Patent Application
20250104961
The disclosure relates to a method for operating a multi-beam particle microscope, to an associated computer program product and to a multi-beam particle microscope.
With the continuous development of ever smaller and ever more complex microstructures such as semiconductor components, there is a desire to further develop and optimize planar production techniques and inspection systems for producing and inspecting small dimensions of the microstructures. By way of example, the development and production of the semiconductor components can involve monitoring of the design of test wafers, and the planar production techniques can involve process optimization for a reliable production with a high throughput. Moreover, there have been recent demands for an analysis of semiconductor wafers for reverse engineering and for a customer-specific, individual configuration of semiconductor components. Therefore, there is a desire for an inspection mechanism which can be used with a high throughput for examining the microstructures on wafers with great accuracy.
Typical silicon wafers used in the production of semiconductor components have diameters of up to 300 millimeters (mm). Each wafer is divided into 30 to 60 repeating regions (“dies”) with a size of up to 800 square millimeters (mm2). A semiconductor apparatus comprises a plurality of semiconductor structures, which are produced in layers on a surface of the wafer by planar integration techniques. Semiconductor wafers typically have a plane surface on account of the production processes. The structure size of the integrated semiconductor structures in this case extends from a few μm to the critical dimensions (CD) of 5 nanometers (nm), with the structure sizes becoming even smaller in the near future; in future, structure sizes or critical dimensions (CD) are expected to be less than 3 nm, for example 2 nm, or even under 1 nm. In the case of the aforementioned small structure sizes, defects in the size of the critical dimensions is to be identified quickly in a very large area. For several applications, the desired accuracy of a measurement provided by inspection equipment is even higher, for example by a factor of two or one order of magnitude. By way of example, a width of a semiconductor feature is to be measured with an accuracy of below 1 nm, for example 0.3 nm or even less, and a relative position of semiconductor structures is to be determined with an overlay accuracy of below 1 nm, for example 0.3 nm or even less.
The MSEM, a multi-beam scanning electron microscope, is a relatively new development in the field of charged particle systems (charged particle microscopes, CPMs). By way of example, a multi-beam scanning electron microscope is disclosed in U.S. Pat. No. 7,244,949 B2 and in US 2019/0355544 A1. In the case of a multi-beam electron microscope or MSEM, a sample is irradiated simultaneously with a plurality of individual electron beams, which are arranged in a field or raster. By way of example, 4 to 10,000 individual electron beams can be provided as primary radiation, with each individual electron beam being separated from an adjacent individual electron beam by a pitch of 1 to 200 micrometres (μm). By way of example, an MSEM has approximately 100 separate individual electron beams (“beamlets”), which are arranged for example in a hexagonal raster, with the individual electron beams being separated by a pitch of approximately 10 μm. The plurality of charged individual particle beams (primary beams) are focused on a surface of a sample to be examined by way of a common objective lens. By way of example, the sample can be a semiconductor wafer which is secured to a wafer holder mounted on a movable stage. During the illumination of the wafer surface with the charged primary individual particle beams, interaction products, for example secondary electrons or backscattered electrons, emanate from the surface of the wafer. Their start points correspond to those locations on the sample on which the plurality of primary individual particle beams are focused in each case. The amount and the energy of the interaction products generally depend 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 which are incident on a detector arranged in a detection plane as a result of a projection imaging system of the multi-beam inspection system. The detector comprises a plurality of detection regions, each of which comprises a plurality of detection pixels, and the detector captures an intensity distribution for each of the secondary individual particle beams. An image field of, for example, 100 μm×100 μm is obtained in the process.
Certain known multi-beam electron microscopes comprise a sequence of electrostatic and magnetic elements. At least some of the electrostatic and magnetic elements are adjustable in order to adapt the focus position and the stigmation of the plurality of charged individual particle beams. These multi-beam systems with charged particles moreover comprise at least one cross-over plane of the primary or the secondary charged individual particle beams. Moreover, these systems comprise detection systems to make the adjustment easier. These multi-beam particle microscopes comprise at least one beam deflector (“deflection scanner”) for collective scanning of a region of the sample surface via the plurality of primary individual particle beams in order to obtain an image field of the sample surface. Further details regarding a multi-beam electron microscope and a method for operating same are described in the German patent application with the application Ser. No. 10/202,0206739.2, filed on May 28, 2020, and in the associated patent family documents, the disclosure of which is fully incorporated by reference in this patent application.
An accurate alignment of the secondary individual particle beams when incident on the detector is relevant in order to obtain a high resolution within the scope of a sample inspection, for example a semiconductor sample inspection. It is standard for the alignment of the raster of second individual particle beams to be carried out by virtue of carrying out referencing in relation to a centrally arranged beam in the raster. The latter is aligned or adjusted to the best possible extent in relation to a detection region assigned thereto. This alignment is usually carried out prior to each image recording.
However, it is also possible that an alignment of the second individual particle beams changes in relation to the detection regions of the detection unit while the image is recorded, for example as a result of the occurrence of a drift or due to the sample properties themselves. By way of example, charging effects on the sample may lead to secondary individual beams emanating or starting from the sample being slightly warped and therefore not being incident at the desired reference position on the detection unit. In such cases, it would be desirable to carry out a correction or readjustment in real time.
In this context, DE 10 2015 202 172 B4 proposes the use of a pixelated detection unit in which the detection regions, which are each provided for the detection of a second individual particle beam and assigned to the latter, each have a plurality of detection fields. If the incidence locations of the second individual particle beams on the detector change during an inspection, then the assignment of the detection fields to the detection regions is modified. On the one hand, this procedure restricts the type of used detection units to pixelated detection units and, on the other hand, such an assignment modification is algorithmically quite complex and comparatively slow.
U.S. Pat. No. 10,896,800 B2 avoids the issue of the restriction to the pixelated detector type for image generation by virtue of an additional pixelated detector in the form of a fast CCD camera being used in addition to the non-pixelated detector for the image generation (a combination of a particle detector and a downstream light optical unit with an optical fibre for each detection region). To this end, a beam splitter is provided in the light-detection path; a portion of the light signal is output to the CCD camera. Positions on the CCD camera can be assigned positions of the light when incident on the signal entrance surface of the optical fibres. Using this, it is possible to indirectly detect positional deviations of second individual beams when incident on the detector used for image generation. In general, this allows a fast positional correction in the secondary path of the multi-beam particle microscope. For the correction of the particle optical beam path in the secondary path itself, use is made of quickly controllable electrostatic lenses, electrostatic deflectors and/or electrostatic stigmators. According to U.S. Pat. No. 10,896,800 B2, the light incident on the pixelated additional detector for positional deviation recognition purposes is obtained by beam splitting, which attenuates the original light signal. Moreover, with respect to the detection unit, one is bound to the combination of a particle detection with a light detection as a result of the beam splitting in the light optical system. Additionally, the signal evaluation in the case of the CCD camera with an evaluation of signals from all pixels is algorithmically comparatively complicated.
US 2021/0005423 A1 also discloses a combination of a particle detector and a downstream light optical unit with an optical fibre for each detection region. A beam splitter is provided in the light-detection path; and a portion of the light signal is output to a CCD camera which can be used to identify changes of the locations of the interaction products in a detection plane due to a charging of a sample. Furthermore, US 2021/0005423 A1 discloses a diaphragm which is arranged in the detection system at a position of a cross-over of secondary particle beams. The circular opening of the diaphragm is surrounded in a radial direction by a couple of electrodes which can serve as current detectors. By detecting asymmetries in the currents or charges induced in the electrodes, a decentering of the charged particle beams passing the aperture of the diaphragm can be detected and thus corrected, accordingly.
The present disclosure proposes a method for operating a multi-beam particle microscope in an inspection mode, and an associated multi-beam particle microscope, which can allow a relatively simple and universal fast positional correction of the secondary beams when incident on a detection unit.
According to a first aspect, the disclosure provides a method for operating a multi-beam particle microscope in an inspection mode of operation, the method including the following steps:
The first charged individual particle beams can be, for example, electrons, positrons, muons or ions or other charged particles. The individual field regions of the object that are assigned to each first individual particle beam are raster scanned, for example line by line or column by column. In this case, it can be desirable for the individual field regions to be adjacent to one another or to cover the object or a part thereof in tessellated fashion. The individual field regions are substantially separate from one another, but they can also overlap one another in the marginal regions. In this way, it is possible to obtain an image of the object that is as complete and contiguous as possible. The individual field regions can be embodied in rectangular or square fashion since this is the easiest to realize for the scanning process with the aid of particle radiation. The individual field regions can be arranged as rectangles in different lines one above another so as to result overall in a hexagonal structure. It can be desirable for the number of particle beams to be 3n (n−1)+1, where n is any natural number, in the hexagonal case. Other arrangements of the individual field regions, for example in a square or rectangular raster, are likewise possible.
The second individual particle beams can be backscattered electrons or else secondary electrons. In this case, for analysis purposes it is desirable for the low-energy secondary electrons to be used for image generation. However, it is also possible for mirror ions/mirror electrons to be used as second individual particle beams, that is to say first individual particle beams undergoing reversal directly upstream of or at the object.
According to the disclosure, the second individual particle beams can be projected in focused fashion onto detection regions of a detection unit so that the second individual particle beams emerging or emanating from two different individual field regions are projected onto different detection regions. In this case, each detection region is fixedly assigned a detection channel or a predetermined plurality of detection channels. The fact that a detection region may therefore correspond to a detection channel or else that a detection region may comprise a plurality of detection channels and hence smaller units allows the application of the method basically independently of the type of detection unit. It is not necessary for a detection region per second individual particle beam to be pixelated or subdivided more finely. Instead, the method involves the fixed assignment of a detection channel or a predetermined plurality of detection channels to a respective detection region. Thus, in some embodiments according to the disclosure, there is no change in this assignment as described above in the context of known technology (DE 10 2015 202 172 B4). Overall, the disclosure therefore can simplify the method and it becomes more universally applicable.
According to the disclosure, the detection unit can be additionally modified or extended. In addition to the detection regions used to generate individual images, the detection unit can comprise additional detection channels. The second individual particle beams are not projected onto these additional detection channels in a targeted manner and the detection channels are not assigned to any detection region. Thus, if the second individual particle beams are incident on the detection unit at their respective reference incidence position, no signal, in general, is detected in these additional detection channels. The additional detection channels only detect a signal if at least one of the second individual particle beams, but optionally a plurality of the second individual particle beams, deviate(s) from its/their respective reference incidence position. Consequently, the additional detection channels serve to determine a positional deviation. Such a positional deviation can be recognized as such and optionally also be characterized in more detail. This can help make it possible to correct the positional deviation of the second individual particle beams when incident on the detection unit.
With respect to their structure, the additional detection channels may correspond to the detection channels also used for the normal image generation. However, it is also possible to design the additional detection channels differently. Specific exemplary embodiments will still be discussed in more detail below.
The fixedly assigned detection channels and the additional detection channels can belong to the same detection unit. Therefore, the fixedly assigned detection channels and the additional detection channels can be provided within the same detection plane. In other words, an image detection plane and a positional deviation detection plane are identical according to the present disclosure. This identity enhances the precision with which a positional deviation can be detected.
According to the disclosure, the positional deviation of the second individual particle beams when incident on the detection unit can be corrected in real time. In general, mechanisms in the secondary path of the multi-beam particle microscope usable to this end are already known. Attention is drawn to the fact that, within the scope of a correction in real time, the correction of a positional deviation can be implemented, in particular implemented multiple times, still during the generation of the individual images. Thus, if desired, there can be multiple readjustments or corrections per individual image. As a result, a better resolution overall can be obtained within the scope of a sample inspection.
According to an embodiment of the disclosure, the correction of the positional deviation of the second individual particle beams comprises an adjustment of the particle optical beam path of the second individual particle beams in real time. Alternatively, it would also be possible for the positional deviation to be corrected by a modification of the position of the detection unit itself; however, such a correction would not be implemented in real time.
According to an embodiment of the disclosure, the method furthermore includes the following step: classifying the determined positional deviation and, on the basis thereof, correcting the positional deviation. A positional deviation often relates to the raster of second individual particle beams equally or globally. Classes or types of a positional deviation are for example a global displacement of the second individual particle beams when incident on the detection unit, a global rotation, a magnification of the entire raster or overall anamorphic imaging. In the process, it may be possible to determine merely one class or one type of a global positional deviation, but it is also possible to simultaneously recognize a plurality of the aforementioned types (as a superposition).
According to an embodiment of the disclosure, the correction of the positional deviation comprises a correction of a global displacement of the second individual particle beams when incident on the detection unit. By way of example, a fast deflection system in the second particle optical beam path/secondary path of the multi-beam particle microscope can be used for correction purposes. Solely the type of beam correction in the secondary path has already been described in U.S. Pat. No. 10,896,800 B2, the disclosure of which is incorporated in its entirety by reference into this patent application.
According to an embodiment of the disclosure, the correction of the positional deviation comprises a correction of a global rotation of the second individual particle beams when incident on the detection unit. By way of example, a rotation lens in the second particle optical beam path/secondary path of the multi-beam particle microscope can be used for this global rotation of the raster of second individual particle beams. It can be controlled quickly. It is also possible to use a rotation correction mechanism in the secondary path as are described in a plurality of embodiment variants in the German patent DE 10 2020 125 534 B3, for example. The entirety of the disclosure of DE 10 2020 125 534 B3 is incorporated in the present patent application by reference.
According to an embodiment of the disclosure, the correction of the positional deviation comprises a correction of a magnification of the second individual particle beams in one direction or in two directions when incident on the detection unit. In this case, the two directions may be orthogonal to one another, but this is not mandatory. If a magnification is the same size in both directions, this relates overall to a global enlargement as a positional deviation. For correction purposes, it is once again possible to use a system with fast electrostatic lenses, for example as described in the above-cited U.S. Pat. No. 10,896,800 B2
A magnification of the raster in one direction only corresponds to anamorphic imaging. By way of example, this can be corrected by way of a fast electrostatic stigmator or stigmation system in the secondary path, as likewise has already been described in exemplary fashion in U.S. Pat. No. 10,896,800 B2.
According to an embodiment of the method, the latter comprises the following step: correcting an individual positional deviation of at least one second individual particle beam when incident on the detection unit in real time. This type of correction is an even finer correction which is not implemented globally, that is to say not implemented equally for all second individual particle beams. However, it is generally desirable for the detection unit to meet further desired properties in that case; for example, it is the case that the deviation of a specific second individual particle beam from its reference position can only be detected if the associated detection region is arranged adjacent, or in great relative proximity, to the additional detection channel detecting the deviation. Examples enabling this detection are presented in more detail below. By way of example, a multi-deflector array can be used for the individual positional deviation correction, which multi-deflector array is arranged, for example, in the secondary path in the direction of the particle optical beam path after the so-called anti-scan.
According to an embodiment of the disclosure, the positional deviation is only corrected if a threshold value is exceeded. This prevents basically superfluous corrections from being carried out. Even if the second individual particle beams are projected in focused fashion on their respective detection regions, it naturally nevertheless is the case that the focus does not consist of a mathematical point but instead has an extent, albeit a small extent. Thus, strictly speaking, the intensity of each second individual particle beam has an intensity distribution when incident on the detection surface. Thus, a signal may only be detected bit by bit or gradually via the additional detection channels in the case of a deviation. For example, it is possible that the vast majority of the detection of the second individual particle beam is still carried out correctly via the assigned detection region. Should this be the case, it may not be necessary to correct the detected but insignificant positional deviation. Only once a threshold-which may be defined in advance-is exceeded is it, in general, desirable to actually correct the positional deviation.
The above-described embodiment variants according to the first aspect of the disclosure can be combined with one another in full or in part, provided that no technical contradictions arise as a result.
According to a second aspect, the disclosure provides a computer program product having a program code for carrying out the method as described above in a plurality of embodiments. In this case, the program code can be divided into one or more partial codes. The program code can be written in any desired programming language.
According to a third aspect, the disclosure provides a multi-beam particle microscope configured to carry out the method according to any one of the preceding exemplary embodiments.
According to a fourth aspect, the disclosure provides a multi-beam particle microscope comprising the following:
The multi-beam particle microscope according to the fourth aspect of the disclosure is configured and suitable for carrying out the method according to the disclosure according to the first aspect of the disclosure. All explanations and definitions made in the context of the first and/or second and/or third aspect of the disclosure also apply to the fourth aspect of the disclosure.
The fast detection position adjustment mechanism of the multi-beam particle microscope according to the disclosure can be designed in one part or multiple parts. It is possible that each mechanism of the detection position adjustment mechanism serves the (predominant) correction of a certain class of positional deviation or image aberration (e.g., displacement, rotation, magnification, anamorphic imaging). The detection position adjustment mechanism allows a correction of the position of the second individual particle beams when incident on the detection unit in real time and consequently still allows this during an inspection task and, in particular, still during the generation of one or more individual images. Expediently, there is therefore high-frequency control of the fast detection position adjustment mechanism.
The controller of the multi-beam particle microscope can likewise be formed in one part or in multiple parts. By way of example, it may comprise one or more control computers or other controllers; it may also be subdivided into a plurality of modules. The at least one correction signal serving to correct the positional deviation may in turn represent a single signal or a superposition of a plurality of signals. The method involves the fast detection position adjustment mechanism for positional correction can be meaningfully controlled via the signal or signals. By way of example, it is possible that a signal or a set of signals is used to correct a certain image aberration or a certain class of positional deviations and, accordingly, one or more other correction signals or a corresponding set is used to correct other image aberrations or a different class of positional deviations. By way of example, the number of correction signals corresponds to the number of individually controllable particle optical constituent parts of the fast detection position adjustment mechanism.
According to an embodiment of the disclosure, the detection unit comprises an image generation detection region in which all detection regions are arranged, and the detection unit comprises an adjustment detection region in which all additional detection channels are arranged. Such a subdivision of the detection unit into two functionally different regions is always possible as a matter of principle; both the image generation detection region and the adjustment detection region can be formed as a connected region or as a non-connected region in this case. Expressed differently, both the image generation detection region and the adjustment detection region may comprise subregions. Especially in those cases where each detection region of the image generation detection region comprises exactly one detection channel, it is possible that the detection unit itself comprises only similar or structurally identical detection channels, to be precise both normal detection channels for image recording and also additional detection channels for adjustment purposes. In that case, the subdivision of the detection unit into, firstly, an image generation detection region and, secondly, an adjustment detection region need not be made purely on the basis of the physical unit or structural unit, but very much by the fixed and hence unchanging assignment during the signal evaluation within the scope of the detection.
According to an embodiment of the disclosure, the image generation detection region is path-connected, and the adjustment detection region is likewise path-connected. In this context, the term “path-connected” is used as defined in topology. In this case, the definition of the regions, strictly speaking, is simplifying and a region is defined as a two-dimensional space and hence as a subspace of Rn. If both the image generation detection region and the adjustment detection region are respectively path-connected, then this is equivalent in the two-dimensional subspace of R″ to the statement that the image generation detection region and the adjustment detection region each form a domain. The arrangement of the two domains with respect to one another in the form of path-connected regions is possible in different ways in this case.
According to an embodiment of the disclosure, the adjustment detection region is arranged around the outside of the image generation detection region. This nesting of the two regions may be rotationally symmetric or else have an n-fold symmetry about the centre of both regions, but this is not mandatory. Alternatively, it is for example also possible that the image generation detection region is arranged around the outside of the adjustment detection region. Once again, this can be implemented symmetrically and in particular rotationally symmetrically or with an n-fold symmetry, but irregular non-symmetrical arrangements are also possible. If the adjustment detection region is arranged symmetrically around the outside of the image generation detection region, then this can be desirable for an evaluation of signals in the context of determining a positional deviation of the raster of second individual particle beams since the signal evaluation can be implemented particularly easily in this case. It is also comparatively easy to distinguish between different classes/types of positional deviations. Moreover, the effects of a global positional deviation are particularly large in the edge regions of the raster, and consequently particularly easy to detect. However, naturally, there are also other detection options and ultimately a skilful choice of the physical design of the detection unit also plays a role in this case.
According to an embodiment of the disclosure, the image generation detection region is not path-connected, and the adjustment detection region is path-connected but not simply connected. Here, too, the terms “not path-connected” and “simply connected” are used as is conventional in topology. This embodiment of the disclosure vividly describes at least two spatially separated detection regions (domains) being embedded in the adjustment detection region. Naturally, it is also possible that it is not only two detection regions but every detection region of the image generation detection region that is individually embedded in the adjustment detection region. Then again, the arrangement of image generation detection region and adjustment detection region arising overall as a result may have a regular or irregular, symmetric or non-symmetric design. A further example of a set-up according to this embodiment variant of the disclosure is a cruciform arrangement of the adjustment detection region, which divides the image generation detection region, which is not path-connected, into four subregions (four domains) as a result. Various further embodiments are possible.
According to an embodiment of the disclosure, each detection region is at least partly surrounded by additional detection channels. This comparatively comprehensive embedding of the detection regions into the additional detection channels for adjustment detection purposes allows, for example, not only a global identification of positional deviations of the entire raster of second individual particle beams but also an individual identification of positional deviations of each second individual particle beam.
According to an embodiment of the disclosure, the additional detection channels are arranged so that a positional deviation in the form of a directional deviation of at least one second individual particle beam from its reference incidence position, in particular of a plurality of the second individual particle beams from their respective reference incidence positions, is detectable. In the process, it is therefore not only the absolute value of the positional deviation that is determined but also the direction of the positional deviation. By way of example, on account of the position of the additional detection channels supplying a signal, it is possible to deduce the direction of the positional deviation.
According to an embodiment of the disclosure, each detection region comprises exactly one detection channel. In this case, the structure of the detection unit overall is particularly simple.
According to an embodiment of the disclosure, all detection channels are structurally identical. This therefore means that both the detection channels which define one or more detection regions and the additional detection channels for detecting the positional deviations are structurally identical. In this case, too, the detection unit overall has a particularly simple design.
Alternatively, it is naturally also possible that the detection channels differ. By way of example, it is possible to realize detection channels fixedly assigned to the detection regions in accordance with a first structure and realize the additional detection channels for the detection of the positional deviations in accordance with a second structure, with the first structure and the second structure not being identical. In the process, it is possible to adapt the additional detection channels in terms of their design to their special task, specifically the identification of positional deviations. By way of example, should the detection of a displacement of the raster of second individual particle beams be desirable, then this can already be easily implemented using an edge-shaped and strip-shaped additional detection channel, for example. A person skilled in the art will identify further embodiments without leaving the scope of protection of the disclosure as a result.
According to an embodiment of the disclosure, each detection channel comprises a signal entrance surface, wherein the signal entrance surfaces overall are arranged as a hexagon. A surface can be tessellated using such a hexagonal arrangement and it is particularly easy to compose multi-image fields from individual image fields. In the process, 3n (n−1)+1 individual particle beams can be used for image generation and detection.
According to an embodiment of the disclosure, each detection region is fixedly assigned exactly one detection channel, and the additional detection channels not assigned to any detection region are arranged hexagonally around the outside of the detection regions. Hexagonal arrangements can easily be extended in this way and existing concepts for detection units also only need to be spatially extended but not be modified in detail from a structural point of view.
According to an embodiment of the disclosure, the detection system comprises one or more particle detectors or consists of one or more particle detectors. Alternatively, the detection system comprises one or more particle detectors and also a plurality of light detectors disposed downstream thereof. Thus, the disclosure can be flexibly implemented with respect to the detection system or detection unit; there is no principle binding to a specific design of the detection system.
According to an embodiment of the disclosure, each detection channel comprises exactly one optical fibre and different detection channels comprise different optical fibres.
According to an embodiment of the disclosure, a detection channel comprises no optical fibre and an array of light-sensitive detectors, in particular an array comprising photomultipliers, photodiodes or avalanche photodiodes, is provided as the light detection system. These are all examples for the flexible choice of a detection system or detection unit.
According to an embodiment of the disclosure, the fast detection position adjustment mechanism comprises at least one of the following: an electrostatic lens, an electrostatic deflector, an electrostatic stigmator, an air-core coil, a multi-deflector array. Other fast detection position adjustment mechanisms can also be used and are known to a person skilled in the art. Here, reference is made once again to the above-cited documents.
The various embodiments and aspects of the disclosure can be combined with one another in full or in part, provided that no technical contradictions arise as a result.
The disclosure will be understood even better with reference to the accompanying figures, in which:
The enlarged detail I1 in
In the illustrated embodiment, the field 103 of incidence locations 5 is a substantially regular rectangular field having a constant pitch P1 between adjacent incidence locations. Exemplary values of the pitch P1 are 1 micrometre, 10 micrometres and 40 micrometres. However, it is also possible for the field 103 to have other symmetries, such as a hexagonal symmetry, for example.
A diameter of the beam spots formed in the first plane 101 can be small. Exemplary values of the diameter are 1 nanometre, 5 nanometres, 10 nanometres, 100 nanometres and 200 nanometres. The focusing of the particle beams 3 for shaping the beam spots 5 is carried out by the objective lens system 100.
The primary particles incident on the object generate interaction products, for example secondary electrons, backscattered electrons or primary particles that have experienced a reversal of movement for other reasons, which emanate from the surface of the object 7 or from the first plane 101. The interaction products emanating from the surface of the object 7 are shaped by the objective lens 102 to form secondary particle beams 9. The particle beam system 1 provides a particle beam path 11 for guiding the plurality of secondary particle beams 9 to a detector system 200. The detector system 200 comprises a particle optical unit with a projection lens 205 for directing the secondary particle beams 9 at a particle multi-detector 209.
The detail 12 in
The primary particle beams 3 are generated in a beam generating apparatus 300 comprising 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. The particle source 301 generates a diverging particle beam 309, which is collimated or at least substantially collimated by the collimation lens 303 in order to shape a beam 311 which illuminates the multi-aperture arrangement 305.
The detail 13 in
Particles of the illuminating particle beam 311 pass through the apertures 315 and form particle beams 3. Particles of the illuminating beam 311 which are incident on the plate 313 are absorbed by the latter and do not contribute to the formation of the particle beams 3.
On account of an applied electrostatic field, the multi-aperture arrangement 305 focuses each of the particle beams 3 in such a way that beam foci 323 are formed in a plane 325. Alternatively, the beam foci 323 can be virtual. A diameter of the beam foci 323 can be, for example, 10 nanometres, 100 nanometres and 1 micrometre.
The field lens 307 and the objective lens 102 provide a first imaging particle optical unit for imaging the plane 325, in which the beam foci 323 are formed, onto the first plane 101 such that a field 103 of incidence locations 5 or beam spots arises there. Should a surface of the object 7 be arranged in the first plane, the beam spots are correspondingly formed on the object surface.
The objective lens 102 and the projection lens arrangement 205 provide a second imaging particle optical unit for imaging the first plane 101 onto the detection plane 211. The objective lens 102 is thus a lens that is part of both the first and the second particle optical unit, while the field lens 307 belongs only to the first particle optical unit and the projection lens 205 belongs only to the second particle optical unit.
A beam switch 400 is arranged in the beam path of the first particle optical unit between the multi-aperture arrangement 305 and the objective lens system 100. The beam switch 400 is also part of the second optical unit in the beam path between the objective lens system 100 and the detector system 200.
Further information relating to such multi-beam particle beam systems and components used therein, such as, for instance, particle sources, multi-aperture plate and lenses, can be obtained from the international patent applications WO 2005/024881 A2, WO 2007/028595 A2, WO 2007/028596 A1, WO 2011/124352 A1 and WO 2007/060017 A2 and the German patent applications DE 10 2013 016 113 A1 and DE 10 2013 014 976 A1, the disclosure of which is fully incorporated by reference in the present application.
The multiple particle beam system furthermore comprises a computer system 10 configured both for controlling the individual particle optical components of the multiple particle beam system and for evaluating and analyzing the signals obtained using the multi-detector 209 or the detection unit 209. It can also be used to carry out the method according to the disclosure. The computer system 10 can be constructed from a plurality of individual computers or components.
The scintillator plate 207 contains a scintillator material, which is excited to emit photons by the incident electrons of the electron beams 9. Each of the incidence locations 213 thus forms a source of photons.
In this case,
Detection architectures other than the ones illustrated in
According to the disclosure, additional detection channels 235′ are now added to supplement to the detection regions of the detection unit 209 used in certain known systems. To this end, the existing detection unit 209 can be extended by additional detection channels 235′, which are not assigned to any detection region 215. Various exemplary embodiments of a corresponding multi-beam particle microscope 1 according to the disclosure or of the associated detection unit 209 will be described below. The additional detection channels 235′ serve as a measuring member for detecting a positional deviation of the second individual particle beams 9 when incident on the detection regions 215. This is because if the additional detection channels 235′ do not detect a signal or at least do not detect a significant signal (threshold value has not been reached), then the assumption can be made that the second individual particle beams 9 are incident sufficiently accurately on the detection regions 215. It is possible to correct the positional deviation in real time on the basis of the determined positional deviation and for example via the one part or multi-part fast detection position adjustment mechanism in the secondary path of the multi-beam particle microscope 1, in particular still during the recording of the plurality of individual images.
The image generation control module 840 processes data which were obtained via signals from the detection regions 215 with their fixedly assigned detection channels 235. Individual images and, from these, composite multi-images which can be displayed via an image display unit 850 are generated via image generation algorithms 842. In this respect, the controller 10 illustrated in
According to the disclosure, the adjustment control module 830 is now implemented within the controller 10. As measuring member, this adjustment control module 830 comprises additional detection channels 235′, which are not assigned to any of the detection regions 215. Instead, these additional detection channels 235′ serve to detect a positional deviation of the second individual particle beams 9 when incident on the detection unit 209. The adjustment control module 830 is configured to determine a positional deviation of the second individual particle beams 9 from a reference incidence position when incident on the detection unit 209 from data obtained via signals from each of the additional detection channels 235′ which are not assigned to any of the detection regions 215, and to generate at least one correction signal serving to correct the positional deviation. Algorithms 832 can be used to evaluate the signals and to generate the at least one correction signal. The one or more detection position adjustment mechanisms 833 as actuator or actuators is/are controlled via the correction signal or via the correction signals. This control is implemented in real time, that is to say still while an individual image or a plurality of individual images are generated.
In the further particle optical beam path, in the example illustrated, the first individual particle beams 3 pass through a field lens system having the field lenses 307a, 307b and 307c. Afterwards, they pass through a beam switch 400 and also an in particular magnetic objective lens 102, and then the first individual particle beams 3 are incident in a focused fashion on the object 7 in the object plane 101. The incidence of the first individual particle beams 3 triggers the emergence of the second individual particle beams 9 from the sample or the object 7. The second individual particle beams likewise pass through the objective lens 102 and the beam switch 400 and also, in the example illustrated, subsequently a projection lens system 205a, 205b, 205c. In the projection lens system 205, a contrast stop 222 is arranged in a beam cross-over of the second individual particle beams 9. The contrast stop 222 can be a circular stop or a ring stop, for example. It can be a bright field stop or a dark field stop. The contrast stop has the task of filtering second individual particle beams 9 according to their starting angles from the object plane 101. Second individual particle beams 9 proceeding from/up to a specific starting angle range are cut out from the pencil of the second individual particle beams 9 in the beam cross-over. This is illustrated schematically in the circle shown in an enlarged view in
Moreover,
By contrast,
By contrast,
In summary, a method is therefore disclosed for operating a multi-beam particle microscope 1 in an inspection mode of operation, as is an associated multi-beam particle microscope 1. A detection unit 209 comprises an image generation detection region with fixedly assigned detection channels 235 and an adjustment detection region with additional detection channels 235′. The fixedly assigned detection channels 235 and the additional detection channels 235′ are provided in the same detection plane 211. On the basis of signals obtained via the additional detection channels 235′, it is possible to correct an incidence position of the secondary beams 9 on the detection unit 209 in real time, to be precise independently of the specific structure of the detection unit 209.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2022 114 923.4 | Jun 2022 | DE | national |
The present application is a continuation of, and claims benefit under 35 USC 120 to, international application No. PCT/EP2023/025240, filed May 24, 2023, which claims benefit under 35 USC 119 of German Application No. 10 2022 114 923.4, filed Jun. 14, 2022. The entire disclosure of each of these applications is incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2023/025240 | May 2023 | WO |
| Child | 18975361 | US |
