DE102020125534B3 - Multiple particle beam microscope and associated process with fast autofocus at an adjustable working distance - Google Patents

Abstract

The invention relates to a multitude particle beam microscope and an associated method with fast autofocus around an adjustable working distance. A fast autofocus correction lens and other fast correction means are proposed in order to set a high-frequency adaptation of the focusing, the position, the landing angle and the rotation of individual particle beams when they strike a wafer surface during the wafer inspection. The fast autofocus correction lens can in particular be implemented by electrostatic elements which are arranged at specially selected positions in the particle-optical beam path. In an analogous manner, rapid autofocusing can take place in the secondary path of the particle beam system.

Description

Field of invention

The invention relates to a plurality of particle beam microscopes for inspecting semiconductor wafers with HV structures.

State of the art

With the continuous development of ever smaller and more complex microstructures such as semiconductor devices, there is a need to further develop and optimize planar manufacturing techniques and inspection systems for manufacturing and inspecting small dimensions of the microstructures. For example, the development and manufacture of the semiconductor devices requires a review of the design of test wafers, and the planar manufacturing techniques require process optimization for reliable, high-throughput manufacture. In addition, an analysis of semiconductor wafers for reverse engineering and a customer-specific, individual configuration of semiconductor components has recently been required. There is therefore a need for inspection means which can be used with high throughput for inspecting the microstructures on wafers with high accuracy.

Typical silicon wafers used in the manufacture of semiconductor components have diameters of up to 300 mm. Each wafer is divided into 30 to 60 repeating regions ("dies") with a size of up to 800 mm ² . A semiconductor device comprises a plurality of semiconductor structures which are produced by planar integration techniques in layers on a surface of the wafer. Due to the manufacturing processes, semiconductor wafers typically have a flat surface. The structure size of the integrated semiconductor structures ranges from a few µm to the critical dimensions (CD) of 5 nm, with the structure sizes becoming even smaller in the near future; In future, structure sizes or critical dimensions (CD) below 3 nm, for example 2 nm, or even below 1 nm are expected. With the small structure sizes mentioned above, defects of the size of the critical dimensions must be identified in a short time on a very large area. For several applications, the specification requirement for the accuracy of a measurement provided by an inspection device is even higher, for example by a factor of two or an order of magnitude. For example, a width of a semiconductor feature must be measured with an accuracy of less than 1 nm, for example 0.3 nm or even less, and a relative position of semiconductor structures must be determined with an overlay accuracy of less than 1 nm, for example 0.3 nm or even less will.

Therefore, it is a general object of the present invention to provide a multiple particle beam system employing charged particles and an associated method of operating the same at high throughput that enables high-precision measurement of semiconductor features with an accuracy of less than 1 nm, less than 0, 3 nm or even 0.1 nm possible.

A more recent development in the field of charged particle systems (CPM) is the MSEM, a multi-beam scanning electron microscope. A multi-beam scanning electron microscope is shown in, for example US 7 244 949 B2 and in US 2019/0355544 A1 disclosed. In a multi-beam electron microscope or MSEM, a sample is simultaneously irradiated with a large number of individual electron beams that are arranged in a field or grid. For example, 4 to 10,000 individual electron beams can be provided as primary radiation, each individual electron beam being separated from an adjacent individual electron beam by a distance of 1 to 200 micrometers. For example, an MSEM has approximately 100 separate individual electron beams (“beamlets”), which are arranged, for example, in a hexagonal grid, with the individual electron beams being separated by a distance of approximately 10 µm. The large number of charged individual particle beams (primary beams) are focused by a common objective lens onto a surface of a sample to be examined. For example, the sample may be a semiconductor wafer attached to a wafer holder mounted on a movable table. During the illumination of the wafer surface with the charged primary single particle beams, interaction products, for example secondary electrons or backscattered electrons, emanate from the surface of the wafer. Their starting points correspond to the locations on the sample on which the large number of primary single particle beams are each focused. The amount and energy of the interaction products depends on the material composition and the topography of the wafer surface. The interaction products form a plurality of secondary individual particle beams (secondary beams) which are collected by the common objective lens and impinge through a projection imaging system of the multi-beam inspection system on a detector which is arranged in a detection plane. The detector comprises a plurality of detection areas, each of which comprises a plurality of detection pixels, and the detector detects an intensity distribution for each of the secondary individual particle beams. An image field of 100 μm × 100 μm, for example, is obtained.

The prior art multi-beam electron microscope comprises a sequence of electrostatic and magnetic elements. At least some of the electrostatic and magnetic elements are adjustable to adjust the focus position and stigmation of the plurality of charged single particle beams. The multi-beam system with charged particles of the prior art also comprises at least one plane of intersection of the primary or the secondary charged individual particle beams. Furthermore, the prior art system includes detection systems to facilitate adjustment. The prior art multi-beam particle microscope comprises at least one deflection scanner for collective scanning of an area of the sample surface by means of the multiplicity of primary individual particle beams in order to obtain an image field of the sample surface.

In the scanning electron microscope for wafer inspection, it is desired to keep the imaging conditions stable so that the imaging can be performed with high reliability and high repeatability. The throughput depends on several parameters, e.g. B. the speed of the table and the realignment at new measuring points as well as the measured area per acquisition time. The latter is determined, among other things, by the dwell time on a pixel, the pixel size and the number of individual particle beams. In addition, time-consuming post-processing of images may be required for a multi-beam electron microscope; For example, the signal generated by the detection system of the multi-beam system with charged particles must be digitally corrected before the image field is stitched from several image subfields or partial images.

The grid positions of the individual particle beams on the sample surface can deviate from the ideal grid position in a planar arrangement. The resolution of the multi-beam electron microscope can be different for each of the individual particle beams and depend on the individual position of the individual particle beam in the field of the individual particle beams, hence on its specific grid position.

With the increasing demands on resolution and throughput, conventional systems of charged particle beam systems have reached their limits.

It is therefore an object of the invention to provide a multitude particle beam system which enables high-precision and high-resolution image recording with high throughput.

One approach to improving precision and resolution is to use what is known as an autofocus. During the scanning of the sample surface, the current focus position of the individual electron beams with regard to the sample surface / object plane is continuously determined (“on the fly”) and the focus position is corrected accordingly. For example, the focusing of the individual particle beams is adapted for each image field. This procedure is based, for example, on a model of the sample or on the assumption that the sample properties change only slightly from image field to image field, so that forecast values for improved focusing can be determined by extrapolation or interpolation.

However, the known autofocus method is relatively slow: the focus position is optimized either by changing the working distance (WD) or by changing the control of the objective lens. A change in the working distance by moving the sample table in height (so-called “z-stage”) is only possible with a certain limited precision and speed. In addition, not every sample table can be moved in height. If the objective lens or other magnetic lenses are controlled in a different way to vary the focus position, this setting is relatively slow: In the prior art, magnetic objective lenses and, in particular, immersion lenses are used, the inductance of which is too high to enable even faster adaptation. In this case, too, the time for the change in excitation is in the range of a few tens to a few hundred milliseconds. In addition, the optics of multiple electron microscopes is much more complex than that of single-beam systems, as it is necessary for meaningful recordings, the magnification in the object plane (coupled to the beam spacing ("pitch") of the individual particle beams in the object plane) and also to leave the orientation, ie the rotation, of the array of individual electron beams (grid arrangement) unchanged when tracking the focus position. The same applies to the landing angle of the individual particle beams on the sample. The aforementioned particle-optical parameters (and possibly further parameters) can generally not be set independently of one another using only a single lens. A change in the control of the magnetic objective lens therefore results in a change in the control of other particle-optical components in the primary path. Thus, changes in excitation are typically also required in other magnetic and electrostatic elements, the setting times for the magnetic lenses being time-limiting and likewise in the range from a few tens to a few hundred milliseconds. Analogous considerations apply to particle-optical components in the secondary path and the tracking of the focus position for precise detection.

The existing systems are in need of improvement against the background described above and the increasing demands on throughput / speed and the precise measurement of ever smaller structures. The requirements are enormous, especially when inspecting semiconductor wafers. A surface of a semiconductor wafer that is actually very flat can then no longer generally be assumed to be precisely flat in the context of precision inspection. Smallest variations in the wafer thickness and / or the longitudinal position of the wafer surface relative to the objective lens have an influence on the optimal focus and thus on the accuracy of the measurements. This applies in particular to the inspection of polished wafer surfaces with HV structures. It is therefore no longer sufficient - even under the only partially realistic assumption of missing system drifts and the like - to set the multiple electron microscope once at a predefined working point with an assigned working distance. Instead, the smallest changes in the working distance must be corrected by changing the focus position. Another prerequisite is that the reproduction scale must remain unchanged. The orientation of the grid arrangement on the sample surface must be kept exactly, since semiconductor wafers with HV structures are always mapped exactly parallel or orthogonal to these structures. It is also essential to keep the landing angle precisely constant. And finally, for excellent imaging, the optics in the secondary path must also be adjusted quickly and with high precision.

US 2011/0272576 A1 discloses a multi-beam particle microscope. The document discloses a charge control on a sample in advance of a sample inspection.

DE 10 2004 055 149 A1 discloses a lithography apparatus and method for imaging a multiple particle beam onto a substrate. For more precise positioning of the multiple particle beam, a height measuring system in the form of a laser displacement measuring system is disclosed. Correction lenses for dynamic correction of focus, image field size and image field rotation are disclosed. There is no telecentricity correction.

US 9 922 796 B1 discloses a multi-column microscope used to inspect slanted or inclined samples. For the individual focusing of the individual particle beams on the sample, they pass through an objective lens array so that each individual particle beam can be focused individually on the sample surface.

Description of the invention

It is thus an object of the present invention to provide an improved multiple particle beam system for the inspection of semiconductor wafers with HV structures and an associated method for operating the same. This should work quickly and with high precision.

It is a further object of the invention to provide a multiple particle beam system for the inspection of semiconductor wafers with HV structures and an associated method for operating the same, which enables an additional fast autofocusing of the system at a working point with a predetermined working distance. Other particle-optical parameters such as magnification, telecentricity and rotation should be kept constant with high precision.

The object is achieved by the independent patent claims. Advantageous embodiments of the invention emerge from the dependent claims.

• einen Vielstrahl-Teilchengenerator, welcher konfiguriert ist, um ein erstes Feld einer Vielzahl von geladenen ersten Teilchenstrahlen zu erzeugen;
• eine erste Teilchenoptik mit einem ersten teilchenoptischen Strahlengang, die konfiguriert ist, um die erzeugten Einzel-Teilchenstrahlen auf eine Waferoberfläche in der Objektebene abzubilden, so dass die ersten Teilchenstrahlen an Auftrefforten auf die Waferoberfläche treffen, die ein zweites Feld bilden;
• ein Detektionssystem mit einer Vielzahl von Detektionsbereichen, die ein drittes Feld bilden; eine zweite Teilchenoptik mit einem zweiten teilchenoptischen Strahlengang, die konfiguriert ist, um zweite Einzel-Teilchenstrahlen, die von den Auftrefforten im zweiten Feld ausgehen, auf das dritte Feld der Detektionsbereiche des Detektionssystems abzubilden;
• eine magnetische und/ oder elektrostatische Objektivlinse, insbesondere eine magnetische und/ oder elektrostatische Immersionslinse, durch die sowohl die ersten als auch die zweiten Einzel-Teilchenstrahlen hindurchtreten;
• eine Strahlweiche, die in dem ersten teilchenoptischen Strahlengang zwischen dem Vielstrahl-Teilchengenerator und der Objektivlinse angeordnet ist, und die im zweiten teilchenoptischen Strahlengang zwischen der Objektivlinse und dem Detektionssystem angeordnet ist;
• einen Probentisch zum Halten und/ oder Positionieren eines Wafers während der Waferinspektion;
• ein Autofokus-Messglied, das konfiguriert ist, um während der Waferinspektion Messdaten zum Ermitteln von Autofokus-Istdaten zu erzeugen;
• eine schnelle Autofokus-Korrekturlinse; und
• eine Steuerung;
• wobei die Steuerung für eine statische oder niederfrequente Anpassung einer Fokussierung konfiguriert ist, um an einem ersten Arbeitspunkt mit einem ersten Arbeitsabstand zumindest die Objektivlinse und/ oder einen Aktuator des Probentisches derart anzusteuern, dass die ersten Einzel-Teilchenstahlen auf die im ersten Arbeitsabstand befindliche Waferoberfläche fokussiert werden,
• wobei die Steuerung für eine hochfrequente Anpassung der Fokussierung konfiguriert ist, um am ersten Arbeitspunkt während der Waferinspektion basierend auf den Autofokus-Istdaten ein Autofokus-Korrekturlinsen-Steuerungssignal zu erzeugen, um die schnelle Autofokus-Korrekturlinse während der Waferinspektion am ersten Arbeitspunkt anzusteuern,
• wobei der erste Arbeitspunkt des Weiteren durch einen Landewinkel der ersten Einzel-Teilchenstrahlen in der Objektebene und durch eine Rasteranordnung der ersten Einzel-Teilchenstrahlen in der Objektebene definiert werden, und
• wobei die Steuerung des Weiteren konfiguriert ist, den Landewinkel und die Rasteranordnung während der hochfrequenten Anpassung am ersten Arbeitspunkt im Wesentlichen konstant zu halten.

According to a first aspect of the invention, it relates to a plurality of particle beam system for semiconductor inspection, comprising:

• a multi-beam particle generator configured to generate a first field of a plurality of charged first particle beams;
• a first particle optics with a first particle-optical beam path which is configured to image the generated individual particle beams onto a wafer surface in the object plane, so that the first particle beams strike the wafer surface at locations that form a second field;
• a detection system having a plurality of detection areas which form a third field; a second particle optics with a second particle-optical beam path which is configured to image second individual particle beams, which emanate from the points of incidence in the second field, onto the third field of the detection areas of the detection system;
• a magnetic and / or electrostatic objective lens, in particular a magnetic and / or electrostatic immersion lens, through which both the first and the second individual particle beams pass;
• a beam splitter which is arranged in the first particle-optical beam path between the multi-beam particle generator and the objective lens, and which is arranged in the second particle-optical beam path The beam path is arranged between the objective lens and the detection system;
• a sample table for holding and / or positioning a wafer during wafer inspection;
• an autofocus measuring element which is configured to generate measurement data for determining actual autofocus data during the wafer inspection;
• a fast auto focus correction lens; and
• a controller;
• wherein the controller is configured for a static or low-frequency adjustment of a focusing in order to control at least the objective lens and / or an actuator of the sample table at a first working point with a first working distance in such a way that the first individual particle beams focus on the wafer surface located in the first working distance will,
• wherein the controller is configured for a high-frequency adjustment of the focusing in order to generate an autofocus correction lens control signal at the first operating point during the wafer inspection based on the actual autofocus data in order to control the fast autofocus correction lens during the wafer inspection at the first operating point,
• wherein the first working point is further defined by a landing angle of the first individual particle beams in the object plane and by a grid arrangement of the first individual particle beams in the object plane, and
• wherein the controller is further configured to keep the landing angle and the grid arrangement substantially constant during the high-frequency adaptation at the first operating point.

The charged particles can be, for example, electrons, positrons, muons or ions or other charged particles. They are preferably electrons that are generated, for example, with the help of a thermal field emission source (TFE). But other particle sources can also be used.

The number of the first individual particle beams can be selected variably. However, it is advantageous if the number of particle beams is 3n (n-1) +1, with n being any natural number. This allows a hexagonal grid arrangement of the detection areas. Other grid arrangements of the detection areas, e.g. in a square or rectangular grid, are also possible. For example, the number of the first individual particle beams is more than 5, more than 60 or more than 100 individual particle beams.

The multi-beam particle generator can comprise several real particle sources, each of which emits a single particle beam or also several single particle beams. The multi-beam particle generator can, however, also comprise a single particle source and, in the further particle-optical beam path, a multi-aperture plate in combination with a multi-lens array and / or a multi-reflector array. The multibeam particle generator then generates the multitude of individual particle beams and maps them onto an intermediate image plane. This intermediate image plane can be a real intermediate image plane or a virtual intermediate image plane. In both cases it is the case that the locations of the individual particle beams in the intermediate image can be viewed as virtual particle sources and thus as origins for the further particle-optical imaging with the first particle-optical beam path. The virtual particle sources in this intermediate image plane are thus mapped onto the wafer surface or into the object plane and the wafer to be inspected can be scanned with the large number of individual particle beams.

If the objective lens system comprises a magnetic objective lens, then this can provide a weak or a strong magnetic field. According to a preferred embodiment of the invention, the objective lens is a magnetic immersion lens. This can be a weak immersion lens or a strong immersion lens. Magnetic immersion lenses can be implemented, for example, in that the hole in the lower pole piece (facing the sample) of the lens has a larger diameter than the hole in the upper pole piece (facing away from the sample) of the lens. In contrast to objective lenses, which only provide a small magnetic field on the object, immersion lenses have the advantage of being able to achieve lower spherical and chromatic aberrations, as well as the disadvantage of larger off-axis aberrations. In the magnetic field of the lens, the single particle beams passing through it (both in the primary path and in the secondary path) experience a Larmor rotation.

According to the invention, a sample table is provided for holding and / or positioning a wafer during the wafer inspection. It is possible that the sample table has a mechanism for height adjustment (eg z-stage) in order to set a working distance. But it is also possible that there is no height adjustability. The sample table then only serves to hold the wafer, not to position it in the z-direction. It is possible in both cases, but not it is imperative that the sample table can be moved along an axis (eg x-axis, y-axis) or in a plane (eg xy-plane).

Furthermore, an autofocus measuring element is provided which is configured to generate measurement data for determining actual autofocus data during the wafer inspection. The actual autofocus data directly or indirectly describe the current focus position relative to the wafer surface. Autofocus measuring elements are known in principle from the prior art and are, for example, in the US 9 530 613 B2 and in the US 2017/0117114 A1 described, the disclosures of which are fully incorporated into this application by reference. For example, a height sensor (z-sensor) can be used. In order to determine the focus position, a measurement is used to infer the current focus position of the individual particle beams relative to the wafer surface (conclusion on actual autofocus data). Ideally, all foci are exactly on the wafer surface. The focus position of a single particle beam is defined by the position of the beam waist of a beam.

the US 9 530 613 B2 discloses the use of astigmatic auxiliary beams for focus adjustment. The known astigmatic (eg elliptical) beam profile changes in the imaging depending on the focus. This change allows conclusions to be drawn about the focus and thus about the necessary focus corrections to the stigmatic rays.

the US 2017/0117114 A1 reveals an autofocus "on-the-fly". During the scanning of a sample surface, the current focus position of the individual particle beams is deduced from data from an image field (measured intensities) and the focus is continuously adjusted "on the fly" for the subsequent image field. In particular, it is not necessary to scan the same sample area several times. An object property is determined indirectly in each case by the measurement. This object property can be, for example, a height profile of the sample surface. A prognostic value for the height is then determined from the determined height profile for the subsequent image recording and a different, better adapted focus position is set relative to the sample surface.

The multiple particle beam system according to the invention has a controller. The controller is configured to control particle-optical components in the first and / or in the second particle-optical beam path. The control is preferably a central control for the entire multitude of particle beam systems, but this need not be the case. The control can be designed in one part or in several parts and can be functionally subdivided.

The control is configured for a static or low-frequency adjustment of the focusing in order to control at least the objective lens and / or an actuator of the sample table at a first working point with a first working distance in such a way that the first individual particle beams are focused on the wafer surface located in the first working distance , and it is configured for a high-frequency adaptation in order to generate an autofocus correction lens control signal at the first operating point during the wafer inspection based on the actual autofocus data in order to control the at least one fast autofocus correction lens during the wafer inspection at the first operating point. For high-frequency adaptation, a control of the objective lens is preferably not changed, a change in excitation of the objective lens only occurs regularly with a static or low-frequency adaptation of the focus position. The objective lens comprises at least one magnetic and / or at least one electrostatic objective lens; the objective lens can thus be designed in the form of a corresponding objective lens system.

The control therefore controls two different focal settings at a working point which - possibly in addition to other parameters - is defined by an associated working distance between the objective lens and the wafer surface: On the one hand, it controls the focusing with a large stroke via a control of the objective lens and possibly others Lenses and / or via a control of an actuator for moving the sample table. These actuators respond relatively slowly to the control signal; An adjustment here typically requires a few tens to a few hundred milliseconds and is particularly necessary when approaching an operating point with a selected working distance for the first time, for example when changing a wafer. The stroke for changing the working distance can be, for example, +/- 100, +/- 200 µm or +/- 300 µm.

On the other hand, according to the invention, the controller also controls the focal setting by controlling the fast autofocus correction lens according to the invention. This lens can be designed differently, for example it can be designed as a fast electrostatic lens. Various design variants and possible positioning of the autofocus correction lens in the beam path are described in more detail below. It is also possible to provide several autofocus correction lenses and to control them individually. In either case, an autofocus correction lens can be used for quick adjustment and acts on the focal position of the individual particle beams, whereby this effect can be strong or less strong. It is also possible for the autofocus correction lens to have an effect on other particle-optical parameters in addition to the effect on the focus. Fast means here that the excitation of the autofocus correction lens allows a high-frequency adjustment of the focus position; an adaptation time TA is in the range of μs, for example TA 500 μs, preferably TA 100 μs and / or TA 50 μs. The stroke for changing the working distance is typically a few µm, for example +/- 20 µm, +/- 15 µm and / or +/- 10 µm.

According to a preferred embodiment of the invention, an adaptation time TA for the high-frequency adaptation is at least a factor of 10, preferably at least a factor of 100 or 1000, shorter than the adaptation time TA for the low-frequency or static adaptation. Furthermore, a stroke for setting the work delay for the low-frequency or static adaptation can be at least a factor of 5, preferably at least a factor of 8 and / or 10, greater than the stroke for the high-frequency adaptation.

With both adjustment variants of the focus, it may be necessary to also readjust other particle-optical components of the system. The controller can also provide appropriate control signals for these corrections. In the case of low-frequency or static matching, the actuators can also be slowly adjustable actuators or they can be quickly adjustable actuators. The time-limiting elements are the magnetic lenses, which include, for example, magnetic field lenses as well as the magnetic objective lens, and / or the time it takes to move the sample table in the z-direction. In the case of high-frequency adaptation, it is necessary that the other actuators can also be set essentially quickly. Their respective adaptation times are preferably of the same order of magnitude as the adaptation time of the fast autofocus correction lens. For example, they can be slower by a maximum of a factor of 2. But they can also be faster than the adjustment time of the fast autofocus correction lens. The fast additional actuators can be, for example, electrostatic lenses, electrostatic deflectors, and / or electrostatic stigmators. Air-core coils with only a few turns can also be used as fast correctors.

According to a preferred embodiment of the invention, a second working point is defined at least by a second working distance between the objective lens and the wafer surface, the second working distance differing from the first working distance of the first working point. The controller is then configured to carry out a low-frequency adaptation when changing between the first working point and the second working point and to control at least the magnetic objective lens and / or an actuator of the sample table at the second working point in such a way that the first individual particle beams are reduced to those in the second Working distance located wafer surface are focused. The working point is changed, for example, when changing a wafer; the wafers can be of different thicknesses. A wafer change is a comparatively slow process, so that a slow adjustment is sufficient here. However, it is also possible, for example, to change the working point or the working distance because the inspection task is different.

The controller is preferably configured to generate an autofocus correction lens control signal for high-frequency adjustments at the second working point with the second working distance during the wafer inspection based on the actual autofocus data, in order to control the fast autofocus correction lens during the wafer inspection at the second working point. In addition, everything that has already been stated above in connection with the first working point at the first working distance applies to the setting of the fast autofocus at the second working point with the second working distance.

According to the invention or according to a preferred embodiment of the invention, the first and / or the second working point are furthermore defined by a landing angle of the first individual particle beams in the object plane and by a grid arrangement of the first individual particle beams in the object plane. The controller is then configured to keep the landing angle and the grid arrangement essentially constant during the high-frequency adaptation at the first and / or second operating point. The term grid arrangement includes the distance between the individual particle beams in the object plane and the rotation of the individual particle beam arrangement; the latching arrangement can, for example, be in the form of the hexagon image field mentioned above. Thus, when the grid arrangement is kept constant, both the magnification, which is coupled to the distance between the individual particle beams, and the orientation of the second field of points of incidence of the individual particle beams in the object plane are kept constant. The magnification is preferably kept constant at around 50ppm, 20ppm, 10ppm, 1ppm or better (e.g. 50nm, 20nm, 10nm, 1nm or better to 100 µm image field size). The maximum angular deviation from the desired landing angle on the wafer surface is a maximum of +/- 0.1 °, +/- 0.01 ° or +/- 0.005 °.

According to a further preferred embodiment of the invention, the controller is configured to keep the landing angle and the grid arrangement essentially constant even when there is a change between the first working point and the second working point. The point here is to keep the parameters mentioned constant even with a low-frequency adjustment of the focus. The magnification is preferably kept constant at about 50 ppm, 20 ppm, 10 ppm, 1 ppm or better (for example 50 nm, 20 nm, 10 nm, 1 nm or better to 100 μm). The maximum angular deviation from the desired landing angle on the wafer surface is a maximum of +/- 0.1 °, +/- 0.01 ° or +/- 0.005 °.

The actuators for an adjustment and in particular for keeping constant particle-optical parameters such as landing angle and grid arrangement (position or magnification and rotation) can be completely or partially the same for the low-frequency adjustment as for the high-frequency adjustment. However, if it is completely or partially the same actuators, then these actuators must also be suitable for high-frequency adaptation.

According to a preferred embodiment of the invention, the autofocus correction lens comprises an electrostatic lens or it consists of an electrostatic lens. Settings of electrostatic lenses can basically be changed much faster than settings of magnetic lenses, in which hysteresis effects, eddy currents and self and mutual inductances prevent a quick adjustment. According to the invention, an electrostatic lens can be provided as a complete lens, for example a tubular lens. However, it is also possible that only one additional component is provided as an autofocus correction lens in the form of an additional electrode, which develops its electrostatic lens effect in cooperation with other components or with the voltages surrounding them.

• Gemäß einer bevorzugten Ausführungsform der Erfindung ist die Autofokus-Korrekturlinse in einer Strahlrohrverlängerung, die in die Objektivlinse vom oberen Polschuh her hineinragt, angeordnet. Allgemein ist es so, dass die Einzel-Teilchenstrahlen innerhalb eines Strahlrohres geführt werden. Dieses ist evakuiert. Das Strahlverlängerungsröhrchen ist dabei genau der Bereich des Strahlrohres, der vom oberen Polschuh aus ein Stück weit in die magnetische Objektivlinse hineinragt. Das Strahlrohr liegt auf Erdpotential, so dass die Autofokus-Korrekturlinse bzw. eine dazugehörige Elektrode innerhalb der Strahlrohrverlängerung gut angeordnet werden kann.

The fast autofocus correction lens can be arranged in the first particle-optical beam path at different positions, which offer different advantages and disadvantages. On the one hand, the available installation space in the overall system must be taken into account, and on the other hand, the effect of the autofocus correction lens on other particle-optical parameters than the focus. As already stated at the beginning, in the case of multiple particle beam systems, a lens normally does not only act on a single particle-optical parameter; the effects of particle-optical components are generally not orthogonal to one another. The inventors have examined these relationships more closely and have found out that there are some positions in the particle-optical beam path of multiple particle beam systems that have special properties: Normally there is a crossover point or plane of crossover in the primary beam path of a multiple particle beam system according to the invention. Crossover ”) in which the individual particle beams overlap or cross one another. This crossover plane is usually close in front of the objective lens. Extensive calculations have shown that an additional lens at the crossover essentially affects the focus of the first individual particle beams and (if at all) only weakly affects other particle-optical parameters such as position, telecentricity or rotation. It is therefore generally advantageous to arrange the autofocus correction lens at the crossover or in the plane of intersection of the first individual particle beams. In practice, however, the crossover is not a singular point, but has a spatial extent so that often only an arrangement of the autofocus correction lens near the crossover / near the crossover plane can be achieved. According to the invention, there are several possibilities for this:

• According to a preferred embodiment of the invention, the autofocus correction lens is arranged in a beam pipe extension which protrudes into the objective lens from the upper pole piece. It is generally the case that the individual particle beams are guided within a beam pipe. This is evacuated. The beam extension tube is precisely that area of the beam tube that protrudes a little from the upper pole piece into the magnetic objective lens. The beam tube is at ground potential, so that the autofocus correction lens or an associated electrode can be easily arranged within the beam tube extension.

According to a preferred embodiment of the invention is Furthermore, a beam deflection system is provided between the beam deflector and the objective lens, which is configured to scan the wafer surface with a scanning movement of the individual particle beams, the autofocus correction lens being implemented as an offset on the beam deflection system. A beam deflection system (“deflection scanner” or “scan deflector”) is typically implemented by two or more deflectors arranged one behind the other in the beam path. The offset voltage is now made available to all electrodes involved in the deflection. The lens effect is created by superimposing the deflection field with a single lens field. The embodiment described offers the advantage that no further changes are required to the hardware of the system.

According to one embodiment of the invention, the multiple particle beam system further comprises a beam deflection system between the beam splitter and the objective lens, which is configured to scan the wafer surface with a scanning movement of the single particle beams, the beam deflection system having an upper deflector and a lower deflector, which are arranged one after the other in the direction of the beam path, and wherein the autofocus correction lens is arranged between the upper deflector and the lower deflector. This embodiment is also easy to implement, since only minor changes need to be made to the hardware of existing systems.

According to one embodiment of the invention, the multiple particle beam system further comprises a beam deflection system between the beam splitter and the objective lens, which is configured to scan the wafer surface with a scanning movement of the single particle beams, the beam deflection system having an upper deflector and a lower deflector, which are arranged one after the other in the direction of the beam path, and wherein the autofocus correction lens is arranged between the lower deflector and the upper pole piece of the magnetic objective lens. In this variant, too, the autofocus correction lens is located in the vicinity of the crossover plane.

According to a preferred embodiment of the invention, the autofocus correction lens is arranged between the wafer surface and a lower pole piece of the magnetic objective lens. This position is no longer in the vicinity of the crossover and the effect of the lens no longer extends only predominantly to the focus; however, this embodiment offers the advantage that the autofocus correction lens has only minor follow-up aberrations, since it is normally the last lens directly in front of the wafer surface.

According to another preferred embodiment of the invention, the autofocus correction lens is arranged between the upper and lower pole pieces of the magnetic objective lens. This embodiment also has the advantage that it is implemented far below in the beam path (autofocus correction lens as penultimate lens), so that only minor subsequent aberrations arise here too.

According to a preferred embodiment of the invention, the multiple particle beam system furthermore has an evacuable beam tube which essentially encloses the first particle-optical beam path from the multi-beam particle generator to the objective lens, the beam tube having an interruption and the autofocus correction lens within this Interruption is arranged. The jet pipe is essentially tight in the area mentioned, that is to say designed in such a way that a vacuum or high vacuum can be generated therein. It can have different cross-sections and / or chambers along the beam path. The interruption in which the autofocus correction lens is arranged is preferably the only interruption in the beam tube. The inner wall of the beam pipe is at ground potential, except for the places of interruption where the autofocus correction lens is located. Any connection points / contact points between the vacuum chambers and the actual jet pipe are not to be regarded as interruptions.

According to a preferred embodiment of the invention, the multiple particle beam system also has a field lens system which is arranged in the first particle-optical beam path between the multi-beam particle generator and the beam switch, the interruption of the beam tube in which the autofocus correction lens is arranged between the Field lens system and the beam switch is arranged. This embodiment offers a relatively large amount of space for the arrangement of the autofocus correction lens.

According to a preferred embodiment of the invention, the beam switch has two magnetic sectors and the interruption of the beam tube in which the autofocus correction lens is arranged is provided in the area of the beam switch between the two magnetic sectors. This embodiment offers a relatively large amount of space for the arrangement of the autofocus correction lens.

According to a preferred embodiment of the invention, the multiple particle beam system furthermore has a beam deflection system between the beam splitter and the objective lens, which is configured to scan the wafer surface with a scanning movement of the individual particle beams. Correction lens is arranged, is provided between the beam switch and the beam deflection system. This embodiment offers a relatively large amount of space for the arrangement of the autofocus correction lens.

According to a preferred embodiment of the invention, the multiple particle beam system furthermore has a field lens system which is arranged in the first particle-optical beam path between the multi-beam particle generator and the beam switch. This field lens system can comprise one or more lenses. It comprises at least one magnetic field lens. In this embodiment of the invention, the interruption of the beam pipe in which the autofocus Correction lens is arranged, arranged within the one magnetic field lens of the field lens system. A relatively large amount of installation space is also available in this position. However, in this position the autofocus correction lens acts on the focus, the position and the tilting of the individual particle beams. Nevertheless, it is advantageous that a position and / or beam tilting can (also) be compensated for in this embodiment.

• Gemäß einer bevorzugten Ausführungsform der Erfindung weist das Vielzahl-Teilchenstrahlsystem des Weiteren ein Feldlinsensystem auf, das im ersten teilchenoptischen Strahlengang zwischen dem Vielstrahl-Teilchengenerator und der Strahlweiche angeordnet ist, wobei die Autofokus-Korrekturlinse zwischen dem Feldlinsensystem und der Strahlweiche innerhalb des Strahlrohres angeordnet ist. Diese Ausführungsform bietet verhältnismäßig viel Raum für die Anordnung der Autofokus-Korrekturlinse.

According to a preferred embodiment of the invention, the multiple particle beam system furthermore has an evacuable beam tube which essentially encloses the first particle-optical beam path from the multi-beam particle generator to the objective lens. The autofocus correction lens is designed as a tubular lens and is arranged within the beam tube. The jet pipe therefore has no interruption or breakthrough, which simplifies the sealing / tightness of the jet pipe. For this variant there are in turn several forms of implementation, four of which are specified below:

• According to a preferred embodiment of the invention, the multiple particle beam system also has a field lens system which is arranged in the first particle-optical beam path between the multi-beam particle generator and the beam switch, the autofocus correction lens being arranged between the field lens system and the beam switch within the beam pipe. This embodiment offers a relatively large amount of space for the arrangement of the autofocus correction lens.

According to a preferred embodiment of the invention, the beam switch has two magnetic sectors and the autofocus correction lens is provided between the two magnetic sectors within the beam tube. This embodiment offers a relatively large amount of space for the arrangement of the autofocus correction lens.

According to a preferred embodiment of the invention, the multiple particle beam system further comprises a beam deflection system between the beam splitter and the objective lens, which is configured to scan the wafer surface with a scanning movement of the single particle beams, the autofocus correction lens between the beam splitter and the beam deflection system is provided within the jet pipe. This embodiment offers a relatively large amount of space for the arrangement of the autofocus correction lens.

According to a preferred embodiment of the invention, the multiple particle beam system furthermore has a field lens system which is arranged in the first particle-optical beam path between the multi-beam particle generator and the beam switch, the autofocus correction lens being arranged within a magnetic field lens within the beam tube. This embodiment offers a relatively large amount of space for the arrangement of the autofocus correction lens. In this position, the autofocus correction lens acts in addition to the focus on the position and on the tilting of the individual particle beams. This enables (possibly additional) corrections of the position and land angle of the first individual particle beams.

According to a further embodiment of the invention, the fast autofocus correction lens comprises a fast magnetic lens, in particular an air-core coil, or consists of a fast magnetic lens, in particular an air-core coil. Such an air-core coil has only a relatively low inductance and can therefore also be used to a certain extent as a fast autofocus correction lens. For example, such an air core coil has a few tens to a few hundred turns, for example, for the number k of turns, 10 k 500 and / or 10 k 200 and / or 10 k 50, and for the adaptation times TA of the air core coil can apply: TA ≤ 500 µs, preferably TA ≤ 100 µs and / or TA ≤ 50 µs. This applies in any case when the air-core coil is arranged in such a way that no or at least hardly any magnetic material is in its vicinity.

According to a preferred embodiment of the invention, the multiple particle beam system furthermore has an evacuable beam tube which essentially encloses the first particle-optical beam path from the multi-beam particle generator to the objective lens, the fast magnetic lens being arranged on the outside around the beam tube. In this case, the jet pipe does not have to be broken through or interrupted. A production of this variant is relatively simple.

According to a preferred embodiment of the invention, the multiple particle beam system furthermore has a field lens system which is arranged in the first particle-optical beam path between the multi-beam particle generator and the beam switch, the fast magnetic lens being arranged between the field lens system and the beam switch around the beam pipe. In this case, the jet pipe does not have to be broken through or interrupted. A production of this variant is relatively simple.

According to a preferred embodiment of the invention, the beam switch has two magnetic sectors and the fast magnetic lens is arranged between the two magnetic sectors around the beam pipe. In this case, the jet pipe does not have to be broken through or interrupted. A production of this variant is relatively simple.

According to a preferred embodiment of the invention, the multiple particle beam system further comprises a beam deflection system between the beam splitter and the objective lens, which is configured to scan the wafer surface with a scanning movement of the single particle beams, the fast magnetic lens between the beam splitter and the beam deflection system the jet pipe is arranged around. In this case, the jet pipe does not have to be broken through or interrupted. A production of this variant is relatively simple.

According to a preferred embodiment of the invention, the multiple particle beam system further comprises a beam deflection system between the beam splitter and the objective lens, which is configured to scan the wafer surface with a scanning movement of the single particle beams; wherein the beam deflection system has an upper deflector and a lower deflector which are arranged one after the other in the direction of the beam path; and wherein the fast magnetic lens is disposed between the upper deflector and the lower deflector around the beam pipe. In this case, the jet pipe does not have to be broken through or interrupted. A production of this variant is relatively simple.

According to a preferred embodiment of the invention, the plurality of particle beam system further comprises a fast telecentricity correction means which is configured to contribute significantly to correcting a tangential or radial telecentricity error of the first single particle beams in the second field, and the control of the plurality of The particle beam system is set up to generate a telecentricity correction means control signal for high-frequency adjustments at the respective working point during the wafer inspection based on the actual autofocus data, in order to control the fast telecentricity correction means during the wafer inspection. As already stated above, in the course of the fast autofocusing, a fast adjustment of other particle-optical components is often necessary in order to be able to keep other particle-optical parameters constant. One of these parameters is the telecentricity or the landing angle of the first individual particle beams on the wafer surface (the terms telecentricity and landing angle are used synonymously in this patent application). Even when using an element that is intended for telecentricity correction, this element does not necessarily only act on telecentricity, but in turn interacts with other particle-optical parameters because of the non-orthogonality of the effects of the particle-optical components. Therefore, in the context of this patent application, it is defined that the fast telecentricity correction means should essentially - and thus not necessarily exclusively - act on the telecentricity. An essential effect then affects the telecentricity. Strictly speaking, it is also possible that a fast autofocus correction lens is (also) a fast telecentric correction means and vice versa.

The following explains the occurrence of the tangential telecentricity error and a rotation error, which are generated by an immersion lens as a magnetic objective lens: In a reference arrangement of the magnetic immersion lens with a first imaging scale and a first focal plane in the magnetic field of the magnetic immersion lens, a first grid arrangement with a first beam spacing or pitch of the first individual particle beams and formed in a first orientation. Charged particles are directed onto helical paths in the magnetic field of the magnetic immersion lens. A magnetic immersion lens is used when the magnetic field of an objective lens extends to the sample or the object, for example a semiconductor wafer. The raster arrangement of the beam foci in the object plane in which, for example, a wafer is arranged, is also rotated by the helical particle trajectories. In order to generate a first raster arrangement in the object plane in a desired, predefined orientation, the twisting or rotation of the raster arrangement is usually provided, for example by arranging a generating device of the raster arrangement (e.g. in the form of a multi-aperture plate as part of a multi-beam particle generator) in a predetermined pre-rotated Position which is opposite to the rotation through the magnetic immersion lens. First individual particle beams also receive a tangential velocity component which, in the case of an immersion lens, means that the individual particle beams no longer strike a sample perpendicularly, but tilt in a tangential direction or incline to a perpendicular to the sample surface. In particular, in a multi-beam system, first individual particle beams have different tangential angles of inclination which increase in the radial direction with the distance from the optical axis of the magnetic immersion lens. This error is known as a tangential telecentricity error. The tangential telecentricity error can usually be compensated by specifically generating a corresponding tangential velocity component of the first individual particle beams in front of the magnetic immersion lens, which is directed against the tangential telecentricity error and compensates for it on the wafer surface.

A change in the excitation of the magnetic immersion lens, a change in the focus position or a change in the imaging scale of the first raster arrangement of the plurality of first individual particle beams leads to undesired, parasitic effects. For example, a tangential and / or radial telecentricity error is generated by each of the changes mentioned.

Each of the changes mentioned above changes the fraction of a revolution of the helical electron trajectories or the angle of rotation of the rotation of the grid arrangement. A second raster arrangement of the plurality of primary electron bundles is thus formed, which is rotated relative to the first raster arrangement. This rotation is undesirable and is compensated according to the invention by means for changing the rotation of the grid arrangement.

According to a preferred embodiment of the invention, the telecentricity correction means comprises a first deflector array which is arranged in an intermediate image plane of the first particle-optical beam path. Such a deflector array is, for example, from DE 10 2018 202 421 B3 and from the WO 2019/243349 A1 known; the disclosure of both publications is fully incorporated into this patent application by reference. A deflector array comprises a multiplicity of deflectors arranged in an array, each of the deflectors being penetrated by a group of individual particle beams during operation. A group can also consist of just one single particle beam.

According to a preferred embodiment of the invention, the multiple particle beam system further comprises a rapid rotation correction means which is configured to contribute significantly to correcting a rotation of the first single particle beams in the second field, the controller being set up during the wafer inspection on generate a rotation correction means control signal for high-frequency adjustments based on the actual autofocus data in each operating point, in order to control the fast rotation correction means during the wafer inspection. The rotation correction means does not necessarily act exclusively on the rotation, but in turn interacts with other particle-optical parameters because of the non-orthogonality of the effects of the particle-optical components. Therefore, in the context of this patent application, it is defined that the rapid rotation correction means should essentially - and therefore not necessarily exclusively - act on the rotation. A major effect then concerns the rotation. Strictly speaking, it is also possible that a fast autofocus correction lens is (also) a fast rotation correction means and vice versa.

According to a preferred embodiment of the invention, the rotation correction means comprises an air core coil. For example, such an air core coil has a few tens to a few hundred turns, for example the following applies to the number k of turns 10 k 500 and / or 10 k 200 and / or 10 k 50, and for adaptation times TA of the air core coil can The following apply: TA ≤ 500 µs, preferably TA ≤ 100 µs and / or TA ≤ 50 µs. This applies in any case when the air-core coil is arranged in such a way that no or at least hardly any magnetic material is in its vicinity.

According to a preferred embodiment of the invention, the rotation correction means comprises a second deflector array which is arranged at a distance directly in front of or after the first deflector array, which serves as a fast telecentricity correction means. In this embodiment, a further deflector array is arranged in front of or behind the deflector array for telecentricity correction Grid arrangement causes. The openings of the respective downstream deflector array are made correspondingly larger and designed for beam deflection of the preceding deflector array. With two deflector arrays arranged one behind the other, it is possible to compensate for the rotation and the telecentricity error.

According to a preferred embodiment of the invention, the rotation correction means has a multi-lens array which is arranged at a distance directly before or after the first deflector array, which serves as a telecentricity correction means, in such a way that the first individual particle beams the multi - Enforce lens array off-axis. In addition to a focusing effect, this also creates a distracting effect. By offsetting a single particle beam in a tangential direction to an axis of a microlens, the single particle beam is deflected in a tangential direction. The tangential beam offset can be set, for example, by a preceding deflector array, or by rotating the multi-lens array to form a raster arrangement. A change in the tangential beam deflection can be generated by an active deflector array in front of the multi-lens array, or by a multi-lens array with variable refractive power. With the change in the refractive power, the deflection angle then also changes. The change in the refractive power can be compensated for by a further electrostatic lens, which acts on all individual particle beams, for example. Another possibility is an active rotation of the multi-lens array by a few mrad. Since the deflection is increased by the lens action, a rotation angle can be used to Rotation of the multi-lens array turn out to be smaller than the angle of rotation of the rotation of the grid arrangement.

According to a further preferred embodiment of the invention, the multi-beam particle generator comprises the rapid rotation correction means and the rotation correction means is actively rotated by the rotation correction means control signal. The multi-beam particle generator contains, for example, at least one deflector array or at least one multi-lens array. A rotation of the raster arrangement can be effected by appropriate active rotation of the entire multi-beam particle generator or the entire generating device of the grid arrangement or active rotation of individual array components.

According to a preferred embodiment of the invention, the rapid rotation correction means comprises a first magnetic field generating device for a first weak magnetic field and a second magnetic field generating device for a second weak magnetic field, the first magnetic field generating device only for a rotation in a positive direction of rotation and the second magnetic field generating device is controlled only for a rotation in a negative direction of rotation by the controller by means of the rotation correction means control signal. Since a compensation of the rotation or rotation of the grid arrangement in interaction with a fast autofocus has to be very fast, individual magnetic elements are unsuitable for this. The inventors have found, however, that with at least two magnetic elements a rapid rotation of a grid arrangement together with a change in the focus position can be achieved by using each of the magnetic elements for rotation in one direction only. The hysteresis is avoided by two magnetic components, each of which is operated in one direction, and thus enables the grid arrangement to be rotated quickly in two directions of rotation. Both components can be reset in short pauses between inspection tasks, for example during the positioning of the wafer from a first inspection point to a second inspection point. For example, an axial magnetic field for rotation in the positive direction can be combined with a magnetic immersion lens at the exit of the bundle of primary beams from the generating device for rotation in the negative direction.

According to a preferred embodiment of the invention, the first and the second magnetic field are designed axially and are arranged in a convergent or divergent cluster of the first individual particle beams in the first particle-optical beam path. Such arrangements and the underlying physical effects are, for example, in the German patent application with the application number not yet disclosed at the time of this application 10 2020 123 567.4 , filed on September 9, 2020, the full disclosure of which is incorporated into this application by reference.

According to a preferred embodiment of the invention, a maximum deviation of each individual particle beam from a desired landing position on the wafer surface is a maximum of 10 nm, 5 nm, 2 nm, 1 nm or 0.5 nm. This maximum deviation is absolute - it applies to any direction on the (planar or planar approximated) wafer surface and can in particular by means of the means for telecentricity correction and / or for rotation correction and / or for position correction described above be ensured.

According to a preferred embodiment of the invention, the controller is set up to determine the autofocus correction lens control signal and / or the rotation correction means control signal and / or the telecentricity correction means control signal based on the actual autofocus data using an inverted sensitivity matrix, which describes the influence of changes in excitation of particle-optical components on particle-optical parameters that characterize the particle-optical imaging at the respective working point. Such an inverted sensitivity matrix is in the German patent application DE 10 2014 008 383 A1 described, the disclosure of which is fully incorporated into this patent application by reference. The change in the effect of only one particle-optical component in multi-beam particle optics leads to a change in several parameters that characterize the particle-optical image. In practice, however, it is desirable to change settings of the particle optics in such a way that the change in the setting changes only one parameter which characterizes the particle-optical image, while the other parameters remain unchanged. For this it is necessary to change the settings of the effects of several particle-optical components together. In order to determine which settings have to be changed in order to change only one parameter, for example, the entries of a matrix A can be determined from mxn measurements, which describes these setting changes. Here, n corresponds to the number of particle-optical components and m corresponds to the number of parameters that characterize the particle-optical image. After determining the entries, this matrix can then be inverted and it can be determined which changes in excitation at which particle-optical Components have to be made in order to change exactly one parameter that describes the particle-optical image.

According to a preferred embodiment of the invention, the control of the multiple particle beam system is further configured for a static or low-frequency adjustment of a focusing in the second particle-optical beam path in order to control particle-optical components in the second particle-optical beam path at the respective working point with the associated working distance in such a way that the second individual Particle beams emanating from the wafer surface at the respective working distance are focused on the detection areas in the third field. The particle-optical components that are used to set the focus and / or further particle-optical parameters that describe the particle-optical imaging in the second particle-optical beam path can be, for example, a projective lens system. The particle-optical components and in particular the projection lens system can also comprise a magnetic lens or a plurality of magnetic lenses, the effect (s) of which can be adjusted relatively slowly by the control. Other and / or further magnetic and / or electrostatic lenses, deflectors and / or stigmators can also be used to adjust the focus and / or other parameters such as magnification (distance between the second individual particle beams in the detection plane, position), rotation and / or telecentricity can be controlled by the controller at the respective working point with a specified working distance. It is possible that some or all of the components are controlled quickly and not slowly (low frequency); however, rapid control is not required for the basic adjustment at the first operating point in the secondary path.

According to a preferred embodiment of the invention, the multiple particle beam system furthermore has a fast projection path correction means, which can be multi-part and which is configured for high-frequency adaptation of the focus of the second individual particle beams, the grid arrangement, landing angles and / or the contrast of the second individual particle beams when they hit the detection areas in the third field. The controller is configured to generate a projection path control signal or a set of projection path control signals during the wafer inspection at the respective working point based on the actual autofocus data in order to control the rapid projection path correction means. The set of projection path control signals is generated in particular when the projection path correction means is in several parts and its components are controlled separately.

The high-frequency adaptations in the secondary path are necessary in particular when the second individual particle beams that emanate from the wafer surface also penetrate the fast autofocus correction lens. Then this also has an influence on the path of the second single particle beams. But even if the second individual particle beams do not penetrate the fast autofocus correction lens, it is possible that a readjustment of the focus and / or other parameters that describe the particle-optical imaging in the secondary path takes place in the secondary path or is necessary. In the secondary path, it is normally desired that the second single particle beams hit the detection areas in a focused manner and at predetermined landing angles, in particular telecentrically, and with a predetermined grid arrangement (distance between the points of impact and orientation of the points of impact in the third field). A high-frequency adaptation of fast particle-optical components is therefore also advantageous in the secondary path. The type and manner of adaptation can essentially be carried out analogously to the procedure in the primary path. Here, too, particle-optical components that have been described above in connection with the primary beams, or other components, can be used - if necessary after appropriate orthogonalization - to make rapid / high-frequency corrections in the beam path of the second individual particle beams. For example, another fast autofocus correction lens can be arranged in the (pure) secondary path, that is, between the beam switch and the detection unit. This can be, for example, a fast electrostatic lens or a fast magnetic lens, in particular in the form of an air coil with only a few turns. This second autofocus correction lens can be arranged, for example, in the area of a cross-over plane in the secondary path. Such a cross-over plane in the secondary path is arranged, for example, in the area of the projection lens system in the secondary path. However, a different arrangement of the second autofocus correction lens in the secondary path is also possible. In the secondary path, for example, the fast telecentricity correction means described in connection with the primary path can also be used, in which, for example, a deflector array is arranged in an intermediate image plane in the secondary path. It is also possible, as described for the primary path, to use a rotation correction means which, for example, can be arranged in the form of a further deflector array directly before or after the deflector array for telecentricity correction in the secondary path. According to the embodiment described, the generation of the projection path control signals is based on the determined actual autofocus data for the first particle-optical beam path. It can do this, for example, with empirical values / look-up tables be worked, which assign the actual autofocus data directly or indirectly necessary corrections for the focus on the detector and / or for other parameters in the secondary path. The associated control signals / the set of control signals can / can be stored.

According to a further embodiment of the invention, the multiple particle beam system furthermore has a projection path measuring element in order to generate projection path measurement data for characterizing the particle-optical image in the secondary path during the wafer inspection, wherein the multiple particle beam system furthermore has a fast projection path correction means, which can be in several parts and which is configured to carry out a high-frequency adjustment of the focus of the second individual particle beams, the grid arrangement, landing angles and / or the contrast of the second individual particle beams when they strike the detection areas in the third field, and the controller is configured is to generate a projection path control signal or a set of projection path control signals based on the projection path measurement data at the respective working point during the wafer inspection in order to control the rapid projection path correction means. In this embodiment of the invention, the control for the high-frequency / fast adaptation of the particle-optical components does not, or not only, uses the actual autofocus data, but rather that measurement data in the secondary path are used for the high-frequency adaptation. Fast measurement methods that supply data on the fly for an adjustment are already known in principle from the state of the art. Data for a high-frequency adaptation can be determined, for example, by evaluating images from a CCD camera that are recorded in addition to the scan images that are determined by means of the detection areas in the third field. By means of known measurement methods, in particular the current focus position, the land angle and / or the grid arrangement in the third field when it hits the detection areas can be determined.

There may be a special requirement for the second particle-optical beam path with regard to the topography contrast: It is possible to provide a contrast aperture stop within a cross-over plane in the second particle-optical beam path. By means of an annular diaphragm, the interaction products can be filtered according to their starting angle when they exit the wafer. The contrast aperture stop can then only penetrate those second individual particle beams which have left the wafer surface in a certain angular range. The topographic contrast can be increased by means of such a contrast aperture diaphragm, since the interaction products (eg secondary electrons) primarily emerge at a greater angle of inclination relative to the incident particles at the edges of the wafer surface. Further information on the contrast setting and aperture diaphragms can be found in the DE 10 2015 202 172 B4 as well as the US 2019/035544 A1 the disclosures of which are fully incorporated into this application by reference. According to a preferred embodiment of the invention, a contrast aperture stop is arranged in a cross-over plane in the second particle-optical beam path, the projection path correction means being a fast contrast correction means with at least one electrostatic deflector, at least one electrostatic lens and / or at least one electrostatic Stigmator for influencing the particle-optical beam path through the contrast aperture stop, and wherein the controller is configured to control the contrast correction means with a contrast correction control signal or a set of contrast correction control signals, so that a contrast of the second individual Particle beams are kept essentially constant when they strike the detection areas in the third field. By means of the electrostatic components of the rapid contrast correction means, a high-frequency adjustment and, in particular, keeping the contrast constant can be achieved. The contrast correction control signal can be determined, for example, based on the projection path measurement data of the secondary path and / or based on the actual autofocus data of the primary path.

All of the above statements apply not only to fast autofocusing, but also to fast autostigmation. By definition, within the scope of this application, a focus also includes a stigmation. In principle, stigmation can be physically equated with focusing in only one direction or with different focusing in different directions. The number of particle-optical parameters that describe the particle-optical image increases or doubles when stigmation is taken into account: For example, two parameters each are required for the focus and two parameters for the position, two parameters for the landing angle and two parameters for the rotation . In this context, reference is also made to fast multipole lenses, which are, for example, in the DE 10 2020 107 738 B4 to be discribed; the disclosure of that patent is fully incorporated into the present patent application by reference.

• einen Vielstrahl-Teilchengenerator, welcher konfiguriert ist, um ein erstes Feld einer Vielzahl von geladenen ersten Teilchenstrahlen zu erzeugen;
• eine erste Teilchenoptik mit einem ersten teilchenoptischen Strahlengang, die konfiguriert ist, um die erzeugten Einzel-Teilchenstrahlen auf eine Waferoberfläche in der Objektebene abzubilden, so dass die ersten Teilchenstrahlen an Auftrefforten auf die Waferoberfläche treffen, die ein zweites Feld bilden;
• ein Detektionssystem mit einer Vielzahl von Detektionsbereichen, die ein drittes Feld bilden; eine zweite Teilchenoptik mit einem zweiten teilchenoptischen Strahlengang, die konfiguriert ist, um zweite Einzel-Teilchenstrahlen, die von den Auftrefforten im zweiten Feld ausgehen, auf das dritte Feld der Detektionsbereiche des Detektionssystems abzubilden;
• eine magnetische und/ oder elektrostatische Objektivlinse, insbesondere eine magnetische und/ oder elektrostatische Immersionslinse, durch die sowohl die ersten als auch die zweiten Einzel-Teilchenstrahlen hindurchtreten;
• eine Strahlweiche, die in dem ersten teilchenoptischen Strahlengang zwischen dem Vielstrahl-Teilchengenerator und der Objektivlinse angeordnet ist, und die im zweiten teilchenoptischen Strahlengang zwischen der Objektivlinse und dem Detektionssystem angeordnet ist;
• einen Probentisch zum Halten und/ oder Positionieren eines Wafers während der Waferinspektion;
• ein Autofokus-Messglied, das konfiguriert ist, um während der Waferinspektion Messdaten zum Ermitteln von Autofokus-Istdaten zu erzeugen;
• eine schnelle Autofokus-Korrekturlinse; und
• eine Steuerung;
• wobei die Steuerung für eine statische oder niederfrequente Anpassung einer Fokussierung konfiguriert ist, um an einem ersten Arbeitspunkt mit einem ersten Arbeitsabstand zumindest die magnetische Objektivlinse und/ oder einen Aktuator des Probentisches derart anzusteuern, dass die ersten Einzel-Teilchenstahlen auf die im ersten Arbeitsabstand befindliche Waferoberfläche fokussiert werden.

Bei dieser Ausführungsform der Erfindung ist die Steuerung also eingerichtet, für einen vorgegebenen ersten Arbeitspunkt, dem ein erster Arbeitsabstand zugeordnet ist, die Fokussierung einzustellen. Es ist also möglich, mittels des Systems den Arbeitspunkt in beschriebener Weise zu verstellen und dann die Fokussierung einzustellen.According to one example, a multiple particle beam system for semiconductor inspection includes:

• a multi-beam particle generator configured to generate a first field of a plurality of charged first particle beams;
• a first particle optics with a first particle-optical beam path which is configured to image the generated individual particle beams onto a wafer surface in the object plane, so that the first particle beams strike the wafer surface at locations that form a second field;
• a detection system having a plurality of detection areas which form a third field; a second particle optics with a second particle-optical beam path which is configured to image second individual particle beams, which emanate from the points of incidence in the second field, onto the third field of the detection areas of the detection system;
• a magnetic and / or electrostatic objective lens, in particular a magnetic and / or electrostatic immersion lens, through which both the first and the second individual particle beams pass;
• a beam splitter which is arranged in the first particle-optical beam path between the multi-beam particle generator and the objective lens, and which is arranged in the second particle-optical beam path between the objective lens and the detection system;
• a sample table for holding and / or positioning a wafer during wafer inspection;
• an autofocus measuring element which is configured to generate measurement data for determining actual autofocus data during the wafer inspection;
• a fast auto focus correction lens; and
• a controller;
• wherein the controller is configured for a static or low-frequency adjustment of a focusing in order to control at least the magnetic objective lens and / or an actuator of the sample table at a first working point with a first working distance in such a way that the first individual particle beams hit the wafer surface located in the first working distance be focused.

In this embodiment of the invention, the control is thus set up to set the focusing for a predetermined first working point to which a first working distance is assigned. It is therefore possible to use the system to adjust the operating point in the manner described and then to set the focus.

According to one example, the controller is further configured for a high-frequency adjustment of the focusing in order to generate an autofocus correction lens control signal at the first operating point during the wafer inspection based on the actual autofocus data in order to activate the fast autofocus correction lens during the wafer inspection at the first operating point head for.

In addition, everything that has been defined and / or described in connection with the first aspect of the invention also applies to the example described.

• - Erzeugen von Messdaten an einem ersten Arbeitspunkt für einen aktuellen Fokus auf der Waferoberfläche;
• - Ermitteln von Autofokus-Istdaten basierend auf den Messdaten;
• - Ermitteln eines Autofokus-Korrekturlinsen-Steuerungssignals basierend auf den Autofokus-Istdaten; und
• - Ansteuern eines schnellen Autofokus-Korrekturlinsensystems und hochfrequentes Konstanthalten des Fokus auf der Waferoberfläche, wobei am ersten Arbeitspunkt die Rasteranordnung und der Landewinkel der ersten Einzel-Teilchenstrahlen beim Auftreffen auf der Waferoberfläche ebenfalls konstant gehalten werden.

According to a second aspect of the invention, this relates to a method for operating a plurality of particle beam systems, in particular a plurality of particle beam systems as described in connection with the first aspect of the invention. All terms and definitions which have been explained or introduced in connection with the first aspect of the invention also apply to the method according to the invention. The method for operating a multiple particle beam system has the following steps:

• - Generating measurement data at a first working point for a current focus on the wafer surface;
• Determination of actual autofocus data based on the measurement data;
• Determining an autofocus correction lens control signal based on the actual autofocus data; and
• - Control of a fast autofocus correction lens system and high-frequency keeping the focus constant on the wafer surface, with the grid arrangement and the landing angle of the first individual particle beams also being kept constant at the first working point when they hit the wafer surface.

According to a preferred embodiment of the invention, the fast autofocus correction lens comprises at least one electrostatic lens and / or consists of exactly one electrostatic lens. With regard to the design options of the electrostatic lens and their placement in the beam path, what has already been stated in connection with the multitude of particle beam systems according to the invention applies.

According to another preferred embodiment of the invention, the fast autofocus correction lens comprises at least one fast one Magnetic lens, in particular an air-core coil, and / or consists of exactly one magnetic lens. With regard to the design options of the magnetic lens and their placement in the beam path, what has already been stated in connection with the multitude of particle beam systems according to the invention applies.

As described above in connection with the first aspect of the invention, a fast telecentricity correction means and / or a fast rotation correction means and / or a fast position correction means can be used to keep the grid arrangement on the wafer surface and the land angle constant. The fast telecentric correction means, the fast rotation correction means and / or the fast position correction means then form / form the autofocus correction lens system together with the possibly multi-part autofocus correction lens.

• - Erzeugen eines Telezentrie-Korrektur-Steuerungssignals basierend auf den Autofokus-Istdaten; und
• - Ansteuern des schnellen Telezentrie-Korrekturmittels.

According to a preferred embodiment of the invention, the method furthermore has the following steps:

• Generating a telecentricity correction control signal based on the actual autofocus data; and
• - Control of the fast telecentricity correction means.

• - Erzeugen eines Rotations-Korrektur-Steuerungssignals basierend auf den Autofokus-Istdaten; und
• - Ansteuern des schnellen Rotations-Korrekturmittels.

According to a preferred embodiment of the invention, the method furthermore has the following steps:

• Generating a rotation correction control signal based on the actual autofocus data; and
• - Control of the rapid rotation correction means.

• - Orthogonalisieren von Wirkungen der teilchenoptischen Komponenten, die für die Korrektur oder die Korrekturen des Fokus, des Landewinkels und/ oder der Rasteranordnung verwendet werden.

According to a preferred embodiment of the invention, the method furthermore has the following steps:

• - Orthogonalizing effects of the particle-optical components which are used for the correction or the corrections of the focus, the landing angle and / or the grid arrangement.

• - Erzeugen von Projektionspfad-Messdaten zur Charakterisierung der teilchenoptischen Abbildung im Sekundärpfad;
• - Ermitteln eines Projektionspfad-Steuerungssignals oder eines Sets von Projektionspfad-Steuerungssignalen basierend auf den Projektionspfad-Messdaten; und
• - Ansteuern eines schnellen Projektionspfad-Korrekturmittels, das mehrteilig sein kann, mittels des Projektionspfad-Steuerungssignals oder mittels des Sets von Projektionspfad-Steuerungssignalen, wobei am ersten Arbeitspunkt der Fokus, die Rasteranordnung und der Landewinkel der zweiten Einzel-Teilchenstrahlen beim Auftreffen in einer Detektionsebene konstant gehalten werden.

Bei der Konstanthaltung des Fokus wird also die Fokuslage nachgeführt, die Rasteranordnung und der Landewinkel werden konstant gehalten.According to a preferred embodiment of the invention, the method furthermore has the following steps:

• - Generation of projection path measurement data for characterizing the particle-optical image in the secondary path;
• Determining a projection path control signal or a set of projection path control signals based on the projection path measurement data; and
• - Control of a fast projection path correction means, which can be made up of several parts, by means of the projection path control signal or by means of the set of projection path control signals, the focus, the grid arrangement and the landing angle of the second individual particle beams being constant when they hit a detection plane at the first working point being held.

When the focus is kept constant, the focus position is tracked, the grid arrangement and the landing angle are kept constant.

• - Ansteuern eines schnellen Kontrast-Korrekturmittels mittels eines Kontrast-Korrektur-Steuerungssignals oder einem Set von Kontrast-Korrektur-Steuerungssignalen und Konstanthalten des Kontrasts in der Detektionsebene.

Durch ein Ansteuern des schnellen Kontrast-Korrekturmittels ist es auch möglich, die Lage des Cross-overs im Sekundärpfad gezielt zu beeinflussen, insbesondere konstant zu halten.According to a preferred embodiment of the invention, the method furthermore has the following step:

• Control of a rapid contrast correction means by means of a contrast correction control signal or a set of contrast correction control signals and keeping the contrast constant in the detection plane.

By controlling the rapid contrast correction means, it is also possible to specifically influence the position of the crossover in the secondary path, in particular to keep it constant.

The above-described embodiments of the invention according to the first, second and third aspects of the invention can be combined with one another in whole or in part, provided that no technical contradictions arise as a result.

• 1: zeigt ein Mehrstrahl-Teilchenmikroskop in schematischer Darstellung;
• 2: zeigt einen Ausschnitt einer Steuerung des Mehrstrahl-Teilchenmikroskops mit schneller Autofokus-Korrekturlinse in schematischer Darstellung;
• 3: zeigt einen größeren Ausschnitt einer Steuerung des Mehrstrahl-Teilchenmikroskops mit schneller Autofokus-Korrekturlinse in schematischer Darstellung;
• 4: zeigt schematisch ein Verfahren zum Einstellen eines schnellen Autofokus mittels einer Autofokus-Korrekturlinse;
• 5: zeigt schematisch einen Schnitt durch ein Mehrstrahl-Teilchenmikroskop, in dem die erfindungsgemäße Autofokus-Korrekturlinse angeordnet werden kann;
• 6: illustriert schematisch eine Ausführungsform der Erfindung mit Autofokus-Korrekturlinse;
• 7: illustriert schematisch eine Ausführungsform der Erfindung mit Autofokus-Korrekturlinse;
• 8: illustriert schematisch eine Ausführungsform der Erfindung mit Autofokus-Korrekturlinse;
• 9: illustriert schematisch eine Ausführungsform der Erfindung mit Autofokus-Korrekturlinse;
• 10: illustriert schematisch eine Ausführungsform der Erfindung mit Autofokus-Korrekturlinse;
• 11: illustriert schematisch eine Ausführungsform der Erfindung mit Autofokus-Korrekturlinse;
• 12: illustriert schematisch weitere Ausführungsformen der Erfindung mit Autofokus-Korrekturlinse;
• 13: illustriert schematisch weitere Ausführungsformen der Erfindung mit Autofokus-Korrekturlinse;
• 14: illustriert schematisch eine Ausführungsform der Erfindung mit Autofokus-Korrekturlinse;
• 15: illustriert schematisch eine Ausführungsform der Erfindung mit Autofokus-Korrekturlinse;
• 16: illustriert schematisch eine Ausführungsform der Erfindung mit Autofokus-Korrekturlinse; und
• 17: illustriert schematisch eine Ausführungsform der Erfindung mit Autofokus-Korrekturlinse.

The invention will be better understood with reference to the accompanying figures. Show:

• 1 : shows a multi-beam particle microscope in a schematic representation;
• 2 : shows a section of a control of the multi-beam particle microscope with fast autofocus correction lens in a schematic representation;
• 3 : shows a larger section of a control of the multi-beam particle microscope with fast autofocus correction lens in a schematic representation;
• 4th : shows schematically a method for setting a fast autofocus by means of an autofocus correction lens;
• 5 : shows schematically a section through a multi-beam particle microscope in which the autofocus correction lens according to the invention can be arranged;
• 6th : schematically illustrates an embodiment of the invention with an autofocus correction lens;
• 7th : schematically illustrates an embodiment of the invention with an autofocus correction lens;
• 8th : schematically illustrates an embodiment of the invention with an autofocus correction lens;
• 9 : schematically illustrates an embodiment of the invention with an autofocus correction lens;
• 10 : schematically illustrates an embodiment of the invention with an autofocus correction lens;
• 11th : schematically illustrates an embodiment of the invention with an autofocus correction lens;
• 12th : schematically illustrates further embodiments of the invention with an autofocus correction lens;
• 13th : schematically illustrates further embodiments of the invention with an autofocus correction lens;
• 14th : schematically illustrates an embodiment of the invention with an autofocus correction lens;
• 15th : schematically illustrates an embodiment of the invention with an autofocus correction lens;
• 16 : schematically illustrates an embodiment of the invention with an autofocus correction lens; and
• 17th : schematically illustrates an embodiment of the invention with an autofocus correction lens.

In the following, the same reference symbols denote the same features, even if they are not explicitly mentioned in the text.

1 is a schematic representation of a particle beam system 1 in the form of a multi-beam particle system 1 , which uses a variety of particle beams. The particle beam system 1 generates a large number of particle beams which strike an object to be examined in order to generate interaction products there, for example secondary electrons, which emanate from the object and are subsequently detected. The particle beam system 1 is of the scanning electron microscope (SEM) type, which has multiple primary particle beams 3 that employs in several places 5 on a surface of the object 7th impinge and there generate several spatially separated electron beam spots or spots. The object to be examined 7th can be of any type, for example a semiconductor wafer, in particular a semiconductor wafer with HV structures (ie with horizontal and / or vertical structures), or a biological sample, and an arrangement of miniaturized elements or the like. The surface of the object 7th is on a first level 101 (Object plane) of an objective lens 102 an objective lens system 100 arranged.

The enlarged section I _{1 of} the 1 shows a plan view of the object plane 101 with a regular rectangular field 103 of impact locations 5 which in the first level 101 are formed. In 1 is the number of impact locations 25 which form a 5 x 5 field 103. The number 25 at points of impact is a number chosen for the sake of simplicity of representation. In practice, the number of rays, and thus the number of points of impact, can be chosen to be significantly larger, such as 20 × 30, 100 × 100 and the like.

In the illustrated embodiment, the field is 103 of impact locations 5 a substantially regular rectangular field with a constant distance P ₁ between adjacent impact locations. Exemplary values of the distance P ₁ are 1 micrometer, 10 micrometers and 40 micrometers. However, it is also possible that the field 103 has other symmetries, such as a hexagonal symmetry.

A diameter of the first level 101 shaped beam spots 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 beams 3 for shaping the beam spots 5 takes place through the objective lens system 100 . The objective lens system can include a magnetic immersion lens, for example.

The primary particles hitting the object generate interaction products, for example secondary electrons, backscattered electrons or primary particles that have experienced a movement reversal for other reasons, which are caused by the surface of the object 7th or from the first level 101 go out. The from the surface of the object 7th outgoing interaction products are through the objective lens 102 to secondary particle beams 9 shaped. The particle beam system 1 provides a particle beam path 11 ready to the multiplicity of secondary particle beams 9 a detection system 200 to feed. The detector system 200 comprises particle optics with a projection lens 205 to the secondary particle beams 9 on a particle multi-detector 209 to judge.

The cutout I ₂ in 1 shows a plan view of the plane 211 , in which individual detection areas of the particle multi-detector 209 lie on which the secondary particle beams 9 in places 213 hit. The meeting points 213 lie in a field 217 with a regular distance P _{2 from} one another. Exemplary values of the distance P ₂ are 10 micrometers, 100 micrometers, and 200 micrometers.

The primary particle beams 3 are in a beam generating device 300 generated which at least one particle source 301 (e.g. an electron source), at least one collimation lens 303 , a multi-aperture arrangement 305 and a field lens 307 , or a field lens system comprising a plurality of field lenses. The particle source 301 generates at least one diverging particle beam 309 , which through the at least one collimation lens 303 is collimated or at least largely collimated to a beam 311 to shape which the multi-aperture arrangement 305 illuminated.

The cutout I ₃ in 1 shows a plan view of the multi-aperture arrangement 305 . The multi-aperture arrangement 305 includes a multi-aperture plate 313 which has a plurality of apertures formed therein 315 having. Midpoints 317 of the openings 315 are in a field 319 arranged on the field 103 is imaged, which through the beam spots 5 in the object level 101 is formed. A distance P _{3 of} the center points 317 the apertures 315 each other can have exemplary values of 5 micrometers, 100 micrometers and 200 micrometers. The diameter D of the apertures 315 are smaller than the distance P _{3 between} the centers of the apertures. Exemplary values for the diameter D are 0.2 x P ₃ , 0.4 x P ₃ and 0.8 x P ₃ .

Particles of the illuminating particle beam 311 penetrate the apertures 315 and form particle beams 3 . Particles of the illuminating beam 311 which on the plate 313 hit, are intercepted by them and do not contribute to the formation of the particle beams 3 at.

The multi-aperture arrangement 305 focuses each of the particle beams due to an applied electrostatic field 3 such that in one plane 325 Beam focus 323 are formed. Alternatively, the beam foci 323 be virtual. A diameter of the beam focus 323 can be, for example, 10 nanometers, 100 nanometers and 1 micrometer.

The field lens 307 and the objective lens 102 provide a first imaging particle optics to the plane 325 , in which the beam foci 323 be formed on the first level 101 map so that there is a field 103 of impact locations 5 or beam spots arise. So much for a surface of the object in the first level 7th is arranged, the beam spots are correspondingly formed on the object surface.

The objective lens 102 and the projection lens assembly 205 provide a second imaging particle optic around the first plane 101 on the detection level 211 map. The objective lens 102 is thus a lens which is part of both the first and the second particle optics, while the field lens 307 only the first particle optics and the projection lens 205 belong only to the second particle optics.

A beam switch 400 is in the beam path of the first particle optics between the multi-aperture arrangement 305 and the objective lens system 100 arranged. The beam switch 400 is also part of the second optics in the beam path between the objective lens system 100 and the detector system 200 .

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 the international patent applications WO 2005/024 881 A2 , WO 2007/028 595 A2 , WO 2007 028 596 A1 , WO 2011/124 352 A1 and WO 2007/060 017 A2 and the German patent applications with the publication numbers DE 10 2013 016 113 A1 and DE 10 2013 014 976 A1 are obtained, the disclosure of which is fully incorporated by reference into the present application.

The multiple particle beam system further comprises a computer system 10 on, which is designed both to control the individual particle-optical components of the multitude of particle beam systems, as well as to evaluate and analyze the with the multi-detector 209 signals obtained. The computer system 10 can be made up of several individual computers or components. It can also control the fast autofocus correction lens according to the invention as well as the telecentricity correction means and / or the fast rotation correction means and / or other fast correction means (in 1 each not shown).

2 shows a section of a control of the computer system 10 of the multi-beam particle microscope 1 with fast auto focus correction lens 824 in a schematic representation. Specifically, the section shows the control 821 for fast autofocus. The control 821 for the fast autofocus is set up to carry out high-frequency adjustments of the focus at an operating point during the wafer inspection. This means that adjustments to the focus can be carried out very quickly, for example within a few microseconds. For these quick adjustments are in addition to the higher-level control system 821 (here as part of the computer system 10 ) further components are provided: a measuring element 822 , an autofocus algorithm 823 for processing the measurement data and at least one actuator that is set according to the processing of the measurement data. In the specific example, a Actuator through the auto focus correction lens 824 provided. Additional fast actuators, namely here a telecentricity correction means 825 , a quick rotation correction tool 826 as well as a rapid position correction means 827 are also provided in this example. The measuring element 822 is configured to generate measurement data for determining actual autofocus data during the wafer inspection. The actual autofocus data directly or indirectly describe the current position of the focus relative to the wafer surface. Autofocus measuring elements are known in principle from the prior art. Examples of this are the use of astigmatic auxiliary beams to adjust the focus and height measurements on a sample surface (eg using a z-sensor). It is important that by means of the measuring element 822 or by means of measuring elements 822 Continuous, that is to say, ongoing “on-the-fly” settings of the focus can also be determined for each image field that is obtained by means of the large number of individual particle beams. The autofocus algorithm 823 is now - depending on the measuring element 822 and evaluation mode - set up to generate autofocus actual data from the measurement data and to generate an autofocus correction lens control signal based on the autofocus actual data in order to generate the fast autofocus correction lens 824 to be controlled at a high frequency during the wafer inspection at an operating point. This adjusts the focus position. As already stated several times, the effects of particle-optical components of a multiple particle beam system are normally not orthogonal to one another. This means that by means of a variation of an effect on only one particle-optical component it is normally not possible to change only one single parameter that characterizes the particle-optical image. Instead, the system is more complex and changing a parameter of the particle-optical imaging normally requires a variation of effects on several particle-optical components.

In the specific case, this means that a readjustment / fine adjustment of the focus position results in a change in further particle-optical parameters. These are, for example, the magnification (coupled to the beam spacing of the individual particle beams from one another), the telecentricity and the rotation of the individual particle beams when they strike the sample or the wafer 7th . A change in these additional parameters is not desired, however, so that these too are corrected and / or kept constant in the course of the fast autofocus. Thus, a telecentricity correction means is exemplary 825 , a rotation correction agent 826 and a position correcting means 827 intended. The fast telecentricity correction means is configured to contribute significantly to a tangential or radial telecentricity error of the first single particle beams 3 in the second field 103 to correct, and the fast autofocus control 821 is set up to generate a telecentricity correction means control signal for high-frequency adjustments at the respective working point during the wafer inspection based on the actual autofocus data, in order to control the fast telecentricity correction means during the wafer inspection. A first deflector array can be used as the telecentricity correction means, for example, which is located in an intermediate image plane, for example in the intermediate image plane 325 , of the first particle-optical beam path is arranged. But other design variants are also possible.

To correct the rotation, specifically the unwanted twisting of the grid arrangement in the second field 101 , is also a quick rotation corrector 826 is provided which is configured to contribute significantly to a rotation of the first single particle beams 3 in the second field 101 to correct. There is also the fast autofocus control 821 set up during the wafer inspection at the respective working point based on the actual autofocus data to generate a rotation correction means control signal for high-frequency adjustments to the fast rotation correction means 826 to be controlled during the wafer inspection. Such a rotation correction means can be implemented 826 for example as a second deflector array which is arranged at a distance directly in front of or after the first deflector array for telecentricity correction. However, other embodiments are also possible, for example by means of a multi-lens array which is arranged at a distance directly in front of or after the first deflector array and in such a way that the first individual particle beams 3 enforce the multi-lens array off-axis. Alternatively, the multi-beam particle generator 305 the quick rotation correction tool 826 and the rotation correcting means 826 can be actively rotated by the rotation correction means control signal. It is also possible to combine two magnetic field generating devices for weak magnetic fields which are opposite to one another and to use each of the magnetic fields only for changing the rotation in a specific direction.

3 shows a larger section of a control of the computer system 10 of the multi-beam particle microscope 1 with fast auto focus correction lens 824 in a schematic representation. Control units are shown as examples 810 for the primary path and 830 for the secondary path. The control of the computer system 10 more than the in 3 Have components shown. With regard to the present invention, some important control elements will be discussed below. The control 810 in the primary path includes a controller 811 for setting the operating point and the control 821 for setting of the fast autofocus. The control 811 is configured in particular for a static or low-frequency adjustment of a focusing in order to control at least the magnetic objective lens and / or an actuator of the sample table at a first working point with a first working distance in such a way that the first individual particle beams are focused on the wafer surface located in the first working distance will. In addition to the focus, other parameters of the particle-optical imaging, such as the individual beam distance (pitch), the associated magnification, a rotation of the grid arrangement of the individual particle beams when hitting the wafer surface and the desired landing angle when hitting the wafer surface, are also determined set. The working point setting 811 thus includes a slow auto focus and additional correction functions. There is a measuring element for the setting itself 812 , an adjustment algorithm 813 as well as various actuators 814 intended. To these actuators 814 counts in particular the magnetic and / or electrostatic objective lens 102 and in the case of a height-adjustable sample table, possibly also an actuator for the sample table. The actuators 814 for setting the operating point also include, for example, a field lens system 307 and the multi-beam particle generator 305 . Further particle-optical elements in the first particle-optical beam path can act as further actuators 814 act; they can be magnetic and / or electrostatic lenses. With the means for setting the operating point, a relatively large stroke for changing the operating distance can be generated; this can be, for example, +/- 300, 200, 100 μm. An adjustment time to a selected working distance is relatively long; it can be, for example, in the range of a few tens to a few hundred milliseconds.

The control 821 for fast autofocusing includes the measuring element 822 , an autofocus algorithm 823 and at least the auto focus correction lens 824 ; however, other correction means can also be used, for example the telecentricity correction means described above 825 , the rotation correction means 826 and / or the position correction means 827 be provided. By means of the control 821 A high-frequency adjustment of the focus is possible for the fast autofocus, typical adjustment times are in the range of a few microseconds, for example an adjustment time TA 500 µs, preferably TA 100 µs and / or TA 50 µs. The stroke for changing the focus position is typically a few micrometers, for example +/- 20 µm, +/- 15 µm and / or +/- 10 µm. In this case, for example, an adaptation time TA for the high-frequency adaptation is at least by the factor 10 , preferably at least by the factor 100 and / or 1000, shorter than the adaptation time TA for the low-frequency or static adaptation by means of the control for the operating point setting 811 .

A change in the focus position or the position of the wafer surface can also result in a necessary readjustment or readjustment of particle-optical components in the secondary path. Correspondingly, the controller 830 for controlling the secondary path is part of the control of the computer system 10 . The control elements in the secondary path can also be converted into low-frequency or static control elements 831 and in high-frequency control elements 841 (corresponding to a second fast auto focus, for example). The slow operating point setting is made by the control 831 controlled, this is a measuring element 832 , for example a CCD camera, a second adjustment algorithm 833 as well as an actuator 834 or more actuators 834 intended. To these actuators 834 include magnetic projection lenses 205 , which are controlled in such a way that the foci of the second single particle beams 9 exactly on the surface of the detection areas of the detection unit 209 can be mapped. But also other actuators can by means of the control 831 to set the operating point. The control 841 controls the fast second autofocus in the secondary path: refocusing is carried out in the secondary path during the wafer inspection. It is also possible that other particle-optical parameters such as position, telecentricity and rotation can also be quickly readjusted. For this purpose, in this embodiment includes the controller 841 a measuring element 842 , a second autofocus algorithm 843 as well as rapid projection path correction means 844 , especially electrostatic lenses, electrostatic deflectors, and / or electrostatic stigmators. As a measuring element 842 For example, a fast CCD camera comes into consideration or, for example, means for current measurement around a contrast diaphragm which is arranged in a cross-over plane in the secondary path. But it is also possible to use the measuring element in the secondary path 842 and instead work in a feed-forward loop. In this case, based on values / settings that have been determined for the primary path, using the second autofocus algorithm 843 Control signals for the rapid projection path correction means 844 determined and the projection path correction means 844 are controlled accordingly. The autofocus algorithm 843 can include look-up tables. It is also possible to combine the two variants described with one another, that is to say one measuring element 842 to use in addition and, for example, the settings of the actuators / projection path correction means only in the case of certain measured deviations from a reference value 844 to be explicitly redefined for the secondary path.

The control of the computer system 10 with controls 810 to control the primary path and 830 to control the secondary path is now also set up so that the controls 810 and 830 with their respective components are timed, that is, synchronized with one another. The electronics used for control are also very fast, but it must be ensured that, for example, the best possible setting of the particle-optical components in the primary path and also in the secondary path is guaranteed for each image field (mFOV). Details for realizing a fast control of particle-optical components / for fast electronics are known to the person skilled in the art and they are also, for example, in the German patent application 102020209833.6 , filed on August 5, 2020, the full disclosure of which is incorporated into this patent application by reference.

4th shows schematically a method for setting a fast autofocus by means of an autofocus correction lens 824 . It is assumed that a (slow) setting of the system at a first working point with an assigned first working distance has already taken place by means of setting the magnetic objective lens and / or by activating an actuator for a sample table; other parameters have already been set in accordance with specifications for the operating point (magnification, telecentricity, rotation).

In one process step S1 measurement data are generated for a current focus at the selected working point AP. A working point is thereby defined at least by the working distance between the objective lens and the wafer surface; however, other parameters can also be used to define the operating point. Examples of this are the focus position, the position and the telecentricity or the landing angle of individual particle beams 3 on the wafer surface as well as the rotation of a grid arrangement of single particle beams 3 when hitting the wafer surface. An example is to be used in the following, but is not to be interpreted as restrictive for the invention. In one process step S2 the actual autofocus data is determined based on measurement data. These measurement data can be used with the measuring elements described above 812 can be obtained and by means of the adjustment algorithm 813 can be used to infer the actual autofocus data. The actual autofocus data thus indicate, for example, whether there is overfocusing or underfocusing or how large it is. However, it is also possible for the measurement data to form the actual autofocus data directly (identity mapping). After the actual autofocus data has been determined, the following steps take place S3 , S4 and S5 The generation of control signals based on the actual autofocus data: In step S3 an autofocus correction lens control signal is generated based on the actual autofocus data. In step S4 a telecentricity correction means control signal is generated based on actual autofocus data. In step S5 a rotation correction means control signal is generated based on the actual autofocus data. A setting of the autofocus correction lens changes not only the focus position, but usually also the magnification (position, not shown), the telecentricity and / or the rotation of a grid arrangement of the individual particle beams. In the course of determining the control signals, in the example shown, recourse is made to an orthogonalization matrix or inverted sensitivity matrix 850 , from which it can be deduced which particle-optical components have to be excited differently by what amount in order to set exactly one particle-optical parameter differently. As a result, the autofocus correction lens is then preferably activated simultaneously in step S6 , an activation of the telecentricity correction means in step S7 as well as controlling the rotation correction means in step S8 and, if necessary, other quicker correction means.

Once these settings have been made for the primary path, the secondary path is readjusted at high frequency: In the example shown, this is a feed-forward, while a feedback is implemented in the primary path: in one process step S9 second measurement data for the current second autofocus position (detection plane) are generated in the secondary path. Additionally or alternatively, the current position of the crossover of the second individual particle beams in the secondary path can be determined. In the process step S10 second actual autofocus data are determined for the secondary path. In addition or as an alternative, use can also be made of variables for the secondary path that have already been assigned to the actual autofocus data of the primary path in advance. In the process step S11 Projection path correction means control signals are then determined based on the second actual autofocus data. This can be a set of control signals. The control signals are preferably generated with recourse to a second orthogonalization matrix or a second inverted sensitivity matrix 851 for the secondary path. The control signals are then used in one process step S12 controlled fast projection path correction means. This preferably includes a fast second autofocus correction lens. In addition, a fast telecentricity correction means (e.g. in the form of a deflector array in an intermediate image plane in the secondary path) and / or a fast rotation correction means (e.g. in the form of a second deflector array directly before or after the deflector array for fast telecentricity correction in the Secondary path) and / or more rapid Correction means, such as electrostatic lenses, electrostatic deflectors and / or electrostatic stigmators, can be controlled. A fast contrast correction agent can also be activated. A rapid contrast correction means can for example be integrated into the projection lens system of the secondary path, as is the case, for example, in FIG US 2019/0355544 A1 is described, the disclosure of which is fully incorporated into this application by reference. With the settings from step S12 is then in the process step S13 recorded an image field. Measurement data can then be generated again for the current focus at the operating point (method step S1 ). The same procedure is followed until the entire image recording has ended.

In one example, the first or second orthogonalization or inverted sensitivity matrix can be used 850 , 851 of the operating point setting according to the setting with the controls 811 and 831 depend. For example, a required dynamic correction of a tangential or radial telecentricity error can depend on a fine correction of a focal plane by a few µm from the working point or on the coarse focus setting within the long-range focus area of several 100 µm. In this case the orthogonalization or inverted sensitivity matrices become 850 , 851 for a selected operating point selected from a memory in which several orthogonalization or inverted sensitivity matrices 850 , 851 are stored for different focus settings within the long-range focus range.

5 shows schematically a section through a multi-beam particle microscope 1 , in which the autofocus correction lens according to the invention 824 can be arranged. The multitude particle beam system 1 first assigns a particle source 301 on. In the example shown, this particle source is transmitting 301 a single particle beam with charged particles, e.g. electrons. Particle beams or a particle-optical beam path are in 5 schematically by the dashed line with the reference number 3 shown. The single particle beam first passes through a condenser lens system 303 and then meets a multi-aperture arrangement 305 . This multi-aperture arrangement 305 if necessary serves as a multi-beam generator with other particle-optical components. The one from the multi-aperture arrangement 305 outgoing first particle beams then pass through a field lens or a field lens system 307 and then step into a beam switch 400 a. This beam switch 400 comprises a jet pipe assembly 460 , which is Y-shaped in the example shown and has three legs 461 , 462 and 463 includes. The beam switch 400 has two flat, interconnected structures for holding the magnetic sectors 410 , 420 the magnetic sectors contained therein or fixed thereon 410 and 420 on. After enforcing the jet switch 400 the first particle beams pass through a scan deflector 500 and then a particle optical objective lens 102 before the first particle beams 3 on an object 7th , here a semiconductor wafer with HV structures. Through this impact, the object becomes 7th Secondary particles, such as secondary electrons, dissolved out. These secondary particles form second particle beams to which a second particle-optical beam path 9 assigned. The second particle beams penetrate after exiting the object 7th first the particle-optical objective lens 102 and then the scan deflectors 500 before they get into the beam switch 400 enter. Then the second particle beams emerge 9 from the beam switch 400 out, enforce a projection lens system 205 (shown in very simplified form), enforce an electrostatic element 260 and then hit a particle-optical detection unit 209 on (the reference symbol 260 refers to the so-called antiscan, which is the otherwise occurring scanning movement of the secondary beams 9 when hitting the detection unit 209 compensated).

Inside the beam switch 400 is where the nozzle assembly is located 460 , which in the example shown is also via the beam switch 400 addition continues. The division of the beam path within the beam switch 400 in the first particle-optical beam path 3 and the second particle-optical beam path 9 takes place inside the steel switch 400 using magnetic sectors 410 , 420 . In the in 5 In the illustrated example, the jet pipe arrangement continues 460 also outside the beam switch 400 away. It extends in particular to the particle-optical objective lens 102 or into the particle-optical objective lens 102 in (lance extension). In the area of the particle source 301 , in the area of the multi-aperture arrangement 305 as well as in the area of the detector unit 209 the jet pipe arrangement expands 460 to vacuum chambers 350 , 355 and 250 . At least in the area of the jet switch 400 the jet pipe arrangement is normally formed in one piece, ie it has neither welds nor weld seams, nor solder points or solder seams. In the example shown, the jet pipe arrangement has copper, but it could also have titanium or another element or another compound. In the area of the jet pipe arrangement 460 within the beam switch 400 a high vacuum prevails, preferably with a pressure less than 10 ^-5 mbar, in particular less than 10 ^-7 mbar and / or 10 ^-9 mbar. In the chambers already mentioned 350 , 355 and 250 a vacuum prevails preferably in each case with pressures less than 10 ^-5 mbar, in particular less than 10 ^-7 mbar and / or 10 ^-9 mbar.

The objective lens 102 has an upper pole piece in the example shown 108 and a lower pole piece 109 on. Between the two pole pieces 108 and 109 there is a winding 110 to generate a magnetic field. The upper pole piece 108 and the lower pole piece 109 can be electrically isolated from one another. The particle-optical objective lens 102 is in the example shown a single magnetic lens in the form of an immersion lens; however, the objective lens or the objective lens system can also comprise further magnetic lenses or electrostatic lenses.

In the in 5 Multi-beam particle microscope shown 1 can now use the fast autofocus correction lens according to the invention 824 can be integrated in several configurations and in several positions, possibly together with other fast correctors. The fast autofocus correction lens works depending on the position 824 more or less on the focus of the single particle beams 3 ; however, it can also affect other particle-optical parameters such as the position, the landing angle and / or the rotation of the individual particle beams 3 works. A second or one or more further autofocus correction lens can also be integrated in the primary path and / or in the secondary path; if necessary, further rapid correction means can be provided in the primary path and / or in the secondary path.

6th schematically illustrates an embodiment of the invention with a fast autofocus correction lens 824 . In this embodiment, the auto focus correction lens is 824 provided in the form of an additional electrode. This can for example be designed as a single aperture plate with a central opening to which a voltage U _{AF is} applied. The level and sign of the voltage can be adjusted by means of the control 821 for fast autofocus. This exemplary embodiment has the advantage that the autofocus correction lens is implemented as the penultimate lens relatively far down in the beam path. As a result, only minor subsequent aberrations are generated. The higher the _{magnitude of the voltage U AF} , the more difficult it is to technically realize rapid voltage changes. The embodiment shown is therefore particularly well suited when the sample 7th applied sample voltage U _{Sample is} not too high.

7th schematically illustrates a further embodiment of the invention with an autofocus correction lens 824 . In the example shown is the auto focus correction lens 824 inside the magnetic objective lens 102 arranged. The autofocus correction lens 824 is located between the upper pole piece 108 and the lower pole piece 109 the objective lens 102 . It lies on the upper pole piece 108 a voltage U ₁ and at the lower pole piece 109 a voltage U ₂ . These voltages can be relatively high and amount to a few kilovolts, for example. The same can then also be done for the one on the autofocus correction lens 824 Applicable voltage U _AF apply. The autofocus correction lens can also be used here 824 be operated with a relatively high voltage U _AF . However, if the upper pole piece lies 108 at ground potential, the voltage U _AF can be selected to be relatively low in magnitude. The autofocus correction lens is also used in this embodiment 824 arranged relatively far down in the first particle-optical beam path; in the example shown, it is the penultimate particle-optical element. This in turn has the advantage that any subsequent aberrations are low in this embodiment variant too.

8th Figure 3 shows a further embodiment of the invention with a fast autofocus correction lens 824 in a schematic representation. In this variant there is between the beam deflection system 500 and the upper pole piece 108 the magnetic objective lens 102 the auto focus correction lens 824 intended. This is a rapidly controllable electrode to which the voltage U _AF is applied, the value of which is determined by the control 821 of the fast autofocus is adjustable. This variant has the advantage that the electrode 824 is arranged essentially within the cross-over plane. Extensive calculations by the inventors have shown that the influence of the electrode 824 is essentially focused in this position. The other particle-optical parameters such as position, landing angle and rotation remain essentially unchanged. In addition, this embodiment has the advantage that the effect in the crossover is identical on all individual particle beams. This facilitates the precise setting of the autofocus.

9 schematically illustrates a further embodiment of the invention with an autofocus correction lens 824 . Also in this case is the auto focus correction lens 824 designed as a fast electrostatic element or as a fast electrostatic lens. Into the magnetic objective lens 102 the spray lance extension protrudes 464 starting from the upper pole piece 108 the objective lens 101 a little way in. This lance extension 464 lies - like the entire nozzle 460 - on earth potential. Inside the lance extension 464 is the auto focus correction lens 824 arranged. This in turn is provided by the controller _{with an adjustable voltage U AF} 821 applied. This can be relatively low. The position of the autofocus correction lens shown 824 is located near the crossover level. Extensive calculations have shown that a positioning of the autofocus correction lens 824 at the cross-over or in the vicinity of the cross-over mainly acts on the focus of the individual particle beams. Adjustments of further particle-optical parameters such as position, landing angle and rotation are therefore either not absolutely necessary or they are at least less. This allows a more rapid readjustment of the remaining parameters or the correction elements can be designed to be weaker. This creates fewer follow-up aberrations.

10 illustrates schematically a further embodiment of the invention with a fast autofocus correction lens 824 . In the embodiment shown, the autofocus correction lens is 824 as an offset to the scan deflector 500 intended: The scan deflector 500 comprises, in the example shown, an upper deflector 500a and a lower deflector 500b. The upper deflector 500a and the lower deflector 500b can in principle be of the same construction. They can be designed, for example, as a deflector plate pair, as a quadrupole element or as an octupole element. The voltage U _AF is now applied as an offset both to the upper deflector 500a and to the lower deflector 500b. The corresponding control signal is in turn by means of the controller 821 provided for fast autofocus. This variant has the advantage that the fast autofocus correction lens 824 again close to the crossover of the single particle beams 3 is arranged. An excitation of the autofocus correction lens also acts here 824 therefore essentially on the focus. In addition, no additional hardware is required for this form of implementation: only the voltage U _{AF has to be applied} as an offset to the upper deflector 500a and the lower deflector 500b.

11th Figure 3 shows another embodiment of the invention with a fast electrostatic autofocus correction lens 824 . In this embodiment, the is the fast auto focus correction lens 824 provided as a ring electrode between the upper deflector 500a and the lower deflector 500b. Again, the auto focus correction lens 824 relatively close to the crossover of the individual particle beams 3 is arranged. The Lens 824 therefore acts primarily on the focus of the individual particle beams. There are also changes to the hardware of the system 1 relatively easy to perform. The fast autofocus correction lens can be used instead of a ring electrode 824 also as an air coil around the jet pipe 861 (in 11th not shown) be formed around.

12th shows further embodiments of the invention with a fast autofocus correction lens 824 in a schematic representation. In these embodiments, the jet pipe 460 in the places where the auto focus correction lens 824 is provided, interrupted. It is in these positions in the overall system 1 a relatively large amount of space, which means that the autofocus correction lens is integrated 824 into the system as a whole. Specifically, in 12th three different positions are shown where the auto focus correction lens 824 can be arranged: According to a first example, the autofocus correction lens 824a is in the particle-optical beam path above the beam switch 400 or above the magnet sector 410 . In other words, there is an interruption in the jet pipe 460 , in which the autofocus correction lens 824a is arranged, between the field lens system 307 (in 12th not shown) and the beam switch 400 . A second possibility is to interrupt the jet pipe 460 between the two magnetic sectors 410 and 420 to provide and to arrange the autofocus correction lens 824b in this interruption. A third option is to use the nozzle 460 between the beam switch 400 and the beam deflection system 500 to arrange. Part of the inner wall of the jet pipe 460 is thus replaced in these design variants by the autofocus correction lens 824a, 824b and / or 824c or is not located - like the beam pipe 460 - on earth potential.

13th shows further embodiments of the invention with fast autofocus corrective lenses 824 . This in 13th The example shown differs from the one in 13th example shown in that there is no interruption of the jet pipe 460 is provided. Instead, a tube lens 824a, 824b and 824c is inserted into the radiant tube 460 integrated. This makes it easier to use the nozzle 460 to design a seal and to maintain the vacuum or high vacuum contained therein. In the implementation variant with tubular lenses, the voltage U _{AF is} applied to the central electrode; the upper and lower electrodes are preferably at ground potential. Alternatively, at the points shown around the jet pipe 460 around a fast magnetic lens, for example in the form of an air coil. This has only a few turns k, for example 10 k 500 and / or 10 k 200 and / or 10 k 50.

14th Figure 3 shows a further embodiment of the invention with a fast autofocus correction lens 824 , with the jet pipe 460 is interrupted. The autofocus correction lens 824 is arranged within this interruption. This interruption is located within a magnetic field lens of the field lens system 307 . This variant can be implemented relatively easily because of the space available. In addition, there is the jet pipe 460 to ground potential, which is why the voltage U _AF to the autofocus correction lens 824 only a relatively low voltage has to be applied to the individual particle beams 3 to influence. At this Embodiment, however, it is such that the autofocus correction lens acts both on the focus and on the position as well as on the landing angle of the individual particle beams when they strike the wafer surface. Conversely, it is possible to have a position within the field lens 307 to use to correct a tilting of the beams and also the position of the beams.

15th Figure 3 shows a further embodiment of the invention with a fast autofocus correction lens 824 . Compared to the in 14th The embodiment variant shown here is such that the jet pipe 460 has no interruption. Instead it is inside the jet pipe 460 a tubular lens as a fast autofocus correction lens 824 arranged. In this embodiment variant, too, implementation is relatively simple if there is sufficient installation space. Conversely, it is again so that the autofocus correction lens 824 in addition to the focus, also on the position and the landing angle of the individual particle beams 3 works. It may therefore be advantageous to use the autofocus correction lens to (also) correct the tilting of the individual particle beams and / or the position of the individual particle beams.

16 Figure 3 shows a further embodiment of the invention with a fast autofocus correction lens 824 in a schematic representation. In this embodiment, the auto focus correction lens is 824 near the intermediate image plane 325 arranged: The autofocus correction lens is located here 824 in this example designed as a combined lens with a first component 824a and a second component 824b. These two components 824a and 825b become symmetrical to the intermediate image plane 325 provided, the effect of the combination is the same as if it were the auto focus correcting lens 824 directly within the intermediate image level 325 arranged. This embodiment variant has the advantage that in the intermediate image plane 325 even further particle-optical components of the overall system 1 can be arranged. A positioning in the intermediate image plane 325 is useful, for example, for a first multi-reflector array, since this enables rapid telecentricity correction for the first individual particle beams, as described above in the general part of the application. Alternatively, it is also possible to use the autofocus correction lens 824 in one piece (i.e. only with component 824a or only with component 825b) in the vicinity of the intermediate image plane 325 to train. There is another alternative, the autofocus correction lens 824 in one piece (i.e. only with component 824a or only with component 825b) as precisely as possible within the intermediate image plane 325 to arrange. Then the auto focus corrective lens 824 As with the symmetrical arrangement of the components 824a and 824b, a relatively large effect on the telecentricity of the individual particle beams passing through them 3 .

17th Figure 3 shows a further embodiment of the invention with a fast autofocus correction lens 824 . In this embodiment, the is the fast auto focus correction lens 824 into the multi-aperture arrangement 305 integrated. This multi-aperture arrangement 305 includes in addition to a multi-aperture plate 313 , which is used to generate single beams, further multi-aperture plates or multi-lens arrays and / or multi-deflector arrays (e.g. for individual focusing and / or stigmation of the single-particle beams; in 17th not shown). The fast autofocus correction lens can be used in this sequence of so-called micro-optics 824 be provided in the form of a fast multi-individual lens arrangement. The multi-aperture plate 824a and the multi-aperture plate 824c are at ground potential. In between there is the multi-aperture plate 824b, on which the autofocus correction voltage U _{AF is applied} by means of the controller 821 can be created. The advantage of this embodiment of the invention is that basically no change in position and no tilting of the individual particle beams is caused; however, spherical aberrations may occur in the auto focus correction lens 824 in the form of a multi-individual lens arrangement and manufacturing tolerances for the multi-aperture plates can be critical. In addition, a relatively high voltage must currently be used as the voltage U _AF.

All of the above statements apply not only to fast autofocusing, but also to fast autostigmation. By definition, within the scope of this application, a focus also includes a stigmation. In principle, stigmation can be physically equated with focusing in only one direction or with different focusing in different directions. In this context, reference is also made to fast multipole lenses, which are, for example, in the DE 10 2020 107 738 B4 to be discribed; the disclosure of that patent is fully incorporated into the present patent application by reference.

The embodiments shown can be combined with one another in whole or in part, provided that no technical contradictions arise as a result. In addition, the illustrated embodiments are not to be understood as restricting the invention.

List of reference symbols

1

Multi-beam particle microscope

3

primary particle beams (single particle beams)

5

Beam spots, impact locations

7th

object

9

secondary particle beams

10

Computer system, control

100

Objective lens system

101

Object level

102

Objective lens

103

field

108

upper pole piece of the objective lens

109

lower pole piece of the objective lens

110

Winding

200

Detector system

205

Projection lens

209

Particle multi-detector

211

Detection level

213

Points of impact

217

field

250

Vacuum chamber

260

Scan deflector in the secondary path

300

Beam generating device

301

Particle source

303

Condenser lens system

305

Multi-aperture arrangement

313

Multi-aperture plate

315

Openings of the multi-aperture plate

317

Centers of the openings

319

field

307

Field lens system

309

diverging particle beam

311

illuminating particle beam

323

Beam focus

325

Intermediate image plane

350

Vacuum chamber

355

Vacuum chamber

400

Jet switch

410

Magnetic sensor

420

Magnetic sensor

460

Jet pipe arrangement

461

Leg of the nozzle

462

Leg of the nozzle

463

Leg of the nozzle

464

Lance extension

500

Scan deflector in the primary path

810

Primary path control

811

Control of operating point setting (slow)

812

Measuring element

813

Adjustment algorithm

814

Actuators in the primary path

821

Controls fast autofocus in the primary path

822

Measuring element

823

Autofocus algorithm

824

fast auto focus correction lens

825

fast telecentric corrector

826

quick rotation correction means

827

fast position correction means

831

Control of operating point setting in the secondary path (slow)

832

Measuring element

833

second adjustment algorithm (secondary path)

834

Actuators in the secondary path

841

Second fast autofocus control (secondary path)

842

Measuring element

843

second autofocus algorithm (secondary path)

844

fast projection path correction means

850

Orthogonalization matrix or inverted sensitivity matrix for the primary path

851

Orthogonalization matrix or inverted sensitivity matrix for the secondary path

S1

Generation of measurement data for the current focus at the working point AP

S2

Determination of actual autofocus data based on measurement data

S3

Generate autofocus correction lens control signals based on actual autofocus data

S4

Generate telecentricity correction means control signal based on actual autofocus data

S5

Generate rotation correction means control signal based on actual autofocus data

S6

Control autofocus correction lens

S7

Control telecentricity correction means

S8

Control rotation correction means

S9

Generation of second measurement data for the second autofocus in the secondary path

S10

Determination of second actual autofocus data based on second measurement data

S11

Generate projection path correction means control signal (set)

S12

Control of the projection path correction means including a second autofocus correction lens

S13

Recording field of view

Claims (55)

A multitude particle beam system (1) for wafer inspection, comprising: a multi-beam particle generator configured to generate a first field (327) of a plurality of charged first particle beams (3); a first particle optics with a first particle-optical beam path which is configured to image the generated individual particle beams (3) onto a wafer surface in the object plane (101) so that the first particle beams (3) strike the wafer surface at points of incidence (5) forming a second field (103); a detection system (200) having a plurality of detection areas (215) which form a third field (217); a second particle optics with a second particle-optical beam path which is configured to emit second individual particle beams (9) from the points of incidence (5) in the second field (103) onto the third field (217) of the detection areas (215) of the Map detection system (200); a magnetic and / or electrostatic objective lens (102) through which both the first (3) and the second individual particle beams (9) pass; a beam splitter (400) which is arranged in the first particle-optical beam path between the multi-beam particle generator and the objective lens (102) and which is arranged in the second particle-optical beam path between the objective lens (102) and the detection system (200); a sample table for holding and / or positioning a wafer (7) during the wafer inspection; an autofocus measuring element (812) which is configured to generate measurement data for determining actual autofocus data during the wafer inspection; a fast auto focus correction lens (824); and a controller (10); wherein the controller (10) is configured to control particle-optical components in the first and / or in the second particle-optical beam path, wherein the controller (10) is configured for a static or low-frequency adjustment of a focusing in order to control at least the objective lens (102) and / or an actuator of the sample table at a first working point with a first working distance in such a way that the first individual particle beams (3 ) are focused on the wafer surface located in the first working distance, wherein the controller (10) is configured for a high-frequency adjustment of the focusing in order to generate an autofocus correction lens control signal at the first operating point during the wafer inspection based on the actual autofocus data in order to activate the fast autofocus correction lens (824) during the wafer inspection to control the first working point; wherein the first working point is further defined by a landing angle of the first individual particle beams (3) in the object plane (101) and by a grid arrangement of the first individual particle beams (3) in the object plane (101), and wherein the controller (10) is further configured to keep the landing angle and the grid arrangement substantially constant during the high-frequency adaptation at the first operating point Multiple particle beam system (1) according to Claim 1 , an adaptation time TA for the high-frequency adaptation being at least a factor of 10, in particular at least a factor of 100 or 1000, shorter than the adaptation time TA for the low-frequency adaptation. Multiple particle beam system (1) according to one of the preceding claims, wherein a stroke for setting the work delay for the low-frequency or static is at least a factor of 5, in particular a factor of 8 and / or 10, greater than the stroke for the high-frequency adaptation . Multiple particle beam system (1) according to one of the preceding claims, wherein a second working point is defined at least by a second working distance between the objective lens (102) and the wafer surface and wherein the second working distance differs from the first working distance of the first working point, the controller ( 10) is configured to carry out a low-frequency adjustment when changing between the first working point and the second working point and to control at least the magnetic objective lens (102) and / or an actuator of the sample table at the second working point in such a way that the first individual particle beams (3 ) be focused on the wafer surface located in the second working distance. Multiple particle beam system (1) according to the preceding claim, wherein the controller (10) is configured to generate an autofocus correction lens control signal for high-frequency adjustments at the second operating point during the wafer inspection based on the actual autofocus data in order to control the fast autofocus correction lens (824) during the wafer inspection at the second operating point . Multiple particle beam system (1) according to one of the preceding claims, wherein the second working point is further defined by a landing angle of the first individual particle beams (3) in the object plane (101) and by a grid arrangement of the first individual particle beams (9) in the object plane (101), and wherein the controller (10) is further configured to keep the landing angle and the grid arrangement substantially constant during the high-frequency adaptation at the second operating point. Multiple particle beam system (1) according to the preceding claim, wherein the controller (10) is configured to keep the landing angle and the grid arrangement essentially constant even when there is a change between the first operating point and the second operating point. A plurality of particle beam system (1) according to any one of the preceding claims, wherein the autofocus correction lens (824) comprises a fast electrostatic lens. Multiple particle beam system (1) according to Claim 8 , wherein the autofocus correction lens is arranged in a plane of intersection of the first individual particle beams (3). Multiple particle beam system (1) according to Claim 8 wherein the autofocus correction lens (824) is arranged between the wafer surface and a lower pole piece (109) of the magnetic objective lens (102). Multiple particle beam system (1) according to Claim 8 wherein the autofocus correction lens (824) is arranged between the upper (108) and lower (109) pole pieces of the magnetic objective lens (102). Multiple particle beam system (1) according to Claim 8 , wherein the autofocus correction lens (824) e is arranged in a beam pipe extension (464) which protrudes into the objective lens (102) from the upper pole piece (108). Multiple particle beam system (1) according to Claim 8 which further comprises a beam deflection system (500) between the beam splitter (400) and the objective lens (102), which is configured to scan the wafer surface with a scanning movement of the individual particle beams (3), wherein the autofocus correction lens (824) is implemented as an offset on the beam deflection system (500). Multiple particle beam system (1) according to Claim 8 which further comprises a beam deflection system (500) between the beam splitter (400) and the objective lens (102) which is configured to scan the wafer surface with a scanning movement of the individual particle beams (3); wherein the beam deflection system (500) has an upper deflector (500a) and a lower deflector (500b) which are arranged one after the other in the direction of the beam path; and wherein the auto focus correction lens (824) is disposed between the upper deflector (500a) and the lower deflector (500b). Multiple particle beam system (1) according to Claim 8 which further comprises a beam deflection system (500) between the beam splitter (400) and the objective lens (102) which is configured to scan the wafer surface with a scanning movement of the individual particle beams (3); wherein the beam deflection system (500) has an upper deflector (500a) and a lower deflector (500b) which are arranged one after the other in the direction of the beam path; and wherein the autofocus correction lens (824) is arranged between the lower deflector (500b) and an upper pole piece (109) of the magnetic objective lens (102). Multiple particle beam system (1) according to Claim 8 , which furthermore has an evacuable beam tube (460) which essentially encloses the first particle-optical beam path from the multi-beam particle generator to the objective lens (102), wherein the beam tube (460) has an interruption and wherein the autofocus correction lens (824 ) is arranged within this interruption. Multiple particle beam system (1) according to Claim 16 which further comprises a field lens system (307) which is arranged in the first particle-optical beam path between the multi-beam particle generator and the beam switch (400), the interruption of the beam tube (460) in which the autofocus correction lens (824) is arranged is arranged between the field lens system (307) and the beam switch (400). Multiple particle beam system (1) according to Claim 16 , wherein the beam switch (400) has two magnetic sectors (410, 420) and the interruption of the beam tube (460) in which the autofocus correction lens (824) is arranged in the area of the beam switch (400) between the two magnetic sectors (410 , 420) is provided. Multiple particle beam system (1) according to Claim 16 which further comprises a beam deflection system (500) between the beam splitter (400) and the objective lens (102), which is configured to scan the wafer surface with a scanning movement of the individual particle beams (3), the interruption of the beam pipe (460) , in which the autofocus correction lens (824) is arranged, is provided between the beam switch (400) and the beam deflection system (500). Multiple particle beam system (1) according to Claim 16 , which further comprises a field lens system (307) which is arranged in the first particle-optical beam path between the multi-beam particle generator and the beam switch (400), the interruption of the beam tube (460) in which the autofocus correction lens (824) is arranged , is arranged within a magnetic field lens of the field lens system (307). Multiple particle beam system (1) according to Claim 8 which furthermore has an evacuable beam tube (460) which essentially encloses the first particle-optical beam path from the multi-beam particle generator to the objective lens (102), the autofocus correction lens (824) being designed as a tubular lens and located inside the beam tube (460 ) is arranged. Multiple particle beam system (1) according to Claim 21 which further comprises a field lens system (307) which is arranged in the first particle-optical beam path between the multi-beam particle generator and the beam switch (400), the autofocus correction lens (824) between the field lens system (307) and the beam switch (400) is arranged within the jet pipe (460). Multiple particle beam system (1) according to Claim 21 wherein the beam switch (400) has two magnetic sectors (410, 420) and wherein the autofocus correction lens (824) is provided between the two magnetic sectors (410, 420) within the beam tube (460). Multiple particle beam system (1) according to Claim 21 which further comprises a beam deflection system (500) between the beam splitter (400) and the objective lens (102), which is configured to scan the wafer surface with a scanning movement of the individual particle beams (3), wherein the autofocus correction lens (824) is provided between the jet switch (400) and the jet deflection system (500) within the jet pipe (460). Multiple particle beam system (1) according to Claim 21 which further comprises a field lens system (309) which is arranged in the first particle-optical beam path between the multi-beam particle generator and the beam switch (400), the autofocus correction lens (824) within a magnetic field lens (307) within the beam tube (460 ) is arranged. Multiple particle beam system (1) according to one of the Claims 1 until 7th wherein the fast autofocus correction lens (824) comprises a fast magnetic lens, in particular an air-core coil. Multiple particle beam system (1) according to Claim 26 which furthermore has an evacuable beam pipe (460) which essentially encloses the first particle-optical beam path from the multi-beam particle generator to the objective lens (102), the fast magnetic lens being arranged on the outside around the beam pipe (460). Multiple particle beam system (1) according to Claim 27 , which further has a field lens system (307) which is arranged in the first particle-optical beam path between the multi-beam particle generator and the beam switch (400), the fast magnetic lens between the field lens system (307) and the beam switch (400) around the beam pipe ( 460) is arranged around. Multiple particle beam system (1) according to Claim 27 wherein the beam switch (400) has two magnetic sectors (410, 420) and wherein the fast magnetic lens is arranged between the two magnetic sectors (410, 420) around the beam pipe (460). Multiple particle beam system (1) according to Claim 27 , the further a beam deflection system (500) between the beam splitter (400) and the objective lens (102) which is configured to scan the wafer surface with a scanning movement of the individual particle beams (3), the fast magnetic lens being arranged between the beam switch (400) and the beam deflection system (500) around the beam pipe (460). Multiple particle beam system (1) according to Claim 27 which further comprises a beam deflection system (500) between the beam splitter (400) and the objective lens (102) which is configured to scan the wafer surface with a scanning movement of the individual particle beams (3); wherein the beam deflection system (500) has an upper deflector (500a) and a lower deflector (500a) which are arranged one after the other in the direction of the beam path; and wherein the fast magnetic lens is disposed between the upper deflector (500a) and the lower deflector (500b) around the beam pipe (460). Multiple particle beam system (1) according to one of the preceding claims, wherein the plurality of particle beam system (1) further comprises a fast telecentricity correction means (825) which is configured to contribute significantly to correcting a tangential telecentricity error of the first single particle beams (3) in the second field (103), and wherein the controller (10) is set up to generate a telecentricity correction means control signal for high-frequency adjustments at the respective operating point during the wafer inspection based on the actual autofocus data, in order to control the fast telecentricity correction means (825) during the wafer inspection. Multiple particle beam system (1) according to Claims 32 wherein the telecentricity correction means (825) comprises a first deflector array which is arranged in an intermediate image plane (325) of the first particle-optical beam path. Multiple particle beam system (1) according to one of the preceding claims, wherein the plurality of particle beam system (1) further comprises a rapid rotation correction means (826) which is configured to contribute significantly to correcting a twist of the first single particle beams (3) in the second field (103), and wherein the controller (10) is set up to generate a rotation correction means control signal for high-frequency adjustments during the wafer inspection at the respective operating point based on the actual autofocus data in order to control the fast rotation correction means during the wafer inspection. A plurality of particle beam system (1) according to the preceding claim, wherein the rotation correcting means (826) comprises an air core coil. Multiple particle beam system (1) according to the Claims 33 and 34 wherein the rotation correcting means (826) comprises a second deflector array spaced just before or after the first deflector array. Multiple particle beam system (1) according to the Claims 33 and 34 , wherein the rotation correction means (826) comprises a multi-lens array which is arranged at a distance directly in front of or after the first deflector array and in such a way that the first individual particle beams (3) pass through the multi-lens array off-axis . Multiple particle beam system (1) according to Claim 34 wherein the multi-beam particle generator comprises the rapid rotation correcting means and the rotation correcting means (826) is actively rotated by the rotation correcting means control signal. Multiple particle beam system (1) according to Claim 34 wherein the rapid rotation correction means (826) comprises a first magnetic field generating device for a first weak magnetic field and a second magnetic field generating device for a second weak magnetic field, and wherein the first magnetic field generating device is only for a rotation in a positive direction of rotation and the second magnetic field generating device is controlled by the controller by means of the rotation correction means control signal only for a rotation in a negative direction of rotation. Multiple particle beam system (1) according to Claim 39 wherein the first and the second magnetic field are axially designed and arranged in a convergent or divergent tuft of the first individual particle beams (3) in the first particle-optical beam path. Multiple particle beam system (1) according to one of the preceding claims, a maximum deviation of each individual particle beam (3) from a desired landing position on the wafer surface is a maximum of 10 nm, in particular a maximum of 5 nm, 2 nm, 1 nm or 0.5 nm. Multiple particle beam system (1) according to one of the preceding claims, wherein the controller (10) is set up to determine the autofocus correction lens control signal and / or the rotation correction means Control signal and / or the telecentricity correction means control signal based on the actual autofocus data using an inverted sensitivity matrix that describes the influence of control changes of particle-optical components on particle-optical parameters that characterize the particle-optical image at the respective working point. Multiple particle beam system (1) according to one of the preceding claims, wherein the controller (10) is configured for a static or low-frequency adjustment of a focusing in the second particle-optical beam path in order to control particle-optical components in the second particle-optical beam path at the respective working point with the associated working distance in such a way that the second individual particle beams (9) coming from of the wafer surface located at the respective working distance, onto which the detection areas (215) in the third field (217) are focused. Multiple particle beam system (1) according to one of the preceding claims, wherein the multiple particle beam system (1) furthermore has a fast projection path correction means (844) which can be in several parts and which is configured to carry out a high-frequency adjustment of the focus of the second individual particle beams (9), the grid arrangement, landing angles and / or the contrast of the second individual particle beams when they strike the detection areas (215) in the third field (217), and wherein the controller (10) is configured to generate a projection path control signal or a set of projection path control signals during the wafer inspection at the respective operating point based on the actual autofocus data in order to control the rapid projection path correction means (844). Multiple particle beam system (1) according to one of the preceding claims, wherein the multiple particle beam system (1) furthermore has a projection path measuring element (842) in order to generate projection path measurement data for characterizing the particle-optical image in the secondary path during the wafer inspection, wherein the multiple particle beam system (1) furthermore has a fast projection path correction means (844) which can be in several parts and which is configured to carry out a high-frequency adjustment of the focus of the second individual particle beams (9), the grid arrangement, landing angles and / or the contrast of the second individual particle beams (9) when they strike the detection areas (215) in the third field (217), and wherein the controller (10) is configured to generate a projection path control signal or a set of projection path control signals during the wafer inspection at the respective operating point based on the projection path measurement data in order to control the rapid projection path correction means (844). Multiple particle beam system (1) according to one of the two Claims 44 until 45 , wherein a contrast aperture diaphragm is arranged in a cross-over plane in the second particle-optical beam path, the projection path correction means (844) being a fast contrast correction means with at least one electrostatic deflector, at least one electrostatic lens and / or at least one electrostatic stigmator for influencing the particle-optical beam path through the contrast aperture diaphragm, and wherein the controller (10) is configured to control the contrast correction means with a contrast correction control signal or a set of contrast correction control signals, so that a contrast of the second Individual particle beams (9) are kept essentially constant when they strike the detection areas (215) in the third field (217). Multiple particle beam system (1) according to one of the preceding claims, which has a further autofocus correction lens (824) or a plurality of further fast autofocus correction lenses (824). Method for operating a multiple particle beam system (1) according to one of the preceding Claims 1 until 47 which has the following steps: generating measurement data at a first operating point for a current focus on the wafer surface (101); Determining actual autofocus data based on the measurement data; Determining an autofocus correction lens control signal based on the actual autofocus data; and controlling a fast autofocus correction lens system (824) and high-frequency keeping the focus constant on the wafer surface, the grid arrangement and the landing angle of the first individual particle beams (3) also being kept constant at the first working point when they strike the wafer surface (101) . A method of operating a multiple particle beam system (1) according to the preceding claim, wherein the fast autofocus correction lens (824) comprises an electrostatic lens. Method for operating a plurality of particle beam systems (1) according to one of the Expectations 48 until 49 wherein the fast auto focus correction lens (824) comprises a magnetic lens. Method for operating a plurality of particle beam systems (1) according to one of the Claims 48 until 50 further comprising the steps of: generating a telecentricity correction control signal based on the actual autofocus data; and driving the fast telecentricity correction means (825). Method for operating a plurality of particle beam systems (1) according to one of the Claims 48 until 49 further comprising the steps of: generating a rotation correction control signal based on the actual auto focus data; and driving the rapid rotation correction means (826). Method for operating a plurality of particle beam systems (1) according to one of the Claims 48 until 52 further comprising the step of: orthogonalizing effects of the particle-optical components used for the correction or corrections. Method for operating a plurality of particle beam systems (1) according to one of the Claims 48 until 53 which further comprises the following steps: generating projection path measurement data for characterizing the particle-optical image in the secondary path; Determining a projection path control signal based on the projection path measurement data; and controlling the fast projection path correction means (844), which can be multi-part, by means of the projection path control signal or by means of a set of projection path control signals, the focus, the raster arrangement and the landing angle of the second individual particle beams upon impingement in the detection plane (211) are kept constant. Method for operating a plurality of particle beam systems (1) according to one of the Claims 48 until 54 which further comprises the following steps: controlling a rapid contrast correction means by means of a contrast correction control signal or a set of contrast correction control signals and keeping the contrast constant in the detection plane (211).

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