Particle beam system and its use for flexible setting of the current intensity of individual particle beams

Abstract

The present invention relates to a particle beam system, in particular a multi-beam particle microscope, in which the current intensity of the individual particle beams can be set flexibly and within a wide range of values ​​without changing the structure. The particle beam system according to the present invention comprises a focusing lens system, a front multi-lens array having a specific front counterelectrode and a front multi-aperture plate, and a multi-lens array. The system includes a controller configured to provide adjustable excitation to the focusing lens system and the front counterelectrode so that charged particles can be incident on the front multi-aperture plate in a telecentric manner.

Description

Technical Field

[0001] The present invention relates to a particle beam system 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 its surface. This allows, for example, to analyze the structure of the surface. While single-beam particle microscopes use a single beam of charged particles (e.g., electrons, positrons, muons, or ions) to analyze an object, multi-beam particle microscopes use multiple particle beams for this purpose. By simultaneously directing multiple particle beams (also called beams) onto the surface of an object, significantly larger surface areas can be sampled and analyzed compared to single-beam particle microscopes in the same timeframe.

[0003] WO 2005 / 024 881A2 discloses a multi-particle beam system under a kind of electron microscope system form, and it uses many electron beams to operate, so that the clustering of electron beam is used in parallel to scan the object to be inspected.By the electron beam that electron source produces is directed to the porous plate with many openings, the clustering of this electron beam is produced.A part of electron impact of electron beam is this porous plate and thus plate absorbs, and other parts of electron beam pass the opening in this porous plate, so in the electron beam path of each opening downstream, electron beam is shaped, and the cross section of this electron beam is defined by the cross section of this opening.Further, the electric field that provides suitable selection in this electron beam path upstream and / or in this porous plate downstream has each opening in this porous plate as a lens, allows this electron beam to pass through this opening, so this electron beam focuses in the plane with section distance from this porous plate.Wherein the plane that forms electron beam focus is imaged on the surface of the object to be inspected by downstream optical unit, and the individual electron beam that impacts this object focuses and becomes main electron beam. This generates interaction products emanating from the object, such as backscattered electrons or secondary electrons, which form a second electron beam and are directed via another optical unit to a detector. Each secondary electron beam impinges on a separate detector element, so that the electron intensity detected by this detector element provides information about the object at the location where the corresponding primary electron beam impinged on the object. The primary electron beam is systematically scanned over the surface of the object to produce an electron microscopic image of the object in a manner conventionally used in scanning electron microscopy.

[0004] In fact, the high resolution within the particle optical imaging range in the described multi-particle beam system is highly correlated. Resolution depends on the numerical aperture in the object plane and the beam current of each particle beam. In principle, due to diffraction, the following applies to aberration-free optical units: the larger the numerical aperture of the object plane, the better the resolution, because this allows obtaining a smaller illumination point in the object plane. The smaller the beam current of a single particle beam, the better the resolution. Here, the numerical aperture of each particle beam and the value of the beam current are closely related or associated with each other by the imaging scale. Aberration is another factor affecting resolution, and these influences depend on numerical aperture in different ways. At a known working point, particularly under a specified beam current, and under setting system parameters (for example, aberration coefficient, the image representation magnification of the light source, beam current), in any case there is a value for the numerical aperture at the sample, and the spot size of the single particle beam on the object is minimum. At this, numerical aperture is usually only optimized for a working point of the system, and at this, despite all calculations, numerical aperture may not be optimal for this working point.

[0005] Therefore, it is desirable to be able to change the numerical aperture of a multi-particle beam system. This would allow for improved or optimized resolution during operation. Furthermore, it would be desirable to improve or optimize resolution for a specific operating point and, in particular, for a specific beam current intensity, or conversely, to continuously and as flexibly as possible set the beam current intensity for a desired resolution over a wide range of values ​​without having to perform structural modifications to the multi-particle beam system. Summary of the Invention

[0006] The object of the present invention is therefore to provide a particle beam system which allows, independently and over a large range of values, a corresponding optimization of the beam current and the numerical aperture for an optimized resolution, i.e., in particular in a simple manner and without structural modifications to the particle beam system. It should be possible, but not necessary, to vary other particle optical parameters, for example, the distance between the individual particle beams when incident on the sample (so-called "spacing").

[0007] This object is achieved by the subject matter of the independent patent claim. Advantageous embodiments of the invention are evident from the dependent patent claims.

[0008] This patent application claims priority to German patent application No. DE 10 2019 005 362.1 and international patent application No. PCT / DE2020 / 000101, the entire contents of which are incorporated by reference into this application.

[0009] According to a first aspect of the invention, the latter relates to a particle beam system comprising the following:

[0010] at least one particle source configured to generate a diverging beam of charged particles;

[0011] a focusing lens system through which the charged particle beam passes;

[0012] a front multi-lens array, wherein the front multi-lens array has a front counter-electrode with a central opening through which the charged particle beam passes, and wherein the front multi-lens array has a front multi-aperture plate disposed in the beam path downstream of the front counter-electrode, the front multi-aperture plate being arranged such that the charged particles pass through the front multi-aperture plate in the form of a plurality of charged single-particle beams;

[0013] a multi-lens array arranged in the beam path downstream of the preceding multi-lens array, wherein the multi-lens array comprises a multi-aperture plate with a plurality of openings through which at least a portion of the charged individual particle beam passes, and wherein the multi-lens array comprises a counter electrode in the beam path downstream of the multi-aperture plate, the counter electrode having a central opening provided therein, through which substantially the plurality of individual particle beams pass; and

[0014] A controller is configured to provide adjustable excitation to the focusing lens system and the front counter electrode so that the charged particles are incident on the front multi-aperture plate in a telecentric manner.

[0015] Preferably, the controller is arranged to set the current intensity of the individual particle beams.

[0016] Thus, according to the present invention, a particle source is provided, although multiple particle sources may be provided. The charged particles may be, for example, electrons, positrons, muons, or ions, or other charged particles. Preferably, the charged particles are electrons, for example, generated using a thermal field emission source (TFE). However, other particle sources may also be used.

[0017] The condenser lens system may have one, two or more condenser lenses. Preferably, the condenser lens system has a double condenser lens. Preferably, the condenser lens system includes exactly two condenser lenses, more preferably two magnetic condenser lenses.

[0018] Within the scope of this patent application, a linguistic distinction is made between multi-aperture plates, on the one hand, and multi-lens arrays, on the other hand. A multi-aperture plate is a plate with a plurality of openings. A voltage can be applied to the entire multi-aperture plate. This is possible, but not required. In any case, all openings in the multi-aperture plate have a uniform, globally identical electric and magnetic potential. Within the scope of this patent application, a multi-lens array comprises a plurality of lenses arranged essentially parallel to one another, whose refractive power can be varied. The lens effect is generated by the combination of the multi-aperture plate and a counterelectrode, and the refractive power of the lenses can be varied, in particular by differential excitation of the counterelectrode.

[0019] Multi-lens array forms the particle beam system core with a plurality of independent particle beams.Here, multi-lens array comprises multi-aperture plate and counter electrode.Individual particle beam produces no later than during passing through multi-lens array, and this independent particle beam focuses on the downstream of multi-lens array respectively.The focus produced in this process corresponds to a plurality of images of particle source, and can be considered as initial point or the virtual multi-source array for follow-up particle optical imaging subsequently.Here, the focusing effect of multi-lens array is caused by the electric field intensity that is different from the upstream and downstream of multi-aperture plate, and the central opening of counter electrode is arranged in multi-aperture plate downstream in particle beam path, further guarantees that this independent particle beam is pulled apart, or the focus of this independent particle beam is further separated from each other than each opening of this multi-aperture plate.In principle, these facts are known in the prior art.

[0020] Furthermore, it is known to arrange a front multi-aperture plate in the beam path upstream of a multi-lens array, which is then used to shape the individual particle beams or to cut them out of the charged particle beam. Arranging the front multi-aperture plate upstream of the multi-lens array is advantageous because the multi-aperture plates of the multi-lens array are not charged by particles incident thereon; however, particle beam systems according to the prior art can also operate without such a front multi-aperture plate. However, according to the present invention, a front multi-aperture plate is provided, which is a functional component of the front multi-lens array.

[0021] According to the prior art, the current intensity of the individual particle beams is now set as follows: the focusing lens system undergoes different excitations. In this process, the originally divergent beams of charged particles are collimated by the focusing lens system, and these collimated beams are incident on a multi-lens array or a front multi-aperture plate that may be arranged upstream thereof. Strictly speaking, therefore, the focusing lens system is a collimating lens system. Here, depending on the excitation of the focusing lens system, the total particle beam of charged particles has different particle beam diameters. This means that the current or beam current density assigned to the individual particle beams can be changed by the setting of the focusing lens system. However, due to structural reasons, the range of beam current density variation within which this result can be achieved is limited in a multi-particle beam system. In order to achieve a more significant change in small currents, the focal length of the focusing lens system must be significantly increased; this is not possible in existing systems and would even be associated with major structural measures (increasing the ceiling height of the laboratory). Now, this is the starting point of the present invention:

[0022] In addition to the known focusing lens system and the known multi-lens array, the particle beam system according to the present invention also includes a front multi-lens array having the following structure: the front multi-lens array includes a front counter-electrode with a central opening, through which the charged particle beam passes. Furthermore, the front multi-lens array includes a multi-aperture plate arranged in the beam path downstream of the front counter-electrode, the multi-aperture plate being arranged so that the charged particles pass through the front multi-aperture plate in the form of multiple charged individual particle beams. The front multi-aperture plate can be a known / existing front multi-aperture plate. However, the important point is that the front counter-electrode is combined with the front multi-aperture plate to form a multi-lens array, and an adjustable voltage can be applied to the front counter-electrode. Therefore, overall, the front multi-lens array also has a focusing effect on the passing charged individual particle beam. At the same time, a global lens field is generated in the region of the front counter-electrode, which acts on the charged particle beam passing through the focusing lens system. As a result, the irradiation conditions of the focusing lens system can vary over a wide range, since, according to the present invention, the charged particle beam does not need to be collimated by passing through the focusing lens system. On the contrary, the charged particle beam can enter the global lens field of the front counter electrode in a converging or diverging manner after passing through the focusing lens system. The controller provides adjustable excitation, i.e. voltage and / or current, to the focusing lens system and the front counter electrode, thereby allowing the selection of these excitations so that the charged particles can meet the telecentricity condition when incident on the front multi-aperture plate. For the optical imaging quality of the particles in the subsequent beam path through the particle beam system, it is better to meet this telecentricity condition because it simplifies the construction of the particle optical components. By setting appropriate voltages on the focusing lens system and the front counter electrode, the beam current of the individual particle beam can be changed without changing / extending the column to the structure. Here, the main effect of the feature combination according to the present invention is to change the effective numerical aperture of the source for the purpose of current change. Therefore, what is determined in the image is the emission angle / solid angle of the particle source from which the individual particle beam obtains the charged particles in each case. Therefore, the particle beam system according to the present invention presents that the controller can be set in the following way so that the current intensity of the individual particle beam can be adjusted within a wider range without the need to modify the structure of the system.

[0023] The opening of the front multi-aperture plate of the multi-lens array and the opening of the multi-aperture plate can have the same diameter, however, they can also have different diameters. Here, in particular, the aperture of the front multi-aperture plate can be smaller than the aperture of the multi-aperture plate of the multi-lens array. Preferably, the opening of the front multi-aperture plate of the multi-lens array and the multi-aperture plate is circular, and generally, each opening is arranged in a hexagonal structure; however, other arrangement options are also possible. Ideally, the number of openings in the front multi-aperture plate and the multi-aperture plate matches the number of individual particle beams. If, in the case of a hexagonal arrangement, the number of particle beams is 3n(n-1)+1, where n is any natural number, it is advantageous.

[0024] According to a preferred embodiment of the present invention, the particle beam system has a micro-optical unit, which includes a multi-lens array. According to another preferred embodiment, the micro-optical unit also includes a front multi-aperture plate. In principle, the micro-optical unit is an assembly of particle optical elements, which are combined in the micro-optical unit. In this case, the assembly can have a specific holder for the assembly or a common frame for the assembly. In this way, the micro-optical unit can also have other particle optical components. Examples of such are, for example, multi-stigmators or other multi-lens arrays, in which the lens effect of the individual openings of the multi-aperture plate can be set separately for each individual particle beam, for example for individually correcting the focal length of the individual particle beams to correct any field curvature. Components other than the above-mentioned components can also be part of the micro-optical unit.

[0025] In contrast, the front counter electrode of the front multi-lens array is typically not a necessary component of the micro-optical unit as a component. Typical distances between individual elements of the micro-optical unit range from approximately 50 μm to approximately 1 mm. In contrast, the front counter electrode is typically further spaced from the front multi-aperture plate; the distance A is approximately 3 mm ≤ A ≤ 30 mm, preferably 5 mm ≤ A ≤ 20 mm, for example, A = 6 mm.

[0026] According to a preferred embodiment of the present invention, the micro-optical unit has a frame at ground potential. Typically, the front multi-aperture plate and the multi-aperture plate of the multi-lens array are also at ground potential. In contrast, a voltage of several thousand volts, such as +-12 kV, +-15 kV, +-16 kV, or +-20 kV, is applied to the counter electrode or the front counter electrode.

[0027] Replace the framework of the micro-optical unit that is in ground potential, the particle beam system according to preferred embodiments can have the front auxiliary electrode containing central opening, it is configured in the beam path of front counter-electrode downstream, and only in the upstream of front multi-aperture plate, and can be provided with adjustable voltage by controller.This allows to change overall lens field or the focusing caused thereby, and generally allows to provide further variation option for particle optical imaging by particle beam system.The spacing of independent particle beam in the focal position of virtual particle source and intermediate image can change more flexibly in this process.In addition, field curvature can be corrected.

[0028] Similarly, additionally or alternatively, the particle beam system may further comprise a rear auxiliary electrode having a central opening, which is arranged in the beam path downstream of the multi-aperture plate and upstream of the counter electrode and may be provided with an adjustable voltage by the controller.

[0029] The selected distances between the front auxiliary electrode and the front multi-aperture plate, as well as the distance between the rear auxiliary electrode and the multi-aperture plate, influence the intensity of other adjustment options due to the excitation or voltage applied to the front auxiliary electrode or the rear auxiliary electrode. The smaller the distance, the greater the sensitivity when achieving settings, especially with regard to adjustments for field curvature correction and telecentricity. Therefore, the smallest distance still achievable from a structural point of view is preferably selected between the front auxiliary electrode and the front multi-aperture plate, i.e., approximately 50 μm to approximately 1 mm. The voltage applied to the front auxiliary electrode can then be between approximately -1000 V and +1000 V.

[0030] The distance between the rear auxiliary electrode and the multi-aperture plate can be slightly greater than the distance between the front auxiliary electrode and the multi-aperture plate. The voltage applied to the rear auxiliary electrode can then be selected to approximate the average value between the voltage applied to the counter electrode and ground potential. This has the advantage that the field curvature correction can essentially be set by the excitation of the front auxiliary electrode, while the spacing can be set using the rear auxiliary electrode. Other arrangements of distance and excitation level, and therefore other adjustment options, are also possible.

[0031] According to a preferred embodiment of the present invention, the condenser lens system has two condenser lenses. Preferably, both condenser lenses are magnetic condenser lenses.

[0032] In addition, the condenser lens system has exactly one magnetic condenser lens and one electrostatic condenser lens, wherein the electrostatic condenser lens is arranged in the beam path downstream of the magnetic condenser lens, and wherein a booster electrode, which can be driven by a controller, is arranged between the magnetic condenser lens and the electrostatic condenser lens, and the electrostatic condenser lens can be excited by the booster electrode. The front counter electrode and the lower end of the booster electrode are combined to form a variable electrostatic lens, which acts as a lower condenser lens. The top end of the booster electrode, together with the cathode of the emitter and the magnetic lens, forms a field for the upper condenser lens at the top.

[0033] According to a preferred embodiment of the present invention, the particle beam system further includes a beam current-limiting multi-aperture plate system, comprising a beam current-limiting multi-aperture plate having multiple openings. The beam current-limiting multi-aperture plate system is arranged in the beam path between the front multi-lens array and the multi-lens array and is specifically designed to be insertable into the beam path. Sufficient mounting space is provided between the front multi-lens array and the multi-lens array for variably manipulating the multi-aperture plate system. This insertability can be achieved with the aid of a mechanical actuator. The beam current-limiting multi-aperture plate system serves to further limit the beam current reaching the front multi-aperture plate and the subsequent particle optics unit. The insertability of the beam current-limiting multi-aperture plate system allows for greater flexibility or variability. The beam current-limiting multi-aperture plate system can include exactly one beam current-limiting multi-aperture plate; however, the multi-aperture plate system can also include two or more beam current-limiting multi-aperture plates. Mechanically, a positioning accuracy of approximately one micron for the beam current-limiting multi-aperture plate can be achieved. The beam current-limiting multi-aperture plate system can be used to vary or reduce the current intensity by a factor of approximately ten. However, diffraction errors at small apertures and lens errors at large apertures can reduce the achievable resolution within the current variation range. The present invention helps minimize resolution variation and optimize resolution.

[0034] In principle, a beam current limiting multi-aperture plate can also be fixedly arranged between the front multi-lens array and the multi-lens array. The beam current limiting multi-aperture plate is preferably at ground potential.

[0035] According to a preferred embodiment, at least one opening of the beam-current-limiting multi-aperture plate is formed in a circular and / or annular pattern. Annular openings have the advantage over circular openings that the numerical aperture remains unchanged or does not decrease. Strictly speaking, the central maximum of the diffraction pattern of an annular opening is even narrower than that of a conventional circular opening; however, higher secondary maxima occur in the case of annular openings. In addition to a central, smaller circular opening, the aperture can also have multiple annular rings.

[0036] According to another preferred embodiment, a beam current-limiting multi-aperture plate system comprises two multi-aperture plates that are movable substantially parallel to one another, each plate having a plurality of openings, such that the effective multi-aperture plate opening size can be adjusted for individual particle beams passing through the beam current-limiting multi-aperture plate system. Preferably, the openings of the two multi-aperture plates that are movable relative to one another are substantially identical in size and have substantially identical geometries. Consequently, when the two multi-aperture plates are moved relative to or displaced relative to one another, the size of the resulting multi-aperture plate openings can be readily adjusted, and the relative motion can be selected in such a way that the resulting multi-aperture plate openings do not change during the process. Furthermore, providing uniform openings simplifies the manufacture of the multi-aperture plates.

[0037] According to a preferred embodiment, the openings of the multi-aperture plates that can be displaced relative to each other are circular or square. In the case of square holes, the plates can be moved relative to each other in the XY plane, if Z represents the central optical axis of the system. The resulting multi-aperture plate opening can then have the same form as the corresponding opening of the multi-aperture plate; in particular, it can also be square. If the displacement process is carried out in a different way, the final opening may represent a rectangle or even a triangle (the plates are twisted relative to each other); however, this is not disadvantageous. If the openings of two multi-aperture plates that can be displaced substantially parallel to each other are circular, a so-called lens shape that is approximately elliptical is produced as the effective multi-aperture plate opening. Due to the essentially elliptical resulting individual particle beams, the multi-stigmator is advantageous for correcting the astigmatism caused by the elliptical particle beam profile on another route of the beam path.

[0038] According to a further embodiment, a beam current limiting multi-aperture plate system comprises two or more multi-aperture plates arranged sequentially in the beam path, each multi-aperture plate having a plurality of openings, wherein two deflectors are arranged between the two multi-aperture plates and can be driven in such a way that a substantially parallel displacement of the individual particle beams relative to the optical axis is achieved during their passage through the multi-aperture plate system. The two multi-aperture plates preferably have identical structures, and their openings are arranged exactly overlapping one another, in particular in the Z direction or beam current direction. If both deflectors are deactivated, the particle beam passes through the two multi-aperture plates substantially unimpeded; i.e., substantially all particles of the individual particle beam pass through the sequence of both multi-aperture plates. In contrast, if both deflectors are activated, the parallel displacement results in the individual particle beam only partially passing through the multi-aperture plate arranged further downstream in the beam path. Part of the individual particle beam strikes the multi-aperture plate arranged further downstream in the beam path and is absorbed or no longer available for the individual particle beam in the further course of the beam. This also allows the current intensity of the individual particle beams to be further varied.

[0039] According to another embodiment of the present invention, the particle beam system further comprises the following:

[0040] an intermediate image plane, which is arranged downstream of the multi-lens array in the direction of the beam path and in which the real foci of the individual particle beams are formed, which are separated by a spacing 1;

[0041] a field lens system arranged downstream of the intermediate image plane in the direction of the beam path;

[0042] an objective lens, in particular a magnetic objective lens, which is arranged downstream of the field lens system in the direction of the beam path; and

[0043] - an object plane in which the individual particle beams undergo particle optical imaging and in which the individual particle beams are separated by a distance 2. The particle beam system according to the invention can thus be combined with the remaining components of known multi-particle beam systems, in particular with known multi-particle microscopes.

[0044] Preferably, the controller of particle beam system according to the present invention is arranged to drive the particle optics of particle beam system in the following manner so that spacing 2 can be set in the object plane, and especially can maintain constancy when the beam current intensity of individual particle beam is different. In order to carry out this adjustment, particle beam system according to the present invention needs enough degrees of freedom or particle optics, which can change independently of each other. This is particularly important, with respect to this background, in the case of multi-beam particle beam system, the particle beam interval or the spacing of the scanning configuration of a plurality of individual particle beams on the selected multi-aperture plate are predetermined in a fixed manner in principle. At this, spacing and numerical aperture are connected to each other and themselves can not change independently. If a plurality of individual particle beams are imaged by a common optical unit, the variation of numerical aperture must always also cause spacing variation, which is not desirable. Therefore, traditional multi-beam particle microscopes do not allow to change numerical aperture simultaneously when not changing spacing. Instead, for this setting, other particle optics are needed, which introduces extra degree of freedom into the system. For example, this can be an extra field lens. A conventional multi-beam particle microscope with a field lens system consisting of three field lenses can be supplemented, for example, by a fourth field lens outside the field lens system. In this case, it is important to provide an additional overall lens field in order to satisfy the Helmholtz-Lagrange invariant.

[0045] According to another embodiment of the present invention, the controller is arranged to drive the particle optics of the particle beam system in such a way that the numerical aperture in the object plane is adjustable, and the resolution of imaging in the object plane can be optimized, particularly for specific beam current intensity. Preferably, the controller is arranged to drive the particle optics in such a way that other parameters of particle optical imaging, such as focusing, rotation and / or telecentricity in the object plane are adjustable as well. Preferably, the controller is arranged so that when changing the numerical aperture in beam current intensity and / or the object plane, the values ​​of these other particle optics parameters can remain constant.

[0046] According to another aspect of the invention, the latter relates to the use of a particle beam system as described above for setting the current intensity of the individual particle beams. In this case, setting the current intensity of the individual particle beams opens up a variety of options for varying other parameters of the particle optical imaging. In particular, it allows switching the operation of the particle beam system between low resolution on the one hand and high resolution on the other hand, since the resolution strongly depends on the beam current.

[0047] According to another aspect of the invention, the latter relates to the use of the particle beam system as described above in setting the resolution in the object plane, in particular the optimum resolution. As has been explained many times, beam current, numerical aperture, the spacing of the individual particle beams in the object plane, and the imaging ratio of the source image representation are closely related to each other. Here, the use of the particle beam system according to the invention provides particularly good flexibility and is particularly helpful in setting the optimum resolution even when the beam current of the individual particle beams is predetermined.

[0048] According to another aspect of the present invention, the latter relates to a multi-beam particle microscope having a particle beam system as described above. Thus, the particle beam system according to the present invention can be supplemented by components of multi-beam particle beam microscopes known per se; in particular, this includes any known detection unit. For details, reference is made, for example, to WO 2015 024 881 A2, which has been cited numerous times. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The present invention will be better understood with reference to the accompanying drawings:

[0050] Figure 1 Schematic diagram showing a multibeam particle microscope;

[0051] Figure 2 Schematic illustration of current variation by means of a focusing lens according to the prior art;

[0052] Figure 3 Schematic representation of the illumination of a micro-optical unit by means of a condenser lens system according to the prior art;

[0053] Figure 4 Schematically shows an embodiment of the invention with converging beam guidance downstream of a condenser lens system;

[0054] Figure 5 Schematic showing a diverging beam guide downstream of a condenser lens system Figure 4 The embodiment of the present invention shown in FIG.

[0055] Figure 6 Another embodiment of the present invention is schematically shown with a beam current limiting multi-aperture plate system;

[0056] Figure 7 Schematically shows another embodiment of the present invention having an electrostatic focusing lens and a boost electrode;

[0057] Figure 8 Schematic showing an additional front auxiliary electrode Figure 7 The embodiment of the present invention shown in FIG.

[0058] Figure 9Schematic showing a multi-aperture plate system having two or more multi-aperture plates that are displaceable relative to each other for beam current variation;

[0059] Figure 10 Schematic diagram of a multi-aperture plate system with two sequentially arranged multi-aperture plates and a deflector system therebetween for beam current variation;

[0060] Figure 11 Schematic showing various apertures for beam current variation; and

[0061] Figure 12 Schematic representation of a multibeam particle microscope with particle optics for setting the optimal resolution. DETAILED DESCRIPTION

[0062] Figure 1 It is a schematic diagram of a particle beam system 1 in the form of a multi-beam particle microscope 1 that adopts multi-particle beams. Particle beam system 1 produces multi-particle beams, which impact on the object to be inspected, so that interaction products, such as secondary electrons, are produced at this object and then detected. Particle beam system 1 is a scanning electron microscope (SEM, scanning electron microscope) type, which uses a plurality of primary particle beams 3, which are incident on the surface of an object 7 at a plurality of positions 5, and produces a plurality of electron beam spots that are spatially separated from each other at this. The object 7 to be inspected can be any type, such as a semiconductor wafer or a biological sample, and comprises the configuration of miniaturized components or the like. The surface of object 7 is arranged in the first plane 101 (object plane) of the object lens 102 of an objective lens system 100.

[0063] Figure 1 The enlarged excerpt I1 in FIG. 1 shows a plan view of the object plane 101 with a generally rectangular field 103 of the incident position 5 formed in the first plane 101. Figure 1 The number of incident positions is 25, forming a 5×5 field 103. To simplify the diagram, the number of incident positions is chosen to be 25. In practice, a significantly larger number of beams and incident positions can be chosen, for example 20×30, 100×100, etc.

[0064] In the illustrated embodiment, the field 103 of the incident locations 5 is a generally rectangular field with a constant pitch P1 between adjacent incident locations. Exemplary values ​​for pitch P1 are 1 micron, 10 microns, and 40 microns. However, the field 103 may also have other symmetries, such as, for example, hexagonal symmetry.

[0065] The beam spot formed in the first plane 101 has a small diameter, and 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 performed using the objective lens system 100 .

[0066] The primary particles strike the object and generate interaction products, such as secondary electrons, backscattered electrons, or primary particles that undergo reverse motion due to other factors, which are emitted from the surface of the object 7 or from the first plane 101. The interaction products emerging from the surface of the object 7 are shaped by the objective lens 102 to form a secondary particle beam 9. The particle beam system 1 provides a particle beam path 11 for guiding the plurality of secondary particle beams 9 to the detector system 200. The detector system 200 includes a particle optical unit having a projection lens 205 for guiding the secondary particle beam 9 to a particle multi-detector 209.

[0067] Figure 1 Excerpt I2 in FIG. 1 shows a plan view of plane 211, where individual detection zones of particle multi-detector 209 are located, with secondary particle beam 9 incident on positions 213. Incident positions 213 are located within field 217 and have regular spacing P2 between them. Exemplary values ​​for spacing P2 are 10 microns, 100 microns, and 200 microns.

[0068] A primary particle beam 3 is generated within a beam generation device 300, which includes at least one particle source 301 (e.g., an electron source), at least one collimating lens 303, a multi-aperture configuration 305, and a field lens 307, or a field lens system consisting of a plurality of field lenses. The particle source 301 generates a divergent particle beam 309, which is collimated or substantially collimated by the collimating lens 303 to form a particle beam 311 that illuminates the multi-aperture configuration 305.

[0069] Figure 1 Excerpt 13 in FIG. 1 shows a plan view of a multi-aperture arrangement 305. Multi-aperture arrangement 305 includes a multi-aperture plate 313 having a plurality of openings or holes 315 formed therein. The midpoints 317 of openings 315 are arranged within a field 319 corresponding to field 103 formed by beam spot 5 in object plane 101. The spacing P3 between the midpoints 317 of holes 315 can have exemplary values ​​of 5 microns, 100 microns, and 200 microns. The diameter D of holes 315 is less than the spacing P3 between the midpoints of the holes. Exemplary values ​​for diameter D are 0.2 x P3, 0.4 x P3, and 0.8 x P3.

[0070] The particles of the illumination particle beam 311 pass through the hole 315 and form the particle beam 3. The plate 313 absorbs the particles of the illumination beam 311 that hit the plate 313, so that the particles do not form the particle beam 3.

[0071] Due to the applied electrostatic field, the multi-aperture arrangement 305 focuses the particle beam 3, thus forming a beam focus 323 in a plane 325. In addition, the beam focus 323 can be virtual. The diameter of the beam focus 323 can be, for example, 10 nanometers, 100 nanometers, and 1 micrometer.

[0072] The field lens 307 and the objective lens 102 form a first imaging particle optical unit for imaging the plane 325 (in which the beam focus 323 is formed) onto the first plane 101, thereby forming a field 103 or beam spot at the incident position 5. The surface of the object 7 should be arranged in the first plane, so that the beam spot is formed on the surface of the object.

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

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

[0075] Further information on such multi-beam particle beam systems used herein and the components used, such as particle sources, multi-aperture plates and lenses, can be obtained from the international patent applications WO 2005 / 024881, WO 2007 / 028595, WO 2007 / 028596, WO 2011 / 124352 and WO 2007 / 060017, and from the German patent applications with application numbers DE 10 2013 026 113.4 and DE 10 2013 014976.2, the complete disclosures of which are incorporated by reference into the present application.

[0076] The multi-particle beam system further has a computer system 10, which is arranged to control the individual particle optics components of the multi-particle beam system, and is used to assess and analyze the signals obtained by multi-detector 209. In this case, the computer system 10 can be made up of a plurality of independent computers or components. It can also comprise a controller according to the present invention.

[0077] The components of the particle beam system according to the present invention can be integrated into this multi-particle beam system.

[0078] Figure 2Schematic illustration of the current variation with the aid of a focusing lens according to the prior art. An excerpt from a particle beam system, such as a multi-beam particle microscope, is shown. The system comprises a particle source 301, which generates a diverging particle beam 309. The latter then reaches a focusing lens system having two focusing lenses 330 and 331, which in the illustrated example are magnetic focusing lenses. Figure 2 In FIG. 3 , the condenser lenses 330 and 331 are shown as ellipses. A wide ellipse indicates a strong excitation of the magnetic lens, while a narrow ellipse indicates little or no excitation of the corresponding condenser lens. The two condenser lenses 330 and 331 form a condenser lens system or collimating lens system 303, which has been illustrated in FIG. Figure 1 Here, according to the prior art, the illuminating particle beam 311 is collimated upon reaching another particle-optical component, particularly a micro-optical unit, after passing through the collimating lens system 303. In the example shown, the illuminating particle beam 311 first reaches a front multi-aperture plate 380, which serves to limit the current and, upon passing through it, forms individual particle beams 3. The individual particle beams 3 thus formed then pass through another component of the micro-optical unit; two micro-optical correctors 353 and 354 are shown here by way of example. In the example shown, these micro-optical correctors 353, 354 are arranged upstream of the core of the micro-optical unit, particularly upstream of the multi-aperture plate 351 and its counter-electrode 352. Depending on the excitation of the counter-electrode 352, the electric field changes during passage through the multi-aperture plate 351, and the individual particle beams 3 are focused and more or less strongly stretched. The focused individual particle beams 3 then reach the field lens system 307, which in the example shown is represented by a single field lens. A controller (not shown) ensures that the condenser lens system with the condenser lenses 330 and 331 can be driven in different ways. In the process, the condenser lenses 330 and 331 are excited to different degrees. Depending on the actuation, the illuminating particle beam 311 is expanded more or less strongly, e.g. Figure 2 As shown by the wide double arrow in . Here, the characteristics of the actual particle source 301 are assumed to be constant. This means that the total number of charged particles emitted by the particle source per unit time or the associated particle flux is assumed to be constant. Due to the different expansions of the illuminating particle beam 311, the result is a change in the beam current density, i.e. the number of charged particles per unit area and per unit time. In each case, a certain proportion of all charged particles can be assigned to one of the individual particle beams 3 formed in this way. In the case of an otherwise mechanically identical aperture, which is determined here by the opening diameter of the opening in the front multi-aperture plate 380, the different expansions of the illuminating particle beam 311 produce a change in the current intensity of each individual particle beam. In this case, Figure 2 a and Figure 2 The case in b shows an equivalent option of how to achieve a relatively large beam current for a single particle beam: according to Figure 2a), the condenser lens 330 is strongly activated and the condenser lens 331 is actually deactivated. Figure 2 In b), the two condenser lenses 330, 331 have approximately the same excitation, in particular the average excitation. Figure 2 a) and Figure 2 In both cases b), the current density of the illuminating particle beam 311 is the same; so is the current intensity of the generated individual particle beams 3. Figure 2 c) shows the illumination of the micro-optical unit with a low beam current density: for this purpose, the first condenser lens 330 is practically not excited, but the second condenser lens 331 is very strongly excited. This results in a strongly expanded illuminating particle beam 311, which reaches the same aperture in the front multi-aperture plate 380 and the downstream elements of the micro-optical unit. Thus, according to Figure 2 The configuration in c) reduces the current intensity of the individual particle beams. By changing the excitation of the first and second condenser lenses 330 and 331, a zoom factor of 4 can be achieved, for example, thereby allowing the beam current to be varied by a factor of approximately 15.

[0079] In addition to the current variation caused by different excitations of the focusing lens or collimating lens system, other relationships are also known: for example, the focal length of the focusing lens system can be increased (see focal length f CL ) to further reduce the beam current intensity. The disadvantage of this approach is that the overall system column height increases dramatically. The structural measures required for this purpose are generally unacceptable (lengthening the entire system requires a different spatial height than usual), thus not offering a real alternative. For example, if the zoom factor of the condenser lens system is increased from 4x to 5x to achieve a beam current variation of approximately 25x, the column height would need to be extended by 30 to 50 cm.

[0080] Alternatively or additionally, it is conceivable to reduce the aperture in the micro-optical unit, in this case, for example, in the front multi-aperture plate 380, thereby achieving a lower beam intensity. However, this has the disadvantage that the numerical aperture is also reduced, and thus the resolution is reduced due to diffraction effects.

[0081] Regarding particle source 301, there are also several options for variation: In principle, a smaller particle source can achieve a lower current density. However, the maintenance time required to replace the particle source ("tip") is unnecessary. Another approach involves varying the extractor potential, which allows for a change in beam current of approximately a factor of 2. However, varying the extractor potential can lead to undesirable drift in beam current density.

[0082] The aperture of the micro-optical unit can be reduced, while simultaneously increasing the object distance of the objective lens or the distance between the multiple intermediate images of the particle source and the sample. In principle, this allows for lower beam currents and also allows the numerical aperture to be adapted to an optimal value. However, these advantages come at the cost of significant variations in the distances between the individual particle beams generated at the sample. Furthermore, this would significantly increase the height of the overall system, or column height, which is also unacceptable under the known conditions in the laboratory. Furthermore, this would also lead to significant variations in the spacing of the particle beams at the sample, which is generally undesirable.

[0083] It's also possible to reduce the aperture in the micro-optical unit and, at the same time, the focal length of the micro-optical unit. In principle, this also favors lower beam current intensities and adapts the numerical aperture to good resolution. However, in these cases, the beam spacing also varies significantly. To compensate for the spacing changes caused by the changes in the micro-optical unit's focal length, mechanical changes are required, making the system overall very inflexible.

[0084] Figure 3 The schematic diagram shows the illumination of the micro-optics unit 399 by means of a condenser lens system 303 according to the prior art. Figure 2 In comparison, Figure 3 The beam paths of the illumination particle beam 311 and the individual particle beams 3 can be more clearly seen in FIG. The illumination particle beam 311 is represented by a plurality of trajectories. Parts of the illumination particle beam 311 pass through the front multi-aperture plate 380, which forms the first component of the micro-optical unit 399 in the example shown. Figure 3 Some equipotential lines of the electric field within the micro-optical unit are shown, and it is possible to generally identify the focusing effect of the micro-optical unit 399, and more specifically the focusing effect on the individual particle beams 3 when passing through the multi-aperture plate 351 due to the electric field applied to the counter electrode 352, which causes the electric field to change in the region of the multi-aperture plate 351. Before the individual particle beams are focused on the focal point 323, they are stretched apart by the overall lens field of the counter electrode 352. Figure 3 , components of the illuminating particle beam 311 arrive at the front multi-aperture plate 380 in a telecentric manner, which simplifies subsequent passage through the remaining particle optics components of the micro-optics unit 399 and other components of the overall system (not shown).

[0085] By utilizing this condition, the present invention helps to set the optimum values ​​of beam current and numerical aperture, respectively, to obtain the best resolution, in a particularly simple manner and without structural modifications to the particle beam system, independently and within a relatively large value range. In doing so, the column height does not have to be substantially changed. In particular, the present invention facilitates a variation of the beam current intensity of each individual particle beam by a factor of more than 15, preferably more than 25, without having to extend the column height in the process. In one example, it is possible to obtain a variation of the beam current intensity of each individual beam by a factor of more than 50, for example 100.

[0086] at this time Figure 4 An embodiment of the invention is schematically shown with a converging beam guide downstream of a converging lens system comprising magnetic converging lenses 330 and 331. After passing through the converging lens system, the illumination beam 311a converges and a portion of the charged particles emitted from the same solid angle of the particle source 301 is compressed so that the beam current intensity of the individual particle beams formed by this solid angle increases. The greater the convergence, the higher the beam current density. However, it is still necessary or at least advantageous to illuminate the micro-optical unit starting from the front multi-aperture plate 380 in the shown example in a telecentric manner. This is achieved by providing an additional front counter electrode 362 between the converging lens 331 and the front multi-aperture plates 380, 361. A controller (not shown) is arranged to provide an adjustable voltage to the converging lens system 330, 331 and the front counter electrode 362 so that the charged particles can be incident on the front multi-aperture plate 361 in a telecentric manner. Figure 4 , this telecentric condition can be identified on the central individual particle beam or the associated beam trajectories. In the region of the optical axis Z, the trajectories of the particle beams are parallel when incident on the front multi-aperture plate 361. Away from the optical axis (e.g. the upper trajectory) the telecentric condition is also satisfied, but this cannot be seen in the figure due to the simplified schematic. In the present case, the desired effect of telecentric incidence is achieved by combining the global lens field generated by the front counter electrode 362 with the local lens field of the front multi-aperture plate 361. Overall, this produces a focusing effect, which is added to the focusing effect of the systematic combination of the multi-lens array 351 and the counter electrode 352. This also shortens the focal length of the micro-optical unit; i.e. Figure 4 In the embodiment, the focus 323 moves further to the left in the direction of the optical axis Z. Figure 4 In the embodiment of the present invention, the multi-lens array 350 and the front multi-lens array 360 are constructed as mirror images of each other. In this case, the combination of the front multi-lens array 360 or the combination of the target actuation and the appropriately selected actuation of the condenser lens systems 330, 331 enables the beam current intensity to be set. Figure 4 In the exemplary embodiment, the beam current intensity of the individual beams is increased so that in addition to changing the Figure 2 In addition to increasing the beam current intensity by using the focusing lenses 330 and 331 shown in FIG. 1 , the beam current intensity can be further increased without increasing the installation length of the focusing lens system or the column length. Similarly, by appropriately selecting additional setting parameters (such as the additional field lens 370 (see FIG. 1 )), the beam current intensity can be further increased. Figure 12 ) to set the multi-lens array 350, a change in the numerical aperture in the object plane can be achieved, resulting in an overall improvement, especially optimized resolution.

[0087] although Figure 4 An intermediate beam current density is illustrated with converging incident radiation 311a, but Figure 5 Showing low beam current density with diverging beam guide 311b. Here, Figure 5 The illustration in FIG. 3 is very schematic, so that the two condenser lenses 330, 331 are only very weakly excited, so that in the simplified schematic diagram, the diverging particle beam 309 is not actually deflected. The diverging illuminating particle beam 311b passes through the front counter electrode 362. However, Figure 4 In contrast, a different potential is now applied to the front counter electrode 362, so that due to the selected settings, a telecentric incidence of the particle beam on the front multi-aperture plate 361 is again achieved. Figure 4 Compared to the example of , the beam current absorbed by each individual particle beam 3 is smaller. The targeted actuation of the focusing lens system, in particular the focusing lens 331, in combination with the specially selected actuation of the front counter electrode 362, also allows in this case an individual setting of the beam current, which in turn facilitates a targeted improvement in the resolution of the entire system. Figure 5 In the exemplary embodiment, the beam current intensity of the individual beams is reduced so that, in addition to Figure 2 In addition to reducing the beam current intensity by modifying the condenser lenses 330 and 331 as shown in Figure c, further reductions in beam current intensity can be achieved without increasing the installation length or column length of the condenser lens system. Thus, a multi-beam particle microscope having multiple individual beams is provided, wherein the beam current intensity of each individual beam can be varied by a factor of greater than 15, preferably greater than 20, greater than 30, or greater than 50, while maintaining the numerical aperture of each individual beam. Furthermore, the column length of the multi-beam particle microscope remains constant, particularly less than 1.5 meters, preferably less than 1 meter.

[0088] Typically, a voltage of -30 kV is applied to the emitter 301 if the emitter emits electrons. The associated extractor 302 typically has 3 to 7 kV. The micro-optical unit itself is typically at ground potential, i.e. 0 kV. The front counter electrode according to the invention typically operates in a range between approximately + / - 12 and + / - 20 kV. This is therefore of the same order of magnitude as the voltage supply of the counter electrode 352 of the multi-lens array 350. However, other voltage values ​​are also possible. According to the invention, in particular, the controller is configured to supply an adjustable voltage to the particle optical component. For this purpose, in particular, charged particles can be incident on the front multi-aperture plate 361 in a telecentric manner. The controller can be a central controller, which also controls the particle beam system as a whole, such as the control unit of the present patent application. Figure 1 Certain values ​​used to drive the particle optics may be stored in a lookup table.

[0089] Figure 7Another embodiment of the present invention is schematically shown, comprising an electrostatic focusing lens and a boost electrode 332. Here, the focusing lens system includes a magnetic focusing lens 330 and an electrostatic focusing lens 332b arranged downstream thereof. Their respective excitations are indicated by double arrows. A boost potential is applied between the two focusing lenses 330 and 332b via the boost electrode 332. Again, according to the present invention, a front multi-lens array 360 comprising a front counter electrode 362 and a front multi-aperture plate 361 is arranged in the beam path downstream of the electrostatic focusing lens 332b. The focal length of the front multi-lens array 360 can be set by the electric field of the front counter electrode 362. The front counter electrode 362 and the lower end of the boost electrode 332 combine to form a variable electrostatic lens, which acts as the lower focusing lens 332b. The cathode 301 of the emitter, together with the magnetic lens 330 and the upper end of the boost electrode 332 (near the cathode) form the field of the upper focusing lens 330. The beam current may be set using respective condenser lenses 330 and 332b and a telecentric illumination condition may be established.

[0090] Figure 8 Schematic display Figure 7 In the embodiment of the present invention shown herein, a front auxiliary electrode 363 is provided. For example, this front auxiliary electrode 363 can be used to correct for field curvature. Generally speaking, the electric field E varies with different settings of the front auxiliary electrode 363, resulting in a change in the focal length between the beams and, therefore, in "negative" field curvature of the beam array. The closer the front auxiliary electrode is positioned to the front multi-aperture plate 361, the greater the impact on the resulting field curvature. Therefore, according to the present invention, a telecentric incidence condition on the front multi-aperture plate 361 can still be precisely achieved by appropriately driving the focusing lens systems 330, 332a and the front counter electrode 362.

[0091] Figure 9 The schematic diagram shows a multi-aperture plate system having two or more multi-aperture plates 386, 387 which can be displaced relative to each other for beam current variation. The multi-aperture plate system has been embodied so as to be insertable into the beam path, as is apparent from the fact that at least one of the multi-aperture plates 386, 387 can be displaced relative to the particle beam system or the particle beam generated therein. Figure 6The arrangement shown is a so-called slide-in hole 399: the insertable beam current limiting multi-aperture plate system 385 is located between the front multi-lens array 360 and the multi-lens array 350, and therefore between the front multi-aperture plate 361 and the multi-aperture plate 351, preferably upstream of the micro-optical correctors 354, 353 downstream of the front multi-aperture plate 361, but outside the multi-lens field 398. The displaceability of the two multi-aperture plates 386 and 387 relative to each other can be achieved with the help of suitable mechanisms and actuators, such as piezoelectric actuators. In this case, the positioning accuracy of the multi-aperture plates 386, 387 is approximately one micrometer. With the help of corresponding variably insertable holes, the beam current can be further reduced (by a factor of approximately 6). In this case, one of the two multi-aperture plates 386, 387 can also be identical to the front multi-aperture plate 361 described above. However, this does not have to be the case. In the side view of the multi-aperture plates 386 and 387 offset relative to each other, Figure 9 It shows how the illuminating particle beam 311 generates individual particle beams 3 of defined diameter. The further the two plates 386, 387 are moved relative to each other, the narrower the diameter of the individual particle beams 3 and the lower the current intensity in the individual particle beams 3.

[0092] Here, the openings of the multi-aperture plates 386 , 387 that are displaceable relative to each other may have substantially the same size and substantially the same geometry. Figure 9 b) and 9c) show two examples. Figure 9 b), the openings 386, 387a are each circular or ring-shaped. Displaced relative to each other, this produces a so-called lens shape 388. This lens shape can be approximately elliptical, which is why it is preferred to combine this implementation with a multi-stigmator to regain a circular particle beam profile. Figure 9 The embodiment variant of c) shows square openings 386a and 387a. In this case, if the two multi-aperture plates 486 and 387 are chosen to be offset relative to each other and scaled accordingly, the resulting opening 388 can also be square.

[0093] Figure 10Schematically showing a multi-aperture plate system with two multi-aperture plates 390, 391 arranged in sequence and a deflector system positioned therebetween for beam current variation. Illustrated are dual deflectors with separate deflectors 392 and 393. These contribute to the parallel offset of the illumination beam 311 incident on the multi-aperture plate 393. If the deflector system 392, 393 is deactivated and the two multi-aperture plates 390 and 391 are aligned accordingly, i.e., their respective openings have equal size and are positioned at the center of each other, then the entire particle beam 311 passes through the multi-aperture plate system and produces a separate particle beam 3 with maximum particle beam diameter. On the contrary, if the deflectors 392, 393 are activated, this realizes the parallel offset of the particle beam, and the offset particle beam has a part to impact the second multi-aperture plate 391 and only a part to pass through the second multi-aperture plate. This causes the separate particle beam 3 to have a reduced diameter and a generally reduced current intensity.

[0094] In one example, by changing the excitation of the focusing lens, such as Figure 2 a to Figure 2 As shown in c, by changing the openings of the multi-aperture plates 386 and 387 or two sequentially arranged multi-aperture plates 390 and 391 and a deflector system for changing the beam current located therebetween, the intensity of the individual beam current can be changed, and without increasing the column length of the multi-beam particle microscope, the individual beam current can be changed by more than 20 times, for example, 30 times or 50 times. In one example, by changing the excitation of the focusing lens, such as Figure 2 a to Figure 2 c, the excitation changes of the front counter electrode 362 are shown, as shown in FIG. Figure 5 and Figure 6 As shown, the opening changes of the multi-aperture plates 386 and 387 or two multi-aperture plates 390 and 391 configured in sequence and the deflector system located therebetween for beam current variation are used to change the current intensity of the individual beams, and without increasing the column length of the multi-beam particle microscope, the individual beam current variation is achieved by more than 30 times, for example, 50 times or 100 times.

[0095] Figure 11 Various apertures for beam current variation are shown schematically, as can be used, for example, in the described beam current limiting multi-aperture plate system. Figure 11 a) First a circular beam profile 710 is shown. If the beam current intensity is reduced by an aperture, this can be calculated according to Figure 11 a) is achieved by a circular opening. However, in the case of a smaller aperture 711, the limited current reduces the individual beam apertures, resulting in a reduction in resolution. In contrast, Figure 11Arrangement b) offers a better solution: here, while maintaining the same maximum aperture diameter, the current is limited to the annular aperture 712. In this case, the central obstruction diaphragm is fixed by a delicate mechanical connection. Using an annular aperture maintains lateral resolution. Comparing a conventional circular aperture with an annular aperture, it's noteworthy that the annular aperture produces a Bessel bundle with an even smaller central maximum, thus resulting in higher resolution. However, this comes at the expense of higher secondary maxima, so the trade-off between using a conventional circular aperture and an annular aperture should be considered in individual cases. Figure 11 c) shows an aperture with two annular apertures. The central shielding diaphragm and the annular diaphragm are again fixed by web 715. The aperture shown is also known as a Toraldo filter. Compared to a single annular aperture, it achieves a similar diffraction maximum as an annular opening, but with a lower secondary maximum. The use of annular apertures, in particular a system of at least two annular apertures arranged side by side, allows further reduction of the individual beam currents while maintaining the numerical aperture and resolution, without increasing the column length of the multibeam particle microscope. In particular, resolution can be maintained by performing digital image processing downstream of the imaging, for example, by deconvolution of the raw image data using a convolution kernel corresponding to the diffraction image of the annular aperture (in particular a system of at least two annular apertures arranged within one another).

[0096] Figure 12In a more simplified manner, a multi-beam particle microscope 1 is schematically shown with particle optical components for setting the optimal resolution. Starting from a particle source 301 that emits electrons, for example, the charged particles pass through a focusing lens system 303, which in the illustrated example has two magnetic focusing mirrors 330 and 331, each of which can be driven by a controller (not shown). Thus, the charged particles pass through a front multi-lens array 360 in the downstream beam path and then through a multi-lens array 350. Here, the front multi-lens array 360 and the multi-lens array 350 have substantially mirror-image embodiments relative to each other. The front multi-lens array 360 includes a front counter-electrode 362 and a front multi-aperture plate 361. The multi-lens array 350 includes a multi-aperture plate 351 and a counter-electrode 352. In this case, the front counter-electrode 362 and the counter-electrode 352 are driven by a controller (not shown) and supplied with appropriate potentials. Appropriate actuation allows the current intensity of the individual particle beams 3 to be varied, as described in more detail above. The focal length or position of the focal points 323, 323a in the intermediate image plane E1 is varied by varying the voltage applied to the counter electrode 352. This changes both the spacing of the focal points in the intermediate image plane E1 and (when the particle optics are appropriately driven) the position of plane E1 relative to the system optical axis Z (not shown). The focal points 323, 323a in the intermediate image plane E1 can be considered as multiple images of the particle source 301. Thus, they form virtual particle sources 323, 323a. Here, the solid line illustrates the particle beam 3; in contrast, the dashed-dotted line illustrates the particle beam 3a when the adjustment conditions of the counter electrode 352 are changed. In contrast to the circle 323, the asterisk 323a indicates the altered focal position in the intermediate image plane E1.

[0097] In the downstream of intermediate image plane E1, a field lens system 307 consisting of three field lenses and a beam switch 400 and an object lens 102, particularly a magnetic objective lens, is provided in the beam path. As a result, charged individual particle beam 3 is imaged onto object plane E2 from intermediate image plane E1 in a particle optical manner. The numerical aperture of the individual particle beam incident on object plane E2 can be changed by the position change of focus 323, 323a in intermediate image plane E1, and the displacement of the intermediate image plane E1 selectively realizing the optical axis Z direction (not shown), and the spacing (spacing 2) between the individual particle beams on object plane E2 can be kept constant. This additional condition of keeping spacing 2 constant on object plane E2 can be achieved by providing an additional field lens 370, which is arranged between intermediate image plane E1 and the field lens system 307 consisting of three field lenses in the illustrated example. The remaining particle optical parameters such as focusing, rotation and / or telecentricity in this object plane can also be kept constant.

[0098] Then, the second particle beam 9 emitted by the sample 7 passes through the projection lens 205 and the aperture 210 and finally reaches the particle multi-detector 209 .

[0099] Here, due to two additional integral particle optical components, the illustrated multi-beam particle microscope 1 allows for an overall improvement and possible optimization of the resolution in particle optical imaging. First, the targeted drive of the focusing lens system 303 is combined with the targeted drive of the front counter electrode 362, making it possible to achieve a targeted adjustment of the current intensity of the individual particle beams. A telecentric condition can be achieved when incident on the micro-optical unit or, in a simplified manner, on the front multi-aperture plate 361, which is advantageous and may be necessary for the subsequent particle optical imaging. In a further process, the targeted drive of the counter electrode 352 is combined with the additional field lens 370, making it possible to change the numerical aperture in the object plane E2 without changing the spacing 2 in the object plane in the process. The additional field lens 370 thus represents the particle optical variation component and introduces an additional degree of freedom into the system to facilitate such detailed settings.

[0100] In one example, the targeted drive of the counter electrode 352 is combined with an additional field lens 370 so that the numerical aperture of the individual beams is maintained at least approximately constant according to Figure 9 The multi-aperture plates 386 and 387 of one exemplary embodiment or according to Figure 10 The exemplary embodiment of the present invention is combined with the variation of the apertures of the two sequentially arranged multi-aperture plates 390 and 391 and the deflector system located therebetween. Thus, a multi-beam particle microscope with multiple particle beams is provided, which is designed to vary the beam current intensity of the individual beams by a factor of more than 20, for example, by a factor of 30, 50, or even 100, while maintaining a constant column length of less than 1.5 meters, preferably less than 1 meter, and while maintaining a substantially constant resolution of each individual beam when varying the beam current intensity.

[0101] The illustrated multi-beam particle microscope can be used in combination with other particle optical components.In this respect, the illustrated embodiment should be understood to be purely exemplary.

[0102] Reference Signs List

[0103] 1Multi-beam particle microscope

[0104] 3 Primary particle beam (single particle beam)

[0105] 3a Primary particle beam (single particle beam)

[0106] 5 beam points, incident position

[0107] 7 Objects

[0108] 9 Secondary particle beam

[0109] 10Computer systems, controllers

[0110] 100 objective lens system

[0111] 101 Object Plane

[0112] 102 objective lens

[0113] 103 games

[0114] 200 Detector System

[0115] 205 Projection Lens

[0116] 209 Particle Multi-Detector

[0117] 210 aperture

[0118] 211 Detection plane

[0119] 213 Incident Position

[0120] 217 games

[0121] 300 beam generating equipment

[0122] 301 Particle Source

[0123] 302 Extractor

[0124] 303 collimating lens system or focusing lens system

[0125] 305 Multi-aperture Configuration

[0126] 313 multi-aperture plate

[0127] 315 Openings of multi-aperture plates

[0128] 317 midpoint of opening

[0129] 319 games

[0130] 307 Field Lens System

[0131] 309 Divergent Particle Beam

[0132] 311 Illuminating Particle Beam

[0133] 323 beam focus

[0134] 323a beam focus

[0135] 325 Intermediate Image Plane

[0136] 330 condenser lens (magnetic)

[0137] 331 condenser lens (magnetic)

[0138] 332 focusing lens (electrostatic)

[0139] 333 Boost Potential

[0140] 350 Multi-lens Array

[0141] 351 multi-aperture plate

[0142] 352 counter electrode

[0143] 353 Micro-optical correctors, especially multi-stigmators

[0144] 354 Micro-optical correctors, especially focusing multi-lens arrays

[0145] 355 Framework

[0146] 360 front multi-lens array

[0147] 361 front multi-aperture plate

[0148] 362 front counter electrode

[0149] 363 front auxiliary electrode

[0150] 370 Extra Field Lens

[0151] 380 front multi-aperture plate

[0152] 385 Insertable, Beam Current Limiting Multi-Aperture Plate System

[0153] 386 The first multi-aperture plate

[0154] 386a Openings in the first multi-aperture plate

[0155] 387 Second Multi-Aperture Plate

[0156] 387a Opening in the second multi-aperture plate

[0157] 388 Effective opening

[0158] 390 First multi-aperture plate

[0159] 391 Second Multi-Aperture Plate

[0160] 392 First Deflector

[0161] 393 Second Deflector

[0162] 397 Insertable Multi-Aperture Plate System

[0163] 398 Multi-lens field

[0164] 399 Micro-Optics Unit

[0165] 400 beam switches

[0166] 410 bundled tube

[0167] 710 Circular Particle Beam Profile

[0168] 711 round hole

[0169] 712 annular hole

[0170] 713Toraldo filter

[0171] 715 belly plate

[0172] E1 intermediate image plane

[0173] E2 Object Plane

[0174] Z optical axis

Claims

1. A particle beam system for flexibly setting the current intensity of individual particle beams, comprising: at least one particle source configured to generate a diverging beam of charged particles; a focusing lens system through which the charged particle beam passes; a front multi-lens array, wherein the front multi-lens array has a front counter-electrode with a central opening through which the charged particle beam passes, and wherein the front multi-lens array has a front multi-aperture plate disposed in the beam path downstream of the front counter-electrode, the front multi-aperture plate being arranged such that the charged particles pass through the front multi-aperture plate as a plurality of charged individual particle beams; a multi-lens array arranged in the beam path downstream of the preceding multi-lens array, wherein the multi-lens array has a multi-aperture plate with a plurality of openings through which at least a portion of the charged individual particle beam passes, and wherein the multi-lens array has a counter electrode having a central opening located in the beam path downstream of the multi-aperture plate, the counter electrode being substantially passed through by the plurality of individual particle beams; and A controller is configured to provide adjustable excitation to the focusing lens system and the front counter electrode so that the charged particle beam can enter the global lens field of the front counter electrode in a converging or diverging manner, and so that the charged particles can be incident on the front multi-aperture plate in a telecentric manner.

2. The particle beam system of claim 1, wherein the controller is configured to set the current intensity of the individual particle beams. 3 . The particle beam system according to claim 1 , wherein the particle beam system comprises a micro-optical unit comprising the multi-lens array. The particle beam system of claim 3 , wherein the micro-optical unit comprises the front multi-aperture plate.

5. as claim 1 or 2 particle beam systems, wherein this particle beam system also has the front auxiliary electrode that contains central opening, this front auxiliary electrode is arranged in the beam path of this front counter-electrode downstream and this front multi-lens array upstream, and can be provided with adjustable voltage by this controller.

6. as claim 1 or 2 particle beam systems, wherein this particle beam system also can have the back auxiliary electrode containing central opening, this back auxiliary electrode is arranged in the beam path of this multi-lens array downstream and this counter-electrode upstream, and can be provided with adjustable voltage by this controller.

7. The particle beam system of claim 3, wherein the micro-optical unit has a frame at ground potential.

8. The particle beam system of claim 1 or 2, wherein the condenser lens system has two condenser lenses.

9. The particle beam system of claim 8, wherein both condenser lenses are magnetic condenser lenses.

10. The particle beam system according to claim 1 or 2, wherein the condenser lens system comprises a magnetic condenser lens and an electrostatic condenser lens, wherein the electrostatic condenser lens is arranged in the beam path downstream of the magnetic condenser lens, and A boosting electrode that can be driven by the controller is arranged between the magnetic focusing lens and the electrostatic focusing lens, and the electrostatic focusing lens can be excited by the boosting electrode.

11. The particle beam system of claim 1 or 2, further comprising a beam current limiting multi-aperture plate system comprising a beam current limiting multi-aperture plate having a plurality of openings, wherein the beam current limiting multi-aperture plate system is arranged in the beam path downstream of the front multi-lens array and upstream of the multi-lens array, and is configured to be insertable into the beam path.

12. The particle beam system of claim 11, wherein the opening is formed in a circular and / or annular manner.

13. The particle beam system of claim 11 , wherein the beam current limiting multi-aperture plate system has two or more multi-aperture plates that are capable of moving substantially parallel to each other, each plate having a plurality of openings, such that the effective multi-aperture plate opening size can be adjusted for an individual particle beam passing through the beam current limiting multi-aperture plate system.

14. The particle beam system of claim 13, wherein the openings of the multi-aperture plate that are movable relative to each other are of substantially the same size and have substantially the same geometry. 15 . The particle beam system of claim 14 , wherein the openings of the multi-aperture plate that are movable relative to each other are circular or square.

16. The particle beam system of claim 11, wherein the beam current limiting multi-aperture plate system has two multi-aperture plates sequentially arranged in the beam path, each multi-aperture plate having a plurality of openings, The two deflectors are arranged between the two multi-aperture plates and can be driven so as to achieve a substantially parallel movement of the individual particle beam relative to the optical axis during the individual particle beam's passage through the multi-aperture plate system.

17. The particle beam system of claim 1 or 2, further comprising: an intermediate image plane, which is arranged downstream of the multi-lens array in the direction of the beam path and in which the real foci of the individual particle beams are formed, the foci being separated by a spacing 1; a field lens system arranged downstream of the multi-lens array in the direction of the beam path; an objective lens, which is arranged downstream of the field lens system in the direction of the beam path; as well as An object plane in which the individual particle beams undergo particle optical imaging and in which the individual particle beams are separated by a distance.

18. The particle beam system of claim 17, wherein the objective lens is a magnetic objective lens.

19. The particle beam system of claim 17, wherein the controller is configured to drive particle optics of the particle beam system in such a way that the spacing can be set in the object plane.

20. The particle beam system of claim 19, wherein the spacing remains constant when the beam current intensities of the individual particle beams are different.

21. The particle beam system of claim 19, wherein the controller is configured to drive particle optics of the particle beam system in such a manner that the numerical aperture in the object plane is set and the resolution in the object plane is optimized.

22. The particle beam system of claim 21, wherein the resolution within the object plane is optimized for a particular beam current of the individual particle beam.

23. Use of a particle beam system according to claim 1 or 2 for setting the current intensity of an individual particle beam.

24. Use of a particle beam system as claimed in claim 17 for setting the resolution in the object plane.

25. Use of a particle beam system as claimed in claim 24, wherein the use is for setting an optimum resolution.

26. A multi-beam particle microscope comprising the particle beam system according to claim 1 or 2.

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