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

Abstract

Improved alignment of the magnetic lens of a multi-beam particle microscope is disclosed. For this purpose, an electrically controllable mechanical alignment and fixation means with an actuator system is provided for at least one, in particular alignable global magnetic lens, which means is configured to mechanically align and mechanically fix the position of at least one alignable magnetic lens in the particle optical beam path in a plane orthogonal to the optical axis of the multi-beam particle microscope, and a controller is provided which is configured to electrically control the electrically controllable mechanical alignment and fixation means.

Description

[Technical Field]

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

[0002] As smaller and more complex microstructures, such as semiconductor components, continue to be developed, planar manufacturing techniques and inspection systems for producing and inspecting small-dimension microstructures need to be further developed and optimized. For example, the development and production of semiconductor components requires the monitoring of test wafer designs, and planar manufacturing techniques require process optimization for high-throughput, reliable production. More recently, there has been a demand for the analysis of semiconductor wafers in reverse engineering and for the individual, customer-specific configuration of semiconductor components. Therefore, there is a need for inspection tools that can be used at high throughput to examine the microstructures on wafers with high accuracy.

[0003] Typical silicon wafers used in the production of semiconductor components have a diameter of up to 300 mm. Each wafer can be up to 800 mm 2A semiconductor device comprises a plurality of semiconductor structures produced in layers on the surface of a wafer by planar integration techniques. Semiconductor wafers typically have a flat surface due to the production process. The structure sizes of integrated semiconductor structures range from a few microns to 5 nm in critical dimension (CD), with even smaller structure sizes expected in the near future. Structure sizes or critical dimensions (CD) are expected to be less than 3 nm, e.g., 2 nm, or even less than 1 nm in the future. With these small structure sizes, defects of the critical dimension size must be quickly identified over very large areas. In some applications, the specification requirements for measurement accuracy achieved by inspection equipment are even higher, e.g., two times or an order of magnitude higher. For example, the width of semiconductor features must be measured with an accuracy of less than 1 nm, e.g., 0.3 nm or better, and the relative positions of semiconductor structures must be determined with an overlay accuracy of less than 1 nm, e.g., 0.3 nm or better.

[0004] Multi-beam scanning electron microscopes (MSEMs) are a relatively new development in the field of charged particle systems (charged particle microscopes, CPMs). Examples of multi-beam scanning electron microscopes are disclosed in U.S. Pat. No. 7,244,949 and U.S. Patent Application Publication No. 2019 / 0355544. In a multi-beam electron microscope, or MSEM, a sample is simultaneously illuminated with multiple individual electron beams arranged in a field or grid. For example, 4 to 10,000 individual electron beams can be provided as primary radiation, with each individual electron beam separated from its neighbor by a pitch of 1 to 200 micrometers. For example, an MSEM has approximately 100 separated individual electron beams ("beamlets"), which are arranged, for example, in a hexagonal grid, with the individual electron beams separated by a pitch of approximately 10 micrometers. The multiple charged individual particle beams (primary beams) are focused onto the surface of the test sample by a common objective lens. The sample may be, for example, a semiconductor wafer secured to a wafer holder mounted on a movable stage. During irradiation of the wafer surface with a charged primary particle beam, interaction products, such as secondary electrons or backscattered electrons, are emitted from the wafer surface. The starting points of the secondary electrons all correspond to locations on the sample where multiple primary particle beams are focused. The amount and energy of the interaction products depend on the material composition and surface topography of the wafer surface. The interaction products form multiple secondary particle beams (secondary beams), which are collected by a common objective lens and incident on a detector located at the detection plane as a result of the projection imaging system of the multi-beam inspection system. The detector has multiple detection areas, each with multiple detection pixels, and captures the intensity distribution of each of the secondary particle beams. This process results in an image plane of, for example, 100 μm × 100 μm.

[0005] Prior art multi-beam electron microscopes include a series of electrostatic and magnetic elements. At least some of the electrostatic and magnetic elements are adjustable to adapt the focal positions and astigmatism of the multiple charged individual particle beams. Prior art charged particle multi-beam systems further include at least one crossover plane for the primary or secondary charged individual particle beams. Prior art systems also include a detection system to facilitate easier adjustment. Prior art multi-beam particle microscopes include at least one beam deflector ("deflection scanner") for simultaneously scanning an area of ​​the sample surface with multiple primary individual particle beams to obtain an image plane of the sample surface. Further details regarding multi-beam electron microscopes and methods for operating them are described in International Application Publication No. 2021239380, the disclosure of which is incorporated herein by reference in its entirety.

[0006] The alignment of a multi-beam electron microscope, or more generally a multi-beam particle microscope, is very important for precision applications. One aspect of the alignment is the alignment of the magnetic lenses of the system. Such magnetic lenses may in particular be so-called global magnetic lenses, through which substantially all charged particles or all charged individual particle beams pass. Such lenses must therefore be aligned particularly precisely. Furthermore, due to the geometric dimensions of such magnetic lenses, the magnetic field generated by the lenses cannot be accurately estimated. In other words, the magnetic fields of lenses that are identically manufactured within the manufacturing accuracy range may actually differ from each other to a measurable extent, which is why alignment of the individual lenses is necessary.

[0007] According to the prior art, the magnetic lenses of a multi-beam particle microscope are mechanically aligned, and experienced technicians manually perform the alignment of the magnetic lenses. Such alignment often takes weeks or even months. The alignment is performed by simultaneous observation of the image of the multi-beam particle microscope. Screws on the outside of the multi-beam particle microscope or its housing are adjusted to align the magnetic lenses. The alignment and subsequent fixation of the magnetic lenses is usually performed during production commissioning of the multi-beam particle microscope. The alignment is then usually kept unchanged and is only performed in situ at the customer's premises after a module or magnetic lens exchange. In this case, updating the alignment in situ at the customer's premises is more difficult, as the multi-beam particle microscope is often integrated into the production facility and the associated process chain at the customer's premises. This can result in long and expensive downtimes at the production facility, which must be avoided.

[0008] U.S. Patent Application Publication No. 2013 / 0299697 discloses a charged particle beam applied apparatus for observing a sample. The charged particle beam applied apparatus includes a beam forming section for forming multiple charged particle beams on the sample, an energy control unit for controlling the incident energy of the multiple charged particle beams irradiated onto the sample, a beam current control unit for controlling the beam current of the multiple charged particle beams irradiated onto the sample, and a beam alignment control unit for controlling the alignment of the multiple charged particle beams irradiated onto the sample. The beam forming section includes a beam splitting electrode, a lens array upper electrode, a lens array middle electrode, a lens array lower electrode, and a movable stage. The beam forming section functions as either the beam current control unit or the beam alignment control unit by selecting multiple aperture pattern sets using the movable stage. U.S. Patent Application Publication No. 2013 / 0299697 does not address the specific problem of aligning particle optical components. In particular, it does not address the alignment of global magnetic lenses.

[0009] British Patent No. 894569, published in 1962, discloses a device for correcting axial astigmatism in an electron lens. The patent refers to a single beam system and a specific objective lens, which is an electron lens. Correction coils are movably positioned around the objective lens and outside the vacuum chamber. The objective lens itself is not mechanically aligned. Summary of the Invention [Problem to be solved by the invention]

[0010] It is therefore an object of the present invention to provide a multi-beam particle microscope that is improved with regard to the alignment of the magnetic lenses, which alignment is intended in particular to be able to be carried out more quickly and, if possible, also more accurately.

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

[0012] This patent application claims priority from German Patent Application No. 102022114098.9, filed June 3, 2022, the disclosure of which is incorporated by reference in its entirety into this patent application.

[0013] In the case of single-beam particle microscopes, the alignment of magnetic lenses according to the prior art is no longer performed solely mechanically, but using deflectors that deflect the particle beam and guide it through the center of the magnetic lens. Therefore, it would appear that also in the case of multi-beam particle microscopes, it would be an option to perform alignment, or at least fine alignment, using electrical and / or magnetic deflectors. However, this approach has been found to be problematic after thorough investigation by the inventors.

[0014] Multi-beam particle microscopes typically use landing energies ranging from about 0.3 keV to about 5 keV, resulting in relatively high beam energies of about 30 keV within the column. These high beam energies also require high electric field strengths to allow deflection of the individual particle beams within the column. The use of high deflection field strengths further requires high voltages and / or currents, which are associated with parasitic effects that adversely affect beam quality. Therefore, for multi-beam particle microscopes, mechanical alignment is surprisingly preferable.

[0015] The present invention therefore proposes an electrically controllable mechanical alignment, which allows for rapid alignment while improving accuracy. [Means for solving the problem]

[0016] The present invention particularly relates, according to a first aspect, to a multi-beam particle microscope for inspecting a sample, the multi-beam particle microscope comprising: at least one particle source configured to generate a divergent beam of charged particles; a focusing lens system through which the beam of charged particles passes; a multi-beam generator arranged downstream of the focusing lens system in a direction of the particle beam path, and configured to generate a first field of multiple charged first particle beams, such that at least some of the charged particles pass through an opening of the multi-beam generator in the form of multiple individual particle beams; a first particle-optical unit comprising a first particle-optical beam path configured to image the generated first individual particle beam onto a sample surface in an object plane, whereby the first particle beam is incident on the sample surface at an incidence location and forms a second field; a detection system comprising a number of detection regions forming a third field; a second particle-optical unit comprising a second particle-optical beam path and configured to image a second individual particle beam emerging from an incidence location in the second field onto a third field of a detection region of the detection system; a magnetic and / or electrostatic objective lens through which both the first and second individual particle beams pass; a beam switch disposed in the first particle-light beam path between the multi-beam generator and the objective lens and in the second particle-light beam path between the objective lens and the detection system; a controller configured to electrically control the electrically controllable mechanical alignment and fixation means; Equipped with the collecting lens system and / or the first particle-optical unit and / or the second particle-optical unit comprises at least one alignable magnetic lens arranged in the housing using a mount so that the charged particles pass through it; Electrically controllable mechanical alignment and fixation means with an actuator system are further provided for the at least one alignable magnetic lens, which means are configured to mechanically align and mechanically fix the position of the at least one alignable magnetic lens in the particle light beam path in a plane perpendicular to the optical axis of the multi-beam particle microscope.

[0017] 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), although other particle sources may also be used.

[0018] The individual particle beams are in this case preferably arranged in a grid arrangement, i.e., their arrangement relative to one another is fixed or selectable. This is preferably a regular grid arrangement, which may be, for example, a square, rectangular or hexagonal arrangement, in which the individual particle beams are spaced apart from one another in particular with a uniform spacing. Advantageously, the number of individual particle beams is 3n(n-1)+1, where n is any natural number.

[0019] Although the multi-beam particle microscope is preferably a system that operates with a single column, it is also possible to realize a multi-beam particle microscope with a multi-column system.

[0020] The focusing lens system and / or the first particle-optical unit and / or the second particle-optical unit comprise at least one adjustable magnetic lens arranged in the housing by means of a mount so that the charged particles pass through. This adjustable magnetic lens can, in principle, be any of the magnetic lenses typically present in a multi-beam particle microscope. The magnetic lens is preferably a global magnetic lens through which multiple, in particular all, individual particle beams pass. However, it is also possible to place an adjustable magnetic lens upstream of the multi-beam generator in the particle-optical beam path so that, instead of the individual particle beams, for example, a divergent beam of charged particles passes through this lens. Examples of adjustable magnetic lenses are focusing lenses, field lenses, and projection lenses. In the context of this patent application, an adjustable magnetic lens is understood to mean, quite generally, a magnetic lens whose position in the particle-optical beam path can be targetably changed in a plane perpendicular to the optical axis of the system. The purpose of the adjustment, in this case, is to guide the beam of charged particles or multiple individual particle beams parallel to the optical axis passing through the center of the magnetic lens. In this case, the center of the magnetic lens generally does not coincide exactly with the geometric center of the magnetic lens, which, as explained above, firstly requires alignment of the magnetic lens and secondly makes alignment more difficult in principle.

[0021] The mount of the alignable magnetic lens in principle holds the magnetic lens in place, but allows the freedom of movement necessary for the alignment process. A typical mount for a magnetic lens is, for example, a so-called clamping ring, which clamps the lens pot of the magnetic lens (which can be subdivided into a lens pot and a lens cover). The mount is suitably connected to a housing in which the alignable magnetic lens is arranged, which housing can, for example, be the external housing of a multi-beam particle microscope.

[0022] According to the present invention, electrically controllable mechanical alignment and fixation means with an actuator system are provided for at least one alignable magnetic lens, which means are configured to mechanically align and fix the position of the at least one alignable magnetic lens in the particle-light beam path in a plane perpendicular to the optical axis of the system. This plane is also referred to hereinafter as the alignment plane. Maintaining mechanical alignment and fixation avoids parasitic effects that occur in the case of electrical and / or magnetic deflection and adversely affect the beam quality. At the same time, electrical control allows advantages in terms of alignment accuracy and reproducibility that cannot be achieved with purely manual mechanical alignment. Electrical control can realize an approximately 100-fold improvement in the achievable alignment accuracy.

[0023] Furthermore, by skillfully arranging electronically controllable mechanical alignment and fixation means, even magnetic lenses that previously could not be aligned manually can be aligned. Specifically, not all magnetic lenses of a multi-beam particle microscope are actually accessible for alignment through the outer housing without any problems. For example, if alignment and fixation screws are used for mechanical alignment and fixation, it is immediately apparent that a technician must reach these screws specifically during purely manual mechanical alignment, which is typically the case when the screws to be adjusted are located near the wall of the housing of the multi-beam particle microscope, which wall is usually embodied in a tubular shape. For magnetic lenses that are further inside, this manual alignment is not possible.

[0024] The electrically controllable mechanical positioning and fastening means comprising the actuator system according to the present invention can, in principle, be embodied in one piece or in several pieces. It is also possible for the electrically controllable mechanical positioning and fastening means to comprise several electrically controllable mechanical positioning and fastening means. The term "means" therefore, by definition, encompasses both the singular "means" and the plural "means." According to a preferred embodiment of the present invention, the electrically controllable mechanical positioning and fastening means is multi-pieced and comprises an electrically controllable mechanical positioning means and an electrically controllable mechanical fastening means in the form of two separate structural units. In this case, it is still true that these structural units can be embodied in one piece or in several pieces, and it is also possible for the electrically controllable mechanical positioning means to comprise several electrically controllable mechanical positioning means and for the electrically controllable mechanical fastening means to comprise several electrically controllable mechanical fastening means.

[0025] However, it is of course also possible to provide a combination of electrically controllable mechanical positioning and fastening means with an actuator system, rather than functionally separating the positioning means on the one hand and the fastening means on the other hand. The functional subdivision ultimately depends on the structural type of the embodiment of the electrically controllable mechanical positioning and fastening means with an actuator system.

[0026] Alignment or alignment is properly understood to mean, in a very general sense, adjusting the position of the magnetic lens in the alignment plane. In contrast, fixation fixes the adjusted position by alignment. Fixation is therefore a constraint, and in the context of this patent application, the two terms are used synonymously. In this case, the fixing or constraint force is stronger than the prevailing force and preferably stronger than the applied actuator force. An actuator is defined in the context of this patent application very generally as a structural unit in terms of drive technology that converts an electrical signal into a mechanical movement and thus actively intervenes in the controlled process, i.e., alignment and / or fixation. According to the invention, the electrical signal or signals are generated by a controller, which may be a controller of the multi-beam particle microscope itself or a controller module, although in principle, a separate controller is also possible.

[0027] The term alignment means, in the context of this patent application, suggests a mounting or guidance of the means for alignment. The mounting or guidance can in this case be performed by conventional bearings, for example plain bearings, or by forced guidance via joints. Examples of this are hexapods, parallel kinematics, shear kinematics, flexures, etc. Plain bearings have the disadvantage that static friction must be overcome. This makes manual adjustment more difficult, since the point at which static friction is overcome is unpredictable and the adjustment can change suddenly. In this regard, electric actuator systems can, for example, reduce the threshold for static friction by means of vibrations, for example ultrasonic vibrations.

[0028] Actuator systems are limited by the associated force, range, and resolution or precision. In principle, actuators known per se can be used in the present invention. By way of example, linear or rotary motors, and combinations thereof, are in principle suitable. Piezoelectric elements are also known, for example piezoelectric stacks with small range and high force, or piezoelectric drives with any range but low force. Gear mechanisms for conversion can be used as well (for example a screw whose thread is driven by a rotary motor, which converts rotary motion into linear motion). Pneumatic or hydraulic actuators are also known and in principle suitable.

[0029] According to a preferred embodiment of the invention, the electrically controllable mechanical positioning means comprises as actuator a stepping motor with a gear mechanism. The gear mechanism is used for translation, and by a corresponding selection of the gear mechanism it is possible to achieve a high precision of positioning, for example an accuracy of 0.1 μm or better. In contrast, a purely manual mechanical positioning can usually achieve an accuracy of only about 10 μm.

[0030] The electrically controllable mechanical fastening means additionally or alternatively comprises a combination of a stepper motor and a piezoelectric element as actuator. This combination can be used in particular with a fastening screw as fastening means. In this case, it is possible to use a first actuator with a stepper motor to initially fasten the fastening means, e.g., a fastening screw, and only afterwards to use a second actuator in the form of a piezoelectric element. In this case, the piezoelectric element can apply a final contact pressure to the fastening means used, e.g., a fastening screw, thereby allowing for an overall better fastening.

[0031] According to one preferred embodiment of the invention, the electrically controllable mechanical fastening means very generally comprises at least one two-stage actuator system for generating the contact pressure of the fastening means. It is also possible to comprise, for example, a three-stage actuator system or a four-stage actuator system. In addition, the actuator combination can be supplemented with a mechanism for increasing and / or decreasing the contact force, and additionally or alternatively, a pneumatic system can also be provided.

[0032] According to a preferred embodiment of the present invention, the actuators used are electrically unloaded during operation of the multi-beam particle microscope. That is, the actuators used do not require a supply current or voltage during operation of the multi-beam particle microscope, although, of course, a mechanical load is still present on the actuators. In this case, operation should be understood to mean that the normal operation of the multi-beam particle microscope has been completed, i.e., the routine operation after alignment and fixation. The lack of electrical load therefore avoids possible parasitic effects caused by existing fields, making the operation of the multi-beam particle microscope more energy-efficient and sustainable.

[0033] According to a preferred embodiment of the present invention, the electrically controllable mechanical alignment means is configured for alignment in Cartesian coordinates and includes two first alignment units arranged orthogonally to each other for aligning 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 relates to the direction in which alignment is performed using each of the two first alignment units. In this case, the two first alignment units can be, but do not have to be, structurally identical. Additionally, the bearing or interaction regions of the two first alignment units, together with the alignable magnetic lens or its mount, can be arranged so that the portions between the bearing regions and the optical axis of the multi-beam particle microscope are perpendicular to each other. This allows for the optimal possible mounting location and most efficient alignment of the alignable magnetic lens in the particle optical beam path due to the rotational symmetry typically achieved with magnetic lenses.

[0034] According to a preferred embodiment of the present invention, two first alignment units arranged orthogonally to each other are arranged on the housing, each of the first alignment units being movable in a plane orthogonal to the optical axis by means of an actuator assigned to the pressure screw and comprising a pressure screw coupled to at least one magnetic lens via a magnetic lens mount for changing the position of the magnetic lens. According to the present invention, the thrust acting on such pressure screw is typically 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 magnetic lens mount is embodied as a clamping ring, and the pressure screw presses against this clamping ring from the outside.

[0035] According to a preferred embodiment of the present invention, each of the counter bearings is provided on the housing at a position radially opposite the first alignment unit with respect to the optical axis. The counter bearings can be embodied, for example, as spring assemblies.

[0036] According to an alternative embodiment of the invention, an associated second alignment unit, particularly a structurally identical second alignment unit, is provided on the housing at a position radially opposite the first alignment unit with respect to the optical axis, and the controller is configured to control the associated first and second alignment units to cooperate with each other in opposite directions. The controller may thus, for example, change the position of the first alignment unit by dx and the associated second alignment unit by a corresponding -dx. The use of associated first and second alignment units may further increase alignment accuracy, since possible inaccuracies in parts of the counter-bearing are eliminated or replaced by the precisely known position of the second alignment unit.

[0037] According to a preferred embodiment of the present invention, the electrically controllable mechanical fixing means comprises a plurality of separate fixing units, in particular fixing screws, each of which acts on an element of the mount of at least one alignable magnetic lens, thereby fixing the position of the at least one alignable magnetic lens. For example, two, three, four or even more fixing units can be provided. Particularly preferably, four separate fixing units are provided, which are, for example, arranged on the outside with respect to the alignable magnetic lens, alternating with the first and second positioning units in the circumferential direction. In this example, the fixing unit is therefore always located between two alignment units (regardless of whether it is the first alignment unit or the second alignment unit).

[0038] According to a preferred embodiment of the invention, the fixing is performed by frictional forces or geometric blocking. Fixing by frictional forces is advantageous, for example, when the mount of the alignable magnetic lens is not fixedly connected to the lens. For example, if a clamping ring is provided as the mount of the magnetic lens, the clamping ring can only move axially and is not connected to the lens. When the clamping ring is fixed, the position of the magnetic lens is likewise fixed indirectly, in particular by frictional forces resulting from the contact pressure of the fixing means. If the mount or the clamping ring is not fixedly connected to the lens, this allows for freer movement during alignment of the magnetic lens.

[0039] According to an alternative embodiment of the invention, the mount, and in particular the clamping ring, is fixed to the lens and follows the lens during alignment, with the set screws being attached so that movement of the lens is then geometrically blocked, and in particular ideally blocked both axially and radially.

[0040] According to a preferred embodiment of the invention, the fixing direction is oblique to the optical axis of the multi-beam particle microscope and also oblique to the alignment plane, which results in the alignable magnetic lens being fixed both radially and axially by a mount, e.g., a clamping ring.

[0041] According to a preferred embodiment of the present invention, a plurality of fixing units are respectively arranged between adjacent alignment units or between an alignment unit and an opposing bearing adjacent to the alignment unit, in the circumferential direction around the magnetic lens, which allows for very uniform and secure fixing.

[0042] According to a further preferred embodiment of the present invention, the electrically controllable mechanical alignment and fastening means are designed not as two separate, functionally distinct structural units, but as a combined electrically controllable mechanical alignment and fastening means. Unlike the above-described variant of the embodiment with functionally separate structural units, this variant of the present invention cannot be retrofitted into existing systems. In this variant of the embodiment, for example, the alignable magnetic lens can be coupled to an actuator via a fixed connection, such as a flexure, which can move the magnetic lens back and forth. In this way, it is possible to require just one actuator per alignment direction, i.e., in the x- or y-direction, for example, and counter-bearings, such as spring assemblies, and it is no longer necessary to have first and second alignment units facing each other.

[0043] According to a preferred embodiment of the invention, the combination of electrically controllable mechanical alignment and fixing means comprises a plurality of structurally identical combinations of electrically controllable mechanical alignment and fixing means, for example it is possible to have two combined electrically controllable mechanical alignment and fixing means so that alignment in Cartesian coordinates can be achieved.

[0044] According to a preferred embodiment of the present invention, at least one alignable magnetic lens comprises a lens pot and a lens cover, and the lens pot and / or lens cover can be aligned and fixed independently of one another using electrically controllable mechanical alignment and fixing means. For example, each alignable magnetic lens can be provided with two electrically controllable mechanical alignment and fixing means, each with an actuator system, which can be subdivided into multiple means and structural and / or alignment units, as already described above. Separate alignment of the lens pot on the one hand and the lens cover on the other hand has the advantage that possible tilts of the alignable magnetic lens can also be corrected. In particular, if the lens pot on the one hand and the lens cover on the other hand are not centrally positioned one above the other, this corresponds to a tilt of the magnetic field axis. Interestingly, this allows for the simulation of tilt without actually tilting mechanical parts for this purpose.

[0045] According to a further preferred embodiment of the present invention, the at least one alignable magnetic lens is further alignable and fixable in the direction of the optical axis of the system by means of this electrically controllable mechanical alignment and fixation means or by means of another electrically controllable mechanical alignment and fixation means, in other words, alignment in the z direction can also be performed by means of a corresponding actuator system.

[0046] According to a further preferred embodiment of the present invention, the multi-beam particle microscope comprises a user interface for the controller. Control of the electrically controllable mechanical alignment and fixation means can thus be performed electronically via the user interface. The user interface preferably also comprises an image display unit for displaying a particle-optical image. The particle-optical image may, for example, be recorded together with the current alignment adjustment values ​​and may enable a technician to draw conclusions about the state or progress of the alignment.

[0047] In a preferred embodiment of the present invention, the user interface is remote from the multi-beam particle microscope and is configured for remote maintenance of the multi-beam particle microscope. Remote maintenance is possible due to the fact that on-site technicians no longer need to manually perform mechanical alignment. The fact that multi-beam particle microscopes at customer premises are often integrated into process chains or production facilities that are difficult to access no longer poses any problems for the alignment of the magnetic lens. Furthermore, since the necessary actuator systems and corresponding wiring can be simultaneously integrated into the multi-beam particle microscope from the beginning, more magnetic lens alignments are possible in principle than were possible with prior art. Accessibility near the particle beam microscope housing is no longer necessarily required. Additionally, electrically controllable mechanical alignment and fixation using an actuator system offers the additional advantage of being able to log alignments. It is also possible to leave an alignment location and then return to it precisely, which is practically impossible with manual alignment. Furthermore, it is possible to fully automate alignment and develop alignment algorithms for alignment in order to quickly and efficiently achieve optimal adjustment of the magnetic lens.

[0048] According to a further aspect of the invention, the invention therefore relates to a method for aligning a multi-beam particle microscope as described in the above embodiment variants, the method comprising the following steps: a) operating a multi-beam particle microscope comprising a number N of actuated magnetic lenses, each of which comprises electrically controllable mechanical positioning and fixing means comprising an actuator system, each actuator system enabling movement of one of the N magnetic lenses with one or more degrees of freedom f. The total number of degrees of freedom available during the positioning of the actuated magnetic lenses is therefore given by the sum of all degrees of freedom f of all actuated magnetic lenses. Thus, by way of example, if 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 multiple degrees of freedom, for example 2, 3 or even more, in particular if the lens socket on the one hand and the lens cover on the other hand are independently positionable. b) for each actuated magnetic lens and for each degree of freedom of the actuated magnetic lens, determining the sensitivity to changes in position and, based on the determined sensitivities, determining the associated influence vectors; c) generating a particle optical image by a multi-beam particle microscope and checking the image aberration; d) Determining the total aberration vector of the identified image aberrations. e) performing a singular value decomposition of the total aberration vector with respect to the identified influence vector, and identifying a manipulated variable for each actuated magnetic lens and for each degree of freedom of the actuated magnetic lens based on the singular value decomposition; f) electrically controlling, by the controller, the mechanical positioning and fixing means of the actuated magnetic lens in response to the ascertained manipulation amount, to reduce or eliminate image aberrations.

[0049] The method according to the invention is therefore based on linear systems theory, which assumes that the individual elements behave linearly and that the behavior of the whole system is linearly constructed from the individual elements, and this assumption of linear systems theory is always valid, at least locally.

[0050] According to a preferred embodiment of the present invention, the method further comprises the following steps: g) Producing a further optical image by multi-beam particle microscope and checking for residual image aberrations. h) if the residual image aberration is greater than a predetermined upper limit, iteratively performing method steps d) to g). This iterative procedure is particularly useful when, as a result of nonlinearities, it is not possible to immediately obtain a total aberration vector below a threshold, for example.

[0051] According to a further preferred embodiment of the present invention, the method further comprises: - determining the influence vectors for different operating points of the multi-beam particle microscope; and / or Storing the influence vector in a look-up table. This has the advantage that the multi-beam particle microscope can be aligned for each operating point of the multi-beam particle microscope, thereby increasing the overall resolution and accuracy that can be achieved with the multi-beam particle microscope. Different operating points are understood in this case to mean, for example, different beam currents, different incident energies, different working distances, etc. Various other ambient parameters of the multi-beam particle microscope, such as the ambient temperature around the multi-beam particle microscope, can also be included in the definition of the operating point. In this case, depending on the selection of the operating point, the best possible alignment can be called up or set using a look-up table.

[0052] According to a further embodiment of the invention, the method is carried out in the form of remote maintenance of the multi-beam particle microscope, whereby an on-site system engineer is no longer absolutely necessary, at least as far as the alignment itself is concerned, thereby saving time and costs.

[0053] According to a third aspect of the present invention, the present invention relates to a computer program product having a program code for executing the method described in the variants of the above embodiments. The program code can be programmed in any desired programming language. The program code can be subdivided into modules. The program code can be executed, for example, by a controller of a multi-beam particle microscope or by an associated computer system.

[0054] The present invention may be better understood with reference to the accompanying drawings. [Brief explanation of the drawings]

[0055] [Figure 1] FIG. 1 is a schematic diagram of a multi-beam particle microscope (MSEM). [Figure 2] FIG. 10 is a diagram illustrating an outline of alignment of a magnetic lens in Cartesian coordinates. [Figure 3] FIG. 2 shows a schematic diagram of electrically controllable mechanical alignment and fixation of a global magnetic lens according to a first embodiment. [Figure 4] FIG. 10 is a diagram illustrating a schematic of electrically controllable mechanical alignment and fixation of a global magnetic lens according to a second embodiment. [Figure 5] FIG. 10 is a diagram illustrating a schematic of electrically controllable mechanical alignment and fixation of a global magnetic lens according to a third embodiment. [Figure 6] FIG. 10 shows a schematic diagram of an electrically controllable mechanical alignment means comprising a stepper motor with a gear mechanism. [Figure 7] 1 shows a schematic diagram of an electrically controllable mechanical fixing means comprising a two-stage actuator system with a stepper motor and a piezoelectric element. [Figure 8] 8 is a diagram illustrating the functional principle of the two-stage actuator system shown in FIG. 7. [Figure 9]1A and 1B show a schematic diagram of a method for aligning a multi-beam particle microscope according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0056] FIG. 1 is a schematic illustration of a particle beam system 1 in the form of a multi-beam particle microscope 1 that uses multiple particle beams. The particle beam system 1 generates multiple particle beams that are incident on an object under test to generate interaction products therein, such as secondary electrons, that are emitted from the object and subsequently detected. The particle beam system 1 is of the scanning electron microscope (SEM) type and uses multiple primary particle beams 3 that are incident on multiple locations 5 on the surface of the object 7 and generate multiple spatially separated electron beam spots or spots therein. The object under test 7 can be of any desired type, such as a semiconductor wafer or a biological sample, and can comprise an array of miniaturized elements or the like. The surface of the object 7 is located in a first plane 101 (object plane) of an objective lens 102 of an objective lens system 100.

[0057] Enlarged detail I1 of Figure 1 shows a plan view of an object plane 101 with a regular rectangular field 103 of incidence locations 5 formed in a first plane 101. In Figure 1, the number of incidence locations is 25, forming a 5 x 5 field 103. The number of incidence locations, 25, is chosen to simplify the illustration. The number of beams, and therefore the number of incidence locations, can in practice be chosen to be much larger, for example 20 x 30, 100 x 100, etc.

[0058] In the illustrated embodiment, the field 103 of incidence locations 5 is a substantially regular rectangular field with a constant pitch P1 between adjacent incidence locations. Exemplary values ​​for the pitch P1 are 1 micrometer, 10 micrometers, and 40 micrometers. However, it is possible for the field 103 to have other symmetries, such as, for example, a hexagonal symmetry.

[0059] The diameter of the beam spot formed at the first plane 101 can be small. Exemplary values ​​for this diameter are 1 nanometer, 5 nanometers, 10 nanometers, 100 nanometers, and 200 nanometers. The focusing of the particle beam 3 to form the beam spot 5 is performed by the objective lens system 100.

[0060] Primary particles incident on the object generate interaction products, such as secondary electrons, backscattered electrons, or primary particles that have traveled back for other reasons, which are emitted from the surface or first plane 101 of the object 7. The interaction products emitted from the surface of the object 7 are shaped by an objective lens 102 to form a secondary particle beam 9. The particle beam system 1 comprises a particle beam path 11 that directs the multiple secondary particle beams 9 to a detector system 200. The detector system 200 comprises a particle optical unit that comprises a projection lens 205 for directing the secondary particle beams 9 to a particle multi-detector 209.

[0061] Detail I2 of Figure 1 shows a plan view of plane 211 in which the individual detection areas of particle multi-detector 209 are located, with secondary particle beam 9 incident at locations 213. The incident locations 213 lie within field 217 and have a regular pitch P2 relative to one another. Exemplary values ​​for pitch P2 are 10 micrometers, 100 micrometers, and 200 micrometers.

[0062] The primary particle beam 3 is generated in a beam generator 300 comprising at least one particle source 301 (e.g., an electron source), at least one collimation lens 303, a multi-aperture array 305, and a field lens 307. The particle source 301 generates a diffuse particle beam 309, which is collimated, or at least substantially collimated, by the collimation lens 303 to shape a beam 311 that illuminates the multi-aperture array 305.

[0063] Detail I3 of FIG. 1 shows a plan view of the multi-aperture array 305. The multi-aperture array 305 includes a multi-aperture plate 313 having a plurality of openings or apertures 315 formed therein. Center points 317 of the openings 315 are located in a field 319 that is imaged onto a field 103 formed by the beam spots 5 at the object plane 101. The pitch P3 between the center points 317 of the apertures 315 can have exemplary values ​​of 5 micrometers, 100 micrometers, and 200 micrometers. The diameter D of the apertures 315 is shorter than the pitch P3 between the center points of the apertures. Exemplary values ​​of the diameter D are 0.2×P3, 0.4×P3, and 0.8×P3.

[0064] Particles of the illumination particle beam 311 pass through the aperture 315 and form the particle beam 3. Particles of the illumination beam 311 that are incident on the plate 313 are absorbed by the plate 313 and do not contribute to the formation of the particle beam 3.

[0065] The multi-aperture array 305 focuses each of the particle beams 3 such that, due to the applied electrostatic field, a beam focus 323 is formed at a plane 325. The beam focus 323 may alternatively be a virtual focus. The diameter of the beam focus 323 may be, for example, 10 nanometers, 100 nanometers, and 1 micrometer.

[0066] The field lens 307 and the objective lens 102 realize a first imaging particle-optical unit for imaging a plane 325 where the beam focus 323 is formed onto the first plane 101, whereby a field 103 of incidence locations 5 or beam spots results in the first plane 101. If the surface of an object 7 is arranged in the first plane, a corresponding beam spot is formed on the surface of the object.

[0067] The objective lens 102 and the projection lens array 205 realize a second imaging particle-optical unit, which images the first plane 101 onto the detection plane 211. The objective lens 102 is therefore a lens that is part of both the first particle-optical unit and the second particle-optical unit, 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.

[0068] The beam switch 400 is disposed in the beam path of the first particle-optical unit between the multi-aperture array 305 and the objective lens system 100. The beam switch 400 is also part of the second optical unit and is in the beam path between the objective lens system 100 and the detector system 200.

[0069] Further information on such multi-beam particle beam systems and the components used therein, such as particle sources, multi-aperture plates, and lenses, can be found in WO 2005 / 024881, WO 2007 / 028595, WO 2007 / 028596, WO 2011 / 124352, and WO 2007 / 060017, as well as DE 102013016113 and DE 102013014976, the full disclosures of which are incorporated herein by reference.

[0070] The multiple particle beam system 1 further comprises a computer system 10 configured to control the individual particle optical components of the multiple particle beam system and to evaluate and analyze the signals obtained by the multi-detector 209. The computer system 10 can be constructed by several individual computers or components.

[0071] The multi-beam particle microscope 1 according to Fig. 1 may comprise components according to the invention, namely in particular one or more alignable magnetic lenses and electrically controllable mechanical alignment and fixing means. The computer system 10 may comprise a controller according to the invention, although the controller may also be provided separately.

[0072] FIG. 2 shows a schematic diagram of the alignment of the magnetic lens 500 in Cartesian coordinates. The illustration shows a cross section of the magnetic lens 500, with the plane of the drawing corresponding to the alignment plane of the magnetic lens 500. The alignment plane is spanned by the vectors x and y. The optical axis of the system or multi-beam particle microscope 1 is oriented perpendicular to the alignment plane and extends along the z direction. The portion shown diagrammatically in FIG. 2 extends through the lens pod of the magnetic lens 500. The magnetic lens 500 is held by a mount 510, which in this example is embodied in the form of a clamping ring 510. The clamping ring holds the magnetic lens 500 in place by clamping, i.e., by friction. The clamping ring also extends in the z direction, thus securely clamping the lens pod of the magnetic lens 500. The magnetic lens 500, along with its mount 510, is disposed within a housing 520. The housing 520, in the illustrated example, is a tubular section that may form the outer housing of the multi-beam particle microscope. However, the housing may be embodied in various ways, and the specific shape and design of the housing will depend largely on where the alignable magnetic lens 500 is actually located in the particle-light beam path. In this regard, the illustration of Figure 2 should be understood to be merely an example.

[0073] When the magnetic lens 500 is properly aligned, the fanned particle beam or multiple individual particle beams 3 pass centrally through the aperture 504 of the magnetic lens 500, and a central ray or beams centrally located within the field of the multi-beam particle beam are directed through the magnetic lens center of the magnetic lens 500. In this case, the magnetic lens center may be slightly offset from the geometric lens center because it is impossible to accurately predict how the magnetic field generated by the magnetic lens 500 will actually be shaped based on the geometric and mechanical properties of the magnetic lens 500. Therefore, accurate alignment is necessary for accurate use of the multi-beam particle microscope 1.

[0074] In the illustrated example, alignment screws 501 are used for alignment. The screws are pressed against a clamping ring 510 via attachment points or regions 505 in the x- or y-direction, respectively, for alignment, displacing the magnetic lens 500 held within the clamping ring 510 in the x- or y-direction, respectively. This displacement function is indicated by the double-headed arrows in FIG. 2 . The displacement required for alignment is typically about 1-2 mm. In practice, larger displacements are usually not required. In the illustrated example, opposing bearings 502, embodied in the form of spring assemblies, are located radially opposite each of the alignment screws 501. In this way, the entire magnetic lens 500 can follow the movement of the alignment screws 501 in the alignment plane x and y.

[0075] 2 shows, in addition to the alignment means 501 shown, fixation means in the form of fixing screws 503, each of which acts on a clamping ring 510, by means of which the position of the magnetic lens 500 can be fixed. In the example shown, the fixation direction of the fixing screws 503 is indicated by a single arrow, which in this case is oriented obliquely with respect to the optical axis z and with respect to the alignment plane (x, y plane). This corresponding oblique fixation makes it possible to fix the magnetic lens 500 both radially and axially (z-direction).

[0076] FIG. 3 then shows a schematic diagram of electrically controllable mechanical alignment and fixation of the global magnetic lens 500 according to the first embodiment. While in FIG. 2 the mechanical alignment is performed entirely manually, FIG. 3 shows electrically controllable mechanical alignment and fixation according to the present invention using an actuator system. The alignment screw 501 is no longer manually operated in this case, but is provided with an alignment actuator 530. The controller 10 electrically controls the actuator 530. This allows for very accurate, documentable, and precise alignment of the alignment screw 501. Similarly, the fixing screw 503 is connected or coupled to a fixing actuator 531. This actuator 531 is also electrically controlled by the controller 10. The embodiment variant shown in FIG. 3 shows, in principle, a variant of an embodiment that can be retrofitted. However, it should be noted that the embodiment variant shown in FIG. 3 is merely an example and should in no way be understood as limiting the present invention.

[0077] FIG. 4 shows a schematic diagram of electrically controllable mechanical alignment and fixation of a global magnetic lens 500 according to a second embodiment. Compared to the variant of the embodiment shown in FIG. 3, in FIG. 4 the counter bearing or spring assembly 502 is replaced by an alignment screw 501 and an actuator system 530 coupled to the alignment screw 501. This obviously results in more signal lines 801-808. However, in this case, signals from alignment means associated with specific alignment directions are coupled to each other. The signals on lines 801 and 805 control first and second alignment units 530, 501 associated with each other, which position the magnetic lens 500 in the x-direction, in opposite directions and in coordination with each other. The first and second alignment units 530, 501 assigned to each other may here be structurally identical, but this does not have to be the case. In a similar manner, the signals on wires 803 and 807 of the first and second alignment units 530, 501 that align the magnetic lens 500 in the y-direction are linked to each other and controlled in opposite directions. After alignment is performed, the four fixed units 531, 503 are then controlled via signal lines 802, 804, 806, and 808.

[0078] In a variant of the embodiment shown in Figures 3 and 4, the electrically controllable mechanical positioning and fastening means is divided into parts and designed in the form of two separate structural units (one structural unit for positioning, which is further divided into parts, and another structural unit for fastening, which is further divided into parts). However, it is of course also possible to embody the electrically controllable mechanical positioning and fastening means as one structural unit. This requires that the electrically controllable mechanical positioning and fastening means be equipped with an actuator system and, on the other hand, a restraining device, which are combined in one part. In this case, it is possible to dispense with separate fastening means.

[0079] FIG. 5 schematically illustrates electrically controllable mechanical alignment and fixation of a global magnetic lens 500 according to a third embodiment. In this embodiment, the electrically controllable mechanical alignment and fixation means is realized by a combined structural unit used for both alignment and fixation. According to a variant shown in FIG. 5, the combined alignment and fixation means realizes separate alignment and fixation means for each alignment direction. That is, the combined alignment and fixation means is further embodied in multiple parts. In the illustrated example, the magnetic lens 500 is coupled to actuators 540 via fixed connections, such as flexures 541, such that each actuator 540 can displace the magnetic lens 500 in the positive and negative x- or y-directions, respectively. As a result, only one actuator 540 is required for each alignment in the x- or y-direction, respectively.

[0080] Furthermore, it is also possible to allow the lens pot and lens cover of the magnetic lens 500 to be aligned independently of each other, which makes it possible to simulate tilt of the magnetic lens 500 and also to perform tilt correction of the particle beam system 1 if the lens pot and lens cover are not exactly centered relative to each other.

[0081] Additionally or alternatively, it is also possible to provide further actuation elements in the direction of the optical axis (z-direction), which can, for example, compensate for thermal influences. According to a further preferred embodiment of the invention, the at least one adjustable magnetic lens 500 is furthermore alignable and fixable in the direction of the optical axis of the system (z-direction) by means of this electrically controllable mechanical alignment and fixation means or by means of another electrically controllable mechanical alignment and fixation means. In other words, alignment in the z-direction can also be performed by means of a corresponding actuator system.

[0082] While the actuators 530, 531, and 540 are shown only conceptually in FIGS. 3-5, FIGS. 6 and 7 show schematic diagrams of specific embodiments of the actuator systems for alignment and fixation, respectively. FIG. 6 shows a schematic diagram of an electrically controllable mechanical alignment means 530, comprising a stepper motor 534 with a gear mechanism. The motor 535 causes the gear mechanism 534 to rotate, which, in turn, translates the pressure pin 532 in interaction with the pin. A step counter 536 allows the position of the pressure pin 532 to be determined, thus documenting the alignment. The motor 535 and the step counter 536 are connected to the controller 10 for this purpose. The alignment actuator 530 can be directly or indirectly coupled to the magnetic lens 500 (not shown) to be aligned via a flange 533. The flange 533 can, for example, be fastened or screwed to the housing 520 of the multi-beam particle microscope 1. Typical dimensions of the exemplary embodiment shown in Figure 6 are a few centimetres in length and less than 2cm in diameter. Achievable thrust forces are greater than 150N, for example greater than 180N, with alignment accuracies of 0.01µm or better.

[0083] Figure 6 shows an example of an actuator system with a linear gear mechanism. However, it is of course also possible to use a bevel gear mechanism instead of or in addition to the linear gear mechanism. In this case, the choice of gear mechanism can be adapted to the available construction space / geometry.

[0084] FIG. 7 shows a schematic diagram of an electrically controllable mechanical fixing means 531, which includes a two-stage actuator system with a stepping motor 552 and a piezoelectric element 554. In the illustrated example, the two-stage actuator system is arranged in a housing 553 with a cover 555. A plunger 550 is movably arranged inside a bushing 551 and can be translated by a motor 552. A relatively large stroke can be achieved by the motor 552. While the stroke of the piezoelectric actuator 554 is relatively small, the second stage provides additional contact pressure, which causes the fixing element, the plunger 550, to press directly or indirectly against the magnetic lens 500 to fix the magnetic lens 500. This two-stage actuator system has proven advantageous when it is necessary to apply the largest possible fixing or holding force to the magnetic lens 500 or to elements of the mount 510 for the magnetic lens 500. At least in the case of the second stage of the actuator system (piezoelectric actuator 554), no rotation is required to apply the holding force, which allows for greater precision and a greater holding / contact pressure.

[0085] Figure 8 shows the functional principle of the two-stage actuator system shown in Figure 7. The situation without applied contact pressure or holding force is shown in the upper part of Figure 8.

[0086] The first stage of the actuator system is shown in the center of Figure 8. A negative voltage is applied to piezoelectric actuator 554, causing it to contract, i.e., become shorter. A mechanical prestress is built up. In addition, spindle-equipped motor 552 is controlled to drive plunger 550 to move axially, so that the entire unit is supported between the mount of magnetic lens 500 and fixedly positioned piezoelectric actuator 554. The bearings are only indicated diagrammatically in Figure 8 by bearing areas 560 and 570.

[0087] In the second stage of the actuator system (see the illustration at the bottom of FIG. 8 ), the voltage is switched off again and the piezoelectric actuator 554 tries to lengthen further. The mechanical prestress of the piezoelectric actuator 554 now presses the motor 552 together with the spindle, which in turn presses the plunger 550. In this way, a high fixing force can be established on the mount 510 of the magnetic lens 500 or on the clamping ring 510 mentioned above.

[0088] In the case of the embodiment of the actuator system described in more detail as an example, it is advantageous that the actuator system can operate without electrical load during operation of the multi-beam particle microscope 1. This means that no voltage needs to be applied to the actuator during normal operation of the multi-beam particle microscope 1, i.e. no electromagnetic fields that could contribute to parasitic effects are present due to the actuator system. This fact should further be evaluated positively in terms of the sustainability of the multi-beam particle microscope 1.

[0089] 9 shows a schematic diagram of a method for aligning a multi-beam particle microscope 1 according to the present invention. The method for aligning a multi-beam particle microscope can be realized by applying linear systems theory. It is at least a locally valid expression that the individual elements of a system behave linearly and that the behavior of the entire system is linearly constructed from the individual elements. With this in mind, the method for aligning a multi-beam particle microscope 1 can be designed, for example, as follows:

[0090] A first method step S1 comprises operating a multi-beam particle microscope 1 comprising a number N of actuated magnetic lenses 500, each of the magnetic lenses 500 being provided with electrically controllable mechanical positioning and fixing means comprising an actuator system, each actuator system enabling movement of one of the N magnetic lenses 500 with one or more degrees of freedom f.

[0091] A second method step S2 comprises determining, for each actuated magnetic lens 500 and for each degree of freedom f of the actuated magnetic lens 500, the sensitivity to position changes and, based on the determined sensitivities, determining the associated influence vectors.

[0092] A further method step S3 comprises generating a particle optical image by means of the multi-beam particle microscope 1 and checking the image aberrations.

[0093] A fourth method step S4 comprises determining the total aberration vector of the identified image aberrations.

[0094] A further method step S5 comprises performing a singular value decomposition of the total aberration vector for the identified influence vectors and identifying, based on the singular value decomposition, the manipulated variable for each actuated magnetic lens 500 and for each degree of freedom f of each actuated magnetic lens 500.

[0095] A further method step S6 comprises electrically controlling, by the controller, the mechanical positioning and fixing means of the magnetic lens 500 which are actuated in response to the ascertained manipulation amount in order to reduce or eliminate image aberrations.

[0096] A further method step S7 comprises generating a further particle optical image by means of the multi-beam particle microscope 1 and checking the residual image aberration. If this residual image aberration is below a predetermined upper limit, the method ends in method step S8. Otherwise, method steps S4 to S7 are repeated.

[0097] It is possible to ascertain the influence vectors for different operating points of the multi-beam particle microscope 1 and / or to store the influence vectors in a look-up table. In this way, an optimal alignment for different operating points can be achieved. This type of alignment of the magnetic lens may even be actually performed for the first time for different operating points.

[0098] The monitored alignment and repeatability, as well as the electronic control of the alignment, further enable the above-described method for aligning the multi-beam particle microscope 1 to be performed as a form of remote maintenance. Therefore, there is no need for a technician to perform the alignment on-site. Furthermore, even in the case of a multi-beam particle microscope installed in a production facility, it is possible to perform the alignment, or realignment if appropriate, without significant disruption to the overall operation.

[0099] The present invention enables automatic alignment of multi-beam particle microscopes with high beam energies. For example, at high beam energies above 10 keV, especially above 20 keV, and especially in multi-beam systems, beam deflection, for example using electrostatic deflectors, becomes more difficult. According to the present invention, alignment is instead performed by mechanical repositioning, particularly of magnetic lenses. In this case, the exemplary embodiment describes lateral repositioning. Equivalent repositioning includes tilting the magnetic lenses in at least one direction. Mechanical repositioning also generally includes offsetting the magnetic lenses in the axial, i.e., Z, direction. In addition to the magnetic lenses, the mechanical position of electrostatic elements can also be changed.

[0100] (Explanation of symbols) 1. Multibeam particle microscope 3 Primary particle beam (individual particle beam) 5 Beam spot, incident point 7 Object 9 Secondary particle beam (individual particle beam) 10 Computer system, controller 11 Secondary particle beam path 13 Primary particle beam path 25 Sample surface, wafer surface 100 Objective Lens System 101 Object surface 102 Objective Lens 103 Field 200 detector system 205 Projection Lens 209 Particle Multi-Detector 211 Detection surface 213 Incidence location 215 detection area 217 Field 300 Beam Generator 301 Particle source 303 Collimation lens system, condenser lens system 305 Multi-aperture array, multi-beam generator 307 Field Lens 309 Diffuse Particle Beam 311 Irradiation Particle Beam 313 Multi-aperture plate 315 Multi-aperture plate opening 317 Center point of opening 319 Field 323 Beam Focus 325 Intermediate image plane 327 Field 400 Beam Switch 500 magnetic lens 501 Precision Thread Alignment Screw 502 Opposed bearing, spring assembly 503 Fixing screw 504 Opening 505 Alignment mounting points or areas 506 Fixed attachment points or areas 507 Mounting points or areas for opposing bearings 510 Mount, Clamping Ring 520 chassis 530 Positioning actuator 531 Fixing Actuator 532 Pressure Pin 533 flange 534 Gear Mechanism 535 Motor 536 Step Counter 540 Alignment and Fixation Actuator 541 Connecting elements, e.g., flexures 550 pressure element, e.g. plunger 551 Bush 552 Motor with spindle 553 Case 554 Piezoelectric Actuator 555 Case Cover 560 bearing area 570 Bearing area 801 signal line 802 signal line 803 signal line 804 signal line 805 signal line 806 signal line 807 Signal Line 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 said beam of charged particles passes; a multi-beam generator arranged downstream of the focusing lens system in a direction of particle beam paths, such that at least some of the charged particles pass through an opening of the multi-beam generator in the form of a plurality of individual particle beams, and configured to generate a first field of a plurality of charged first particle beams; a first particle-optical unit comprising a first particle-optical beam path configured to image the generated first individual particle beam onto a sample surface in an object plane, whereby the first particle beam is incident on the sample surface at an incidence location and forms a second field; a detection system comprising a number of detection regions forming a third field; a second particle-optical unit comprising a second particle-optical beam path and configured to image a second individual particle beam emitted from the incidence location of 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 individual particle beam and the second individual particle beam pass; a beam switch disposed in the first particle-light beam path between the multi-beam generator and the objective lens and in the second particle-light beam path between the objective lens and the detection system; a controller configured to electrically control the electrically controllable mechanical alignment and fixation means; Equipped with the collecting lens system and / or the first particle-optical unit and / or the second particle-optical unit comprises at least one alignable magnetic lens arranged in a housing using a mount so that charged particles pass through it; a multi-beam particle microscope, wherein the electrically controllable mechanical positioning and fixing means comprising an actuator system is further provided for the at least one positionable magnetic lens, the means being configured to mechanically align and mechanically fix the position of the at least one positionable magnetic lens in the particle light beam path in a plane perpendicular to an optical axis of the multi-beam particle microscope.

2. 2. The multi-beam particle microscope according to claim 1, wherein the electrically controllable mechanical positioning and fixing means is divided into several parts and comprises electrically controllable mechanical positioning means and electrically controllable mechanical fixing means in the form of two separate structural units.

3. the electrically controllable mechanical positioning means comprises a stepper motor with a gear mechanism as an actuator; and / or 3. The multi-beam particle microscope of claim 2, wherein the electrically controllable mechanical fixing means comprises a combination of a stepping motor and a piezoelectric element as an actuator.

4. 3. The multi-beam particle microscope of claim 2, wherein the electrically controllable mechanical clamping means comprises at least a two-stage actuator system for generating a contact pressure of the clamping means.

5. 3. The multi-beam particle microscope of claim 2, wherein the electrically controllable mechanical alignment means is configured for alignment in Cartesian coordinates and comprises two first alignment units arranged orthogonally to each other for aligning the position of the at least one magnetic lens in the plane orthogonal to the optical axis of the multi-beam particle beam system.

6. 6. The multi-beam particle microscope according to claim 5, wherein each of the two first alignment units arranged orthogonally to each other is arranged on the housing, is movable in the plane orthogonal to the optical axis by means of an actuator assigned to a pressure screw, and comprises the pressure screw coupled to the at least one magnetic lens via the mount of the magnetic lens to change the position of the magnetic lens.

7. 7. The multi-beam particle microscope according to claim 6, wherein a counter bearing, in particular a spring assembly, is provided on the housing at a position diametrically opposite the first alignment unit with respect to the optical axis.

8. 7. The multi-beam particle microscope of claim 6, wherein any associated second alignment unit, in particular any associated structurally identical second alignment unit, is provided on the housing at a position radially opposite the first alignment unit with respect to the optical axis, and wherein the controller is configured to control the mutually associated first and second alignment units to cooperate with each other in opposite directions.

9. 3. The multi-beam particle microscope according to claim 2, wherein the electrically controllable mechanical fixing means comprises a plurality of separate fixing units, in particular fixing screws, each of which acts on an element of the mount of the at least one magnetic lens, thereby fixing the position of the at least one magnetic lens.

10. 10. The multi-beam particle microscope of claim 9, wherein the fixing is performed by frictional forces or by geometric blocking.

11. The multi-beam particle microscope according to claim 10 , wherein each of the plurality of fixing units is disposed between adjacent alignment units or between an alignment unit and an opposing bearing adjacent to the alignment unit.

12. 2. The multi-beam particle microscope according to claim 1, wherein the electrically controllable mechanical positioning and fixing means are not designed in the form of two separate structural units that are functionally distinct, but as a combination of electrically controllable mechanical positioning and fixing means.

13. 13. The multi-beam particle microscope according to claim 12, wherein the combination of electrically controllable mechanical positioning and fixing means comprises a plurality of, in particular structurally identical, combinations of electrically controllable mechanical positioning and fixing means.

14. 2. The multi-beam particle microscope of claim 1, wherein the at least one magnetic lens comprises a lens pot and a lens cover, and the lens pot and / or the lens cover are alignable and fixable independently of each other using the electrically controllable mechanical alignment and fixation means.

15. 2. The multi-beam particle microscope of claim 1, wherein the at least one magnetic lens is further alignable and fixable in the direction of the optical axis of the system using the electrically controllable mechanical alignment and fixation means or using another electrically controllable mechanical alignment and fixation means.

16. The multi-beam particle microscope of claim 1 , wherein the at least one magnetic lens is one of a condenser lens, a field lens, and a projection lens.

17. 2. The multi-beam particle microscope according to claim 1, wherein the actuators used are electrically unloaded during operation of the multi-beam particle microscope.

18. The multi-beam particle microscope of claim 1 , further comprising a user interface for the controller.

19. 20. The multi-beam particle microscope of claim 18, wherein the user interface is remote from the multi-beam particle beam system and configured 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 claims 1 to 19, said method comprising: a) operating the multi-beam particle microscope comprising a number N of actuated magnetic lenses, each of said magnetic lenses comprising electrically controllable mechanical positioning and fixing means comprising an actuator system, each actuator system enabling movement of one of said N magnetic lenses with one or more degrees of freedom f; b) for each actuated magnetic lens and for each degree of freedom of said actuated magnetic lens, determining a sensitivity to a change in position and, based on said determined sensitivities, determining an associated influence vector; c) generating a particle optical image by the multi-beam particle microscope and checking image aberrations; d) determining a total aberration vector of the identified image aberrations; e) performing a singular value decomposition of the total aberration vector with respect to the identified influence vector, and identifying, based on the singular value decomposition, manipulated variables for each actuated magnetic lens and for each degree of freedom of the actuated magnetic lens; f) electrically controlling, by the controller, the mechanical positioning and fixing means of the actuated magnetic lens in response to the determined amount of manipulation, to reduce or eliminate the image aberration; A method comprising:

21. g) generating a further particle-optical image with said multi-beam particle microscope to identify residual image aberrations; h) if the residual image aberration is greater than a predetermined upper limit, repeatedly performing method steps d) to g); 21. The method of claim 20, further comprising:

22. - determining the influence vectors for different operating points of the multi-beam particle microscope; and / or storing the influence vectors in a look-up table; 21. The method of claim 20, further comprising:

23. 21. The method of claim 20, wherein the method is performed in the form of remote maintenance of the multi-beam particle microscope.

24. 21. A computer program product having program code for performing the method of claim 20.

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