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 a related computer program product.

Background Art

[0002] As more and more miniaturized and more complex microstructures such as semiconductor components are continuously developed, it is necessary to further develop and optimize planar production techniques and inspection systems for producing and inspecting microstructures of small dimensions. For example, the development and production of semiconductor components require monitoring the design of test wafers, and planar production techniques require process optimization for high-throughput and reliable production. More recently, there have been requirements for the analysis of semiconductor wafers in reverse engineering and for semiconductor components with respect to customer-specific individual configurations. Therefore, in order to examine the microstructures on a wafer with high precision, inspection means that can be used with high throughput are required.

[0003] The diameter of a typical silicon wafer used in the production of semiconductor components is at most 300 mm. Each wafer is at most 800 mm 2It is divided into 30 to 60 repeating regions ( "dies" ) having a size of. The semiconductor device includes a plurality of semiconductor structures formed in layers on the surface of the wafer by planar integration techniques. The semiconductor wafer typically has a flat surface for the production process. In this case, the structure size of the integrated semiconductor structure ranges from several μm to a critical dimension (CD) of 5 nm, and in the near future, the structure size will become even smaller. The structure size or critical dimension (CD) is expected to be less than 3 nm in the future, for example 2 nm, or even less than 1 nm. In the case of the small structure sizes described above, defects in the size of the critical dimension must be quickly identified in a very wide area. In some applications, the specification requirements regarding the measurement accuracy achieved by inspection equipment are even higher, for example twice or one order of magnitude higher. As an example, the width of the semiconductor feature must be measured with an accuracy of less than 1 nm, for example 0.3 nm or less, and the relative position of the semiconductor structures must be determined with an overlay accuracy of less than 1 nm, for example 0.3 nm or less.

[0004] A multi-beam scanning electron microscope, MSEM (multi-beam scanning electron microscope), is a relatively newly developed device in the field of charged particle systems (charged particle microscopes, CPM: charged particle microscope). The multi-beam scanning electron microscope is disclosed, for example, in U.S. Patent No. 7,244,949 and U.S. Patent Application Publication No. 2019 / 0355544. In the case of a multi-beam electron microscope, i.e., MSEM, the sample is simultaneously irradiated with a plurality of individual electron beams arranged within a field or grid. As an example, 4 to 10,000 individual electron beams can be supplied as primary radiation, and each individual electron beam is separated from an adjacent individual electron beam by a pitch of 1 to 200 micrometers. As an example, the MSEM has about 100 separated individual electron beams ("beamlets"), which are arranged, for example, in a hexagonal grid, and the individual electron beams are separated by a pitch of about 10 μm. The plurality of 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 firmly held in a wafer holder mounted on a movable stage. While irradiating the wafer surface with the charged primary individual particle beams, interaction products, such as secondary electrons or backscattered electrons, are emitted from the surface of the wafer. The starting points of all secondary electrons coincide with the locations on the sample where the plurality of primary individual particle beams are focused. The amount and energy of the interaction products depend on the material composition and the surface shape of the wafer surface. The interaction products form a plurality of secondary individual particle beams (secondary beams), and the secondary beams are collected by a common objective lens and, as a result of the projection imaging system of the multi-beam inspection system, are incident on a detector arranged on the detection surface. The detector comprises a plurality of detection regions each having a plurality of detection pixels, and the detector captures the intensity distribution of each of the secondary individual particle beams. In this process, for example, an image plane of 100 μm × 100 μm is obtained.

[0005] Conventional multi-beam electron microscopes comprise a series of electrostatic and magnetic elements. At least some of the electrostatic and magnetic elements are adjustable to adapt the focal positions and spherical aberrations of a plurality of charged individual particle beams. Conventional multi-beam systems with charged particles further comprise at least one crossover plane of the primary or secondary charged individual particle beams. Conventional systems further comprise a detection system to facilitate adjustment. Conventional multi-beam particle microscopes comprise at least one beam deflector (“deflection scanner”) for collectively scanning a region of a sample surface with a plurality of primary individual particle beams to obtain an image plane of the sample surface. Further details regarding multi-beam electron microscopes and methods of operating the same are described in International Application Publication No. 2021239380, the disclosure of which is hereby incorporated by reference in its entirety into this patent application.

[0006] Alignment of a multi-beam electron microscope, or more generally a multi-beam particle microscope, is very important in precision applications. One aspect of 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 accurately. Furthermore, due to the geometric dimensions of such magnetic lenses, there is the fact that the magnetic fields generated by the lenses cannot be accurately estimated. In other words, the magnetic fields of lenses manufactured identically within the scope of manufacturing precision may actually differ from each other to a measurable extent, which is the reason why individual lens alignment is necessary.

[0007] According to the prior art, the magnetic lens of a multi-beam particle microscope is mechanically aligned, and an experienced technician manually performs the alignment of the magnetic lens. Such alignment often takes several weeks or even months. The alignment is performed by simultaneous observation of the image of the multi-beam particle microscope. The screws outside the multi-beam particle microscope or its housing are adjusted to align the magnetic lens. The alignment and subsequent fixation of the magnetic lens are usually performed during the trial operation at the time of production of the multi-beam particle microscope. The alignment is then usually retained without change and is only performed at the on-site within the customer's premises after module replacement or magnetic lens replacement. In this case, the update of the alignment at the on-site within the customer's premises is more difficult because the multi-beam particle microscope is often integrated into the production equipment and related process chains within the customer's premises. Therefore, there may be a long and costly downtime in the production equipment, which needs to 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 is provided with a beam forming unit for forming a plurality of charged particle beams on the sample, an energy control unit for controlling the incident energy of the plurality of charged particle beams irradiated on the sample, a beam current control unit for controlling the beam current of the plurality of charged particle beams irradiated on the sample, and a beam array control unit for controlling the array in which the plurality of charged particle beams are irradiated on the sample. The beam forming unit includes a beam splitting electrode, an upper lens array electrode, an intermediate lens array electrode, a lower lens array electrode, and a movable stage. By selecting a plurality of aperture pattern sets using the movable stage, it functions as a beam current control unit or a beam array control unit. U.S. Patent Application Publication No. 2013 / 0299697 does not address the specific problem of alignment of particle optical components. In particular, it does not deal with the alignment of the global magnetic lens.

[0009] British Patent No. 894569, published in 1962, discloses a device for correcting the axial aberration of an electron lens. This patent refers to a single-beam system and a particular objective lens which is an electron lens. The correction coils are movably arranged around the objective lens and outside the vacuum chamber. The objective lens itself is not mechanically aligned. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

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

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

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

[0013] In the case of a single-beam particle microscope, the alignment of the magnetic lens according to the prior art is no longer carried out only mechanically, but is carried out using a deflector which deflects the particle beam and guides it through the center of the magnetic lens. Therefore, in the case of a multi-beam particle microscope as well, it would seem to be an option to carry out the alignment or at least a fine alignment using an electrical and / or magnetic deflector. However, this approach has been found to be problematic as a result of a thorough investigation by the inventors and the like.

[0014] A multi-beam particle microscope typically uses an incident energy (landing energy) in the range of about 0.3 keV to about 5 keV, and for this purpose, a relatively high beam energy of about 30 keV is used within the column. Due to such high beam energy, a high electric field strength is also required to be able to deflect individual particle beams within the column. To use a high deflection electric field strength, a high voltage and / or a large current are further required, which is accompanied by parasitic effects that adversely affect the quality of the beam. Therefore, in the case of a multi-beam particle microscope, performing mechanical alignment is surprisingly excellent.

[0015] The present invention thus proposes an electrically controllable mechanical alignment. Thereby, the accuracy is improved and at the same time rapid alignment becomes possible.

Means for Solving the Problem

[0016] Specifically, according to a first aspect, the present invention relates to a multi-beam particle microscope for sample inspection, and the multi-beam particle microscope includes at least one particle source configured to generate a diffused beam of charged particles, a condenser lens system through which the beam of charged particles 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 the aperture of the multi-beam generator in the form of a plurality of individual particle beams, and configured to generate a first field of a large number of charged first particle beams, a first particle optical unit having a first particle optical beam path configured to image the generated first individual particle beam onto a sample surface of an object plane, whereby the first particle beam is incident on the sample surface at an incident location and forms a second field, a detection system including a large 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 an incident location of a second field onto a third field of a detection region of a 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 a first particle optical beam path between a multi-beam generator and the objective lens and in a second particle optical beam path between the objective lens and the detection system; A controller configured to electrically control electrically controllable mechanical alignment and fixation means; Comprising; The condenser lens system and / or the first particle optical unit and / or the second particle optical unit comprises at least one alignable magnetic lens disposed in a housing using a mount such that charged particles can pass through; Electrically controllable mechanical alignment and fixation means with an actuator system are further provided for at least one alignable magnetic lens, the means being configured to mechanically align and mechanically fix the position of at least one alignable magnetic lens in a plane orthogonal to the optical axis of the multi-beam particle microscope within the particle optical beam path.

[0017] The charged particles can be, for example, electrons, positrons, muons, or ions, or other charged particles. The charged particles are preferably electrons generated using, for example, a thermal field emission source (TFE). However, other particle sources can also be used.

[0018] The individual particle beams are, in this case, arranged in a grid pattern. That is, it is preferable that the arrangement of the individual particle beams relative to each other is fixed or selectable. This is preferably a regular grid pattern in which the individual particle beams can have a particularly uniform spacing relative to each other, for example, a square, rectangular, or hexagonal arrangement. It is advantageous if the number of individual particle beams is 3n(n - 1)+1, where n is any natural number.

[0019] The multi-beam particle microscope is preferably a system operating with a single column, but it is also possible to implement the multi-beam particle microscope with a multi-column system.

[0020] The condenser lens system and / or the first particle optical unit and / or the second particle optical unit comprise at least one alignable magnetic lens arranged in the housing using a mount so that charged particles can pass through. This adjustable magnetic lens can, in principle, be any of the magnetic lenses that are normally present in a multi-beam particle microscope. The magnetic lens is preferably a global magnetic lens through which a large number, in particular all, of the individual particle beams pass. However, it is also possible to place an alignable 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 diffuse beam of charged particles passes through this lens. Examples of alignable magnetic lenses include condenser lenses, field lenses, and projection lenses. An alignable magnetic lens in the context of this patent application is generally understood appropriately if it means a magnetic lens whose position in the particle optical beam path can be changed to target in a plane orthogonal to the optical axis of the system. The purpose of the alignment is, in this case, to direct a beam of charged particles or a number of individual particle beams parallel to the optical axis passing through the center of the magnetic lens. In this case, generally, the center of the magnetic lens does not exactly coincide 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] A mount for an alignable magnetic lens holds the magnetic lens in a predetermined position in principle, but gives the freedom of movement required for the alignment process. A typical mount for a magnetic lens is, for example, a so-called clamping ring that clamps the lens pot of the magnetic lens (the magnetic lens 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, and this housing may be, for example, the outer housing of a multi-beam particle microscope.

[0022] According to the present invention, an electrically controllable mechanical alignment and fixing means with an actuator system is provided for at least one alignable magnetic lens, and this means is configured to mechanically align and mechanically fix the position of at least one alignable magnetic lens in the particle light beam path in a plane orthogonal to the optical axis of the system. The aforementioned plane is hereinafter also referred to as the alignment plane. By maintaining mechanical alignment and fixation, parasitic effects that adversely affect the quality of the beam that occur in the case of electrical and / or magnetic deflection are avoided. Electrical control simultaneously enables advantages that cannot be achieved in the case of purely manual mechanical alignment with respect to the accuracy and reproducibility of alignment. With electrical control, it is possible to achieve an improvement of about 100 times with respect to the achievable accuracy of alignment.

[0023] Furthermore, by skillfully arranging electronically controllable mechanical alignment and fixing means, even magnetic lenses that could not be aligned manually before can be aligned. Specifically, not all magnetic lenses of a multi-beam particle microscope can actually be accessed without problems through the outer housing for alignment purposes. For example, when alignment screws and fixing screws are used for mechanical alignment and fixing, it is immediately obvious that the technician specifically needs to reach these screws during purely manual mechanical alignment, which typically applies when the screws to be adjusted are located near the wall of the housing of the multi-beam particle microscope, and this wall is usually embodied in a tubular form. In the case of magnetic lenses that are even further inside, this manual alignment is impossible.

[0024] The electronically controllable mechanical alignment and fixing means equipped with the actuator system according to the present invention can, in principle, be embodied integrally or divided into a plurality of parts. It is also possible for the electronically controllable mechanical alignment and fixing means to comprise a plurality of electronically controllable mechanical alignment and fixing means. The term "means" thus, by definition, encompasses both the singular "means" and the plural "means". According to a preferred embodiment of the present invention, the electronically controllable mechanical alignment and fixing means are divided into a plurality of parts and, in the form of two separate structural units, comprise electronically controllable mechanical alignment means and electronically controllable mechanical fixing means. In this case, it is still a fact that these structural units can be embodied integrally or divided into a plurality of parts, and it is also possible for the electronically controllable mechanical alignment means to comprise a plurality of electronically controllable mechanical alignment means and for the electronically controllable mechanical fixing means to comprise a plurality of electronically controllable mechanical fixing means.

[0025] However, instead of functionally separating the alignment means on one side and the fixing means on the other side, it is of course also possible to provide a combination of electrically controllable mechanical alignment and fixing means with an actuator system. The functional subdivision ultimately depends on the structural type of the embodiments of the electrically controllable mechanical alignment and fixing means with an actuator system.

[0026] Aligning or alignment generally means adjusting the position of the magnetic lens on the alignment surface. On the other hand, in the case of fixing, the position adjusted by alignment is fixed. Thus, fixing is restraint, and in the context of this patent application, these two terms are used synonymously. In this case, the fixing or restraining force is preferably stronger than the prevailing force and further stronger than the force of the actuator applied. An actuator is generally defined in the context of this patent application as a structural unit related to drive technology that converts an electrical signal into mechanical movement and thus actively intervenes in the controlled process, i.e., alignment and / or fixing. According to the present invention, one or more electrical signals are generated by a controller, which may be the controller of the multi-beam particle microscope itself or a module of the controller, but in principle, it is also possible to provide a separate controller.

[0027] The term "alignment means" in the context of this patent application implies the mounting or guidance of means for alignment. The mounting or guidance can, in this case, be carried out by conventional bearings such as sliding bearings, or by forced guidance via joints. Examples of this are hexapods, parallel kinematics, shear kinematics, flexures, etc. Sliding bearings have the disadvantage that they need to overcome static friction. This makes manual adjustment more difficult because the locations where static friction is overcome cannot be predicted and the adjustment can change suddenly. In this regard, an electric actuator system can lower the threshold of static friction, for example, by vibrations such as ultrasonic vibrations.

[0028] Actuator systems are limited by the associated forces, ranges, and resolution or accuracy. In principle, actuators known per se can be used in the present invention. As examples, linear motors or rotary motors, and combinations thereof are, in principle, suitable. Piezoelectric elements, for example, piezoelectric laminates with a narrow range and strong force, or piezoelectric drives with an arbitrary range but weak force are also known. Gear mechanisms for conversion can likewise be used (for example, a screw driven by a rotary motor, whereby the rotary motion is converted into a linear motion). Pneumatic or hydraulic actuators are also known and are, in principle, suitable.

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

[0030] The electrically controllable mechanical fixing means additionally or alternatively comprises a combination comprising a stepping motor and a piezoelectric element as actuators. This combination can in particular be used together with a fixing screw which is the fixing means. In this case, for example, in order to first fix the fixing means such as a fixing screw, a first actuator comprising a stepping motor is used, and only thereafter is it possible to use a second actuator in the form of a piezoelectric element. The piezoelectric element can in this case apply a final contact pressure to the fixing means used, such as a fixing screw, for example, so that overall better fixing is possible.

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

[0032] According to a preferred embodiment of the invention, the actuator used is electrically unloaded during the operation of the multi-beam particle microscope. That is, the actuator used does not require a supply current or supply voltage during the operation of the multi-beam particle microscope, although of course there is still a mechanical load on the actuator. In this case, the operation should be understood to mean that the normal operation of the multi-beam particle microscope, that is to say, in other words, the routine operation after alignment and fixing has ended. Therefore, the absence of an electrical load avoids parasitic effects that can occur depending on the presence, and the operation of the multi-beam particle microscope becomes more energy-efficient and more 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 comprises 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 with respect to each other is related to the direction in which alignment is performed using each of the two first alignment units. In this case, the two first alignment units may be structurally identical, but do not have to be structurally identical. In addition, the bearing regions or interaction regions of the two first alignment units can be arranged such that, together with the alignable magnetic lens or the mount of the magnetic lens, the portions between the bearing regions and the optical axis of the multi-beam particle microscope are perpendicular to each other. This enables the most optimal mounting position and the most efficient alignment of the alignable magnetic lens in the particle optical beam path due to the rotational symmetry usually obtained with magnetic lenses.

[0034] 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 of the first alignment units is movable in a plane orthogonal to the optical axis using an actuator assigned to a pressure screw, and comprises a pressure screw coupled to at least one magnetic lens via a mount of the magnetic lens to change the position of the magnetic lens. According to the present invention, the thrust acting on such a pressure screw typically exceeds 150 N, preferably exceeds 170 N, and most preferably exceeds 180 N. According to a preferred embodiment of the present invention, the mount of the magnetic lens is embodied as a clamping ring, and the pressure screw presses this clamping ring from the outside.

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

[0036] According to an alternative embodiment of the present invention, any associated second alignment unit, in particular a structurally identical second alignment unit, is provided on the housing, radially opposite the first alignment unit with respect to the optical axis, and the controller is configured to control the mutually associated first and second alignment units to cooperate with each other in opposite directions. The controller thus changes the position by dx, for example, with the first position adjustment unit and correspondingly changes the position by -dx with the associated second position adjustment unit. By using the mutually associated first and second position adjustment units, inaccuracies that may occur in a part of the opposed bearing are not caused, or are replaced by the accurately known position of the second position adjustment unit, so that the alignment accuracy can be further increased.

[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 fixing unit acting on an element of the mount of at least one alignable magnetic lens, thereby fixing the position of at least one alignable magnetic lens. For example, it is possible to provide two, three, four or even more fixing units. Particularly preferably, it comprises four separate fixing units, which are provided, for example, to be arranged alternately in the circumferential direction with the first and second position adjustment units outside the alignable magnetic lens. The fixing units thus always lie between two alignment units in this example (irrespective of whether this is the first alignment unit or the second alignment unit).

[0038] According to a preferred embodiment of the present invention, the fixing is performed by frictional force or geometric blocking. Fixing by frictional force is advantageous, for example, when the mount of the alignable magnetic lens is not fixedly connected to the lens. As an example, when 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 also indirectly fixed, specifically by the frictional force generated from the contact pressure of the fixing means. When the mount or the clamping ring is not fixedly connected to the lens, this enables freer movement during the alignment of the magnetic lens.

[0039] According to an alternative embodiment of the present invention, the mount, particularly the clamping ring, is fixed to the lens and follows the lens during alignment. As a result of attaching the fixing screw, it is desirable that the movement of the lens is geometrically blocked at that time, specifically blocked in both the axial and radial directions.

[0040] According to a preferred embodiment of the present invention, the fixing direction is oblique with respect to the optical axis of the multi-beam particle microscope and also oblique with respect to the alignment plane. As a result, an alignable magnetic lens is fixed in both the radial and axial directions by a mount such as a clamping ring, for example.

[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 this alignment unit. Adjacent means in the circumferential direction around the magnetic lens. This enables a very uniform and reliable fixing.

[0042] According to a further preferred embodiment of the present invention, the electrically controllable mechanical alignment and fixing means are not in the form of two functionally distinct separate structural units, but are designed as a combination of electrically controllable mechanical alignment and fixing means. Different from the variant of the embodiment of the functionally separate structural unit described above, the variant of this embodiment of the present invention cannot be retrofitted to an existing system. In a variant of this embodiment, for example, an alignable magnetic lens can be coupled to an actuator via a fixed connection such as a flexure, whereby this actuator can move the magnetic lens back and forth. In this way, it is also possible to require only one actuator for each alignment direction, i.e., for example, in the x-direction or the y-direction, and no longer require opposing bearings such as spring assemblies, nor the need to provide first and second alignment units facing each other.

[0043] According to a preferred embodiment of the present 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 provide 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 the lens cover can be aligned and fixed independently of each other using electrically controllable mechanical alignment and fixing means. For example, for each alignable magnetic lens, it is possible to provide a total of two electrically controllable mechanical alignment and fixing means each having an actuator system, and these means can be subdivided into a plurality of means and structural units and / or alignment units as already described above. By separately aligning the lens pot on the one hand and the lens cover on the other hand, as a result, the advantage is obtained that the inclination that can occur in the alignable magnetic lens can also be corrected. Specifically, if the lens pot is not arranged vertically above and below the center on the one hand and the lens cover on the other hand, this corresponds to an inclination of the axis of the magnetic field. What is interesting here is that in this way, the inclination can be simulated without actually tilting the mechanical parts for this purpose.

[0045] According to a further preferred embodiment of the present invention, at least one alignable magnetic lens can also be aligned and fixed in the direction of the optical axis of the system using this electrically controllable mechanical alignment and fixing means or using another electrically controllable mechanical alignment and fixing means. In other words, the alignment in the z direction can also be carried out using the 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. Therefore, it is possible to electrically control the electrically controllable mechanical alignment and fixing means via the user interface. The user interface preferably also comprises an image display unit for displaying the particle optical image. The particle optical image may be recorded, for example, together with the adjustment values of the current alignment, and may enable a technician to draw conclusions about the alignment state or progress.

[0047] In a preferred embodiment of the present invention, the user interface is provided remotely from the multi-beam particle microscope and is configured for remote maintenance of the multi-beam particle microscope. The ability to perform remote maintenance is due to the fact that on-site technicians no longer need to perform mechanical alignment manually. The fact that the multi-beam particle microscope on the customer's premises is often incorporated into a process chain or production facility that is difficult to access also no longer causes any problems here with respect to the alignment of the magnetic lenses. Furthermore, since the necessary actuator system and the corresponding wiring can be integrated into the multi-beam particle microscope simultaneously from the start, in principle, more magnetic lens alignments are possible than were possible with the prior art. Accessibility to the vicinity of the housing of the particle beam microscope is no longer necessarily required. In addition, there is the further advantage that an alignment log can be taken by means of electrically controllable mechanical alignment and fixation using the actuator system. It is also possible to leave the alignment location and then accurately return to that location later, which would not be possible with manual alignment in practice. Furthermore, it is possible to fully automate the alignment and develop an alignment algorithm for alignment in order to quickly and efficiently achieve optimal adjustment of the magnetic lenses.

[0048] According to a further aspect of the present invention, the present invention thus relates to a method of aligning a multi-beam particle microscope, as described in a variation of the above-described plurality of embodiments, the method comprising the following steps. a) Operating a multi-beam particle microscope comprising a plurality of N actuated magnetic lenses, each of the magnetic lenses comprising electrically controllable mechanical alignment and fixation means comprising an actuator system, each actuator system enabling the movement of one of the N magnetic lenses having one or more degrees of freedom f. The total number of degrees of freedom available during the alignment of the actuated magnetic lenses is thus given by the sum of all degrees of freedom f of all actuated magnetic lenses. Thus, as an 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, such as two, three, or more, specifically, for example, when the lens pot and the lens cover can be individually aligned on the one hand and on the other hand. b) For each actuated magnetic lens and for each degree of freedom of the actuated magnetic lens, checking the sensitivity of the change in position and, based on the checked sensitivity, checking the associated influence vector. c) Generating a particle optical image with the multi-beam particle microscope and checking for image aberrations. d) Determining the total aberration vector of the checked image aberrations. e) Performing a singular value decomposition of the total aberration vector with respect to the checked influence vectors and, based on the singular value decomposition, checking the operation amounts for each actuated magnetic lens and for each degree of freedom of the actuated magnetic lenses. And, f) Electrically controlling the mechanical alignment and fixation means of the actuated magnetic lenses by a controller according to the checked operation amounts in order to reduce or eliminate the image aberrations.

[0049] Thus, the method according to the invention is based on linear system theory. It is assumed that the individual elements behave linearly and that the behavior of the entire system is linearly composed of the individual elements. This assumption of linear system theory is always valid at least locally.

[0050] According to a preferred embodiment of the present invention, this method further includes the following steps. g) Generating a further optical image by a multi-beam particle microscope and checking for remaining image aberrations. h) If the remaining image aberrations are greater than a predetermined upper limit, repeatedly executing method steps d) to g). This iterative procedure is particularly useful as a result of non-linearity, for example when a total aberration vector below a threshold cannot be obtained immediately.

[0051] According to an even more preferred embodiment of the present invention, this method further includes the following. Checking an influence vector for various 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 alignment of the multi-beam particle microscope can be adjusted for each operating point of the multi-beam particle microscope, thereby overall improving the resolution and accuracy achievable with the multi-beam particle microscope. By various operating points is meant in this case, for example, various beam currents, various incident energies, various working distances, etc. It is also possible to include various other ambient parameters of the multi-beam particle microscope, such as the ambient temperature around the multi-beam particle microscope, in the definition of the operating point. In this case, depending on the choice of the operating point, it is possible to call or set the most optimal alignment possible using the look-up table.

[0052] According to a further embodiment of the present invention, this method is carried out in the form of remote maintenance of the multi-beam particle microscope. At least as far as the alignment itself is concerned, on-site system engineers are no longer absolutely necessary, thereby saving time and cost.

[0053] According to a third aspect of the present invention, the present invention relates to a computer program product having program code for executing the methods described in the variations of the above-described embodiments. The program code can in this case be programmed in any desired programming language. The program code can be subdivided into a plurality of 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 will be more suitably understood with reference to the accompanying drawings.

Brief Description of the Drawings

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Figure 9

DETAILED DESCRIPTION OF THE INVENTION

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

[0057] The enlarged detail I1 of FIG. 1 shows a plan view of the object plane 101 having a regular rectangular field 103 of incident locations 5 formed on the first plane 101. In FIG. 1, the number of incident locations is 25, and these form a 5×5 field 103. The number 25, which is the number of incident locations, is a number selected to simplify the explanatory diagram. The number of beams, and thus the number of incident locations, can actually be selected to be much larger numbers, such as 20×30, 100×100, etc.

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

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

[0060] The primary particles incident on the object generate interaction products, such as secondary electrons, backscattered electrons, or primary particles that have moved back for other reasons, and the interaction products are emitted from the surface of the object 7 or 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 includes a particle beam path 11 that guides a plurality of secondary particle beams 9 to the detector system 200. The detector system 200 comprises a particle optical unit including a projection lens 205 for directing the secondary particle beam 9 towards the particle multi-detector 209.

[0061] Detail I2 of FIG. 1 shows a plan view of a plane 211 in which individual detection regions of the particle multi-detector 209, where the secondary particle beam 9 is incident at location 213, are located. The incident location 213 is within the field 217 and has a regular pitch P2 relative to each other. Exemplary values of the pitch P2 are 10 micrometers, 100 micrometers, and 200 micrometers.

[0062] The primary particle beam 3 is generated by 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, and the diffuse particle beam is collimated or at least substantially collimated by the collimation lens 303 to form a beam 311 that irradiates the multi-aperture array 305.

[0063] Detail I3 of FIG. 1 shows a plan view of a multi-aperture array 305. The multi-aperture array 305 includes a multi-aperture plate 313, and the multi-aperture plate 313 has a plurality of openings or apertures 315 formed therein. The center points 317 of the apertures 315 are arranged in a field 319 that is imaged onto the field 103 formed by the beam spot 5 on 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 aperture 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] The particles of the irradiation particle beam 311 pass through the apertures 315 to form the particle beam 3. The particles of the irradiation beam 311 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 a beam focus 323 is formed on a plane 325 due to the applied electrostatic field. The beam focus 323 can alternatively be a virtual focus. The diameter of the beam focus 323 can 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 the plane 325 on which the beam focus 323 is formed onto the first plane 101, whereby the incident location 5 or the field 103 of the beam spot occurs on the first plane 101. When the surface of the object 7 is arranged on the first plane, a beam spot is correspondingly 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 that images the first plane 101 onto the detection surface 211. The objective lens 102 is thus 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 arranged in the beam path between the multi-aperture array 305 and the objective lens system 100 of the first particle optical unit. The beam switch 400 is further 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 regarding such a multi-beam particle beam system and the components used therein, such as particle sources, multi-aperture plates, and lenses, etc., can be obtained from International Application Publication No. WO 2005 / 024881, International Application Publication No. WO 2007 / 028595, International Application Publication No. WO 2007 / 028596, International Application Publication No. WO 2011 / 124352, and International Application Publication No. WO 2007 / 060017, as well as German Patent Application Publication No. DE 102013016113 and German Patent Application Publication No. DE 102013014976, the entire disclosures of which are incorporated herein by reference.

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

[0071] The multi-beam particle microscope 1 according to FIG. 1 can comprise parts 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 can comprise a controller according to the invention, but the controller can also be provided separately.

[0072] FIG. 2 schematically shows the alignment mode of the magnetic lens 500 in orthogonal coordinates. The explanatory drawing shows a cross-section of the magnetic lens 500, and the plane of the drawing corresponds to the alignment plane of the magnetic lens 500. The alignment plane extends by the vectors x and y. The optical axis of the system or the multi-beam particle microscope 1 is directed perpendicular to the alignment plane, and the optical axis extends along the z direction. The part schematically shown in FIG. 2 extends through the lens pot 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 a predetermined position by clamping, i.e. by frictional force. The clamping ring also has an extension in the z direction, and in this way securely clamps the lens pot of the magnetic lens 500. The magnetic lens 500 is arranged together with its mount 510 in a housing 520. The housing 520 is, in the example shown, a tubular part that can form the outer housing of the multi-beam particle microscope. However, the housing can also be embodied in various ways, and the specific shape and design of the housing depend largely on the location where the alignable magnetic lens 500 within the particle light beam path is actually arranged. In this regard, it should be understood that the explanatory drawing of FIG. 2 is merely an example.

[0073] When the magnetic lens 500 is correctly aligned, the fan-shaped or multiple individual particle beams 3 that spread out pass centrally through the aperture 504 of the magnetic lens 500, and the beam centered within the field of the central ray or multi-beam particle beam is guided through the magnetic lens center of the magnetic lens 500. In this case, it is impossible to accurately predict how the magnetic field generated by the magnetic lens 500 is actually shaped based on the geometric and mechanical characteristics of the magnetic lens 500, so the magnetic lens center may deviate slightly from the geometric lens center. Therefore, precise use of the multi-beam particle microscope 1 requires accurate alignment.

[0074] In the illustrated example, alignment screws 501 are used for alignment. These screws are pressed against the clamping ring 510 in the x-direction or y-direction respectively via the mounting points or mounting areas 505 for alignment, and in this way, the magnetic lens 500 held within the clamping ring 510 is displaced in the x-direction or y-direction respectively. This displacement function is indicated by double-headed arrows in both cases in Figure 2. The displacement required for alignment is typically about 1 - 2 mm. In practice, displacements larger than this are usually not necessary. In the illustrated example, on each opposite side of the alignment screw 501 in the radial direction, respective opposing bearings 502 embodied in the form of spring assemblies are arranged. In this way, the entire magnetic lens 500 can follow the movement of the alignment screw 501 within the alignment planes x and y.

[0075] Figure 2 shows fixing means in the form of fixing screws 503 in addition to the shown alignment means 501. Each of the fixing screws 503 acts on the clamping ring 510, by which the position of the magnetic lens 500 can be fixed. In the illustrated example, the fixing direction of the fixing screw 503 is indicated by a single-headed arrow. In this case, the fixing direction is inclined with respect to the optical axis z and also inclined with respect to the alignment plane (x, y plane). By fixing in this corresponding inclined direction, it is possible to fix the magnetic lens 500 in both the radial direction and the axial direction (z-direction).

[0076] Next, FIG. 3 schematically shows the electrically controllable mechanical alignment and fixation of the global magnetic lens 500 according to the first embodiment. In FIG. 2, the mechanical alignment is entirely manual, whereas FIG. 3 shows the electrically controllable mechanical alignment and fixation according to the present invention using an actuator system. In this case, the alignment screw 501 no longer operates manually, but an alignment actuator 530 is provided. The controller 10 electrically controls the actuator 530. This enables a very accurate and documentable precise alignment of the alignment screw 501. Similarly, the fixing screw 503 is connected or coupled to a fixing actuator 531. Such an actuator 531 is also electrically controlled by the controller 10. The modification of the embodiment shown in FIG. 3 shows, in principle, a modification of the retrofittable embodiment. However, it should be pointed out that the modification of the embodiment shown in FIG. 3 is merely an example and in no way limits the present invention.

[0077] Figure 4 schematically shows the electrically controllable mechanical alignment and fixation of the global magnetic lens 500 according to the second embodiment. Compared with the variant of the embodiment shown in Figure 3, in Figure 4, the opposed bearing or spring assembly 502 is replaced by an alignment screw 501 and an actuator system 530 coupled to the alignment screw 501. As a result, clearly more signal lines 801 - 808 are provided. However, in this case, signals from the alignment means related to a specific alignment direction are coupled to each other. The signals of the wirings 801 and 805 control the first and second alignment units 530, 501, which are related to each other and position the magnetic lens 500 in the x - direction, in opposite directions and in cooperation with each other. The first and second alignment units 530, 501 assigned to each other may be structurally identical here, but do not necessarily have to be. In a similar manner, the signals of the wirings 803 and 807 of the first and second alignment units 530, 501 that align the magnetic lens 500 in the y - direction cooperate with each other and the control is performed in opposite directions. After the alignment is executed, the four fixing units 531, 503 are then controlled via the signal lines 802, 804, 806, and 808.

[0078] In the variants of the embodiments shown in Figures 3 and 4, the electrically controllable mechanical alignment and fixation means are divided into multiple parts and designed in the form of two separate structural units (one structural unit for alignment, which is further divided into multiple parts, and another structural unit for fixation, which is also further divided into multiple parts). However, of course, it is also possible to embody the electrically controllable mechanical alignment and fixation means as one structural unit. For this, it is necessary to equip the electrically controllable mechanical alignment and fixation means with an actuator system combined in one part on the one hand and a restraint on the other hand. In this case, it is possible to do without separate fixing means.

[0079] FIG. 5 schematically shows the electrically controllable mechanical alignment and fixation of the global magnetic lens 500 according to the third embodiment. The electrically controllable mechanical alignment and fixation means are realized in this embodiment by a combined structural unit that is used for both alignment and fixation. According to the variant shown in FIG. 5, this combined alignment and fixation means realizes alignment means and fixation means respectively for each alignment direction. That is, the combined alignment and fixation means are further divided into a plurality of parts for implementation. In the illustrated example, the magnetic lens 500 is coupled to the actuator 540 via a fixed connection part such as a flexure 541, whereby each of the actuators 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 alignment in each of the x or y directions.

[0080] Furthermore, it is also possible to enable the lens pot and the lens cover of the magnetic lens 500 to be aligned separately from each other. If the lens pot and the lens cover are not accurately centered with respect to each other, it is thereby possible to simulate the tilt of the magnetic lens 500 and also possible to perform correction of the tilt of the particle beam system 1.

[0081] Additionally or alternatively, in the direction of the optical axis (z direction), it is also possible to provide another operating element that can compensate for, for example, the influence of heat. According to a further preferred embodiment of the present invention, at least one adjustable magnetic lens 500 can be further aligned and fixed in the direction of the optical axis (z direction) of the system using this electrically controllable mechanical alignment and fixation means or using another electrically controllable mechanical alignment and fixation means. In other words, alignment in the z direction can also be performed using a corresponding actuator system.

[0082] Actuators 530, 531, 540 are shown only conceptually in FIGS. 3 to 5, but FIGS. 6 and 7 schematically show specific embodiments of the alignment and fixing actuator system, respectively. FIG. 6 schematically shows an electrically controllable mechanical alignment means 530 comprising a stepping motor 534 with a gear mechanism. Motor 535 causes the gear mechanism 534 to perform a rotational movement, resulting in a translational movement of the pressure pin 532 due to the interaction with the pin. The position of the pressure pin 532 can be determined by the step counter 536, and thus the alignment can be documented. 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 connected to a magnetic lens 500 (not shown) to be aligned via the flange 533. The flange 533 can be firmly attached or screwed, for example, to the housing 520 of the multi-beam particle microscope 1. The typical dimensions of the exemplary embodiment shown in FIG. 6 are a length of several centimeters and a diameter of less than 2 cm. The achievable thrust is more than 150 N, for example more than 180 N, and the alignment accuracy is 0.01 μm or more.

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

[0084] FIG. 7 schematically shows an electrically controllable mechanical fixing means 531 comprising a two-stage actuator system with a stepping motor 552 and a piezoelectric element 554. In the example shown, the two-stage actuator system is arranged within a housing 553 with a cover 555. The plunger 550 is movably arranged inside a bush 551 and can be translated by the motor 552. The motor 552 can achieve a relatively large stroke. The stroke of the piezoelectric actuator 554 is relatively small, but since the second stage provides an additional contact pressure, the plunger 550, which is the fixing element, presses directly or indirectly on the magnetic lens 500 to fix the magnetic lens 500. This two-stage actuator system has proven to be advantageous when it is necessary to apply the largest possible fixing force or holding force to the magnetic lens 500 or an element of the mount 510 of the magnetic lens 500. At least in the case of the second stage of the actuator system (the piezoelectric actuator 554), rotation is not required when applying the holding force, which thereby increases the accuracy and makes it possible to increase the holding pressure / contact pressure.

[0085] FIG. 8 shows the functional principle of the two-stage actuator system shown in FIG. 7. The situation without applying contact pressure or holding force is shown at the top of FIG. 8.

[0086] The first stage of the actuator system is shown in the center of FIG. 8. A negative voltage is applied to the piezoelectric actuator 554, whereby the piezoelectric actuator 554 contracts, i.e., becomes shorter. Mechanical prestress is accumulated. In addition, the motor 552 with a spindle is controlled and the plunger 550 is driven to move axially so that the whole unit is supported between the mount of the magnetic lens 500 and the piezoelectric actuator 554 fixedly arranged. The bearings are only schematically shown in FIG. 8 by bearing regions 560 and 570.

[0087] In the second stage of the actuator system (see the explanatory diagram at the bottom of FIG. 8), the voltage is switched off again, and the piezoelectric actuator 554 attempts to become longer. At this time, the mechanical prestress of the piezoelectric actuator 554 presses the motor 552 together with the spindle, and the spindle mediates to press the plunger 550. In this way, it is possible to establish a high fixing force on the mount 510 of the magnetic lens 500 or the above-mentioned clamping ring 510.

[0088] In the case of the embodiment of the actuator system described in more detail as an example, the actuator system is advantageous in that it can operate without an electrical load during the operation of the multi-beam particle microscope 1. This means that during the normal operation of the multi-beam particle microscope 1, it is not necessary to apply a voltage to the actuator, that is, there is no electromagnetic field that may contribute to parasitic effects by the actuator system. This fact should be positively evaluated in terms of the sustainability of the multi-beam particle microscope 1.

[0089] FIG. 9 schematically shows a method for aligning the multi-beam particle microscope 1 according to the present invention. The method for aligning the multi-beam particle microscope can be realized by applying linear system theory. The fact that the individual elements of the system behave linearly and the behavior of the entire system is linearly composed of the individual elements is at least a locally valid representation. Against this background, the method for aligning the multi-beam particle microscope 1 can be designed, for example, as follows.

[0090] The first method step S1 includes the step of operating a multi-beam particle microscope 1 including a large number of N actuated magnetic lenses 500, each of the magnetic lenses 500 having electrically controllable mechanical alignment and fixing means including an actuator system, and each actuator system enables the movement of one of the N magnetic lenses 500 having one or more degrees of freedom f.

[0091] The second method step S2 includes, for each activated magnetic lens 500 and for each degree of freedom f of the activated magnetic lens 500, checking the sensitivity of the change in position and checking the associated influence vector based on the checked sensitivity.

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

[0093] The fourth method step S4 includes determining the total aberration vector of the checked image aberrations.

[0094] A further method step S5 includes performing a singular value decomposition of the total aberration vector with respect to the checked influence vectors and checking the operation amount for each activated magnetic lens 500 and for each degree of freedom f of the activated magnetic lens 500 based on the singular value decomposition.

[0095] A further method step S6 includes electrically controlling the mechanical alignment and fixing means of the activated magnetic lens 500 by the controller according to the checked operation amount in order to reduce or eliminate the image aberration.

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

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

[0098] The alignment to be monitored, the reproducibility of the alignment, and the electrical control of the alignment further enable the method of aligning the multi-beam particle microscope 1 described above to be carried out in the form of remote maintenance. Therefore, it is not necessary 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 re-alignment if appropriate, without a significant obstacle to the overall operation and without a significant obstacle to the overall operation.

[0099] According to the present invention, automatic alignment of a multi-beam particle microscope using high beam energy becomes possible. For example, in the case of high beam energy exceeding 10 keV, particularly exceeding 20 keV, and especially in the case of a multi-beam system, beam deflection using, for example, an electrostatic deflector becomes more difficult. According to the present invention, the alignment is instead carried out particularly by mechanical repositioning of a magnetic lens. In this case, in an exemplary embodiment, the lateral repositioning is described. Equivalent repositioning includes tilting of at least one direction of the magnetic lens. Mechanical repositioning generally also includes an offset of the magnetic lens in the axial direction, that is, the Z direction. In addition to the magnetic lens, the mechanical position of an electrostatic element can also be changed.

[0100] (Description of reference numerals) 1 Multi-beam particle microscope 3 Primary particle beam (individual particle beam) 5 Beam spot, incident location 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 plane 102 Objective lens 103 Field 200 Detector system 205 Projection lens 209 Particle Multi-Detector 211 Detection Surface 213 Incident Location 215 Detection Region 217 Field 300 Beam Generation Device 301 Particle Source 303 Collimation Lens System, Condensing Lens System 305 Multi-Aperture Array, Multi-Beam Generator 307 Field Lens 309 Diffused Particle Beam 311 Irradiated Particle Beam 313 Multi-Aperture Plate 315 Aperture of Multi-Aperture Plate 317 Center Point of Aperture 319 Field 323 Beam Focus 325 Intermediate Image Plane 327 Field 400 Beam Switch 500 Magnetic Lens 501 Alignment Screw with Precision Thread 502 Opposing Bearing, Spring Assembly 503 Fixing Screw 504 Aperture 505 Alignment Mounting Point or Mounting Area 506 Fixing Mounting Point or Mounting Area 507 Mounting Point or Mounting Area for Opposing Bearing 510 Mount, Clamping Ring 520 Housing 530 Alignment Actuator 531 Fixing Actuator 532 Pressure Pin 533 Flange 534 Gear Mechanism 535 Motor 536 Step Counter 540 Alignment and Fixing Actuator 541 Connecting Element, e.g. Flexure 550 Pressure element, e.g., plunger 551 Bush 552 Motor with spindle 553 Housing 554 Piezoelectric actuator 555 Housing 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, wherein the multi-beam particle microscope comprises: at least one particle source configured to generate a diffused beam of charged particles; a condenser lens system through which the beam of charged particles 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 aperture of the multi-beam generator in the form of a plurality of individual particle beams, and configured to generate a first field of a number 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 of an object plane, whereby the first particle beam is incident on the sample surface at an incident 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 configured to image a second individual particle beam emitted from the incident location of the second field onto the third field of the detection regions 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 arranged in the first particle optical beam path between the multi-beam generator and the objective lens and arranged in the second particle optical beam path between the objective lens and the detection system; a controller configured to electrically control electrically controllable mechanical alignment and fixation means; and wherein the condenser 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 such that charged particles can pass through; the electrically controllable mechanical alignment and fixation means provided with an actuator system is further provided for the at least one alignable magnetic lens, and the means is configured to mechanically align and mechanically fix the position of the at least one alignable magnetic lens within the particle optical beam path in a plane orthogonal to the optical axis of the multi-beam particle microscope. A multi-beam particle microscope.

2. The electrically controllable mechanical alignment and fixing means are divided into a plurality of parts and are in the form of two separate structural units, comprising electrically controllable mechanical alignment means and electrically controllable mechanical fixing means, the multi-beam particle microscope according to claim 1.

3. The electrically controllable mechanical alignment means comprises a stepping motor with a gear mechanism as an actuator, and / or The electrically controllable mechanical fixing means comprises a combination comprising a stepping motor and a piezoelectric element as actuators, the multi-beam particle microscope according to claim 2.

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

5. 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, the multi-beam particle microscope according to any one of claims 2 to 4.

6. Each of the two first alignment units arranged orthogonally to each other is arranged on the housing and is movable in the plane orthogonal to the optical axis using 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 for changing the position of the magnetic lens, the multi-beam particle microscope according to claim 5.

7. Both the opposing bearings, in particular the spring assembly, are provided on the housing at a position radially opposite to the first alignment unit with respect to the optical axis, the multi-beam particle microscope according to claim 6.

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

9. The electrically controllable mechanical fixing means comprises a plurality of separate fixing units, in particular fixing screws, each of said fixing units acting on an element of the mount of said at least one magnetic lens, thereby fixing the position of said at least one magnetic lens. The multi-beam particle microscope according to any one of claims 2 to 8.

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

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

12. The multi-beam particle microscope according to claim 1, wherein the electrically controllable mechanical alignment and fixing means is not in the form of two separate structural units with different functions, but is designed as a combination of electrically controllable mechanical alignment and fixing means.

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

14. The at least one magnetic lens comprises a lens pot and a lens cover, and the lens pot and / or the lens cover can be aligned and fixed independently of each other using the electrically controllable mechanical alignment and fixing means. The multi-beam particle microscope according to any one of claims 1 to 13.

15. The at least one magnetic lens can be further aligned and fixed in the direction of the optical axis of the system using the electrically controllable mechanical alignment and fixing means or using another electrically controllable mechanical alignment and fixing means. The multi-beam particle microscope according to any one of claims 1 to 14.

16. The at least one magnetic lens is one of a condenser lens, a field lens, and a projection lens. The multi-beam particle microscope according to any one of claims 1 to 15.

17. The multi-beam particle microscope according to any one of claims 1 to 16, wherein during operation of the multi-beam particle microscope, the actuator used is electrically unloaded.

18. The multi-beam particle microscope according to any one of claims 1 to 17, comprising the user interface for the controller.

19. The multi-beam particle microscope according to claim 18, wherein the user interface is provided remotely from the multi-beam particle beam system and is set for remote maintenance of the multi-beam particle beam system.

20. A method of aligning the multi-beam particle microscope according to any one of claims 1 to 19, the method comprising: a) operating the multi-beam particle microscope comprising a number of N actuated magnetic lenses, each of the magnetic lenses comprising electrically controllable mechanical alignment and fixing means comprising an actuator system, each actuator system enabling movement of one of the N magnetic lenses having one or more degrees of freedom f; b) for each actuated magnetic lens and for each degree of freedom of the actuated magnetic lens, checking the sensitivity of the change in position and checking the associated influence vector based on the checked sensitivity; c) generating a particle optical image with the multi-beam particle microscope and checking for image aberrations; d) determining the total aberration vector of the checked image aberrations; e) performing singular value decomposition of the total aberration vector with respect to the checked influence vector and checking the operation amount 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 the mechanical alignment and fixing means of the actuated magnetic lens by the controller according to the checked operation amount to reduce or eliminate the image aberration A method comprising.

21. g) generating a further particle optical image with the multi-beam particle microscope and checking for residual image aberrations; h) repeating method steps d) to g) if the residual image aberration is greater than a predetermined upper limit The method according to claim 20, further comprising.

22. The step of checking the influence vectors for various operating points of the multi-beam particle microscope, and / or the step of storing the influence vectors in a look-up table The method according to claim 20 or 21, further comprising.

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

24. A computer program product having program code for executing the method according to any one of claims 20 to 23.

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