Multi-beam particle microscope with improved alignment, and method and computer program product for aligning multi-beam particle microscope

Abstract

An improved alignment of magnetic lenses in a multi-beam particle microscope is disclosed. For this purpose, an electrically controlled mechanical alignment and fixing device with an actuator system is provided for at least one, in particular integrally alignable, magnetic lens, the device is configured to mechanically align and mechanically fix the position of at least one alignable magnetic lens in the particle beam path in a plane orthogonal to the optical axis of the multi-beam particle microscope, and is provided with a controller configured to electrically control the electrically controlled mechanical alignment and fixation device.

Description

Technical Field

[0001] The present invention relates to a multi-beam particle microscope with improved alignment, to a method for aligning a multi-beam particle microscope and to a related computer program product. Background Art

[0002] With the continuous development of ever smaller and more complex microstructures such as semiconductor components, there is a need for further development and improvement of planar production technology and inspection systems for the production and inspection of small-sized microstructures. For example, the development and production of semiconductor components requires the design of test wafers to be monitored, and planar production technology requires process improvements to achieve reliable production with high throughput. In addition, there is a recent need to analyze semiconductor wafers for reverse engineering and customer-specific individual construction of semiconductor components. Therefore, there is a need for an inspection device that can be used at high throughput to inspect microstructures on wafers with high accuracy.

[0003] Typical silicon wafers used to produce semiconductor components have a diameter of up to 300 mm. Each wafer is divided into 30 to 60 repeating areas ("die") and measures up to 800 mm. 2 . Semiconductor devices include a plurality of semiconductor structures, which are produced in layers on a wafer surface by planar integration technology. Due to the production process, semiconductor wafers usually have a flat surface. The structural dimensions of the integrated semiconductor structures in this case extend from a few micrometers to a critical dimension (CD) of 5 nanometers, and the structural dimensions will become even smaller in the near future; in the future, the structural dimensions or critical dimensions (CD) are expected to be less than 3 nanometers, such as 2 nanometers, or even less than 1 nanometer. In the case of the above-mentioned small structural dimensions, dimensional defects of the critical dimension must be identified quickly over a very large area. For many applications, the specification requirements for the measurement accuracy provided by the inspection equipment are even higher, such as twice or an order of magnitude. For example, the width of semiconductor features must be measured with an accuracy of less than 1 nm, such as 0.3 nm or even less, and the relative position of the semiconductor structure must be determined with an overlay accuracy of less than 1 nm, such as 0.3 nm or even less.

[0004] MSEM is a multi-beam scanning electron microscope, which is a relatively new development in the field of charged particle systems (charged particle microscope, CPM). For example, multi-beam scanning electron microscopes are disclosed in US7244949B2 and US2019 / 0355544A1. In the case of a multi-beam electron microscope or MSEM, a sample is irradiated simultaneously with multiple individual electron beams, which are arranged in a field or grid. For example, 4 to 10,000 individual electron beams can be provided as a primary radiation, wherein each individual electron beam is separated from the adjacent individual electron beam by a spacing of 1 to 200 microns. For example, MSEM has about 100 separate individual electron beams ("beamlets"), which are arranged, for example, in a hexagonal grid, wherein the individual electron beams are separated by a spacing of about 10 μm. Multiple charged individual particle beams (primary beams) are focused on the surface of the sample to be inspected using a common objective lens. For example, the sample can be a semiconductor wafer fixed to a wafer holder mounted on a movable stage. During the irradiation of the wafer surface with a charged primary individual particle beam, interaction products, such as secondary electrons or backscattered electrons, are emitted from the wafer surface. Their starting points correspond to those positions on the sample (on which each of the multiple primary individual particle beams is focused). The number and energy of the interaction products depend on the material composition and the topography of the wafer surface. The interaction products form multiple secondary individual particle beams (secondary beams), which are focused by a common objective lens and incident on a detector arranged in a detection plane due to the projection imaging system of the multi-beam inspection system. The detector includes multiple detection areas, each detection area includes multiple detection pixels, and the detector captures the intensity distribution of each secondary individual particle beam. In this process, an image field of, for example, 100 μm×100 μm is obtained.

[0005] A multi-beam electron microscope of the prior art includes a series of electrostatic and magnetic elements. At least some of the electrostatic and magnetic elements are adjustable to adapt the focal position and stigmation of multiple charged individual particle beams. The prior art multi-beam system with charged particles further includes at least one intersection plane of the primary or secondary charged individual particle beams. In addition, the prior art system includes a detection system to make adjustment easier. The prior art multi-beam particle microscope includes at least one beam deflector ("deflection scanner") for scanning an area of ​​the sample surface by a plurality of primary individual particle beams to obtain an image field of the sample surface. More details about the multi-beam electron microscope and its operating method are described in the international patent application with application number WO 2021239380 A1, the disclosure of which is fully incorporated by reference into this patent application.

[0006] The alignment of a multibeam electron microscope, or more generally of a multibeam particle microscope, is very important for precision applications. One aspect of the alignment is the alignment of the magnetic lenses of the system. These magnetic lenses can in particular be so-called global magnetic lenses, through which essentially all charged particles or all charged individual particle beams pass. Therefore, these lenses must be aligned particularly accurately. Furthermore, it is a fact that, taking into account the geometrical dimensions of such magnetic lenses, it is not possible to infer exactly the magnetic field generated in the lens. In other words, the magnetic fields of identically manufactured lenses within the manufacturing accuracy can indeed differ significantly from one another, which is why individual lens alignment is necessary.

[0007] According to the prior art, the magnetic lenses in multibeam particle microscopes are aligned mechanically. The alignment of the magnetic lenses is performed manually by experienced technicians. This adjustment usually takes several weeks or even months; it is performed while observing the multibeam particle microscope image at the same time. Screws on the outside of the multibeam particle microscope or its housing are adjusted to align the magnetic lenses. The alignment and subsequent fixing of the magnetic lenses are usually performed during the multibeam particle microscope production adjustment test; thereafter, the alignment usually remains unchanged and is only re-aligned on-site at the customer's site after a module replacement or a magnetic lens replacement. In this case, on-site realignment at the customer's site is more difficult, because at the customer's site the multibeam particle microscope is usually integrated into the production plant and the associated process chain. As a result, long and expensive downtimes in the production plant can occur, which need to be avoided.

[0008] US2013 / 0299697A1 discloses a device for observing a sample using a charged particle beam, which is provided with: a beam forming part, which forms a plurality of charged particle beams on the sample; an energy control unit, which controls the incident energy of the plurality of charged particle beams irradiated onto the sample; a beam current control unit, which controls the beam current of the plurality of charged particle beams irradiated onto the sample; and a beam arrangement control unit for controlling the beam arrangement, in which the plurality of charged particle beams are irradiated onto the sample. The beam forming part includes a beam separation electrode, an upper electrode of a lens array, a middle electrode of a lens array, a lower electrode of a lens array and a movable platform, and by selecting a plurality of aperture pattern groups, the movable platform is utilized to function as a beam control unit or a beam arrangement control unit. US 2013 / 0299697 A1 does not address the specific problem of alignment of particle optical components. In particular, the alignment of the global magnetic lens is not addressed.

[0009] GB894569A published in 1962 discloses a device for compensating the axial astigmatism of an electron lens. It involves a single beam system and a specific objective lens as an electron lens. The correction coil is movably arranged around the objective lens and outside the vacuum chamber. The objective lens itself has no mechanical alignment. Summary of the invention

[0010] One of the objects of the present invention is therefore to provide a multi-beam particle microscope with an improved alignment of the magnetic lenses, in particular to enable the alignment to be performed more quickly and, if possible, more accurately.

[0011] This object is achieved by the subject matter of the independent patent claims. Advantageous embodiments of the invention are evident from the dependent patent claims.

[0012] This patent application claims the priority of German patent application No. 10 2022 114 098.9 filed on June 3, 2022, the disclosure of which is incorporated by reference in its entirety into the present patent application.

[0013] In the case of single-beam particle microscopy, according to the prior art, the alignment of the magnetic lens is no longer performed solely mechanically, but the particle beam is deflected by a deflector so that it is guided through the center of the magnetic lens. Therefore, in the case of multi-beam particle microscopy, it seems to be an option to perform the alignment or at least fine alignment by electrical and / or magnetic deflectors. However, after intensive research by the inventors, this method has proven to be problematic.

[0014] Multi-beam particle microscopes use landing energies in the range of about 0.3keV to about 5keV conventionally, and for this purpose, use relatively high beam energies, about 30keV, in a column. Due to these high beam energies, high field strengths are also required to be able to deflect the individual particle beams in the column. The use of high deflection field strengths requires high voltage and / or high current again, which can generate parasitic effects that adversely affect beam quality. Therefore, surprisingly, it is better to carry out mechanical alignment in the case of multi-beam particle microscopes.

[0015] Therefore, the present invention proposes an electrically controlled mechanical alignment, which can be quickly aligned while improving accuracy.

[0016] Specifically, according to a first aspect, the present invention relates to a multi-beam particle microscope for sample inspection, comprising the following:

[0017] at least one particle source configured to generate a divergent charged particle beam;

[0018] A focusing lens system through which the charged particle beam passes;

[0019] a multi-beam generator arranged downstream of the condenser lens system in the direction of the beam path of the particles, such that at least some of the charged particles pass through an opening in the multi-beam generator in the form of a plurality of individual particle beams, and the multi-beam generator is configured to generate a first field of a plurality of charged first particle beams;

[0020] a first particle optical unit having a first particle optical beam path and configured to image the generated first individual particle beam onto the sample surface in the object plane such that the first particle beam is incident on the sample surface at an incident position, the incident position forming a second field;

[0021] a detection system having a plurality of detection areas forming a third field;

[0022] a second particle optical unit having a second particle optical beam path and configured to image a second individual particle beam emanating from an incident position in the second field onto a third field of detection area of ​​the detection system;

[0023] a magnetic and / or electrostatic objective lens through which both the first individual particle beam and the second individual particle beam pass;

[0024] a beam switch disposed in a first particle optical beam path between the multi-beam generator and the objective lens, and in a second particle optical beam path between the objective lens and the detection system;

[0025] The focusing lens system and / or the first particle optical unit and / or the second particle optical unit comprises at least one alignable magnetic lens, and the alignable magnetic lens is arranged in the housing by means of a mounting member so that the charged particles pass through the alignable magnetic lens.

[0026] wherein an electrically controlled mechanical alignment and fixation device having an actuator system is provided to the at least one alignable magnetic lens, the electrically controlled mechanical alignment and fixation device being configured to mechanically align and mechanically fix the position of the at least one alignable magnetic lens in a particle optical beam path in a plane orthogonal to an optical axis of the multibeam particle microscope, and

[0027] A controller is configured to electrically control the electrically controlled mechanical alignment and fixturing device.

[0028] 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.

[0029] Here, each particle beam is arranged in a grid arrangement, that is to say, the arrangement of each particle beam relative to each other is preferably fixed or can be selected. Preferably, this is a regular grid arrangement, for example, each particle beam is arranged in a square, rectangular or hexagonal shape relative to each other, in particular with uniform spacing. It is advantageous if the number of individual particle beams is 3n(n-1)+1, where n is any natural number.

[0030] The multi-beam particle microscope is preferably a system operated with a single column, but the multi-beam particle microscope can also be realized by a multi-column system.

[0031] The focusing lens system and / or the first particle optical unit and / or the second particle optical unit comprises at least one alignable magnetic lens, which is arranged in the housing by a mounting so that the charged particles pass through the alignable magnetic lens. In principle, the alignable magnetic lens can be any magnetic lens that is usually present in a multi-beam particle microscope. Preferably, it is a global magnetic lens, through which multiple, in particular all individual particle beams pass; however, the alignable magnetic lens can also be located upstream of the multi-beam generator in the particle optical beam path, and instead of individual particle beams, such as a divergent beam of charged particles, passes through the lens. Examples of alignable magnetic lenses are focusing lenses, field lenses and projection lenses. Very generally, the alignable magnetic lens in the context of the present patent application is understood to refer to a magnetic lens whose position in the particle optical beam path can be changed in a targeted manner in a plane orthogonal to the optical axis of the system. In this case, the purpose of alignment is to guide the charged particle beam or multiple individual particle beams parallel to the optical axis through the center of the magnetic lens. In this case, generally speaking, the magnetic lens center does not exactly correspond to the geometrical center of the magnetic lens, which, as described above, firstly requires an alignment of the magnetic lens and secondly makes the alignment more difficult in principle.

[0032] In principle, a mount for the alignable magnetic lens holds the alignable magnetic lens in its position but allows the freedom of movement required for the alignment process. For example, a typical mount for a magnetic lens is a so-called clamping ring, which clamps the barrel of the magnetic lens (which can be further subdivided into barrel and cover). The mount is suitably connected to a housing in which the alignable magnetic lens is arranged; this housing can be, for example, the outer housing of a multibeam particle microscope.

[0033] According to an embodiment of the present invention, an electrically controlled mechanical alignment and fixing device with an actuator system is provided for at least one alignable magnetic lens, wherein the device is configured to mechanically align and mechanically fix the position of at least one alignable magnetic lens in a particle optical beam path in a plane orthogonal to the optical axis of the system. The above plane is also referred to as the alignment plane hereinafter. Maintaining mechanical alignment and fixing avoids parasitic effects that negatively affect beam quality generation in the event of electrical and / or magnetic deflection. At the same time, the advantages of electrical control in terms of accuracy and reproducibility of alignment cannot be achieved in the case of pure manual mechanical alignment. Electrical control increases the achievable alignment accuracy by about 100 times.

[0034] Furthermore, the clever arrangement of electrically controlled mechanical alignment and fixing devices makes it possible to align even magnetic lenses that could not be aligned manually before: Specifically, not every magnetic lens in a multibeam particle microscope can actually be aligned without problems via the outer housing. It is obvious that if alignment screws and fixing screws are used for mechanical alignment and fixing, for example, the technician must specifically access these screws during a purely manual mechanical alignment, which often happens if the screws to be adjusted are arranged near the housing wall of the multibeam particle microscope, which is usually implemented in a tubular form; for magnetic lenses further inside, manual alignment is not possible.

[0035] In principle, the electromechanical alignment and fixing device with an actuator system according to the invention is implemented in one piece or in multiple parts. The electromechanical alignment and fixing device can also include multiple electromechanical alignment and fixing devices; therefore, the term "device" covers the singular and plural of "devices" according to the definition. According to a preferred embodiment of the invention, the electromechanical alignment and fixing device is multi-part, including an electromechanical alignment device and an electromechanical fixing device in the form of two independent structural units. In this case, it turns out again that these structural units can be implemented in one piece or in multiple parts, and it is also possible that the electromechanical alignment device includes multiple electromechanical alignment devices and the electromechanical fixing device includes multiple electromechanical fixing devices.

[0036] However, in contrast to the functional separation of the alignment device and the fixing device, it is of course also possible to provide a combination of an electromechanical alignment and fixing device with an actuator system. The functional subdivision ultimately depends on the type of implementation of the electromechanical alignment and fixing device with the actuator system.

[0037] Very generally, alignment or alignment is understood to mean adjusting the position of the magnetic lens in the alignment plane. In the case of fixing, on the other hand, the position adjusted by the alignment is fixed. Fixing is therefore a restriction and the two terms are used synonymously in the context of the present patent application. In this case, the fixing force or restraining force is stronger than the main force and preferably also stronger than the force of the provided actuator. In the context of the present patent application, an actuator is defined very generally as a structural unit related to drive technology, which converts electrical signals into mechanical movements and thus actively intervenes in the controlled process, i.e. alignment and / or fixing. According to the invention, the one or more electrical signals are generated by a controller, which can be a controller of the multi-beam particle microscope itself or a module of the controller. However, in principle, the controller can also be provided individually.

[0038] In the context of this patent application, the term alignment means means the installation or guidance of a device for alignment. In this case, the installation or guidance can be achieved by conventional bearings, such as sliding bearings, or by forced guidance via joints. Examples thereof can be hexapod mechanisms, parallel kinematic mechanisms, shear kinematic mechanisms, bending mechanisms, etc. A disadvantage of sliding bearings is that static friction must be overcome. This makes manual alignment more difficult, because the point at which static friction is overcome is unpredictable and the adjustment process may change suddenly. In this regard, the motorized actuator system can reduce the threshold of static friction, for example, by vibrations such as ultrasonic vibrations.

[0039] The actuator system is limited by the relevant forces, range and resolution or accuracy. In principle, the present invention can use actuators known per se. For example, linear or rotary motors and combinations thereof are suitable in principle. Piezoelectric elements are also known, such as piezoelectric stacks with low range and high strength forces or piezoelectric drives with arbitrary range but low strength forces. Gear mechanisms for conversion can also be used (e.g. screws in threads driven by rotary motors; rotary motion is thus converted into linear motion). Pneumatic or hydraulic actuators are also known and suitable in principle.

[0040] According to a preferred embodiment of the invention, the electrically controlled mechanical alignment device comprises a stepper motor with a gear mechanism as an actuator. The gear mechanism is used for the transformation, and the corresponding selection of the gear mechanism makes it possible to obtain a high-precision alignment, for example, an accuracy of 0.1 μm or better. In contrast, the accuracy that can usually be achieved with purely manual mechanical alignment is only about 10μm.

[0041] Additionally or alternatively, the electromechanical fixing device comprises a combination as an actuator, which comprises a stepper motor and a piezoelectric element. This combination can be used in particular with a fixing screw as a fixing device. In this case, a first actuator with a stepper motor can be used to first fix the fixing device (such as a fixing screw) and only then a second actuator in the form of a piezoelectric element can be used. In this case, the piezoelectric element can exert a final contact pressure on the fixing device used (such as a fixing screw) and thus achieve an overall better fixation.

[0042] Very generally, according to a preferred embodiment of the invention, the electrically controlled mechanical fixture comprises at least one two-stage actuator system for generating the contact pressure for the fixture. It is also possible to provide, for example, a three-stage actuator system or a four-stage actuator system, etc. Furthermore, the combination of actuators can be supplemented with a mechanism for increasing and / or releasing the contact force; additionally or alternatively, a pneumatic system can also be provided.

[0043] According to a preferred embodiment of the invention, the actuator used is electrically load-free during operation of the multibeam particle microscope, i.e., during operation of the multibeam particle microscope, the actuator used does not require a supply current or a supply voltage; however, of course, a mechanical load is still present on the actuator. In this case, operation is understood to be the normal operation of the multibeam particle microscope, in other words, the routine operation after alignment and fixation have been completed. Thus, the absence of electrical load avoids parasitic effects that may be generated due to the presence of the field, and the operation of the multibeam particle microscope is more energy-efficient and more sustainable.

[0044] According to a preferred embodiment of the present invention, the electrically controlled mechanical alignment device is configured for Cartesian alignment and includes two first alignment units arranged orthogonally to each other to align the position of at least one alignable magnetic lens in a plane (alignment plane) orthogonal to the optical axis of the multi-beam particle beam system. In this case, the orthogonal arrangement of the two first alignment units relative to each other is related to the direction of alignment achieved by each of the two first alignment units. In this case, the two first alignment units can be structurally identical, but not necessarily. In addition, the bearing area or interaction area of ​​the two first alignment units and the alignable magnetic lens or its mounting can be arranged so that the cross-section between the bearing area and the optical axis of the multi-beam particle microscope is at right angles to each other. Since the magnetic lens usually has rotational symmetry, this enables the alignable magnetic lens in the particle optical beam path to achieve the best attachment point and the most effective alignment.

[0045] According to a preferred embodiment of the present invention, each of the two first alignment units arranged orthogonally to each other is arranged on the housing, and each first alignment unit includes a pressure screw, which can be moved in a plane orthogonal to the optical axis by an actuator assigned to it, and is coupled to at least one magnetic lens through a mounting part of the magnetic lens to change its position. According to the present invention, the thrust acting on such a pressure screw is generally greater than 150 Newtons, preferably greater than 170 Newtons, and most preferably greater than 180 Newtons. According to a preferred embodiment of the present invention, the mounting part of the magnetic lens is implemented as a clamping ring, and the pressure screw is pressed onto the clamping ring from the outside.

[0046] According to a preferred embodiment of the present invention, a counter bearing may be arranged on the housing at a position diametrically opposite to the first alignment unit with respect to the optical axis. For example, the counter bearing may be implemented as a spring element.

[0047] According to an alternative embodiment of the invention, an associated second alignment unit, in particular a structurally identical second alignment unit, can in each case be arranged at a position on the housing diametrically opposite the first alignment unit with respect to the optical axis, wherein the controller is configured to control the associated first and second alignment units in an opposite direction in a coordinated manner. Thus, the controller, for example, causes a position change dx at the first alignment unit and a corresponding position change -dx at the associated second alignment unit. The use of an associated first and second alignment unit allows the accuracy of the alignment to be further increased, since inaccuracies of a portion of the counter-bearing do not occur or are replaced by the accurately known position of the second alignment unit.

[0048] According to a preferred embodiment of the present invention, the electrically controlled mechanical fixing device comprises a plurality of separate fixing units, in particular fixing screws, each of which acts on an element of the mounting of at least one alignable magnetic lens, thereby fixing the position of at least one alignable magnetic lens. For example, two or three or four or even more fixing units can be provided. It is particularly preferred to provide four separate fixing units, which are arranged circumferentially on the outside relative to the alignable magnetic lens, for example in an alternating manner with the first and second alignment units. Therefore, in this example, the fixing unit is always located between two alignment units (regardless of whether this is the first alignment unit or the second alignment unit).

[0049] According to a preferred embodiment of the invention, the fixation is achieved by means of friction or geometrical blocking. For example, if the mounting of the alignable magnetic lens is not fixedly connected to the lens, fixation by means of friction is advantageous. For example, if a clamping ring is provided as a mounting for the magnetic lens, the clamping ring can only move axially and is not connected to the lens. The fixation performed by the clamping ring then also indirectly fixes the position of the magnetic lens, in particular by means of friction generated by the contact pressure of the fixing device. If the mounting or the clamping ring is not fixedly connected to the lens, it can move more freely during the alignment of the magnetic lens.

[0050] According to an alternative embodiment of the invention, the mounting element, in particular the clamping ring, is fixed to the lens and follows the lens during alignment. Due to the mounting of the fixing screws, the movement of the lens is geometrically blocked, particularly preferably the axial and radial movement is blocked.

[0051] According to a preferred embodiment of the invention, the fixing direction is tilted both relative to the optical axis of the multibeam particle microscope and relative to the alignment plane. This results in radial and axial fixing of the alignable magnetic lens by means of a mounting such as a clamping ring, for example.

[0052] According to a preferred embodiment of the present invention, a plurality of fixing units are arranged between mutually adjacent alignment units or between an alignment unit and a counter bearing adjacent to the alignment unit. The adjacent refers to the circumferential direction around the magnetic lens. This achieves a very uniform and safe fixation.

[0053] According to another preferred embodiment of the present invention, the electrically controlled mechanical alignment and fixing device is not designed in the form of two independent structural units with different functions, but as a combination of electrically controlled mechanical alignment and fixing devices. Compared with the above-mentioned specific embodiment variant with functionally independent structural units, this specific embodiment variant of the present invention is not retrofittable in existing systems. In this specific embodiment variant, for example, the alignable magnetic lens can be coupled to an actuator via a fixed connection such as a flexure, so that the actuator can move the magnetic lens back and forth. In this way, only one actuator is required for each alignment direction, that is, for example, in the x-direction or the y-direction; there is no need for a counter bearing such as a spring assembly, nor is there a need to provide a first and a second alignment unit relative to each other.

[0054] According to a preferred embodiment of the present invention, the combined electromechanical alignment and fixing device comprises a plurality of combined electromechanical alignment and fixing devices of the same structure. For example, two combined electromechanical alignment and fixing devices may be provided so that Cartesian alignment can be achieved.

[0055] According to a preferred embodiment of the invention, the at least one alignable magnetic lens comprises a lens pot and a lens cover, wherein the lens pot and / or the lens cover can be aligned and fixed independently of each other by means of an electrically controlled mechanical alignment and fixing device. For example, a total of two electrically controlled mechanical alignment and fixing devices can be provided for each alignable magnetic lens, each of which has an actuator system, which, as described above, can be subdivided into a plurality of devices and structural units and / or alignment units. The individual alignment of the lens pot on the one hand and the individual alignment of the lens cover on the other hand provides the advantage that a possible tilt of the alignable magnetic lens can therefore also be corrected. In particular, if the lens pot on the one hand and the lens cover on the other hand are not placed centered up and down, this corresponds to a tilt of the magnetic field axis. It is interesting here that the tilt can be simulated in this way without actually having to tilt the mechanical components for this purpose.

[0056] According to another preferred embodiment of the present invention, in addition, the at least one alignable magnetic lens can be aligned and fixed in the optical axis direction of the system by the electromechanical alignment and fixing device or by another electromechanical alignment and fixing device. In other words, the alignment in the z direction can also be performed using a corresponding actuator system.

[0057] According to another preferred embodiment of the invention, the multibeam particle microscope comprises a user interface for the controller. Thus, the control of the electrically controlled mechanical alignment and fixation device can be performed electrically via the user interface. Preferably, the user interface also comprises an image display unit to display the particle optical image. For example, the particle optical image can be recorded together with the current alignment adjustment and can enable the technician to draw conclusions about the state or progress of the alignment.

[0058] According to a preferred embodiment of the present invention, the user interface is arranged to be away from the multi-beam particle microscope and used for remote maintenance of the multi-beam particle microscope. Remote maintenance may be required because it is no longer necessary for the on-site technician to manually perform mechanical alignment. In fact, at the customer site, the multi-beam particle microscope is usually combined in a process chain or production device that is difficult to approach. Now, this part no longer poses any problems for the alignment of the magnetic lens. In addition, in principle, more magnetic lenses can be aligned than in the prior art, because the required actuator system and the corresponding circuits can be integrated into the multi-beam particle microscope at the same time from the beginning. It is no longer necessary to be close to the housing of the particle beam microscope. In addition, the advantages of electrically controlled mechanical alignment and fixation by the actuator system also include the ability to record the alignment. It is also possible to leave the alignment point and then accurately go to the point again, which is eliminated by manual alignment in actual implementation. In addition, the alignment can be fully automated and an alignment algorithm for alignment can be developed to quickly and effectively achieve the optimal adjustment of the magnetic lens.

[0059] According to another aspect of the present invention, the present invention relates to a method for aligning a multi-beam particle microscope according to a variant of the above-mentioned embodiments, the method comprising the following steps:

[0060] a) operating a multi-beam particle microscope with a plurality N of actuated magnetic lenses, each magnetic lens comprising an electrically controlled mechanical alignment and fixing device with an actuator system, wherein each actuator system allows one of the N magnetic lenses to be moved with one or more degrees of freedom f. The total number of degrees of freedom available during the alignment of the actuated magnetic lenses is therefore provided by the sum of all degrees of freedom f of all actuated magnetic lenses. Thus, if, for example, five magnetic lenses each have two actuated degrees of freedom, this results in a total of 10 degrees of freedom. However, it is also possible that some lenses have only one degree of freedom, while other magnetic lenses have several degrees of freedom, for example two, three or even more, in particular if the mirror grooves on the one hand and the mirror covers on the other hand can be aligned individually;

[0061] b) determining the position change of each actuated magnetic lens and the sensitivity of each degree of freedom of the actuated magnetic lens, and determining the associated influence vector based on the determined sensitivity;

[0062] c) generating an optical image of the particles by a multi-beam particle microscope and determining image aberrations;

[0063] d) determining a total aberration vector of the determined image aberrations;

[0064] e) performing a singular value decomposition of the total aberration vector with respect to the determined influence vector and, on this basis, determining the manipulated variables of each actuated magnetic lens and the manipulated variables of each degree of freedom of the actuated magnetic lens; and

[0065] f) electrically controlling, by a controller, a mechanical alignment and fixture of the actuated magnetic lens based on the determined manipulated variables to reduce or eliminate image aberrations.

[0066] The method according to the invention is therefore based on linear system theory. It is assumed that the individual components behave linearly and that the behavior of the entire system is linearly composed of the individual components. This assumption of linear system theory is always valid at least regionally.

[0067] According to a preferred embodiment of the present invention, the method further comprises the following steps:

[0068] g) generating another optical image of the particle by multibeam particle microscopy and determining residual image aberrations;

[0069] h) if the residual image aberration is greater than a predetermined upper limit, iteratively performing method steps d) to g).

[0070] This iterative process is particularly useful if, due to non-linear factors, for example, a total aberration vector below a threshold value cannot be immediately obtained.

[0071] According to another preferred embodiment of the present invention, the method further comprises the following steps:

[0072] determining an influence vector for each operating point of the multi-beam particle microscope; and / or

[0073] The influence vector is stored in a lookup table.

[0074] This has the advantage that for each operating point of the multibeam particle microscope, the alignment of the multibeam particle microscope can be performed in a customized manner, so that the achievable resolution and precision of the multibeam particle microscope is improved overall. Various operating points are in this case understood to be, for example, various beam currents, various landing energies, various working distances, etc. Various other environmental parameters of the multibeam particle microscope can also be included in the operating point definition, for example, the ambient temperature around the multibeam particle microscope. Depending on the selection of the operating point, the best possible alignment can be called up or set by means of a lookup table.

[0075] According to another specific embodiment of the present invention, the method is performed in the form of remote maintenance of the multi-beam particle microscope. At least as far as the alignment itself is concerned, an on-site system engineer is no longer absolutely necessary, which saves time and costs.

[0076] According to a third aspect of the invention, the invention relates to a computer program product having a program code for executing the method described in the above-mentioned multiple embodiment variants. In this case, the program code can be programmed in any desired programming language. The program code can be subdivided into multiple modules. For example, the program code can be executed by a controller of a multi-beam particle microscope or by an associated computer system. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] The present invention will be better understood with reference to the accompanying drawings, in which

[0078] Figure 1 A schematic diagram showing a multi-beam particle microscope (MSEM);

[0079] Figure 2 schematically illustrating aspects of the Cartesian alignment of a magnetic lens;

[0080] Figure 3 Schematically illustrates the electrically controlled mechanical alignment and fixation of the global magnetic lens according to the first specific embodiment;

[0081] Figure 4 schematically illustrates the electrically controlled mechanical alignment and fixation of the global magnetic lens according to the second specific embodiment;

[0082] Figure 5 Schematically illustrates the electrically controlled mechanical alignment and fixation of the global magnetic lens according to the third specific embodiment;

[0083] Figure 6 schematically shows an electrically controlled mechanical alignment device comprising a stepper motor with a gear mechanism;

[0084] Figure 7 Schematically illustrating an electrically controlled mechanical fixture comprising a two-stage actuator system having a stepper motor and a piezoelectric element;

[0085] Figure 8 Show Figure 7 The functional principle of the two-stage actuator system shown; and

[0086] Fig. 9 A method according to the invention for aligning a multi-beam particle microscope is schematically illustrated. DETAILED DESCRIPTION

[0087] Figure 1Schematic diagram of a particle beam system 1 in the form of a multi-beam particle microscope, which uses a plurality of particle beams. The particle beam system 1 generates a plurality of particle beams, which are incident on an object to be inspected in order to generate interaction products there, such as secondary electrons, which are subsequently detected after being emitted from the object. The particle beam system 1 is of the scanning electron microscope (SEM) type, which uses a plurality of primary particle beams 3, which are incident on the surface of an object 7 at a plurality of incidence positions 5 and generate a plurality of electron beam spots or spots separated from each other in space there. The object 7 to be inspected can be of any desired type, such as a semiconductor wafer or a biological sample, and can include an arrangement of miniaturized components, etc. The surface of the object 7 is arranged in a first plane 101 (object plane) of an objective 102 of an objective system 100.

[0088] Figure 1 The enlarged detail I1 in FIG. 1 shows a plan view of the object plane 101 with a regular rectangular field 103 of incident positions 5 formed in the first plane 101. Figure 1 , the number of incident positions is 25, which forms a 5×5 field 103. The number of incident positions 25 is a number selected for the sake of simplicity of explanation. In practice, the number of beams and the resulting number of incident positions can be selected to be significantly higher, for example 20×30, 100×100, etc.

[0089] In the specific embodiment shown, the field 103 of the incident positions 5 is a substantially regular rectangular field with a constant spacing P1 between adjacent incident positions. Exemplary values ​​of the spacing P1 are 1 micron, 10 microns and 40 microns. However, the field 103 may also have other symmetries, such as hexagonal symmetry.

[0090] The diameter of the beam spot shaped in the first plane 101 can be very small. Exemplary values ​​for this diameter are 1 nm, 5 nm, 10 nm, 100 nm and 200 nm. Focusing of the particle beam 3 for the shaped beam spot 5 is performed by the objective lens system 100 .

[0091] The primary particles incident on the object generate interaction products, such as secondary electrons, backscattered electrons or primary particles that have undergone reverse motion for other reasons and are emitted from the surface of the object 7 or from the first plane 101. The interaction products emitted 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 multiple secondary particle beams 9 to the detector system 200. The detector system 200 includes a particle optical unit with a projection lens 205 for guiding the secondary particle beam 9 to a particle multi-detector 209.

[0092] Figure 1Detail I2 in shows a plan view of a plane 211 in which the respective detection areas of the particle multi-detector 209 where the secondary particle beam 9 is incident at the incident position 213 are located. 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.

[0093] A primary particle beam 3 is generated in a beam generating device 300, which comprises at least one particle source 301, for example an electron source, at least one collimating lens 303, a multi-aperture device 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 which illuminates the multi-aperture device 305.

[0094] Figure 1 Detail 13 in FIG. 1 shows a plan view of a multi-aperture device 305. The multi-aperture device 305 includes a multi-aperture 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.

[0095] Particles of the illumination beam 311 pass through the aperture 315 and form the particle beam 3. Particles of the illumination beam 311 incident on the plate 313 are absorbed by the plate 313 and therefore are not used to form the particle beam 3.

[0096] Due to the applied electrostatic field, the multi-aperture device 305 focuses each particle beam 3 in such a way that a beam focus 323 is formed in a plane 325. Alternatively, the beam focus 323 may be virtual. The diameter of the beam focus 323 may be, for example, 10 nanometers, 100 nanometers and 1 micrometer.

[0097] 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 323 is formed onto the first plane 101 so that the field 103 of the incident position 5 or beam spot appears there. If the surface of the object 7 is located in the first plane, the beam spot is formed accordingly on the object surface.

[0098] 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. The objective lens 102 is thus a lens that is part of both the first and second particle optical units, 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.

[0099] The beam switch 400 is arranged in the beam path of the first particle optical unit between the multi-aperture device 305 and the objective system 100. The beam switch 400 is also part of a second optical unit in the beam path between the objective system 100 and the detector system 200.

[0100] Further information about such multi-beam particle beam systems and the components used therein, for example, particle sources, multi-aperture plates and lenses, can be obtained from international patent applications WO 2005 / 024881 A2, WO 2007 / 028595 A2, WO 2007 / 028596 A1, WO 2011 / 124352 A1 and WO 2007 / 060017 A2 and German patent applications DE 10 2013 016 113 A1 and DE 10 2013 014 976 A1, the full scope of the disclosures of which are incorporated herein by reference.

[0101] The particle beam system 1 further comprises a computer system 10 which is configured for controlling the individual particle optical components of the multi-particle beam system and for evaluating and analyzing the signals obtained by the multi-detector 209. The computer system 10 may be constituted by a plurality of individual computers or components.

[0102] according to Figure 1 The multibeam particle microscope may comprise components according to the invention, that is to say in particular one or more alignable magnetic lenses and electrically controlled mechanical alignment and fixing devices. The computer system 10 may comprise a controller according to the invention, but the controller may also be individually arranged.

[0103] Figure 2 Schematically illustrating aspects of the Cartesian alignment of a magnetic lens 500. The figure shows a cross-section of the magnetic lens 500, the drawing corresponding to the alignment plane of the magnetic lens 500. The alignment plane is spanned by vectors x and y. The optical axis of the system or multibeam particle microscope 1 is oriented perpendicularly thereto; the optical axis extends along the z direction. Figure 2The schematically shown cross section extends through the mirror groove of the magnetic lens 500. The magnetic lens 500 is held by a mounting 510, which in this example is in the form of a clamping ring 510. The clamping ring holds the magnetic lens 500 in position by clamping and therefore by friction. The clamping ring also has a certain range in the z direction and in this way firmly clamps the barrel of the magnetic lens 500. The magnetic lens 500 is arranged in a housing 520 together with its mounting 510. In the example shown, the housing 520 is a tubular part that can form the outer shell of a multi-beam particle microscope. However, the embodiment of the housing can also be different, or the specific shape and design of the housing depends largely on the position in the particle optical beam path where the magnetic lens 500 can be actually arranged. In this respect, Figure 2 The illustrations in should be understood as examples only.

[0104] When the magnetic lens 500 is correctly aligned, the fan-shaped particle beam or the plurality of individual particle beams 3 pass centrally through the opening 504 of the magnetic lens 500, wherein the central ray or the beam arranged in the center of the multi-beam particle beam field is guided through the magnetic lens center of the magnetic lens 500. In this case, the magnetic lens center may deviate slightly from the geometric lens center, since it is not possible to accurately predict how the magnetic field generated by the magnetic lens 500 is actually shaped based on the geometric and mechanical properties of the magnetic lens 500. Therefore, precise alignment is required for precision applications of the multi-beam particle microscope 1.

[0105] In the example shown, alignment screws 501 are used for alignment, which are pressed onto the clamping ring 510 via attachment points or attachment areas 505 for alignment in the x-direction or respectively y-direction and in this way for displacement of the magnetic lens 500 held in the clamping ring 510 in the x-direction or respectively y-direction. This displacement capability is provided by Figure 2 The double-headed arrow in . The displacement required for alignment is usually about 1 to 2 mm. In practice, a larger displacement is usually not required. Arranged diametrically opposite to each alignment screw 501 is a corresponding counter bearing 502, which in the example shown is in the form of a spring assembly. In this way, the entire magnetic lens 500 can follow the displacement of the alignment screw 501 in the alignment plane x, y.

[0106] In addition to the alignment device 501 shown, Figure 2 Also shown are fixing means in the form of fixing screws 503, which act on the clamping ring 510 respectively, thereby fixing the position of the magnetic lens 500. In the illustrated example, the fixing direction of the fixing screws 503 is indicated by a unidirectional arrow. In this case, the fixing direction is oriented obliquely relative to the optical axis z and is oriented obliquely relative to the alignment plane (x, y plane). By corresponding fixing in this oblique direction, the magnetic lens 500 can be fixed in the radial direction and the axial direction (z direction).

[0107] Then Figure 3 The electrically controlled mechanical alignment and fixation of the global magnetic lens 500 according to the first specific embodiment is schematically shown. Figure 2 Mechanical alignment in Figure 3 The electrically controlled mechanical alignment and fixation by means of an actuator system according to the invention is shown. Manual operation of the alignment screws 501 is no longer necessary; instead, actuators 530 are provided for alignment. The controller 10 electrically controls the actuators 530. This allows a very precise and recordable fine alignment of the alignment screws 501. In a similar manner, the fixing screws 503 are connected or engaged to the actuators 531 for fixation. These actuators 531 are also electrically controlled by the controller 10. Figure 3 The specific embodiment variants shown also show, in principle, the embodiment variants that can be improved. However, it should be pointed out that Figure 3 The embodiment variations described herein should be understood as merely illustrative and not limiting of the present invention.

[0108] Figure 4 Schematically illustrates the electrically controlled mechanical alignment and fixation of the global magnetic lens 500 according to the second embodiment. Figure 3 Compared with the embodiment variation, in Figure 4 In the embodiment of the present invention, the counter bearing or spring element 502 is replaced by an alignment screw 501 and an actuator 530 coupled thereto. This does have the effect of providing more signal lines 801 to 808. However, the situation is now that the signals from the alignment devices associated with a specific alignment direction are coupled to each other: the signals of the signal lines 801 and 805 are in each case opposite to each other and coordinately control the mutually associated first alignment unit 530 and second alignment unit 501 to position the magnetic lens 500 in the x-direction. Here, the first alignment unit 530 and the second alignment unit 501 assigned to each other can be structurally identical, but this is not necessary. Similarly, the signals of the signal lines 803 and 807 of the first alignment unit 530 and the second alignment unit 501 for aligning the magnetic lens 500 in the y-direction are coordinated with each other and opposite control is achieved. After alignment, the four fixing units 531, 503 are controlled using the signal lines 802, 804, 806 and 808.

[0109] exist Figure 3 and Figure 4In the embodiment variant shown, the electromechanical alignment and fixing device is designed in multipartite form and is in the form of two separate structural units (one structural unit (again multipartite) for alignment and another structural unit (again multipartite) for fixing). Of course, however, the electromechanical alignment and fixing device can also be implemented as one structural unit. On the other hand, this requires that the electromechanical alignment and fixing device is equipped with an actuator system and a limiting device combined in one component. The separate fixing device can then be omitted.

[0110] Figure 5 The electrically controlled mechanical alignment and fixation of the global magnetic lens 500 according to the third embodiment is schematically shown. In this specific embodiment, the electrically controlled mechanical alignment and fixation device is arranged in a combined structural unit for both alignment and fixation. Figure 5 In the variant shown, the combined alignment and fixing device provides alignment and fixing means for each alignment direction, that is, the combined alignment and fixing device is also in the form of multiple parts. In the example shown, the magnetic lens 500 is coupled to the actuator 540, for example, by a fixed connection such as a flexure 541, so that the actuator 540 displaces the magnetic lens 500 in the positive and negative x-direction or y-direction, respectively. Therefore, only one actuator 540 is required in each case for alignment along the x-direction or respectively along the y-direction.

[0111] In addition, the mirror groove and the mirror cover of the magnetic lens 500 can also be aligned separately. If the mirror barrel and the mirror cover are not completely centered relative to each other, a tilt of the magnetic lens 500 can be simulated and a tilt correction in the particle beam system 1 can be performed.

[0112] Additionally or selectively, further actuating elements may also be provided in the optical axis direction (z direction), which may compensate for thermal effects, for example. According to another preferred embodiment of the present invention, in addition, at least one alignable magnetic lens 500 may be aligned and fixed in the optical axis direction (z direction) of the system by means of the electrically controllable mechanical alignment and fixing device or another electrically controllable mechanical alignment and fixing device. In other words, alignment in the z direction may also be performed using a corresponding actuator system.

[0113] although Figures 3 to 5 The actuators 530, 531, and 540 are shown only conceptually, but Figure 6 and Figure 7 Specific embodiments of actuator systems for alignment and fixing, respectively, are schematically shown. Figure 6An electrically controlled mechanical alignment device 530 is schematically shown, which comprises a stepper motor with a gear mechanism 534. A motor 535 causes the gear mechanism 534 to produce a rotational movement and interacts with the pin to produce a translational movement of the pressure pin 532. A step counter 536 can determine the position of the pressure pin 532 and thus record the alignment. For this purpose, the motor 535 and the step counter 536 are connected to the controller 10. The actuator 530 for alignment can be connected directly or indirectly to the magnetic lens 500 to be aligned (not shown) by means of a flange 533; for example, the flange 533 can be fixed or screwed into the housing 520 of the multi-beam microscope 1. Figure 6 Typical dimensions of the exemplary embodiment shown in are a length of several centimeters and a diameter of less than 2 centimeters. Achievable thrust forces are greater than 150 N, for example greater than 180 N, and alignment accuracy is 0.01 μm or better.

[0114] Figure 6 An exemplary embodiment of an actuator system with a linear gear mechanism is shown. However, it is of course also possible to use a bevel gear mechanism instead of a linear gear mechanism or in addition to a linear gear mechanism. In this case, the choice of the gear mechanism is adapted to the available construction space / geometry conditions.

[0115] Figure 7 An electrically controlled mechanical fixture 531 is schematically shown, which comprises a two-stage actuator system with a stepper motor 552 and a piezoelectric element 554. The two-stage actuator system is arranged in a housing 553, which in the example shown has a cover 555. A plunger 550 is movably arranged in a bushing 551 and can be moved in translation by means of a motor 552. A relatively large stroke can be achieved by means of the motor 552. The piezoelectric actuator 554 has a relatively small stroke, but the second stage provides further contact pressure, by which the plunger 550 as a fixing element is directly or indirectly pressed on the magnetic lens 500 in order to fix the magnetic lens 500. If the maximum possible fixing force or clamping force must be applied to the elements of the magnetic lens 500 or its mount 510, a two-stage actuator system has proven to be advantageous. At least in the case of the second stage of the actuator system (piezoelectric actuator 554), no rotation is required during the application of the holding force, which can achieve higher precision and greater holding pressure / contact pressure.

[0116] Figure 8 Show Figure 7 Functional principle of the two-stage actuator system shown in: Figure 8 The top portion of the center shows the situation where no contact pressure or holding force is applied.

[0117] Figure 8The middle shows the first stage of the actuator system: a negative voltage is applied to the piezoelectric actuator 554, so the piezoelectric actuator 554 contracts or becomes shorter. A mechanical prestress is established. In addition, a motor 552 with a spindle is controlled and drives the plunger 550 to cause its axial displacement, and the entire unit is supported between the mounting of the magnetic lens 500 and the fixedly arranged piezoelectric actuator 554. Only through the bearing areas 560 and 570 in Figure 8 The bearing is schematically shown in FIG.

[0118] In the second stage of the actuator system (see Figure 8 The voltage is turned off again and an attempt is made to lengthen the piezoelectric actuator 554. The mechanical prestress of the piezoelectric actuator 554 now presses together with the spindle on the motor 552 and indirectly on the plunger 550. In this way, a high holding force can be established on the mounting 510 of the magnetic lens 500 or on the clamping ring 510 mentioned above.

[0119] In the case of the embodiments of the actuator systems described in more detail by way of example, it is advantageous that they can be operated in an electrically load-free manner during operation of the multi-beam particle microscope 1. This means that during normal operation of the multi-beam particle microscope 1, no voltage needs to be present at the actuators, that is, because of the actuator system, no electromagnetic fields are present that could cause parasitic effects. Furthermore, this fact should be positively evaluated from the perspective of the sustainability of the multi-beam particle microscope 1.

[0120] Fig. 9 The method for aligning a multi-beam particle microscope 1 according to the present invention is schematically shown. The method for aligning a multi-beam particle microscope can be implemented by applying the theory of linear systems. This is a statement that is valid at least in some areas: the individual components of the system behave linearly, and the behavior of the entire system is composed of the linearity of the individual components. In this context, the method for aligning a multi-beam particle microscope 1 can be designed as follows, for example:

[0121] A first method step S1 involves operating a multi-beam particle microscope 1 having a plurality N of actuated magnetic lenses 500, each of which comprises an electrically controlled mechanical alignment and fixation device having an actuator system, wherein each actuator system allows one of the N magnetic lenses 500 to move with one or more degrees of freedom f.

[0122] A second method step S2 involves determining the sensitivity of the position change of each actuated magnetic lens 500 and of each degree of freedom f of the actuated magnetic lens 500 and determining the associated influence vector based on the determined sensitivities.

[0123] A further method step S3 involves generating an optical image of the particles using the multibeam particle microscope 1 and determining the image aberrations.

[0124] A fourth method step S4 involves determining the total aberration vector of the determined image aberrations.

[0125] A further method step S5 involves performing a singular value decomposition of the total aberration vector with respect to the determined influence vectors and, on this basis, determining the manipulated variables for each actuated magnetic lens 500 and for each degree of freedom f of the respective actuated magnetic lens 500 .

[0126] A further method step S6 involves electrically controlling, by a controller, the mechanical alignment and fixing means of the actuated magnetic lens 500 in dependence on the determined manipulated variables in order to reduce or eliminate image aberrations.

[0127] A further method step S7 involves generating another particle optical image by means of the multibeam particle microscope 1 and determining the residual image aberration. If the residual image aberration is less than or equal to a predetermined upper limit, the method ends with method step S8. Otherwise, method steps S4 to S7 are repeated.

[0128] The influence vectors for each operating point of the multibeam particle microscope 1 can be determined and / or stored in a lookup table. In this way, an optimal alignment can be achieved for different operating points. This is even the first time that this type of magnetic lens alignment has been performed for different operating points.

[0129] The supervised alignment and its reproducibility as well as its electrical control further enable the above-described method for aligning the multi-beam particle microscope 1 to be performed in the form of remote maintenance. It is thus not necessary for a technician to be present on site to perform the alignment. Furthermore, even in the case of an installation of the multi-beam particle microscope in a production plant, the alignment can be performed without relatively large disturbances or, if appropriate, realignment can be performed without significant disturbances to the overall operation.

[0130] The present invention enables automatic alignment of a multi-beam particle microscope with high beam energy. In the case of high beam energies, for example greater than 10 keV, in particular greater than 20 keV, and in particular in the case of multi-beam systems, beam deflection, for example by electrostatic deflectors, becomes more difficult. According to the invention, alignment is achieved in particular by means of a mechanical position change of the magnetic lens. In this case, a lateral position change is described in an exemplary embodiment. An equivalent position change includes a tilt of the magnetic lens in at least one direction. In general, a mechanical position change also includes a displacement of the magnetic lens in the axial or z-direction. In addition to the magnetic lens, the mechanical position of the electrostatic element can also be changed.

[0131] Reference numerals list

[0132] 1Multi-beam particle microscope

[0133] 3. Primary particle beam (individual particle beam)

[0134] 5 beam spot, incident position

[0135] 7 Objects

[0136] 9 Secondary particle beam (individual particle beam)

[0137] 10Computer systems, controllers

[0138] 11 Secondary particle optical beam path

[0139] 13 Primary particle optical beam path

[0140] 25 Sample surface, chip surface

[0141] 100 objective lens system

[0142] 101 Object Plane

[0143] 102 objective lens

[0144] 103 games

[0145] 200 detector system

[0146] 205 projection lens

[0147] 209 Particle Multi-Detector

[0148] 211 detection plane

[0149] 213 Incident position

[0150] 215 detection area

[0151] 217 games

[0152] 300 beam generator

[0153] 301 Particle Source

[0154] 303 collimating lens system, focusing lens system

[0155] 305 Multi-aperture device, multi-beam generator

[0156] 307 Field Lens

[0157] 309 Divergent Particle Beam

[0158] 311 Illumination Particle Beam

[0159] 313 multi-aperture plate

[0160] 315 Openings in a multi-aperture plate

[0161] 317 midpoint of opening

[0162] 319 games

[0163] 323 beam focus

[0164] 325 Intermediate Image Plane

[0165] 327 games

[0166] 400 beam switch

[0167] 500 magnetic lens

[0168] 501 Alignment screw with fine thread

[0169] 502 reverse bearing, spring assembly

[0170] 503 fixing screw

[0171] 504 opening

[0172] 505 attachment point or attachment area for alignment

[0173] 506 Attachment point or attachment area for fixing

[0174] 507 Attachment point or attachment area for counter bearing

[0175] 510 mounting parts, clamping ring

[0176] 520 Shell

[0177] 530 Actuator for alignment

[0178] 531 Actuator for fixing

[0179] 532 pressure pin

[0180] 533 flange

[0181] 534 gear mechanism

[0182] 535 Motor

[0183] 536 step counter

[0184] 540Actuators for alignment and fixing

[0185] 541 Connecting element, such as flexure

[0186] 550 Pressure element, such as plunger

[0187] 551 Bushing

[0188] 552 Motor with spindle

[0189] 553 Shell

[0190] 554 Piezoelectric Actuator

[0191] 555 housing cover

[0192] 560 Loading Area

[0193] 570 Loading Area

[0194] 801 signal line

[0195] 802 signal line

[0196] 803 signal line

[0197] 804 signal line

[0198] 805 signal line

[0199] 806 signal line

[0200] 807 signal line

[0201] 808 signal line

Claims

1. A multi-beam particle microscope for sample inspection, comprising: at least one particle source configured to generate a divergent beam of charged particles; a focusing lens system through which the charged particle beam passes; a multi-beam generator arranged downstream of the condenser lens system in the direction of the beam path of the particles such that at least some of the charged particles pass through an opening in the multi-beam generator in the form of a plurality of individual particle beams, and the multi-beam generator is configured to generate a first field of a plurality of first particle beams; a first particle optical unit having a first particle optical beam path and configured to image the generated first particle beam onto a sample surface in an object plane such that the first particle beam is incident on the sample surface at an incident position, the incident position forming a second field; a detection system having a plurality of detection areas forming a third field; a second particle optical unit having a second particle optical beam path and configured to image a plurality of second particle beams emitted from the incident position in the second field onto the third field of the detection area of ​​the detection system; a magnetic and / or electrostatic objective lens through which both the first particle beam and the second particle beam pass; a beam switch arranged in the first particle optical beam path between the multi-beam generator and the magnetic and / or electrostatic objective lens, and in the second particle optical beam path between the magnetic and / or electrostatic objective lens and the detection system; Wherein, the focusing lens system and / or the first particle optical unit and / or the second particle optical unit comprises at least one alignable magnetic lens, and the alignable magnetic lens is arranged in the housing by means of a mounting member so that the charged particles pass through the alignable magnetic lens. wherein an electrically controlled mechanical alignment and fixing device having an actuator system is further provided for the at least one alignable magnetic lens, the electrically controlled mechanical alignment and fixing device being configured to mechanically align and mechanically fix the position of the at least one alignable magnetic lens in a particle optical beam path in a plane orthogonal to the optical axis of the multi-beam particle microscope, and A controller is configured to electrically control the electrically controlled mechanical alignment and fixation device.

2. A multi-beam particle microscope as claimed in claim 1, wherein: The electromechanical alignment and fixing device is multi-part and comprises an electromechanical alignment device and an electromechanical fixing device in the form of two independent structural units.

3. A multi-beam particle microscope as claimed in claim 2, in, The electrically controlled mechanical alignment device comprises a stepper motor as an actuator and having a gear mechanism, and / or The electrically controlled mechanical fixing device comprises a combination as an actuator, which comprises a stepping motor and a piezoelectric element.

4. The multi-beam particle microscope according to any one of claims 2 and 3, wherein: The electrically controlled mechanical fixture includes at least a two-stage actuator system for generating a contact pressure for the fixture.

5. The multi-beam particle microscope according to any one of claims 2 to 4, wherein: The electromechanical alignment device is configured for Cartesian alignment and comprises two first alignment units arranged orthogonally to each other so as to align the position of the at least one magnetic lens in a plane orthogonal to the optical axis of the multi-beam particle beam system.

6. The multi-beam particle microscope as claimed in claim 5, wherein: Each of the two first alignment units arranged orthogonally to each other is arranged on the housing and includes a pressure screw, which can be moved in a plane orthogonal to the optical axis by an assigned actuator and is coupled to the at least one magnetic lens through the mounting of the magnetic lens so as to change its position.

7. The multi-beam particle microscope as claimed in claim 6, wherein: A counter-bearing, in particular a spring element, is in each case arranged on the housing at a position diametrically opposite the first alignment unit with respect to the optical axis.

8. The multi-beam particle microscope as claimed in claim 6, wherein: An associated second alignment unit, in particular an associated second alignment unit of identical structure, is in each case arranged on the housing at a position diametrically opposite to the first alignment unit with respect to the optical axis, wherein the controller is configured to control the associated first alignment unit and the second alignment unit in reverse in a coordinated manner with respect to each other.

9. The multi-beam particle microscope according to any one of claims 2 to 8, wherein: The electrically controlled mechanical fixing device comprises a plurality of separate fixing units, in particular fixing screws, each fixing unit acting on an element of the mounting part of the at least one magnetic lens, thereby fixing the position of the at least one magnetic lens.

10. The multi-beam particle microscope as claimed in claim 9, wherein: The fixation is achieved by friction or geometric resistance.

11. The multi-beam particle microscope as claimed in claim 10, wherein: The plurality of fixing units are each arranged between the aligning units adjacent to each other or between an aligning unit and a counter bearing adjacent to the aligning unit.

12. The multi-beam particle microscope as claimed in claim 1, wherein: The electromechanical alignment and fixing device is not designed as two independent structural units with different functions, but is designed as a combined electromechanical alignment and fixing device.

13. A multi-beam particle microscope as claimed in claim 12, wherein: The combined electromechanical alignment and fixing device comprises a plurality of, in particular structurally identical, combined electromechanical alignment and fixing devices.

14. A multi-beam particle microscope as claimed in any preceding claim, wherein: The at least one magnetic lens comprises a mirror groove and a mirror cover, wherein the mirror groove and / or the mirror cover can be aligned and fixed independently of each other by the electrically controlled mechanical alignment and fixing device.

15. A multi-beam particle microscope as claimed in any preceding claim, wherein: The at least one magnetic lens can be further aligned and fixed in the direction of the optical axis of the system by means of the electromechanical alignment and fixing device or by means of a further electromechanical alignment and fixing device.

16. A multi-beam particle microscope as claimed in any preceding claim, wherein: The at least one magnetic lens is one of the following lenses: a condenser lens, a field lens, and a projection lens.

17. A multi-beam particle microscope as claimed in any preceding claim, wherein: During operation of the multibeam particle microscope, the brakes used are free of electrical load.

18. A multi-beam particle microscope as claimed in any preceding claim, comprising a user interface for the controller.

19. A multi-beam particle microscope as claimed in claim 18, wherein: The user interface is remotely provided by the multi-beam particle beam system for remote maintenance of the multi-beam particle beam system.

20. A method for aligning a multi-beam particle microscope according to any one of the preceding claims, the method comprising the steps of: a) operating the multi-beam particle microscope with a plurality N of actuated magnetic lenses, each magnetic lens comprising an electrically controlled mechanical alignment and fixation device having an actuator system, wherein each actuator system allows one of the N magnetic lenses to move with one or more degrees of freedom f; b) determining the sensitivity of the position change of each actuated magnetic lens and the sensitivity of each degree of freedom of said actuated magnetic lens, and determining the associated influence vector according to the determined sensitivity; c) generating an optical image of the particles by the multi-beam particle microscope and determining an image aberration; d) determining a total aberration vector of the determined image aberrations; e) performing a singular value decomposition of the total aberration vector with respect to the determined influence vector and, on this basis, determining the manipulated variable of each actuated magnetic lens and the manipulated variable of each degree of freedom of the actuated magnetic lens; f) electrically controlling, by the controller, a mechanical alignment and fixation device of the actuated magnetic lens based on the determined manipulated variables to reduce or eliminate image aberrations.

21. The method of claim 20, further comprising: g) generating another particle optical image by the multibeam particle microscope and determining residual image aberration; as well as h) if the residual image aberration is greater than a predetermined upper limit, iteratively performing method steps d) to g).

22. The method of any one of claims 20 and 21, further comprising: determining an influence vector of each operating point of the multi-beam particle microscope; and / or The influence vector is stored in a lookup table.

23. The method according to any one of claims 20 to 22, wherein: The method is performed in a form of remote maintenance of the multi-beam particle microscope.

24. A computer program product having a program code for executing the method as claimed in any one of claims 20 to 23.

Images