Tomography stage control

Abstract

To provide a method and system for obtaining electron tomography data from a sample.SOLUTION: The method comprises the steps of: a) focusing an electron beam at a first location on a surface of the sample; b) tilting the surface of the sample to a tilt angle to the electron beam while maintaining the surface of the sample at the focus of the electron beam; c) detecting the electron beam focused at the first location on the surface of the sample; d) translating the sample at the tilt angle to parallelly move the focus of the electron beam to at least a second location of the surface of the sample; and e) detecting the electron beam focused on at least the second location on the surface of the sample. The steps b) to e) are repeated at one or more different tilt angles.SELECTED DRAWING: Figure 12

Description

Technical Field

[0001] The present invention relates to systems and methods for generating tomographic data and images, and more particularly to improving the acquisition of tilt series data collection.

[0002] A planar sample includes structures and features over its surface and throughout the thickness of the sample. The features can interact with an electron beam, and these interactions are detected to provide structural information about the sample.

[0003] The electron beam can be directed to specific locations on and within the sample. Further, the electron beam can be deflected over a short distance (e.g., 1 - 3 μm) across the surface of the sample to image adjacent features. However, to measure interactions with more distant features, the sample must be mechanically translated using a translation stage under the electron beam. Three - dimensional structural information can be obtained by tilting the sample in small increments (e.g., 3°) such that the electron beam is detected at different tilt angles and the electron beam is focused on the same feature. The tilt series data can include, for example, tilting the sample over ±60° or 70°. The collected data can be processed to provide an output image showing the three - dimensional structure of the features on the sample. FIG. 1 shows a schematic diagram illustrating how data is collected using samples at different tilt angles with the electron beam focused on the same location of the sample. FIG. 1A shows a continuous tilt scheme and FIG. 1B shows a dose - symmetric tilt scheme.

[0004] Figure 2 illustrates an existing process for obtaining exemplary tilt series from eight different features on a sample. Since the features are more widely separated than the electron beam can be steered, the sample must be mechanically translated by a translation stage during each tilt series collection of data. Each time the tilted sample is translated, the electron beam must be refocused. This can be accomplished by a combination of moving the sample towards or away from the beam source (i.e., z-axis translation to achieve coarse focus correction), and using a focusing optical system with an electron beam source. The solid arrows in Figure 2 indicate the mechanical translation of the sample. Arrow 230 illustrates an initial X-Y translation (e.g., perpendicular to the electron beam) at the start of a series of acquisitions. Arrow 220 indicates a long-range translation using the mechanical stage (X-Y). Arrow 220 indicates a short-range translation between adjacent features using the mechanical stage. The stage moves to a point of interest. The sample is tilted about the focus of the electron beam on the sample. This is repeated for all tomographic image positions. While effective, this data collection is time-consuming and can result in low sample throughput.

[0005] Figure 2 also shows, as a legend within the figure, the interaction steps for completing a tilt series with each feature investigated at different tilt angles. The mechanical translation of the sample (arrow 220) is performed for each feature or point of interest. For all features, a full tilt series is performed. For example, the angle of the sample surface is changed by + / - 70 degrees in 3° steps, with data collected from the features under the electron beam at each step. This is repeated for all tomographic image positions. These data are applied to a computed tomography algorithm to form a computer image. In the example shown in Figure 2, there are eight features that are investigated using mechanical translation for each feature. Thus, in this particular example, eight separate data sets are required, which requires a significant amount of acquisition time.

[0006] Furthermore, the sample is mainly flat, but some features extend from the surface more than other features, and it is difficult to obtain accurate height information regarding these features.

[0007] Therefore, there is a need for methods and systems to overcome these problems. SUMMARY OF THE INVENTION

[0008] The method and system provide an efficiency improvement in collecting data used to generate computer tomography images. While translating the sample at the current tilt angle, data is collected from points on the surface of the sample at specific different tilt angles. The focus of the electron beam is maintained at the sample surface while being translated at the tilt angle (e.g., using a mechanical or piezoelectric stage). This eliminates the need to refocus the electron beam between imaging points. This can be achieved by accurately translating the sample at a specific tilt angle (three-dimensional) using a translation stage.

[0009] The first step is to direct the electron beam at a first point or feature of the sample. Next, the sample is tilted while maintaining the focus of the electron beam on the surface of the sample. The feature is imaged by detecting the electron beam passing through this point, and data is collected and stored. The sample is translated at this tilt angle to move the electron beam so that the electron beam is directed at a second location on the surface of the sample. The electron beam is detected at this new location. These steps are repeated.

[0010] According to a first aspect, a method for obtaining electron tomography data from a sample (e.g., a planar sample and / or a lamella sample) is provided, the method comprising: a) focusing an electron beam at a first location on the surface of the sample; b) tilting the surface of the sample at an inclination angle with respect to the electron beam while maintaining the surface of the sample at the focus of the electron beam; c) detecting the electron beam focused at the first location on the surface of the sample; d) moving the sample in a parallel movement at an inclination angle to move the focus of the electron beam to at least a second location on the surface of the sample; e) detecting the electron beam focused on at least a second location on the surface of the sample; repeating steps b) to e) at one or more different inclination angles. Thus, since the electron beam does not need to be refocused on the sample surface after being translated to a new location or sample feature, data can be collected faster and more efficiently. This is because all rotations (i.e., alpha tilts) over all angles take more time than the X-Y-Z translations of the parallel movement, so fewer tilt series are required. Instead of only using the lateral X-Y mechanical translation of the sample (i.e., movement in a plane perpendicular to the electron beam axis) that changes the height of the tilted sample with respect to the electron beam and causes defocus on the sample surface, the sample is translated in all X-Y-Z dimensions (i.e., also translated in the direction of the electron beam axis). In other words, the sample is translated so that the beam is focused on the surface of the sample at a second location, and the translation includes a component in the direction of the electron beam.

[0011] Preferably, the method may further include generating a computed tomography (CT) image of the sample using the data obtained when detecting the electron beam. Different CT algorithms may be used.

[0012] Optionally, the tilt angle may be an angle non-perpendicular to the electron beam. The tilt angle may start perpendicular or non-perpendicular to the axis of the electron beam. When the tilt angle is non-perpendicular to the electron beam, the sample needs to be translated three-dimensionally, i.e., the translation stage must move the sample in the same X, Y, and Z directions. The Z component is used during this translation. Otherwise, the electron beam will not maintain focus on the sample. The X-Y plane can be considered as a plane perpendicular (normal) to the electron beam. Translating the sample so that the beam is focused on the surface of the sample at a second location may require that the translation of the sample includes a component in the direction of the electron beam (i.e., defined as the Z component) when the tilt angle is non-perpendicular to the electron beam.

[0013] Preferably, a first feature of the sample may be located at a first location and a second feature of the sample may be located at a second location. Thus, multiple features within the sample can be analyzed more quickly. The translation can be performed during a tilt series. Each feature or multiple features can be investigated using the sample at the same tilt angle. Thus, the translation (one or more times) of the sample using a mechanical stage can be performed at the same tilt angle and the translation is repeated for different tilt angles.

[0014] Optionally, the method f) measuring a first distance between a first feature and a second feature perpendicular to the electron beam using a sample tilted at a tilt angle; g) measuring a second distance between a first feature and a second feature perpendicular to the electron beam with the sample tilted at one or more different tilt angles; h) calculating a difference in separation of the first and second features from the surface of the sample based on a difference between the first distance and the second distance, and a difference between the tilt angle and one or more different tilt angles; This additional method step provides information about the height on the surface of the sample of different features. This additional information is obtained by stereogrammetry. The more different tilt angles are used, the higher the accuracy of the height information that can be provided. The process can be repeated at different tilt angles to improve accuracy.

[0015] Optionally, either the tilt angle or one or more different tilt angles can be perpendicular to the axis of the electron beam.

[0016] Optionally, the sample is a lamella sample. However, any planar sample can be used.

[0017] Optionally, the method after step c) and before step d), adjusting the electron beam to be focused at a third location (or more than three locations); detecting the electron beam focused at the third location on the surface of the sample. The electron beam can be deflected by a small amount (e.g., less than 3 μm) without requiring translation of the sample using a mechanical stage. Thus, by simply deflecting or moving the electron beam at the same tilt angle, features that are close to each other (e.g., clusters of features) can be investigated more quickly (without sacrificing optical quality). A combination of electron beam deflection and mechanical translation can be performed at the same tilt angle during a tilt series. Thus, this provides improved flexibility and further speeds up data acquisition. Further, when there is a greater distance between features, the data acquisition time can be shortened without sacrificing optical quality and without throughput penalty.

[0018] Optionally, the method After step d), and before or after step e), adjusting the electron beam to be focused at a fourth location; further comprising detecting an electron beam focused at a fourth location (or more than four locations) on the surface of the sample. The electron beam may be adjusted or deflected in different steps of the method.

[0019] Optionally, the angular difference between the tilt angle and one or more different tilt angles may be from 0.1° to 10° (e.g., from 1° to 5°). For example, the angle between the tilts may be 3° or less (e.g., 2°, 1°, or less than 1°).

[0020] Optionally, the sample may be translated at the tilt angle to move the location of the electron beam on the sample by 1 μm to 3 μm. Depending on the location where a particular feature is located, other translation distances may be used.

[0021] According to a second aspect, an electron beam source; an electron beam focusing optical system configured to focus the electron beam on the surface of the sample; a sample translation stage configured to translate the sample in a plane perpendicular to the electron beam and to change the tilt angle of the surface of the sample with respect to the axis of the electron beam; communicating with the sample translation stage and the electron beam focusing optical system, a) focusing the electron beam at a first location on the surface of the sample; b) tilting the surface of the sample at an angle with respect to the electron beam while maintaining the surface of the sample at the focus of the electron beam; c) detecting the electron beam focused at the first location on the surface of the sample; d) translating the sample at the tilt angle to move the focus of the electron beam to at least a second location on the surface of the sample; e) detecting the electron beam focused at at least the second location on the surface of the sample; A control unit configured to perform steps b) to e) repeatedly at one or more different tilt angles, and an electron microscope system comprising the control unit are provided.

[0022] Preferably, the electron microscope system may further comprise a processor, a memory storing executable instructions that, when executed by the processor, configure a controller of the electron microscope system, such as the electron microscope system or a workstation, server, or external computer, to generate a computed tomography image of the sample using data obtained when an electron beam is detected. This function may also be provided by a computer system external to the electron microscope system.

[0023] Optionally, the control unit may further be configured to f) measure a first distance between a first feature and a second feature perpendicular to the electron beam while the sample is tilted at a tilt angle; g) measure a second distance between the first feature and the second feature perpendicular to the electron beam while the sample is tilted at one or more different tilt angles; h) calculate a difference in separation of the first feature and the second feature from the surface of the sample based on a difference between the first distance and the second distance and a difference between the tilt angle and the one or more different tilt angles.

[0024] Optionally, the sample translation stage may further comprise a plurality of electric motors or other actuators.

[0025] The above method may be implemented as a computer program comprising program instructions for operating a computer. The computer program may be stored on a computer-readable medium, including a non-transitory computer-readable medium.

[0026] A computer system can include one or more processors (e.g., local, virtual, or cloud-based), such as a Central Processing Unit (CPU), and / or a Graphics Processing Unit (GPU) or a collection thereof, such as a single GPU. The processor may execute logic in the form of a software program. The computer system can include memory that includes volatile and non-volatile storage media. A computer-readable medium (CRM) may be included for storing logic or program instructions. For example, an embodiment may include a non-transitory CRM that stores software including instructions executable by one or more computers, and such instructions, when executed, cause one or more computers to perform the methods disclosed herein. A non-transitory CRM may refer to a CRM that stores data for a short period or in the presence of power, such as a memory device or Random Access Memory (RAM). For example, a non-transitory computer-readable medium may include storage components such as a hard disk (e.g., magnetic disk, optical disk, magneto-optical disk, and / or solid-state disk), a compact disc (CD), a digital versatile disc (DVD), a floppy disk, a cartridge, and / or a magnetic tape. Different parts of the system may be connected using a network (e.g., a wireless network and a wired network). The computer system can include one or more interfaces. The computer system can include a suitable operating system, such as UNIX®, Windows®, or Linux®.

[0027] It should be noted that any of the above features may be used with any particular aspect or embodiment of the present invention.

Brief Description of the Drawings

[0028] The present invention can be implemented in many ways, and embodiments will be described below by way of example only with reference to the accompanying drawings.

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[0029] Note that the figure is shown for simplicity and is not necessarily drawn to scale. The same reference numbers are assigned to similar features.

Mode for Carrying Out the Invention

[0030] FIG. 3 shows a system 100 for implementing the electron beam computed tomography imaging process described herein. The system 100 includes a transmission electron microscope (TEM) system 200 and a computer system 110. The computer system 110 itself includes several components including a communication interface 120, a system circuit 130, an input / output (I / O) circuit 140, a display circuit and interface 150, and a data store 170. The system circuit 120 can include one or more processors or CPUs 180 and a memory 190. The system circuit 130 can include any combination of hardware, software, firmware, and / or other circuits. The system circuit 130 can be implemented using one or more systems on a chip (SoCs), application specific integrated circuits (ASICs), microprocessors, and / or analog and digital circuits. The computer system 100 may be located within the TEM system 200 or may be connected to the TEM system 200 by a cable or computer network.

[0031] The display circuit may provide one or more graphical user interfaces (GUIs) 160, and the I / O interface circuit 140 may include a touch sensor type or non-touch display, sound, voice or other recognition inputs, buttons, switches, speakers, acoustic devices, and other user interface elements. The I / O interface circuit 140 may include a microphone, a camera, a headset and a microphone input / output connector, a Universal Serial Bus (USB) connector, and an SD or other memory card socket. The I / O interface circuit 140 may further include a data medium interface (e.g., a CD-ROM or DVD drive) and other buses and a display interface.

[0032] The memory 190 may include volatile (RAM) or non-volatile memory (e.g., ROM or flash memory). The memory may store the operating system 192, applications or software 194, dynamic data 196, and / or static data 198 of the computer system 100. The data store or data source 170 may include, for example, one or more databases 172, 174 and / or a file store or file system.

[0033] The method and system may be implemented in hardware, software, or a combination of hardware and software. The method and system may be implemented as a server with a single computer system or as a distributed network of servers connected via a network. Any type of computer system or other electronic device may be adapted to implement the described method.

[0034] In the TEM system 200, the electron beam may be deflected across the sample (e.g., using an electromagnetic deflector), which can be achieved with high precision and reproducibility. Further, during such beam deflection, the focus of the electron beam on the surface of the sample can be maintained with high reliability. To investigate features of the sample far from the deflection range, the sample may be mechanically translated under the electron beam, which is achieved using a mechanical translation stage. In the following description, "multi-shot" describes the process by which the translation stage moves the sample to a cluster of features. If the features within the cluster are closer than about 3 μm, the electron beam is deflected to sequentially investigate each feature without the need for mechanical translation of the sample. If multi-shot is not used, the sample is mechanically translated such that each feature is sequentially positioned under the electron beam and the electron beam remains stationary (see FIG. 1). In any case, a high-precision and repeatable translation stage reduces the amount of refocusing required for the electron beam on the sample surface, thus improving data acquisition. An example of a suitable mechanical translation stage is the Smart Stage by Thermo Fisher Scientific. Preferably, the positioning accuracy and reproducibility of the translation stage for small movements (up to 500 nm) should also be on the order of 10 nm for small movements (less than 500 nm) and up to 50 nm for large movements of several micrometers.

[0035] In order to generate a computed tomography image using an electron beam signal, each feature must be repeatedly analyzed at different tilt angles. In existing techniques, this is achieved by using a translation stage to translate the sample to identify the location of the feature and the electron beam, tilting the sample at small angular steps (e.g., 3°) around the feature so that the focus of the electron beam is maintained between tilt steps over the feature on the surface of the sample, and processing the resulting data to form a computed tomography image of the feature. Once the full tilt series of the feature is obtained, the translation stage returns the sample so that its surface is perpendicular to the beam axis, the sample is translated so that a new feature is under the electron beam, and the process is repeated. Suitable software for generating images from the data includes Tomography 5 and Tomo Live, both provided by Thermo Fisher Scientific.

[0036] This can be automated to some extent, but each time the lamella sample is translated perpendicular to the electron beam axis (X-Y translation), the electron beam may need to be refocused. This is illustrated in Figure 4A, which shows an image of the sample, with the circles indicating the areas containing the features investigated during mechanical translation of the sample. The diameter of the circles is the size of the electron beam. For example, the diameter may be less than 1 μm, or the size may be increased.

[0037] Figure 4B shows an exemplary implementation of an improved approach where multiple positions on the sample can be reached in a single tilt series with less optical aberration. This improved process is described with respect to the following figures.

[0038] Figure 5 illustrates the current process for obtaining computer tomography data from a sample. Region 520 in Figure 5 corresponds to a multi-micron area on the sample that includes clusters A and B. Each of clusters A and B can include a plurality of features. The surface of the sample may be inclined through axis 510 passing through cluster A. However, the electron beam cannot be deflected beyond the area of the cluster shown in region A. To investigate the features within cluster B, a mechanical translation of the sample is required. Diagram i) of this figure illustrates the translation of the sample across the plane of the sample having an inclination angle of 0°. In this case, a translation dXdY is required to move the electron beam over cluster B.

[0039] In this configuration, since feature B remains at substantially the same (Z) distance from the electron beam source at an inclination angle of 0°, significant refocusing of the electron beam is not required. However, Figure ii shows the effect of translating the sample within the same inclination angle using the same inclination axis 510. As can be seen from Figure ii), when the electron beam is over cluster B, a height (dZ) difference becomes apparent between cluster A and cluster B. Therefore, between the same inclination series having a non-zero inclination (60° in this example), refocusing of the electron beam within the same inclination sequence using the same inclination axis 510 is required (e.g., by changing the electromagnetic characteristics of the TEM until focus is achieved). This increases the time taken to acquire data from multiple clusters within the sample.

[0040] Figure 6 shows an exemplary implementation of an improved method for acquiring data within the same tilt sequence. Again, the same sample is used with clusters A and B, and a single tilt series across axis 510 on the sample. However, when translating the stage so that the new feature cluster B is under the electron beam, instead of translating the sample perpendicular to the electron beam (using only X-Y translation), the sample is translated within a plane at an angle of inclination (60° in this example) along line 610 of the figure. Thus, when moving between clusters on the sample, the focus of the electron beam is substantially maintained on the surface of the sample, resulting in faster data acquisition. This results in less aberration and can reach the entire sample using X, Y, and Z changes using a mechanical translation stage.

[0041] Figure 7 illustrates a further existing implementation showing different steps and iterations used to obtain computed tomography information from a sample. This process can be described with respect to the process shown in Figure 2. Arrow 710 indicates an initial X-Y translation to the starting position on the sample. In the process illustrated by Figure 7, three tilt sequences are performed using the individual clusters enclosed by the dotted lines. Within each cluster, the deflection of the electron beam is indicated by the dotted arrow 730 and the mechanical translation between clusters is indicated by the solid arrow 720. Thus, this process can be described as a multi-shot acquisition where each cluster contains features within the deflection range of the electron beam. The legend in Figure 7 indicates the data acquisition iterations.

[0042] The stage is moved to the first cluster or initial starting point (arrow 710). The full tilt series is performed within each cluster region (740). Data is acquired from each feature within the cluster at the same tilt angle using an electron beam that is deflected (arrow 730) at the same tilt angle using a sample in the tilt series. This is repeated for all positions within a particular cluster (i.e., each feature within the cluster) such that the sample is tilted to a new tilt position (e.g., + / - 3°). No mechanical translation is performed within the same tilt series. Overall, this process is repeated for the clusters by mechanical translation between the clusters (arrow 720), but electron beam focusing is required whenever a mechanical translation (between cluster regions 740) is performed. The translation of the sample is only within the X-Y plane, and thus, re-focusing of the electron beam is required at each different cluster following an X-Y translation. This is for the reason provided with respect to FIG. 5. The use of multi-shot can reduce the time taken to acquire data, but has the drawback that re-focusing is required between each cluster.

[0043] FIG. 8 shows an exemplary example by an improved method for obtaining computer tomography electron beam data. In this case, only a single tilt series is required for the entire sample of all clusters even if mechanical translation is required beyond the range of electron beam deflection. Similar to the previous figure, the dotted lines indicate the deflection of the electron beam between features within an individual cluster. The solid arrows indicate the mechanical translation of the sample. In the exemplary process shown in FIG. 8, only mechanical translation is used. However, when the sample is translated, the sample is moved according to the process described with respect to FIG. 6. That is, the sample is translated within the plane of the surface of the sample regardless of its tilt angle rather than being restricted to the X-Y plane. In other words, the Z component is included to maintain the focus of the electron beam on the surface of the sample when the sample is mechanically translated.

[0044] Therefore, each feature in all clusters can be investigated using an electron beam at a single tilt position, and thus a single tilt series is required for all features in all clusters of the sample. As shown in FIG. 8, the translation stage moves between and within clusters while maintaining the focus of the electron beam on the surface of the sample.

[0045] Again, the legend in FIG. 8 shows the steps within each tilt iteration. For a single angle, the translation stage moves to a particular cluster, moves to positions within that cluster, and acquires data at each position. Once each feature within all clusters has been imaged, the tilt angle is changed and the process is repeated for different tilt angles. No significant refocusing of the electron beam is required following mechanical translation.

[0046] FIG. 9 shows a process similar to the process described with reference to FIG. 8. However, in FIG. 9, instead of mechanical translation within individual clusters to investigate features, the electron beam is deflected (see dotted arrow 930), which can shorten the acquisition time because this deflection can be faster than the X-Y-Z translation of the sample. Overall, this can achieve a speed improvement of up to 30% over existing multi-shot techniques. Mechanical translation between clusters (arrow 920) is still performed within the same tilt series.

[0047] FIG. 10 shows schematic views of samples with different configurations (A and B). However, in this example, the features on the sample have different heights relative to each other above the surface of the sample.

[0048] Height information from different features may be obtained simultaneously with the implementation of the aforementioned tilt series or as a separate process. Existing techniques can obtain height information using only the measured distances between the tilt angles and features, but the accuracy is limited. An improved method for obtaining a more accurate estimate of feature height can be achieved by comparing the measured and estimated distances between points at two or more different angles. In FIGS. 10A and 10B, dX1 represents the apparent distance between features having a sample perpendicular to the electron beam axis, and dX2 represents the apparent distance between features on the sample when tilted at an angle perpendicular to the electron beam axis (e.g., during the aforementioned tilt series). Due to this tilt angle, dX1 is not equal to dX2 (i.e., in the X-Y plane). The delta or difference between dX1 and dX2 is a measure of the height or difference between the top of the feature and the surface of the sample, and the greater the change in height, the greater the delta caused between dX1 and dX2. This can be determined as a function of the alpha tilt. When repeated at different angles, this height estimation can be further improved using, for example, trigonometric analysis incorporating known tilt angles.

[0049] FIG. 11 shows exemplary results between different existing methods for obtaining tilt series computed tomography electron data and the improved method described throughout this specification. As previously described, these improvements can reduce the time taken to acquire the entire tilt series by approximately 30%.

[0050] FIG. 12 shows a flowchart of method 1200 for obtaining electron tomography data from a sample. In step 1210, the electron beam is focused on a first location on the surface of the sample. In step 1220, while maintaining the surface of the sample at the focus of the electron beam, the surface of the sample is tilted at an angle with respect to the electron beam.

[0051] In step 1230, the electron beam is detected when focused on a first location on the surface of the sample. In step 1240, the sample is translated at an inclination angle (i.e., in the X, Y, Z planes) to move the focus of the electron beam to at least a second location (or further locations) on the surface of the sample. In step 1250, the electron beam is detected when focused on the second location on the surface of the sample. Step 1260 indicates that this is repeated for all inclination angles in the inclination series (e.g., for two or more features).

[0052] When all data is collected from all features, a computed tomography image is generated in step 1270.

[0053] As described above, accurate mechanical translation can improve the data acquisition time when the sample is translated at the same angle as the inclination angle applied to the sample. FIGS. 13, 14, and 15 show the components of an exemplary translation stage (e.g., a SmartStage device) that can achieve this. The translation stage provides translation of the sample in three dimensions (X, Y, and Z), which is stacked on an alpha tilt.

[0054] Rx may be described as an alpha tilt and can be realized using a (rigid) bearing with a worm wheel (see FIG. 13). The worm wheel is driven by a worm on a DC motor. The Rx position is measured on the DC motor. In this exemplary mechanism, there are two bearings stacked on top of each other. There is a so-called "dirty" bearing for driving torque and a "clean" bearing to which no force or a very small force is applied. A second sensor for measuring rotation using an encoder is placed on the clean bearing. Although there is friction and play in the drive train, the second sensor that directly measures sample rotation allows for an accurate sample Rx to be known and can be controlled more accurately.

[0055] The translation stage can be friction-free with respect to XYZ translation. The position can be measured where there is no friction or play and only rigidity towards the sample position. Preferably, only elastic components are used in the translation stage.

[0056] There are three (similar) drive units (T1, T2 and T3 in Figure 14), which are arranged in a tripod structure with a pivot point at the front. Tilt tubes that move in the XYZ directions at the rear of each arm are used (see Figure 15). The holder is arranged inside the tilt tube but does not move with respect to this tube. Using the front pivot point consisting of leaf springs, the XYZ position of the sample can be controlled and measured. Since there is no friction from the measurement position to the sample position, play can be reduced or eliminated, the sample position can be accurately controlled, and reproducibility and accuracy on the order of several tens of nm can be obtained. Other suitable translation stages that can accurately control three-dimensional movement may also be used.

[0057] Throughout the present disclosure, including within the scope of the claims, unless the context clearly indicates otherwise, singular terms in this specification are to be construed as including the plural, and vice versa. For example, unless the context clearly indicates otherwise, singular references in the claims, including "a" or "an" (such as "an ion multipole device"), mean "one or more" (e.g., one or more ion multipole devices). Throughout the specification and claims of the present disclosure, words such as "comprise", "including", "having", and "contain", and variations of the words, such as "comprising" and "comprises" or the like, mean "including but not limited to", and are not intended to exclude other components. Also, the use of "or" is inclusive, such that the phrase "A or B" applies when A applies, when B applies, or when both A and B apply.

[0058] Any and all examples provided in this specification, or the use of exemplary language (such as "for instance", "such as", "for example", and the like), are merely intended to better illustrate the invention and do not indicate a limitation to the scope of the disclosure, unless otherwise claimed. Any language in this specification should not be construed as indicating any element essential to the practice of the disclosure that is not claimed.

[0059] The terms "first" and "second" can be reversed without changing the scope of the invention. That is, an element called the "first" element can instead be called the "second" element, and an element called the "second" element can instead be regarded as the "first" element.

[0060] Any of the processes described in this specification can be performed in any order or simultaneously, unless otherwise described or the context requires a different meaning. Further, if a step is described as being performed after another step, this does not exclude the possibility that intervening steps are being performed.

[0061] Furthermore, unless otherwise implicitly or explicitly understood or described, for any given component or embodiment described throughout, it is understood that any of the candidates or alternatives that may be listed for that component can be generally used individually or in combination with each other. Further, unless otherwise implicitly or explicitly understood or described, any such listing of candidates or alternatives is merely exemplary and not limiting.

[0062] Unless otherwise stated, all technical and scientific terms used throughout have the meaning commonly understood by one of ordinary skill in the art to which the various embodiments described in this specification belong.

[0063] As will be understood by those skilled in the art, the details of the above embodiments can be changed without departing from the scope of the invention defined by the appended claims.

[0064] For example, different translation stages may be used. The microscope may also be, for example, an energy filtered transmission electron microscope (EFTEM) or a scanning TEM.

[0065] The term "focus" in the present disclosure is used, for example, to describe directing an electron beam so as to achieve a particular required set of beam characteristics when intersecting a feature. These characteristics can include, when the electron beam passes through a particular plane such as a sample plane, the beam or spot size (e.g., diameter or circular diameter), the beam or spot shape (e.g., circular), the intensity, the beam uniformity (e.g., the variation of intensity across the beam or spot), and / or the beam direction. Thus, focusing the electron beam can also mean forming or directing the electron beam so that the electron beam has particular characteristics at a particular plane or location. "Focusing" or "focus" can be used interchangeably with "directing", "directing", "detecting", "detecting", "imaging", or "imaging".

[0066] Those skilled in the art will readily recognize many combinations, changes, or modifications to the features of the above embodiments, which are intended to form part of the present invention. Any of the features specifically described in connection with one embodiment or example can be used in any other embodiment by making appropriate changes.

Claims

1. 1. A method for obtaining electron tomography data from a sample, comprising: a) focusing an electron beam at a first location on a surface of the specimen; b) tilting the surface of the specimen at a tilt angle with respect to the electron beam while maintaining the surface of the specimen at a focal point of the electron beam; c) detecting the electron beam focused at the first location on the surface of the specimen; and d) translating the specimen at the tilt angle to move the focal point of the electron beam to at least a second location on the surface of the specimen; e) detecting the electron beam focused at least at the second location on the surface of the specimen; and repeating steps b) through e) at one or more different tilt angles.

2. The method of claim 1 , further comprising generating a computed tomography image of the sample using data obtained when detecting the electron beam.

3. The method of claim 1 or 2, wherein the tilt angle is a non-perpendicular angle to the electron beam.

4. 3. The method of claim 1 or 2, wherein a first feature of the sample is located at the first location and a second feature of the sample is located at the second location.

5. The method comprises: f) measuring a first distance between the first feature and the second feature perpendicular to the electron beam with the specimen tilted at the tilt angle; g) measuring a second distance between the first feature and the second feature perpendicular to the electron beam with the specimen tilted at the one or more different tilt angles; h) calculating a difference in separation of the first feature and the second feature from the surface of the specimen based on a difference between the first distance and the second distance and a difference between the tilt angle and the one or more different tilt angles.

6. The method of claim 5 , wherein either the tilt angle or the one or more different tilt angles are perpendicular to an axis of the electron beam.

7. The method according to claim 1 or 2, wherein the sample is a lamellar sample.

8. After step c) and before step d), adjusting the electron beam to be focused at a third location; detecting the electron beam focused at the third location on the surface of the specimen. The method of claim 1 or 2, further comprising:

9. After step d) and before or after step e), adjusting the electron beam to be focused at a fourth location; 3. The method of claim 1, further comprising: detecting the electron beam focused at the fourth location on the surface of the specimen.

10. The method according to claim 1 or 2, wherein the angle difference between the tilt angle and the one or more different tilt angles is between 0.1 and 10 degrees.

11. The method of claim 1 or 2, wherein translating the sample to the tilt angle moves the location of the electron beam on the sample by between 1 μm and 3 μm.

12. 1. An electron microscope system, comprising: an electron beam source; electron beam focusing optics configured to focus the electron beam onto a surface of a specimen; a specimen translation stage configured to translate the specimen in a plane perpendicular to the electron beam to vary the tilt angle of the surface of the specimen relative to the axis of the electron beam; a control unit in communication with the specimen translation stage and the electron beam focusing optics, a) focusing the electron beam at a first location on the surface of the specimen; b) tilting the surface of the specimen at a tilt angle with respect to the electron beam while maintaining the surface of the specimen at a focal point of the electron beam; c) detecting the electron beam focused at the first location on the surface of the specimen; and d) translating the specimen at the tilt angle to move the focal point of the electron beam to at least a second location on the surface of the specimen; e) detecting the electron beam focused at least at the second location on the surface of the specimen; and repeating steps b) to e) at one or more different tilt angles; and a control unit configured to perform the steps.

13. A processor; 13. The electron microscope system of claim 12, further comprising: a memory storing executable instructions that, when executed by the processor, configure the electron microscope system to generate a computed tomography image of the sample using data obtained upon detecting the electron beam.

14. The control unit f) measuring a first distance between the first feature and the second feature perpendicular to the electron beam with the specimen tilted at the tilt angle; g) measuring a second distance between the first feature and the second feature perpendicular to the electron beam with the specimen tilted at the one or more different tilt angles; h) calculating a difference in separation of the first feature and the second feature from the surface of the sample based on a difference between the first distance and the second distance and a difference between the tilt angle and the one or more different tilt angles.

15. 15. The electron microscope system of claim 13 or claim 14, wherein the sample translation stage further comprises a plurality of electric motors.

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