Slice alignment based on reconstructed volume

Abstract

Slice alignment based on reconstructed volume. Disclosed herein are apparatuses and methods for aligning a charged particle beam based on a volume reconstruction. An example method includes at least: forming a reconstructed volume of a portion of a sample, the sample including a plurality of structures, and the reconstructed volume including a portion of the plurality of structures; performing a mathematical transformation on each of a plurality of planes of the reconstructed volume over a range of angles; and determining a target orientation of the sample over the range of angles based on the mathematical transformation of each of the plurality of planes, wherein the target orientation aligns the plurality of structures parallel to an optical axis of a charged particle beam.

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to charged particle microscopes, and more particularly to techniques for aligning a sample to an optical axis of a charged particle microscope. BACKGROUND

[0002] In many industries, samples are analyzed using various charged particle microscopes such as transmission electron microscopes (TEMs). However, to view a sample in a TEM, a lamella is formed from the sample, the lamella containing the specific structures / objects that are desired to be imaged in the TEM. Typically, the lamella is a thin film that is at least partially electron transparent and can be 7 nm to 25 nm thick, sometimes even more. At such small dimensions, it is easy for the specific structures / objects of interest to be removed during lamella formation, especially when many of the lamella formation steps are performed manually. While there are some techniques that can address this issue, many of the techniques still lack overall satisfaction and require highly skilled operators to perform or monitor them. Therefore, there is a need for better techniques to align structures within a lamella to ensure that the structures are not removed during lamella formation. SUMMARY

[0003] Disclosed herein are apparatuses and methods for aligning a lamella to a charged particle beam based on volume reconstruction. An example method includes at least: forming a reconstructed volume of a portion of a sample, the sample including a plurality of structures, and the reconstructed volume including a portion of the plurality of structures; performing a mathematical transformation on each of a plurality of planes of the reconstructed volume over a range of angles; and determining a target orientation of the sample over the range of angles based on the mathematical transformation of each of the plurality of planes, wherein the target orientation aligns the plurality of structures parallel to an optical axis of a charged particle beam.

[0004] An example apparatus includes at least: a focused ion beam column coupled to provide an ion beam along an optical axis; an electron beam column coupled to provide an electron beam; and a controller coupled to or including a non-transitory memory, the non-transitory memory including code. When the code is executed by the controller, the controller causes the apparatus to perform operations of: forming a reconstructed volume of a portion of a sample using a combination of the ion beam and the electron beam, the sample including a plurality of structures, and the reconstructed volume including a portion of the plurality of structures; performing a mathematical transformation on each of a plurality of planes of the reconstructed volume over a range of angles; and determining a target orientation of the sample over the range of angles based on the mathematical transformation of each of the plurality of planes, wherein the target orientation aligns the plurality of structures parallel to an optical axis of a charged particle beam. BRIEF DESCRIPTION OF DRAWINGS

[0005] Figure 1is an example dual-beam system for determining an orientation of a sample and adjusting the orientation according to embodiments of the present disclosure;

[0006] Figure 2 is an example sample processing workflow according to embodiments of the present disclosure;

[0007] Figure 3A is an example image series according to embodiments of the present disclosure;

[0008] Figure 3B is an example reconstructed volume according to embodiments of the present disclosure;

[0009] Figure 3C shows an example plane or cross-section of a reconstructed volume 303 according to embodiments of the present disclosure;

[0010] Figure 4A is a representative plane and associated integral transform 409A according to embodiments of the present disclosure;

[0011] Figure 4B is a representative plane and associated integral transform 409B according to embodiments of the present disclosure;

[0012] Figure 5 is a representative plot of a statistical characterization of a plurality of integral transforms according to embodiments of the present disclosure;

[0013] Figure 6 is an example method for determining an optimal orientation of a sample according to embodiments of the present disclosure; and

[0014] Figure 7 is an example functional block diagram according to embodiments of the present disclosure.

[0015] Throughout the drawings, like reference numerals will be used to refer to like or corresponding parts throughout the several views of the drawings. DETAILED DESCRIPTION

[0016] Embodiments of the present invention are described below in the context of a charged particle beam system that implements a technique to determine an optimal orientation of a sample for lamella formation. For example, a slice-and-view method is used in a dual-beam system to remove a portion of a sample to form a reconstructed volume that provides planes for radon transforms over a range of angles. The radon transforms over the range of angles are then statistically analyzed to determine an optimal orientation of the sample relative to an axis of a focused ion beam of the dual-beam system. It should be appreciated, however, that the techniques described herein are generally applicable to a wide range of different sample orientation methods and apparatuses.

[0017] As used in this application and in the claims, the singular forms “a,” “an,” and “the” include the plural forms unless the context clearly dictates otherwise. Additionally, the term “include” means “comprise.” Further, the term “coupled” does not exclude the presence of intermediate elements between the coupled items.

[0018] The systems, devices, and methods described herein should not be construed as limiting in any way. Indeed, the present disclosure seeks to cover all novel and non-obvious features and aspects of the various disclosed embodiments alone or in various combinations and sub-combinations thereof. The disclosed systems, methods, and devices are not limited to any specific aspect or feature or combination of aspects and features, nor do the disclosed systems, methods, and devices require that any one or more specific advantages be present or problems be solved.

[0019] Although the operations of some of the disclosed methods are described in a particular, sequential order for convenient presentation, it should be understood that unless specifically stated otherwise, this description is not intended to limit the described implementations to any particular order. For example, in some cases, the operations described can be performed in an order different than the order described. Further, some of the described operations can be performed in parallel or concurrently. In addition, for simplicity of explanation, the illustrations can not show the various ways in which the disclosed systems, methods, and devices can be used. Additionally, the description sometimes uses terms like “produce” and “provide” to describe the disclosed methods. These terms are high-level abstractions of the actual operations that are performed. The actual operations that correspond to these terms will vary depending on the particular implementation and are readily discernible by one of ordinary skill in the art.

[0020] In some instances, a value, program, or device is referred to as “lowest,” “best,” “smallest,” etc. It should be appreciated that such descriptions are intended to indicate that a choice can be made among many used functional alternatives, and that such choice need not be better, smaller, or more preferred than other choices.

[0021] In many industries where micron or nanometer sized objects need to be analyzed, such as the semiconductor industry, charged particle microscopes are used to view and analyze such objects. The images acquired are used for yield improvement or process control, for example, in the semiconductor industry. In many, if not all, cases, the object is buried in a larger assembly, such as a field effect transistor (FET) formed within a silicon wafer. If it is desired to image one or more adjacent FETs with a charged particle microscope, such as a transmission electron microscope (TEM), scanning TEM (STEM), or related technique, a lamella is formed and removed from the wafer that will contain the structure forming the FET, which is typically done using a dual beam (DB) system, which is a combination of a scanning electron microscope (SEM) and a focused ion beam (FIB). This process has become routine in many industries, not just the semiconductor industry, and is used to image and analyze almost any type of micron or nanometer scale structure buried in a surrounding substrate.

[0022] While this process has been used in the industry for some years now, the size of the devices, such as FETs and other connected circuitry, is continually shrinking and their spacing makes the formation of the lamella more error prone. For example, if the sample is not aligned or oriented with the FIB optical axis during lamella formation, the structure needed for imaging can inadvertently be removed from the lamella, for example, ground away. For a 2 nm device within a 7 nm lamella, it is critical to maintain the needed orientation because it is very easy for the loss of the needed structure to occur. This is so because a lamella of such small thickness is too easily deformed, and the deformation affects the positioning of the needed structure within the lamella relative to the surface of the lamella. To ensure that the needed device is within the lamella, and more importantly, aligned with the optical axis of the FIB column, the conventional approach is to manually inspect images during the thinning of the lamella and move, for example, re-orient, the lamella when the structure is deemed not to be in the proper position. Such movement of the lamella can include rotation, tilt, lateral shift, and combinations thereof. While a highly skilled operator can be able to perform such analysis and operations, such re-orientation is time consuming and still prone to error. Therefore, there is a need for a more automated technique for the alignment of the structure with the FIB column optical axis.

[0023] One solution includes virtually orienting one or more planes / slices of the reconstructed volume of a portion of the sample over a range of different orientations and analyzing the data to determine the optimal position of the lamella, ensuring that the device structure is parallel to the FIB column optical axis. Different orientations can include rotation of the sample about the FIB optical axis, tilting of the sample in the FIB optical axis plane, or a combination thereof. While it is also possible for the sample to be translated in the X, Y, and Z coordinates, other techniques can address this misalignment issue. Virtual orientation of the reconstructed volume or at least several planes within the reconstructed volume includes performing an integral transform, such as a radon transform, to project each plane at a plurality of different angles. Each projection can also be a one-dimensional function / projection of that plane, and each projection can be statistically analyzed for variation in amplitude, such as by using a standard deviation or variance. The data can then be analyzed at each projection and each angle to determine a maximum, which can determine the optimal angle to orient the lamella. The optimal angle information can then be used to automatically re-orient the lamella for further processing.

[0024] Figure 1 is an example dual-beam system 100 for determining an orientation of a sample and adjusting the orientation according to embodiments of the present disclosure. The system 100 can be used to implement the sample orientation techniques discussed herein. In some embodiments, the system 100 will perform sample milling, orientation algorithms, and sample orientation. However, in other embodiments, the orientation algorithms can be performed by a computing system coupled to the system 100, such as at a user’s desk or a cloud-based computing system. In either embodiment, the determination of the optimal orientation can be provided to the system 100 for automatic sample re-orientation to ensure that structures within the sample are parallel to the FIB optical axis. Although examples of suitable hardware are provided below, the present invention is not limited to implementation in any particular type of hardware.

[0025] The SEM 141, along with the power supply and control unit 145, are provided to the dual-beam system 100. The electron beam 143 is emitted from the cathode 152 by applying a voltage between the cathode 152 and the anode 154. The electron beam 143 is focused into a fine point by the condenser lens 156 and the objective lens 158. The electron beam 143 is scanned two-dimensionally over the sample by the deflector 160. The operation of the condenser lens 156, the objective lens 158, and the deflector 160 are controlled by the power supply and control unit 145.

[0026] An electron beam 143 can be focused onto a substrate 122 positioned on a stage 125 within a lower chamber 126. The substrate 122 can be positioned on a surface of the stage 125 or on a TEM sample holder 124 extending from the surface of the stage 125. Secondary electrons are emitted when electrons in the electron beam strike the substrate 122. These secondary electrons are detected by a secondary electron detector 140. In some embodiments, a STEM detector 162 positioned below the TEM sample holder 124 and the stage 125 collects electrons transmitted through a sample mounted on the TEM sample holder.

[0027] The system 100 also includes a FIB system 111 including a vacuum chamber having an ion column 112 within which an ion source 114 and focusing assembly 116 are positioned, the focusing assembly including an extractor electrode and electrostatic optics. The axis of the focusing column 116 can be tilted, for example, 52 degrees from the axis of the electron column 141. The ion column 112 includes an ion source 114, an extraction electrode 115, focusing elements 117, deflection elements 120, which operate in unison to form a focused ion beam 118. The focused ion beam 118 travels from the ion source 114 through the focusing assembly 116 and between electrostatic deflection devices, indicated schematically at 120, toward a substrate 122, which can include, for example, a semiconductor wafer positioned on a moveable stage 125 within a lower chamber 126. In some embodiments, a sample can be positioned on a TEM grid holder 124, where the sample can be a thick piece extracted from the substrate 122. The thick piece can then be further processed with the FIB to form a final lamella having a desired thickness in accordance with the techniques disclosed herein.

[0028] The stage 125 can be moved in the horizontal plane (X and Y axes) and the vertical plane (Z axis). The stage 125 can also be tilted and rotated about the Z axis. In some embodiments, a separate TEM sample table 124 can be used. Such a TEM sample table would also preferably be movable in the X, Y, and Z axes, as well as tiltable and rotatable. In some embodiments, the tilt of the stage 125 / TEM holder 124 can be in and out of the plane of the ion beam 118, and the rotation of the stage about the ion beam 118. As used herein to illustrate the disclosed techniques, this relationship will be maintained when discussing the rotation and tilt of the sample. Of course, the opposite definitions can be used, but would still fall within the scope of the present disclosure.

[0029] The door 161 is opened to insert the substrate 122 onto the stage 125. Depending on the tilt of the stage 124 / 125, the Z axis will be in the direction of the optical axis of the relevant column. For example, during the data collection phase of the disclosed techniques, the Z axis will be in the direction parallel to the FIB optical axis, indicated by the ion beam 118, for example. In such a coordinate system, the X and Y axes will be referenced to the Z axis. For example, the X axis can be in the direction of the optical axis of the electron beam 143, and the Y axis can be in the direction of the optical axis of the STEM detector 162. Figure 1The X-axis will be out of the page, the Y-axis will be in the page, while all three axes maintain their property of being perpendicular to each other.

[0030] A turbo-molecular and mechanical pumping system 130 is used to evacuate the chamber 126 under the control of a vacuum controller 132. The vacuum system provides a vacuum of between about 1 x 10"7Torr and 5 x 10"4Torr within the chamber 126. If an etch assist, etch delay gas, or deposition precursor gas is used, the chamber background pressure can rise, typically to about 1 x 10"5Torr.

[0031] A high voltage power supply provides the appropriate accelerating voltage to the electrodes in the focusing column 116 for energizing and focusing the ion beam 118. As it strikes the substrate 122, material is sputtered, i.e., physically ejected from the sample. Alternatively, the ion beam 118 can dissociate a precursor gas to deposit material.

[0032] A high voltage power supply 134 is connected to the ion source 114 and to the appropriate electrodes in the ion beam focusing assembly 116 for forming and directing the ion beam 118 toward the sample at about 1 keV to 60 keV. A deflection controller and amplifier 136, operated according to a prescribed pattern provided by a pattern generator 138, is coupled to the deflection plates 120, whereby the ion beam 118 can be manually or automatically controlled to trace a corresponding pattern on the upper surface of the substrate 122. In some systems, the deflection plates are placed before the final lens, as is well known in the art. A beam blanking electrode (not shown) within the ion beam focusing column 116 causes the ion beam 118 to impinge on a blanking aperture (not shown) instead of the substrate 122 when a blanking controller (not shown) applies a blanking voltage to the blanking electrode.

[0033] The ion source 114 provides the ion beam, typically based on the type of ion source. In some embodiments, the ion source 114 is a liquid metal ion source, for example, which can provide a gallium ion beam. In other embodiments, the ion source 114 can be a plasma type ion source, which can deliver a variety of different ion species, such as oxygen, xenon, and nitrogen, to name a few. The ion source 114 is typically capable of focusing to a beam of sub-tenth micron width at the substrate 122 or TEM grid holder 124 for the purpose of modifying the substrate 122 by ion milling, ion-induced etching, material deposition, or for the purpose of imaging the substrate 122.

[0034] A charged particle detector 140, such as an Everhart Thornley or multi-channel plate, is connected to a video circuit 142 that provides drive signals to a video monitor 144 and receives deflection signals from the system controller 119. The location of the charged particle detector 140 within the lower chamber 126 can vary in different embodiments. For example, the charged particle detector 140 can be coaxial with the ion beam and contain a hole for allowing the ion beam to pass through. In other embodiments, secondary particles can be collected through a final lens and then deflected off axis for collection.

[0035] A micro manipulator 147 can precisely move objects within the vacuum chamber. The micro manipulator 147 can include a precision motor 148 positioned outside the vacuum chamber to provide X, Y, Z, and theta control of a portion 149 positioned within the vacuum chamber. The micro manipulator 147 can be fitted with different end effectors for manipulating small objects. In the embodiments described herein, the end effector is a fine probe 150.

[0036] A gas delivery system 146 extends into the lower chamber 126 for introducing and directing gaseous vapors to the substrate 122. For example, iodine can be delivered to enhance etching, or metal organic compounds can be delivered to deposit metals.

[0037] The system controller 119 controls the operation of the various parts of the dual beam system 110. Through the system controller 119, a user can scan the ion beam 118 or electron beam 143 (not shown) in a desired manner through commands entered into a conventional user interface. Alternatively, the system controller 119 can control the dual beam system 110 according to programmed instructions stored in memory 121. In some embodiments, the dual beam system 110 incorporates image recognition software to automatically identify regions of interest, and then the system can manually or automatically extract samples according to the present invention. For example, the system can automatically locate similar features on a semiconductor wafer containing multiple devices, and sample these features on different (or the same) devices.

[0038] In operation according to the techniques disclosed herein, the system 100 images a working surface of a sample 122 that is a thick piece that was previously removed from a substrate. In this example, a thick piece that can be about 1 micron in thickness can be attached to a TEM holder 124. As used herein, the working surface is a side surface of the thick piece that needs to be thinned to a final lamella thickness. The sample 122 can contain structures that should be aligned / oriented with the ion beam 118, such as in terms of rotation and / or tilt, so that during final lamella formation, structures that need to be imaged later are not removed. An image of the newly exposed surface can be acquired using the electron column 141 or the FIB 111.

[0039] After image acquisition, a layer of sample 122 is removed from the work surface. Layer or slice removal can be performed using FIB milling or ion-induced etching using a gas precursor. The thickness of the layer removed can be, for example, 2 to 5 nanometers. After the slice is removed, the newly exposed surface is imaged. The process of image acquisition and slice removal can be repeated 25, 50, 75, or 100 times, although any other number of slices is contemplated herein. Typically, a small portion of sample 122 (e.g., a small volume of thick block) is removed that contains 2 lines or more of structure (such as a FET), which allows for analysis of the orientation of the structure relative to ion beam 118. This process can be referred to by those skilled in the art as slice and view, and can be used to acquire data to reconstruct a 3D volume of sample 122.

[0040] The 3D reconstructed volume can then be used as a basis for determining an optimal orientation (e.g., rotation and tilt) of sample 122 to ensure that the buried structure is parallel to ion beam 118. In terms of coordinates, the Z direction of the reconstructed volume is in the direction of the removed slices, and the X and Y directions are in the plane of these slices. To determine the optimal orientation, a plurality of planes in the XZ or YZ plane of the reconstructed volume are subjected to an integral transform, such as a radon transform, to aid in the orientation determination. For example, each plane is virtually rotated to a plurality of different angles within a range about the current orientation of sample 122, such as -1.5° to +1.5°, and a corresponding transform is obtained at each angle. Alternatively, each of the plurality of planes is mathematically transformed at different angles within an angle range. Of course, a single plane can be extracted from the volume and mathematically transformed at different angles, but the statistical correlation of this data can not be as sufficient.

[0041] Each transform can then be statistically characterized. For example, a standard deviation or variance can be computed for each transform. Subsequently, the statistical data of each transform can then be evaluated to determine the optimal orientation. For example, the maximum standard deviation value or interpolation based on a correlation plot can indicate the optimal orientation, e.g., rotation and / or tilt, of sample 122 to ensure that the buried structure is aligned as desired. The optimal orientation can then be relayed back to control system 119, for example, so that platform 125 is automatically reoriented based on the analysis.

[0042] Figure 2 is an example sample processing workflow 201 according to embodiments of the present disclosure. Workflow 201 illustrates a sample milling and imaging technique that can also be referred to as slice and view. In the disclosed technique, slice and view is used to obtain data about a sample to inform a desired orientation relative to a work charged particle beam, such as an ion beam. Workflow 201 can be performed by a dual beam charged particle microscope, such as system 100 for example, and is more directed to data collection aspects of the disclosed technique. Analysis aspects will be discussed in more detail below.

[0043] Workflow 201 is performed on a sample 222, which is an instance of sample 122, and can be mounted on a platform, such as platform 125, or on a TEM grid holder, TEM grid holder 124. Regardless of the mounting configuration, sample 222 can be a larger sample in its entirety, such as a patterned wafer or packaged IC, and contain a region of interest (ROI) 270. ROI 270 can contain one or more lines or rows of structures, such as FET structures, that are desired to be analyzed by subsequent imaging techniques, such as TEM or STEM. Imaging such structures can require that they be extracted from sample 222 in the form of a lamella. However, to extract such structures, sample 222 is processed to form a lamella that contains primarily ROI 270, which involves removing a volume of sample 222 surrounding ROI 270 in the Z direction. In some instances, the thickness of sample 222 in the Z direction in this instance can be about 1 micron, but a lamella of 7 to 25 nanometers in thickness is required for TEM / STEM analysis. Thus, a volume of sample 222 surrounding ROI 270 in the Z direction needs to be removed. However, if sample 222 (or more importantly, the structures within sample 222) is not aligned parallel to the working charged particle beam (in this instance, ion beam 218=), the structures that need to be imaged can be removed during the lamella formation process. Thus, the disclosed orientation techniques acquire data about the orientation of the structures at an early stage of the lamella formation, which allows for adjustments to the orientation of the structures relative to ion beam 218 to limit or prevent removal of such desired structures.

[0044] To this end, workflow 201 uses ion beam 218 to remove material from sample 222 and images newly exposed surface 272 with electron beam 243. After each slice of sample 222 is removed, a newly exposed surface 272 is formed. For example, ion beam 218 removes a slice 274A that exposes a new surface 272. The removal of slice 274A and subsequent slices can be performed by milling away the slice using ion beam 218, or it can be removed using ion beam-induced etching by discharging a gas precursor to surface 272 and then etching away the slice through interaction with ion beam 218. The thickness of each slice can be on the order of 2 to 5 nanometers, but the size of the structures within sample 222 can determine the required slice thickness. For example, smaller structures can require thinner slices, while larger structures can tolerate thicker slices. As the workflow progresses, slice 274B is removed, and then an image of newly exposed surface 272 is acquired. This two-step process can then be repeated to remove slices 247C and 274D.

[0045] The workflow 201 can remove only or use a relatively small volume of the sample 222 to determine the orientation of the structure and how to adjust the orientation so that the structure is parallel to the ion beam 218. For example, 50 to 100 nanometers of material can be removed from the sample 222 to perform the analysis disclosed herein. Generally, the thickness of the sample 222 required by the disclosed technology can depend on the number of lines / structures removed and whether the amount of data resulting is sufficient for the analysis. For example, a three-line structure can be sufficient to implement the disclosed technology. The re-orientation can include rotation about the y-axis, tiling about the x-axis, and / or translation in any direction.

[0046] Figure 3A is an example image series 301 according to embodiments of the present disclosure. The image series 301 shows four images, but this number is for illustration only and the actual number of images can be similar or greater, such as 50 to 100. The images 301 can be acquired by the system 100, such as by implementing the workflow 201. Figure 3B is an example reconstructed volume 303 according to embodiments of the present disclosure. The reconstructed volume 303 is formed from the image series 301, which are representative of structures in a sample, such as the sample 222, and at least how the structures were oriented relative to the ion beam at the time the data was collected.

[0047] Figure 3C are example planes or cross-sections 305 and 307 of the reconstructed volume 303 according to embodiments of the present disclosure. The plane 305 is a cross-section in the XZ plane, see the orientation axes below the reconstructed volume 303, and the plane 307 is a cross-section in the YZ plane. For example, the disclosed technology uses multiple planes from the XZ plane to determine a reasonable orientation about the ion beam axis, and / or for example, the technology uses multiple planes from the YZ plane to determine a tilted orientation in and out of the ion beam axis.

[0048] Figure 4A is a representative plane 405A and associated integral transform 409A according to embodiments of the present disclosure. The plane 405A illustrates an XZ plane of a volume reconstruction, such as the reconstruction 303. The plane 405A is an illustration of such a plane in a non-ideal orientation. For example, the structures shown in the plane 405A are angled slightly downward in the image. Thus, for example, the integral transform 409A obtained using a Radon transform shows a blurred image. While the integral transform 409A is represented with a 2D image, one skilled in the art will appreciate that the integral transform will result in a vector. The 2D image is for illustration only. The blurriness of the integral transform 409A indicates that the orientation of the plane 405A is not as desired. Thus, a different rotational or tilted orientation is needed.

[0049] Figure 4Bis a representative plane 405B and associated integral transform 409B according to embodiments of the present disclosure. Plane 405B illustrates the XZ plane that is the same as the volume reconstruction in 405A but in an ideal orientation. This is at least visually shown in integral transform 409B as indicated by the relative clarity of the individual fringes in 409B. Thus, the angle associated with integral transform 409B can indicate or be very close to the optimal orientation of the sample represented by the image.

[0050] Figure 5 is a representative plot 501 of a statistical characterization of a plurality of integral transforms according to embodiments of the present disclosure. Plot 501 shows the score for each of a plurality of integral transforms (such as transforms 409A, B) over a range of angles. For example, with reference to the initial position of the sample, the range of angles is -1.5° to +1.5°. Of course, other ranges of angles can be used and the values shown in plot 501 are for illustrative purposes only. As noted, the integral transforms can produce a range of vectors that can be obtained, for example, using a Radon transform. The statistical characterization of each integral transform can be assigned as the score indicated in plot 501. The total score can then be evaluated for a maximum value, as shown in the plot, or a minimum value, the associated value indicating the optimal orientation. For example, plot 501 shows the maximum score interpolated from the data points (e.g., points) to be approximately -0.15°. It should be noted that it is not necessary to plot the data shown in plot 501 and the same analysis can be implemented without using a visual representation of the data. Plot 501 is included for illustrative purposes.

[0051] As noted above, the statistical characterization can be performed by calculating the standard deviation of each integral transform or by calculating the variance thereof. In general, any statistical characterization can be used to qualitatively distinguish each integral transform in a manner that indicates how fuzzy / clear each integral transform is.

[0052] Figure 6 is an example method 601 for determining an optimal orientation of a sample according to embodiments of the present disclosure. Method 600 can be performed using a dual beam charged particle microscope (such as, for example, DB system 100). Method 601 can begin at process block 603, which includes forming a reconstructed volume of a portion of a sample, the sample including a plurality of structures, and the reconstructed volume including a portion of the plurality of structures. In some embodiments, for example, the reconstructed volume can be obtained using the slicing and viewing process outlined in workflow 201. The process includes removing a relatively thin volume from the sample so that an integral transform and statistical analysis can be performed. In general, only enough of the sample needs to be removed to perform the disclosed techniques, but the removal should not result in removal of structures that need to remain in the target slice.

[0053] Process block 303 can be followed by process block 305, which includes performing a mathematical transform on each of a plurality of planes of the reconstructed volume over a range of angles. The transform can be a radon transform using a plurality of different angles over a range of angles, with the range of angles centered on a current orientation of the sample relative to the ion beam (e.g., ion beam 118). In some embodiments, each of the plurality of planes is subjected to the transform at each of the plurality of angles over the range of angles. In other embodiments, each of the plurality of planes is subjected to one of the plurality of angles. In either embodiment, the end result is a plurality of transforms at each of the angles over the range of angles, which provides data over the range of angles.

[0054] Process block 305 can be followed by process block 307, which includes determining, based on the mathematical transform on each of the plurality of planes, a target orientation of the sample over the range of angles, where the target orientation has the plurality of structures aligned parallel to an optical axis of the charged particle beam. The determination of the target orientation includes performing a statistical analysis on the plurality of transforms to determine a best orientation. For example, a standard deviation can be determined for each transform, and the resulting set of standard deviation data can be analyzed, as shown in plot 501, to determine a maximum standard deviation. This maximum can be indicative of the best orientation. The maximum standard deviation can be indicative of the best orientation because the transform closest to the best orientation will have the clearest image / data resulting in the maximum standard deviation. Alternatively, a plot of all of the statistical data can be formed and an interpolation performed to identify a best angle, which can be between the angles used for the transforms. In some embodiments, a variance is calculated instead of a standard deviation, but the end analysis should be the same.

[0055] Once the best orientation is determined, which can be a rotation, tilt, or combination thereof, the best orientation is provided by a controller (e.g., controller 119) such that the sample is automatically moved to the best orientation.

[0056] Figure 7 is an example functional block diagram 700 according to embodiments of the present disclosure. Figure 7 is a block diagram showing a computer system 700 that can be used to implement embodiments of the present disclosure. For example, the computing system 700 can be an instance of the computing hardware included in the system 100 and / or EM 200, such as the controller 30 / 230, and it can incorporate the memory 32 and be coupled to the display 31 and user input device 33. The computer system 700 includes at least a hardware processor, such as core 730 for processing information, which can be coupled to a communication bus. The computing system 700 can be used to implement the methods and techniques disclosed herein, such as the method 301, and can also be used to obtain images based on synchronization of a sample scan with a pulse period of a pulsed electron beam.

[0057] The computer system 700 also includes a main memory 732, such as a random access memory (RAM) or other dynamic storage device, coupled to bus 710 for storing information and instructions to be executed by processor core 730. Main memory 732 also can be used for storing temporary variables or other intermediate information during execution of instructions to be executed by processor core 730. Such instructions can be stored in non-transitory storage medium accessible to processor core 730, when the instructions are stored in a non-transitory storage medium accessible to processor core 730, the instructions cause the computer system 700 to be an special purpose machine uniquely programmed by the instructions to perform the operations specified in the instructions. The main memory 732 can be the memory 32 or separate from the memory 32.

[0058] The computer system 700 further includes a read only memory (ROM) 734 or other static storage device coupled to the bus 710 for storing static information and instructions for the processor core 730. A storage device 736, such as a magnetic disk or optical disk, is provided and coupled to the bus 710 for storing information and instructions.

[0059] A display, such as the display 31, is coupled to bus 710 via an interface, such as a video adapter, for displaying information to a computer user. An input device 33, including alphanumeric and other keys, is coupled to bus 710 for communicating information and command selections to the processor core 730. Another type of user input device is a cursor control 35, such as a mouse, a trackball, or cursor direction keys, for communicating direction information and command selections to processor core 730 and for controlling cursor movement on the display. This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), that allows the device to specify positions in a plane.

[0060] The computer system 700 can implement the techniques described herein using customized hard-wired logic, one or more ASICs or FPGAs, firmware and / or program logic which in combination with the computer system causes or programs computer system 700 to be a special-purpose machine. According to one embodiment, the techniques herein are performed by computer system 700 in response to processor core 730 executing one or more sequences of instructions contained in main memory 732. Such instructions can be read into main memory 732 from another storage medium, such as storage device 736. Execution of the sequences of instructions contained in main memory 732 causes processor core 730 to perform the process steps described herein. In alternative embodiments, hard-wired circuitry can be used in place of or in combination with software instructions.

[0061] As used herein, the term "storage medium” refers to any non-transitory medium that stores data and / or instructions that cause a machine to operate in a specific fashion. Such storage media can comprise non-volatile media and / or volatile media. Non-volatile media includes, for example, optical or magnetic disks, such as storage device 736. Volatile media includes dynamic memory, such as main memory 732. Common forms of storage media include, for example, a floppy disk, a flexible disk, hard disk, solid-state drive, magnetic tape, or any other magnetic data storage medium, a CD-ROM, any other optical data storage medium, any physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, NVRAM, any other memory chip or cartridge, content-addressable memory (CAM), and ternary content-addressable memory (TCAM).

[0062] Storage media are tangible and non-transitory. Storage media do not include a modulated data signal or carrier wave. Storage media does not include a signal per se. Storage media does not include a signal per se. Rather, storage media includes a physical medium that stores data and / or instructions that cause a machine to operate in a specific fashion. However, storage media can be used in combination with transmission media to facilitate the transfer of data and / or instructions. Transmission media can be used in combination with storage media to facilitate the transfer of data and / or instructions. Transmission media can be used in combination with storage media to facilitate the transfer of data and / or instructions. Transmission media can include coaxial cables, copper wires, and fiber optic cables, including wires that form bus 640. Transmission media can also take the form of acoustic or light waves, such as those generated during radio frequency and infrared data communications.

[0063] Various forms of media can be involved in carrying one or more sequences of one or more instructions to the processor 730 for execution. For example, the instructions can initially be carried on a magnetic disk or solid state drive of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a network.

[0064] Computer system 700 also includes a communication interface 738 coupled to bus. Communication interface 738 provides a two-way data communication coupling to a network link that is connected to a local network. For example, communication interface 738 can be an integrated services digital network (ISDN) card, cable modem, satellite modem, or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, communication interface 738 can be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links can also be implemented. In any such implementation, communication interface 738 sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.

[0065] Computer system 700 can send messages and receive data, including program code, through the network(s), network link(s), and communication interface(s) 738. In the Internet example, a server might transmit a requested code for an application program through the Internet 666, ISP, local network and / or communication interface 738.

[0066] The received code can be executed by processor(s) 730 as it is received, and / or stored in storage device 736, or other non-volatile storage for later execution.

[0067] The embodiments discussed herein for illustrating the disclosed technology should not be considered to be limiting, but merely provide examples of implementations. Those skilled in the art will understand that there are numerous ways of implementing the disclosed technology, which are contemplated herein and within the scope of the present disclosure.

Claims

1. A method comprising: forming a reconstructed volume of a portion of a sample, the sample comprising a plurality of structures, and the reconstructed volume comprising a portion of the plurality of structures; performing a mathematical transform on each of a plurality of planes of the reconstructed volume over a range of angles; and determining a target orientation of the sample over the range of angles based on the mathematical transform of each of the plurality of planes, wherein the target orientation aligns the plurality of structures parallel to an optical axis of a charged particle beam.

2. The method of claim 1, wherein performing a mathematical transform on each of a plurality of planes over a range of angles comprises: performing a mathematical transform on each of the plurality of planes at a plurality of angles of the range of angles for each plane.

3. The method of claim 1, wherein performing a mathematical transform on each of a plurality of planes over a range of angles comprises: performing a mathematical transform on each of the plurality of planes at different angles of the range of angles for each plane.

4. The method of claim 1, wherein performing a mathematical transform on each of a plurality of planes over a range of angles comprises: performing a radon transform on each of the plurality of planes over the range of angles.

5. The method of claim 4, wherein performing a radon transform on each of a plurality of planes over the range of angles comprises: performing the radon transform on each of the plurality of planes at a plurality of angles of the range of angles for each plane.

6. The method of claim 1, further comprising: performing a statistical characterization of each mathematical transform on each of the plurality of planes, wherein forming a range of statistical characterization data over the range of angles.

7. The method of claim 6, further comprising: analyzing a maximum of the range of statistical data, wherein the maximum indicates the target orientation.

8. The method of claim 6, wherein the statistical characterization comprises a standard deviation.

9. The method of claim 6, wherein the statistical characterization comprises a variance.

10. The method of claim 1, wherein forming a reconstructed volume of a portion of a sample, the reconstructed volume comprising a plurality of structures, comprises: acquiring a surface image of the sample; removing a slice of the sample; acquiring an image of a new exposed face of the sample, the new exposed face exposed from the removal of the slice; and repeating the image acquisition and slice removal steps a plurality of times.

11. An apparatus comprising: a focused ion beam column coupled to provide an ion beam along an optical axis; an electron beam column coupled to provide an electron beam; and a controller coupled to or comprising a non-transitory memory, the non-transitory memory comprising code that, when executed by the controller, causes the apparatus to: form a reconstructed volume of a portion of a sample using a combination of the ion beam and the electron beam, the sample comprising a plurality of structures, and the reconstructed volume comprising a portion of the plurality of structures; performing a mathematical transform on each of a plurality of planes of the reconstructed volume over a range of angles; and determining a target orientation of the sample over the range of angles based on the mathematical transform of each of the plurality of planes, wherein the target orientation aligns the plurality of structures parallel to an optical axis of a charged particle beam.

12. The apparatus of claim 11, wherein the code that causes the apparatus to perform a mathematical transform on each of a plurality of planes over a range of angles further comprises code that, when executed by the controller, causes the apparatus to: perform a mathematical transform on each of the plurality of planes at a plurality of angles of the range of angles for each plane.

13. The apparatus of claim 11, wherein the code that causes the apparatus to perform a mathematical transform on each of a plurality of planes over a range of angles further comprises code that, when executed by the controller, causes the apparatus to: perform a mathematical transform on each of the plurality of planes at a different angle of the range of angles for each plane.

14. The apparatus of claim 11, wherein the code that causes the apparatus to perform a mathematical transform on each of a plurality of planes over a range of angles further comprises code that, when executed by the controller, causes the apparatus to: perform a radon transform on each of the plurality of planes over the range of angles.

15. The apparatus of claim 14, wherein the code that causes the apparatus to perform a radon transform on each of a plurality of planes over the range of angles further comprises code that, when executed by the controller, causes the apparatus to: perform the radon transform on each of the plurality of planes at a plurality of angles of the range of angles for each plane.

16. The apparatus of claim 11, wherein the non-transitory memory comprises code that, when executed by the controller, causes the apparatus to: perform a statistical characterization of each mathematical transform on each of the plurality of planes, wherein form a range of statistical characterization data over the range of angles.

17. The apparatus of claim 16, wherein the code that causes the apparatus to perform a statistical characterization of each mathematical transform on each of the plurality of planes further comprises code that, when executed by the controller, causes the apparatus to: analyze a maximum of the range of statistical data, wherein the maximum is indicative of the target orientation.

18. The apparatus of claim 16, wherein the statistical characterization comprises a standard deviation.

19. The apparatus of claim 16, wherein the statistical characterization comprises a variance.

20. The apparatus of claim 11, wherein the non-transitory memory comprises code that, when executed by the controller, causes the apparatus to: acquire a surface image of the sample; remove a slice of the sample; acquiring an image of a newly exposed surface of the sample, the newly exposed surface being exposed from the section removal; and repeating the image acquisition and section removal steps multiple times.

Images