figure 9, the reference marking 732 is arranged at the highest point of the joining surface 731. However, this should be understood to be merely exemplary. Self-evidently, the referencing 732 may also be provided at another location on the joining surface 731 . Moreover, it is possible to provide a reference marking 732 not on the joining surface 731 itself but laterally or on a side wall of the pole shoe 721 to be aligned visible from the outside. Naturally, a corresponding reference marking is also provided on the reference pole shoe 720 in that case.

[0129] For the method according to the invention for passively aligning a pole shoe 721 for a magnetic lens 700, it is important that the pole shoe 721 to be aligned can be releasably arranged relative to the reference pole shoe 720 in a predefined reference position. Although working with a reference marking 732 is possible in principle, working with a reference marking 732 does not yet replace the actual arrangement process or fastening process for the reference pole shoe 720 on the pole shoe 721 to be aligned. A very good and practical solution for the releasable arrangement on the reference pole shoe 720 of the pole shoe 721 to be aligned is depicted schematically in Figure 10: According to this example, a fit 733 can be used firstly for the arrangement and fixation and secondly for the definition of the reference position. The term fit 733 is used in the context of this patent application in the sense that is customary in engineering. A fit denotes the dimensional relationship between two parts that should fit together with a defined residual tolerance without rework. In most cases, these parts have the same contour at the joining point, once as an inner shape and once as an outer shape.

[0130] Figure 10 depicts a sectional view of the reference pole shoe 720, which has a flange-like embodiment in the region of its joining surface 730 or a flange 734. A fit is provided at the underside of the joining surface 730, or the positive shape 733a of the fit 733 is formed there.

[0131] In the example shown, the pole shoe 721 to be aligned is formed as a lower pole shoe again; it is not flange-like in the example shown, but this could be the case. The negative shape 733b of the fit 733 is formed in the region of the surface or joining surface 731. The positive shape 733a fits very precisely into the negative shape 733b. This is also depicted in Figure 10 by the two arrows between the pole shoes 720, 721. By using the fit or fits 733, the reference pole shoe 720 can be arranged very exactly with respect to the pole shoe 721 to be aligned. The play that the positive shape 733a has when sliding into the negative shape 733b is very small. For example, this may be a fit with an accuracy of 100 pm, preferably of 10 pm or most preferably of 1 pm.

[0132] After using the two fits 733 to join the reference pole shoe 720 and the pole shoe 721 to be aligned, the geometrically fitting connection created thus is fixed by means of a screw connection. This is indicated in Figure 10 by the two screws 735 and the two nuts 736.

[0133] If a joining surface 731 of the pole shoe 721 to be aligned is now mechanically modified, for example if material is removed, then this has an influence on the fits 733. However, the passive alignment of a magnetic lens 700 is a precision alignment, and so the functionality of the fits 733 is not impaired by this: This is depicted schematically and by way of example in Figure 11.

[0134] Figure 11a depicts the initial situation, in which the axes of symmetry S of the positive shape 733a and of the negative shape 733b of the fit 733 correspond to each other. It is also evident from Figure 11a that there is some play available in the region of the side walls 739a, 739b and in the region of the base 738a, 738b. The magnitude of this play emerges from the tolerance of the fit 733.

[0135] If there is only a slight tilt as a result of bevelling the joining surface 731 of the pole shoe 721 to be aligned, then the positive shape 733a can still slide into the negative shape 733b. This is ensured by the appropriate tolerance provided. However, it is naturally also evident that the inner side wall 739a is tilted vis-a-vis the outer side wall 739b. Moreover, the base 738a is tilted vis-a-vis the base 738b of the fit 733. However, the contact faces of the fit 733 that are assigned to the reference pole shoe 720 still rest on the joining surface 731 in flat or planar fashion - even after the asymmetric, mechanical modification of joining surface 731 . By way of a corresponding tightening of the screw 735, the fit can be fixed in its position, and the angle between firstly the axis of symmetry of the positive shape 733a and secondly the axis of symmetry 733b of the negative shape can also be fixed in this way.

[0136] The tilt angle provided by means of the described asymmetric mechanical modification of the joining surface 731 is typically located in the range of 0.01 mrad to 5 mrad. Figure 12 schematically shows a plan view of a reference pole shoe 720 with fits or screw connections 735: In Figure 12a, a total of four fits with associated screw connections 735 are arranged equidistantly from one another. In Figure 12b, by contrast, a total of eight fits, each with an associated screw connection 735, are arranged equidistantly from one another. Figure 12 thus shows a plan view of the flange 734. The top side of the reference pole shoe 721 is also plotted in Figure 12 in each case, just like the upper pole shoe opening 706. Here, the number and arrangement of the fits or screw connections 735 in Figure 12 should be understood to be merely exemplary; the equidistant arrangement should also be interpreted as merely exemplary.

[0137] Figure 13 schematically shows a measuring device 900 for testing pole shoes 721 to be aligned. For example, the measuring device 900 may take the form of a measuring stand. In the example shown, it comprises a particle source 901 for emitting charged particles, for example electrons. Moreover, in the example shown, the measuring device 900 comprises a particle optics unit 902, which is depicted only schematically. This particle optics unit 902 may comprise one or more components and, in particular, one or more lenses, deflectors and / or stigmators. The beam preparation of one or more charged particle beams is important for the functional test of the magnetic lens 700, which is assembled from the reference pole shoe 720 and the pole shoe 721 to be aligned. In addition to the beam-generating and beam-preparing unit 901 , 902, the measuring device 900 further comprises the reference pole shoe 720, which has already been described in detail in conjunction with the preceding figures. In the example shown, the reference pole shoe 720 once again is an upper pole shoe, which also comprises the winding 703. However, the reference pole shoe 720 could also be a lower pole shoe. In this respect, the illustration as lower pole shoe should be understood to be merely exemplary.

[0138] In Figure 13, a sample stage 903 is arranged below the reference pole shoe 720 in the example shown. Said sample stage might be adjustable in one or more spatial directions but need not be adjustable. A test sample 904 is arranged on the sample stage 903. The nature of the sample will be selected appropriately by the competent person skilled in the art. In the example shown, a detection device 905 is depicted schematically above the test sample 904. This detection device 905 may have a different configuration, for example as a secondary electron detector of different design. Furthermore, a controller 906 is provided in the example according to Figure 13. In the example shown, the controller 906 serves both to control the measuring device 900 itself and to evaluate the data generated with the measuring device 900. To this end, the controller 906 for example may be connected to a monitor, an input unit and a computer or else comprise these. According to a preferred embodiment of the invention, the measuring device 900 comprises everything required in terms of both hardware and software for testing a pole shoe to be aligned.

[0139] Figure 14 shows the measuring device 900 depicted in Figure 13 during operation: In the measuring device 900 or in the measuring stand, a pole shoe 721 to be aligned is releasably arranged on the reference pole shoe 720 in a predefined reference position. As a result, the functional unit - the magnetic lens 700 - is assembled. The predefined reference position is once again illustrated only schematically in Figure 14 by way of the connection element 722. For example, the connection element 722 might be the fit or fits 733 that were described in conjunction with Figures 10 and 11. However, the connection element 722 might also be realized differently.

[0140] During the operation of the measuring device 900, particle radiation is generated by means of the particle source 901 and prepared by the particle optics unit 902 for the actual functional test of the magnetic lens 400. A particle beam 907 that is focused on the test sample 904 by means of the magnetic lens 700 is shown schematically in Figure 14. As a result, secondary particles and secondary electrons in particular are emitted by the test sample 904 in the example shown and are schematically denoted by the reference sign 908 in Figure 14. These secondary particles 908 can be detected by the detection system 905. The detected particle- optical image overall may be processed, evaluated and / or displayed by means of the controller 906.

[0141] It is self-evidently possible to test and qualify the magnetic lens 700 by means of an individual beam 907. However, it is also possible to qualify a magnetic lens 700 by means of a multibeam particle beam system. In that case, a multiplicity of individual particle beams are generated by the beam-generating device 901 , 902 and prepared in a suitable manner for the subsequent qualification of the magnetic lens 700.

[0142] For example, the wobble method, already known per se, may be used for the characterization of the magnetic field generated by the magnetic lens 700. To this end, the excitation of the magnetic lens 700 or of its coil 703 is varied, whereby, ideally, the generated particle-optical image varies only in terms of its sharpness and not in terms of its position. A deviation from the perfect positioning and / or inclination can be ascertained, and the pole shoe 721 to be aligned may be mechanically modified on the basis thereof.

[0143] The measuring devices 900 shown schematically in Figures 13 and 14 should be understood to be merely exemplary for the invention. In principle, the measuring devices 900 may also be constructed differently. What is important is that the functionality of the magnetic lens 700 can be suitably tested or analysed and evaluated in the measuring device 900 in order to ascertain the required mechanical modification for the pole shoe 721 to be aligned, so that the pole shoe 721 to be aligned is pre-qualified with the required accuracy in this manner.

[0144] It is also possible to provide a corresponding measuring device 900 for other functional units. For example, such functional units may comprise elements of the following list: an electrostatic lens, an electrostatic deflection system, an electrostatic stigmation system, an electrostatic multipole system of higher order, a magnetic lens, a magnetic deflection system, a magnetic stigmation system, a magnetic multipole of higher order, an aperture arrangement having a plurality of apertures, a Wien filter, a beam splitter.

[0145] In all functional units, particle-optical characteristics of the functional unit are determined in a corresponding measuring device; particle-optical characteristics refer to measurements of electrostatic and / or magnetic fields. It is not a matter of purely a mechanical precision measurement or a pure position measurement of mechanical parts.

[0146] Fig. 15 schematically shows a method for passively aligning a pole shoe 721 for a magnetic lens 700 of a particle beam system 1 . In a first method step S1 , a reference pole shoe 720 with a predefined magnetic minimum homogeneity is provided in a measuring device 900. This reference pole shoe 720 is a pole shoe that meets all requirements for quality and grade and has been manufactured with special care and precision. With regard to the reference pole shoe 720, it is important that the suitability of the latter as a reference standard has been ensured once, for example by testing.

[0147] In a second method step S2, the pole shoe 721 to be aligned is releasably arranged relative to the reference pole shoe 720 in a predefined reference position within the measuring device 900. A magnetic lens 700 is thus assembled in the measuring device 900. For example, the reference position could relate to a pair of reference markings 732 and / or the provision of a fit 733 or the provision of multiple fits 733. However, the predefined reference position may also be provided or implemented constructively in other ways.

[0148] In a method step S3, the assembled magnetic lens 700 is excited in the measuring device 900. For example, the magnetic lens 400 may be excited in accordance with the known wobble method, in which the strength of the excitation of the magnetic lens 700 is varied. The characteristics of the magnetic field generated by means of the magnetic lens 700 are measured in a further method step S4. This measurement may comprise the recording of a particle-optical image and the evaluation of said particle-optical image. In the aforementioned wobble method, for example, a position of a beam spot or focus spot can be observed during a varying excitation of the magnetic lens 400, whereby conclusions can be drawn about the position and / or orientation of the magnetic axis of the magnetic field generated by means of the magnetic lens 700. In addition to that or in an alternative, a round symmetry of the generated magnetic field may be measured.

[0149] In a further method step S5, a deviation of the characteristics of the generated magnetic field from corresponding characteristics of a predefined reference magnetic field is determined. In this method step, the actual state is compared with the target state. After determining the deviation of the characteristics of the generated magnetic field from corresponding characteristics of the predefined reference magnetic field, it is possible to establish whether the deviation, if present, falls below a threshold value. Should this be the case, the method ends with the final method step S8. However, if the deviation is present and exceeds the threshold value, the method is continued:

[0150] In method step S6, the pole shoe 721 to be aligned is mechanically modified on the basis of the ascertained deviation in order to adapt the magnetic field that can be generated by the magnetic lens 400. This method step corresponds to the passive alignment in the narrower sense. In this case, the mechanical modification of the pole shoe 721 to be aligned is carried out in a targeted manner, i.e. the type of required modification of the pole shoe can be inferred from the deviation ascertained in step S5. According to a preferred embodiment of the invention, the mechanical modification of the pole shoe 721 to be aligned comprises a materialremoving method, for example a machining method such as turning and / or milling. According to an alternative embodiment variant of the invention, a bending method can be used for mechanical modification. However, a material-removing method is preferred because this generates fewer stresses that can influence the properties of the magnetic material or of the generated magnetic flux in the pole shoe material, at least in connection with magnetic lenses 700 as functional units.

[0151] The specific mechanical modification of the pole shoe 721 to be aligned is carried out on the basis of the determined characteristics or on the basis of the deviation of the characteristics of the generated magnetic field from corresponding characteristics of the predefined reference magnetic field: For example, it is possible that the pole shoe to be aligned is modified in the region of the pole shoe opening. In addition to that or in an alternative, it is possible that a pole shoe joining surface that corresponds to a reference pole shoe joining surface of the reference pole shoe 720 is mechanically modified during the mechanical modification of the pole shoe. For example, a position and / or a shape of the pole shoe opening 707 can be modified in a targeted manner in the case of mechanical modifications to the pole shoe 721 in the region of the pole shoe opening 707. For example, specific measures for the mechanical modification may be taken from a lookup table, which links deviations of characteristics of the measured magnetic field from characteristics of a reference magnetic field with a concrete measure for the mechanical modification of the pole shoe 721. For example, the magnetic field generated in the measuring device 900 may be characterized in relation to the position and orientation of its magnetic axis Z, wherein the position of the magnetic axis Z is characterized by means of a positional deviation from a reference point and wherein the orientation is characterized by means of a tilt relative to a reference axis. For example, the positional deviation of the magnetic axis and / or the tilt of the magnetic axis Z can be linked specifically to a measure for the mechanical modification of the pole shoe which brings about a displacement of the position of the opening 707 of the pole shoe 721 on the pole shoe 721. In addition to that or in an alternative, the generated magnetic field may be characterized in relation to its round symmetry. In that case, it is for example possible that a deviation of the magnetic field from the round symmetry is linked in the lookup table to a measure for material removal in the region of the opening 707 of the pole shoe 721 to be aligned which brings about a change in the ellipticity of the opening 707. For example, an opening 707 that was originally round may obtain an elliptical embodiment.

[0152] In addition to that or in an alternative, it is possible that the pole shoe joining surface 731 that corresponds to the reference pole shoe joining surface is mechanically modified on the basis of the deviation ascertained in step S5 during the mechanical modification of the pole shoe 721 to be aligned. For example, in order to adjust a tilt between the pole shoe 721 and the reference pole shoe 720, the pole shoe joining surface may be asymmetrically removed such that this leads to the formation of a new pole shoe joining surface 731 which also corresponds to the reference pole shoe joining surface 730. If quite significant amounts of material are removed at the pole shoe joining surface, it may be the case that, in order to compensate for the material loss, a spacer, in particular a spacer ring, is required between the mechanically modified pole shoe joining surface 731 and the reference pole shoe joining surface 730 in the case of a renewed releasable assembly of the magnetic lens 700 in the measuring device 900.

[0153] A mechanical modification of the pole shoe 721 to be aligned, for example by means of turning and / or milling, causes forces to act on the pole shoe to be aligned, and stresses may occur. For this reason, it is advantageous that the pole shoe 721 is annealed in an optional method step S7 in order to (re-)homogenize its magnetic properties. This annealing of the pole shoe 721 may occur in full or in part. Annealing should be performed at least in the regions of the pole shoe 721 where the mechanical modifications have been made.

[0154] Method steps S2 to S5 are repeated after optional method step S7. This repetition corresponds to a test of the mechanically modified pole shoe 721 in the test device 900. It is possible that the test of the mechanically modified pole shoe 721 in the measuring device 900 already has a positive result after one iteration, i.e. the performed mechanical modifications have thus already been sufficient to reduce deviations of the generated magnetic field from corresponding characteristics of the predefined reference magnetic field to below a threshold value. In this case, the method ends in method step S8. Alternatively, a further iteration may be performed, i.e. method steps S6 and S7 are performed again. In the process, the mechanical modifications made in method step S6 may be the same as in the first iteration, but it is also possible that the mechanical modifications undertaken are different. The pole shoe 721 to be aligned may thus be mechanically modified elsewhere and / or in another way.

[0155] The great advantage of the described method for passive alignment of a pole shoe 721 for a magnetic lens 700 of a particle beam system 1 is the fact that a pole shoe 721 mechanically passively aligned in this manner is immediately ready for use in a corresponding particle beam system 1 , assuming an appropriately equipped particle beam system 1. A time-consuming mechanical active alignment in the particle beam system 1 is therefore no longer necessary. This saves time and costs.

[0156] Fig. 16 schematically shows a method for equipping a particle beam system 1 with a magnetic lens 700. In an initial method step S100, a first pole shoe is provided by applying the method for passively aligning a pole shoe for a magnetic lens of a particle beam system 1 , as described in multiple configurations above. This first pole shoe is therefore mechanically passively aligned in an appropriate manner.

[0157] The first pole shoe is arranged in the particle beam system 1 , which should be equipped, in a further method step S101.

[0158] In a further method step S102, a second pole shoe is provided by applying the method for passively aligning a pole shoe for a magnetic lens 700 of a particle beam system 1 , as described in multiple embodiment variants above. This second pole shoe is therefore also mechanically passively aligned. In a further method step S103, the second pole shoe is releasably arranged relative to the first pole shoe in the predefined reference position and the magnetic lens 700 in the particle beam system 1 is thereby assembled. Both the first pole shoe and the second pole shoe have undergone a respective passive mechanical alignment using an appropriate reference pole shoe. Naturally, the first pole shoe was associated with a different reference pole shoe to the second reference pole shoe. The first pole shoe can for example be an upper pole shoe, and the second pole shoe can for example be a lower pole shoe. However, it is possible that the first pole shoe is a lower pole shoe, and the second pole shoe is an upper pole shoe. In this case, each pole shoe was passively aligned with an associated reference pole shoe. It is already possible to resort to the first reference pole shoe during the production of a second reference pole shoe. Nevertheless, attempts will be made to ensure that the second reference pole shoe really meets the predefined minimum requirements in respect of magnetic homogeneity as far as possible. A second reference pole shoe may therefore also be subjected to further tests and examinations, for example by means of X-ray analysis. This is important in order to rule out error propagation as far as possible for the pole shoes 721 to be aligned.

[0159] In principle, the magnetic lens 700 may be any desired magnetic lens. However, it is an objective lens according to a preferred embodiment of the invention. Objective lenses are often subject to special requirements in particle beam systems: The objective lens is the lens with the greatest refractive power, which is why alignment errors of the magnetic lens may have a particularly detrimental effect on the overall system. Moreover, a high voltage of several kV, for example of more than 25 kV, is applied to a lower pole shoe of the objective lens 102 in some particle beam systems, for example in a multi-beam particle microscope 1. Therefore, electric flashovers may occur during the operation of such a multi-beam particle microscope 1 , and these may possibly damage a lower pole shoe of the objective lens 102. The latter would have to be replaced in that case. Moreover, a lower pole shoe of an objective lens 101 might also experience mechanical damage on account of its proximity to a sample 7, which can be positioned on a movable sample stage 600, and this also necessitates a replacement.

[0160] Alternatively, it is naturally also possible that the magnetic lens 700 in the particle beam system represents a condenser lens, a field lens, a projection lens, etc. Moreover, it is naturally possible to equip a particle beam system 1 with a plurality of magnetic lenses 700, in particular different magnetic lenses, in the manner described.

[0161] The particle beam system may be of any desired type, in principle. By preference, the particle beam system 1 comprises an element of the following list: a SEM, a TEM, a STEM, a SEM- STEM, a dual particle beam system, a multi-beam particle microscope, a mask repair system, a LEEM, a PEEM. In this context, this list should not be construed as exhaustive.

[0162] Fig. 17 schematically shows a method for replacing a pole shoe 721 of a magnetic lens 700 in a particle beam system 1. In this method, a particle beam system 1 has been equipped in advance in accordance with the method schematically illustrated in Fig. 16. In a further method step S104, the pole shoe 721 to be replaced is released from its associated pole shoe within the particle beam system 1. The releasability of the pole shoe 721 has already been ensured in principle by the method according to the invention for passively aligning a pole shoe for a magnetic lens 700 of a particle beam system 1. The pole shoe 721 to be replaced can therefore be removed in a very simple manner.

[0163] In a further method step S105, a replacement pole shoe 721a is once again provided by applying the method according to the invention for passively aligning a pole shoe for a magnetic lens 700 of a particle beam system 1. Once again, this replacement pole shoe is therefore mechanically passively aligned.

[0164] In a further method step S106, the replacement pole shoe is releasably arranged relative to the pole shoe that remains within the particle beam system 1 in the predefined reference position. This reassembles the magnetic lens 700 in the particle beam system 1. A separate active mechanical alignment is not necessary here, and this saves valuable time when replacing a pole shoe.

[0165] In principle, the methods described in Figures 15 to 17 may be transferred to other functional units of a particle beam system 1 ; the assembled functional unit need not be a magnetic lens 700. Accordingly, Fig. 18 schematically shows a method for passively aligning a particle-optical element for a functional unit of a particle beam system 1 :

[0166] In an initial method step S200, a reference element with a reference joining surface is provided in a measuring device. Moreover, in a method step S201 , the particle-optical element that should be passively aligned is provided with an element joining surface that corresponds to the reference joining surface.

[0167] In a method step S202, the particle-optical element to be aligned is releasably arranged relative to the reference element in a predefined reference position. As a result, the functional unit for the particle beam system 1 is assembled in the measuring device. The functional unit is operated in the measuring device in method step S203. Preferably, this is an operation of the functional unit in the manner in which the functional unit should also be operated in the particle beam system 1. However, it is also possible to modify the operation of the functional unit appropriately for as long as it is possible to draw conclusions about the alignment state or characteristics of the functional unit from the operation of the functional unit in the measuring device.

[0168] Particle-optical characteristics of the functional unit are measured in method step S204. For example, the particle-optical characteristics of the functional unit may describe a centring and / or an orientation of an electrostatic field generated by means of the functional unit. In addition to that or in an alternative, the particle-optical characteristics of the functional unit may describe a centring and / or an orientation of a magnetic field generated by means of the functional unit.

[0169] A deviation of measured particle-optical characteristics of the functional unit from corresponding characteristics of a predefined reference functional unit is determined in step S205. The method ends in step S208 if the ascertained deviation is less than a predefined threshold value.

[0170] Otherwise - and this is the rule, at least in the first implementation of the method described in Fig. 18 -the particle-optical element is mechanically modified by means of a material-removing method in method step S206, on the basis of the ascertained deviation for adapting the functional unit. For example, it is possible here that the element joining surface is mechanically modified, whereby a new element joining surface which also corresponds to the reference joining surface is formed. For example, the mechanical modification may comprise a machining method, in particular turning and / or milling. However, it is also possible that the element joining surface remains mechanically unmodified, but a different region or a different location of the particle-optical element, which together with the reference element forms the functional unit, is modified mechanically and in particular by means of a material-removing method on the basis of the deviation ascertained in step S205.

[0171] In order to adjust a tilt between the particle-optical element to be passively aligned and the reference element, it is possible according to one example for the element joining surface to be asymmetrically removed such that this leads to the formation of a new element joining surface which also corresponds to the reference element joining surface. A spacer, in particular a spacer ring, is arranged between the mechanically modified element joining surface and the reference joining surface in an optional method step S207.

[0172] Subsequently, method steps S202 to S205 are repeated, and this corresponds to a test of the mechanically modified element joining surface. In the event of a successful test, for example when the threshold value of the ascertained deviation is undershot as discussed previously, the method ends in step S208. Otherwise, the method may be repeated one or more times. In this case, the mechanical modification in method step S206 may be implemented in accordance with the same or a different mechanical method, and / or the mechanical modification may be performed at a different position or at different positions of the particle- optical element to be aligned.

[0173] Before the method described in Fig. 18, the particle-optical element and the reference element can be interconnected by means of a fit or by means of multiple fits. For example, the fit in this case has an accuracy of 100 pm, preferably of 10 pm or most preferably of 1 pm.

[0174] Moreover, it is possible that the element joining surface and / or the reference joining surface have a flange-like form and in particular are screwed to each other. However, also other releasable arrangements in a predefined reference position are in principle possible.

[0175] The method described in Fig. 18 develops particular strengths if the particle-optical characteristics of the functional unit describe a centring and / or an orientation of an electrostatic field generated by means of the functional unit. A corresponding statement applies when the particle-optical characteristics of the functional unit describe a centring and / or an orientation of a magnetic field generated by means of the functional unit.

[0176] In this case, the functional unit of the particle beam system may comprise an element from the following list: an electrostatic lens, an electrostatic deflection system, an electrostatic stigmation system, an electrostatic multipole system of higher order, a magnetic lens, a magnetic deflection system, a magnetic stigmation system, a magnetic stigmation system of higher order, an aperture arrangement having a plurality of apertures, a Wien filter, a beam splitter. In this context, this list should not be construed as exhaustive.

[0177] Optionally, the particle-optical element to be aligned may be annealed after each mechanical modification to the element joining surface. According to a preferred embodiment of the invention, the method according to Fig. 18 is carried out in cascade-like fashion for a plurality of particle-optical elements, wherein the particle-optical elements from the second particle-optical element onward are in each case assembled in cascade-like fashion to form an augmented new particle-optical element, for which the method is carried out in each case. As a result, it is possible to mount on each other and passively align different particle-optical elements in sequence. The cascade thus starts with a first particle-optical element, which has been passively aligned. The first particle-optical element is followed by a second particle-optical element, which is mounted on and fitted to the first particle-optical element. A third particle-optical element follows this or this overall unit made up of the first and the second particle-optical element, etc. In this context, the particle- optical elements may be of different physical types. In this respect, different structural units of a particle beam system may be successively mounted on each other and fitted together.

[0178] Fig. 19 schematically shows a method for equipping a particle beam system 1 with a functional unit. A first particle-optical element of the functional unit is initially provided in a method step S300 by applying the method described in connection with Fig. 18.

[0179] In a method step S301 , the provided first particle-optical element is arranged in the particle beam system 1.

[0180] Accordingly, a second particle-optical element is provided in method step S302 by applying the method according to Fig. 17.

[0181] In method step S303, the second particle-optical element is releasably arranged relative to the first particle-optical element in the reference position already predefined by the method according to Fig. 17, and hence the functional unit is assembled in the particle beam system 1.

[0182] Thus, in the method shown in Fig. 19, a particle-optical element of the functional unit is also provided in each case with recourse to a reference element. As a result, the particle-optical elements are already passively aligned and can be assembled to form the functional unit in the particle beam system 1 both immediately and in time-saving fashion.

[0183] A replacement of the first particle-optical element and / or the second particle-optical element in the particle beam system is also correspondingly easy. Once again, use can be made of a passively aligned replacement element, which has been passively aligned in a corresponding measuring device. The particle beam system may be of any desired type, in principle. By preference, it comprises an element of the following list: a SEM, a TEM, a STEM, a SEM-STEM, a dual particle beam system, a multi-beam particle microscope, a mask repair system, a LEEM, a PEEM. In this context, this list should not be construed as exhaustive.

[0184] As a result of the invention, it is possible to avoid a time-consuming active mechanical alignment in a particle beam system. Resorting to one or more reference standards and the passive alignment of a particle-optical element such as a pole shoe for a magnetic lens by way of a mechanical modification of this element saves valuable time and costs, and also allows a quick and uncomplicated replacement of a particle-optical element of a particle beam system

[0185] The embodiments of the invention described in the figures may in turn be combined with one another in full or in part, provided that this does not result in any technical contradictions. Moreover, the examples described in the figures should only be understood as being exemplary for the invention and do not limit this invention to the examples described in the figures.

[0186] List of reference signs

[0187] 1 Multiple particle beam system, multi-beam particle microscope

[0188] 3 Primary particle beams, first individual particle beams

[0189] 5 Beam spots, incidence locations

[0190] 7 Object, sample, wafer

[0191] 9 Secondary particle beams, second individual particle beams

[0192] 10 Computer system, controller

[0193] 15 Sample surface, wafer surface

[0194] 25 Image point of a second individual particle beam

[0195] 101 Object plane

[0196] 102 Objective lens

[0197] 103 Field lens

[0198] 105 Axis

[0199] 108 Beam crossover

[0200] 200 Detector system

[0201] 205 Projection lens system

[0202] 206 Projection lens

[0203] 207 Multi-particle detector

[0204] 208 Projection lens Projection lens

[0205] Beam crossover

[0206] Aperture filter, contrast stop

[0207] Collective anti-deflection system

[0208] Beam-generating device

[0209] Collimation lens system, condenser lens system

[0210] Multi-aperture plate, filter plate

[0211] Multi-beam particle generator

[0212] Multi-aperture plate

[0213] Field lens

[0214] Field lens

[0215] Particle beam

[0216] Illuminating particle beam

[0217] Intermediate image plane

[0218] Beam foci

[0219] Beam splitter, magnet arrangement

[0220] Scan deflector

[0221] Displacement stage or positioning device

[0222] Magnetic lens

[0223] Upper pole shoe

[0224] Lower pole shoe

[0225] Winding

[0226] Mechanical adjustment element

[0227] Spring

[0228] Opening in the upper pole shoe

[0229] Opening in the lower pole shoe

[0230] Magnetic field line

[0231] Inhomogeneity

[0232] Reference pole shoe

[0233] Pole shoe to be aligned

[0234] Connection element

[0235] Mechanically modified region

[0236] Reference pole shoe joining surface

[0237] Pole shoe joining surface

[0238] Reference marking

[0239] Fit

[0240] Flange 735 Screw 736 Nut 737 Opening 738 Base 739 Side wall 740 Top side 900 Measuring device

[0241] 901 Particle source 902 Particle optics unit

[0242] 903 Sample stage 904 Test sample 905 Detection device 906 Controller 907 Particle beam(s) 908 Secondary particles x Direction y Direction z Direction

[0243] Z Particle-optical axis A Geometric axis, main axis d Displacement of the lower pole shoe relative to the upper pole shoe

Claims

Claims1. Method for passively aligning a pole shoe for a magnetic lens of a particle beam system, including the following steps: providing a reference pole shoe with a predefined minimum magnetic homogeneity in a measuring device; releasably arranging the pole shoe to be aligned relative to the reference pole shoe in a predefined reference position and thereby assembling a magnetic lens in the measuring device; exciting the magnetic lens in the measuring device; measuring characteristics of the magnetic field generated by the magnetic lens; determining a deviation of the characteristics of the generated magnetic field from corresponding characteristics of a predefined reference magnetic field; mechanically modifying the pole shoe on the basis of the ascertained deviation in order to adapt the magnetic field that can be generated by the magnetic lens.

2. Method according to the preceding claim, furthermore including the following step: at least partly annealing the pole shoe in order to homogenize its magnetic properties.

3. Method according to one of the preceding claims, wherein the pole shoe and the reference pole shoe are connected to each other by way of a fit.

4. Method according to the preceding claim, wherein the fit has an accuracy of 100 pm, in particular of 10 pm or of 1 pm.

5. Method according to one of the preceding claims, wherein the mechanical modification of the pole shoe comprises a material-removing method.

6. Method according to Claim 5, wherein the mechanical modification of the pole shoe comprises a machining method, in particular turning and / or milling.

7. Method according to either of Claims 5 and 6,wherein the pole shoe has an opening, which is penetrated by charged particles during the operation of the magnetic lens; wherein the opening has a position and a shape, and wherein the position and / or shape of the opening is modified when the pole shoe is subject to mechanical modification.

8. Method according to one of the preceding claims, wherein the pole shoe has a pole shoe joining surface and wherein the reference pole shoe has a reference pole shoe joining surface; wherein the pole shoe joining surface and the reference pole shoe joining surface correspond to each other; and wherein the pole shoe joining surface is modified when the pole shoe is subject to mechanical modification.

9. Method according to Claim 8, wherein the pole shoe joining surface and / or the reference pole shoe joining surface have a flange-like form and in particular are screwed to each other.

10. Method according to either of Claims 8 and 9, wherein in order to adjust a tilt between the pole shoe and the reference pole shoe, the pole shoe joining surface is asymmetrically removed such that this leads to the formation of a new pole shoe joining surface which also corresponds to the reference pole shoe joining surface.

11. Method according to any of Claims 8 to 10, furthermore including the following step: arranging a spacer, in particular a spacer ring, between the mechanically modified pole shoe joining surface and the reference pole shoe joining surface.

12. Method according to either of Claims 8 and 9, wherein the pole shoe joining surface is bent by means of a bending method when the pole shoe is subject to mechanical modification.

13. Method according to one of the preceding claims, wherein the reference position between the pole shoe and the reference pole shoe is defined by means of a reference marking.

14. Method according to the preceding claim, wherein the reference marking is formed as a stop of a kinematic mount and, during mechanical modification of the pole shoe, the pole shoe is modified in the region of the reference marking and hence in the region that rests against the stop such that a / the position of a / the opening of the pole shoe is modified.

15. Method according to one of the preceding claims, wherein the determination of characteristics of the generated magnetic field in the measuring device includes recording an image of a test sample and subjecting this image to an image evaluation method.

16. Method according to the preceding claim, wherein the determination of characteristics of the generated magnetic field in the measuring device includes recording multiple images of the test sample, each for different excitations of the magnetic lens, and subjecting each image to the image evaluation method, wherein the various images are moreover compared with one another in the image evaluation method.

17. Method according to one of the preceding claims, furthermore including the following step: providing a lookup table that links deviations of magnetic fields from a reference magnetic field to measures for the mechanical modification of the pole shoe; wherein the mechanical modification of the pole shoe is carried out on the basis of the lookup table.

18. Method according to one of the preceding claims, wherein the generated magnetic field is characterized in relation to a position of its magnetic axis, wherein the position of the magnetic axis is characterized by means of a positional deviation from a reference point and / or by means of a tilt relative to a reference axis.

19. Method according to Claims 17 and 18, wherein the positional deviation of the magnetic axis and / or the tilt of the magnetic axis is linked to a measure for the mechanical modification of the pole shoe which brings about a displacement of the position of the opening of the pole shoe on the pole shoe.

20. Method according to Claims 17 and 18,wherein the positional deviation of the magnetic axis and / or the tilt of the magnetic axis is linked to a measure for the mechanical modification of the pole shoe which brings about a tilt of the pole shoe relative to the reference pole shoe.

21. Method according to one of the preceding claims, wherein the generated magnetic field is characterized in relation to its round symmetry.

22. Method according to Claims 17 and 21, wherein a deviation of the magnetic field from the round symmetry is linked to a measure for material removal in the region of the opening of the pole shoe which brings about a change in the ellipticity of the opening.

23. Method according to any of the preceding claims, furthermore including the following step: testing the mechanically modified pole shoe in the measuring device.

24. Method according to one of the preceding claims, wherein the method is carried out repeatedly until a threshold value is undershot when determining the deviation of the characteristics of the generated magnetic field from corresponding characteristics of the predefined reference magnetic field.

25. Method for equipping a particle beam system with a magnetic lens, including the following steps: providing a first pole shoe by applying the method according to any of the preceding claims; arranging the first pole shoe in the particle beam system; providing a second pole shoe by applying the method according to any of the preceding claims; releasably arranging the second pole shoe relative to the first pole shoe in the predefined reference position and thereby assembling the magnetic lens in the particle beam system.

26. Method according to Claim 25, wherein the first pole shoe is an upper pole shoe and wherein the second pole shoe is a lower pole shoe.

27. Method according to Claim 25, wherein the first pole shoe is a lower pole shoe and wherein the second pole shoe is an upper pole shoe.

28. Method according to any of Claims 25 to 27, wherein the magnetic lens is an objective lens.

29. Method according to any of Claims 25 to 27, wherein the magnetic lens in the particle beam system is one of the following: a condenser lens, a field lens, a projection lens.

30. Particle beam system, wherein the particle beam system has been equipped in accordance with the method according to any of Claims 25 to 29.

31. Particle beam system according to Claim 30, wherein the particle beam system comprises an element of the following list: a SEM, a TEM, a STEM, a SEM-STEM, a dual particle beam system, a multi-beam particle microscope, a mask repair system, a LEEM, a PEEM.

32. Method for passively aligning a particle-optical element for a functional unit of a particle beam system, including the following steps: providing a reference element with a reference joining surface in a measuring device; providing the particle-optical element with an element joining surface that corresponds to the reference joining surface; releasably arranging the particle-optical element to be aligned relative to the reference element in a predefined reference position and thereby assembling a functional unit for a particle beam system in the measuring device; operating the functional unit in the measuring device; measuring particle-optical characteristics of the functional unit; determining a deviation of the measured particle-optical characteristics of the functional unit from corresponding characteristics of a predefined reference functional unit; mechanically modifying the particle-optical element by means of a material-removing method on the basis of the ascertained deviation for adapting the functional unit.

33. Method according to Claim 32,wherein the element joining surface is mechanically modified, whereby a new element joining surface which also corresponds to the reference joining surface is formed.

34. Method according to either of Claims 32 and 33, wherein the mechanical modification of the particle-optical element comprises a machining method, in particular turning and / or milling.

35. Method according to any of Claims 32 to 34, wherein in order to adjust a tilt between the particle-optical element and the reference element, the element joining surface is asymmetrically removed such that this leads to the formation of a new element joining surface which also corresponds to the reference element joining surface.

36. Method according to any of Claims 32 to 35, wherein the particle-optical element and the reference element are connected to each other by way of a fit.

37. Method according to the preceding claim, wherein the fit has an accuracy of 100 pm, in particular of 10 pm or 1 pm.

38. Method according to any of Claims 32 to 37, wherein the element joining surface and / or the reference joining surface have a flange-like form and in particular are screwed to each other.

39. Method according to any of Claims 32 to 38, furthermore including the following step: arranging a spacer, in particular a spacer ring, between the mechanically modified element joining surface and the reference joining surface.

40. Method according to any of Claims 32 to 39, wherein the particle-optical characteristics of the functional unit describe a centring and / or an orientation of an electrostatic field generated by means of the functional unit.

41. Method according to any of Claims 32 to 40, wherein the particle-optical characteristics of the functional unit describe a centring and / or an orientation of a magnetic field generated by means of the functional unit.

42. Method according to any of Claims 32 to 41 , further including the following step: at least partly annealing the particle-optical element in order to homogenize its magnetic properties.

43. Method according to any of Claims 32 to 42, wherein the functional unit comprises an element from the following list: an electrostatic lens, an electrostatic deflection system, an electrostatic stigmation system, an electrostatic multipole system of higher order, a magnetic lens, a magnetic deflection system, a magnetic stigmation system, a magnetic stigmation system of higher order, an aperture arrangement having a plurality of apertures, a Wien filter, a beam splitter.

44. Method according to any of Claims 32 to 43, wherein the method is carried out in cascade-like fashion for a plurality of particle- optical elements, wherein the particle-optical elements from the second particle-optical element onward are in each case assembled in cascade-like fashion to form an augmented new particle- optical element, for which the method is carried out in each case.

45. Method for equipping a particle beam system with a functional unit, including the following steps: providing a first particle-optical element of the functional unit by applying the method according to any of Claims 32 to 44; arranging the first particle-optical element in the particle beam system; providing a second particle-optical element by applying the method according to any of Claims 32 to 44; and releasably arranging the second particle-optical element relative to the first particle- optical element in the predefined reference position and thereby assembling the functional unit in the particle beam system.

46. Particle beam system, wherein the particle beam system has been equipped in accordance with the method according to Claim 45.

47. Particle beam system according to Claim 46, wherein the particle beam system comprises an element of the following list: a SEM, a TEM, a STEM, a SEM-STEM, a dual particle beam system, a multi-beam particle microscope, a mask repair system, a LEEM, a PEEM.

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