X-ray tomography stage control

Abstract

The invention relates to X-ray tomography objective table control. A method and system for obtaining electron tomography data from a sample is provided. A) focusing an electron beam at a first location on a surface of a sample. B) tilting the surface of the sample to an angle of inclination with 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 position of the surface of the sample. E) detecting the electron beam focused on at least the second location on the surface of the sample. Step b) to step e) are repeated at one or more different inclination angles.

Description

Technical Field

[0001] The present invention relates to a system and method for generating electron tomography data and images, and more particularly to improving the acquisition of tilt series data collection. Background Art

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

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

[0004] Figure 2 An existing process for obtaining an example tilt series from eight different features on a sample is shown. Since the features are spaced apart by a distance greater than the distance the electron beam can be directed, the sample must be mechanically translated by a translation stage between each tilt series collection of data. Each time the tilted sample is translated, the electron beam needs to be refocused. This can be achieved by moving the sample towards or away from the beam source (i.e., z-axis translation for coarse focus correction) and by using a combination of focusing optics with the electron beam source. Figure 2 The solid arrows in show the mechanical translation of the sample. Arrow 230 shows the initial X-Y translation (e.g., perpendicular to the electron beam) at the start of the acquisition series. Arrow 220 indicates the remote translation (X-Y) using the mechanical stage. Arrow 220 indicates the short-range translation using the mechanical stage between adjacent features. The stage is moved to the point of interest. The sample is tilted about the electron beam focus point on the sample. This operation is repeated for all X-ray tomogram positions. Although effective, this data collection can be time-consuming and result in low sample throughput.

[0005] Figure 2Also shown are the interaction steps for completing a tilt series, where each feature is studied at different tilt angles as a legend in the figure. Mechanical translation of the sample (arrow 220) is performed for each feature or point of interest. For each feature, a complete tilt series is performed. For example, the angle of the surface of the sample is changed in 3° steps + / - 70 degrees, where data is collected from the feature at each step under the electron beam. This operation is repeated for all tomogram positions. These data are applied to a computed tomography algorithm to form a computer image. In Figure 2 In the example shown in Figure 2 , eight features are studied, where mechanical translation is performed for each feature. Thus, in this particular example, eight independent data sets are required, which requires a considerable amount of acquisition time.

[0006] In addition, although the sample is mainly flat, some features extend more from the surface than others and it is difficult to obtain accurate height information about these features.

[0007] Therefore, methods and systems are needed to overcome these problems. SUMMARY OF THE INVENTION

[0008] When collecting data for generating a computed tomography image, a method and system provide an efficiency improvement. Data is collected from points on the surface of the sample at specific different tilt angles while translating the sample at the current tilt angle. The focus of the electron beam is maintained (e.g., using a mechanical or high-voltage stage) at the sample surface while being translated at the tilt angle. This avoids having to refocus the electron beam between imaging points. This can be achieved by using a translation stage to precisely translate the sample at a specific tilt angle (in three dimensions).

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

[0010] According to a first aspect, there is provided a method for obtaining electron tomography data from a sample (e.g., a planar sample and / or a layered sample), the method comprising the steps of:

[0011] a) focusing an electron beam at a first position on the surface of the sample;

[0012] b) tilting the surface of the sample to an angle of the electron beam while maintaining the surface of the sample at the focus of the electron beam;

[0013] c) Detect an electron beam focused at a first location on the surface of the sample;

[0014] d) Translate the sample at an oblique angle to move the focus of the electron beam to at least a second location on the surface of the sample;

[0015] e) Detect the electron beam focused at at least the second location on the surface of the sample; and

[0016] Repeat steps b) to e) at one or more different oblique angles. Thus, data can be collected faster and more efficiently because it is not necessary to refocus the electron beam on the sample surface after the electron beam has been translated to a new location or sample feature. This is because fewer tilt series are required because all rotations through all angles (i.e., α tilt) are more time-consuming than translational X-Y-Z movements. The sample is translated in all X-Y-Z dimensions (i.e., also in the direction of the electron beam axis), rather than using only the lateral X-Y mechanical translation of the sample (i.e., movement in a plane perpendicular to the electron beam axis), which causes the height of the tilted sample to change relative to the electron beam and results in defocus on the sample surface. In other words, the sample is translated such that the beam is focused at a second location on the surface of the sample, where the translation includes a component in the direction of the electron beam.

[0017] Preferably, the method can further include the step of generating a computed tomography (CT) image of the sample using the data obtained when detecting the electron beam. Different CT algorithms can be used.

[0018] Optionally, the oblique angle can be a non-normal angle to the electron beam. The oblique angle can start orthogonal or non-orthogonal to the axis of the electron beam. In the case where the oblique angle is non-orthogonal to the electron beam, the sample will need to be translated in three dimensions, i.e., the translation stage must move the sample equally in the X, Y, and Z directions. The Z component is used during this translation. Otherwise, the electron beam will not remain focused on the sample. The X-Y plane can be considered as the plane perpendicular to (orthogonal to) the electron beam. When translating the sample such that the beam is focused at a second location on the surface of the sample and the oblique angle is non-orthogonal to the electron beam, the translation of the sample may need to include a component in the direction of the electron beam (i.e., defined as the Z component).

[0019] Preferably, a first feature of the sample can be located at the first location, and a second feature of the sample can be located at the second location. Thus, multiple features within the sample can be analyzed faster. The translation can occur during the tilt series. Each feature or multiple features can be studied with the sample at the same oblique angle. Thus, the translation of the sample (one or more times) using a mechanical stage can occur at the same oblique angle, where the translation is repeated for different oblique angles.

[0020] Optionally, the method can further include the following steps:

[0021] f) Measuring a first distance between a first feature and a second feature orthogonally to an electron beam when the sample is tilted at an inclined angle;

[0022] g) Measuring a second distance between the first feature and the second feature orthogonally to the electron beam when the sample is tilted at one or more different inclined angles; and

[0023] h) Calculating a difference in the spacing 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 inclined angle and the one or more different inclined angles. These additional method steps provide information about the height above the sample surface of different features. This additional information is obtained by stereophotogrammetry. The more different inclined angles used, the higher the accuracy of the height information that can be provided. The process can be repeated at different inclined angles to improve accuracy.

[0024] Optionally, either the inclined angle or one of the one or more different inclined angles can be orthogonal to the axis of the electron beam.

[0025] Optionally, the sample is a layered sample. However, any planar sample can be used.

[0026] Optionally, the method can further include the following steps:

[0027] After step c) and before step d), adjusting the electron beam to be focused at a third position or more than three positions; and

[0028] Detecting the electron beam focused at a third position on the surface of the sample. The electron beam can be deflected slightly (e.g., less than 3 μm) without using a mechanical stage to translate the sample. Thus, by only deflecting or moving the electron beam but at the same inclined angle, features (e.g., feature clusters) that are close to each other can be studied faster (and without sacrificing optical quality). The combination of electron beam deflection and mechanical translation can be carried out at the same inclined angle during the tilt series. Thus, this provides improved flexibility and further accelerates data acquisition. In addition, the data acquisition time can be reduced when there is a large distance between features, without sacrificing optical quality and without loss of throughput.

[0029] Optionally, the method can further include the following steps:

[0030] After step d) and before or after step e), adjusting the electron beam to be focused at a fourth position; and

[0031] Detect an electron beam focused at a fourth position (or more than four positions) on the surface of the sample. The electron beam can be adjusted or deflected on different stages of the method.

[0032] Optionally, the angular difference between the tilt angle and one or more different tilt angles can be between 0.1° and 10° (e.g., at 1° and 5° or between the two). For example, the angle between the tilts can be 3° or less (e.g., 2°, 1° or less than 1°).

[0033] Optionally, the sample can be translated at a tilt angle to move the position of the electron beam on the sample between 1 μm and 3 μm. Depending on the location of the specific feature, other translation distances can be used.

[0034] According to a second aspect, there is provided an electron microscope system comprising: an electron beam source;

[0035] Electron beam focusing optics configured to focus the electron beam on the surface of the sample;

[0036] A sample translation stage configured to translate the sample in a plane orthogonal to the electron beam and change the tilt angle of the surface of the sample relative to the axis of the electron beam; and

[0037] A control unit in communication with the sample translation stage and the electron beam focusing optics and configured to perform the following steps:

[0038] a) Focus the electron beam at a first position on the surface of the sample;

[0039] b) Tilt the surface of the sample to the tilt angle of the electron beam while keeping the surface of the sample at the focus of the electron beam;

[0040] c) Detect the electron beam focused at the first position on the surface of the sample;

[0041] d) Translate the sample at the tilt angle to move the focus of the electron beam to at least a second position on the surface of the sample;

[0042] e) Detect the electron beam focused at at least the second position on the surface of the sample; and repeat steps b) to e) at one or more different tilt angles.

[0043] Preferably, the electron microscope system can further comprise:

[0044] A processor; and

[0045] A memory storing executable instructions that, when executed by a processor, configure an electron microscope system or a controller of the electron microscope system, such as a workstation, a server, or an external computer, to perform:

[0046] Generate a computed tomography image of a sample using data obtained when detecting an electron beam. This function can also be provided by a computer system external to the electron microscope system.

[0047] Optionally, the control unit can be further configured to:

[0048] f) Measure a first distance between a first feature and a second feature orthogonal to the electron beam when the sample is tilted at an inclined angle;

[0049] g) Measure a second distance between the first feature and the second feature orthogonal to the electron beam when the sample is tilted at one or more different inclined angles; and

[0050] h) Calculate a difference in the spacing 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 inclined angle and the one or more different inclined angles.

[0051] Optionally, the sample translation stage can also include a plurality of electric motors or other actuators.

[0052] The method described above can be implemented as a computer program including program instructions for operating a computer. The computer program can be stored in a computer-readable medium, including a non-transitory computer-readable medium.

[0053] 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 single graphics processing unit (GPU) or a collection thereof. The processor can execute logic in the form of a software program. The computer system can include a memory that includes volatile and non-volatile storage media. A computer-readable medium (CRM) can be included to store logic or program instructions. For example, an embodiment can include a non-transitory CRM storing software that includes instructions executable by one or more computers, which when executed cause the one or more computers to perform the disclosed methods. A non-transitory CRM can refer to a CRM that stores data for a short period of time or in the presence of power, such as a memory device or random access memory (RAM). For example, a non-transitory computer-readable medium can include storage components such as a hard disk (e.g., magnetic disk, optical disk, magneto-optical disk, and / or solid state disk), compact disc (CD), digital versatile disc (DVD), floppy disk, cartridge, and / or magnetic tape. Different parts of the system can be connected using a network (e.g., wireless network and wired network). The computer system can include one or more interfaces. For example, the computer system can include a suitable operating system such as UNIX, Windows(RTM), or Linux.

[0054] It should be noted that any of the above features can be used with any particular aspect or embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The present invention can be practiced in many ways and embodiments will now be described by way of example only and with reference to the following drawings, in which:

[0056] Figure 1 A schematic diagram showing two scenarios (A and B) for obtaining electron beam tomography data is shown;

[0057] Figure 2 A schematic diagram showing how a sample moves under the electron beam of an electron beam microscope is shown;

[0058] Figure 3 A schematic diagram of a computer system for controlling a transmission electron microscope (TEM) is shown;

[0059] Figure 4 Images A and B of regions of a sample showing different imaging techniques are shown;

[0060] Figure 5 A schematic diagram showing the tilting process of a sample according to an existing imaging technique is shown;

[0061] Figure 6 A schematic diagram showing an imaging technique according to an example embodiment is shown;

[0062] Figure 7 A schematic diagram of features on a sample showing the translation of the sample and the movement of the electron beam;

[0063] Figure 8 A schematic diagram of features on a sample showing the translation of the sample under an electron beam according to an exemplary embodiment;

[0064] Figure 9 A schematic diagram of features of a sample showing the translation of the sample and the movement of the electron beam across the sample according to another exemplary embodiment;

[0065] Figure 10 A schematic diagram of a sample showing a process for obtaining height information from the sample;

[0066] Figure 11 A graph showing a comparison of acquisition times for different imaging techniques;

[0067] Figure 12 Shows a method for operating Figure 3 a system to obtain a computed tomography image of a sample;

[0068] Figure 13 Shows Figure 3 components of the translation stage of a TEM system;

[0069] Figure 14 Shows Figure 3 components of the translation stage of a TEM system; and

[0070] Figure 15 Shows Figure 3 components of the translation stage of a TEM system.

[0071] Note that the figure is shown for simplicity and is not necessarily drawn to scale. Similar features are provided with the same reference numerals. Detailed Description

[0072] Figure 3FIG. 0 shows a system 100 for implementing the electron beam computed tomography imaging process described within this specification. System 100 includes a transmission electron microscope (TEM) system 200 and a computer system 110, which in turn includes a number of 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 storage 170. System circuit 120 can include one or more processors or CPUs 180 and a memory 190. System circuit 130 can include any combination of hardware, software, firmware, and / or other circuitry. System circuit 130 can be implemented with one or more system-on-chips (SoCs), application-specific integrated circuits (ASICs), microprocessors, and / or analog and digital circuitry. Computer system 100 can also be located within TEM system 200 or connected to the TEM system via a cable or computer network.

[0073] The display circuit can provide one or more graphical user interfaces (GUIs) 160, and the I / O interface circuit 140 can include a touch-sensitive or non-touch display, sound, voice, or other recognition inputs, buttons, switches, speakers, sound generators, and other user interface elements. The I / O interface circuit 140 can include a microphone, a camera, a headset and microphone input / output connector, a universal serial bus (USB) connector, and an SD or other memory card slot. The I / O interface circuit 140 can also include a data medium interface (e.g., a CD-ROM or DVD drive) and other bus and display interfaces.

[0074] Memory 190 can include volatile (RAM) or non-volatile memory (e.g., ROM or flash memory). The memory can store an operating system 192, application programs or software 194, dynamic data 196, and / or static data 198 of computer system 100. The data storage or data source 170 can include, for example, one or more databases 172, 174, and / or a file storage or file system.

[0075] The method and system can be implemented in hardware, software, or a combination of hardware and software. The method and system can be implemented as a server including a single computer system or as a distributed network of servers connected across a network. Any kind of computer system or other electronic device can be adapted to perform the described method.

[0076] In the TEM system 200, the electron beam can be deflected across the sample (e.g., using an electromagnetic deflector), and this can be achieved with high precision and repeatability. In addition, during such beam deflection, the focusing of the electron beam on the surface of the sample can be maintained highly reliably. To study features of the sample that are further away and beyond the deflection range, the sample can be mechanically translated under the electron beam and this is achieved using a mechanical translation stage. In the following description, "multiple excitation" describes the process in which the translation stage moves the sample to a cluster of features. In the case where the features in the cluster are closer than about 3 μm, the electron beam is deflected to study each feature in turn without mechanical translation of the sample. Without using multiple excitation, the sample is mechanically translated such that each feature is again placed under the stationary electron beam (see Figure 1 ). In any case, a highly precise and repeatable translation stage improves data acquisition as this reduces the amount of refocusing required of the electron beam on the sample surface. An example of a suitable mechanical translation stage is the Smart Stage by Thermo Fisher Scientific. Preferably, for the positioning accuracy of the translation stage for small movements (up to 500 nm), for small movements (less than 500 nm), the reproducibility should also be on the order of 10 nm, and for large movements of several microns, the reproducibility should be up to 50 nm.

[0077] To generate a computed tomography image using the electron beam signal, each feature must be repeatedly analyzed at different tilt angles. In the prior art, this is achieved by: using a translation stage to translate the sample to position the feature and the electron beam, tilting the sample around the feature in small angular steps (e.g., 3°) such that the focusing of the electron beam is maintained on the feature on the sample surface between the tilt steps, and processing the resulting data to form a computed tomography image of the feature. Once a complete tilt series of the feature is obtained, the translation stage returns the sample such that its surface is perpendicular to the beam axis and the sample is translated such that a new feature is under the electron beam in the case of repeating the process. Suitable software for generating an image from the data includes both Tomography 5 and Tomo Live provided by Thermo Fisher Scientific.

[0078] Although this can be somewhat automated, whenever the layered sample is translated perpendicular to the electron beam axis (X-Y translation), the electron beam may need to be refocused. This is shown in Figure 4 A, which shows an image of the sample where the circles indicate the regions containing the features studied between mechanical translations of the sample. The diameter of the circles is the size of the electron beam. For example, the diameter can be less than 1 μm or the size can increase.

[0079] Figure 4B shows an exemplary embodiment of an improved method in which multiple positions on a sample can be reached in a single tilt series with fewer optical aberration values. The improved process is described with respect to the following figures.

[0080] Figure 5 Shows the current process for obtaining computed tomography data from a sample. Figure 5 The region 520 in corresponds to a multi-micron region on the sample that includes cluster A and cluster B. Each of cluster A and cluster B can contain multiple features. The surface of the sample can be tilted through axis 510, which passes through cluster A. However, the electron beam cannot be deflected beyond the region of the cluster shown in region A. To study the features within cluster B, mechanical translation of the sample is required. Illustration i) in this figure shows the translation of the sample across the plane of the sample at a tilt angle of 0°. In this case, a translation dXdY is required to bring the electron beam onto cluster B.

[0081] With this configuration, since feature B remains at substantially the same (Z) distance from the electron beam source with a tilt angle of 0°, significant refocusing of the electron beam is not required. However, illustration ii shows the effect of translating the sample within the same tilt angle using the same tilt axis 510. As can be seen from illustration ii), when the electron beam is above cluster B, there will be a significant height (dZ) difference between cluster A and cluster B. Therefore, during the same tilt series with a non-zero tilt (60° in this example), then it will be necessary to refocus the electron beam within the same tilt sequence using the same tilt axis 510 (e.g., by changing the electromagnetic properties of the TEM until focus is achieved). This increases the time taken to acquire data from multiple clusters in the sample.

[0082] Figure 6 Shows an exemplary embodiment of an improved method for acquiring data within the same tilt sequence. Again, the same sample is used with cluster A and cluster B and a single tilt series across axis 510 on the sample. However, when the stage is translated such 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 along line 610 in the plane of the tilt angle (60° in this example) in the figure. Thus, when moving between clusters on the sample, the focus of the electron beam is substantially maintained at the surface of the sample, resulting in faster data acquisition. This results in fewer aberration values and enables the use of a mechanical translation stage to reach the entire sample using X, Y, and Z variations.

[0083] Figure 7 Shows another existing embodiment showing different steps and iterations for obtaining computed tomography information from a sample. The process can be with respect to Figure 2The process shown is described. Arrow 710 indicates the initial X-Y translation to the starting position on the sample. At Figure 7 In the process shown, three tilt series are performed, where a single cluster is bounded by a dashed line. In each cluster, the deflection of the electron beam is indicated by the dashed arrow 730 and the mechanical translation between the clusters is indicated by the solid arrow 720. Thus, the process can be described as multiple excitation acquisitions, where each cluster contains features within the deflection range of the electron beam. Figure 7 The legend in

[0084] The stage is moved to the first cluster or the initial starting point (arrow 710). A complete tilt series (740) is performed within each cluster region. Data is acquired from each feature in the cluster at the same tilt angle, where the electron beam is deflected in the tilt series with the sample at the same tilt angle (arrow 730). This is repeated for all positions within a particular cluster (i.e., each feature in the cluster) such that the sample is tilted to a new tilt position (e.g., + / - 3°). No mechanical translation occurs within the same tilt series. In summary, the process is repeated for the clusters, where mechanical translation occurs between the clusters (arrow 720), but electron beam focusing is required whenever mechanical translation occurs (between the cluster regions 740). The translation of the sample is only in the X-Y plane, so re-focusing of the electron beam is required at each different cluster after the X-Y translation. This is for the reason regarding Figure 5 provided. While the use of multiple excitations can reduce the time taken to acquire data, the need for re-focusing between each cluster has drawbacks.

[0085] Figure 8 An illustrative example according to an improved method for obtaining electron beam data for computed tomography is shown. In this case, only a single tilt series is required for the entire sample for all clusters, even when mechanical translation beyond the deflection range of the electron beam is needed. As in the previous figure, the dashed line indicates the deflection of the electron beam between the features within a single cluster. The solid arrow indicates the mechanical translation of the sample. At Figure 8 In the example process shown, only mechanical translation is used. However, when the sample is translated, it is moved according to the process regarding Figure 6 described. That is, regardless of the tilt angle of the sample, the sample is translated within the plane of the sample surface rather than being restricted to the X-Y plane. In other words, a Z component is included to maintain the focusing of the electron beam on the surface of the sample when the electron beam is mechanically translated.

[0086] Thus, the electron beam at a single tilt position can be used to study each feature in each cluster, and thus only a single tilt series is required for all features in all clusters of the sample. As Figure 8 shown, the translation stage moves between and within the clusters while maintaining the focusing of the electron beam on the surface of the sample.

[0087] Again, Figure 8 The illustration in shows the steps within each tilt iteration. For a single angle, the translation stage is moved to a particular cluster, moved to a position within that cluster and data is acquired at each location. Once every feature in each cluster 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 after mechanical translation.

[0088] Figure 9 shows a process similar to the process described with reference Figure 8 However, in Figure 9 , the electron beam is deflected (see dashed arrow 930), rather than mechanically translated, to investigate features within a single cluster, which further reduces the acquisition time since the deflection can be faster than the X-Y-Z translation of the sample. Overall, this can achieve a speed improvement of up to 30% relative to existing multiple excitation techniques. The mechanical translation between clusters (arrow 920) still takes place within the same tilt series.

[0089] Figure 10 shows a schematic illustration of samples of 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.

[0090] Height information from different features can be obtained while performing the previously described tilt series or as a separate process. Prior art can only obtain height information using the measured distance between the tilt angle and the feature, but with limited accuracy. An improved method for obtaining a more accurate estimate of the feature height can be achieved by comparing the measured distance between points at two or more different angles with the estimated distance. In Figure 10 Figs. A and B of, dX1 shows the apparent distance between features when the sample is perpendicular to the electron beam axis, and dX2 is the apparent distance between features on the sample when tilted at an angle orthogonal to the electron beam axis (e.g., during the previously described tilt series). Due to this tilt angle, dX1 is not equal to dX2 (i.e., in the X-Y plane). The increment 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, where the larger the change in height results in a larger increment between dX1 and dX2. This can be determined as a function of the α tilt. When repeated at different angles, this estimate of the height can be further improved, for example, using trigonometric analysis incorporating known tilt angles.

[0091] Figure 11Example results between different existing approaches for obtaining tilt-series computer tomography electronic data and the improved methods described throughout this specification are shown.As mentioned previously, these improvements can reduce the time taken to acquire a complete tilt-series by approximately 30%.

[0092] Figure 12 A flow chart of a method 1200 for obtaining electron tomography data from a sample is shown. At step 1210, an electron beam is focused at a first location on a surface of the sample. At step 1220, the surface of the sample is tilted to an angle to the electron beam while maintaining the surface of the sample at the focus of the electron beam.

[0093] At step 1230, the electron beam is detected when the electron beam is focused on a first location on the sample surface. At step 1240, the sample is translated at a tilt angle (i.e., in the X, Y, Z plane) to move the focus of the electron beam to at least a second location (or additional locations) on the surface of the sample. At step 1250, the electron beam is detected when the electron beam is focused on a second location on the surface of the sample. Step 1260 indicates repeating this operation for all tilt angles in the tilt series (e.g., for two or more features).

[0094] Once all data from all of the features has been collected, a computed tomography image is generated at step 1270 .

[0095] As mentioned previously, precise mechanical translation can improve data acquisition time if the sample is translated at the same angle as the tilt angle applied to the sample. Figure 13 , Figure 14 and Figure 15 Components of an example translation stage (eg, a SmartStage device) that can accomplish this are shown.The translation stage provides translation of a sample stacked on an alpha tilt in three dimensions (X, Y, and Z).

[0096] Rx can be described as an α tilt and can be realized using a (rigid) bearing with a worm wheel (see Figure 13 ). The worm wheel is driven by a worm on a DC motor. The Rx positioning is measured on the DC motor. In this example mechanism, there are two bearings stacked on top of each other. A so-called "dirty" bearing for driving torque and a "clean" bearing that applies no force or very little force. On the clean bearing is placed a second sensor that measures the rotation using an encoder. There is friction and play in the drive train, but thanks to the second sensor that directly measures the sample rotation, the exact sample Rx is known and can be controlled more accurately.

[0097] The translation stage can be frictionless for XYZ translation. The positioning can be measured at positions where there is only stiffness and no friction or play towards the sample positioning. Preferably, only elastic components are used in the translation stage.

[0098] There are three (similar) drive units ( Figure 14 T1, T2, and T3 in Figure 15 ), which are placed in a tripod configuration with a pivot point at the front. At the rear of each arm, tilt tubes that move in the XYZ directions are used (see

[0099] ). The holder is placed inside the tilt tube but does not move relative to the tube. By using a front pivot point consisting of leaf springs, the XYZ positioning of the sample can be controlled and measured. Since there is no friction from the measurement positioning to the sample positioning, play can be reduced or eliminated, and the sample positioning can be precisely controlled, resulting in repeatability and accuracy on the order of approximately several tens of nm. Other suitable translation stages that can precisely control the movement in three dimensions can be used.

[0099] As used throughout this document, including in the claims, unless the context otherwise indicates, the singular forms of the terms herein shall be construed to include the plural forms and vice versa. For example, unless the context otherwise indicates, a singular reference herein (including in the claims), such as "a" (such as an ion multipole device) means "one or more" (e.g., one or more ion multipole devices). In the specification and claims of this disclosure, the words "comprise," "include," "have," and "contain" and variations of these words, e.g., "comprising" or like terms mean "including but not limited to," and are not intended to (and do not) exclude other components. Additionally, the use of "or" is inclusive such that the phrase "A or B" is true when "A" is true, "B" is true, or both "A" and "B" are true.

[0100] Any and all examples or exemplary language (such as "for example," "such as," "e.g." and similar language) used herein is intended only to better illustrate the disclosure and does not indicate a limitation on the scope of the disclosure unless otherwise required. No language in this specification should be construed as indicating any element not claimed as necessary for practicing the disclosure.

[0101] The terms "first" and "second" can be reversed without changing the scope of the disclosure. That is, an element referred to as the "first" element can instead be referred to as the "second" element, and an element referred to as the "second" element can instead be regarded as the "first" element.

[0102] Unless otherwise specified or the context otherwise requires, any steps described in this specification can be performed in any order or simultaneously. Additionally, where steps are described as being performed after a step, this does not preclude intermediate steps being performed.

[0103] It should also be understood that, unless otherwise implicitly or explicitly understood or stated, for any given component or embodiment described throughout the text, any one of the possible candidates or alternatives listed for that component can generally be used alone or in combination with each other. It should be understood that any such list of candidates or alternatives is merely illustrative and not restrictive, unless otherwise implicitly or explicitly understood or stated.

[0104] Unless otherwise specified, all technical and scientific terms used throughout the text have the meanings commonly understood by one of ordinary skill in the art to which the various embodiments described herein belong.

[0105] Those skilled in the art will understand that the details of the above-described embodiments can be changed without departing from the scope of the invention as defined by the appended claims.

[0106] For example, different translation stages can be used. The microscope can also be, for example, an energy-filtering transmission electron microscope (EFTEM) or a scanning TEM.

[0107] The term "focusing" in the present disclosure is used to describe, for example, guiding an electron beam to achieve a particular desired set of electron beam characteristics when intersecting a feature. When the electron beam passes through a particular plane (such as a sample plane), these characteristics can include beam or spot size (e.g., diameter or circle diameter), beam or spot shape (e.g., circle), intensity, beam uniformity (e.g., intensity variation across the beam or spot), and / or beam direction. Thus, focusing an electron beam can also mean forming or guiding the electron beam such that it has particular characteristics at a particular plane or location. "Focusing" or "focused" can be used interchangeably with "directing", "guiding", "detecting", "detected", "imaging", or "imaged".

[0108] Many combinations, modifications, or variations of the features of the above-described embodiments will be apparent to those skilled in the art and are intended to form part of the invention. By making appropriate changes, any of the features specifically described in relation to one embodiment or example can be used in any other embodiment.

Claims

1. A method for obtaining electron tomography data from a sample, the method comprising the steps of: a) focusing an electron beam at a first position on a surface of the sample; b) tilting the surface of the sample to an oblique 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 position 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 of the surface of the sample; e) detecting the electron beam focused on at least the second location on the surface of the sample; as well as Steps b) to e) are repeated at one or more different tilt angles.

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

3. A method according to any preceding claim, wherein the tilt angle is a non-normal angle to the electron beam.

4. A method according to any preceding claim, wherein a first feature of the sample is located at the first position and a second feature of the sample is located at the second position.

5. The method according to claim 4, further comprising the steps of: f) measuring a first distance between the first feature and the second feature orthogonally to the electron beam when the sample is tilted at the tilt angle; g) measuring a second distance between the first feature and the second feature orthogonally to the electron beam with the sample tilted at the one or more different tilt angles; as well as h) calculating a difference in spacings 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. 6 . The method of claim 5 , wherein the tilt angle or any of the one or more different tilt angles is orthogonal to an axis of the electron beam.

7. A method according to any preceding claim, wherein the sample is a laminar sample.

8. The method according to any preceding claim, further comprising the steps of: After step c) and before step d), adjusting the electron beam to focus on a third position; as well as The electron beam focused at the third position on the surface of the sample is detected.

9. The method according to any preceding claim, further comprising the steps of: After step d) and before or after step e), adjusting the electron beam to focus on a fourth position; as well as The electron beam focused at the fourth position on the surface of the sample is detected.

10. A method according to any preceding claim, wherein the angular difference between the tilt angle and the one or more different tilt angles is between 0.1 degrees and 10 degrees.

11. A method according to any preceding claim, wherein the sample is translated at the tilt angle to move the position of the electron beam on the sample by between 1 μm and 3 μm.

12. An electron microscope system, comprising: Electron beam source; electron beam focusing optics configured to focus the electron beam on a surface of the sample; a sample translation stage configured to translate the sample in a plane orthogonal to the electron beam and to change a tilt angle of the surface of the sample relative to an axis of the electron beam; and a control unit in communication with the sample translation stage and the electron beam focusing optics and configured to perform the following steps: a) focusing the electron beam at a first location on the surface of the sample; b) tilting the surface of the sample to an oblique 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 position 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 of the surface of the sample; e) detecting the electron beam focused on at least the second location on the surface of the sample; as well as Steps b) to e) are repeated at one or more different tilt angles.

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

14. The electron microscope system according to claim 13, wherein the control unit is further configured to: f) measuring a first distance between the first feature and the second feature orthogonally to the electron beam when the sample is tilted at the tilt angle; g) measuring a second distance between the first feature and the second feature orthogonally to the electron beam with the sample tilted at the one or more different tilt angles; and h) calculating a difference in spacings 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. An electron microscope system according to claim 13 or claim 14, wherein the sample translation stage further comprises a plurality of electric motors.

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