Multibeam particle microscope and related methods with high-speed autofocus near an adjustable working distance

Abstract

The present invention relates to a multi-beam particle microscope and related method with fast autofocus near an adjustable working distance. A system is proposed that includes one or more fast autofocus correction lenses for high-frequency adaptation of the focus, position, angle of incidence, and rotation of individual particle beams at incidence on the wafer surface during wafer inspection. Fast autofocus in secondary paths of the particle beam system is also feasible. Accuracy can be further improved by fast aberration correction means in the form of deflectors and / or astigmatism correctors.

Description

[Technical Field]

[0001] This invention relates to a multibeam particle microscope for inspecting semiconductor wafers having an HV structure. [Background technology]

[0002] With the continued miniaturization and increasing complexity of microstructures such as semiconductor components, there is a growing need for the development and optimization of planar generation technologies and inspection systems for generating and inspecting minute dimensions of these microstructures. For example, the development and production of semiconductor components require design monitoring of test wafers, and planar generation technologies require process optimization for reliable, high-throughput production. Furthermore, in recent years, the analysis of semiconductor wafers has become necessary for reverse engineering of semiconductor components and for customer-specific configurations. Therefore, there is a demand for high-throughput inspection methods to accurately examine microstructures on wafers.

[0003] Typical silicon wafers used in the production of semiconductor components have a maximum diameter of 300 mm. Each wafer has a maximum diameter of approximately 800 mm. 2The size is subdivided into 30 to 60 repeating regions ("dies"). Semiconductor devices contain multiple semiconductor structures layered on the surface of a wafer using planar integration technology. Semiconductor wafers typically have a planar shape for production process considerations. The structural size of the integrated semiconductor structures in this case has shrunk from a few micrometers to a critical dimension (CD) of 5 nm, and will become even smaller in the near future. In the future, the structural size or critical dimension (CD) is expected to be less than 3 nm (e.g., 2 nm) or even less than 1 nm. With the aforementioned small structural sizes, it is necessary to identify defects of critical dimension size over a very large area in a short amount of time. For some applications, the specification requirements for the measurement accuracy provided by the inspection equipment are even higher, for example, by twice or an order of magnitude. For example, the width of a semiconductor feature needs to be measured with an accuracy of less than 1 nm (e.g., less than 0.3 nm), and the relative position of a semiconductor structure needs to be determined with an overlay accuracy of less than 1 nm (e.g., less than 0.3 nm).

[0004] Therefore, a general objective of the present invention is to provide a multi-beam particle system operating with charged particles and related methods for its high-throughput operation, thereby facilitating high-precision measurement of semiconductor features with accuracies of less than 1 nm, 0.3 nm, or less than 0.1 nm.

[0005] MSEM (Multibeam Scanning Electron Microscope) is a relatively new development in the field of charged particle systems (charged particle microscopes (CPM)). For example, a multibeam scanning electron microscope is disclosed in U.S. Patent No. 7,244,949 and U.S. Patent Application Publication No. 2019 / 0355544. In a multibeam electron microscope or MSEM, a sample is simultaneously irradiated by multiple individual electron beams arranged in a field of view or grid. For example, 4 to 10,000 individual electron beams can be provided as primary irradiation, with each individual electron beam separated by a distance of 1 to 200 micrometers from adjacent individual electron beams. For example, in an MSEM, for instance, approximately 100 individual electron beams ("beamlets") are arranged in a hexagonal grid and separated by a distance of approximately 10 μm. Multiple individual charged particle beams (primary beams) are then focused onto the surface of the sample under inspection by a common objective lens. For example, the sample can be a semiconductor wafer fixed in a wafer holder assembled on a movable stage. During irradiation of the wafer surface with individual primary charged particle beams, interaction products (e.g., secondary electrons or backscattered electrons) are emitted from the wafer surface. Each starting point corresponds to a location on the sample where multiple individual primary particle beams are focused in each case. The amount and energy of the interaction products are determined by the material composition and topography of the wafer surface. The interaction products form multiple individual secondary particle beams (secondary beams), which are collected by a common objective lens and incident on a detector positioned in the detection plane as a result of the projection imaging system of a multi-beam inspection system. The detector contains multiple detection regions, each with multiple detection pixels, and captures the intensity distribution of each individual secondary particle beam. In this process, an image field of view of, for example, 100 μm × 100 μm is obtained.

[0006] Conventional multibeam electron microscopes comprise a series of electrostatic and magnetic elements. By adjusting at least some of the electrostatic and magnetic elements, the focal positions and stigmas of multiple individual charged particle beams can be adapted. Furthermore, conventional multibeam charged particle systems comprise at least one crossover plane for individual primary or secondary charged particle beams. In addition, conventional systems comprise a detection system to facilitate adjustment. Conventional multibeam particle microscopes comprise at least one beam deflector ("deflection scanner") for obtaining an image field of view of the sample surface by scanning a region of the sample surface simultaneously with multiple individual primary particle beams. Further details regarding multibeam electron microscopes and their operating methods are described in German Patent Application No. 102020206739.2, filed on 28 May 2020, and all disclosures thereof are incorporated herein by reference.

[0007] For scanning microscopes used for wafer inspection, it is desirable to maintain stable imaging conditions to ensure highly reliable and reproducible imaging. Throughput is determined by several parameters (e.g., the speed of repositioning at the stage and new measurement sites) as well as the measurement area per unit time of acquisition. The latter is determined, in particular, by the dwell time on the pixel, the pixel size, and the number of individual particle beams. In addition, multi-beam electron microscopes may require time-consuming image post-processing. For example, before stitching together image fields from multiple subfields or partial images, it may be necessary to digitally correct the signals generated from charged particles by the detection system of the multi-beam system.

[0008] Here, the lattice positions of individual particle beams on the sample surface may deviate from the ideal lattice positions in a planar configuration. The resolution of a multibeam electron microscope varies for each individual particle beam and can be determined by the position of each individual particle beam in the field of view of each particle beam; therefore, it can be determined by the specific lattice positions of the individual particle beams.

[0009] Conventional charged particle beam systems have reached their limits in terms of resolution and throughput.

[0010] Therefore, an object of the present invention is to provide a multi-beam particle system that facilitates the recording of high-precision and high-resolution images at high throughput.

[0011] One technique for improving accuracy and resolution is the use of so-called autofocus. This involves scanning the sample surface while considering the sample surface / object plane to continuously determine the current relative focal position of each electron beam ("on-the-fly"), and then making appropriate corrections to the relative focal position. For example, the focusing of individual particle beams is adapted for each image field. This procedure, for example, is based on the assumption that the sample model or sample characteristics do not change significantly from image field to image, and predictive values ​​for focusing improvement can be determined by extrapolation or interpolation.

[0012] Despite the above, known autofocus methods are relatively slow. This is because the relative focal position is optimized by changing the working distance (WD) or by different controls of the objective lens. Here, changing the working distance by displacing the height of the sample stage (the so-called "z-stage") is only possible with a limited degree of precision and speed. Furthermore, not all sample stages are displacing in relation to their height. When there are changes in the control of the objective lens or other magnetic lenses aimed at changing the relative focal position, this adjustment is relatively slow. Conventional techniques use magnetic objective lenses, especially immersion lenses, and their high inductance makes faster adaptation impossible. Even in this case, the time required to change the excitation is in the range of tens to hundreds of milliseconds. Moreover, for meaningful recording, the magnification on the object plane (related to the beam pitch of individual particle beams on the object plane) and the orientation, i.e., rotation, of the array (grid arrangement) of individual electron beams must be kept constant when updating the relative focal position, making the optical elements of a multi-beam electron microscope far more complex than those of a single-beam system. The same applies to the landing angle of individual particle beams on the sample. In principle, the aforementioned particle optics parameters (and optionally, other parameters) cannot be set independently of each other using only a single lens. Therefore, changing the control of the magnetic objective lens involves changing the control of other particle optics components in the primary path. For this reason, changes in the excitation of other magnetic and electrostatic elements are usually necessary, but the adjustment time for the magnetic lens is limited, similarly in the range of tens to hundreds of milliseconds. Similar considerations apply to the adjustment of particle optics components in the secondary path and the focal position for high-precision detection.

[0013] Therefore, given the aforementioned background and the increasing demand for throughput / speed and high-precision measurement of smaller structures, existing systems need to be improved. In particular, there is a significant demand for the inspection of semiconductor wafers. And, normally, the surface of a semiconductor wafer, which is itself very flat, cannot be assumed to be perfectly flat within the scope of precision inspection. Changes in wafer thickness and / or the longitudinal position of the wafer surface relative to the objective lens, even if very small, affect the optimal focus and, consequently, the accuracy of the measurement. This is especially true for the inspection of polished wafer surfaces with HV structures. For this reason, even under some unrealistic assumptions such as the absence of system drift, simply adjusting the multibeam electron microscope once at a predetermined working point associated with the working distance is insufficient. Instead, even very small changes in the working distance must be compensated for by changing the relative focal position. Another prerequisite here is that the magnification must be constant. Furthermore, the orientation of the lattice arrangement on the sample surface must be precisely observed. This is because, in the case of semiconductor wafers with HV structures, imaging is always performed strictly parallel or perpendicular to these structures. Additionally, the angle of incidence must be kept precisely constant. Finally, in order to obtain excellent image formation, it is necessary to quickly and accurately update the optical units in the secondary path. [Overview of the Initiative]

[0014] As a result, an object of the present invention is to provide an improved multibeam particle system and its associated operating method for inspecting semiconductor wafers having an HV structure. This system is intended to operate at high speed and with high precision.

[0015] Another object of the present invention is to provide a multibeam particle system and its associated operating method for inspecting semiconductor wafers having an HV structure, thereby enabling faster autofocus of the system at an operating point of a specific working distance. In this case, other particle optical parameters such as magnification, eccentricity, and rotation are kept constant with high precision.

[0016] The above object is achieved by the independent patent claims. Advantageous embodiments of the invention become apparent from the dependent patent claims.

[0017] This patent application claims the priority of German Patent Application No. 102020125534.9 filed on September 30, 2020 and German Patent Application No. 102021105201.7 filed on March 4, 2021, and incorporates the entire disclosures of both applications into this patent application.

[0018] According to a first aspect of the invention, the invention is a multi-beam particle system for semiconductor inspection, comprising: a multi-beam particle generator configured to generate a first field of view of a plurality of first individual charged particle beams; a first particle optical unit having a first particle optical beam path configured to image the first individual particle beams onto the wafer surface such that the generated first individual particle beams collide at the incidence locations on the wafer surface in the object plane to form a second field of view; a detection system having a plurality of detection regions forming a third field of view; a second particle optical unit having a second particle optical beam path configured to image the second individual particle beams emitted from the incidence locations in the second field of view onto the third field of view of the detection regions of the detection system; a magnetic and / or electrostatic objective lens through which both the first individual particle beams and the second individual particle beams pass, in particular, a magnetic and / or electrostatic immersion lens; a beam switch disposed between the multi-beam particle generator and the objective lens in the first particle optical beam path and between the objective lens and the detection system in the second particle optical beam path; a sample stage for holding and / or positioning the wafer during wafer inspection; an autofocus determination element configured to generate data for determining actual autofocus data during wafer inspection; a high-speed autofocus correction lens; a controller; and comprising. The controller is configured to control at least the objective lens and / or the actuator of the sample stage at the first operating point of the first operating distance by static or low-frequency adaptation of the focusing so that the first individual particle beam is focused on the wafer surface placed at the first operating distance. Relates to a multi-beam particle system configured such that the controller generates an autofocus correction lens control signal by high-frequency adaptation of the focusing based on the actual autofocus data at the first operating point during wafer inspection, thereby controlling the high-speed autofocus correction lens during wafer inspection at the first operating point.

[0019] The charged particles can be, for example, charged particles such as electrons, positrons, muons, or ions. The charged particles are preferably electrons generated using, for example, a thermionic field emission source (TFE). However, other particle sources can also be used.

[0020] In this case, the number of the first individual particle beams can be variously selected. However, it is convenient if the number of the particle beams is 3n(n - 1)+1. Here, n is an arbitrary natural number. This enables a hexagonal lattice arrangement of the detection regions. Other lattice arrangements of the detection regions (for example, square or rectangular lattices) are similarly possible. As an example, the first individual particle beams are 5, 60, or more than 100 individual particle beams.

[0021] A multi-beam particle generator may comprise multiple real particle sources, each emitting an individual particle beam or multiple individual particle beams. However, in addition to a single particle source, the multi-beam particle generator may also comprise a multi-aperture plate combined with a multi-lens array and / or multi-deflector array in the downstream particle optical beam path. As a result of the multi-beam particle generator, multiple individual particle beams are generated and imaged into an intermediate image plane. This intermediate image plane can be a real or virtual intermediate image plane. In either case, the positions of the individual particle beams in the intermediate image are considered to be virtual particle sources and therefore can be considered as starting points for another particle optical imaging using the first particle optical beam path. These virtual particle sources in the intermediate image plane are consequently imaged onto the wafer surface or object surface, and by using multiple individual particle beams, the wafer to be inspected can be scanned.

[0022] When an objective lens system includes a magnetic objective lens, the magnetic objective lens can provide either a weak or strong magnetic field. According to a preferred embodiment of the present invention, the objective lens is a magnetic immersion lens. Here, both weak and strong immersion lenses are possible. A magnetic immersion lens can be realized, for example, by perforating a lower (sample-facing) magnetic pole piece with a larger diameter than the perforation of the upper (sample-distal) magnetic pole piece of the lens. In contrast to objective lenses that provide only a weak magnetic field in an object, immersion lenses have the advantage of suppressing spherical and chromatic aberrations, but the disadvantage of increased off-axis aberrations. In the magnetic field of the lens, individual particle beams passing through it undergo Larmor rotation (in both the primary and secondary paths).

[0023] The present invention provides a sample stage for holding and / or positioning a wafer during wafer inspection. Here, the sample stage may have a mechanism for adjusting the height (e.g., z-stage) to set the working distance. However, the option for adjusting the height is not required. The sample stage serves only to hold the wafer and not to position it in the z-direction. In either case, the sample stage may be movable along one axis (e.g., x-axis, y-axis) or a plane (e.g., xy-plane), although this is not mandatory.

[0024] Furthermore, an autofocus determination element is provided, configured to generate data for determining the actual autofocus data during wafer inspection. In this case, the actual autofocus data directly or indirectly represents the current focal position relative to the wafer surface. As an example, the autofocus determination element may include or consist of an autofocus measurement element, and this data may be measurement data. However, as an addition or alternative, it is also possible to generate data for determining the actual autofocus data based on a model. For example, this is possible when a sufficiently precise model of the wafer being scanned exists.

[0025] In principle, autofocus measurement elements are known from the prior art, for example, described in U.S. Patent No. 9,530,613 and U.S. Patent Application Publication No. 2017 / 0117114, and all disclosures thereof are incorporated herein by reference. As an example, a height sensor (z sensor) can be used. In principle, to determine the focal position, the current focal position of individual particle beams relative to the wafer surface is estimated by measurement (estimation of actual autofocus data). Ideally, all focal points should be precisely located on the wafer surface. In this case, the focal position of individual particle beams is defined by the position of the beam waist of the beam.

[0026] U.S. Patent No. 9,530,613 discloses the use of an astigmatic auxiliary beam for setting or adjusting the focus. Depending on the current focusing, a known astigmatic (e.g., elliptical) beam profile changes during imaging. This change allows for conclusions regarding the focus correction required for the focus and, consequently, for an aberration-free beam.

[0027] U.S. Patent Application Publication 2017 / 0117114 discloses an "on-the-fly" type of autofocus. In this process, the current focal position of individual particle beams is estimated from image field data (measured intensity) during scanning of the sample surface, and continuous / "on-the-fly" focus adjustment is performed for subsequent image fields. In particular, there is no need to scan the same sample area multiple times. In each case, object properties are indirectly determined by measurement, at the discretion of the user. For example, one such object property can be the height profile of the sample surface. Subsequently, for subsequent image recordings, a predicted height value is determined from the determined height profile, and a different focal position that is more adapted to the sample surface is set.

[0028] The multi-beam particle system according to the present invention comprises a controller. The controller is configured to control particle optical components in the first and / or second particle optical beam paths. Preferably, the controller is a central controller for the entire multi-beam particle system, but this is not mandatory. The controller can have a partial or multi-part configuration and is functionally subdivided.

[0029] The controller is configured to control at least the objective lens and / or the actuator of the sample stage at a first working point at a first working distance by static or low-frequency adaptation of focusing, so that a first individual particle beam is focused onto the wafer surface placed at a first working distance, and to control at least one high-speed autofocus correction lens during wafer inspection at the first working point by generating an autofocus correction lens control signal by high-frequency adaptation based on actual autofocus data at the first working point during wafer inspection. In this case, it is preferable that the control of the objective lens is not changed for the high-frequency application. Changes in the excitation of the objective lens are usually performed only in the case of static or low-frequency adaptation of the focal position. In this case, the objective lens includes at least one magnetic objective lens and / or at least one electrostatic objective lens. That is, the objective lens can be embodied in the form of a corresponding objective lens system.

[0030] Thus, the controller controls two different focus settings at a single operating point defined by the relevant working distance between the objective lens and the wafer surface, as well as other parameters as an option. Firstly, the controller controls focusing over a large stroke by controlling the objective lens and other lenses as an option, and / or the actuator for displacing the sample stage. These final control elements respond relatively slowly to the control signals. In this case, adaptation typically takes tens to hundreds of milliseconds, especially when the working distance is first focused at the selected operating point (for example, when the wafer is changed). As an example, possible strokes for changing the working distance are ±100 μm, ±200 μm, or ±300 μm.

[0031] Furthermore, according to the present invention, the controller secondly controls the focus setting by controlling the high-speed autofocus correction lens according to the present invention. This lens can have various embodiments. For example, it can be embodied as a high-speed electrostatic lens. Variations of various embodiments and possible positions of the autofocus correction lens in the beam path will be described in more detail below. It is also possible to provide multiple autofocus correction lenses and control them individually. In any case, the autofocus correction lens can be used for high-speed adjustment and acts on the relative focal position of individual particle beams, and this effect can be made significant or suppressed. In addition to the effect on focus, the autofocus correction lens may also have effects on other particle optical parameters. In this case, high speed means that high-frequency adaptation of the relative focal position is possible by excitation of the autofocus correction lens. The adaptation time TA is in the range of μs (for example, TA ≤ 500 μs, preferably TA ≤ 100 μs and / or TA ≤ 50 μs). The stroke required to change the working distance is typically a few micrometers (e.g., ±20 μm, ±15 μm, and / or ±10 μm).

[0032] According to a preferred embodiment of the present invention, the adaptation time TA for high-frequency adaptation is at least 10 times, preferably at least 100 times or 1000 times shorter than the adaptation time TA for low-frequency or static adaptation. Furthermore, the stroke for setting the working distance for low-frequency or static adaptation can be at least 5 times, preferably at least 8 times and / or 10 times larger than the stroke for high-frequency adaptation.

[0033] In the two variations concerning focus adjustment, updating other particle optics components of the system may also be required. The controller can also supply appropriate control signals for these corrections. For low-frequency or static adaptation, the final control element can be either slow-adjustable or fast-adjustable. In this case, the temporal constraint is the time required to displace the magnetic lens (e.g., including the magnetic field lens and magnetic objective lens) and / or the sample stage in the z-direction. For high-frequency adaptation, other final control elements must also be essentially fast-adjustable. Here, the respective adaptation times are preferably on the same order as the adaptation time of the fast autofocus correction lens. For example, up to twice as slow is possible; however, it is also possible to make them faster than the adaptation time of the fast autofocus correction lens. For example, additional fast final control elements can include electrostatic lenses, electrostatic deflectors, and / or electrostatic astigmatism correctors. A few turns of air coil can also be used as a fast corrector.

[0034] According to a preferred embodiment of the present invention, a second working point is defined by a second working distance between at least the objective lens and the wafer surface, the second working distance being different from the first working distance of the first working point. The controller is configured to perform low-frequency adaptation in the event of a change between the first and second working points and to control at least the magnetic objective lens and / or the actuator of the sample stage at the second working point so that the first individual particle beam is focused onto the wafer surface at the second working distance. For example, a change in the working point is performed when the wafer is changed. In this case, the wafer thickness may be different. Since changing the wafer is a relatively slow procedure, a slow adaptation is sufficient in this case. However, it is also possible to change the working point or working distance due to a change in the inspection task, for example.

[0035] The controller is preferably configured to control the high-speed autofocus correction lens during wafer inspection at the second operating point by generating an autofocus correction lens control signal for high-frequency adaptation based on the actual autofocus data at the second operating point of the second working distance during wafer inspection. Furthermore, all of the above descriptions apply to setting the high-speed autofocus at the second operating point of the second working distance, together with the first operating point at the first working distance.

[0036] According to a preferred embodiment of the present invention, the first operating point and / or the second operating point are further defined by the angle of incidence of the first individual particle beams on the object plane and the grid arrangement of the first individual particle beams on the object plane. The controller is configured to keep the angle of incidence and the grid arrangement substantially constant in high-frequency adaptation at the first and / or second operating points. In this case, the term grid arrangement includes the pitch between the individual particle beams on the object plane and the rotation of the arrangement of the individual particle beams. As an example, the grid arrangement may exist in the form of the hexagonal field of view described above. Thus, if the object plane is kept constant, both the magnification related to the pitch of the individual particle beams and the orientation of the second field of view at the point of incidence of the individual particle beams are also kept constant. Here, the magnification is preferably kept constant at about 50 ppm, 20 ppm, 10 ppm, 1 ppm or more (for example, 50 nm, 20 nm, 10 nm, 1 nm or more for a field of view size of 100 μm). The maximum angular deviation from the desired incident angle on the wafer surface is ±0.1°, ±0.01°, or ±0.005° or less.

[0037] According to another preferred embodiment of the present invention, the controller is configured to keep the incident angle and grid arrangement substantially constant even during changes between the first and second operating points. This is related to keeping the aforementioned parameters constant, even in the case of low-frequency adaptation of the focus. Here, the magnification is preferably kept constant at about 50 ppm, 20 ppm, 10 ppm, and 1 ppm or more (for example, 50 nm, 20 nm, 10 nm, and 1 nm or more for 100 μm). The maximum angular deviation from the desired incident angle on the wafer surface is ±0.1°, ±0.01°, or ±0.005° or less.

[0038] The adaptation of particle optical parameters (e.g., angle of incidence and grid arrangement (position or magnification and rotation)), particularly the final control elements for keeping these constant, can be entirely or partially identical for low-frequency adaptation to high-frequency adaptation. However, if all or part of these final control elements are the same, these final control elements must necessarily also be suitable for high-frequency adaptation.

[0039] According to a preferred embodiment of the present invention, the autofocus correction lens includes or comprises an electrostatic lens. In principle, the settings of the electrostatic lens can be changed considerably faster than the settings of a magnetic lens, where high-speed adaptation is hindered by hysteresis effects, eddy currents, and self-mutual inductance. According to the present invention, the electrostatic lens can be provided as a complete lens (e.g., a tube lens). However, it is also possible to provide only an additional component in the form of an additional electrode as the autofocus correction lens, and the effect of the electrostatic lens occurs in conjunction with other components or ambient voltage.

[0040] High-speed autofocus correction lenses can be positioned at various locations in the first particle optical beam path, resulting in different advantages and disadvantages. Firstly, there is the available installation space within the overall system; secondly, there is the influence of the autofocus correction lens on particle optical parameters other than the focal point. As already mentioned at the beginning, lenses in multi-beam particle systems do not typically act on only a single particle optical parameter. In principle, the effects of particle optical components are not mutually orthogonal. The inventors have investigated these relationships in more detail and found that specific properties exist at multiple locations in the particle optical beam path of a multi-beam particle system. Typically, the primary beam path of a multi-beam particle system according to the present invention includes a crossover point or crossover plane where individual particle beams are superimposed or intersected. This crossover plane is usually located immediately upstream of the objective lens. Comprehensive calculations have shown that additional lenses on the crossover substantially act on the focal point of the first individual particle beams, while having only a slight (if any) effect on other particle optical parameters such as position, eccentricity, or rotation. As a result, it is generally advantageous to position the autofocus correction lens within the crossover or crossover plane of the first individual particle beam. However, in practice, since the crossover is not a singularity but has spatial extent, the placement of the autofocus correction lens is often only possible near the crossover / crossover plane. According to the present invention, many options exist for this purpose.

[0041] According to a preferred embodiment of the present invention, the autofocus correction lens is positioned in a beam tube extension that protrudes into the objective lens from the direction of the upper pole piece. Generally, individual particle beams are guided within the beam tube. The beam tube is exhausted. Here, the beam tube extension is strictly a region of the beam tube that protrudes slightly into the magnetic objective lens from the upper pole piece. Since the beam tube is at ground potential, the autofocus correction lens or associated electrode can be reliably positioned within the beam tube extension.

[0042] According to a preferred embodiment of the present invention, a beam deflection system is further provided between the beam switch and the objective lens, configured to raster scan the wafer surface by scanning movement of individual particle beams, and an autofocus correction lens is implemented as an offset to the beam deflection system. Typically, the beam deflection system ("deflection scanner" or "scanning deflector") is implemented by two or more deflectors arranged in succession along the beam path. The offset voltage is supplied to all electrodes involved in the deflection. Here, the lens effect occurs as a result of the superposition of the deflection magnetic field and the Einzel lens magnetic field. The described embodiment has the advantage that no further modifications to the system's hard wafer are required.

[0043] According to one embodiment of the present invention, the multi-beam particle system further comprises a beam deflection system between the beam switch and the objective lens, configured to raster scan the wafer surface by scanning the individual particle beams, the beam deflection system comprising an upper deflector and a lower deflector arranged in a continuous manner in the direction of the beam path, and an autofocus correction lens positioned between the upper and lower deflectors. This embodiment is also easy to implement, as it requires only minor modifications to the hardware of existing systems.

[0044] According to one embodiment of the present invention, the multi-beam particle system further comprises a beam deflection system between the beam switch and the objective lens, configured to raster scan the wafer surface by scanning movement of individual particle beams, the beam deflection system comprising an upper deflector and a lower deflector arranged in a continuous manner in the direction of the beam path, and an autofocus correction lens positioned between the lower deflector and the upper magnetic pole piece of the magnetic objective lens. In a modified example of this embodiment, the autofocus correction lens is also close to the crossover plane.

[0045] According to a preferred embodiment of the present invention, the autofocus correction lens is positioned between the wafer surface and the lower pole piece of the magnetic objective lens. Although this position is no longer near the crossover and the lens effect no longer extends only slightly to the focal point, this embodiment offers the advantage that, since the autofocus correction lens is typically the last lens just before the wafer surface, subsequent aberrations are minimal.

[0046] According to another preferred embodiment of the present invention, the autofocus correction lens is positioned between the upper and lower pole pieces of the magnetic objective lens. This embodiment also has the advantage that, since it is implemented far towards the bottom of the beam path (the autofocus correction lens is the second to last lens), subsequent aberrations are minimal.

[0047] According to a preferred embodiment of the present invention, the multibeam particle system further comprises an evacuable beam tube substantially enclosing a first particle optical beam path from a multibeam particle generator to an objective lens, wherein the beam tube has a shielding section, and an autofocus correction lens is located within this shielding section. Here, the beam tube is substantially sealed in the aforementioned region, that is, it is embodied in such a way that a vacuum or high vacuum can be generated inside. The beam tube may also have different cross-sections and / or chambers along it. Here, it is preferable that the shielding section in which the autofocus correction lens is located is the only shielding section in the beam tube. Except for the location of the shielding section where the autofocus correction lens is located, the inner wall of the beam tube is at ground potential. In this context, possible connection / contact points between the vacuum chamber and the actual beam tube are not considered shielding sections.

[0048] According to a preferred embodiment of the present invention, the multibeam particle system further comprises a field lens system positioned between a multibeam particle generator and a beam switch in a first particle optical beam path, wherein a beam tube cutoff section, on which an autofocus correction lens is located, is positioned between the field lens system and the beam switch. This embodiment provides relatively large space for the placement of the autofocus correction lens.

[0049] According to a preferred embodiment of the present invention, the beam switch includes two magnetic sectors, and the section of the beam tube where the autofocus correction lens is located is provided in the region of the beam switch between the two magnetic sectors. This embodiment provides a relatively large space for arranging the autofocus correction lens.

[0050] According to a preferred embodiment of the present invention, the multi-beam particle system further comprises a beam deflection system configured to raster scan the wafer surface by scanning movement of individual particle beams between the beam switch and the objective lens, and a beam tube cutoff section, in which an autofocus correction lens is located, is provided between the beam switch and the beam deflection system. This embodiment provides a relatively large space for arranging the autofocus correction lens.

[0051] According to a preferred embodiment of the present invention, the multibeam particle system further comprises a field lens system positioned between a multibeam particle generator and a beam switch in a first particle optical beam path. This field lens system may include one or more lenses, including at least one magnetic lens. In this embodiment of the present invention, the cutoff section of the beam tube where the autofocus correction lens is located is positioned within one of the magnetic lenses of the field lens system. A relatively large installation space is available in this position as well. However, the autofocus correction lens in this position acts on the focus, position, and tilt of individual particle beams. In this embodiment as well, it is advantageous that the position and / or tilt of the beams can be compensated.

[0052] According to a preferred embodiment of the present invention, the multibeam particle system further comprises an exhaustable beam tube substantially enclosing the first particle optical beam path from the multibeam particle generator to the objective lens. In this case, the autofocus correction lens is embodied as a tubular lens and is located within the beam tube. Therefore, the beam tube has no cutoffs or perforations, facilitating sealing / enclosure of the beam tube. Again, there are several ways of carrying out modifications of this embodiment, four of which are specified below.

[0053] According to a preferred embodiment of the present invention, the multibeam particle system further comprises a field lens system positioned between a multibeam particle generator and a beam switch in a first particle optical beam path, and an autofocus correction lens positioned in the beam tube between the field lens system and the beam switch. This embodiment provides a relatively large space for the placement of the autofocus correction lens.

[0054] According to a preferred embodiment of the present invention, the beam switch has two magnetic sectors, and the autofocus correction lens is provided in the beam tube between the two magnetic sectors. This embodiment provides a relatively large space for arranging the autofocus correction lens.

[0055] According to a preferred embodiment of the present invention, the multi-beam particle system further comprises a beam deflection system configured to raster scan the wafer surface by scanning movement of individual particle beams between the beam switch and the objective lens, and an autofocus correction lens provided in the beam tube between the beam switch and the beam deflection system. This embodiment provides a relatively large space for the placement of the autofocus correction lens.

[0056] According to a preferred embodiment of the present invention, the multi-beam particle system further comprises a field lens system positioned between the multi-beam particle generator and the beam switch in the first particle optical beam path, wherein the autofocus correction lens is positioned within the beam tube in a magnetic lens. This embodiment provides relatively large space for the placement of the autofocus correction lens. At this position, the autofocus correction lens acts on the position and tilt, as well as the focal point of the individual particle beams. This facilitates (potentially additional) correction of the position and incident angle of the first individual particle beams.

[0057] According to another embodiment of the present invention, the high-speed autofocus correction lens includes or comprises a high-speed magnetic lens, in particular an air coil. Such an air coil can be used to some extent as a high-speed autofocus correction lens because it has a relatively small inductance. As an example, the number of turns of such an air coil is several tens to several hundred, and for example, 10≦k≦500, 10≦k≦200, and / or 10≦k≦50 corresponds to the number of turns k. Furthermore, the adaptation time TA of the air coil can be set to TA≦500μs, preferably TA≦100μs and / or TA≦50μs. In either case, the above applies when no magnetic material is placed near the air coil or when very little magnetic material is placed near it.

[0058] According to a preferred embodiment of the present invention, the multibeam particle system further comprises an evacuable beam tube substantially enclosing a first particle optical beam path from a multibeam particle generator to an objective lens, with the high-speed magnetic lens located outside the beam tube. In this case, neither perforation nor blocking of the beam tube is required. Modifications of this embodiment are relatively easy to construct.

[0059] According to a preferred embodiment of the present invention, the multibeam particle system further comprises a field lens system positioned between a multibeam particle generator and a beam switch in a first particle optical beam path, and a high-speed magnetic lens positioned around the beam tube between the field lens system and the beam switch. In this case, neither perforation nor blocking of the beam tube is required. Modifications of this embodiment are relatively easy to construct.

[0060] According to a preferred embodiment of the present invention, the beam switch has two magnetic sectors, and the high-speed magnetic lens is arranged around the beam tube between the two magnetic sectors. In this case, neither drilling nor blocking of the beam tube is required. Modifications of this embodiment are relatively easy to construct.

[0061] According to a preferred embodiment of the present invention, the multi-beam particle system further comprises a beam deflection system configured to raster scan the wafer surface by scanning movement of individual particle beams between the beam switch and the objective lens, and a high-speed magnetic lens is arranged around the beam tube between the beam switch and the beam deflection system. In this case, neither drilling nor blocking of the beam tube is required. Modifications of this embodiment are relatively easy to construct.

[0062] According to a preferred embodiment of the present invention, the multi-beam particle system further comprises a beam deflection system between the beam switch and the objective lens, configured to raster scan the wafer surface by scanning movement of individual particle beams, the beam deflection system comprising an upper deflector and a lower deflector arranged in a continuous manner in the direction of the beam path, and a high-speed magnetic lens arranged around the beam tube between the upper and lower deflectors. In this case, neither drilling nor blocking of the beam tube is required. Modifications of this embodiment are relatively easy to construct.

[0063] According to a preferred embodiment of the present invention, the multi-beam particle system further comprises high-speed eccentricity correction means configured to substantially contribute to correcting tangential or radial eccentricity errors of the first individual particle beams in a second field of view, wherein the controller of the multi-beam particle system is configured to control the high-speed eccentricity correction means during wafer inspection by generating eccentricity correction means control signals for high-frequency adaptation at each operating point during wafer inspection based on actual autofocus data. As described above, within the range of high-speed autofocus, high-speed adaptation of other particle optics components is often required so that other particle optics parameters can be kept constant. One of these parameters is the eccentricity or incident angle of the first individual particle beams on the wafer surface (in this patent application, the terms eccentricity and incident angle are used synonymously). Here, when an element provided for eccentricity correction is applied, this element does not necessarily act only on eccentricity, but also interacts with other particle optics parameters due to the non-orthogonality of the effects of the particle optics components. Therefore, within the scope of this patent application, the high-speed eccentricity correction means is defined to act substantially (and therefore not necessarily exclusively) on eccentricity. Furthermore, the essential effect relates to eccentricity. Strictly speaking, a high-speed autofocus correction lens is also a means of high-speed eccentricity correction, and vice versa.

[0064] The following describes how tangential eccentricity and rotational errors occur due to an immersion lens acting as a magnetic objective lens. In a standard configuration of a magnetic immersion lens having a first imaging scale and a first focal plane in the magnetic field of the magnetic immersion lens, a first grid array having a first beam pitch or first individual particle beam pitch and a first orientation is formed on the object surface. In this process, charged particles in the magnetic field of the magnetic immersion lens are guided into a helical trajectory. If the magnetic field of the objective lens extends to a sample or object (e.g., a semiconductor wafer), the magnetic immersion lens is used as the reference. As a result of the helical particle trajectory, the grid array of the beam focus on the object surface on which, for example, a wafer is placed, also rotates. To generate the first grid array on the object surface with a desired and predetermined orientation, the twisting or rotation of the grid array is typically pre-held by, for example, positioning a grid array generation device (e.g., in the form of a multi-aperture plate as a component of a multi-beam particle generator) in a predetermined pre-rotation position to counteract the rotation caused by the magnetic immersion lens. Furthermore, since each individual particle beam of the first particle beam receives a tangential velocity component, in the case of an immersion lens, the individual particle beams do not incident perpendicularly to the sample, but rather are incident at a tangential inclination or gradient with respect to the perpendicular to the sample surface. In particular, in the case of a multi-beam system, each individual particle beam of the first particle beam has a different tangential gradient angle, and these gradient angles increase with the radial distance from the optical axis of the magnetic immersion lens. This error is called the tangential eccentricity error. Typically, the tangential eccentricity error can be compensated by generating an appropriate tangential velocity component of each individual particle beam of the first particle beam, targeted upstream of the magnetic immersion lens, which cancels out and compensates for the tangential eccentricity error at the wafer surface.

[0065] Unwanted parasitic effects can arise from changes in the excitation of the magnetic immersion lens, or from changes in the relative focal positions or imaging scales of the first grating array of multiple first individual particle beams. For example, each of the aforementioned changes can result in tangential and / or radial eccentricity errors.

[0066] Each of the aforementioned modifications alters the rotation rate of the helical electron orbitals or the rotation angle of the lattice arrangement. As a result, a second lattice arrangement of multiple primary electron beams is formed that rotates in the opposite direction to the first lattice arrangement. This rotation is unnecessary and, according to the present invention, is compensated for by changing the rotation of the lattice arrangement.

[0067] According to a preferred embodiment of the present invention, the eccentricity correction means comprises a first deflector array positioned in the intermediate image plane of a first particle optical beam path. For example, such a deflector array is known from German Patent No. 102018202421 and International Patent Publication No. WO2019 / 243349, all disclosures of both documents are incorporated herein by reference. Here, the deflector array includes a plurality of deflectors arranged on the array, and during operation, a group consisting of individual particle beams passes through each deflector. Here, the group may consist of only one particle beam.

[0068] According to a preferred embodiment of the present invention, the multi-beam particle system further comprises high-speed rotation compensation means configured to substantially contribute to the correction of the rotation of the first individual particle beams in a second field of view, wherein the controller is configured to control the high-speed rotation compensation means during wafer inspection by generating rotation compensation means control signals for high-frequency adaptation based on actual autofocus data during wafer inspection at each operating point. The rotation compensation means does not necessarily act only on rotation, but also interacts with other particle optical parameters due to the non-orthogonality of the effects of the particle optical components. Therefore, within the scope of this patent application, the high-speed rotation compensation means is defined to act substantially (and therefore not necessarily exclusively) on rotation, and its essential effect is related to rotation. Strictly speaking, a high-speed autofocus correction lens is also a high-speed rotation compensation means, and vice versa.

[0069] According to a preferred embodiment of the present invention, the rotational correction means comprises an air coil. For example, the number of turns of such an air coil is several tens to several hundred, and the number of turns k is such that, for example, 10 ≤ k ≤ 500, 10 ≤ k ≤ 200, and / or 10 ≤ k ≤ 50. Furthermore, the adaptation time TA of the air coil can be set to TA ≤ 500 μs, preferably TA ≤ 100 μs and / or TA ≤ 50 μs. In either case, the above applies when no magnetic material is placed near the air coil or when very little magnetic material is placed there.

[0070] According to a preferred embodiment of the present invention, the rotational compensation means comprises a second deflector array positioned at a distance immediately upstream or downstream of a first deflector array acting as a high-speed eccentricity compensation means. Thus, in this embodiment, another deflector array is positioned at a distance upstream or downstream of the eccentricity compensation deflector array, and the grid array as a whole is rotated with appropriate control by changing the focal position on the wafer surface as a result of the deflection of individual beams. In this case, the apertures of each downstream deflector array are correspondingly large and designed to match the beam deflection of the preceding deflector array. As a result, the compensation of rotational and eccentricity errors is facilitated by the two consecutively arranged deflector arrays.

[0071] According to a preferred embodiment of the present invention, the rotational compensation means comprises a multi-lens array positioned at a distance immediately upstream or downstream of a first deflector array acting as an eccentricity compensation means, such that the first individual particle beams pass through the multi-lens array off-axis. Thus, in addition to the focusing effect, a deflection effect also occurs. The individual particle beams are deflected tangentially as a result of the tangential offset with respect to the axis of the microlenses. For example, the tangential beam offset can be set by rotating the deflector array or multi-lens array upstream of the grid array. Alternatively, an active deflector array or a multi-lens array with variable refractive power upstream of the multi-lens array can cause a change in the tangential beam deflection. The deflection angle also changes with the change in refractive power. The change in refractive power can be compensated, for example, by another electrostatic lens acting on all individual particle beams. Another option is the active rotation of the multi-lens array by a few milliradians. Since the deflection is amplified by the lensing effect, the angle by which the multi-lens array is rotated can be smaller than the rotation angle of the grid array.

[0072] According to another preferred embodiment of the present invention, the multibeam particle generator comprises a high-speed rotation compensation means, which rotates actively by a rotation compensation means control signal. As an example, the multibeam particle generator includes at least one deflector array or at least one multilens array. Furthermore, twisting of the grid array can be introduced by appropriate active rotation of the multibeam particle generator as a whole or the entire generating apparatus, or by active rotation of individual array components.

[0073] According to a preferred embodiment of the present invention, the high-speed rotation compensation means comprises a first magnetic field generator for a first weak magnetic field and a second magnetic field generator for a second weak magnetic field, the first and second magnetic field generators being controlled by a controller via a rotation compensation means control signal with respect only to rotation in the positive and negative directions. Because compensation for twisting or rotation of the grid array needs to be extremely fast to accommodate high-speed autofocus, individual magnetic elements are unsuitable for this purpose. However, the inventors have found that high-speed rotation of the grid array, combined with a change in focal position, can be achieved by using at least two magnetic elements, each for rotation in only one direction. As a result of avoiding hysteresis by using two magnetic components, each operating in only one direction, high-speed rotation of the grid array in two rotation directions is possible. Both components can be reset during short interruptions between inspection tasks, such as when placing a wafer from a first inspection area to a second inspection area. Therefore, for example, an axial magnetic field for positive rotation can be combined with a magnetic immersion lens at the exit of the pencil of the primary beam from a generator for negative rotation.

[0074] According to a preferred embodiment of the present invention, the first and second magnetic fields have an axial configuration and are arranged in the first particle optical beam path as focusing or diverging pencils of the first individual particle beams. Such a configuration and the underlying physical effects are described, for example, in German Patent Application No. 102020123567.4, filed on September 9, 2020, which is not yet published at the time of this application, and all of its disclosures are incorporated herein by reference.

[0075] According to a preferred embodiment of the present invention, the maximum deviation of individual particle beams from a desired incident position on the wafer surface is 10 nm, 5 nm, 2 nm, 1 nm, or 0.5 nm or less. This is an absolute maximum deviation and applies to any direction on the wafer surface (planar or substantially planar), and can be ensured in particular by one or more of the above-described means for eccentricity correction, rotational correction, and / or positional correction.

[0076] According to a preferred embodiment of the present invention, the controller is configured to determine autofocus correction lens control signals, rotation correction means control signals, and / or eccentricity correction means control signals based on actual autofocus data by using a sensitivity inverse matrix representing the effect of excitation changes of particle optical components on particle optical parameters characterizing particle optical imaging at each operating point. Such a sensitivity inverse matrix is ​​described in German Patent Application No. 102014008383, all of which are incorporated herein by reference. A change in the effect of only one particle optical component of a multibeam particle optics unit also changes several parameters characterizing particle optical imaging. However, in practice, it is desirable to change the settings of the particle optics unit such that, as a result of the setting change, only one parameter characterizing particle optical imaging changes, while the other parameters remain unchanged. For this reason, it is necessary to change the settings of the effects of multiple particle optical components simultaneously. To determine the settings that need to be changed in order to change only one parameter, and to determine how to perform these changes, entries in a matrix A describing these setting changes can be determined, for example, from m × n measurement results. Here, n corresponds to the number of particle optical components, and m corresponds to the number of parameters characterizing the particle optical image. After determining the entries, this matrix can be inverted, and by determining which excitation changes to perform on which particle optical components, it is possible to change exactly one parameter representing the particle optical image.

[0077] According to a preferred embodiment of the present invention, the high-speed autofocus correction lens includes a high-speed electrostatic lens, which is positioned as a first high-speed autofocus correction lens between the upper and lower pole pieces of the magnetic objective lens. Here, the expression “first high-speed autofocus correction lens” indicates that particularly good autofocus correction can be obtained with multiple high-speed autofocus correction lenses, and does not indicate that they should not be used. Here, the first high-speed autofocus correction lens is positioned to contribute to high-speed autofocus correction and is controlled by a controller. This contribution may consist of the first high-speed autofocus correction lens realizing a high-frequency focusing stroke. However, as an addition or alternative, other beam parameters such as incidence angle, position, and / or rotation may also be recorrected in the high-speed autofocus step.

[0078] According to a preferred embodiment of the present invention, the first high-speed autofocus correction lens is incorporated into a beam tube extension portion that protrudes into the objective lens from the direction of the upper magnetic pole piece. The beam tube extension portion is the portion connected to the exhaustable beam tube, as described above. The first high-speed autofocus correction lens can be a first high-speed autofocus correction lens with a partial configuration or a first autofocus correction lens with a multi-part configuration. In the latter case, a first high-speed autofocus correction lens with a two-part configuration is preferred.

[0079] According to a preferred embodiment of the present invention, the first autofocus correction lens has at least two parts. Preferably, the first autofocus correction lens comprises exactly two parts. In this case, the two parts of the first autofocus correction lens are relative adjacent or relatively close to each other. In this case, both parts of the first autofocus correction lens act on individual particle beams passing through in the manner of a high-speed autofocus correction lens. However, the specific operation may differ.

[0080] According to one preferred embodiment of the present invention, the beam tube extension section has two cutoff sections, and a portion of a two-part first autofocus correction lens is arranged in each of the two cutoff sections. According to another preferred embodiment, each of the two portions of a two-part or at least two-part first autofocus correction lens is embodied as a tube lens and arranged within the beam tube extension section.

[0081] In this case, a two-part or, more generally, multi-part embodiment of the first high-speed autofocus correction lens, positioned between the upper and lower pole pieces of the objective lens, has the following advantages or advantages. That is, a high-speed electrostatic lens positioned between the upper and lower pole pieces of the objective lens, and thus within the magnetic field, has a relatively large influence on the focus of the first individual particle beams in the second field of view or object plane. However, the velocity of individual particle beams may change temporarily as they pass through the electrostatic lens. Here, if the velocity profile of individual particle beams changes in a (non-uniform) magnetic field, this change in velocity profile also changes the azimuth beam parameter in the object plane. And, if at least a two-part high-speed autofocus correction lens is positioned within the objective lens instead of a single high-speed autofocus correction lens, the influence on the azimuth beam parameter can be greatly compensated for by the skillful control of the second part of the first high-speed autofocus correction lens. However, since only circular optical lenses without focusing space charges exist, it can be considered advantageous to control the two parts of the first autofocus correction lens with voltages of opposite signs. This allows the integral ∫B(z) / v(z)dz of the individual particle beam in the objective lens's magnetic field to be kept constant even during the autofocus step. In this case, the absolute values ​​of the two voltages are not identical, but are roughly different. Furthermore, instead of the two-part configuration, it is also possible to select a three-part configuration or, more generally, a multi-part configuration. In such configurations as well, the path integral as a whole can be kept constant.

[0082] According to a preferred embodiment of the present invention, the control of at least two parts of the first autofocus correction lens provides not only high-frequency adaptation of focusing but also high-frequency correction of the image field rotation and consequently the azimuth position of individual particle beams on the object plane. Therefore, in addition to the task of correcting focus, the two-part first autofocus correction lens is also intended to function as a rotation correction means. However, even in this case, it should be emphasized again that, since the effects of the lenses are generally not mutually orthogonal, it is usually not possible to strictly assign the lenses to precisely defined tasks or precisely defined effects in each case.

[0083] According to a preferred embodiment of the present invention, the multibeam particle system comprises a second high-speed autofocus correction lens including a high-speed electrostatic lens, The second autofocus correction lens is positioned within the magnetic field of the field lens system. The controller is configured to control the second high-speed autofocus correction lens at high frequency during wafer inspection at each operating point by generating a second autofocus correction lens control signal based on the actual autofocus data during wafer inspection.

[0084] In this case, the term "second" high-speed autofocus correction lens indicates that the system also includes another high-speed autofocus correction lens (for example, a first high-speed autofocus correction lens). However, from this point forward, the ordinal numbers are used to distinguish variations of various embodiments of the autofocus correction lens and do not specify the number of high-speed autofocus correction lenses implemented. Variations of this embodiment can be combined in particular with embodiments in which a partial high-speed autofocus correction lens is positioned as a first high-speed autofocus correction lens between the upper and lower pole pieces of the magnetic objective lens. The concept of this embodiment or the combination of the first high-speed autofocus correction lens and the second high-speed autofocus correction lens is substantially the same as the concept realized by a two-part first high-speed autofocus correction lens. Here, correction of the azimuth beam parameter is also intended. However, this is realized by providing a separate high-speed autofocus correction lens positioned in the magnetic field, rather than a second lens portion of the first high-speed autofocus correction lens. This second high-speed autofocus correction lens is positioned in the magnetic field of the field lens system. For example, in this process, the field lens system may be placed within the first lens, the second lens, or the third magnetic lens. Importantly, the second autofocus correction lens is placed in a magnetic field to obtain the effect of changes in particle velocity on image field rotation as individual particle beams pass through the second high-speed autofocus correction lens. Here, the first and second high-speed autofocus correction lenses may, but are not necessarily, be controlled by a controller with voltages of opposite signs. Furthermore, it should be noted that the configuration of the second high-speed autofocus correction lens is primarily for correcting other beam parameters (particularly image field rotation in this case) that inevitably accompany it, rather than changing the focus itself. More detailed information regarding the field lens system can be found, for example, in U.S. Patent Application Publication No. 2019 / 0355545, all of which are incorporated herein by reference.

[0085] According to a preferred embodiment of the present invention, the control of the second high-speed autofocus correction lens substantially performs high-frequency correction of the image field rotation or azimuthal position of individual particle beams.

[0086] In this case as well, by providing a shielding section in the beam tube and placing the high-speed electrostatic lens within this shielding section, the second high-speed autofocus correction lens can be placed within the magnetic field of the field lens system. Alternatively, the second high-speed autofocus correction lens can be implemented as a tube lens and placed within the magnetic field of both the beam tube and the field lens system. However, in conjunction with these embodiments, the required voltage range is known to be, for example, 2 to 20 kV (for example, around 5 kV).

[0087] According to another preferred embodiment of the present invention, the multibeam particle system comprises a third high-speed autofocus correction lens, The third high-speed autofocus correction lens includes a high-speed magnetic lens, in particular an air coil, positioned outside the beam tube in the first particle optical beam path, in a substantially magnetic-free location. The controller is configured to control the third high-speed autofocus correction lens at a high frequency during wafer inspection at each operating point by generating a third autofocus correction lens control signal based on the actual autofocus data during wafer inspection.

[0088] In this case, the term "third" high-speed autofocus correction lens indicates that the system comprises at least one other high-speed autofocus correction lens. However, it is not necessary to have three or more high-speed autofocus correction lenses. Hereafter, the use of ordinal numbers is for better distinguishing the various embodiments of the present invention and does not specify the number of high-speed autofocus correction lenses used. The above description applies to magnetic lenses, in particular air coils. As an example, the number of turns of such an air coil is tens to hundreds, and for example, 10 ≤ k ≤ 500, 10 ≤ k ≤ 200, and / or 10 ≤ k ≤ 50 corresponds to the number of turns k. Also, the adaptation time tA of the air coil can be set to tA ≤ 500 μs, preferably tA ≤ 100 μs and / or tA ≤ 50 μs. In either case, the above applies when no magnetic material is placed near the air coil or when very little magnetic material is placed near it. The adaptation time tA represents how quickly or at what intervals the beam parameters can be set by the air coil. In this embodiment, the adaptation time of the air coil is short enough to allow for high-frequency adaptation of beam parameters by the air coil.

[0089] According to a preferred embodiment of the present invention, the first particle optical beam path has an intermediate image plane, and the third high-speed autofocus correction lens is positioned immediately downstream of this intermediate image plane in the direction of the particle optical beam path. In one example, there is little to no magnetic material present at this position.

[0090] According to a preferred embodiment of the present invention, the control of the third high-speed autofocus correction lens substantially performs high-frequency correction of the azimuth position of individual particle beams on the object plane. Thus, the third high-speed autofocus correction lens substantially acts on image field rotation but not on focus. As a result, the third high-speed autofocus correction lens functionally also corresponds to rotation correction means.

[0091] According to another preferred embodiment of the present invention, the multibeam particle system further comprises a fourth high-speed autofocus correction lens including a high-speed electrostatic lens, The beam tube has a shielding section within the magnetic field lens of the field lens system, and the fourth high-speed autofocus correction lens is located within this shielding section. The controller is configured to control the fourth high-speed autofocus correction lens at a high frequency during wafer inspection at each operating point by generating a fourth autofocus correction lens control signal based on the actual autofocus data during wafer inspection.

[0092] Here, the fourth high-speed autofocus correction lens may have a partial configuration or a multi-part configuration. The fourth high-speed autofocus correction lens may have a physically identical configuration to the second high-speed autofocus correction lens. However, the fourth high-speed autofocus correction lens differs from the second high-speed autofocus correction lens with respect to its main function. According to a preferred embodiment of the present invention, the control of the fourth high-speed autofocus correction lens substantially performs high-frequency correction of the radial incidence angle of individual particle beams on the object plane. In contrast, the second high-speed autofocus correction lens is substantially, preferably in combination with the partial configuration of the first high-speed autofocus correction lens, and is precisely used for high-frequency correction of image field rotation. Furthermore, the fourth high-speed autofocus correction lens can be used without problems in combination with the partial configuration of the first high-speed autofocus correction lens, in combination with the two-part configuration of the first high-speed autofocus correction lens, and optionally in combination with other high-speed autofocus correction lenses.

[0093] According to another preferred embodiment of the present invention, the multibeam particle system further comprises a fifth high-speed autofocus correction lens including a high-speed electrostatic lens, The fifth high-speed autofocus correction lens is located in the multi-beam particle generator. The controller is configured to control the fifth high-speed autofocus correction lens at high frequency during wafer inspection at each operating point by generating a fifth autofocus correction lens control signal based on the actual autofocus data during wafer inspection.

[0094] Here, the fifth high-speed autofocus correction lens may have a partial or multi-part configuration. The fifth high-speed autofocus correction lens is located in the multi-beam particle generator. That is, it can be part of the multi-beam particle generator, or it can be located in close proximity to the components of the multi-beam particle generator.

[0095] According to a preferred embodiment of the present invention, the multi-beam particle generator comprises a multi-lens array with a multi-aperture plate and a counter electrode, and a fifth high-speed autofocus correction lens is implemented as an offset voltage that can be applied to the counter electrode. The voltage applied to the multi-beam particle generator or the voltage applied to the micro-optical unit is typically a high voltage in the range of several kilovolts (e.g., 20kV, 60kV, or 90kV). However, if a small offset is applied to the counter electrode, this offset voltage significantly affects the magnification of individual particle beams on the object plane, but does not significantly affect the relative position of the focal point. As a result, the fifth high-speed autofocus correction lens makes it possible to correct the radial image position of individual particle beams on the object plane. However, high-speed voltage changes, such as offsets in the range of several kilovolts, tend to be more difficult to implement and tend to be associated with specific designs of the multi-beam particle generator.

[0096] Accordingly, according to another preferred embodiment of the present invention, the fifth high-speed autofocus correction lens is implemented alternatively. According to a modification of this embodiment, the multi-beam particle generator comprises a multi-lens array with a multi-aperture plate and a counter electrode, and the fifth high-speed autofocus correction lens is implemented as an additional electrode positioned between the multi-aperture plate and the counter electrode, or immediately downstream of the counter electrode with respect to the particle optical beam path. Thus, in this embodiment, instead of eliminating the offset in the two modifications, work is performed with a separate additional electrode that can be controlled at a low potential.

[0097] According to a preferred embodiment of the present invention, the control of the fifth high-speed autofocus correction lens substantially performs high-frequency correction of the radial position of individual particle beams on the object plane. However, as an addition or alternative, the fifth high-speed autofocus correction lens may also correct other beam parameters.

[0098] According to a preferred embodiment of the present invention, the multibeam particle system further comprises a sixth high-speed autofocus correction lens including a high-speed electrostatic lens, The sixth high-speed autofocus correction lens is realized near the intermediate image plane as a two-part lens, with the first part positioned upstream of the intermediate image plane and the second part positioned downstream of the intermediate image plane, when viewed in the direction of the particle optical beam path. The controller is configured to control the sixth high-speed autofocus correction lens at a high frequency during wafer inspection at each operating point by generating a sixth autofocus correction lens control signal based on the actual autofocus data during wafer inspection.

[0099] Here, it is preferable that the two parts of the sixth high-speed autofocus correction lens are arranged symmetrically with respect to the intermediate image plane. As a result, the sixth high-speed autofocus correction lens as a combination of lenses can achieve the same effect as a single high-speed correction lens positioned on the intermediate image plane. As an example, the sixth high-speed autofocus correction lens allows for high-frequency setting of the eccentricity of individual particle beams on the object plane.

[0100] According to a preferred embodiment of the present invention, a bias is applied to the sixth high-speed autofocus correction lens. The bias can be negative or positive.

[0101] According to another preferred embodiment of the present invention, this multibeam particle system further comprises a magnetic field compensating lens including a magnetic lens, The magnetic field compensation lens is placed between the objective lens and the object plane. The controller is configured to statically or low-frequency control the magnetic field compensation lens using a magnetic field compensation control signal so that the value of the magnetic field on the object surface becomes zero.

[0102] Unlike the first to fifth high-speed autofocus correction lenses (and optionally one or more high-speed autofocus correction lenses), magnetic field compensation lenses are not useful for high-frequency autofocus correction. Typically, magnetic field compensation lenses are unsuitable for high-speed autofocus correction because they comprise magnetic lenses. These magnetic lenses typically have slower switching speeds due to hysteresis effects; that is, lower frequencies in the sense defined in this patent application. According to the present invention, magnetic field compensation lenses are used to set the magnetic field in an object plane or on a wafer to zero. As a result, the azimuthal incidence angle can be kept constant or zero in an object plane or on a wafer. Our simulations have shown that the theoretically corrected residual error is proportionally smaller than that of other beam parameters after high-frequency correction, and in particular significantly smaller than the residual error of the radial incidence angle after high-frequency correction, indicating that high-frequency correction of the azimuthal incidence angle is not essential.

[0103] According to a preferred embodiment of the present invention, a magnetic field compensating lens is coupled to an objective lens. Such configurations of magnetic field compensating lenses are already known in the prior art. One example is described in International Patent Application Publication WO2007 / 060017, the entirety of which is incorporated herein by reference. The coupling of the magnetic field compensating lens to the objective lens relates to the magnetic flux in the lower pole piece of the objective lens in the aforementioned example. Furthermore, since a wound magnetic field compensating lens is placed below the objective lens, excitation of this winding can also generate magnetic flux in the lower pole piece of the objective lens. The magnetic flux generated in the lower pole piece of the objective lens by the first winding (which shall be assigned to the objective lens) is oriented substantially in the same direction as the magnetic flux generated by excitation of the winding belonging to the magnetic field compensating lens. Specifically, the direction of the current in the winding belonging to the objective lens is opposite to the direction of the current in the winding belonging to the magnetic field compensating lens. By appropriate control of the magnetic field compensating lens and / or the objective lens at the operating point, the value of the magnetic field on the object plane can be substantially zero. Furthermore, magnetic field compensation lenses can also be implemented using different methods.

[0104] This patent application describes various embodiments of high-speed autofocus correction lenses, eccentricity correction means, rotation correction means, and position correction means. Specific configurations and arrangements of the first, second, third, fourth, fifth, sixth, and other high-speed autofocus correction lenses are also described. All of these contribute to the configuration of a multi-beam particle system in which, through high-frequency correction, beam parameters such as focal point, angle of incidence, and grid arrangement at the object plane are kept constant at the operating point. Through comprehensive investigation and simulation by the inventors, it has become clear that combinations of autofocus correction lenses and other correctors are particularly suitable for achieving high-speed autofocus in the first particle optical beam path of a multi-beam particle system. In particular, two combinations have been found to be especially suitable. These combinations enable high-speed autofocus at different operating points, respectively, while keeping other beam parameters such as angle of incidence, rotation, and position at the object plane constant. These two exemplary embodiments are described in more detail below.

[0105] According to a preferred embodiment of the present invention, this multibeam particle system is A high-speed electrostatic lens comprising at least two parts, a first high-speed autofocus correction lens positioned between the upper and lower magnetic pole pieces of a magnetic objective lens, A fourth high-speed autofocus correction lens, which includes a high-speed electrostatic lens positioned within the magnetic field of the field lens system's magnetic lens, A fifth high-speed autofocus correction lens is positioned in the multibeam particle generator, Furthermore, The controller is configured to control a high-speed autofocus correction lens consisting of at least two parts by a first autofocus correction lens control signal having voltages of opposite signs during wafer inspection at each operating point, by generating an autofocus correction lens control signal based on actual autofocus data during wafer inspection. The controller is configured to control the fourth high-speed autofocus correction lens at high frequency during wafer inspection at each operating point by generating a fourth autofocus correction lens control signal based on the actual autofocus data during wafer inspection. The controller is configured to control the fifth high-speed autofocus correction lens at high frequency during wafer inspection at each operating point by generating a fifth autofocus correction lens control signal based on actual autofocus data during wafer inspection. The constraint applied here is that the value of the magnetic field on the object plane is zero, which can be achieved, for example, by using the magnetic field compensation lens described above. Furthermore, it is preferable that both the focal stroke and the image field rotation are set by the first high-speed autofocus correction lens, which is at least two-part. It is even more preferable that the radial image position on the object plane is preferentially set by the fifth high-speed autofocus correction lens. Finally, the radial incidence angle on the object plane is substantially corrected or made zero (normal incidence) by the fourth high-speed autofocus correction lens (preferably located within the beam tube's cutoff section in the magnetic lens of the field lens system).

[0106] According to another particularly preferred embodiment of the present invention, this multibeam particle system is In particular, having an embodiment of a certain configuration, the high-speed electrostatic lens includes a first high-speed autofocus correction lens positioned between the upper and lower magnetic pole pieces of the magnetic objective lens, A high-speed magnetic lens, in particular a third high-speed autofocus correction lens including an air coil, is positioned outside the beam tube in the first particle optical beam path, in a substantially magnetic-free location. A fourth high-speed autofocus correction lens, which includes a high-speed electrostatic lens positioned within the magnetic field of the field lens system's magnetic lens, A fifth high-speed autofocus correction lens is positioned in the multibeam particle generator, Furthermore, The controller is configured to control the first high-speed autofocus correction lens at high frequency during wafer inspection at each operating point by generating a first autofocus correction lens control signal based on actual autofocus data during wafer inspection. The controller is configured to control the third high-speed autofocus correction lens at high frequency during wafer inspection at each operating point by generating a third autofocus correction lens control signal based on the actual autofocus data during wafer inspection. The controller is configured to control the fourth high-speed autofocus correction lens at high frequency during wafer inspection at each operating point by generating a fourth autofocus correction lens control signal based on the actual autofocus data during wafer inspection. The controller is configured to control the fifth high-speed autofocus correction lens at each operating point during wafer inspection by generating a fifth autofocus correction lens control signal based on the actual autofocus data during wafer inspection. In this case as well, the constraint that applies is that the value of the magnetic field on the object plane is zero, as can be achieved, for example, by the magnetic field compensation lens described above. Here, it is preferable that the focus is set by the first high-speed autofocus correction lens while the rotation is set by the third high-speed autofocus correction lens. The radial incidence angle can be set or kept constant by the fourth high-speed autofocus correction lens, and the radial position on the object plane can be set or kept constant by the fifth high-speed autofocus correction lens.

[0107] According to a preferred embodiment of the present invention, the controller is configured to determine an autofocus correction lens control signal based on actual autofocus data by using a sensitivity inverse matrix that represents the effect of control changes of the particle optical component on the particle optical parameters that characterize particle optical imaging at each operating point. For further details regarding the sensitivity inverse matrix, refer again to German Patent Application No. 102014008383, all of which disclosures are incorporated herein by reference.

[0108] According to a preferred embodiment of the present invention, the controller is configured to determine the autofocus correction lens control signal by using a multidimensional lookup table. The multidimensional nature of the lookup table is due to the fact that the multi-beam particle system according to the present invention can achieve high-speed autofocus at two or more operating points. Values ​​for a specific operating point are arranged in each dimension of the lookup table. In particular, the lookup table can be used when a feedforward loop is implemented in the system for the purpose of determining the autofocus correction lens control signal.

[0109] According to a preferred embodiment of the present invention, the multibeam particle system further comprises a hysteresis correction measurement element in the second particle optical beam path that generates hysteresis correction measurement data characterizing particle optical imaging on an object plane after a low-frequency control change of at least one magnetic lens in the first particle optical beam path, in particular after a change in the working distance, without changing the settings in the second particle optical beam path. The controller is configured to high-frequency correct at least one autofocus correction lens control signal at each operating point by generating a hysteresis correction control signal based on hysteresis control measurement data during wafer inspection.

[0110] A variation of this embodiment provides an option to implement an additional feedback loop in a multi-beam particle system. The autofocus determination element is configured to generate data, in particular measured data, during wafer inspection for the purpose of determining the actual autofocus data, and to perform high-frequency adaptation of focusing based on this data. This means that the parameters to be adapted are either directly improved by these data or measurements, or adapted in the feedback loop. For other beam parameters (e.g., rotation and magnification), conventional feedback loops are not implemented in the system. Instead, adaptation of other beam parameters is performed based on the focusing data, in particular measured data, i.e., the generated or measured actual autofocus data (so-called feedforward). This situation differs when a hysteresis correction measurement element is implemented. According to the hysteresis correction measurement element, measurements of particle optical parameters other than the focus are generated and can be used in the feedback loop for high-frequency correction. This correction is particularly effective in systems where hysteresis occurs. This is the case when using conventional magnetic lenses. When feedforward control is implemented instead of additional feedback for other corrective lenses, it is done under the assumption that system hysteresis has no effect on the settings used. Nevertheless, the feedforward setting is not optimal for the system. In this case, the optimization benefits are obtained by implementing additional feedback for other beam parameters.

[0111] According to a preferred embodiment of the present invention, the hysteresis correction measurement element includes a CCD camera in the second particle optical beam path. Such a CCD camera is always located in the projection path in known multi-beam particle systems. It can be used to characterize particle optical imaging on the object surface. The CCD camera can be the same camera described later for acquiring projection path measurement data characterizing particle optical imaging in the secondary path.

[0112] According to a preferred embodiment of the present invention, the hysteresis correction control signal enables the correction of individual beam parameters for radial and / or azimuth positions on the object plane. In other words, the correction of individual beam parameters with respect to magnification and image field rotation can be determined. The insights obtained can be used to generate a feedback signal for controlling an autofocus correction lens. The autofocus correction lens to be controlled can be a correction lens that targets more than just relative focal position correction. However, an autofocus correction lens that prioritizes setting the system's focus on the object plane can also be controlled.

[0113] According to a preferred embodiment of the present invention, the multibeam particle system further comprises at least one high-speed electrostatic aberration correction means positioned upstream of any high-speed autofocus correction lens in the particle optical beam path, particularly upstream of each implemented high-speed autofocus correction lens, and configured to maintain a constant path for individual particle beams as they pass through the column with high precision. The controller is configured to control one or more high-speed aberration correction means at each operating point with high frequency by generating aberration correction control signals during wafer inspection.

[0114] One or more high-speed electrostatic aberration correction means are intended to compensate for permissible aberrations that occur at all times. When autofocus is set, it is crucial that the relative positions of individual particle beams do not change in the column. This should prevent offset and tilt, and also prevent astigmatism.

[0115] As an example, a high-speed electrostatic deflector or a corresponding deflector configuration can be used as a means for correcting high-speed electrostatic aberrations.

[0116] According to one preferred embodiment, the aberration correction means has an octupole-shaped electrode arrangement. This octupole allows for correction of both beam offset and tilt, as well as any astigmatism that may occur.

[0117] Maintaining a constant beam path during column passage is crucial. In particular, it is essential that the individual particle beams at the crossover point precisely center the positioned scanning deflector (octupole). This is necessary to ensure that the pixel size does not change from left to right during scanning of the image field. If the condition that the crossover point is perfectly centered on the scanning deflector is not met, the pixel size changes by approximately 0.01 to 0.1 ppth from left to right across the image field. While this value may not seem large, it is too large for high-precision applications. This can be corrected by the measures described above. Further details are available in German Patent Application No. 102020209833.6, filed on August 5, 2020, and all its disclosures are incorporated herein by reference.

[0118] In autofocus settings, it is particularly preferable that the beam position of individual particle beams does not change while passing through the entire column. However, as already mentioned, it is advantageous that the position of individual particle beams does not change, or is kept constant with high precision, when incident on the crossover itself and the objective lens. For this reason, the multi-beam particle system according to the present invention is equipped with high-speed electrostatic aberration correction means positioned upstream of the crossover of the first individual particle beams in the first particle optical beam path, and set to keep the position of the first individual particle beams constant with high precision for the purpose of forming the crossover. The controller is configured to control the high-speed aberration correction means at each operating point with high frequency by generating an aberration correction control signal during wafer inspection. In a modified example of this embodiment, for example, an octupole electrode configuration can be used as the aberration correction means.

[0119] According to another preferred embodiment of the present invention, the multi-beam particle system further comprises, between the beam switch and the objective lens, a scanning unit and a beam deflection system configured to raster scan the wafer surface by scanning movement of individual particle beams and controllable by the scanning unit, The controller controls the scanning unit with a scanning unit control signal during wafer inspection at each operating point, and is configured to perform high-frequency correction of the scanning unit control signal based on the actual autofocus data at each operating point.

[0120] High-frequency correction of these scanning parameters is necessary to compensate for small changes resulting from the overall system adaptation during autofocus settings. Furthermore, slight changes in the control of the deflector and / or astigmatism corrector can also cause slight changes in the scanning parameters. These scanning parameters include pixel dimension, rotation, skew, and quadratics. Pixel order represents the order of the pixel, rotation represents the rotation of the image around the x-axis, skew represents the angle between the x and y axes of the image, and quadratics specifies whether the pixel size is the same along both axes. In fact, these scanning parameters are described by a simple 2x2 matrix. Correction of the scanning parameters can be performed dynamically in the autofocus step using a lookup table. Therefore, according to a preferred embodiment of the present invention, the scanning parameters of pixel size, rotation, skew, and / or quadratics are high-frequency corrected by a lookup table.

[0121] The multi-beam particle systems described in the various embodiments above facilitate high-frequency correction of the focal point on the object plane at one or more operating points. However, other beam parameters (e.g., rotation, position, and angle of incidence) can also be kept constant. This is essential for many applications in the field of multi-beam particle systems. However, in principle, there are applications where it is not necessary to actually keep all beam parameters constant on the object plane. For example, it may be necessary to keep only the focal point and angle of incidence constant. Therefore, according to a preferred embodiment of the present invention, the system is configured to perform high-frequency correction of the beam parameters of focal point and angle of incidence on the object plane by high-speed autofocus correction means, in particular a high-speed autofocus correction lens, and to perform high-frequency correction of the beam parameters of magnification and image field rotation on the object plane by control of the scanning unit. In this case, it is preferable that beam parameters that are not physically corrected on the object plane are corrected only by calculation. This is because there are beam parameters that can be corrected with a relatively small amount of computation. Beam position is one example. Image displacement requires a relatively small amount of computation and does not directly change the data. In contrast, rotational correction requires far more computation, and the data is modified by interpolation used in the process. On the other hand, incident angle correction cannot be performed computationally, and physical correction is effective or essential when the sample being inspected has a 3D structure. According to the present invention, only beam parameters that are complex or impossible to correct numerically are physically corrected by the correction means using a high-speed autofocus correction lens / correction means in a modified example of this embodiment. The result is a hybrid system.

[0122] According to a preferred embodiment of the present invention, changes in the image field rotation of individual particle beams on the object plane are compensated by adjusting the rotation by the scanning unit, and changes in magnification on the object plane are corrected by adjusting the pixel size by the scanning unit. Preferably, the image displacement of individual particle beams on the object plane is corrected by the controller solely by calculation. Therefore, there is no need to change the obtained image data itself, only the tag (position of pixel 1) needs to be changed. In such applications, the advantage is very great because multiple correction elements / lens elements can be eliminated. For example, empirically, this step is necessary in any case within the range of a multi-beam system to correct image displacement caused by sample charging artifacts and other distortion effects.

[0123] Furthermore, according to a preferred embodiment of the present invention, the system is configured to perform high-frequency correction of beam parameters using only high-speed correction means located downstream of the crossover in the direction of the particle optical beam path. These correction means may include high-speed autofocus correction lenses and / or high-speed electrostatic aberration correction means (deflectors and / or astigmatism correctors).

[0124] According to a preferred embodiment of the present invention, the controller of the multi-beam particle system is further configured to control the particle optical components in the second particle optical beam path at each operating point associated with the working distance, by static or low-frequency adaptation of focusing in the second particle optical beam path, so that the second individual particle beams emitted from the wafer surface placed at each working distance are focused into a detection area in a third field of view. As an example, a projection lens system can be used as a particle optical component that can be used to set the focus and / or other particle optical parameters representing particle optical imaging in the second particle optical beam path. The particle optical component, in particular the projection lens system, may also comprise one or more magnetic lenses, the effect of which can be adjusted relatively slowly by the controller. Other and / or other magnetic and / or electrostatic lenses, deflectors, and / or astigmatism correctors can also be controlled by the controller to set other parameters such as focus and / or magnification (pitch of the second individual particle beams at the detection surface and position), rotation, and / or eccentricity at each operating point of a given working distance. It is possible to control some or all of the components at high speed (low frequency) rather than low speed. However, high-speed control in the secondary path is not necessary for basic adjustments at the first operating point.

[0125] According to one preferred embodiment of the present invention, the multi-beam particle system may have a multi-part configuration and further comprises a high-speed projection path correction means configured to perform high-frequency adaptation of the focus, grid arrangement, incident angle, and / or contrast of the second individual particle beams upon incidence to a detection area in a third field of view. Here, the controller is configured to control the high-speed projection path correction means by generating one or a set of projection path control signals based on actual autofocus data during wafer inspection at each operating point. The set of projection path control signals is generated particularly when the projection path correction means has a multi-part configuration and its components are controlled separately.

[0126] In particular, high-frequency adaptation in the secondary path is necessary when the second individual particle beams emitted from the wafer surface also pass through the high-speed autofocus correction lens. This is because the high-speed autofocus correction lens affects the trajectory of the second individual particle beams. However, even if the second individual particle beams do not pass through the high-speed autofocus correction lens, it is possible, and may be necessary, to reset the focus and / or other parameters representing particle optical imaging in the secondary path. In the secondary path, it is usually desirable that the second individual particle beams enter the detection region focused at a predetermined angle of incidence and, in particular, eccentrically with a predetermined grid arrangement (pitch and orientation of the incident points in the third field of view). Therefore, high-frequency adaptation of high-speed particle optics components is also convenient in the secondary path. Here, the mode of adaptation can be carried out substantially the same as the procedure in the primary path. Also here, high-speed / high-frequency correction can be performed on the beam profile of the second individual particle beams (optionally, after appropriate orthogonalization) by using the aforementioned particle optics components or other components in conjunction with the primary beam. As an example, another high-speed autofocus correction lens can be placed in the secondary beam path (only), i.e., between the beam switch and the detection unit. As an example, this lens can be a high-speed electrostatic lens or a high-speed magnetic lens, particularly in the form of an air coil with only a few turns. As an example, this second autofocus correction lens can be placed in the region of the crossover plane in the secondary path. As an example, such a crossover plane in the secondary path is located in the region of the projection lens system in the secondary path. However, different arrangements of the second autofocus correction lens in the secondary path are also possible. As an example, in the secondary path, the high-speed eccentricity correction means described in conjunction with the primary path can also be used. In the means, for example, a deflector array is placed in the intermediate image plane in the secondary path. Also, as described with respect to the primary path, rotation correction means, for example in the form of another deflector array, can be placed and used immediately upstream or downstream of the deflector array for correcting eccentricity in the secondary path.According to the described embodiment, the generation of projection path control signals is based on actual autofocus data determined for the first particle optical beam path. Therefore, the work can be performed by using empirical / lookup tables to directly or indirectly assign necessary corrections to the actual autofocus data, for example, the focus on the detector and / or other parameters in the secondary path. The associated control signals / sets of control signals can then be stored.

[0127] According to another embodiment of the present invention, the multi-beam particle system may have a multi-part configuration and further comprises a projection path measurement element for generating projection path measurement data characterizing particle optical imaging in the secondary path during wafer inspection, and further comprises high-speed projection path correction means configured to perform high-frequency adaptation of the focus, grid arrangement, incident angle, and / or contrast of the second individual particle beams upon incidence to a detection area in a third field of view, and the controller is configured to control the high-speed projection path correction means by generating one or a set of projection path control signals based on the projection path measurement data during wafer inspection at each operating point. Thus, in a modification of this embodiment of the present invention, the controller does not use or use alone actual autofocus data for high-frequency / high-speed adaptation of particle optical components. Instead, measurement data in the secondary path is used for high-frequency adaptation. In principle, high-speed measurement methods that supply data for adaptation "on the fly" are already known in the prior art. Data for high-frequency adaptation can be determined, for example, by evaluation of a CCD camera image recorded in addition to a scanning image obtained by the detection area in the third field of view. Known measurement methods can be used to determine the current relative focal position, angle of incidence, and / or grid arrangement in the third field of view, particularly when incident on the detection area.

[0128] With respect to topographic contrast, specific requirements can be imposed on the second particle optical beam path. In the second particle optical beam path, a contrast aperture can be provided within the crossover plane. By using a ring-shaped aperture, interaction products can be filtered depending on the starting angle at which they are emitted from the wafer. Then, only the second individual particle beams that are far from the wafer surface within a specific angular range can pass through the contrast aperture. Such a contrast aperture can increase the topographic contrast because interaction products (e.g., secondary electrons) are mainly emitted at a larger gradient angle than the incident particles at the edges of the wafer surface. Further information regarding contrast settings and aperture apertures can be found in German Patent No. 102015202172 and U.S. Patent Application Publication 2019 / 0355544, all of which are incorporated herein by reference. According to a preferred embodiment of the present invention, a contrast aperture is positioned in the path of a second particle optical beam in a crossover plane, and the projection path correction means comprises a high-speed contrast correction means comprising at least one electrostatic deflector, at least one electrostatic lens, and / or at least one electrostatic astigmatism corrector for influencing the path of the particle optical beam passing through the contrast aperture, and the controller is configured to control the contrast correction means using one or a set of contrast correction control signals such that the contrast of the second individual particle beams is kept substantially constant when incident on a detection area in a third field of view. What can be achieved by the electrostatic components of the high-speed contrast correction means is high-frequency adaptation, in particular contrast invariance. Here, the contrast correction control signals can be determined, for example, based on projection path measurement data of the secondary path and / or actual autofocus data of the primary path.

[0129] All of the above explanations apply not only to high-speed autofocus but also to high-speed autostigma. By definition, stigma within the scope of this application is also included in focusing. In principle, stigma can be physically identified with focusing in only one direction or with different focusing in different directions. When stigma is taken into account, the number of particle optical parameters representing particle optical imaging increases or doubles. For example, two parameters for focus and two parameters for position, and two parameters for incidence angle and two parameters for rotation are required in each case. In this context, we also refer to high-speed multipolar lenses, which are described, for example, in the unpublished German Patent Application No. 102020107738.6 filed on March 20, 2020, and all of its disclosures are incorporated herein by reference.

[0130] According to a second aspect of the present invention, the present invention relates to a multibeam particle system for semiconductor inspection, A multi-beam particle generator configured to generate a first field of view for multiple first individual charged particle beams, A first particle optical unit having a first particle optical beam path configured to image the first individual particle beams onto the wafer surface such that the generated first individual particle beams collide with the wafer surface on the object surface at the point of incidence to form a second field of view, A detection system having multiple detection regions that form a third field of view, A second particle optics unit having a second particle optical beam path configured to image second individual particle beams emitted from an incident point in a second field of view into a third field of view of the detection region of the detection system, A magnetic and / or electrostatic objective lens, particularly a magnetic and / or electrostatic immersion lens, through which both the first individual particle beam and the second individual particle beam pass, A beam switch is positioned between the multibeam particle generator and the objective lens in the first particle optical beam path, and between the objective lens and the detection system in the second particle optical beam path. A sample stage for holding and / or positioning wafers during wafer inspection, An autofocus determination element configured to generate data for determining the actual autofocus data during wafer inspection, High-speed autofocus correction lens, Controller and Equipped with, The present invention relates to a multi-beam particle system in which a controller is configured to control at least a magnetic objective lens and / or an actuator of a sample stage at a first working point at a first working distance, by static or low-frequency adaptation of focusing, such that a first individual particle beam is focused onto a wafer surface placed at a first working distance.

[0131] Thus, in this embodiment of the present invention, the controller is configured to set a focus with respect to a given first operating point to which a first working distance is assigned. Therefore, according to this system, after adjusting the operating point as described, focusing can be set.

[0132] According to a preferred embodiment of the present invention, the controller is further configured to control a high-speed autofocus correction lens during wafer inspection at a first operating point by generating an autofocus correction lens control signal by high-frequency adaptation of focusing based on actual autofocus data at a first operating point during wafer inspection.

[0133] Furthermore, all other provisions and / or descriptions set forth in conjunction with the first aspect of the present invention also apply to the second aspect of the present invention.

[0134] According to a third aspect of the present invention, the present invention relates to a method for operating a multibeam particle system, in particular a multibeam particle system as described in conjunction with the first aspect of the present invention. All terms and definitions described or introduced in conjunction with the first aspect of the present invention also apply to the method according to the present invention. The method for operating a multibeam particle system is: A step of generating measurement data at a first operating point with respect to the current focal point on the wafer surface, The steps include determining the actual autofocus data based on the measurement data, The steps include determining the autofocus correction lens control signal based on actual autofocus data, A step of controlling a high-speed autofocus correction lens system including a first high-speed autofocus correction lens, and maintaining a constant focal point on the wafer surface at high frequency, wherein the incident angle, rotation, and / or position of the first individual particle beams upon incidence on the wafer surface are similarly kept constant at the first operating point. Includes.

[0135] According to a preferred embodiment of the present invention, the high-speed autofocus correction lens includes and / or consists of at least one electrostatic lens. The provisions already described in conjunction with the multi-beam particle system according to the present invention also apply to the options for constituting the electrostatic lens and its arrangement in the beam path.

[0136] According to another preferred embodiment of the present invention, the high-speed autofocus correction lens includes at least one high-speed magnetic lens, in particular an air coil, and / or consists of strictly one magnetic lens. The provisions already described in conjunction with the multi-beam particle system according to the present invention also apply to the options for constituting the magnetic lens and its arrangement in the beam path.

[0137] To maintain a constant grid arrangement and incidence angle on the wafer surface, high-speed eccentricity correction means, high-speed rotation correction means, and / or high-speed position correction means can be used, as described above in conjunction with the first aspect of the present invention. The high-speed eccentricity correction means, high-speed rotation correction means, and / or high-speed position correction means can be used together with an autofocus correction lens having a multi-part configuration, as an optional embodiment, to constitute an autofocus correction lens system.

[0138] According to a preferred embodiment of the present invention, this method is A step of generating an eccentricity correction control signal based on actual autofocus data, A step of controlling a high-speed eccentricity correction means, It also includes.

[0139] According to a preferred embodiment of the present invention, this method is A step of generating a rotation correction control signal based on actual autofocus data, A step of controlling the high-speed rotation correction means, It also includes.

[0140] According to a preferred embodiment of the present invention, this method is The steps include generating a second high-speed autofocus correction lens control signal based on actual autofocus data, and controlling the second high-speed autofocus correction lens with high frequency, A step of generating a third high-speed autofocus correction lens control signal based on actual autofocus data, and controlling the third high-speed autofocus correction lens with high frequency, The steps include generating a fourth high-speed autofocus correction lens control signal based on actual autofocus data, and controlling the fourth high-speed autofocus correction lens with high frequency, The steps include generating a fifth high-speed autofocus correction lens control signal based on actual autofocus data, and controlling the fifth high-speed autofocus correction lens with high frequency, A step of generating a sixth high-speed autofocus correction lens control signal based on actual autofocus data, and controlling the sixth high-speed autofocus correction lens with high frequency, It also includes.

[0141] The second, third, fourth, fifth, and / or sixth high-speed autofocus correction lenses are high-speed autofocus correction lenses already described in conjunction with the first aspect of the present invention. The details described in this background also apply without limitation to the method described in the third aspect of the present invention.

[0142] According to another preferred embodiment of the present invention, this method is The steps include: changing the operating point, particularly the working distance, and generating hysteresis-corrected measurement data that characterizes the particle optical imaging on the object surface; The steps include: performing high-frequency correction on one or more autofocus correction lens control signals based on hysteresis correction measurement data; It also includes.

[0143] Depending on the measurement data available as hysteresis correction measurement data, a separate feedback loop can be incorporated into the workflow for the purpose of controlling another autofocus correction lens. For example, by using a CCD camera positioned in the second particle optical beam path, actual data on the magnification and / or rotation of individual particle beams on the object plane can be generated. This data can then be used as actual data for correcting an autofocus correction lens that high-frequency corrects the corresponding beam parameters. This additional information does not need to be used (although it can be used) to correct the first autofocus correction lens control signal, which is mainly used for focus correction. Other points already stated in conjunction with the first embodiment also apply to this embodiment of the present invention. Further details regarding the generation of measurement data in the second particle optical beam path are available in U.S. Patent Application Publication 2019 / 0355544, all of which are incorporated herein by reference.

[0144] According to a preferred embodiment of the present invention, the method further includes the step of generating an aberration correction control signal and performing high-precision correction of the beam position using the aberration correction control signal. Such high-precision correction can be implemented particularly upstream of each high-speed autofocus correction lens. This correction is intended to keep the position of individual particle beams constant with high precision as they pass through the column. This correction also keeps the path of individual particle beams constant as they pass through various lens elements. However, high-precision correction is particularly effective upstream of the autofocus correction lens. In this way, it is also possible to keep the crossover position strictly constant so that the pixel size in the image field does not change virtually (with an accuracy in the range of 0.01 to 0.1 ppth) during the scanning procedure. Furthermore, the points already described in conjunction with the first aspect of the present invention also apply in this respect.

[0145] According to another preferred embodiment of the present invention, the method further includes the step of generating a scanning unit control signal and, in particular, high-frequency correcting the scanning unit control signal at each operating point by using a multidimensional lookup table. These method steps take into account the fact that the scanning parameters of the scanning unit need to be adapted even after optionally performing autofocus adaptation and corresponding aberration correction. In addition, all of the other points already stated in conjunction with the first aspect of the present invention also apply in this respect.

[0146] According to another preferred embodiment of the present invention, the method further includes the step of correcting image data using calculations relating to at least one beam parameter, in particular, correcting image data using calculations relating to image displacement alone. Furthermore, it is particularly possible to compensate for changes in magnification on the object plane by corresponding to the rotation of the beam parameter by reversing the rotation of the scanning unit and by changing the pixel size setting on the scanning unit.

[0147] Based on the above, the present invention, in another embodiment (fourth embodiment), is a method for operating a multibeam particle system for high-speed autofocus correction at the operating point, The steps include physically setting the focus on the object plane using at least one high-speed autofocus correction lens, The steps include physically setting the angle of incidence on the object plane using at least one high-speed autofocus correction means, By quickly setting the reverse rotation, the scanning unit sets the magnetic field rotation, By quickly setting the pixel size, the scanning unit sets the magnification, A step of compensating for image field displacement solely through calculation, This includes methods.

[0148] Herein, the above-mentioned multi-beam particle system is possible in multiple embodiments. As a high-speed autofocus correction means for physically setting the incident angle, at least one high-speed autofocus correction lens having the corresponding characteristics is possible. However, other embodiments are also possible.

[0149] According to a preferred embodiment of the present invention, this method is A step to quickly set the secondary scanning parameters of the scanning unit, and / or A step to quickly set the scanning parameters for the skew of the scanning unit. It also includes.

[0150] In this case, it is preferable that this step / these steps be performed prior to compensation by calculation of image displacement alone.

[0151] According to a preferred embodiment of the present invention, this method further includes the step of orthogonalizing the effects of particle optical components used to correct one or more beam parameters.

[0152] According to a preferred embodiment of the present invention, this method is A step of generating projection path measurement data that characterizes particle optical imaging in the secondary path, The steps include determining one or a set of projection path control signals based on projection path measurement data, A step of controlling a high-speed projection path correction means, which may have a multi-part configuration, by one or a set of projection path control signals, wherein the focus, grid arrangement, and incident angle of the second individual particle beams upon incidence on the detection surface are kept constant at the first operating point. It also includes.

[0153] Therefore, if the focus is kept constant, the relative focal position is updated while the grid arrangement and incident angle remain constant.

[0154] According to a preferred embodiment of the present invention, the method further includes the step of controlling a high-speed contrast correction means with one or a set of contrast correction control signals and maintaining a constant contrast on the detection surface.

[0155] By controlling the high-speed contrast correction means, it is possible to specifically influence the relative position of the crossover in the secondary path, thereby keeping the crossover constant.

[0156] According to another aspect of the present invention, the present invention relates to a computer program product having program code for performing the methods described above in conjunction with the third and fourth aspects of the present invention.

[0157] The embodiments of the present invention described above, according to the above-described aspects of the present invention, can be combined in whole or in part, provided that no technical contradictions result.

[0158] The present invention will be further understood by referring to the accompanying drawings. [Brief explanation of the drawing]

[0159] [Figure 1] This is a schematic diagram of a multibeam particle microscope. [Figure 2]This is a schematic diagram showing part of the controller for a multi-beam particle microscope equipped with a high-speed autofocus correction lens. [Figure 3] This is a schematic diagram showing a magnified view of a part of the controller of a multi-beam particle microscope equipped with a high-speed autofocus correction lens. [Figure 4] This diagram schematically illustrates a method for setting up high-speed autofocus using an autofocus correction lens. [Figure 5] This figure schematically shows a cross-section of a multi-beam particle microscope capable of accommodating an autofocus correction lens according to the present invention. [Figure 6] This figure schematically shows one embodiment of the present invention, including an autofocus correction lens. [Figure 7] This figure schematically shows one embodiment of the present invention, including an autofocus correction lens. [Figure 8] This figure schematically shows one embodiment of the present invention, including an autofocus correction lens. [Figure 9] This figure schematically shows one embodiment of the present invention, including an autofocus correction lens. [Figure 10] This figure schematically shows one embodiment of the present invention, including an autofocus correction lens. [Figure 11] This figure schematically shows one embodiment of the present invention, including an autofocus correction lens. [Figure 12] This figure schematically illustrates another embodiment of the present invention, which includes an autofocus correction lens. [Figure 13] This figure schematically illustrates another embodiment of the present invention, which includes an autofocus correction lens. [Figure 14] This figure schematically shows one embodiment of the present invention, including an autofocus correction lens. [Figure 15] This figure schematically shows one embodiment of the present invention, including an autofocus correction lens. [Figure 16] This figure schematically shows one embodiment of the present invention, including an autofocus correction lens. [Figure 17] This figure schematically shows one embodiment of the present invention, including an autofocus correction lens. [Figure 18] This figure schematically shows one embodiment of the present invention, which includes a two-part first autofocus correction lens. [Figure 19] This figure schematically shows one embodiment of the present invention, which includes a high-speed autofocus correction lens within the magnetic field of a field lens. [Figure 20] This figure schematically illustrates one embodiment of the present invention, including a high-speed autofocus correction lens in a multi-beam particle generator. [Figure 21] This figure schematically shows one embodiment of the present invention, which includes multiple high-speed autofocus correction lenses. [Figure 22] This figure schematically shows one embodiment of the present invention, which includes multiple high-speed autofocus correction lenses. [Figure 23] This figure schematically shows one embodiment of the present invention, which includes multiple high-speed autofocus correction lenses. [Figure 24] This figure schematically shows one embodiment of the present invention, which includes multiple high-speed autofocus correction lenses. [Figure 25] This is a schematic diagram showing part of the controller for a multi-beam particle microscope equipped with multiple high-speed autofocus correction lenses. [Figure 26] This diagram schematically illustrates the workflow for high-speed autofocus correction. [Figure 27] This diagram schematically illustrates the workflow for high-speed autofocus correction in a multi-beam particle system where high-speed autofocus correction is implemented as a hybrid system. [Modes for carrying out the invention]

[0160] In the following, the same reference symbols represent the same characteristics even if they are not explicitly mentioned in the text.

[0161] Figure 1 is a schematic diagram of a particle beam system 1 in the form of a multi-beam particle system 1 that uses multiple particle beams. The multiple particle beams generated by the particle beam system 1 collide with the object to be inspected, generating interaction products (e.g., secondary electrons), which are then detected after being emitted from the object. The particle beam system 1 is a scanning electron microscope (SEM) type and uses multiple primary particle beams 3 that are incident on multiple locations 5 on the surface of the object 7, generating multiple spatially separated electron beam spots (or spots). The object 7 to be inspected can be of any desired type (e.g., semiconductor wafers, particularly semiconductor wafers with an HV structure (i.e., horizontal and / or vertical structure), or biological samples), and may include arrays of miniature elements, etc. The surface of the object 7 is positioned on the first surface 101 (object surface) of the objective lens 102 of the objective lens system 100.

[0162] The enlarged section I1 of Figure 1 is a plan view of the object surface 101 having a regular rectangular field of view 103 formed on the first surface 101 at the incident points 5. In Figure 1, there are 25 incident points, forming a 5x5 field of view 103. The number of incident points (25) was selected for the sake of simplifying the illustration. In practice, it is possible to select a number that significantly increases the number of beams and thus the number of incident points, for example, 20x30, 100x100, etc.

[0163] In the illustrated embodiment, the field of view 103 of the incident points 5 is a substantially regular rectangular field of view with a constant pitch P1 between adjacent incident points. Exemplary values ​​of the pitch P1 are 1 micrometer, 10 micrometers, and 40 micrometers. However, the field of view 103 may also have other symmetries, such as hexagonal symmetry.

[0164] The diameter of the beam spot formed on the first surface 101 can be small. Exemplary values ​​of the diameter are 1 nanometer, 5 nanometers, 10 nanometers, 100 nanometers, and 200 nanometers. Focusing the particle beam 3 to form the beam spot 5 is performed by the objective lens system 100. In this case, the objective lens system may include, for example, a magnetic immersion lens.

[0165] Primary particles that collide with an object generate interaction products (e.g., secondary electrons, backscattered electrons, or primary particles whose trajectory is reversed for other reasons), which are emitted from the surface of object 7 or a first surface 101. The interaction products emitted from the surface of object 7 are shaped by the objective lens 102 to form a secondary particle beam 9. The particle beam system 1 provides a particle beam path 11 for guiding multiple secondary particle beams 9 to a detection system 200. The detection system 200 comprises a particle optics unit including a projection lens 205 for guiding the secondary particle beams 9 to a particle multi-detector 209.

[0166] Part I2 of Figure 1 is a plan view of the plane 211 in which the individual detection regions of the particle multi-detector 209 are arranged, into which the secondary particle beam 9 is incident at location 213. The incident location 213 is located in the field of view 217 at a regular pitch P2. Exemplary values ​​of the pitch P2 are 10 micrometers, 100 micrometers, and 200 micrometers.

[0167] The primary particle beam 3 is generated in a beam generator 300 comprising at least one particle source 301 (e.g., an electron source), at least one collimator lens 303, a multi-aperture configuration 305, and a field lens system comprising a field lens 307 or a plurality of field lenses. When the particle source 301 generates at least one divergent particle beam 309, it is parallelized or at least substantially parallelized by at least one collimator lens 303 to form a beam 311 that irradiates the multi-aperture configuration 305.

[0168] Part I3 of Figure 1 is a plan view of the multi-aperture configuration 305. The multi-aperture configuration 305 comprises a multi-aperture plate 313 on which a plurality of apertures 315 are formed. The center points 317 of the apertures 315 are located in a field of view 319 which is imaged into a field of view 103 formed by a beam spot 5 on the object plane 101. The pitch P3 between the center points 317 of the apertures 315 may have exemplary values ​​of 5 micrometers, 100 micrometers, and 200 micrometers. The diameter D of the apertures 315 is smaller than the pitch P3 between the center points of the apertures. Exemplary values ​​of the diameter D are 0.2 × P3, 0.4 × P3, and 0.8 × P3.

[0169] The particles of the irradiated particle beam 311 pass through the aperture 315 to form the particle beam 3. Particles of the irradiated beam 311 that collide with the plate 313 are absorbed by the plate 313 and therefore do not contribute to the formation of the particle beam 3.

[0170] By applying an electrostatic field, the multi-aperture configuration 305 focuses each particle beam 3 so that a beam focus 323 is formed on the surface 325. Alternatively, a virtual beam focus 323 is also possible. The diameter of the beam focus 323 can be, for example, 10 nanometers, 100 nanometers, and 1 micrometer.

[0171] The field lens 307 and the objective lens 102 provide a first imaging particle optical unit for imaging the surface 325 on which the beam focus 323 is formed onto the first surface 101, such that a field of view 103 of the incident point or beam spot 5 is produced. When the surface of the object 7 is located on the first surface, the beam spot is formed correspondingly on the object surface.

[0172] The objective lens 102 and projection lens configuration 205 provide a second imaging particle optical unit for imaging the first surface 101 onto the detection surface 211. Thus, the objective lens 102 is a lens as part of both the first and second particle optical units. On the other hand, the field lens 307 belongs only to the first particle optical unit, and the projection lens 205 belongs only to the second particle optical unit.

[0173] In the beam path of the first particle optics unit, a beam switch 400 is positioned between the multi-aperture configuration 305 and the objective lens system 100. The beam switch 400 is also part of the second optical unit in the beam path between the objective lens system 100 and the detection system 200.

[0174] Such multibeam particle systems and the components used therein (for example) Further information regarding particle sources, multi-aperture plates, and lenses, etc., is available in International Patent Publications WO2005 / 024881, WO2007 / 028595, WO2007 / 028596, WO2011 / 124352, and WO2007 / 060017, as well as German Patent Publications 102013016113 and 102013014976, the entire scope of which these disclosures are incorporated herein by reference.

[0175] The multibeam particle system further comprises a computer system 10 configured to control the individual particle optical components of the multibeam particle system and to evaluate and analyze the signals acquired by the multi-detector 209. In this case, the computer system 10 can be composed of multiple individual computers or components. It is also possible to control the high-speed autofocus correction lens and eccentricity correction means, high-speed rotation correction means, and / or other high-speed correction means (not shown in Figure 1) according to the present invention.

[0176] Figure 2 is a schematic diagram showing a portion of the controller of the computer system 10 of a multi-beam particle microscope 1 equipped with a high-speed autofocus correction lens 824. Specifically, this portion shows the controller 821 for high-speed autofocus. The controller 821 for high-speed autofocus is configured to perform high-frequency adaptation of focusing at the operating point during wafer inspection. This means that focusing adaptation can be performed very quickly (e.g., within a few microseconds). In addition to the overall control system 821 (in this case, part of the computer system 10), other components are provided for the above-mentioned high-speed adaptation, such as a measurement element 822, an autofocus algorithm 823 for processing measurement data, and at least one final control element configured according to the processing of measurement data. In this specific example, the autofocus correction lens 824 provides the final control element. In this example, additional high-speed final control elements (in this case, specifically eccentricity correction means 825, high-speed rotation correction means 826, and high-speed position correction means 827) are also provided. In this case, these additional final control elements can be formed by other high-speed autofocus correction lenses, but configurations different from the high-speed lenses are also possible. The measurement element 822 is configured to generate measurement data for determining the actual autofocus data during wafer inspection. In this case, the actual autofocus data directly or indirectly represents the current focal position relative to the wafer surface. As an alternative to the autofocus measurement element 822, more generally, an autofocus determination element can also be provided that generates data for determining the actual autofocus data based, for example, on a wafer model. In principle, autofocus measurement elements are known from the prior art. Examples in this regard include the use of astigmatism-assisted beams for setting the focus and height measurement on the sample surface (e.g., by a z-sensor). Importantly, one or more measurement members 822 also enable the determination of a continuous, or ongoing, "on-the-fly," setting of the focus for each image field obtained by multiple individual particle beams, respectively.Here, depending on the measurement element 822 and the evaluation method, the autofocus algorithm 823 is configured to high-frequency control the high-speed autofocus correction lens 824 during wafer inspection at the operating point by generating actual autofocus data from the measurement data and generating an autofocus correction lens control signal based on the actual autofocus data. As a result, the relative focal position is adapted. As has been explained many times already, the effects of particle optics components in a multi-beam particle system are not usually orthogonal to each other. This means that even if the effect of only one particle optics component is changed, there can usually not be only one change in the parameters characterizing particle optical imaging. Instead, the system is more complex, and changing the parameters of particle optical imaging usually requires changing the effects of multiple particle optics components. In the particular case above, this means that readjusting / fine-tuning the relative focal position involves changing other particle optics parameters. As an example, these are the magnification (related to the beam pitch of the individual particle beams), eccentricity, and rotation of the individual particle beams when incident on the sample or wafer 7. However, since these additional parameter changes are undesirable, correction and / or constant maintenance within the range of high-speed autofocus are also performed. Therefore, eccentricity correction means 825, rotation correction means 826, and position correction means 827 are provided exemplary. The high-speed eccentricity correction means is configured to substantially contribute to correcting tangential or radial eccentricity errors of the first individual particle beams 3 in the second field of view 103, and the high-speed autofocus controller 821 is configured to control the high-speed eccentricity correction means during wafer inspection by generating eccentricity correction means control signals for high-frequency adaptation at each operating point during wafer inspection based on actual autofocus data. As an example, a first polarizer array positioned at an intermediate image plane (e.g., intermediate image plane 325) of the first particle optical beam path can be used as the eccentricity correction means. However, modifications of other embodiments are also possible.

[0177] To compensate for rotation (specifically, unwanted rotation of the grid array in the second field of view 101), a high-speed rotation compensation means 826 is further provided, configured to substantially contribute to the compensation of rotation of the first individual particle beams 3 in the second field of view 101. Here, a high-speed autofocus controller 821 is configured to control the high-speed rotation compensation means 826 during wafer inspection by generating rotation compensation means control signals for high-frequency adaptation based on actual autofocus data during wafer inspection at each operating point. As an example, such rotation compensation means 826 may be implemented as a second deflector array positioned at a distance immediately upstream or downstream of the first deflector array for eccentricity compensation. However, other embodiments are also possible, for example, by a multi-lens array positioned at a distance immediately upstream or downstream of the first deflector array so that the first individual particle beams 3 pass through the multi-lens array off-axis. Alternatively, the multi-beam particle generator 305 may include the high-speed rotation compensation means 826, which may be actively rotated by the rotation compensation means control signals. Furthermore, by combining the two magnetic field generators, it is possible to obtain mutually opposing weak magnetic fields, and to use each magnetic field only for rotational changes in a specific direction.

[0178] Figure 3 is a schematic diagram showing a magnified view of a portion of the controller of the computer system 10 of a multibeam particle microscope 1 equipped with a high-speed autofocus correction lens 824. Control units 810 and 830 for the primary and secondary paths are shown exemplarily. In this case, the controller of the computer system 10 may have other components than those shown in Figure 3. In view of the present invention, several important control elements will be discussed below. The controller 810 for the primary path comprises a controller 811 for setting the operating point and a controller 821 for setting the high-speed autofocus. In this case, in particular, the controller 811 is configured to control at least the magnetic objective lens and / or the actuator of the sample stage at the first operating point of the first working distance by static or low-frequency adaptation of focusing, so that the first individual particle beams are focused on the wafer surface placed at a first working distance. In addition to the focus, other parameters of particle optical imaging (e.g., the spacing (pitch) of the individual beams, the associated magnification, the rotation of the lattice arrangement of the individual particle beams upon incidence to the wafer surface, and the desired incidence angle upon incidence to the wafer surface) are also set. Therefore, the working point setting 811 includes slow autofocus and additional correction functions. For the setting itself, a measuring element 812, an adjustment algorithm 813, and various final control elements 814 are provided. These final control elements 814 include, in particular, a magnetic and / or electrostatic objective lens 102 and, optionally in the case of a height-adjustable sample stage, an actuator for the sample stage. The final control elements 814 for setting the working point further include, for example, a field lens system 307 and a multi-beam particle generator 305. Other particle optical elements in the first particle optical beam path may also act as other final control elements 814, such as magnetic and / or electrostatic lenses. The means for setting the working point can generate relatively long strokes for changing the working distance. For example, the strokes can be ±300, 200, or 100 μm. In this case, the adaptation time to the selected working distance is relatively long, for example, in the range of tens to hundreds of milliseconds.

[0179] The controller 821 for high-speed autofocus comprises a measuring element 822 (or, more generally, an autofocus determination element), an autofocus algorithm 823, and at least an autofocus correction lens 824. However, other correction means (e.g., the eccentricity correction means 825, rotation correction means 826, and / or position correction means 827 described above) may also be provided. The controller 821 for high-speed autofocus enables high-frequency adaptation of the focus, with typical adaptation times in the range of several microseconds. As an example, the adaptation time is TA ≤ 500 μs, preferably TA ≤ 100 μs and / or TA ≤ 50 μs. The stroke for changing the relative focus position is typically several micrometers (e.g., ±20 μm, ±15 μm, and / or ±10 μm). In this case, the adaptation time TA for high-frequency adaptation is at least 10 times, preferably at least 100 times and / or 1000 times shorter than the adaptation time TA for low-frequency or static adaptation by the controller to set the operating point 811.

[0180] Furthermore, changes in the relative focal position or wafer surface position may necessitate the resetting or readjustment of particle optical components in the secondary path. Therefore, the controller 830 for controlling the secondary path is part of the controller of the computer system 10. The control elements in the secondary path can also be subdivided into low-frequency or static control elements 831 and high-frequency control elements 841 (for example, corresponding to a second high-speed autofocus). The low-speed operating point setting is controlled by the controller 831. For this purpose, a measurement element 832 (e.g., a CCD camera), a second adjustment algorithm 833, and one or more final control elements 834 are provided. As an example, these final control elements 834 include a magnetic projection lens 205 controlled so that the focus of the second individual particle beam 9 is precisely imaged onto the surface of the detection area of ​​the detection unit 209. However, other final control elements can also be controlled by the controller 831 for setting the operating point. The controller 841 controls the second high-speed autofocus in the secondary path. In this case, refocusing is performed in the secondary path during wafer inspection. Similarly, other particle optics parameters such as position, eccentricity, and rotation can be quickly readjusted. For this purpose, in this embodiment, the controller 841 comprises a measuring element 842, a second autofocus algorithm 843, and a high-speed projection path correction means 844, in particular an electrostatic lens, an electrostatic deflector, and / or an electrostatic astigmatism corrector. As an example, a high-speed CCD camera could be used as the measuring element 842, or for measuring the current around a contrast aperture located on the crossover plane in the secondary path, for example. However, it is also possible to operate the measuring element 842 in the secondary path in a feedforward loop instead of omitting it. The second autofocus algorithm 843 then determines a control signal for the high-speed projection path correction means 844 based on the value / setting determined for the primary path, and controls the projection path correction means 844 accordingly. In this case, the autofocus algorithm 843 may include a lookup table. Furthermore, the two modifications can be combined only when a certain deviation from a reference value is measured.In other words, by using the additional measurement element 842, it is also possible to clearly re-determine the settings of, for example, the final control element / projection path correction means 844 of the secondary path.

[0181] Here, the controller of the computer system 10, which includes a control element 810 for controlling the primary path and a control element 830 for controlling the secondary path, is further configured so that controllers 810 and 830 are temporally synchronized with their respective components. Similarly, the electronic equipment used for control is also very fast, but it is necessary to ensure that the settings of the particle optics components in the primary and secondary paths are as optimal as possible, for example, for each image field of view (mFOV). Details regarding the realization of high-speed control of particle optics components / high-speed electronic equipment are familiar to those skilled in the art and are disclosed, for example, in German Patent Application No. 102020209833.6 filed on August 5, 2020, all of which are incorporated herein by reference.

[0182] Figure 4 schematically illustrates the method for setting high-speed autofocus using the autofocus correction lens 824. It is assumed that the (low-speed) adjustment of the system at the first working point associated with the first working distance has been performed by adjusting the magnetic objective lens and / or controlling the actuator of the sample stage. In this process, other parameters have also been set according to the specifications of the working point (magnification, eccentricity, rotation).

[0183] In step S1 of the method, measurement data of the current focus at the selected operating point AP is generated. The operating point is defined by at least the working distance between the objective lens and the wafer surface. However, other parameters can also be used to define the operating point. Examples include the relative focal position, position and eccentricity, or incident angle of individual particle beams 3 on the wafer surface, and the rotation of the lattice arrangement of individual particle beams 3 when incident on the wafer surface. The following is intended to be an example, but should not be construed as limiting the invention. In step S2 of the method, the actual autofocus data is determined based on the measurement data. This measurement data can be obtained using the measurement element 812 described above, and from this, the actual autofocus data can be determined by the adjustment algorithm 813. Therefore, for example, the actual autofocus data defines the presence or magnitude of hyperfocus or underfocus. However, it is also possible to directly construct the actual autofocus data from the measurement data (identification information map). After determining the actual autofocus data, in steps S3, S4, and S5, control signals are generated based on the actual autofocus data. In step S3, an autofocus correction lens control signal is generated based on the actual autofocus data. In step S4, an eccentricity correction means control signal is generated based on the actual autofocus data. In step S5, a rotation correction means control signal is generated based on the actual autofocus data. In this case, adjusting the autofocus correction lens not only changes the relative focal position, but also typically changes the magnification (position (not shown)), eccentricity, and / or rotation of the lattice array of individual particle beams. In the illustrated example, an orthogonalization matrix or the inverse sensitivity matrix 850 is used within the scope of determining the control signal. This allows for strictly different settings of particle optical parameters by deriving particle optical components requiring different excitations and their absolute values. As a result, it is preferable that the control of the autofocus correction lens in step S6, the control of the eccentricity correction means in step S7, the control of the rotation correction means in step S8, and the control of any other optional high-speed correction means are performed simultaneously.

[0184] Once these adjustments are performed on the primary path, the secondary path is updated at a high frequency. This is feedforward in the illustrated example, but feedback is performed on the primary path. In method step S9, second measurement data is generated for the current second relative autofocus position (detection surface) in the secondary path. Alternatively, the current relative position of the crossover of the second individual particle beams in the secondary path can be determined. In method step S10, the second actual autofocus data for the secondary path is determined. Alternatively, a value pre-assigned for the actual autofocus data of the primary path can be used for the secondary path. Then, in method step S11, the projection path correction means control signal is determined based on the second actual autofocus data. This can also be a set of control signals. Preferably, the second orthogonalization matrix or the second inverse sensitivity matrix 851 of the secondary path is used to generate the control signal. Then, in method step S12, the high-speed projection path correction means is controlled using the control signal. Preferably, this includes a second high-speed autofocus correction lens. Furthermore, high-speed eccentricity correction means (for example, in the form of a deflector array in the intermediate image plane of the secondary path), high-speed rotation correction means (for example, in the form of a second deflector array immediately upstream or downstream of the deflector array for high-speed eccentricity correction in the secondary path), and / or other high-speed correction means (for example, electrostatic lenses, electrostatic deflectors, and / or electrostatic astigmatism correctors) can be controlled. High-speed contrast correction means can also be controlled. As an example, high-speed contrast correction means can be incorporated into the projection lens system of the secondary path, as described, for example, in U.S. Patent Application Publication 2019 / 0355544, the entire disclosure thereof is incorporated herein by reference. Then, in method step S13, the image field is recorded by using the settings of step S12. Subsequently, new measurement data of the current focus at the operating point can be generated (method step S1). The corresponding procedures are performed until the entire image recording process is completed.

[0185] In one example, the first or second orthogonalization or sensitivity inverse matrices 850, 851 may be determined by the operating point setting in accordance with the adjustments made by controllers 811 and 831. For example, the dynamic correction required for tangential or radial eccentricity errors parallel to the detailed correction of the focal plane may be determined by an operating point of a few micrometers or a coarse focus setting within a long-range focal range of several hundred micrometers. In this case, the orthogonalization or sensitivity inverse matrices 850, 851 for the selected operating point are selected from a memory containing multiple orthogonalization or sensitivity inverse matrices 850, 851 for different focus settings within the long-range focal range.

[0186] Figure 5 schematically shows a cross-section of a multi-beam particle microscope 1 on which an autofocus correction lens 824 according to the present invention can be installed. The multi-beam particle system 1 first comprises a particle source 301. In the illustrated example, this particle source 301 emits individual particle beams containing charged particles (e.g., electrons). In Figure 5, the particle beam or particle optical beam path is schematically shown by a dashed line with reference numeral 3. The individual particle beams first pass through a condenser lens system 303 and then collide with a multi-aperture configuration 305. This multi-aperture configuration 305 (which may include other particle optical components) functions as a multi-beam generator. The first particle beam emitted from the multi-aperture configuration 305 then passes through a field lens or field lens system 307 and then enters a beam switch 400. This beam switch 400 comprises a Y-shaped embodiment and a beam tube configuration 460 having three rims 461, 462, and 463 in the illustrated example. Here, the beam switch 400 includes two flat interconnect structures for holding magnetic sectors 410 and 420, and the magnetic sectors 410 and 420 enclosed in or fixed to the structures. After passing through the beam switch 400, the first particle beam 3 passes through the scanning deflector 500 and simultaneously the particle optical objective lens 102 before being incident on object 7 (in this case, a semiconductor wafer having an HV structure). As a result of this incident, secondary particles (e.g., secondary electrons) are emitted from object 7. These secondary particles constitute a second particle beam to which a second particle optical beam path 9 is assigned. After emission from object 7, the second particle beam first passes through the particle optical objective lens 102 and the subsequent scanning deflector 500 before entering the beam switch 400. Subsequently, the second particle beam 9 is emitted from the beam switch 400, passes through the projection lens system 205 (very simply illustrated), passes through the electrostatic element 260, and then enters the particle optical detection unit 209 (in this case, reference symbol 260 indicates so-called anti-scan, which compensates for any scanning movement that may occur in the secondary beam 9 when it enters the detection unit 209).

[0187] The beam tube configuration 460 is located within the beam switch 400 and, in the illustrated example, extends from the beam switch 400. The splitting of the beam paths into the first particle optical beam path 3 and the second particle optical beam path 9 within the beam switch 400 is performed by magnetic sectors 410 and 420 within the beam switch 400. In the example shown in Figure 5, the beam tube configuration 460 continues outside the beam switch 400. In this case, in particular, it extends to or enters the particle optical objective lens 102 (beam tube extension). The beam tube configuration 460 enters the vacuum chambers 350, 355, and 250 in the region of the particle source 301, the region of the multi-aperture configuration 305, and the region of the detection unit 209. At least in the region of the beam switch 400, the beam tube configuration usually has a partial configuration embodiment. That is, there are no weld points or weld lines, nor solder points or solder lines. In the illustrated example, the beam tube configuration includes copper. However, it may also include titanium or any other element or any other compound. Here, the region of the beam tube configuration 460 within the beam switch 400 has a high degree of vacuum, 10 -5 Less than mbar, especially 10 -7 mbar and / or 10 -9 The pressure is preferably less than mbar. As mentioned above, chambers 350, 355, and 250 are also under vacuum, and each is 10 -5 Less than mbar, especially 10 -7 mbar and / or 10 -9 A pressure of less than mbar is preferable.

[0188] In the illustrated example, the objective lens 102 has an upper pole piece 108 and a lower pole piece 109. A winding 110 for generating a magnetic field is placed between the two pole pieces 108 and 109. Here, the upper pole piece 108 and the lower pole piece 109 are electrically insulated from each other. In the illustrated example, the particle optical objective lens 102 is a single magnetic lens in the form of an immersion lens. However, the objective lens or objective lens system may also include other magnetic or electrostatic lenses.

[0189] Here, the high-speed autofocus correction lens 824 according to the present invention can be incorporated into the multi-beam particle microscope 1 shown in FIG. 5 at a plurality of configurations and positions, optionally together with other high-speed correctors. In this case, the high-speed autofocus correction lens 824 has different strengths of action on the focus of each individual particle beam 3 depending on the position, while it can also act on other particle optical parameters such as the position, incident angle, and / or rotation of each individual particle beam 3. In addition, a second or additional, or a plurality of other autofocus correction lenses can be incorporated into the primary path and / or the secondary path. Optionally, another high-speed correction means can be provided in the primary path and / or the secondary path.

[0190] FIG. 6 schematically shows an embodiment of the present invention including the high-speed autofocus correction lens 824. In this embodiment, the autofocus correction lens 824 is provided in the form of an additional electrode. As an example, it can be implemented as a single aperture plate with a central opening, and a voltage U AF is applied. In this case, the level and sign of the voltage can be provided by the controller 821 for high-speed autofocus. This exemplary embodiment is advantageous in that the autofocus correction lens is realized relatively below the beam path as the penultimate lens. As a result, only a small amount of subsequent aberration occurs. From a technical point of view, the larger the absolute value of the voltage U AF , the more difficult it is to realize a rapid change in voltage. Therefore, the illustrated exemplary embodiment is particularly suitable when the sample voltage U Sample applied to the sample 7 is not so high.

[0191] Figure 7 schematically shows another embodiment of the present invention including an autofocus correction lens 824. In the illustrated example, the autofocus correction lens 824 is located within the magnetic objective lens 102. Here, the autofocus correction lens 824 is positioned between the upper pole piece 108 and the lower pole piece 109 of the objective lens 102. In this case, voltage U1 is applied to the upper pole piece 108 and voltage U2 is applied to the lower pole piece 109. These voltages can be relatively high, for example, several kilovolts. Also, voltage U2 can be applied to the autofocus correction lens 824. AF The same can be said for this as well. Therefore, in this case too, the autofocus correction lens 824 uses a relatively high voltage U AF It can operate with the voltage U. However, if the upper pole piece 108 is at ground potential, AF The absolute value can be selected to be relatively small. In this embodiment as well, the autofocus correction lens 824 is positioned relatively low to the first particle optical beam path, and in the illustrated example, it is the second to last particle optical element. Here again, a favorable aspect of this modified embodiment is that the conceivable subsequent aberrations are reduced.

[0192] Figure 8 schematically shows another embodiment of the present invention, including a high-speed autofocus correction lens 824. In a modified version of this embodiment, the autofocus correction lens 824 is located between the beam deflection system 500 and the upper magnetic pole piece 108 of the magnetic objective lens 102. This is a high-speed controllable electrode and is controlled by a controller 821 for high-speed autofocus, applying a voltage U AF The value of is adjustable. A modification of this embodiment is advantageous in that electrode 824 is substantially located within the crossover plane. Our comprehensive calculations in this regard have shown that the effect of electrode 824 at this position is substantially directed towards the focal point. Other particle optics parameters such as position, angle of incidence, and rotation are substantially constant. Furthermore, this embodiment is advantageous in that the effect of the crossover is identical for all individual particle beams. This facilitates precise setting of autofocus.

[0193] Figure 9 schematically illustrates another embodiment of the present invention, including an autofocus correction lens 824. In this case as well, the autofocus correction lens 824 is embodied as a high-speed electrostatic element or high-speed electrostatic lens. Starting from the upper magnetic pole piece 108 of the objective lens 101, the beam tube extension 464 protrudes slightly into the magnetic objective lens 101. This beam tube extension 464, like the entire beam tube 460, is at ground potential. Here, the autofocus correction lens 824 is located within the beam tube extension 464. The autofocus correction lens 824 is also controlled by a controller 821, and an adjustable voltage U AF A voltage is applied. This allows for a relatively low voltage. In this case, the illustrated position of the autofocus correction lens 824 is close to the crossover plane. Comprehensive calculations show that placing the autofocus correction lens 824 on or near the crossover plane primarily acts on the focus of individual particle beams. Therefore, the adaptation of other particle optics parameters such as position, angle of incidence, and rotation becomes unnecessary or at least minimal. This allows for faster readjustment of other parameters and a weaker design for the correction element. Thus, subsequent aberrations are reduced.

[0194] Figure 10 schematically shows another embodiment of the present invention, including a high-speed autofocus correction lens 824. In the illustrated exemplary embodiment, the autofocus correction lens 824 is provided as an offset relative to the scanning deflector 500. In the illustrated example, the scanning deflector 500 includes an upper deflector 500a and a lower deflector 500b. Here, in principle, the upper deflector 500a and the lower deflector 500b may have the same design. For example, they can be embodied as a deflector plate pair, a quadrupole element, or an octupole element. Here, voltage U is applied to both the upper deflector 500a and the lower deflector 500b. AFA voltage U is applied as an offset. In this case as well, the corresponding control signal is provided by the controller 821 for high-speed autofocus. A modification of this embodiment is advantageous in that the high-speed autofocus correction lens 824 is similarly positioned near the crossover of the individual particle beams 3. Therefore, in this case as well, the excitation of the autofocus correction lens 824 substantially acts on the focus. Furthermore, this implementation does not require additional hardware, and the voltage U is applied to the upper deflector 500a and the lower deflector 500b. AF All you need to do is apply it as an offset.

[0195] Figure 11 shows another embodiment of the present invention, including a high-speed electrostatic autofocus correction lens 824. In this embodiment, the high-speed autofocus correction lens 824 is provided as a ring electrode between the upper deflector 500a and the lower deflector 500b. In this case as well, the autofocus correction lens 824 is similarly positioned relatively close to the crossover of the individual particle beams 3. Thus, the lens 824 primarily acts on the focus of the individual particle beams. Furthermore, hardware modifications of system 1 can be carried out relatively easily. The high-speed autofocus correction lens 824 can also be embodied as an air coil around the beam tube 861 (not shown in Figure 11) instead of a ring electrode.

[0196] Figure 12 schematically illustrates other embodiments of the present invention, including the high-speed autofocus correction lens 824. In these embodiments, the beam tube 460 is blocked at the location where the autofocus correction lens 824 is provided. These locations provide relatively large spaces throughout System 1, simplifying the integration of the autofocus correction lens 824 into the overall system. Specifically, Figure 12 shows three different locations where the autofocus correction lens 824 can be positioned. According to the first example, the autofocus correction lens 824a is positioned above the beam switch 400 or magnetic sector 410 in the particle optical beam path. In other words, the blockage of the beam tube 460 where the autofocus correction lens 824a is located is situated between the field lens system 307 (not shown in Figure 12) and the beam switch 400. In the second option, the blockage of the beam tube 460 is located between two magnetic sectors 410 and 420, and the autofocus correction lens 824b is positioned in this blockage. In the third option, the beam tube 460 is positioned between the beam switch 400 and the beam deflection system 500. Thus, in these modifications of the embodiments, a portion of the inner wall of the beam tube 460 is replaced by autofocus correction lenses 824a, 824b, and / or 824c, and is not at ground potential like the beam tube 460.

[0197] Figure 13 shows another embodiment of the present invention, including a high-speed autofocus correction lens 824. The example shown in Figure 13 differs from the example shown in Figure 12 in that there is no cutoff section in the beam tube 460. Instead, tube lenses 824a, 824b, and 824c are incorporated into the beam tube 460, respectively. This makes the sealing design of the beam tube 460 and the maintenance of vacuum or high vacuum easier. In the case of the modified implementation with tube lenses, voltage U AFPreferably, a voltage is applied to the central electrode, and the upper and lower electrodes are at ground potential. Alternatively, a high-speed magnetic lens, for example in the form of an air coil, can be placed around the beam tube 460 in the illustrated region. The number of turns k of this lens is only a few turns, for example, 10 ≤ k ≤ 500, 10 ≤ k ≤ 200, and / or 10 ≤ k ≤ 50.

[0198] Figure 14 shows another embodiment of the present invention, which includes a high-speed autofocus correction lens 824 with the beam tube 460 blocked. The autofocus correction lens 824 is located within this blockage, which is located within the magnetic field lens of the field lens system 307. Modifications of this embodiment are relatively easy to implement due to the available installation space. Furthermore, because the beam tube 460 is at ground potential, a relatively low voltage is applied to the autofocus correction lens 824 to affect individual particle beams 3, voltage U AF It is sufficient to simply apply it as such. However, in this embodiment, the autofocus correction lens acts on both the focal point and position and incident angle of the individual particle beams when incident on the wafer surface. Conversely, it is also possible to correct the beam tilt and beam position by utilizing the position within the field lens 307.

[0199] Figure 15 shows another embodiment of the present invention including a high-speed autofocus correction lens 824. Compared to the modification of the embodiment shown in Figure 14, here the beam tube 460 does not have a cutoff section. Instead, a tube lens as the high-speed autofocus correction lens 824 is located inside the beam tube 460. This modification of the embodiment is also relatively easy to implement if sufficient installation space is available. On the other hand, in this case as well, the autofocus correction lens 824 acts on the position and incident angle of the individual particle beams 3, as well as the focal point. Therefore, it is convenient in an optional sense to correct the tilt and / or position of the individual particle beams with the autofocus correction lens (similarly).

[0200] Figure 16 schematically illustrates another embodiment of the present invention, including a high-speed autofocus correction lens 824. In this exemplary embodiment, the autofocus correction lens 824 is positioned near the intermediate image plane 325. Here, the autofocus correction lens 824 in this example is embodied as a combination lens comprising a first component 824a and a second component 824b. If these two components 824a and 824b are provided symmetrically with respect to the intermediate image plane 325, the combined effect is the same as if the autofocus correction lens 824 were positioned directly within the intermediate image plane 325. An advantage of the modifications of this embodiment is that other particle optics components of the entire system 1 can be positioned on the intermediate image plane 325 itself. As an example, the positioning on the intermediate image plane 325 is effective for a first multi-deflector array because it enables high-speed eccentricity correction for the first individual particle beams, as described above in the abstract of this application. However, the autofocus correction lens 824 can also be implemented as a partial configuration (i.e., only component 824a or component 824b in the vicinity of the intermediate image plane 325). Alternatively, the autofocus correction lens 824 can be arranged as a partial configuration (i.e., only component 824a or component 824b within the intermediate image plane 325 as strictly as possible). In this case, the autofocus correction lens 824 has a relatively large effect on the eccentricity of the individual particle beams 3 passing through, as in the case of the symmetrical arrangement of components 824a and 824b.

[0201] Figure 17 shows another embodiment of the present invention including a high-speed autofocus correction lens 824. In this embodiment, the high-speed autofocus correction lens 824 is incorporated into a multi-aperture configuration 305. This multi-aperture configuration 305 includes, in addition to the multi-aperture plate 313 used for generating individual beams, other multi-aperture plates or multi-lens arrays and / or multi-deflector arrays (for example, for individual focusing and / or stigma of individual particle beams (not shown in Figure 17)). In this series of so-called micro-optical units, the high-speed autofocus correction lens 824 can be provided in the form of a high-speed multi-Einzel lens configuration. In this case, multi-aperture plates 824a and 824c are at ground potential. A multi-aperture plate 824b is placed between them, and the autofocus correction voltage U is controlled by the controller 821. AF It is possible to apply the voltage U. An advantage of this embodiment of the present invention is that, in principle, neither the position nor the inclination of the individual particle beams changes. However, the spherical aberration of the autofocus correction lens 824 in the form of a multi-Einzel lens configuration and the manufacturing tolerance of the multi-aperture plate can be considered important. Also, here, the voltage U AF Therefore, a relatively high voltage is required.

[0202] Figure 18 schematically shows one embodiment of the present invention, which includes a two-part first autofocus correction lens 901. Here, the first high-speed autofocus correction lens 901 is positioned between the upper pole piece 108 and the lower pole piece 109 of the objective lens 102. Specifically, the two-part first high-speed autofocus correction lens 901 is incorporated into the beam tube extension section 464. The beam tube extension section 464, like the entire beam tube 460, is at ground potential. The two parts 824a and 824b are each embodied as high-speed electrostatic lenses. For example, they can be positioned in the cutoff section of the beam tube extension section 464, but they can also be provided as tube lenses within the beam tube extension section 464. In this respect, Figure 18 is merely a schematic diagram. In the illustrated example, the two parts 824a and 824b of the first high-speed autofocus correction lens 901 perform different tasks. In the illustrated example, the first portion 824a is substantially for setting the focal point (and consequently the object surface) at high frequency upon incidence to object 7. An electrostatic lens normally does not affect the azimuthal beam parameter of individual passing particle beams 3. However, if the electrostatic lens (in this case, lens 824a) is in a magnetic field (in this case, within the magnetic objective lens 102 with two pole pieces 108 and 109), the azimuthal beam parameter changes within the lens's field of view because the velocity of charged particles in the heterogeneous magnetic field changes. The second portion 824b of the first high-speed autofocus correction lens 901 is substantially for compensating for this unwanted effect. In principle, lens 824b also has a focusing effect on individual passing particle beams 3. However, if the polarities of the two portions 824a and 824b are different, compensation for the azimuthal deviation can be substantially achieved. Here, it is not necessarily required, but possible, for the magnitudes and signs of the voltages applied to the two portions 824a and 824b to be equal. One thing to consider here is that the magnetic field of the objective lens is not homogeneous. Overall, the two parts 824a and 824b of the first high-speed autofocus correction lens 901 are set so that ∫B(z) / v(z)dz disappears as it passes through the objective lens 102.This compensates for unwanted azimuth influences while facilitating focus adjustment in the case of rapid readjustment on the object plane 101.

[0203] Figure 19 schematically illustrates another embodiment of the present invention, which includes a high-speed autofocus correction lens 902 in the magnetic field of a field lens 307. The field lens 307 can be one of several field lenses in a field lens system. Modifications of the embodiment shown in this figure can be combined, in particular, with a partially configured first high-speed autofocus correction lens 824a or 901 positioned between the upper and lower pole pieces 108 and 109 of the objective lens 102. As a basic concept, as described above in conjunction with Figure 18, a corresponding reverse rotation is required to correct undesirable changes in the azimuth beam parameter occurring in a magnetic field. In the exemplary embodiment shown in Figure 18, the reverse rotation is achieved by a second lens portion 824b within the same magnetic lens; however, in the modification of the embodiment shown in Figure 19, this reverse rotation is achieved by providing a second high-speed autofocus correction lens 902 in a different magnetic lens. In the illustrated example, the beam tube 460 is shielded for this purpose, and the second high-speed electrostatic autofocus correction lens 902 is positioned within this shielding. In the illustrated example, the second high-speed autofocus correction lens 902 is high-frequency controlled during wafer inspection at each operating point so that image field rotation is high-frequency corrected. In practice, in this embodiment of the present invention, it has been found that the work should be performed at a relatively high voltage in the range of several kV (for example, about 5 kV). This is relatively high due to the fast voltage adaptation. With appropriate techniques, it is also possible to perform correction in this high voltage range rapidly.

[0204] Figure 20 schematically shows one embodiment of the present invention, including a fifth high-speed autofocus correction lens 905 in a multibeam particle generator. In the illustrated exemplary embodiment, the multibeam particle generator comprises a multi-lens array including a multi-aperture configuration 305 and a counter electrode 306. Overall, the voltage applied to the counter electrode 306 brings about a lens effect in the multibeam particle generator, and individual particle beams 3 are focused to different locations as they pass through the multibeam particle generator, depending on the voltage level. Here, the effect on the relative position of the focal plane in the z direction is much smaller than the effect on the magnification or pitch of individual particle beams 3 within the focal plane or intermediate image plane 325 (not shown in Figure 20). Here, the magnification of imaging at the object plane 101 can be set by changing the voltage of the multibeam particle generator. In this case, the fifth high-speed autofocus correction lens 905 can be realized as an offset voltage that can be applied to the counter electrode 306, although typically a voltage in the range of several kV is applied to the counter electrode 306. In this case, achieving high-speed change, even if possible, comes with corresponding technical challenges. Therefore, Figure 20 specifically shows another implementation using an additional fifth high-speed autofocus correction lens 905. This fifth high-speed autofocus correction lens 905 is implemented as an additional electrode placed between the multi-aperture configuration 305 and the counter electrode 306. Alternatively, such an additional electrode can be placed immediately downstream of the counter electrode 306.

[0205] Figure 21 schematically shows one embodiment of the present invention, which includes a plurality of high-speed autofocus correction lenses 901, 903, 904, 905, and 906. The high-speed autofocus correction lenses 901, 903, 904, 905, and 906 allow for setting and keeping constant different beam parameters within the range of high-speed autofocus at each or a plurality of operating points. Here, the various high-speed autofocus correction lenses 901, 903, 904, 905, and 906 have different (primary) tasks with respect to the high-frequency correction they perform. In the illustrated example, a partially configured first high-speed autofocus correction lens 824 or 901 is positioned between the upper pole piece 108 and the lower pole piece 109 of the objective lens 102, and the controller is configured to high-frequency control the first high-speed autofocus correction lens 901 during wafer inspection at each operating point by generating a first autofocus correction lens control signal based on actual autofocus data during wafer inspection. The primary function of lens 901 is autofocus correction itself. The other high-speed autofocus correction lenses 903, 904, 905, and 906 are for correcting other beam parameters at each operating point, and their respective controls may be based on a feedback loop and / or feedforward loop. Here again, actual autofocus data is available within the feedforward loop, and the values ​​of the autofocus correction lens control signals for high-speed autofocus correction lenses 903, 904, 905, and 906 are generated based on this actual autofocus data by a multidimensional lookup table. However, for the purpose of correction, additional actual data may also be used, which may be generated by, for example, evaluation of the image of a CCD camera in a second particle optical beam path (not shown) (performing a different feedback) or by a z-level sensor measuring the distance from the lowest pole piece of the objective lens to the sample surface.

[0206] In the illustrated exemplary embodiment, as already described in conjunction with Figure 20, a fifth high-speed autofocus correction lens 905 is located in the region of the multi-beam particle generator. In addition, a two-part high-speed electrostatic autofocus correction lens 906 is located in the region of the intermediate image plane 325. Since its components are symmetrically arranged upstream and downstream of the intermediate image plane 325, the lens 906 can be treated as if it were entirely located within the intermediate image plane 325. In the illustrated example, the lens 906 can be supplied with a positive or negative bias (for example, a negative bias of several hundred volts (e.g., -200V, -300V, -400V, etc.)).

[0207] Furthermore, the illustrated example shows that the third high-speed autofocus correction lens 903 includes a high-speed magnetic lens in the form of an air coil positioned substantially without a magnetic field outside the beam tube 460 in the first particle optical beam path. This condition is satisfied only after passing through the intermediate image plane 325, however, it can also be satisfied at other positions in the particle optical beam path. As an example, the third high-speed autofocus correction lens 903 can achieve high-frequency correction of the azimuth position of individual particle beams and, consequently, correction of image field rotation in the object plane.

[0208] In the illustrated example, a fourth high-speed autofocus correction lens 904, which is a high-speed electrostatic lens, is further positioned within the magnetic field lens 307. This fourth high-speed autofocus correction lens 904 can substantially perform high-frequency correction of the radial incidence angle of individual particle beams on the object plane 101. However, as with the second high-speed autofocus correction lens 902, the corresponding lens 904 can also substantially perform high-frequency correction of the image field rotation on the object plane 101.

[0209] In the illustrated example, in addition to the aforementioned high-speed autofocus correction lenses 901, 903, 904, 905, and 906, a magnetic field compensation lens 120 including a magnetic lens is provided, which is positioned between the objective lens 102 and the object surface 101 or object 7. In the illustrated example, the controller 10 is configured to statically or low-frequency control the magnetic field compensation lens 120 by a magnetic field compensation control signal so that the value of the magnetic field when incident on the object surface 100 or object 7 is zero. In the illustrated example, the magnetic field compensation lens 120 is coupled to the objective lens 102. Currents of opposite signs are applied to the two windings 110 and 121 in both cases so that the magnetic flux generated passing through the lower magnetic pole piece 109 of the objective lens 102 is directed in the same direction. Thus, appropriate control is possible. Further information regarding the design of the magnetic field compensation lens 120 can be obtained, for example, from International Patent Publication WO2007 / 060017, and all disclosures thereof are incorporated herein by reference. The magnetic field compensation lens 120 is statically or low-frequency controlled by a controller. This means that the setting of the azimuthal incidence angle on the object plane is not high-frequency recorrected. However, it has been found that static or low-frequency control of the magnetic field compensation lens 120 is absolutely sufficient. Other errors related to the azimuthal incidence angle are proportionally smaller than the errors in the radial incidence angle after high-frequency correction. For example, correction is possible by a fourth high-speed autofocus correction lens 904 located on the field lens 307.

[0210] Generally speaking, the effect of additional high-speed autofocus correction lenses on beam parameters such as focus, beam position, and eccentricity depends on their position within the column. Here, the inventors have found that there are substantially three different positions that exhibit different effects. Near the crossover, the effect is primarily on focus. Near the intermediate image plane, the effect is primarily on eccentricity. Near or directly below the micro-optical unit, the effect is primarily on magnification. At other positions, the electrostatic lens has various effects on each beam parameter.

[0211] Here, the inventors investigated the sensitivity of the additional high-speed autofocus correction lenses 901, 903, 904, 905, and 906 shown in Figure 21 to beam parameters of focal point, beam position, and eccentricity using the paraxial approximation. In principle, only five elements need to be added to set the focal point, azimuth and radial position, as well as the azimuth and radial eccentricity.

[0212] However, the inventors investigated six or more additional elements and, for each case, examined the excitation required for the lens at a focal point of several tens of micrometers, while keeping other beam parameters constant. A total of more than 21 combinations of elements and different methods were investigated. More detailed information regarding the possible arrangement and control of particle optical components in the beam path can be obtained, for example, from U.S. Patent Application Publication 2019 / 0355545, all of which disclosures are incorporated herein by reference. Furthermore, to determine the control of the fast autofocus correction lens, a sensitivity inverse matrix was used, representing the effect of changes in the operation of the particle optical component on the particle optical parameters characterizing particle optical imaging at each operating point. Here, the goal is a solution in which the column vectors of the sensitivity matrix are largely dominated by one entry in each column. Here, it has been found that for some fast autofocus correction lenses, there is no dominant entry in the column vector, and therefore the sensitivity of these autofocus correction lenses becomes very low in the desired optimization at this point.

[0213] Surprisingly, the solution space was found to be very small in several possible solutions. It is also possible to determine two particularly favorable solutions. One of these solutions is shown in Figure 22. Figure 22 schematically shows one embodiment of the present invention, which includes multiple high-speed autofocus correction lenses 901, 903, 904, and 905. In this solution, the high-speed autofocus correction lens 906 in the region of the intermediate image plane 325 is unnecessary. The first high-speed autofocus correction lens 901 or 824 is provided in a partial configuration between the upper pole piece 108 and the lower pole piece 109. In this solution, a high-speed magnetic lens 903 in the form of an air coil is essential. Furthermore, as a constraint to be satisfied, the magnetic field compensation coil 120 makes the magnetic field on sample 7 zero. In the combination shown in Figure 21, the high-speed autofocus correction lens 905 substantially sets the magnification. The third high-speed autofocus correction lens 903 substantially compensates for image field rotation. Furthermore, the fourth high-speed autofocus correction lens 904 substantially compensates for the radial incidence angle. The azimuth incidence angle is not explicitly compensated for. However, its accuracy is sufficiently high, and even in the case of high-frequency correction, it is clearly superior to the accuracy obtained with respect to the radial incidence angle.

[0214] Figure 23 schematically illustrates another embodiment of the present invention, including a plurality of high-speed autofocus correction lenses 901, 904, 905, and 906. In the illustrated example, the first high-speed autofocus correction lens 901 has a two-part embodiment including components 901a and 901b. Instead, the third high-speed autofocus correction lens 903, which is embodied in the form of a high-speed magnetic lens in Figures 21 and 22, is omitted. In the configuration shown in Figure 23 as well, particularly excellent solutions can be obtained by using the aforementioned sensitivity matrix. In this case as well, the solution space is very small.

[0215] A particularly excellent solution is shown in Figure 24. The sixth high-speed autofocus correction lens 906 in the region of the intermediate image plane 325 is found to contribute substantially nothing to this setting solution. Therefore, its implementation may also be omitted, as shown in Figure 24. In the illustrated example, the focusing is substantially set by the first portion 901a and the second portion 901b of the first high-speed autofocus correction lens 901. The azimuth position is substantially corrected by the second portion 901b of the first high-speed autofocus correction lens 901, as described above in the summary of this patent application. The fifth high-speed autofocus correction lens 905 substantially facilitates the adjustment of the radial image position (magnification adjustment). The fourth high-speed autofocus correction lens substantially corrects the radial incidence angle. Similar to the example shown in Figure 22, no high-frequency correction is performed on the azimuth incidence angle; instead, the azimuth incidence angle is statically and / or low-frequency set to zero with sufficient precision by the magnetic field compensation lens 122.

[0216] It should be emphasized that a particularly preferred solution of the configuration shown in Figures 22 and 24 provides autofocus adjustment options not only at a single operating point but also at multiple operating points in question. Furthermore, similarly, several interesting application options for the multi-beam particle system according to the present invention can be facilitated by readjusting other beam parameters or keeping them constant.

[0217] Figure 25 is a schematic diagram showing part of the controller for a multi-beam particle microscope equipped with multiple high-speed autofocus correction lenses. In this case, the controller 821 for high-speed autofocus, which is integrated into the controller 10 or computer system 10, comprises various final control elements, as well as a measurement element or autofocus determination element 822 and an autofocus algorithm 823. In the illustrated example, these final control elements are realized by the first high-speed autofocus correction lens 901 or 824, other high-speed autofocus correction lenses 902, 903, 904, 905, and 906, and optionally other high-speed autofocus correction lenses. The controller 821 for high-speed autofocus shown in Figure 25 can be similarly integrated into the entire controller 10, as already shown in Figure 3. Therefore, for further details, please refer to Figures 2 and 3 above.

[0218] Figure 26 schematically illustrates the workflow for high-speed autofocus correction, which also has more precise adjustment options. In the first step S20, the autofocus correction lens is adjusted, for example, based on a feedback and / or feedforward loop. This has already been described in detail above in conjunction with the high-speed autofocus correction lenses 901-906.

[0219] In the next step S21, aberration correction means can be configured. These may include, for example, a deflector and / or astigmatism corrector positioned in the first particle optical beam path. As an example, a high-speed electrostatic aberration correction means can be positioned upstream of each implemented high-speed autofocus correction lens 901, 902, 903, 904, 905, 906. This is to keep the path of individual particle beams constant with high precision as they pass through the column. The high-speed aberration correction means is high-frequency controlled with high precision by the controller 10 described above, preferably using a multidimensional lookup table for each operating point. As an example, the aberration correction means can be implemented in the form of an octupole that can be used equivalently to a deflector and / or astigmatism corrector.

[0220] In the next step S22, the scanning parameters are updated. Within the range of high-frequency correction for autofocus and other beam parameters, the required scanning parameters can be slightly modified. As an example, these scanning parameters include pixel size, rotation, skew, and / or quadraticity. In this case as well, these scanning parameters can be high-frequency corrected on a per-operating-point basis by a lookup table.

[0221] Figure 27 schematically illustrates the workflow for high-speed autofocus correction in a multi-beam particle system where high-speed autofocus correction is implemented as a hybrid system. According to method step S30, the focal point at the object plane 101 is physically set by at least one high-speed autofocus correction lens 901. This can be implemented by one of the modifications of the embodiments described in more detail above, for example, as a high-speed electrostatic lens consisting of a part or multiple parts between the upper pole piece 108 and the lower pole piece 109 of the objective lens 110. In method step S31, the angle of incidence at the object plane 101 is physically set by at least one high-speed autofocus correction means. This means can be one or more high-speed autofocus correction lenses 824 (for example, a fourth high-speed autofocus correction lens 904). In this way, the focal point and angle of incidence are physically corrected, and at least the focal point and radial angle of incidence are high-frequency corrected. For correction of the azimuthal angle of incidence, low-frequency correction (i.e., after the selection of the operating point) is usually sufficient.

[0222] In the next step S32, the scanning unit sets the image field rotation on the object plane 101 by quickly setting the reverse rotation. In the next step S33, the scanning unit similarly sets the magnification on the object plane 101 by quickly setting the pixel size. These two steps S32 and S33 can be performed quickly and easily because the scanning deflector 500 is easily controlled by the scanning unit. Optionally, rapid adjustment of the scanning parameters for quadratic and / or skew is also possible (not shown).

[0223] In the next step S34, the image displacement is compensated solely by calculation. For this purpose, there is no need to modify the obtained image data itself; it is sufficient to simply adapt each tag (metadata or position of pixel 1) through calculation.

[0224] All of the above explanations apply not only to high-speed autofocus but also to high-speed autostigma. By definition, stigma within the scope of this application is also included in focusing. In principle, stigma can be physically identified with focusing in only one direction or with different focusing in different directions. In this context, we also refer to high-speed multipolar lenses, which are described, for example, in the unpublished German Patent Application No. 102020107738.6 filed on March 20, 2020, and all of its disclosures are incorporated herein by reference.

[0225] The embodiments described above can be combined in whole or in part, provided that no technical inconsistencies result. Furthermore, the embodiments described above should not be construed as limiting the present invention.

[0226] Other examples relating to the present invention are listed below. These examples can be combined with the embodiments of the invention described in the claims, provided that no technical inconsistencies result.

[0227] Example 1: A multi-beam particle system for wafer inspection, A multi-beam particle generator configured to generate a first field of view for multiple first individual charged particle beams, A first particle optical unit having a first particle optical beam path configured to image the first individual particle beams onto the wafer surface such that the generated first individual particle beams collide with the wafer surface on the object surface at the point of incidence to form a second field of view, A detection system having multiple detection regions that form a third field of view, A second particle optics unit having a second particle optical beam path configured to image second individual particle beams emitted from an incident point in a second field of view into a third field of view of the detection region of the detection system, A magnetic and / or electrostatic objective lens, particularly a magnetic and / or electrostatic immersion lens, through which both the first individual particle beam and the second individual particle beam pass, A beam switch is positioned between the multibeam particle generator and the objective lens in the first particle optical beam path, and between the objective lens and the detection system in the second particle optical beam path. A sample stage for holding and / or positioning wafers during wafer inspection, An autofocus determination element configured to generate data for determining the actual autofocus data during wafer inspection, High-speed autofocus correction lens, Controller and Equipped with, The controller is configured to control the particle optical components in the first particle optical beam path and / or the second particle optical beam path. The controller is configured to control at least the objective lens and / or the actuator of the sample stage at a first working point at the first working distance, by static or low-frequency adaptation of focusing, such that a first individual particle beam is focused onto the wafer surface placed at a first working distance. A multi-beam particle system configured to control a high-speed autofocus correction lens during wafer inspection at a first operating point by generating an autofocus correction lens control signal through high-frequency adaptation of focusing, based on actual autofocus data at the first operating point during wafer inspection.

[0228] Example 2: The multi-beam particle system described in Example 1, wherein the adaptation time TA for high-frequency adaptation is at least 10 times, in particular, at least 100 times or 1000 times shorter than the adaptation time TA for low-frequency adaptation.

[0229] Example 3: A multi-beam particle system according to Example 1 or 2, wherein the stroke for setting the working distance for low-frequency or static adaptation is at least 5 times, in particular, at least 8 times and / or 10 times, larger than the stroke for high-frequency adaptation.

[0230] Example 4: A second working point is defined by a second working distance between the objective lens and the wafer surface, wherein the second working distance is different from the first working distance of the first working point. A multibeam particle system according to any one of Examples 1 to 3, wherein the controller is configured to perform low-frequency adaptation in case of a change between a first operating point and a second operating point, and to control at least the magnetic objective lens and / or the actuator of the sample stage at the second operating point so that the first individual particle beams are focused onto the wafer surface placed at a second working distance.

[0231] Example 5: The multi-beam particle system according to Example 4, wherein the controller is configured to control a high-speed autofocus correction lens during wafer inspection at a second operating point by generating an autofocus correction lens control signal for high-frequency adaptation based on actual autofocus data at a second operating point during wafer inspection.

[0232] Example 6: The first operating point and / or the second operating point are further defined by the incident angle of the first individual particle beam on the object surface and the lattice arrangement of the first individual particle beam on the object surface. The multi-beam particle system according to any one of Examples 1 to 5, further configured such that the controller substantially maintains the incident angle and the lattice arrangement in high-frequency adaptation at the first operating point and / or the second operating point.

[0233] Example 7: The multi-beam particle system according to Example 6, wherein the controller is configured to substantially maintain the incident angle and the lattice arrangement even during a change between the first operating point and the second operating point.

[0234] Example 8: The multi-beam particle system according to any one of claims 1 to 7, wherein the autofocus correction lens includes a high-speed electrostatic lens.

[0235] Example 9: The multi-beam particle system according to Example 8, wherein the autofocus correction lens is disposed on the crossover plane of the first individual particle beam.

[0236] Example 10: The multi-beam particle system according to Example 8, wherein the autofocus correction lens is disposed between the wafer surface and the lower pole piece of the magnetic objective lens.

[0237] Example 11: The multi-beam particle system according to Example 8, wherein the autofocus correction lens is disposed between the upper pole piece and the lower pole piece of the magnetic objective lens.

[0238] Example 12: The multi-beam particle system according to Example 8, wherein the autofocus correction lens is disposed on a beam tube extension protruding into the objective lens from the direction of the upper pole piece.

[0239] Example 13: Further comprising a beam deflection system configured to raster-scan the wafer surface by the scanning movement of individual particle beams between the beam switch and the objective lens. A multi-beam particle system as described in Example 8, in which an autofocus correction lens is implemented as an offset for the beam deflection system.

[0240] Example 14: A beam deflection system is further provided between the beam switch and the objective lens, configured to raster scan the wafer surface by scanning movement of individual particle beams. The beam deflection system comprises an upper deflector and a lower deflector arranged in a continuous manner in the direction of the beam path. A multi-beam particle system as described in Example 8, wherein an autofocus correction lens is positioned between the upper and lower deflectors.

[0241] Example 15: A beam deflection system is further provided between the beam switch and the objective lens, configured to raster scan the wafer surface by scanning movement of individual particle beams. The beam deflection system comprises an upper deflector and a lower deflector arranged in a continuous manner in the direction of the beam path. A multi-beam particle system as described in Example 8, wherein an autofocus correction lens is positioned between the lower deflector and the upper magnetic pole piece of the magnetic objective lens.

[0242] Example 16: Further comprising an evacuable beam tube substantially surrounding the first particle optical beam path from the multibeam particle generator to the objective lens, The multi-beam particle system according to Example 8, wherein the beam tube has a shielding section, and an autofocus correction lens is positioned within the shielding section.

[0243] Example 17: Further comprising a field lens system positioned between the multibeam particle generator and the beam switch in the first particle optical beam path, A multi-beam particle system according to Example 16, wherein a beam tube cutoff section, in which an autofocus correction lens is located, is positioned between the field lens system and the beam switch.

[0244] Example 18: The multi-beam particle system according to Example 16, wherein the beam switch includes two magnetic sectors, and a beam tube cutoff section, in which an autofocus correction lens is located, is provided in the beam switch region between the two magnetic sectors.

[0245] Example 19: A beam deflection system is further provided between the beam switch and the objective lens, configured to raster scan the wafer surface by scanning movement of individual particle beams. A multi-beam particle system according to Example 16, wherein a beam tube cutoff section, in which an autofocus correction lens is located, is provided between the beam switch and the beam deflection system.

[0246] Example 20: Further comprising a field lens system positioned between the multibeam particle generator and the beam switch in the first particle optical beam path, A multi-beam particle system according to Example 16, wherein the cutoff section of the beam tube, which has an autofocus correction lens, is located within the magnetic lens of the field lens system.

[0247] Example 21: Further comprising an evacuable beam tube substantially surrounding the first particle optical beam path from the multibeam particle generator to the objective lens, The multi-beam particle system described in Example 8, wherein the autofocus correction lens is embodied as a tube lens and placed inside the beam tube.

[0248] Example 22: Further comprising a field lens system positioned between the multibeam particle generator and the beam switch in the first particle optical beam path, A multi-beam particle system as described in Example 21, wherein an autofocus correction lens is positioned in the beam tube between the field lens system and the beam switch.

[0249] Example 23: The multi-beam particle system according to Example 21, wherein the beam switch has two magnetic sectors and an autofocus correction lens is provided in the beam tube between the two magnetic sectors.

[0250] Example 24: Further comprising a beam deflection system configured to raster scan the wafer surface by the scanning movement of individual particle beams between the beam switch and the objective lens, An autofocus correction lens is provided in the beam tube between the beam switch and the beam deflection system, the multi-beam particle system described in Example 21.

[0251] Example 25: Further comprising a field lens system arranged between the multi-beam particle generator and the beam switch in the first particle optical beam path, An autofocus correction lens is arranged in the magnetic lens in the beam tube, the multi-beam particle system described in Example 21.

[0252] Example 26: A high-speed autofocus correction lens, particularly including an air coil, the multi-beam particle system according to any one of Examples 1 to 7.

[0253] Example 27: Further comprising an evacuable beam tube substantially surrounding the first particle optical beam path from the multi-beam particle generator to the objective lens, A high-speed magnetic lens is arranged outside the beam tube, the multi-beam particle system described in Example 26.

[0254] Example 28: Further comprising a field lens system arranged between the multi-beam particle generator and the beam switch in the first particle optical beam path, A high-speed magnetic lens is arranged around the beam tube between the field lens system and the beam switch, the multi-beam particle system described in Example 27.

[0255] Example 29: The beam switch has two magnetic sectors, and a high-speed magnetic lens is arranged around the beam tube between the two magnetic sectors, the multi-beam particle system described in Example 27.

[0256] Example 30: A beam deflection system is further provided between the beam switch and the objective lens, configured to raster scan the wafer surface by scanning movement of individual particle beams. A multi-beam particle system as described in Example 27, wherein high-speed magnetic lenses are arranged around the beam tube between the beam switch and the beam deflection system.

[0257] Example 31: A beam deflection system is further provided between the beam switch and the objective lens, configured to raster scan the wafer surface by scanning movement of individual particle beams. The beam deflection system comprises an upper deflector and a lower deflector arranged in a continuous manner in the direction of the beam path. A multi-beam particle system as described in Example 27, wherein high-speed magnetic lenses are arranged around the beam tube between an upper and lower deflector.

[0258] Example 32: Further comprising high-speed eccentricity correction means configured to substantially contribute to correcting the tangential eccentricity error of the first individual particle beams in a second field of view, A multibeam particle system according to any one of Examples 1 to 31, wherein the controller is configured to control a high-speed eccentricity correction means during wafer inspection by generating an eccentricity correction means control signal for high-frequency adaptation at each operating point during wafer inspection based on actual autofocus data.

[0259] Example 33: The multi-beam particle system according to Example 32, wherein the eccentricity correction means comprises a first deflector array positioned in the intermediate image plane of the first particle optical beam path.

[0260] Example 34: Further comprising high-speed rotation correction means configured to substantially contribute to the correction of the rotation of the first individual particle beams in the second field of view, A multibeam particle system according to any one of Examples 1 to 33, wherein the controller is configured to control a high-speed rotational compensation means during wafer inspection by generating a rotational compensation means control signal for high-frequency adaptation based on actual autofocus data during wafer inspection at each operating point.

[0261] Example 35: The multi-beam particle system according to Example 34, wherein the rotational correction means is equipped with an air coil.

[0262] Example 36: The multi-beam particle system according to Examples 33 and 34, wherein the rotational correction means comprises a second deflector array positioned at a distance immediately upstream or downstream of the first deflector array.

[0263] Example 37: The multi-beam particle systems according to Examples 33 and 34, wherein the rotational correction means comprises a multi-lens array positioned at a distance immediately upstream or downstream of the first deflector array such that the first individual particle beams pass through the multi-lens array out of axis.

[0264] Example 38: The multibeam particle system according to Example 34, wherein the multibeam particle generator is equipped with a high-speed rotation compensation means, and the rotation compensation means rotates actively by a control signal of the rotation compensation means.

[0265] Example 39: The high-speed rotation correction means comprises a first magnetic field generating device for a first weak magnetic field and a second magnetic field generating device for a second weak magnetic field. The multi-beam particle system according to Example 34, wherein the first magnetic field generator and the second magnetic field generator are controlled by a controller by a rotation correction means control signal, with respect only to rotation in the positive and negative directions.

[0266] Example 40: The multi-beam particle system according to Example 39, wherein the first and second magnetic fields have an axial configuration and are arranged in a converging or diverging pencil of the first individual particle beams in the first particle optical beam path.

[0267] Example 41: A multi-beam particle system according to any one of Examples 1 to 40, wherein the maximum deviation of individual particle beams from a desired incident position on the wafer surface is 10 nm or less, in particular 5 nm, 2 nm, 1 nm, or 0.5 nm or less.

[0268] Example 42: A multi-beam particle system according to any one of Examples 1 to 41, wherein the controller is configured to determine an autofocus correction lens control signal, a rotation correction means control signal, and / or an eccentricity correction means control signal based on actual autofocus data, by using a sensitivity inverse matrix that represents the effect of control changes of particle optical components on particle optical parameters that characterize particle optical imaging at each operating point.

[0269] Example 43: A multi-beam particle system according to any one of Examples 1 to 42, wherein the controller is configured to control the particle optical components in the second particle optical beam path at each operating point associated with the working distance, by static or low-frequency adaptation of focusing in the second particle optical beam path, such that the second individual particle beams emitted from the wafer surface placed at each working distance are focused into a detection area in a third field of view.

[0270] Example 44: A multi-part embodiment may be provided, further comprising high-speed projection path correction means configured to perform high-frequency adaptation of the focus, grid arrangement, incident angle, and / or contrast of the second individual particle beams when incident on a detection area in a third field of view, A multi-beam particle system according to any one of Examples 1 to 43, wherein the controller is configured to control a high-speed projection path correction means by generating one or a set of projection path control signals based on actual autofocus data during wafer inspection at each operating point.

[0271] Example 45: A projection path measurement element for generating projection path measurement data that characterizes particle optical imaging in the secondary path during wafer inspection, The system may have a multi-part configuration, comprising: a high-speed projection path correction means configured to perform high-frequency adaptation of the focus, grid arrangement, incident angle, and / or contrast of individual second particle beams upon incidence to a detection area in a third field of view; Furthermore, A multi-beam particle system according to any one of Examples 1 to 44, wherein the controller is configured to control a high-speed projection path correction means by generating one or a set of projection path control signals based on projection path measurement data during wafer inspection at each operating point.

[0272] Example 46: A contrast aperture is positioned in the path of the second particle optical beam in the crossover plane. The projection path correction means comprises a high-speed contrast correction means comprising at least one electrostatic deflector, at least one electrostatic lens, and / or at least one electrostatic astigmatism corrector that affects the particle optical beam path through the contrast aperture diaphragm, The multi-beam particle system according to Example 44 or 45, wherein the controller is configured to control the contrast correction means by one or a set of contrast correction control signals such that the contrast of the second individual particle beams is kept substantially constant when incident on a detection area in a third field of view.

[0273] Example 47: A multi-beam particle system described in any one of Examples 1-46, with an additional autofocus correction lens or multiple additional high-speed autofocus correction lenses.

[0274] Example 48: A multi-beam particle system for wafer inspection, A multi-beam particle generator configured to generate a first field of view for multiple first individual charged particle beams, A first particle optical unit having a first particle optical beam path configured to image the first individual particle beams onto the wafer surface such that the generated first individual particle beams collide with the wafer surface on the object surface at the point of incidence to form a second field of view, A detection system having multiple detection regions that form a third field of view, A second particle optics unit having a second particle optical beam path configured to image second individual particle beams emitted from an incident point in a second field of view into a third field of view of the detection region of the detection system, A magnetic and / or electrostatic objective lens, particularly a magnetic and / or electrostatic immersion lens, through which both the first individual particle beam and the second individual particle beam pass, A beam switch is positioned between the multibeam particle generator and the objective lens in the first particle optical beam path, and between the objective lens and the detection system in the second particle optical beam path. A sample stage for holding and / or positioning wafers during wafer inspection, An autofocus determination element configured to generate data for determining the actual autofocus data during wafer inspection, High-speed autofocus correction lens, Controller and Equipped with, The controller is configured to control the particle optical components in the first particle optical beam path and / or the second particle optical beam path. A multi-beam particle system in which a controller is configured to control at least a magnetic objective lens and / or an actuator of a sample stage at a first working point at a first working distance, by static or low-frequency adaptation of focusing, such that a first individual particle beam is focused onto a wafer surface placed at a first working distance.

[0275] Example 49: A multibeam particle system, in particular a method for operating a multibeam particle system described in any one of Examples 1 to 47, A step of generating measurement data at a first operating point with respect to the current focal point on the object plane, The steps include determining the actual autofocus data based on the measurement data, The steps include determining the autofocus correction lens control signal based on actual autofocus data, A step of controlling a high-speed autofocus correction lens, wherein, upon incidence onto an object surface at a first operating point, the grid arrangement and incidence angle of the first individual particle beams are kept constant. Methods that include...

[0276] Example 50: A method of operating the multibeam particle system described in Example 49, wherein the high-speed autofocus correction lens includes an electrostatic lens.

[0277] Example 51: A method of operating a multibeam particle system as described in Example 49 or 50, wherein the high-speed autofocus correction lens includes a magnetic lens.

[0278] Example 52: Steps to generate an eccentricity correction control signal based on actual autofocus data, A step of controlling a high-speed eccentricity correction means, A method of operating a multibeam particle system as described in any one of Examples 49 to 51, further including the above.

[0279] Example 53: Steps to generate a rotation correction control signal based on actual autofocus data, A step of controlling the high-speed rotation correction means, A method of operating a multibeam particle system as described in any one of Examples 49 to 52, further including the above.

[0280] Example 54: A method of operating a multibeam particle system according to any one of Examples 49-53, further comprising the step of orthogonalizing the effects of one or more particle optical components used for correction.

[0281] Example 55: A step of generating projection path measurement data that characterizes particle optical imaging in a secondary path, The steps include determining the projection path control signal based on projection path measurement data, A step of controlling a high-speed projection path correction means, which may have a multi-part configuration, by one or a set of projection path control signals, wherein the focus, grid arrangement, and incident angle of the second individual particle beams upon incidence on the detection surface are kept constant at the first operating point. A method of operating a multibeam particle system as described in any one of Examples 49-54, further including the above.

[0282] Method 56: A method for operating a multibeam particle system according to any one of Examples 49 to 55, further comprising the step of controlling a high-speed contrast correction means with one or a set of contrast correction control signals and maintaining a constant contrast on the detection surface.

[0283] Example 57: A multi-beam particle system for wafer inspection, particularly a multi-beam particle microscope, equipped with multiple high-speed autofocus correction lenses for high-frequency adaptation of beam parameters on an object surface.

[0284] Example 58: A multi-beam particle system for wafer inspection, particularly a multi-beam particle microscope, comprising at least two-part autofocus correction lenses for high-frequency adaptation of beam parameters on an object surface, particularly for high-frequency adaptation of focusing, wherein each part of the multi-part autofocus correction lens is spatially close in the particle optical beam path, particularly directly continuous in the particle optical beam path.

[0285] Example 59: A multibeam particle system for wafer inspection, in particular a multibeam particle microscope, comprising exactly three high-speed autofocus correction lenses for high-frequency adaptation of beam parameters on an object surface, wherein one of the autofocus correction lenses has a multi-part embodiment, in particular a two-part embodiment.

[0286] Example 60: A multi-beam particle system for wafer inspection, particularly a multi-beam particle microscope, equipped with four precise high-speed autofocus correction lenses for high-frequency adaptation of beam parameters on an object surface.

[0287] Example 61: A multi-beam particle system for wafer inspection according to Example 59 or 60, further comprising means for setting the magnetic field on the object surface to zero.

[0288] Example 62: A multi-beam particle system for wafer inspection according to Example 61, wherein the means includes a magnetic field compensating lens.

[0289] Example 63: A multi-beam particle system according to Example 61, wherein the means comprises an objective lens or an objective lens system, or consists of an objective lens or an objective lens system. Therefore, in this example, a magnetic field compensation lens is not necessarily required, because the magnetic field on the object plane can be set to zero with sufficient precision by the objective lens alone. This is particularly relevant to the operation of a multi-beam particle system for wafer inspection at only one operating point.

[0290] Example 64: A multi-beam particle system for wafer inspection, particularly a multi-beam particle microscope, equipped with multiple high-speed electrostatic aberration correction means for keeping the paths of individual particle beams constant with very high precision during passage through a column.

[0291] Example 65: A multi-beam particle system for wafer inspection according to Example 64, wherein high-speed electrostatic aberration correction means are located upstream of each high-speed autofocus correction lens.

[0292] Example 66: A multi-beam particle system for wafer inspection, particularly a multi-beam particle microscope, with a controller configured to control a scanning unit at high frequency.

[0293] Example 67: The multi-beam particle system described in Example 66, wherein the scanning parameters of pixel size, rotation, skew, and / or secondaryity are radio-frequency corrected by the control of the scanning unit.

[0294] Example 68: A multi-beam particle system for wafer inspection, A multi-beam particle generator configured to generate a first field of view for multiple first individual charged particle beams, A first particle optical unit having a first particle optical beam path configured to image the first individual particle beams onto the wafer surface such that the generated first individual particle beams collide with the wafer surface on the object surface at the point of incidence to form a second field of view, A detection system having multiple detection regions that form a third field of view, A second particle optics unit having a second particle optical beam path configured to image second individual particle beams emitted from an incident point in a second field of view into a third field of view of the detection region of the detection system, A magnetic and / or electrostatic objective lens, particularly a magnetic and / or electrostatic immersion lens, through which both the first individual particle beam and the second individual particle beam pass, A beam switch is positioned between the multibeam particle generator and the objective lens in the first particle optical beam path, and between the objective lens and the detection system in the second particle optical beam path. A sample stage for holding and / or positioning wafers during wafer inspection, An autofocus determination element configured to generate data for determining the actual autofocus data during wafer inspection, A first high-speed autofocus correction lens, which includes a high-speed electrostatic lens and is positioned between the upper and lower magnetic pole pieces of the objective lens, and which includes a first high-speed autofocus correction lens comprising at least two parts, Controller and Equipped with, The controller is configured to control the particle optical components in the first particle optical beam path and / or the second particle optical beam path. The controller is configured to control at least the objective lens and / or the actuator of the sample stage at a first working point at the first working distance, by static or low-frequency adaptation of focusing, such that a first individual particle beam is focused onto the wafer surface placed at a first working distance. A multi-beam particle system configured to control a first high-speed autofocus correction lens during wafer inspection at a first operating point by generating a first autofocus correction lens control signal through high-frequency adaptation of focusing based on actual autofocus data at a first operating point during wafer inspection.

[0295] Example 69: The multi-beam particle system according to Example 68, wherein a first high-speed autofocus correction lens is incorporated into a beam tube extension that protrudes into the objective lens from the direction of the upper pole piece.

[0296] Example 70: The beam tube extension section has two blocking sections, A multi-beam particle system according to Example 69, wherein a portion of the two-part first high-speed autofocus correction lens is positioned in each of the two shielding sections.

[0297] Example 71: The multi-beam particle system according to Example 69, wherein the two parts of a two-part first autofocus correction lens are each embodied as tube lenses and arranged within the beam tube extension.

[0298] Example 72: A multi-beam particle system according to any one of Examples 68-71, wherein the controller is configured to control two parts of a first autofocus correction lens by voltages of the same or opposite sign, provided by an autofocus correction lens control signal.

[0299] Example 73: A multi-beam particle system as described in Example 72, wherein high-frequency correction of image field rotation is performed as a substantial addition to the high-frequency adaptation of focusing by controlling two parts of the first autofocus correction lens.

[0300] Example 74: A multi-beam particle system for wafer inspection, A multi-beam particle generator configured to generate a first field of view for multiple first individual charged particle beams, A first particle optical unit having a first particle optical beam path configured to image the first individual particle beams onto the wafer surface such that the generated first individual particle beams collide with the wafer surface on the object surface at the point of incidence to form a second field of view, A detection system having multiple detection regions that form a third field of view, A second particle optics unit having a second particle optical beam path configured to image second individual particle beams emitted from an incident point in a second field of view into a third field of view of the detection region of the detection system, A magnetic and / or electrostatic objective lens, particularly a magnetic and / or electrostatic immersion lens, through which both the first individual particle beam and the second individual particle beam pass, A beam switch is positioned between the multibeam particle generator and the objective lens in the first particle optical beam path, and between the objective lens and the detection system in the second particle optical beam path. A field lens system including at least one magnetic lens positioned between a multibeam particle generator and a beam switch in a first particle optical beam path, A sample stage for holding and / or positioning wafers during wafer inspection, An autofocus determination element configured to generate data for determining the actual autofocus data during wafer inspection, A first high-speed autofocus correction lens, which includes a high-speed electrostatic lens and is positioned between the upper and lower magnetic pole pieces of a magnetic objective lens, A second high-speed autofocus correction lens, which includes a high-speed electrostatic lens and is positioned within the magnetic field of the field lens system, Controller and Equipped with, The controller is configured to control the particle optical components in the first particle optical beam path and / or the second particle optical beam path. The controller is configured to control at least the objective lens and / or the actuator of the sample stage at a first working point at the first working distance, by static or low-frequency adaptation of focusing, such that a first individual particle beam is focused onto the wafer surface placed at a first working distance. The controller is configured to control the first high-speed autofocus correction lens during wafer inspection at the first operating point by generating a first autofocus correction lens control signal through high-frequency adaptation of focusing based on actual autofocus data at the first operating point during wafer inspection. A multi-beam particle system configured such that a controller generates a second autofocus correction lens control signal based on actual autofocus data during wafer inspection, thereby high-frequency controlling a second high-speed autofocus correction lens during wafer inspection at the operating point.

[0301] Example 75: The multi-beam particle system described in Example 74, wherein high-frequency correction of image field rotation is substantially performed by control of a second high-speed autofocus correction lens.

[0302] Example 76: A multi-beam particle system for wafer inspection, A multi-beam particle generator configured to generate a first field of view for multiple first individual charged particle beams, A first particle optical unit having a first particle optical beam path configured to image the first individual particle beams onto the wafer surface such that the generated first individual particle beams collide with the wafer surface on the object surface at the point of incidence to form a second field of view, A detection system having multiple detection regions that form a third field of view, A second particle optics unit having a second particle optical beam path configured to image second individual particle beams emitted from an incident point in a second field of view into a third field of view of the detection region of the detection system, A magnetic and / or electrostatic objective lens, particularly a magnetic and / or electrostatic immersion lens, through which both the first individual particle beam and the second individual particle beam pass, A beam switch is positioned between the multibeam particle generator and the objective lens in the first particle optical beam path, and between the objective lens and the detection system in the second particle optical beam path. A purging beam tube substantially encloses the first particle optical beam path from the multibeam particle generator to the objective lens, A sample stage for holding and / or positioning wafers during wafer inspection, An autofocus determination element configured to generate data for determining the actual autofocus data during wafer inspection, A first high-speed autofocus correction lens, which includes a high-speed electrostatic lens and is positioned between the upper and lower magnetic pole pieces of a magnetic objective lens, A high-speed magnetic lens, in particular a third high-speed autofocus correction lens including an air coil, is positioned outside the beam tube in the first particle optical beam path, in a substantially magnetic-free location. Controller and Equipped with, The controller is configured to control the particle optical components in the first particle optical beam path and / or the second particle optical beam path. The controller is configured to control at least the objective lens and / or the actuator of the sample stage at a first working point at the first working distance, by static or low-frequency adaptation of focusing, such that a first individual particle beam is focused onto the wafer surface placed at a first working distance. The controller is configured to control the first high-speed autofocus correction lens during wafer inspection at the first operating point by generating a first autofocus correction lens control signal through high-frequency adaptation of focusing based on actual autofocus data at the first operating point during wafer inspection. A multi-beam particle system configured such that a controller generates a third autofocus correction lens control signal based on actual autofocus data during wafer inspection, thereby high-frequency controlling a third high-speed autofocus correction lens during wafer inspection at each operating point.

[0303] Example 77: The first particle optical beam path has an intermediate image plane, The multi-beam particle system according to Example 76, wherein a third high-speed autofocus correction lens is positioned immediately downstream of the intermediate image plane in the direction of the particle optical beam path.

[0304] Example 78: A multi-beam particle system according to Example 76 or 77, wherein high-frequency correction of the azimuthal position of individual particle beams on the object plane is substantially performed by the control of a third high-speed autofocus correction lens.

[0305] Example 79: Further comprising a fourth high-speed autofocus correction lens including a high-speed electrostatic lens, A fourth high-speed autofocus correction lens is positioned within the magnetic field of the field lens system. A multibeam particle system according to any one of Examples 68 to 78, wherein the controller is configured to high-frequency control a fourth high-speed autofocus correction lens during wafer inspection at each operating point by generating a fourth autofocus correction lens control signal based on actual autofocus data during wafer inspection.

[0306] Example 80: The multi-beam particle system described in Example 79, wherein high-frequency correction of the radial incidence angle of individual particle beams on the object plane is substantially performed by the control of a fourth high-speed autofocus correction lens.

[0307] Example 81: Further comprising a fifth high-speed autofocus correction lens including a high-speed electrostatic lens, A fifth high-speed autofocus correction lens is positioned in the multibeam particle generator. A multibeam particle system according to any one of Examples 68-80, wherein the controller is configured to high-frequency control a fifth high-speed autofocus correction lens during wafer inspection at each operating point by generating a fifth autofocus correction lens control signal based on actual autofocus data during wafer inspection.

[0308] Example 82: The multibeam particle system according to Example 81, wherein the multibeam particle generator comprises a multilens array with a multiaperture plate and a counter electrode, and a fifth high-speed autofocus correction lens is realized as an offset voltage that can be applied to the counter electrode.

[0309] Example 83: The multibeam particle system according to Example 81, wherein the multibeam particle generator comprises a multilens array with a multiaperture plate and a counter electrode, and a fifth high-speed autofocus correction lens is implemented as an additional electrode positioned between the multiaperture plate and the counter electrode, or immediately downstream of the counter electrode with respect to the particle optical beam path.

[0310] Example 84: A multi-beam particle system according to any one of Examples 81-83, wherein high-frequency correction of the radial position of individual particle beams on the object plane is substantially performed by the control of a fifth high-speed autofocus correction lens.

[0311] Example 85: Further comprising a sixth high-speed autofocus correction lens including a high-speed electrostatic lens, The sixth high-speed autofocus correction lens is realized near the intermediate image plane as a two-part lens, with the first part positioned upstream of the intermediate image plane and the second part positioned downstream of the intermediate image plane, when viewed in the direction of the particle optical beam path. A multibeam particle system according to any one of Examples 68 to 84, wherein the controller is configured to high-frequency control a sixth high-speed autofocus correction lens during wafer inspection at each operating point by generating a sixth autofocus correction lens control signal based on actual autofocus data during wafer inspection.

[0312] Example 86: The multi-beam particle system described in Example 85, with a bias applied to the sixth high-speed autofocus correction lens.

[0313] Example 87: Further comprising a magnetic field compensating lens including a magnetic lens, A magnetic field compensation lens is placed between the objective lens and the object plane. A multibeam particle system according to any one of Examples 68-86, wherein the controller is configured to statically or low-frequency control a magnetic field compensation lens by a magnetic field compensation control signal so that the value of the magnetic field on the object surface becomes zero.

[0314] Example 88: A multibeam particle system as described in Example 87, wherein a magnetic field compensating lens is coupled to the objective lens.

[0315] Example 89: A multi-beam particle system for wafer inspection, A multi-beam particle generator configured to generate a first field of view for multiple first individual charged particle beams, A first particle optical unit having a first particle optical beam path configured to image the first individual particle beams onto the wafer surface such that the generated first individual particle beams collide with the wafer surface on the object surface at the point of incidence to form a second field of view, A detection system having multiple detection regions that form a third field of view, A second particle optics unit having a second particle optical beam path configured to image second individual particle beams emitted from an incident point in a second field of view into a third field of view of the detection region of the detection system, A magnetic and / or electrostatic objective lens, particularly a magnetic and / or electrostatic immersion lens, through which both the first individual particle beam and the second individual particle beam pass, A beam switch is positioned between the multibeam particle generator and the objective lens in the first particle optical beam path, and between the objective lens and the detection system in the second particle optical beam path. A field lens system including at least one magnetic lens positioned between a multibeam particle generator and a beam switch in a first particle optical beam path, A sample stage for holding and / or positioning wafers during wafer inspection, An autofocus determination element configured to generate data for determining the actual autofocus data during wafer inspection, A first high-speed autofocus correction lens, which includes a high-speed electrostatic lens and is positioned between the upper and lower magnetic pole pieces of the objective lens, and which includes a first high-speed autofocus correction lens comprising at least two parts, A fourth high-speed autofocus correction lens, which includes a high-speed electrostatic lens positioned within the magnetic field of the field lens system's magnetic lens, A fifth high-speed autofocus correction lens is positioned in the multibeam particle generator, A magnetic lens is included, and a magnetic field compensating lens is positioned between the objective lens and the object plane, Controller and Equipped with, The controller is configured to control the particle optical components in the first particle optical beam path and / or the second particle optical beam path. The controller is configured to control at least the objective lens and / or the actuator of the sample stage at a first working point at the first working distance, by static or low-frequency adaptation of focusing, such that a first individual particle beam is focused onto the wafer surface placed at a first working distance. The controller is configured to statically or low-frequency control the magnetic field compensation lens by a magnetic field compensation control signal so that the value of the magnetic field on the object surface becomes zero. The controller is configured to control a high-speed autofocus correction lens, consisting of at least two parts, at high frequency using a first autofocus correction lens control signal having voltages of opposite signs during wafer inspection at each operating point, by generating a first autofocus correction lens control signal based on actual autofocus data during wafer inspection. The controller is configured to control the fourth high-speed autofocus correction lens at high frequency during wafer inspection at each operating point by generating a fourth autofocus correction lens control signal based on the actual autofocus data during wafer inspection. A multi-beam particle system configured such that a controller generates a fifth autofocus correction lens control signal based on actual autofocus data during wafer inspection, thereby high-frequency controlling a fifth high-speed autofocus correction lens during wafer inspection at each operating point.

[0316] Example 90: A multi-beam particle system for wafer inspection, A multi-beam particle generator configured to generate a first field of view for multiple first individual charged particle beams, A first particle optical unit having a first particle optical beam path configured to image the first individual particle beams onto the wafer surface such that the generated first individual particle beams collide with the wafer surface on the object surface at the point of incidence to form a second field of view, A detection system having multiple detection regions that form a third field of view, A second particle optics unit having a second particle optical beam path configured to image second individual particle beams emitted from an incident point in a second field of view into a third field of view of the detection region of the detection system, A magnetic and / or electrostatic objective lens, particularly a magnetic and / or electrostatic immersion lens, through which both the first individual particle beam and the second individual particle beam pass, A beam switch is positioned between the multibeam particle generator and the objective lens in the first particle optical beam path, and between the objective lens and the detection system in the second particle optical beam path. A field lens system including at least one magnetic lens positioned between a multibeam particle generator and a beam switch in a first particle optical beam path, A purging beam tube substantially encloses the first particle optical beam path from the multibeam particle generator to the objective lens, A sample stage for holding and / or positioning wafers during wafer inspection, An autofocus determination element configured to generate data for determining the actual autofocus data during wafer inspection, In particular, it includes a high-speed electrostatic lens of a certain configuration, and a first high-speed autofocus correction lens positioned between the upper and lower pole pieces of the objective lens, A high-speed magnetic lens, in particular a third high-speed autofocus correction lens including an air coil, is positioned outside the beam tube in the first particle optical beam path, in a substantially magnetic-free location. A fourth high-speed autofocus correction lens, which includes a high-speed electrostatic lens positioned within the magnetic field of the field lens system's magnetic lens, A fifth high-speed autofocus correction lens is positioned in the multibeam particle generator, A magnetic lens is included, and a magnetic field compensating lens is positioned between the objective lens and the object plane, Controller and Equipped with, The controller is configured to control the particle optical components in the first particle optical beam path and / or the second particle optical beam path. The controller is configured to control at least the objective lens and / or the actuator of the sample stage at a first working point at the first working distance, by static or low-frequency adaptation of focusing, such that a first individual particle beam is focused onto the wafer surface placed at a first working distance. The controller is configured to statically or low-frequency control the magnetic field compensation lens by a magnetic field compensation control signal so that the value of the magnetic field on the object surface becomes zero. The controller is configured to generate a first autofocus correction lens control signal based on actual autofocus data during wafer inspection, thereby high-frequency control of the first high-speed autofocus correction lens by the first autofocus correction lens control signal during wafer inspection at each operating point. The controller is configured to control the third high-speed autofocus correction lens at high frequency during wafer inspection at each operating point by generating a third autofocus correction lens control signal based on the actual autofocus data during wafer inspection. The controller is configured to control the fourth high-speed autofocus correction lens at high frequency during wafer inspection at each operating point by generating a fourth autofocus correction lens control signal based on the actual autofocus data during wafer inspection. A multi-beam particle system configured such that a controller generates a fifth autofocus correction lens control signal based on actual autofocus data during wafer inspection, thereby high-frequency controlling a fifth high-speed autofocus correction lens during wafer inspection at each operating point.

[0317] Example 91: A multi-beam particle system according to Example 89 or 90, configured to keep the beam parameters of the focal point, angle of incidence, and grid arrangement constant on the object plane by high-frequency correction.

[0318] Example 92: A multi-beam particle system according to any one of Examples 68-91, wherein the controller is configured to perform the determination of an autofocus correction lens control signal based on actual autofocus data by using a sensitivity inverse matrix that represents the effect of control changes of particle optical components on the particle optical parameters that characterize particle optical imaging at each operating point.

[0319] Example 93: A multi-beam particle system according to any one of Examples 68-92, wherein the controller is configured to determine the autofocus correction lens control signal by using a multidimensional lookup table.

[0320] Example 94: The second particle optical beam path is further provided with a hysteresis correction measurement element that generates hysteresis correction measurement data characterizing particle optical imaging on an object plane after a low-frequency control change of at least one magnetic lens in the first particle optical beam path, in particular after a change in the working distance, without changing the settings in the second particle optical beam path. A multibeam particle system according to any one of Examples 68 to 93, wherein the controller is configured to high-frequency correct at least one autofocus correction lens control signal at each operating point by generating a hysteresis correction control signal based on hysteresis control measurement data during wafer inspection.

[0321] Example 95: The multi-beam particle system described in Example 94, wherein the hysteresis correction measurement element includes a CCD camera in the second particle optical beam path.

[0322] Example 96: A multi-beam particle system according to Example 94 or 95, wherein a hysteresis correction control signal enables correction of beam parameters for radial and / or azimuthal positions on the object plane.

[0323] Example 97: In a particle optical beam path, further comprising at least one high-speed electrostatic aberration correction means positioned upstream of the high-speed autofocus correction lens, in particular upstream of each implemented high-speed autofocus correction lens, and configured to keep the path of individual particle beams constant with high precision as they pass through the column, A multibeam particle system according to any one of Examples 68 to 96, wherein the controller is configured to high-frequency control one or more high-speed aberration correction means at each operating point by generating an aberration correction control signal during wafer inspection.

[0324] Example 98: The multibeam particle system according to Example 97, wherein the aberration correction means includes an electrode arrangement in the form of an octupole.

[0325] Example 99: Further comprising high-speed electrostatic aberration correction means, Aberration correction means is positioned upstream of the crossover of the first individual particle beams in the first particle optical beam path, and is configured to keep the position of the individual particle beams constant with high precision for the purpose of forming the crossover. A multibeam particle system according to any one of Examples 68 to 98, wherein the controller is configured to high-frequency control of a high-speed aberration correction means at each operating point by generating an aberration correction control signal during wafer inspection.

[0326] Example 100: The beam switch and objective lens are further comprising a scanning unit and a beam deflection system configured to raster scan the wafer surface by scanning movement of individual particle beams, and controllable by the scanning unit. A multibeam particle system according to any one of Examples 68 to 99, wherein the controller is configured to control the scanning unit by scanning unit control signals during wafer inspection at each operating point, and to provide high-frequency correction to the scanning unit control signals based on actual autofocus data at each operating point.

[0327] Example 101: A multi-beam particle system as described in Example 100, in which the pixel size, rotation, skew, and / or secondaryity scanning parameters are radiofrequency corrected by a lookup table.

[0328] Example 102: A multi-beam particle system for wafer inspection, A multi-beam particle generator configured to generate a first field of view for multiple first individual charged particle beams, A first particle optics unit having a first particle optical beam path configured to image the first particle beam onto the wafer surface such that the generated first individual particle beams collide with the wafer surface on the object surface at the point of incidence to form a second field of view, A detection system having multiple detection regions that form a third field of view, A second particle optics unit having a second particle optical beam path configured to image second individual particle beams emitted from an incident point in a second field of view into a third field of view of the detection region of the detection system, A magnetic and / or electrostatic objective lens, particularly a magnetic and / or electrostatic immersion lens, through which both the first individual particle beam and the second individual particle beam pass, A beam switch is positioned between the multibeam particle generator and the objective lens in the first particle optical beam path, and between the objective lens and the detection system in the second particle optical beam path. A sample stage for holding and / or positioning wafers during wafer inspection, An autofocus determination element configured to generate data for determining the actual autofocus data during wafer inspection, Scanning unit and High-speed autofocus correction means, in particular, a high-speed autofocus correction lens, Controller and Equipped with, The controller is configured to control the particle optical components in the first particle optical beam path and / or the second particle optical beam path. The controller is configured to control at least the objective lens and / or the actuator of the sample stage at a first working point at the first working distance, by static or low-frequency adaptation of focusing, such that a first individual particle beam is focused onto the wafer surface placed at a first working distance. A multi-beam particle system in which the controller is configured to perform high-frequency correction of beam parameters such as focal point and incident angle on the object plane by high-speed autofocus correction means, particularly a high-speed autofocus correction lens, and to perform high-frequency correction of beam parameters such as magnification and image field rotation on the object plane by high-frequency control of the scanning unit.

[0329] Example 103: By setting the rotation by the scanning unit, changes in the image field rotation of individual particle beams on the object surface are compensated for. A multi-beam particle system as described in Example 102, wherein changes in magnification on the object surface are corrected by setting the pixel size using a scanning unit.

[0330] Example 104: The multi-beam particle system described in Example 103, wherein the image displacement of individual particle beams on the object surface is corrected solely by calculation by a controller.

[0331] Example 105: A multi-beam particle system according to any one of Examples 102-104, wherein a high-speed autofocus correction means, in particular a high-speed autofocus correction lens, is configured to perform high-frequency correction of beam parameters only downstream of the crossover with respect to the particle optical beam path.

[0332] Example 106: A multibeam particle system, in particular a method for operating a multibeam particle system described in any one of Examples 68 to 105, A step of generating data at a first operating point with respect to the current focal point on the object plane, The steps include determining the actual autofocus data based on the data, The steps include generating a first autofocus correction lens control signal based on actual autofocus data and controlling the first high-speed autofocus correction lens with high frequency, The steps include generating a second high-speed autofocus correction lens control signal based on actual autofocus data, and controlling the second high-speed autofocus correction lens with high frequency, A step of generating a third high-speed autofocus correction lens control signal based on actual autofocus data, and controlling the third high-speed autofocus correction lens with high frequency, The steps include generating a fourth high-speed autofocus correction lens control signal based on actual autofocus data, and controlling the fourth high-speed autofocus correction lens with high frequency, The steps of generating a fifth high-speed autofocus correction lens control signal based on actual autofocus data, and high-frequency control of the fifth high-speed autofocus correction lens, and / or, The steps include generating a sixth high-speed autofocus correction lens control signal based on actual autofocus data, and controlling the sixth high-speed autofocus correction lens with high frequency, Includes, A method for operating a multi-beam particle system, wherein the focusing on the object plane is kept constant at a first operating point by controlling one or more high-speed autofocus correction lenses.

[0333] Example 107: A method of operating the multi-beam particle system according to Example 106, wherein at the first operating point, the incidence angle, rotation, and / or position of the first individual particle beams on the object surface are also kept constant.

[0334] Example 108: A method of operating a multibeam particle system as described in Example 106 or 107, wherein the high-speed autofocus correction lens includes an electrostatic lens.

[0335] Example 109: A method of operating a multibeam particle system according to any one of Examples 106-108, wherein the high-speed autofocus correction lens includes a magnetic lens.

[0336] Example 110: A method of operating a multibeam particle system according to any one of Examples 106-109, further comprising the step of orthogonalizing the effects of one or more particle optical components used for correction.

[0337] Example 111: A step of changing the operating point, in particular the working distance, and generating hysteresis-corrected measurement data that characterizes the particle optical imaging on the object surface, The steps include: performing high-frequency correction on one or more autofocus correction lens control signals based on hysteresis correction measurement data; A method of operating a multibeam particle system as described in any one of Examples 106-110, further including the above.

[0338] Example 112: A method for operating a multibeam particle system according to any one of Examples 106 to 111, further comprising the steps of generating an aberration correction control signal and using the aberration correction control signal to perform high-precision correction of the beam position, in particular high-frequency correction.

[0339] Example 113: A method for operating a multibeam particle system according to any one of Examples 106-112, further comprising the step of generating a scanning unit control signal and, in particular, high-frequency correcting the scanning unit control signal at each operating point by using a multidimensional lookup table.

[0340] Example 114: A method for operating a multibeam particle system according to any one of Examples 106-113, further comprising the step of correcting image data with respect to at least one beam parameter, in particular, with respect to image displacement on the object plane.

[0341] Example 115: A method for operating a multibeam particle system described in any one of Examples 106 to 114, particularly for high-speed autofocus correction at the operating point, The steps include physically setting the focus on the object plane using a high-speed autofocus correction lens, The steps include physically setting the angle of incidence on the object surface using a high-speed autofocus correction means, By quickly setting the reverse rotation, the scanning unit sets the magnetic field rotation, By quickly setting the pixel size, the scanning unit sets the magnification, A step of compensating for image displacement solely through calculation, A method for operating a multibeam particle system, including the operation of such systems.

[0342] Example 116: Steps for quickly setting the secondary scanning parameters of a scanning unit, and / or A method for operating a multibeam particle system as described in Example 115, further comprising the step of rapidly setting the scanning parameters for the skew of the scanning unit. [Explanation of symbols]

[0343] 1. Multibeam particle microscope 3. Primary particle beam (individual particle beam) 5. Beam spot, point of incidence 7 Object 9. Secondary particle beam 10. Computer systems, controllers 100 Objective Lens System 101 Object plane 102 Objective lens 103 Field of view 108 Upper magnetic pole piece of the objective lens 109 Lower magnetic pole piece of the objective lens 110 Winding of the objective lens 120 Magnetic field compensating lens 121 Winding of magnetic field compensating lens 122 Lower magnetic pole piece of magnetic field compensating lens 200 detection systems 205 Projection Lens 209-particle multi-detector 211 Detection surface 213 Incidence Point 217 Field of view 250 Vacuum Chamber 260 Scanning deflector in the secondary path 300 Beam Generator 301 Particle source 303 Condenser Lens System 305 Multi-aperture configuration 306 Counter electrode of multibeam particle generator 313 Multi-aperture plate 315 Opening of a multi-aperture plate 317 Center point of the opening 319 Field of view 307 Field of View Lens System 309 Divergent particle beam 311 Irradiated particle beam 323 Beam Focus 325 Intermediate image plane 350 Vacuum Chamber 355 Vacuum Chamber 400 Beam Switch 410 magnetic sectors 420 magnetic sectors 460 beam tubes, beam tube array 461 Beam tube rim 462 Rim of beam tube 463 Rim of beam tube 464 Beam tube extension section 500 Scanning deflector in the primary path 810 Primary path controller 811 Controller for setting the operating point (low speed) 812 Measurement elements 813 Adjustment Algorithm 814 Final control element in the primary path 821 Controller for high-speed autofocus in the primary path 822 measurement elements, autofocus determination elements 823 Autofocus Algorithm 824 High-speed autofocus correction lens 825 High-speed eccentricity correction means 826 High-speed rotation correction means 827 High-speed position correction means 831 Controller for setting the operating point in the secondary path (low speed) 832 Measurement elements 833 Second adjustment algorithm (secondary path) 834 Final control element in secondary path 841 Second controller for high-speed autofocus (secondary path) 842 measurement elements 843 Second autofocus algorithm (secondary path) 844 High-speed projection path correction means 850 Orthogonalization matrix or sensitivity inverse matrix for a first-order path 851 Orthogonalization matrix or sensitivity inverse matrix for quadratic paths 901 First high-speed autofocus correction lens (one-part or two-part configuration) 902 Second high-speed autofocus correction lens 903 Third High-Speed ​​Autofocus Correction Lens 904 Fourth high-speed autofocus correction lens 905 Fifth High-Speed ​​Autofocus Correction Lens 906 6th High-Speed ​​Autofocus Correction Lens S1 generates measurement data of the current focus at the operating point AP. S2 Determine the actual autofocus data based on the measurement data. S3 Generate autofocus correction lens control signal based on actual autofocus data. S4 Generates an eccentricity correction control signal based on actual autofocus data. S5 Generate a control signal for rotation correction based on actual autofocus data. Controlling the S6 autofocus correction lens S7 Control the eccentricity correction means S8 Control the rotation correction means S9 Generate second measurement data for the second autofocus in the secondary path. S10 Determine the second actual autofocus data based on the second measurement data. S11 Generates a set of projection path correction means control signals. S12 Controlling the projection path correction means including the second autofocus correction lens. S13 Record the image field. Adjusting the S20 autofocus correction lens S21 Adjust the aberration correction means (deflection device / astigmatism corrector). S22 Update scan parameters The S30 high-speed autofocus correction lens physically sets the focus on the object's surface. S31 The angle of incidence on the object surface is physically set by one or more high-speed autofocus correction means. S32 By quickly setting the reverse rotation, the scanning unit sets the magnetic field rotation. S33 By quickly setting the pixel size, the scanning unit sets the magnification. S34 Image displacement is compensated solely by calculation.

Claims

1. A multi-beam particle system for wafer inspection, A multi-beam particle generator configured to generate a first field of view for multiple first individual charged particle beams, A first particle optical unit having a first particle optical beam path configured to image the first individual particle beams onto the wafer surface such that the generated first individual particle beams collide with the wafer surface on the object surface at the incident point to form a second field of view, A detection system having multiple detection regions that form a third field of view, A second particle optics unit having a second particle optical beam path configured to image the second individual particle beams emitted from the incident point in the second field of view into the third field of view of the detection region of the detection system, A magnetic objective lens, particularly a magnetic immersion lens, through which both the first individual particle beam and the second individual particle beam pass, A beam switch is positioned between the multi-beam particle generator and the objective lens in the first particle optical beam path and between the objective lens and the detection system in the second particle optical beam path, A sample stage for holding and / or positioning the wafer during the wafer inspection, An autofocus determination element configured to generate data for determining the actual autofocus data during the wafer inspection, High-speed autofocus correction lens, Controller and Equipped with, The controller is configured to control the particle optical components in the first particle optical beam path and / or the second particle optical beam path. The controller is configured to control the actuator of the sample stage at least the objective lens and / or a first operating point at the first working distance, by static or low-frequency adaptation of focusing, such that the first individual particle beam is focused onto the wafer surface, which is positioned at a first working distance between the objective lens and the wafer surface. The controller is configured to control the high-speed autofocus correction lens during wafer inspection at the first operating point by generating an autofocus correction lens control signal by high-frequency adaptation of focusing based on the actual autofocus data at the first operating point during wafer inspection. The first operating point is further defined by the angle of incidence of the first individual particle beams on the object surface and the grid arrangement of the first individual particle beams on the object surface, The controller is further configured to keep the incidence angle and the grid arrangement substantially constant in the high-frequency adaptation at the first operating point. A multi-beam particle system in which the high-speed autofocus correction lens includes a high-speed electrostatic lens and is positioned as a first high-speed autofocus correction lens between the upper and lower magnetic pole pieces of the magnetic objective lens.

2. The multibeam particle system according to claim 1, wherein the adaptation time for changing the excitation of the high-speed autofocus correction lens for high-frequency adaptation is at least 10 times, in particular at least 100 times or 1000 times shorter than the adaptation time for changing the excitation of the objective lens for low-frequency adaptation.

3. The multibeam particle system according to claim 1 or 2, wherein the stroke for setting the working distance for the low-frequency or static adaptation is at least five times, in particular eight times and / or ten times, larger than the stroke for the high-frequency adaptation.

4. A second operating point is defined at least by a second working distance between the objective lens and the wafer surface, wherein the second working distance is different from the first working distance of the first operating point. The multibeam particle system according to any one of claims 1 to 3, wherein the controller is configured to perform low-frequency adaptation in the event of a change between the first operating point and the second operating point, and to control at least the magnetic objective lens and / or the actuator of the sample stage at the second operating point so that the first individual particle beams are focused onto the wafer surface located at the second operating distance.

5. The multibeam particle system according to claim 4, wherein the controller is configured to control the high-speed autofocus correction lens during wafer inspection at the second operating point by generating an autofocus correction lens control signal for high-frequency adaptation based on the actual autofocus data at the second operating point during wafer inspection.

6. The second operating point is further defined by the angle of incidence of the first individual particle beams on the object surface and the grid arrangement of the first individual particle beams on the object surface, The multibeam particle system according to any one of claims 1 to 5, wherein the controller is further configured to keep the incident angle and the grid arrangement substantially constant in the high-frequency adaptation at the second operating point.

7. The multi-beam particle system according to claim 6, wherein the controller is configured to keep the incidence angle and the grid arrangement substantially constant even during changes between the first operating point and the second operating point.

8. The multi-beam particle system according to any one of claims 1 to 7, wherein the first high-speed autofocus correction lens is incorporated into a beam tube extension portion that protrudes into the objective lens from the direction of the upper magnetic pole piece.

9. The multi-beam particle system according to any one of claims 1 to 8, wherein the first high-speed autofocus correction lens includes at least a two-part first autofocus correction lens.

10. The beam tube extension section has two blocking sections, and a part of the two-part first autofocus correction lens is arranged in each of the two blocking sections, or The multi-beam particle system according to claim 9, wherein the two parts of the two-part first autofocus correction lens are each embodied as tube lenses and arranged within the beam tube extension section.

11. The multibeam particle system according to claim 10, wherein the controller is configured to control the two portions of the first autofocus correction lens by a voltage of the same or opposite sign as the autofocus correction lens control signal.

12. The multibeam particle system according to claim 11, wherein high-frequency correction of image field rotation is performed as a substantial addition to the high-frequency adaptation of the focusing by the control of the two portions of the first autofocus correction lens.

13. A beam tube that can be exhausted substantially surrounds the first particle optical beam path from the multibeam particle generator to the objective lens, A field lens system having at least one magnetic field lens disposed between the multi-beam particle generator and the beam switch in the first particle optical beam path, A second high-speed autofocus correction lens including a high-speed electrostatic lens, Furthermore, The second autofocus correction lens is placed within the magnetic field of the field lens system. The multibeam particle system according to any one of claims 1 to 12, wherein the controller is configured to control the second high-speed autofocus correction lens at each operating point during wafer inspection by generating a second autofocus correction lens control signal based on the actual autofocus data during wafer inspection.

14. The multibeam particle system according to claim 13, wherein high-frequency correction of image field rotation is substantially performed by controlling the second high-speed autofocus correction lens.

15. It also features a third high-speed autofocus correction lens. The third high-speed autofocus correction lens includes a high-speed magnetic lens, in particular an air coil, positioned substantially without a magnetic field outside the beam tube in the first particle optical beam path. The multibeam particle system according to any one of claims 1 to 9, wherein the controller is configured to control the third high-speed autofocus correction lens at each operating point with high frequency during wafer inspection by generating a third autofocus correction lens control signal based on the actual autofocus data during wafer inspection.

16. The first particle optical beam path has an intermediate image plane, The multi-beam particle system according to claim 15, wherein the third high-speed autofocus correction lens is positioned immediately downstream of the intermediate image plane in the direction of the particle optical beam path.

17. The multi-beam particle system according to claim 15 or 16, wherein high-frequency correction of the azimuth position of the individual particle beams on the object plane is substantially performed by controlling the third high-speed autofocus correction lens.

18. A beam tube that can be exhausted substantially surrounds the first particle optical beam path from the multibeam particle generator to the objective lens, A field lens system having at least one magnetic field lens disposed between the multi-beam particle generator and the beam switch in the first particle optical beam path, A fourth high-speed autofocus correction lens including a high-speed electrostatic lens, Furthermore, The fourth autofocus correction lens is placed within the magnetic field of the field lens system, The multibeam particle system according to any one of claims 1 to 17, wherein the controller is configured to control the fourth high-speed autofocus correction lens at each operating point during wafer inspection by generating a fourth autofocus correction lens control signal based on the actual autofocus data during wafer inspection.

19. The multi-beam particle system according to claim 18, wherein the control of the fourth high-speed autofocus correction lens substantially performs high-frequency correction of the radial incidence angle of the individual particle beams on the object surface.

20. It further includes a fifth high-speed autofocus correction lens, which includes a high-speed electrostatic lens. The fifth high-speed autofocus correction lens is placed in the multi-beam particle generator, The multibeam particle system according to any one of claims 1 to 19, wherein the controller is configured to control the fifth high-speed autofocus correction lens at each operating point with high frequency during wafer inspection by generating a fifth autofocus correction lens control signal based on the actual autofocus data during wafer inspection.

21. The multi-beam particle generator comprises a multi-lens array with a multi-aperture plate and a counter electrode, and the fifth high-speed autofocus correction lens is realized as an offset voltage that can be applied to the counter electrode, or The multibeam particle system according to claim 20, wherein the multibeam particle generator comprises a multilens array with a multiaperture plate and a counter electrode, and the fifth high-speed autofocus correction lens is implemented as an additional electrode positioned between the multiaperture plate and the counter electrode, or immediately downstream of the counter electrode with respect to the particle optical beam path.

22. The multi-beam particle system according to claim 21, wherein the control of the fifth high-speed autofocus correction lens substantially performs high-frequency correction of the radial position of the individual particle beams on the object surface.

23. It further includes a sixth high-speed autofocus correction lens, which includes a high-speed electrostatic lens. The sixth high-speed autofocus correction lens is realized near the intermediate image plane as a two-part lens, with the first part positioned upstream of the intermediate image plane and the second part positioned downstream of the intermediate image plane when viewed in the direction of the particle optical beam path. The multibeam particle system according to any one of claims 1 to 22, wherein the controller is configured to control the sixth high-speed autofocus correction lens at each operating point during wafer inspection by generating a sixth autofocus correction lens control signal based on the actual autofocus data during wafer inspection.

24. The multi-beam particle system according to claim 23, wherein the sixth high-speed autofocus correction lens is biased.

25. It also includes a magnetic field compensation lens, The magnetic field compensation lens is positioned between the objective lens and the object surface. The multibeam particle system according to any one of claims 1 to 24, wherein the controller is configured to statically or low-frequency control the magnetic field compensation lens by a magnetic field compensation control signal such that the value of the magnetic field on the object surface becomes zero.

26. The multibeam particle system according to claim 25, wherein the magnetic field compensation lens is coupled to the objective lens.

27. A multibeam particle system, in particular a method for operating a multibeam particle system according to any one of claims 1 to 26, A step of generating measurement data at a first operating point with respect to the current focus on the object surface, The steps include determining the actual autofocus data based on the aforementioned measurement data, The steps include determining an autofocus correction lens control signal based on the actual autofocus data, The steps include: controlling the first high-speed autofocus correction lens at a high frequency so that the focusing on the object surface is kept constant at the first operating point; Includes, The incident angle and grid arrangement of the first individual particle beams on the object surface are similarly kept constant at the first operating point. The multi-beam particle system includes a magnetic objective lens and a high-speed autofocus correction lens. The method wherein the high-speed autofocus correction lens includes a high-speed electrostatic lens and is positioned as a first high-speed autofocus correction lens between the upper and lower magnetic pole pieces of the magnetic objective lens.

28. Based on the actual autofocus data, a second high-speed autofocus correction lens control signal is generated, and the second high-speed autofocus correction lens is controlled by high-frequency control. Based on the actual autofocus data, a third high-speed autofocus correction lens control signal is generated, and the third high-speed autofocus correction lens is controlled by high-frequency control. Based on the actual autofocus data, a fourth high-speed autofocus correction lens control signal is generated, and the fourth high-speed autofocus correction lens is controlled by high-frequency control. Based on the actual autofocus data, the steps include generating a fifth high-speed autofocus correction lens control signal and high-frequency controlling the fifth high-speed autofocus correction lens, and / or Based on the actual autofocus data, a sixth high-speed autofocus correction lens control signal is generated, and the sixth high-speed autofocus correction lens is controlled by high-frequency control. A method for operating a multibeam particle system according to claim 27, further comprising:

29. A step of generating projection path measurement data that characterizes particle optical imaging in the secondary path, The steps include determining one or a set of projection path control signals based on the projection path measurement data, The steps include controlling a high-speed projection path correction means, which may have a multi-part configuration, by the aforementioned one or set of projection path control signals, wherein the focus, grid arrangement, and incidence angle of the second individual particle beams upon incidence on the detection surface are kept constant at the first operating point, A method for operating a multibeam particle system according to any one of claims 27 to 28, further comprising:

30. A method for operating a multibeam particle system according to claim 29, further comprising the step of controlling a high-speed contrast correction means with one or a set of contrast correction control signals and maintaining a constant contrast on the detection surface.

31. A computer program product comprising program code for performing the method described in any one of claims 27 to 30.

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