Particle beam system for regulating the current of individual particle beams

Abstract

A particle beam system for setting individual beam currents is disclosed, the particle beam system comprising the following: at least one particle source, which is configured to generate a beam of charged particles; a first multi-lens array, which includes a first plurality of individually adjustable particle lenses for implementing focusing and is arranged in the particle beam path so that at least some of the particles pass through openings in the multi-lens array in the form of multiple individual particle beams; a second porous plate, which includes a plurality of second openings, and is arranged in the particle beam path downstream of the first multi-lens array and is arranged so that particles passing through the first multi-lens array partially illuminate the second porous plate and partially pass through the openings in the second porous plate; and a controller, which is configured to supply individually adjustable voltages to the particle lenses of the first multi-lens array and thereby individually set the focus of the associated particle lens for each individual particle beam.

Description

Technical Field

[0001] The present invention relates to particle beam systems operating with multiple particle beams. Background Art

[0002] Just like single-beam particle microscopes, multi-beam particle microscopes can be used to analyze objects on a microscopic scale. For example, these particle microscopes can be used to record an image of an object that represents the surface of the object. In this way, for example, the structure of the surface can be analyzed. In single-beam particle microscopes, a single particle beam of charged particles (such as, for example, electrons, positrons, muons or ions) is used to analyze the object, while in multi-beam particle microscopes, multiple particle beams are used for this purpose. Multiple particle beams (also referred to as beams) are directed simultaneously to the surface of the object, thereby making it possible to sample and analyze a significantly larger area of ​​the surface of the object in the same time period compared to a single-beam particle microscope.

[0003] WO2005 / 024881 A2 discloses a multi-particle beam system in the form of an electron microscope system, which is operated by a plurality of electron beams so as to use a parallel electron beam to scan an object to be inspected. An electron beam is generated by an electron beam generated by an electron source, and this electron beam points to a porous plate with a plurality of openings. Some electrons in the electron beam irradiate the porous plate and are absorbed there and another part of the beam passes the opening of the porous plate, so the electron beam is formed in the beam path downstream of each opening, and the cross section of the electron beam is limited by the cross section of the opening. In addition, the electric field of the appropriate selection provided in the beam path upstream and / or downstream of the porous plate has the effect of the lens that each opening in the porous plate serves as for the electron beam through the opening, so the electron beam is focused on the plane at a distance from the porous plate. The plane imaging of the focus of the electron beam formed by the downstream optical unit is on the surface of the object to be inspected, so that the single electron beam is used as the primary beam irradiation object in a focused manner. There, they generate interaction products emanating from the object, such as backscattered electrons or secondary electrons, which are shaped to form secondary beams and directed by other optical units to detectors. There, each of the secondary beams impinges on a separate detector element, so that the intensity of the electrons detected by said detector element provides information about the object at the location where the corresponding primary beam impinged on the object. A primary beam is systematically scanned over the surface of the object in order to generate an electron micrograph of the object in the manner customary for scanning electron microscopes.

[0004] In the described multi-particle beam system, high resolution and high throughput are highly relevant for satisfactory and successful use in practice. In this case, in particular, the intensity of the particle beam must be set.

[0005] US 2017 / 0025241 A1 discloses a multi-beam particle beam system in which the current density in the particle beam is variable. Specifically, the irradiance is set before the multi-beam is uniformly formed from the primary electron beam. In order to set the irradiance, according to US 2017 / 0025241 A1, a double collimator is used, which is arranged directly downstream of the electron source in the beam direction. By changing the lens excitation of the double collimator, the current density of the electrons passing through the openings in the porous plate downstream of the double collimator can be changed.

[0006] However, if the number of utilized particle beams is further increased, the above-mentioned multi-beam particle beam system reaches its limit. In order to obtain sufficient beam intensity even for a single beam, it is necessary to use as many particles from a particle source as possible. However, in that case the emission characteristics of the particle source become more important, and the uniformity of the emission characteristics over the entire utilized emission angle is more accurate. When a relatively large emission angle is used, the emission characteristics of the particle source (e.g., a thermal field emission (TFE) source) are no longer uniform throughout the process. Therefore, the irradiation at the first porous plate in the corresponding particle beam system is no longer all uniform, and there are relatively large changes in the current density in different individual beams. However, in the case of a multi-particle inspection system, what the system requires is that the current intensity between each individual beam has only a small change, typically less than a few percent, so that all individual image fields of a multi-image field are scanned with an equal number of particles or electrons. As an example, this is a prerequisite for obtaining individual images with approximately the same brightness. The available resolution of the individual images also depends on the individual beam current.

[0007] Therefore, in inspection systems operating with multi-beam particle systems, the use of particle sources with large emission angles becomes a challenge due to the changing emission characteristics. Summary of the invention

[0008] Therefore, the object of the present invention is to provide a particle beam system with a large number of individual beams, which can largely ensure the uniformity of the individual beams even when a large number of individual beams are used or even when a large emission angle of the particle source is utilized. In particular, the particle beam system should also be suitable for multi-beam inspection systems.

[0009] This object is achieved by the independent patent claims. Advantageous embodiments of the invention are evident from the dependent patent claims.

[0010] According to a first aspect of the invention, the invention relates to a particle beam system comprising the following:

[0011] at least one particle source configured to generate a beam of charged particles;

[0012] a first multi-lens array including first individually adjustable and focusable particle lenses and arranged in a beam path of particles such that at least some of the particles pass through openings in the multi-lens array in the form of a plurality of individual particle beams;

[0013] a second porous plate including a plurality of second openings and arranged in the particle beam path upstream of the first multi-lens array and causing some of the particles passing through the first multi-lens array to illuminate the second porous plate and be absorbed therein, and some of the particles passing through the first multi-lens array to pass through the openings in the second porous plate; and

[0014] A controller is configured to supply individually adjustable voltages to the particle lenses of the first multi-lens array and thereby individually adjust the focus of the associated particle lens for each individual particle beam.

[0015] Thus, according to the present invention, at least one particle source is provided, although multiple particle sources may also be provided. The charged particles may be, for example, electrons, positrons, muons or ions or other charged particles. Preferably, the charged particles are electrons generated, for example, using a thermal field emission source (TFE). However, other particle sources may also be used.

[0016] Within the scope of the present patent application, a distinction is made between a porous plate on the one hand and a multi-lens array on the other hand. A porous plate is a plate with a large number of openings. Here, a voltage can be applied to the porous plate as a whole. This can, but need not be the case. In any case, all openings in the porous plate have a uniform, globally identical electrical and magnetic potential. In contrast, a multi-lens array within the scope of the present patent application is a more complex component than a porous plate: within the scope of the present patent application, a multi-lens array comprises a plurality of lenses arranged substantially parallel to one another, each lens being individually and independently adjustable from one another, so that the individual lenses of the lens array can have different refractive powers from one another, and each lens can change these refractive powers independently from one another on an individual basis.

[0017] The multi-lens array according to the invention comprises, according to an advantageous embodiment variant, the following:

[0018] a lens perforated plate having a plurality of openings; and

[0019] Multiple electrodes,

[0020] Wherein, at each of a plurality of openings, at least one of a plurality of electrodes is arranged in a manner insulated from the lens perforated plate so as to individually affect the individual particle beams passing through the respective openings. According to a preferred embodiment, the electrodes are ring electrodes; however, other embodiment variations are also possible. In the case of electrodes separated in azimuth (such as a quadrupole or an octupole), the same voltage can also be applied to all electrodes. In addition, a focusing effect can be brought about by a coil surrounding each opening in the lens perforated plate in a plane perpendicular to the beam direction. For the deflection coil, this is described in DE 10 2014 008 083 B4.

[0021] According to the present invention, the charged particles first pass through the first multi-lens array, and then pass through the second porous plate. It is important here that some of the particles that have passed through the first multi-lens array irradiate the second porous plate and are absorbed there, and some of the particles that have passed through the first multi-lens array pass through the opening of the second porous plate. Therefore, some particles are cut off or blocked from the corresponding individual particle beams by means of the second porous plate. How many particles this is now depends on the focusing effect of the particle lens in the first multi-lens array. For example, if the first multi-lens array produces a strong focusing effect on particles, then for example the beam diameter of the individual particle beam can be relatively small when arriving at the second porous plate, which is why more particles can then pass through the second porous plate and fewer particles are blocked. In the opposite case of the less strong focusing setting of the particle lens, or even in the case of lack of focusing, more particles are blocked when incident on the second porous plate, and fewer particles pass through the opening of the second multi-aperture plate. This allows setting the current density or ultimately the number of charged particles per individual beam downstream of the second multi-aperture plate by individual adjustments of the focus settings in the particle lenses of the first multi-lens array.

[0022] Controller can be embodied as one or more parts, and this controller is configured to supply the particle lens of the first multi-lens array with independently adjustable voltage and therefore regulates the focusing of the associated particle lens individually for each individual particle beam.If there are a plurality of multi-lens arrays in the particle beam system, then according to an embodiment variation, a central controller for all multi-lens arrays can be provided, for controlling all multi-lens arrays.But, also can use the controller of separation for each multi-lens array.In general, controller is integrated in the computer system of controlling whole particle beam system usually.

[0023] In the perforated plate, the opening in the particularly second perforated plate and the multi-lens array, particularly the first multi-lens array can have a regular arrangement, for example, arranged in a checkerboard or hexagonal pattern. Here, the openings in the multi-lens array are preferably identical or have the same diameter. Preferably, they are circular. Similar statements apply to the openings in the perforated plate. However, it is also possible to deviate from this regular and identical shape. According to a preferred embodiment variation of the present invention, perforated plate and multi-lens array, particularly the first multi-lens array and particularly the second perforated plate, have more than 10 openings, preferably more than 50 or 90, most preferably more than 100 openings. According to a particularly advantageous embodiment variation of the present invention, there are 91 openings for 91 particle beams, or there are 127 openings for 127 individual particle beams, or there are 3n (n-1) + 1 openings in the general case, and can be arranged hexagonally to each other, wherein n is an arbitrary natural number.

[0024] According to a preferred embodiment variation of the present invention, the particle beam system also includes a first porous plate, which has a plurality of first openings and is arranged in the particle beam path upstream of the first multi-lens array and is assigned to the first multi-lens array, wherein the diameter of the first opening is less than the diameter of the opening in the first multi-lens array, so that the particles passing through the first porous plate also pass through the first multi-lens array. Therefore, the first porous plate prevents charged particles from irradiating the area that is not an opening in the first multi-lens array. Therefore, the surface of the first multi-lens array is effectively prevented from being charged unintentionally. In this case, the center of the first opening in the first porous plate is usually accurately arranged on the center of the opening in the first multi-lens array. This improves the accuracy of the particle beam system as a whole. However, it is also possible to select a layout that deviates from it naturally, as long as the protection function to the first multi-lens array is maintained.

[0025] According to other preferred embodiments of the present invention, the particle beam system also includes a second multi-lens array, which has a second plurality of independently adjustable and focused particle lenses and is arranged in the particle beam path downstream of the first multi-lens array, so that at least some of the particles of the independent particle beam passing through the first multi-lens array also pass through the second multi-lens array, wherein there is a suitable distribution of the lenses to the first multi-lens array and the second multi-lens array for independent particle beams. Here, the controller is also configured to supply an independently adjustable voltage to the particle lens of the second multi-lens array, and therefore sets the focusing of the associated particle lens individually for each independent particle beam.

[0026] The second multi-lens array has a correction function in fact. If the individual particle beam through the focusing particle lens in the first multi-lens array is considered, the position of the focus or focal length of the individual particle beam is changed due to the focusing effect of the particle lens in the first multi-lens array. As a result, the individual particle beam can no longer be clearly imaged on the intermediate image plane. If other focusing particle lenses are now arranged at the downstream of the particle lens of the first multi-lens array, in this case other focusing particle lenses are provided in the second multi-lens array, then this can again achieve the accurate focusing of the individual particle beam on the intermediate image plane. If the entire field of the individual particle beam and the focusing or defocusing effect that occurs are now considered, the field curvature that may exist can therefore be corrected in general by means of the second multi-lens array.

[0027] According to a preferred embodiment variant of the invention, the second multi-lens array is arranged in the beam path downstream of the second porous plate. Thus, in this case, only some of the particles of the individual particle beams that have passed through the first multi-lens array also pass through the second multi-lens array, since the second porous plate is used in any case to block some of the particles of the individual particle beams. In this case, the second porous plate can also protect the second multi-lens array from unintentional charging caused by charged particles incident thereon.

[0028] According to an alternative embodiment variant of the invention, a second multi-lens array is arranged in the beam path upstream of the second perforated plate. Then, in this case, substantially all particles of the individual particle beams that have passed through the first multi-lens array also pass through the second multi-lens array. Then, the charged particles are only cut off or blocked after passing through the second multi-lens array.

[0029] According to other preferred embodiments of the present invention, the diameter of the second opening in the second porous plate is smaller than the diameter of the opening in the second multi-lens array. If the second multi-lens array is arranged downstream of the second porous plate, this size of the corresponding opening achieves effective protection for the second multi-lens array. In addition, possible lens defects, in particular spherical aberration, have less damaging effects.

[0030] According to other embodiments of the present invention, the particle beam system also comprises multiple light collectors, particularly dual light collectors. According to preferred embodiment variants of the present invention, the first multi-lens array is arranged in the downstream of multiple light collectors or dual light collectors and in the beam path upstream of the second porous plate. In this case, the particle beams that run into the first multi-lens array have extended substantially in parallel. However, the first multi-lens array may also be arranged in the beam path upstream of multiple light collectors or dual light collectors. Earlier current regulation or shielding of charged particles in the beam path can reduce the particle density of every beam and reduce the Coulomb effect. However, if the first multi-lens array is arranged in the upstream of dual light collectors or multiple light collectors, then in this case, non-parallel illumination must be considered for structure.

[0031] According to other preferred embodiment variations, the first porous plate is arranged between the components of multiple light collectors, particularly in dual light collectors, and the first multi-lens array is arranged in multiple light collectors, particularly in the downstream of dual light collectors, and in the upstream of second porous plate. Therefore, even if the first porous plate and the first multi-lens array are considered as a unit functionally, in whole particle beam system, the components of this unit---specifically the first porous plate on the one hand and the first multi-lens array on the other hand---also can be arranged variably relative to each other or arranged at a distance from each other. This allows to be easier to consider possible structural boundary conditions.

[0032] According to other preferred embodiments of the present invention, a particle optical lens for focusing a single particle beam on an intermediate image plane is also provided in a particle beam system. The particle optical lens can be implemented as one or more parts. As an example, the particle optical lens for focusing a single particle beam on an intermediate image plane can be one or more additional field lenses. In this case, "additional" means that in addition to the above-mentioned components such as lens groups and lens types, other components are actually present. However, for example, the particle optical lens for focusing a single particle beam on an intermediate image plane can also be formed by a second multi-lens array or more generally by other multi-lens arrays. For this reason, it may then be necessary to select the corresponding high refractive power of the particle lens of the second multi-lens array or other multi-lens arrays.

[0033] According to a preferred embodiment of the present invention, the first multi-lens array and the second multi-aperture plate are arranged in the beam path upstream of the intermediate image plane. This arrangement contributes to a compact structure of the particle beam system.

[0034] According to another preferred embodiment variant of the invention, the first multi-lens array and the second multi-aperture plate are arranged in the beam path downstream of the intermediate image plane. This allows the realization of a structure with a relatively large space requirement and usually images the individual particle beams on a further intermediate image plane.

[0035] According to an alternative embodiment variant of the invention, the individually adjustable voltages of the particle lenses and thus the refractive power of the first multi-lens array are selected so that a further intermediate image appears between the first multi-lens array and the second multi-lens array. In this embodiment variant, an embodiment with a telescopic optical system can be realized, in particular when a third multi-lens array is used.

[0036] According to other preferred embodiments of the present invention, the particle beam system also includes a third multi-lens array, which has a third plurality of individually adjustable and focused particle lenses and is arranged in the particle beam path downstream of the first multi-lens array and downstream of the second multi-lens array, so that at least some of the particles of the individual particle beams passing through the first multi-lens array and the second multi-lens array also pass through the third multi-lens array, wherein there is a suitable allocation of lenses to the first multi-lens array, the second multi-lens array and the third multi-lens array for individual particle beams. In addition, the controller is configured to supply an individually adjustable voltage to the particle lenses of the third multi-lens array, thereby individually setting the focusing of the associated particle lenses for each individual particle beam. The aforementioned telescope optical system can be well realized by means of this embodiment variant. Here, the third multi-lens array can also be used to correct the field curvature that may occur. Depending again on the refractive power of the particle lenses of the third multi-lens array, an additional field lens for focusing the individual particle beam on the intermediate image plane may be necessary, or may be omitted.

[0037] According to other preferred embodiment variations of the present invention, the particle beam system also includes the fourth porous plate with a plurality of the fourth openings and the fourth multi-lens array with the fourth multiple focusing particle lenses and arranged in the particle beam path downstream of the fourth porous plate. Here, the fourth porous plate and the fourth multi-lens array are arranged in the beam path of the source side of the first multi-lens array, and are arranged relative to each other so that the particles passing the fourth porous plate also pass through the fourth multi-lens array. In addition, the controller is configured to provide a separately adjustable voltage to the particle lens of the fourth multi-lens array, and therefore sets the focusing of the associated particle lens respectively for each individual particle beam. The described embodiment variation is particularly suitable for those particle beam systems in which the individual particle beam is subjected to current regulation after imaging on the intermediate image plane.

[0038] In principle, in particle beam systems according to the present invention, other multi-lens arrays similar to the above-mentioned variants can also be used. They can be provided with associated porous plates as required. In this case, for example, each porous plate arranged upstream of the associated multi-lens array can then be protected from the unintentional charging caused by charged particles.

[0039] According to other preferred embodiments of the present invention, the particle beam system also includes a measuring device for measuring the current of a single particle beam, in particular for measuring the current in the region of the object plane. Instead of measuring in the region or near the object plane, the current of each single particle beam can be measured near the intermediate image plane or at any other point in the lighting column (where the beams are separated from each other). As an example, the measuring device can include at least one current-sensitive sensor, such as at least one Faraday cup, which can be introduced into the beam path. The current sensor is advantageously provided with an aperture, which only allows particles from a specific area perpendicular to the beam direction to reach the sensor. Advantageously, the maximum lateral range, such as the aperture diameter in the case of a circular aperture, will be less than the spacing of the beam at the measuring point. As an example, the aperture diameter to be selected at the object is 20μ0, preferably 10μ0, and most preferably 5μ. As an example, the current sensor is mounted on a displacement stage, which moves the current sensor substantially perpendicular to the beam path. Then the positions of all the individual particle beams can be approached successively, so that in each case just one particle beam passes through the aperture. The current sensor and the displacement stage are preferably controlled by a computer system, in particular by a central computer system. Thus, the value of the current can be determined for each individual particle beam. These values ​​of the current can then naturally also be determined as a function of the excitation values ​​of the lenses of the multi-lens array MLA.

[0040] According to a preferred embodiment of the present invention, the measuring device is set so that the measurement of current can be realized for multiple individual particle beams at the same time. This allows faster measurement, and then based on this, the current can also be adjusted faster. In this embodiment, the measuring device can include, for example, multiple current sensors and multiple apertures, and the apertures are arranged in space so that each individual particle beam just passes through an aperture and is captured by just one current sensor. If the number of sensors and apertures is less than the number of individual particle beams, it is necessary to move the displacement stage less frequently accordingly. If the number of sensors and apertures is greater than or equal to the number of individual particle beams, there is no need to move the displacement stage during the measurement of the current. Alternatively, all individual particle beams can also be applied to differently arranged, spatially resolved current sensors, such as 2-dim CCDs, and the current of each individual particle beam can be determined, for example, by integrating the CCD signals of the CCD pixels related to the beam.

[0041] According to other aspects of the invention, the latter relates to a method for closed-loop current regulation of an individual particle beam of a particle beam system as described above in a number of embodiment variants. In this case, the method comprises the following steps:

[0042] By means of the first multi-lens array, the individual beam currents are adjusted for a plurality of individual particle beams, in particular for all individual particle beams.

[0043] To set the individual beam currents, the controller of the particle beam system can supply appropriate voltages to the particle lenses of the first multi-lens array, so that the individual particle beams are more or less strongly focused. Depending on the focus setting, an appropriate number of particles are then blocked or shielded at a second porous plate arranged in the beam path downstream of the first multi-lens array.

[0044] According to a preferred embodiment of the present invention, the method further comprises the following steps:

[0045] The focal lengths of the individual particle beams are corrected by means of a second multi-lens array or further multi-lens arrays.

[0046] As an example, the correction focal length is used to correct the focal position that changes after the individual beam current has been set to the focal position to be specified. As an example, the focal position to be specified can be the original focal position or the focal position that pre-compensates for the field curvature in the main path. For the purpose of correction, the controller of the particle beam system can again supply appropriate voltages to the particle lenses of the second multi-lens array or other multi-lens arrays, thereby achieving appropriate focusing again in a separate manner for the individual particle beams. Preferably, the multi-lens array for correction purposes is located in the beam path downstream of the first multi-lens array and / or downstream of the second porous plate; however, it can also be located upstream thereof. Therefore, the correction multi-lens array can be a second multi-lens array; however, this is not mandatory and different multi-lens arrays can also be used.

[0047] According to a preferred embodiment of the present invention, the method further comprises the following steps:

[0048] Before adjusting the individual beam currents, the desired focal lengths of the individual particle beams are adjusted by means of the second multi-lens array or further multi-lens arrays.

[0049] Therefore, in this embodiment variant, the focus is first adjusted before starting the actual adjustment of the individual currents. This procedure creates simpler initial conditions for the subsequent current adjustment by focus correction and simplifies the final correction.

[0050] According to a preferred embodiment of the present invention, the method further comprises the following steps:

[0051] For a plurality of individual particle beams, in particular for an individual particle beam, individual beam currents are measured; and the individual beam currents are adjusted using the measured values.

[0052] As an example, the measurement can be realized by the above-mentioned measuring device. The measured values ​​can then be evaluated automatically or using software. The necessary correction of the individual beam current then occurs in each case for the individual beams therefrom, and the voltage supply is again provided accordingly for each multi-lens by the controller.

[0053] According to a preferred embodiment of the invention, the method is carried out several times and in particular iteratively in whole or in part. In this way, the best possible regulation of the current flow is achieved step by step.

[0054] According to other aspects of the invention, the latter relates to a particle beam system comprising the following:

[0055] at least one particle source configured to generate a beam of charged particles;

[0056] a first multiple stigmator array including a first plurality of individually adjustable first stigmators and arranged in the particle beam path such that at least some particles pass through openings in the multiple stigmator array in the form of a plurality of individual particle beams;

[0057] a second porous plate including a plurality of second openings and disposed in the particle beam path downstream of the first multiple stigmator array and arranged such that some of the particles passing through the first multiple stigmator array impinge on the second porous plate and are absorbed therein, and some of the particles passing through the first multiple stigmator array pass through the openings in the second porous plate;

[0058] a second multiple stigmator array comprising a second plurality of individually adjustable second stigmators and arranged in the particle beam path downstream of the second porous plate such that at least some of the particles that pass through the second porous plate also pass through the second multiple stigmator array; and

[0059] a controller configured to supply respective individually adjustable voltages to the stigmators of the first multi-stigmator array and to the stigmators of the second multi-stigmator array for the purpose of generating a multipole field, in particular a quadrupole or octopole field, and thus to set the astigmatism individually in the associated stigmator for each individual particle beam,

[0060] Therein, the voltages are selected such that the astigmatism setting of the stigmatists of the first multiple stigmatist array is compensated in each case by the opposite astigmatism setting of the associated stigmatist in the second multiple stigmatist array.

[0061] The advantage of using a multi-stigmator array in the manner specified above, compared to a multi-lens array with a focusing effect, is that lower voltages are required to influence the individual particle beams. However, two components (i.e. two multi-stigmator arrays) are required to achieve this, instead of one component (i.e. a single multi-lens array).

[0062] The described embodiment variants of the invention can be combined with one another in whole or in part, provided that no technical contradictions arise as a result. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The invention will be even better understood with reference to the accompanying drawings, in which:

[0064] Figure 1 A schematic diagram of a multi-beam particle microscope is shown;

[0065] Figure 2 shows a schematic diagram of current regulation for an individual particle beam according to a first embodiment;

[0066] Figure 3 shows a schematic diagram of current regulation for individual particle beams according to a second embodiment;

[0067] Figure 4 shows a schematic diagram of current regulation for individual particle beams according to a third embodiment;

[0068] Figure 5 shows a schematic diagram of current regulation for individual particle beams according to a fourth embodiment;

[0069] Figure 6 shows a schematic diagram of current regulation for individual particle beams according to a fifth embodiment;

[0070] Figure 7 The structure of a multi-lens array with ring electrodes is schematically shown;

[0071] Figure 8 A schematic diagram showing current regulation of individual particle beams by means of an stigmator according to a sixth embodiment of the present invention;

[0072] Fig. 9 schematically illustrates the mode of operation of the stigmator; and

[0073] Fig.10 An alternative example of current regulation is schematically shown. DETAILED DESCRIPTION

[0074] Figure 1 It is a schematic diagram of a particle beam system 1 in the form of a multi-beam particle microscope 1 using multiple particle beams. The particle beam system 1 generates multiple particle beams, which irradiate an object to be inspected, so as to generate there an interaction product, such as secondary electrons, emitted from the object and subsequently detected. The particle beam system 1 is a scanning electron microscope (SEM) type, which uses multiple primary particle beams 3, which are incident on multiple positions 5 on the surface of an object 7 and generate there multiple electron beam spots or spots separated from each other in space. The object 7 to be inspected can be any desired type, such as a semiconductor wafer or a biological sample, and includes the arrangement of miniaturized elements, etc. The surface of the object 7 is arranged in a first plane 101 (object plane) of an objective lens 102 of an objective lens system 100.

[0075] Figure 1The enlarged detail I1 in FIG. 1 shows a top view of the object plane 101 with a regular rectangular field 103 of incident positions 5 formed in the first plane 101. Figure 1 In FIG. 1 , the number of incident positions is 25, which forms a 5×5 field 103. The number of incident positions 25 is a number chosen for the sake of simplicity of illustration. In practice, the number of beams and the number of incident positions can be chosen to be significantly larger, for example 20×30, 100×100, etc.

[0076] In the embodiment shown, the field 103 of the incident positions 5 is a substantially regular rectangular field with a constant pitch P1 between adjacent incident positions. Exemplary values ​​of the pitch P1 are 1 micron, 10 microns and 40 microns. However, the field 103 may also have other symmetries, such as hexagonal symmetry.

[0077] The diameter of the beam spot formed in the first plane 101 can be small. Exemplary values ​​of the diameter are 1 nm, 5 nm, 10 nm, 100 nm and 200 nm. Focusing of the particle beam 3 for forming the beam spot 5 is carried out by the objective lens system 100 .

[0078] The primary particles irradiating the object generate interaction products, such as secondary electrons, backscattered electrons or primary particles that have undergone a reversal of motion for other reasons, which are emitted from the surface of the object 7 or from the first plane 101. The interaction products emitted from the surface of the objective 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 directing a plurality of secondary particle beams 9 to a detector system 200. The detector system 200 includes a particle optical unit having a projection lens 205 for directing the secondary particle beam 9 to a particle multi-detector 209.

[0079] Figure 1 The partial view I2 in FIG. 1 shows a top view of a plane 211, where individual detection areas of a particle multi-detector 209 are positioned on which a secondary particle beam 9 is incident at a position 213. The incident positions 213 are located in a field 217 with regular spacing P2 relative to each other. Exemplary values ​​of the spacing P2 are 10 microns, 100 microns and 200 microns.

[0080] The primary particle beam 3 is generated in a beam generating device 300, which comprises at least one particle source 301 (e.g., an electron source), at least one collimating lens 303, a porous arrangement 305, and a field lens 307. The particle source 301 generates a divergent particle beam 309, which is collimated or at least substantially collimated by the collimating lens 303 in order to shape a beam 311 that illuminates the porous arrangement 305.

[0081] Figure 1Detailed view I3 in FIG. 1 shows a top view of a porous arrangement 305. The porous arrangement 305 includes a porous plate 313 having a plurality of openings or holes 315 formed therein. The midpoints 317 of the openings 315 are arranged in a field 319 that is imaged onto the field 103 formed by the beam spot 5 in the object plane 101. Exemplary values ​​of the spacing P3 between the midpoints 317 of the holes 315 may be 5 microns, 100 microns, and 200 microns. The diameter D of the holes 315 is smaller than the spacing P3 between the midpoints of the holes. Exemplary values ​​of the diameter D are 0.2×P3, 0.4×P3, and 0.8×P3.

[0082] Particles of the illumination particle beam 311 pass through the aperture 315 and form the particle beam 3 . Particles of the illumination beam 311 which illuminate the plate 313 are absorbed by the plate 313 and do not contribute to the formation of the particle beam 3 .

[0083] Due to the applied electrostatic field, the porous arrangement 305 focuses each of the particle beams 3 such that a beam focus 323 is formed in a plane 325. The diameter of the beam focus 323 may be, for example, 10 nanometers, 100 nanometers and 1 micrometer.

[0084] The field lens 307 and the objective lens 102 provide a first imaging particle optical unit for imaging the plane 325 in which the beam focus is formed onto the first plane 101 so that the field 103 or beam spot of the incident position 5 appears there. If the surface of the object 7 is arranged in the first plane, the beam spot is correspondingly formed on the object surface.

[0085] The objective lens 102 and the projection lens arrangement 205 provide a second imaging particle optical unit for imaging the first plane 101 onto a detection plane 211. Thus, the objective lens 102 is a lens that is part of both the first particle optical unit and the second particle optical unit, whereas 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.

[0086] The beam switch 400 is arranged in the beam path of the first particle optical unit between the porous arrangement 305 and the objective lens system 100. The beam switch 400 is also part of a second optical unit in the beam path between the objective lens system 100 and the detector system 200.

[0087] More information about such multi-beam particle beam systems and the components used therein, such as particle sources, porous plates and lenses, can be obtained from international patent applications WO 2005 / 024881, WO 2007 / 028595, WO 2008 / 028596, WO 2011 / 124352 and WO 2007 / 060017 and German patent applications with application numbers DE 10 2013 026 113.4 and DE 10 2013 014976.2, the entire disclosure contents of these patent applications are incorporated by reference into the present application.

[0088] The multi-beam particle beam system also includes a computer system 10, which is configured to be used for controlling the individual particle optical components of the multi-beam particle beam system, and for evaluating and analyzing the signals obtained by the multi-detector 209. In this case, the computer system 10 can be composed of a plurality of individual computers or components. Here, the computer system 10 can also be connected to a controller 550 for the first multi-lens array and optionally for other multi-lens arrays and / or multi-stigmator arrays that exist, and / or can include a corresponding controller. In addition, the computer system 10 can be connected to or include a measuring device for measuring the electric current of the individual particle beam.

[0089] By means of the measuring device, the current of each individual particle beam in the vicinity of the object plane 7 or in the vicinity of the intermediate image plane 325 or at any other point in the illumination column (where the beams are spatially separated from each other) can be measured. For this purpose, a current-sensitive sensor, such as a Faraday cup, can be introduced into the beam path. The current sensor advantageously comprises an aperture that allows only particles from a certain area perpendicular to the beam direction to reach the sensor. Advantageously, the maximum lateral range, such as the aperture diameter in the case of a circular aperture, is less than the spacing of the beams at the measuring point. When measuring the current in the object plane, the aperture diameter is, for example, 20 μm, preferably 10 μm and most preferably 5 μm, i.e., ideally between 5 and 20 μm. As an example, the current sensor can be mounted on a displacement stage that moves the current sensor substantially perpendicular to the beam path. The positions of all individual particle beams 3 can be approached successively so that in each case just one beam passes through the aperture. The current sensor and the displacement stage are controlled by a computer system 10. Therefore, the current value of each individual particle beam 3 can be determined. These values ​​of the current can then naturally also be determined as a function of the excitation values ​​of the lenses of the multi-lens array MLA.

[0090] Instead of continuously measuring the current value of each individual particle beam 3, the current value can also be determined in parallel in time, for example, by multiple current sensors and multiple apertures, which are spatially arranged so that each individual particle beam 3 passes through exactly one aperture and is captured by exactly one current sensor. If the number of sensors and apertures is greater than one but less than the number of individual particle beams 3, the displacement stage needs to be moved less frequently during the current measurement accordingly. If the number of sensors and apertures is greater than or equal to the number of individual particle beams 3, the displacement stage does not need to be moved during the current measurement. Alternatively, all individual particle beams 3 can also be applied to differently arranged, spatially resolved current sensors, such as 2-dim CCDs, and the current of each individual particle beam can be determined, for example, by integrating the CCD signals of the CCD pixels associated with the beam.

[0091] Figure 2 A schematic diagram of current regulation for a single particle beam according to a first embodiment is shown. This schematic diagram is not in true proportion and is intended only to illustrate basic aspects of the present invention. In the exemplary case shown, the particle beam system includes a particle source Q, which is configured to generate a beam of charged particles, such as electrons in this case. Here, a divergent electron beam is initially generated, which then encounters a multiple condenser, such as a dual condenser CL1 ... N. In the beam direction of the particles emitted from the particle source Q, this embodiment includes a first porous plate PA1, a first multi-lens array MLA1, a second porous plate PA2, a second multi-lens array MLA2, and a field lens system FL1 ... N downstream of the multiple condenser CL1 ...

[0092] After passing through the double condenser CL1…N, the electron beam first irradiates the first porous plate PA1, which has a plurality of first openings, and then the electron beam passes through the plurality of first openings. Therefore, after passing through the first porous plate PA1, a plurality of individual particle beams S1, S2, S3 appear. These individual particle beams S1, S2, S3 then pass through the first multi-lens array MLA1. Since the first porous plate PA1 is arranged in the particle beam path upstream of the first multi-lens array MLA1, and since the diameter d2 of the opening in the first porous plate PA1 is smaller than the diameter d1 of the opening in the first multi-lens array MLA1, all particles passing through the first porous plate PA1 also pass through the first multi-lens array MLA1. Therefore, the first porous plate PA1 has a protective effect and prevents unintentional incident on the first multi-lens array MLA1 or unintentional charging of the first multi-lens array MLA1. In addition, this size of the opening helps to keep the possible lens defects of the first multi-lens array MLA1, especially the influence of spherical aberration, as small as possible.

[0093] The first multi-lens array MLA1 includes a plurality of individually adjustable and focused particle lenses. Therefore, the focusing effect on each individual particle beam S1, S2, S3 can be selected differently. In the example shown, the focusing effect on the individual particle beam S1 is relatively weak, while the focusing effect on the individual particle beam S3 is relatively strong, and no focusing effect is applied to the individual particle beam S2. Therefore, when each individual particle beam S1, S2, S3 is incident on the second porous plate PA2, the beam diameter of the individual particle beam S1, S2, S3 and the illumination spot produced by the corresponding individual particle beam are different for each individual particle beam S1, S2, S3. The individual particle beam S2 has the largest beam diameter, which will not be further focused by the particle lens of the first multi-lens array MLA1 assigned to it. The strongest focused individual particle beam S3 has the smallest beam diameter when incident on the second porous plate PA2. There is a medium range focusing for the individual particle beam S1, thereby producing a medium range beam diameter when incident on the second porous plate PA2. Depending on the focusing of the individual particle beams S1, S2, S3, there is now a more or less significant shielding or blocking of the particles resulting from the impact on the second porous plate PA2. Therefore, by the previous focusing in the first multi-lens array MLA1, the number of charged particles passing through the porous plate PA2 can be adjusted individually for each opening and therefore for each particle beam S1, S2, S3. Therefore, the arrangement of the second porous plate downstream of the first multi-lens array PA1 ensures that individual current adjustments can be made for the individual particle beams.

[0094] In the example shown, the second multi-lens array MLA2 is located in the beam path downstream of the second porous plate PA2. The second multi-lens array includes a second large number of individually adjustable and focusing particle lenses, and is arranged in the beam path of particles or electrons downstream of the first multi-lens array MLA1, so that at least some of the particles of the individual particle beams S1, S2, S3 passing through the first multi-lens array MLA1 also pass through the second multi-lens array MLA2. Here, for each individual particle beam S1, S2, S3, there is an appropriate allocation of lenses for the first multi-lens array MLA1 and the second multi-lens array MLA2. The number of lenses of each array MLA1 and MLA2 is preferably the same, and the lenses are arranged corresponding to each other. Using the lenses of the second multi-lens array MLA2, the focusing positions of the individual beams S1, S2, S3 can be individually corrected relative to the field curvature of the imaging in the primary beam path 13 (which may exist as a whole). After passing through one or more field lenses FL1...N, focus on the intermediate image plane 325. In the case that the refractive power of the particle lenses of the second multi-lens array MLA2 is large enough, the field lens or the field lens system FL1 . . . N can theoretically be omitted.

[0095] Since the opening diameter d3 in the second porous plate PA2 is smaller than the opening diameter d4 in the second multi-lens array MLA2, charged particles can be successfully prevented from hitting the surface of the second multi-lens array MLA2 and charging it. Therefore, in this case, the second porous plate PA2 also plays its corresponding protective role above the second multi-lens array MLA2. In addition, in the case of appropriate size, possible lens defects, especially spherical aberration, also have a less obvious effect in the second multi-lens array MLA2 in this case.

[0096] With the aid of the measuring device, the adjustment of the values ​​of the current and focus positions can preferably be realized in an iterative manner. As an example, the desired focus position in the intermediate image plane 325 can be adjusted in a first step by means of the second multi-lens array MLA2. Advantageously, this can be realized in the object plane 7 using conventional methods within the scope of an electron microscope, for example by a series of focusing on a high-resolution sample, wherein the position of the beam waist along the beam direction is determined by conventional methods, for example by an edge steepness criterion or by Fourier analysis. In a second step, the current of each individual particle beam S1, S2, S3 is adjusted by means of the first multi-lens array MLA1 by appropriate individual changes in the refractive power of the individual lenses of the first multi-lens array MLA1. Then, in a third step, the focal position in the intermediate image plane 325 can be readjusted by a corresponding individual change in the refractive power of the individual lenses of the second multi-lens array MLA2 or by another other multi-lens array MLA in order to compensate for the displacement of the corresponding focal point in the intermediate image plane 325, which displacement is caused by the change in the refractive power of the first multi-lens array MLA1 and is usually individual for each particle beam S1, S2, S3, so that the focal points of all particle beams S1, S2, S3 are located in the intermediate image plane 325. For this purpose, it can be useful to apply the known sensitivity of the excitation intensity of each lens element of the first multi-lens array MLA1 and the second multi-lens array MLA2 to the focusing position.

[0097] To a certain extent, the second multi-lens array MLA2 should also compensate for the field curvature of the subsequent particle optical unit made of field lenses, beam splitters and objective lenses, the intermediate image plane 325 is not an exact plane but generally a curved area, which is then imaged by the subsequent particle optical unit on the object plane taking into account the field curvature. Even when the particle currents in the individual particle beams are adjusted or balanced by changing the excitation of the individual lenses of the first multi-lens array MLA1, post-correction is also achieved here by changing the excitation of the individual lenses of the second multi-lens array MLA2, so that when taking into account the field curvature, the focal points of all individual particle beams S1, S2, S3 are located in the area imaged in the object plane by the subsequent particle optical unit.

[0098] So, in summary, one can use Figure 2 The embodiment variant shown enables individual current regulation for each individual particle beam in a very simple and elegant manner.

[0099] Figure 3 A schematic diagram of current regulation for individual particle beams S1, S2, S3 according to a second embodiment of the present invention is shown. In order to simplify the illustration, only the combination of a porous plate and a multi-lens array is illustrated as a unit in the form of a dark box in the beam path. The difference between the second embodiment and the first embodiment lies in the position of the first porous plate PA1 and the first multi-lens array MLA1. In this case, both are already arranged above the multi-condenser or double condenser CL1 ... N, that is, on its source side. However, the first embodiment and the second embodiment are otherwise identical. Alternatively, the unit made of the first porous plate PA1 and the first multi-lens array MLA1 can also be separated, and the components can be arranged in other positions; as an example, the first porous plate PA1 can be arranged between the lenses CL1 and CL2 of the multi-condenser, that is, in the double condenser or the multi-condenser, and then the first multi-lens array 1 can be arranged between the second condenser lens CL2 and the second porous plate PA2. However, the function of the optical element remains the same in principle.

[0100] Figure 4 A schematic diagram of current regulation of a separate particle beam according to a third embodiment of the present invention is shown. Since the principle of separate current regulation has been described in detail on the basis of the first embodiment, in this case Figure 4The schematic diagram in has also been kept very simple, and only the uniqueness of this embodiment variant and its difference from the above-mentioned embodiment variants will be discussed below. The left side of the image shows a very strong focusing by the first multi-lens array, while the right side of the image shows a less strong focusing of the individual particle beams by the first multi-lens array MLA1. The optical elements used in this third embodiment variant are in principle the same as those in the first embodiment. In principle, their positioning is also comparable to the first embodiment. However, the basic difference here lies in the refractive power of the particle lenses of the first multi-lens array MLA1. In this case where an intermediate image is generated in each individual particle beam between the first multi-lens array MLA1 and the second multi-lens array MLA2, i.e., the intermediate focus (i.e., the beam waist) of each individual particle beam is between the first multi-lens array MLA1 and the second multi-lens array MLA2, the focusing effect of the individual particle lenses of the first multi-lens array is very strong. However, even if such an intermediate focus is generated in each individual particle beam, there is the following situation: depending on the strength of the focusing in the first multi-lens array MLA1, it is possible to adjust how many particles hit the second porous plate PA2 and are absorbed there or how many particles pass through the openings in the second porous plate PA2. In the example shown, for example, more particles are blocked by the second porous plate PA2 on the left side of the image than on the right side of the image. Subsequently, the second multi-lens array MLA2 can again correct the different positions of the beam focus near or in the intermediate image plane 325 caused by the individual settings of the individual lenses of the first multi-lens array MLA1, and / or compensate for possible field curvature. After passing through one or more field lenses FL1…N, the individual particle beams are imaged or focused on the intermediate image plane 325.

[0101] Figure 5 FIG. 4 is a schematic diagram showing the current regulation of a single particle beam according to a fourth embodiment of the present invention. Figure 4The difference of the third embodiment shown is that a third multi-lens array MLA3 is additionally provided in the beam direction downstream of the second multi-lens array MLA2. The particle lenses of the second multi-lens array MLA2 exert a focusing effect on the individual particle beams only to a certain extent, so that the individual particle beams are collimated in the beam direction downstream of the second multi-lens array MLA2 respectively and these collimated individual particle beams then pass through the subsequently arranged third multi-lens array MLA3. Then, the possible field curvature of the subsequent particle optical unit can be corrected by a plurality of individually adjustable and focusing particle lenses in the third multi-lens array MLA3. Then, the individual particle beams are then focused on the intermediate image plane 325 by one or more field lenses FL1…N; however, these field lenses can also be omitted in the case where the particle lenses of the third multi-lens array MLA3 have appropriate refractive power. In the last-mentioned case, the refractive powers of the individual lenses of the third multi-lens array are then set so that each individual lens of the third multi-lens array focuses the particle beam passing through it into the intermediate image plane 325 or - if the field curvature of the subsequent particle optical unit is corrected - into the area imaged by the subsequent particle optical unit in the object plane.

[0102] Figure 6 A schematic diagram of current regulation of a separate particle beam according to a fifth embodiment of the present invention is shown. Again, the first multi-lens array MLA1 and the second porous plate PA2 are basic components for regulating the separate beam current itself. Here, in the fifth embodiment, the first porous plate PA1, the first multi-lens array MLA1, the second multi-lens array MLA2 and the second porous plate PA2 and the third multi-lens array MLA3 provided additionally and the subsequent objective lens FL1 ... N are arranged only downstream of the intermediate image plane SG in the beam direction. For the purpose of focusing on the intermediate image plane SG, the charged particles emitted from the particle source Q first pass through the multi-condenser CL1 ... N, and then hit the fourth porous plate PA4, which is the porous plate closest to the particle source Q, thereby forming a separate particle beam. Therefore, these separate particle beams pass through the fourth multi-lens array MLA4 and the first field lens group FL1 ... N arranged thereafter, and are therefore imaged on the intermediate image plane SG. Then, the individual currents of the individual particle beams are set only by the series arrangement of the first porous plate PA1, the first multi-lens array MLA1, the second multi-lens array MLA2 and the second porous plate PA2, which are arranged downstream of the intermediate image plane SG in the beam direction. As in the above-described embodiment, the third multi-lens array and the second field lens group FL1 ... N can be arranged downstream of the second porous plate PA2 in the beam direction so as to generate a beam focus in each individual particle beam in the second intermediate image plane SG2.

[0103] It should be emphasized in this embodiment variant that the first multi-lens array MLA1 and the second multi-lens array MLA2 are arranged directly in succession and in front of the second porous plate PA2. Therefore, the lenses of the first multi-lens array MLA1 and the second multi-lens array MLA2 form a type of "micro double condenser", and the individual lenses of the mutually corresponding lenses in the first multi-lens array MLA1 and the second multi-lens array MLA2 - that is, the lenses of the two multi-lens arrays that pass through the same individual particle beams - are excited in a combined manner, so that the individual particle beams always hit the second porous plate PA2 in a substantially parallel manner, that is, in a collimated manner. Even when the refractive power of the first multi-lens array MLA1 and the second multi-lens array MLA2 is changed for the purpose of current regulation in the individual particle beams, the refractive power of the third multi-lens array MLA3 following in the beam direction and / or the refractive power of the subsequent second field lens system does not need to be changed in order to generate a beam focus in the second intermediate image plane SG2, and can instead be operated with a constant refractive power. This achieves the effect that the beam focus in all individual particle beams is generated under telecentric conditions which are uniform and constant for all individual particle beams and which are generated with the same numerical aperture despite the current control.

[0104] As described above, the field curvature that may exist in the subsequent particle optical unit can be corrected again by the third multi-lens array MLA3. In the case where the particle lenses of the third multi-lens array MLA3 have appropriate refractive power, the subsequent field lenses FL1...N can also be omitted. Then, imaging is performed on the second intermediate image plane SG2.

[0105] Figure 7 A schematic diagram of an embodiment variant of a multi-lens array MLA is shown, which is how various multi-lens arrays MLA1 to MLA4 are constructed within the scope of the present invention. The multi-lens array MLA comprises a lens porous plate 510 having a plurality of openings with a diameter d. Typically, the diameter d of the openings is the same for all individual lenses of the multi-lens array. In addition, the multi-lens array MLA comprises a plurality of electrodes 503, 503′ and 503″, which in the example shown are ring electrodes. The ring electrodes 503, 503′ and 503″ are arranged at each opening of the lens porous plate 510 in a manner insulated from the lens porous plate 510 so as to individually affect the individual particle beams passing through the corresponding openings. To this end, for the purpose of supplying voltage, an associated line 504, 504′ and 504″ is provided for each electrode 503, 503′ and 503″, which leads to a controller 550. The controller 550 can individually set the voltages to be applied to the electrodes 503, 503' and 503" of one multi-lens array MLA or a plurality of multi-lens arrays MLA in each case. Figure 7One or more counter electrodes are not shown, and each ring electrode 503, 503' and 503" interacts with the one or more counter electrodes to form an electrostatic lens through an electrostatic acceleration or retardation field. The multi-lens array MLA can be manufactured, for example, by conventional methods in microstructure technology, such as a combination of photolithography methods and subsequent etching and / or deposition methods.

[0106] Reference is made to the fact that components of the controller 550 can also be arranged immediately on the lens porous plate 510, so that some of the lines 504, 504' and 504" for the voltage supply can also be implemented as conductor tracks or in the lens porous plate 510. Thus, the number of supply lines between an external controller and the multi-lens array arranged in the vacuum column of the particle beam device can be reduced.

[0107] Figure 8 A schematic diagram of current regulation for individual particle beams by means of an stigmator according to a sixth embodiment is schematically shown. The arrangement for current regulation according to this embodiment includes a first porous plate PA1 on a first source side or a condenser side, a first multi-stigmator STG1 following in the beam direction of the particle beam, a second porous plate PA2 following the first multi-stigmator STG1 in the beam direction, and a second multi-stigmator STG2 following the second porous plate PA2. The particle beam emitted from the condenser (not shown here) first hits the porous plate PA1 or partially passes through the opening in the porous plate. In this way, a plurality of individual particle beams are formed. Then, when the opening diameter d3 of the opening in the second porous plate PA2 is smaller than the diameter d2 of the opening in the first porous plate PA1, the individual particle beam passes through the first multi-stigmator STG1 and then hits the porous plate PA2 having a plurality of appropriate openings. Therefore, the diameter of the particle beam formed by the first porous plate PA1 is greater than the opening diameter d3 of the opening in the second porous plate PA2. Since the individual particle beam partially hits the plate and partially passes through the opening with diameter d3, a certain number of particles can now be removed or blocked again from the individual particle beam. The remaining particles of the individual particle beam then pass through the second multi-stigmator STG2 and then through other particle optical components (not shown).

[0108] Then Fig. 9 The main operating modes of the multi-stigmator are shown in Figure 2. Fig. 9 a) shows Figure 8 The first multi-stigmator STG1 is deactivated, while Fig. 9 b) shows Figure 8602 and 602' of the individual particle beams are shown. In the case of the first multi-stigmator STG1 being in the deactivated state, the illumination spot 602 is substantially circular ( Fig. 9 a). In contrast, when the first multi-stigmator STG1 is activated, the illumination spot 602' is substantially elliptically distorted. Therefore, depending on whether the first multi-stigmator STG1 is activated or the intensity of the excitation, it is possible to set how many incident particles in the individual particle beams actually pass through the openings 601 of the second porous plate PA2. Therefore, the current of each individual particle beam can be adjusted in this way.

[0109] For subsequent imaging of individual particle beams, the astigmatism brought about by the individual stigmats of the first multiple stigmat STG1 must then be compensated again. To this end, a second multiple stigmat STG2 is provided downstream of the second porous plate PA2, the stigmats (i.e. multipoles) of which are excited in a manner based on the astigmatism generated by the associated stigmats of the first multiple stigmat STG1, so that each stigmat of the second multiple stigmat STG2 accurately compensates for the astigmatism generated by the assigned stigmat of the first multiple stigmat STG1, through which the same individual particle beam passes. Thereafter, the individual particle beams have almost no astigmatism anymore.

[0110] As an example, the individual stigmators of the multiple stigmators STG1 and STG2 can be implemented as quadrupoles or octopoles. In principle, it is sufficient to use a quadrupole. However, if the stigmator is implemented as an octopole, the orientation of the generated quadrupole can be changed as required, so multiple astigmatism directions are therefore available.

[0111] The advantage of using a multi-stigmator in the manner specified above, compared to a multi-lens array with a focusing effect, is that lower voltages are required to influence the individual particle beams in the case of a stigmator than in the case of the lenses of a multi-lens array. However, instead of using at least one multi-lens array, the work must be carried out by at least two multi-stigmators STG1 and STG2.

[0112] Fig.10An alternative example for current regulation by means of an alternative embodiment of a multi-lens array is illustrated. In this embodiment, each individual electrostatic lens of the multi-lens array comprises a cylindrical shield 505, the cylindrical axis of which is aligned parallel to the beam axis of the individual particle beam. A ring electrode 503 is arranged within the cylindrical shield 505 of each individual lens of the multi-lens array, the ring electrode 503 being electrically insulated from the shield 505 and capable of applying a different potential to the ring electrode for each individual lens of the multi-lens array.

[0113] In the example shown, each ring electrode 503 is arranged at the base of a cylindrical shield 505. In this case, the cylindrical shield 505 is at a first potential, which is arbitrarily assumed to be zero potential in this case. At the top, the cylindrical shield 505 has an opening or hole PA through which the individual particle beams 3 enter the cavity 506 of the cylindrical shield 505. The individual particle beams 3 traverse the cavity 506 and leave the cavity through other openings 507 after passing through the ring electrodes 503, which are arranged at the base of the shield 505. The number of charged particles in the individual particle beams 3 when leaving the shield depends on the potential applied to the ring electrodes 503 relative to the potential of the shield 505.

[0114] Fig.10 (Left) shows the case where no voltage is applied to the ring electrode 503, i.e., the ring electrode 503 is at the same electrostatic potential (V=0) as the shield 505. Therefore, negatively charged particles (e.g. Fig.10 The individual particle beam 3 (electrons in the example shown) thus passes through the cavity 506 without being deflected; its beam diameter is cut only by the opening diameter of the ring electrode 503. The ring electrode 503 is not shielded here, and some of the particles hit the ring electrode 503, while others pass through the ring electrode 503. The ring electrode 503 thus additionally assumes the function of a beam-limiting aperture.

[0115] Fig.10 (Middle) shows the case where an electrostatic potential lower than that of the shield 505 is applied to the ring electrode 503, which thus has a delay effect on the particles in the individual particle beam (V<0). As a result, the individual particle beam 3 widens as it passes through the cavity 506 until it hits the surface of the electrode 503. Therefore, there are quantitatively more particles that hit the electrode 503 and are shielded from the individual particle beam 3 than in the initial case where the ring electrode 503 and the shield 503 are at the same electrostatic potential (V=0). However, because the particles that pass through the ring electrode 503 are subsequently accelerated back to the potential of the shield 505, the individual particle beam 3 emitted from the cylindrical shield 505 is then focused again.

[0116] Fig.10(Right) shows the case where a higher electrostatic potential than the electrostatic potential of the shield 505 is applied to the ring electrode 503, which thus has an accelerating effect on the particles in the individual particle beams (V>0). As a result, the individual particle beam 3 is focused while passing through the cavity 506 until it hits the surface of the electrode 503. Therefore, quantitatively fewer particles hit the electrode 503 and are shielded from the individual particle beam 3 than if the ring electrode 503 and the shield 503 were at the same electrostatic potential (V=0). The individual particle beams emanating from the cylindrical shield are also refocused.

[0117] If positively charged particles are used instead of negatively charged particles, then Fig.10 The effects shown in the middle and right figures of are interchanged: in the case of V<0 there is focusing, and in the case of V>0 there is a broadening of the individual particle beams 3 .

Claims

1. Multi-beam particle microscope, including the following: at least one particle source configured to generate a beam of charged particles; a first multi-lens array comprising a first plurality of individually adjustable and focusable particle lenses and arranged in a particle beam path such that at least some of the particles pass through openings in the multi-lens array in the form of a plurality of individual particle beams; a second porous plate comprising a plurality of second openings and arranged in the particle beam path downstream of the first multi-lens array and arranged such that some of the particles passing through the first multi-lens array illuminate the second porous plate and are absorbed therein, and some of the particles passing through the first multi-lens array pass through the openings in the second porous plate; a controller configured to supply individually adjustable voltages to the particle lenses of the first multi-lens array and thereby individually adjust the focusing of the associated particle lenses for each individual particle beam and thereby adjust for each individual charged particle beam: i) the beam diameter of the individual charged particle beam when the individual charged particle beam impinges on the second porous plate to adjust ii) the number of charged particles in the individual charged particle beam that are blocked by the second porous plate; iii) the number of charged particles in the individual charged particle beam that pass through the corresponding second openings in the second porous plate; and iv) the current of the individual charged particle beam downstream of the second porous plate; and An object plane into which the plurality of individual particle beams are incident.

2. The multi-beam particle microscope according to claim 1, further comprising: A first porous plate having a plurality of first openings and arranged in a particle beam path upstream of the first multi-lens array and assigned to the first multi-lens array, wherein the diameter of the first openings is smaller than the diameter of the openings in the first multi-lens array, so that particles passing through the first porous plate also pass through the first multi-lens array.

3. The multi-beam particle microscope according to claim 2, further comprising: a second multi-lens array having a second plurality of individually adjustable and focusable particle lenses and arranged in the particle beam path downstream of the first multi-lens array so that at least some of the particles of the individual particle beams passing through the first multi-lens array also pass through the second multi-lens array, wherein There is a suitable assignment of the individual particle beams to the lenses of the first multi-lens array and the second multi-lens array; Therein, the controller is further configured to supply individually adjustable voltages to the particle lenses of the second multi-lens array and thereby individually adjust the focus of the associated particle lens for each individual particle beam.

4. The multi-beam particle microscope according to claim 3, wherein: The second multi-lens array is arranged in the beam path downstream of the second multi-aperture plate.

5. The multi-beam particle microscope according to claim 3, wherein: The second multi-lens array is arranged in the beam path upstream of the second multi-aperture plate.

6. The multi-beam particle microscope according to claim 4 or 5, wherein: The diameter of the second openings in the second porous plate is smaller than the diameter of the openings in the second multi-lens array.

7. The multi-beam particle microscope according to any one of claims 2 to 5, further comprising: Multiple concentrators.

8. The multi-beam particle microscope according to claim 7, wherein: The multiple concentrator is a dual concentrator.

9. The multi-beam particle microscope according to claim 8, wherein: The first multi-lens array is arranged in the beam path downstream of the multi-condenser and upstream of the second multi-aperture plate.

10. The multi-beam particle microscope according to claim 7, wherein: The first multi-lens array is arranged in the beam path upstream of the multi-condenser.

11. The multi-beam particle microscope according to claim 7, wherein: The first multiwell plate is arranged between components of the multi-light concentrator, and wherein the first multi-lens array is arranged downstream of the multi-light concentrator and upstream of the second multiwell plate.

12. The multi-beam particle microscope according to any one of claims 3 to 5, wherein: Also provided is a particle optical lens for focusing the individual particle beams onto an intermediate image plane.

13. The multi-beam particle microscope according to claim 12, wherein: The particle-optical lens for focusing the individual particle beams onto the intermediate image plane is an additional field lens.

14. The multi-beam particle microscope according to claim 12, wherein: The particle-optical lens for focusing the individual particle beams onto the intermediate image plane is formed by the second multi-lens array.

15. The multi-beam particle microscope according to claim 12, wherein: The first multi-lens array and the second porous plate are arranged in the beam path upstream of the intermediate image plane.

16. The multi-beam particle microscope according to claim 12, wherein: The first multi-lens array and the second porous plate are arranged in the beam path downstream of the intermediate image plane.

17. The multi-beam particle microscope according to any one of claims 3 to 5, wherein: The individually adjustable voltages of the particle lenses of the first multi-lens array are selected such that an intermediate image occurs between the first multi-lens array and the second multi-lens array.

18. The multi-beam particle microscope according to any one of claims 3 to 5, further comprising: a third multi-lens array having a third plurality of individually adjustable and focussable particle lenses and being arranged in the particle beam path downstream of the first multi-lens array and downstream of the second multi-lens array, so that at least some of the particles of the individual particle beams passing through the first multi-lens array and the second multi-lens array also pass through the third multi-lens array, wherein for the individual particle beams there is an appropriate assignment to the lenses of the first multi-lens array, the second multi-lens array and the third multi-lens array; in, The controller is further configured to supply individually adjustable voltages to the particle lenses of the third multi-lens array and thereby individually adjust the focus of the associated particle lens for each individual particle beam.

19. The multi-beam particle microscope according to claim 18, further comprising: a fourth multi-well plate having a plurality of fourth openings, and a fourth multi-lens array having a fourth plurality of individually adjustable and focusable particle lenses and arranged in the particle beam path downstream of the fourth multi-aperture plate; in, The fourth porous plate and the fourth multi-lens array are arranged in the beam path on the source side of the first multi-lens array and are arranged relative to each other so that particles passing through the fourth porous plate also pass through the fourth multi-lens array; and Therein, the controller is further configured to supply individually adjustable voltages to the particle lenses of the fourth multi-lens array and thereby individually adjust the focus of the associated particle lens for each individual particle beam.

20. The multi-beam particle microscope according to claim 19, wherein: The first multi-lens array, the second multi-lens array, the third multi-lens array and / or the fourth multi-lens array respectively include the following: a lens perforated plate having a plurality of openings; as well as Multiple electrodes, Therein, at each of the plurality of openings, at least one of the plurality of electrodes is arranged in a manner insulated from the lens porous plate so as to individually influence individual particle beams passing through the corresponding opening.

21. The multi-beam particle microscope according to claim 20, wherein: The electrode is a ring electrode.

22. The multi-beam particle microscope according to any one of claims 1 to 5, further comprising: Measuring means for measuring the current of the individual particle beams.

23. The multi-beam particle microscope according to claim 22, wherein: The measuring device serves to measure currents in the region of an object plane.

24. The multi-beam particle microscope according to claim 23, wherein: The measuring device is designed such that the current can be measured simultaneously for a plurality of individual particle beams.

25. The multi-beam particle microscope according to claim 22, wherein: The measuring device comprises at least one Faraday cup.

26. A method for current regulation for individual particle beams of a multi-beam particle microscope according to any one of claims 1 to 25, the method comprising the following steps: With the aid of the first multi-lens array, individual beam currents are adjusted for a plurality of individual particle beams.

27. The method according to claim 26, wherein: For all individual particle beams, the individual beam currents are adjusted.

28. The method according to claim 27, further comprising the following method steps: The focal lengths of the individual particle beams are corrected by means of a second multi-lens array or a further multi-lens array.

29. The method according to claim 28, further comprising the steps of: Before adjusting the individual beam currents, the desired focal lengths of the individual particle beams are adjusted by means of the second multi-lens array or other multi-lens arrays.

30. The method according to claim 26, further comprising the steps of: For a plurality of individual particle beams, measuring individual beam currents; as well as The measurements are used to adjust the individual beam currents.

31. The method according to claim 30, wherein: For all individual particle beams, the individual beam currents are measured.

32. The method of claim 26, wherein: The method is performed multiple times.

33. The method of claim 32, wherein: The method is carried out iteratively in whole or in part.

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