Adaptive slice depth in slice and view workflow

Abstract

To provide methods for providing adaptive milling in order to produce a plurality of sectional surfaces which can be imaged to produce a 3D image of a sample.SOLUTION: Milling depth is selected based on sample dimensions to increase the rate at which sample images are acquired. A cut-face height and an associated focused ion beam dose are selected based on an image of a previously acquired sectional surface. Edges in the image can be identified such as those corresponding to a sample mount or a coating applied to the sample and used to establish a CPB dose. Cut-face height can be based on a single or multiple prior sectional surface images.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to adaptive focused ion beam specimen slicing. [Background technology]

[0002] In many applications in materials and life sciences, a series of two-dimensional images of a sample of interest are obtained and these images are combined to generate a three-dimensional image. The series of images may be obtained with an SEM by milling the sample and then imaging the milled surface. The milling / imaging sequence may be repeated as may be desirable to generate enough two-dimensional images to generate a satisfactory three-dimensional image. While this approach allows for the construction of a three-dimensional image, obtaining multiple images in this manner may require lengthy processing times and extensive technician input. In a typical embodiment, 500-1000 two-dimensional images are required, and the milling time for each may be significant. Alternative approaches are needed that can reduce either or both the total time and technician time. Summary of the Invention

[0003] The milling depth is selected based on the sample dimensions to increase the rate at which sample images are acquired. The cut plane height and associated focused ion beam dose are selected based on a previously exposed cross-sectional image. Edges in the image, such as edges corresponding to the sample mount or a coating applied to the sample, can be identified and used to establish the charged-particle beam (CPB) dose for the subsequent milling operation. The dose can be based on a single or multiple previous cross-sectional images.

[0004] The foregoing and other features and advantages of the techniques will become more apparent from the following detailed description, which begins with reference to the accompanying drawings. [Brief description of the drawings]

[0005] [Figure 1] Illustrates obtaining a cross section of a sample. [Diagram 2] Illustrated is an exemplary method for acquiring cross-sectional images to generate a three-dimensional (3D) image of a sample. [Diagram 3] Illustrated is an exemplary dual beam system configured to generate and image a cross-section of a sample using a charged particle beam (CPB) dose that is adaptively determined based on edge detection in one or more previously acquired cross-sectional images. [Figure 4] 1 illustrates a sample positioned for repetitive ion beam milling using an adaptively determined CPB dose. [Figure 5A] 1 is an image of a representative cross section of a non-flat sample. [Figure 5B] 1 is an image of a representative cross section of a non-flat sample. [Figure 5C] 1 is an image of a representative cross section of a non-flat sample. [Figure 6] 13 is a representative sample image illustrating the variable cut face width and variable cut face height selections. [Figure 7] 1 is an image illustrating the exposure of a cross-section of a sample with a focused ion beam (FIB). [Figure 8] 1 illustrates a cross-section exposed for imaging. [Figure 8A] FIG. 9 is a cross-sectional view of FIG. 8 illustrating a representative cross section. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] A method and apparatus is disclosed that provides adaptive milling to generate multiple cross sections that can be imaged to generate a 3D image of a sample. Based on previously imaged cross sections, milling depths are adaptively selected for use in milling to expose subsequent cross sections.

[0007] General Terms Dose generally refers to the total exposure to an ion beam or other charged particle beam (CPB) used to generate the surface being imaged. Dose typically refers to the product of CPB current and exposure time at a fixed ion beam energy and fixed beam spot size. The effectiveness of a particular dose in milling is a function of the composition of the sample being milled, the product of ion beam current and exposure time (dose), CPB energy, CPB spot size on the sample, CPB composition such as the type of ion or other charged particle, and may be selected accordingly. As used herein, milling dose refers to the dose associated with a selected milling depth in the sample. The selected milling depth is referred to herein as the effective milling depth, i.e., the approximate milling depth associated with the exposure of a particular sample to a particular CPB beam configuration. In an embodiment, the dose is adaptively selected based on specimen dimensions and no variation in dose based on sample composition is used, although dose may be adapted in a similar manner. The milling dose may be applied in multiple passes over the sample area, or the milling dose may be applied in a single exposure. Although the embodiments are described with respect to CPB dose because CPB dose is a parameter that can be controlled by the CPB system, in other embodiments, the CPB system may be configured based on the milling depth that corresponds to the effective dose.

[0008] These examples are generally illustrated using systems (such as in an SEM) where milling is accomplished using an ion beam and imaging is based on exposure of the specimen to an electron beam. However, milling can be accomplished using a laser beam other than an ion beam, such as an electron beam, or a light beam, such as a CPB. Similarly, images can be obtained in other ways based on optical radiation or other CPBs, such as an ion beam. Systems combining SEM imaging and ion beam milling are merely convenient examples.

[0009] In various embodiments, the charged particles in the ion beam can be generated from a liquid metal ion source producing ions such as gallium, a plasma ion source producing ions such as argon, nitrogen, oxygen, or xenon difluoride, or a combination of two or more liquid metal ion and / or plasma ion sources.

[0010] As used herein, a cross section (or slice surface) refers to a surface of a specimen from which an image is obtained. Typically, a series of such surfaces are obtained and imaged to generate a 3D image. In an embodiment, a sample can be milled to reveal a series of cross sections, and the associated images can be processed to generate a three-dimensional image of the specimen. The cross sections can be spaced arbitrarily, with adjacent cross sections spaced 2 nm, 10 nm, 20 nm, 50 nm, 100 nm, 0.5 μm, 1.0 μm, 2 μm, 5 μm, 10 μm, 20 μm, 50 μm, or more apart. The spacing need not be uniform, but it may be convenient to use a common cross section spacing. A cross section referred to as an initial cross section is any cross section used to determine a dose or other exposure parameters for use in exposing one or more additional cross sections. A first and second cross section obtained without exposing any intervening cross sections are referred to as adjacent. A previously exposed surface as used herein may be an adjacent or non-adjacent surface. The dose can be determined based on previously exposed adjacent or non-adjacent sections. The sample height that is or will be exposed by milling is referred to herein as the "cut face height."

[0011] The term image is used to refer to a visual representation of a specimen, as well as a representation of the visual representation as data that can be stored, for example, in JPG, TIFF, BMP, MPEG, or other data format.

[0012] As used herein, a boundary is the outer limit of an object, such as a sample, a coated sample, a sample placed on a sample mount, or a mounted and coated sample. A boundary may be delineated by one or more edge locations ("edges"), by one or more curves and / or straight lines at an edge, or by one or more curves and / or straight lines that completely surround the object. Boundaries are typically located in an image by edge detection or other image processing using a general-purpose or special-purpose processor.

[0013] As used in this application and the claims, the singular forms "a," "an," and "the" include the plural forms unless the content clearly dictates otherwise. Additionally, the term "includes" means "having, comprising." Furthermore, the term "coupled" does not exclude the presence of intermediate elements between the coupled items.

[0014] The systems, devices, and methods described herein should not be construed as limiting in any way. Instead, the present disclosure is directed to all novel and non-obvious features and aspects of the various disclosed embodiments, alone and in various combinations and subcombinations with each other. The disclosed systems, methods, and devices are not limited to any particular aspect or feature or combination thereof, and the disclosed systems, methods, and devices do not require that any one or more particular advantages exist or problems be solved. Any theory of operation is provided for ease of explanation, but the disclosed systems, methods, and devices are not limited to such theory of operation.

[0015] Although some operations of the disclosed methods are described in a particular sequential order for convenient presentation, it should be understood that this style of description encompasses reordering unless a particular ordering is required by specific language described below. For example, operations described in sequence may in some cases be reordered or performed simultaneously. Furthermore, for simplicity, the accompanying drawings may not show the various ways in which the disclosed systems, methods, and apparatuses may be used in conjunction with other systems, methods, and apparatuses. In addition, the description may use terms such as "produce" and "provide" to describe the disclosed methods. These terms are high-level abstractions of actual operations that are performed. The actual operations that correspond to these terms vary depending on the particular implementation and are readily discernible by those of ordinary skill in the art.

[0016] In some embodiments, values, procedures, or devices are referred to as "lowest" or "best" or other similar terms. Such descriptions are intended to indicate that a selection may be made from among many functional alternatives used, but it will be understood that such a selection is not necessarily better than, less than, or otherwise preferred to other selections.

[0017] Examples are described with reference to orientations indicated as "above," "below," "upper," "lower," etc. These terms are used for convenient description only and do not imply a particular spatial orientation.

[0018] Example 1 FIG. 1 illustrates the processing of a sample to expose a cross section for imaging and obtaining an image of the exposed surface to generate a 3D sample reconstruction. With reference to FIG. 1, a sample of interest 102 (hereinafter "sample") is placed on a support member 103, such as a conductive grid, which may be placed on a stub 108 or other specimen holder that may be used to position the sample 102 for charged-particle beam (CPB) processing and imaging. The sample 102 may be attached with conductive paint, conductive tape, clamps, or combinations thereof. The sample 102 is typically provided with a conductive coating 104 to reduce or eliminate charging artifacts in SEM imaging and CPB imaging and processing, such as focused ion beam (FIB) milling. The sample 102 is shown as including one or more representative features of interest 120-122 to be included in the image.

[0019] The sample 102 is positioned on the stub 108 for imaging with a CPB 149 incident along one or more axes that are generally approximately parallel to the Y axis of an XYZ coordinate system 150, the X axis of which extends out of the plane of the drawing. A FIB or other processing beam is applied sequentially along axes 130-133 parallel to the Z axis to remove respective sample sections 102A-102D by FIB milling and expose section surfaces 110-113 for imaging using the CPB 149. The particular angles shown in FIG. 1 are chosen for illustrative purposes, and both the FIB and imaging CPB may be incident at different angles. Although the axes 130-133 are shown as different, FIB milling of different sample sections may be accomplished with a fixed FIB and translation of the sample relative to the fixed FIB. In some cases, both the sample position and the FIB axes may be changed.

[0020] In the disclosed technique, the FIB dose applied along each of the axes 130-133 may be selected to avoid or limit FIB milling into the stub 108 and the specimen mount 103, since images thereof are not required. Thus, the dose associated with milling away the section 102A of the specimen 102 is selected to expose the cross section 110 extending from the coating 104 to the support member 103. In some cases, the dose is selected to mill into the support member 103 or deeper to ensure that the entire cross section 102A is exposed. This milling depth (i.e., cut height) and associated dose may be determined by processing the image of the cross section 110. Such processing may be based on identification of a specimen boundary, such as identification of one or more of the coating 104 and the specimen support 108 in the image. The cut height may be selected based on the distance between the coating 104 and the specimen support 108, for example, and the dose may be selected based on the cut height. For subsequent cross sections, the cut plane heights may be redetermined such that the cut plane heights used in determining the doses to expose cross sections 111, 112, 113 and remove sample sections 102B, 102C, 102D are based on the locations determined using images of cross sections 110, 111, 112, respectively. In many practical implementations, the cut plane heights are changed slowly and the redetermining of the cut plane heights (and doses) may be done using images of only a few cross sections or using a series of previous images, which may be consecutive or non-consecutive images.

[0021] In a conventional approach using a fixed dose, milling would proceed into the specimen mount 103 and stub 108 to the depth indicated by lines 160-163. Milling this additional depth would be time consuming, and the process described herein avoids this unnecessary milling.

[0022] Example 2 Referring to FIG. 2, an exemplary method 200 of obtaining a cross-sectional image using an adaptively selected CPB dose includes, at 202, placing a sample in a dual CPB instrument, typically an instrument that includes CPB optics and sources for FIB milling and SEM imaging. The sample is typically positioned so that the FIB can be incident at near normal incidence on a surface of a mounting stub supporting the sample. The electron beam used for SEM imaging is incident on the sample at an angle between about 30-60 degrees, although other angles can be used. At 204, an SEM image of an initial cross-section of the sample is obtained, for example, by retrieval of a previously acquired image or by operating the SEM to obtain an image. In this example, SEM imaging is used, although other types of images, such as images obtained using an ion beam, are suitable. At 208, the image is processed to identify a sample edge, sample boundary, or other spatial constraints associated with the sample. At 210, an intended cut plane height is determined based on the sample edge or other identified sample feature, such as the cut plane height of the initial cross-section. This cut plane height can be based on image portions associated with the sample coating, sample mount, or other structures or components proximate the sample, or by evaluation of image portions associated with the sample itself. At 212, a FIB dose is selected based on the intended cut plane height, typically a dose large enough to accommodate variations in sample thickness so that the subsequent cross section is fully exposed. At 214, the selected FIB dose is applied to expose the subsequent cross section, and at 216, the newly exposed cross section is imaged. If additional images are needed for image reconstruction, as determined at 218, processing returns to 208, where the sample edge in the newly acquired image is used, and the method continues acquiring images of another cross section. If additional images are not to be acquired, at 220, a 3D image is constructed, stored, and / or communicated for viewing, or otherwise made available.

[0023] Example 3. Imaging system Referring to FIG. 3, a dual beam system 300 includes a system controller 302 coupled to an ion beam source and optical column 304 and an electron beam source and optical column 306 that generate an ion beam 305, such as a focused ion beam (FIB), and an electron beam 307, respectively. The ion beam 305 may be scanned or otherwise directed to a sample 320, for example, to process the sample by ion beam milling. The electron beam 307 is directed to the sample 320 to obtain SEM images. In some applications, in addition to processing the sample 320, images are obtained based on the ion beam 305 instead of the electron beam 307. One or more CPB detectors, such as an exemplary CPB detector 310, are positioned to receive CPB 313, for example, based on scattered ions or electrons, secondary electrons in response to the ion beam 305 and / or the electron beam 307, and are used for CPB control and imaging. In other embodiments, characteristic x-rays and x-ray diffraction or transmission electrons are detected and used. A camera may be provided for specimen alignment and inspection, but is not shown.

[0024] The sample 320 is mounted on a sample mount 321 coupled to a stage 322 that communicates with a stage controller 324 responsive to the system controller 302. The stage 322 may typically provide one or more of translation, rotation, or tilt as directed by the system controller 302. The system controller 302 may include electronics 330, such as one or more analog-to-digital converters (ADCs), digital to analog-converters (DACs), amplifiers, and buffers, for controlling the CPB detector, processing (amplifying, digitizing, buffering) signals associated with one or more CPB detectors, such as CPB detector 313, and the optical columns associated with the ion beam and electron beam. In most practical applications, at least one ADC is used to generate digitized detector signals that may be stored in one or more tangible computer-readable media, such as an image (shown as image storage 332). In other embodiments, the image storage is remote, such as via a communication connection, such as a wired or wireless network connection.

[0025] The system controller 302 is coupled to a memory 335 that stores processor-executable instructions for processes such as cross-sectional image acquisition 340, edge and boundary identification 336, dose determination 338, 3D image reconstruction 342, and provides a GUI 344 for various functions including the number of cross-sectional images acquired and the range over which the dose should be selected to compensate for variations in milling rate and variations in sample thickness. In the memory portion 332, cross-sectional images and reconstructed 3D images may be stored. Stage coordinates (including rotation) may be stored in the memory portion 332 as well. The system controller 302 sets image acquisition parameters and is in communication with the stage controller 324. Sample images (such as cross-sectional images and 3D reconstructions) may be presented on a display 352, and system control and imaging parameters may be specified using values ​​stored internally from the memory 335 or may be provided by a user using one or more user input devices 350. It will be appreciated that the layout of FIG. 3 is illustrative for convenience and that the actual alignment of the various beam sources and detectors may vary.

[0026] The system controller 302 may be implemented using one or more of a general-purpose computing device, in the form of an exemplary conventional PC, or special-purpose computing devices, such as complex programmable logic devices (CPLDs) and field programmable gate arrays. The methods may be implemented using such computing devices using computing device-executable instructions stored on one or more non-transitory computer-readable media. Such computer-executable instructions may be configured to implement any available edge detection method, such as those discussed below.

[0027] Example 4 Referring to FIG. 4 , a sample 402 to be investigated is placed on a sample mount 404, such as a metal grid, a conductively coated member, or other suitable support. The sample 404 is shown with a coating 406, typically a conductive coating to reduce charging effects. The sample 402 is positioned between the sample mount 404 and the coating 406. In this example, the sample mount 404 is fixed to a mounting stub 408, which may be coupled to one or more actuators, such that the specimen can be suitably positioned for SEM imaging with the imaging electron beam generally incident from an imaging direction 409. A set of cross-sectional images are taken along respective axes 4181, ..., 418. 18 By FIB milling using a FIB received along each of the surfaces 4101, ..., 410 19 In FIG. 4, only selected planes and FIB axes are labeled; other planes and FIB axes are not labeled for ease of illustration.

[0028] The height of the specimen 402 measured along the Z-axis of the coordinate system 420 as viewed in the imaging direction 409 is variable. 19 To prepare each of the axes 4181, ..., 418 18 Milling along the axial direction only needs to expose the surface portion between the specimen mount 404 and the coating 406 in region 424. Material removal can extend into region 422 associated with the mounting stub 408 and the specimen support 404, but the surface portion in this region is not needed for specimen imaging, and the processing time spent in removing material in region 422 would slow down image acquisition.

[0029] Sections 4101, ..., 410 beyond the specimen support 404 19 The extension of the axis 4181, ..., 418 18 4. The cross section 410 of the sample 402 is illustrated based on the use of a common milling time for each of the nBy milling to expose only the cross-section, milling can be accomplished more quickly, reducing the time required for image acquisition. Milling of the cross-section exposes the sample surface and may expose portions of coating 406, sample mount 404, and sample stub 408 selected to ensure complete exposure of the cross-section as a result of the milling. For example, cross-section 4103 is obtained by milling along axis 4183, but it is not necessary to use milling time to mill in region 422. For each of the milling axes 418, a different milling dose may be selected depending on the cross-section height to be exposed, i.e., the cut plane height. By identifying the sample edge, such as the location of sample 402 relative to sample support 404 and coating 406, the cut plane height can be determined for subsequent images and the appropriate dose to be applied. As discussed above, the time savings can be significant. For example, in the acquisition of 5000 cross-section images, the time saved by avoiding milling in region 422 can be as much as about 7 hours.

[0030] Example 5 5A-5C illustrate cross sections obtained by milling a sample mounted on a sample support without extensive time-consuming milling beyond the sample. In FIGS. 5A-5C, the FIB is directed from approximately above the sample as positioned in the figures. Cut plane heights 508, 514, 520 are shown for cross sections 501, 512, 522, showing a sample 502 (inside the cell) having a coating 504 and positioned on a sample support 506. The portion of the image above the coating 504 corresponds to the coated sample surface viewed from an angle. For cross sections 501, 512, 522, the dose is selected based on the cut plane height of a previously imaged cross section, with FIGS. 5A and 5C being associated with a lower dose than that used to obtain the imaged cross section 511 shown in FIG. 5B. In most cases, the cross sections are closely spaced and the cut plane height changes slowly, so the use of the previous cross section image is satisfactory. Depending on the variation in sample thickness, only a few cross-sectional images may be used to estimate the cut height and dose, such as every other cross-sectional image, every 5th, every 10th, every 100th, or other regularly or irregularly spaced cross-sectional images.

[0031] Example 6 Further time savings for image acquisition can be realized by suitable selection of the sample width to be milled, referred to herein as "cut face width". FIG. 6 is a representative cross-sectional image 600 of a sample 601 (cell) having a coating 604 and placed on a conductive foil 606. Using the previous cross-sectional image, a suitable dose is selected to produce a cut face height 610 that extends to the top and bottom surfaces of the sample 601. The structure of interest 603 in the sample 601 is laterally limited. Other parts of the sample 602 are not required for 3D image reconstruction. Using edge detection, a cut face width, such as cut face width 612, can be selected and milling is performed only within this width. This can further reduce image acquisition time.

[0032] Example 7 Referring to FIG. 7, a representative sample 702 (cell) is placed between a sample mount 706, in this example a conductive foil, and a coating 704, such as a conductive coating or a protective coating or other coating. The sample mount is in contact with a stub 708 used for positioning in a dual CPB instrument. The FIB is applied along axis 710 and the imaging CPB is applied along axis 712. Three cross sections 731-733 associated with respective cut heights H1-H3 are shown. In most examples, hundreds of cross sections will be milled and imaged, and only three are shown in FIG. 7 for ease of illustration. Sample thickness variation between cross sections tends to be small. The FIB dose for cross section 732 may be obtained by processing the image of cross section 731 to identify at least one edge, such as edge 721. The cut height H1 may be calculated based on the identified edge and a suitable dose for milling this height to be used in milling cross section 732. The applied dose may include an additional amount to account for contributions associated with milling of the coating 704 and a possible increase in sample thickness at the cross section 732.

[0033] After milling to expose cross section 732, an image is obtained. The FIB dose for cross section 732 may then be obtained by processing the image of cross section 733 to identify at least one edge, such as edge 722. A cut height H2 may be calculated based on the identified edge and a suitable dose for milling this height to be used in milling cross section 733. The dose applied may include an additional amount to account for contributions associated with milling coating 704 and possible increase in sample thickness at cross section 733. After this milling, a cut height H3 is measured by identifying edge 723 in the image of cross section 733 and used to determine the dose for subsequent milling to expose the cross section.

[0034] In some embodiments, edges associated with the specimen mount 706 or stub 708 are used. In this embodiment, these edges are associated with the tilt θ of the stub 708, and the dose determined to expose a cross section using both the top and bottom edges is reduced compared to the dose associated with only the top edge. For oppositely oriented tilts, the determined dose will increase when the thickness of the specimen is greater than that indicated based on only the top edge. While in most cases a single previously acquired image of the cross section is sufficient, by using two or more previous images it is possible to determine the dose based on the rate of change of specimen thickness or specimen tilt.

[0035] Example 8 FIG. 8 illustrates the processing of a sample 802 to expose cross sections 810-813 for imaging and obtaining images of the exposed surfaces to generate a 3D sample reconstruction. The sample 802 is positioned on a support member 803, such as a conductive grid, which may be positioned on a stub 808, which may be used to position the sample 802 for charged-particle beam (CPB) processing and imaging. The sample 802 is typically provided with a conductive coating 804 to reduce or eliminate charging artifacts in CPB imaging and processing. Processing to expose the cross sections 810-813 may be accomplished as described above with reference to FIG. 1. As shown, the imaging CPB 849 is incident along one or more axes that are approximately parallel to the Y axis of an XYZ coordinate system 850, in which the X axis extends out of the plane of the drawing. The cross sections 810-813 extend along respective XZ planes in the coordinate system 850, and the cut height, measured as a Z coordinate, is determined as a function of the X coordinate, as evidenced by the different cut heights associated with the cross sections 810-813, i.e., the height Z of material removed to expose the cut. mill sZ mill =Z mill (Y) is given by

[0036] FIG. 8A is a cross-sectional view illustrating a cross section 811. The height of the cross section 811 varies along the X-axis. For example, at X-coordinates X1-X3, milling is performed based on heights Z1-Z3, which may all be different heights such that different doses are required. Thus, milling time can be determined based on identification of one or more edges in one or more cross-sectional images, which can be further reduced based on specimen thickness variation in the XZ plane (in addition to thickness variation in the YZ plane). A series of cross-sectional images, such as nearby or adjacent cross-sectional images, can be used to determine the height to be milled. Similar to what was discussed above, the rate of change of specimen height can be used to determine how much of which cross-sectional images should be used to establish the dose required to expose the subsequent cross section. In this approach, the height Z of material removed to expose the cut surface is determined based on the height Z of material removed to expose the cut surface. mill is Z mill =Z mill (X,Y). Varying the dose as a function of the Y coordinate provides substantial time savings, but using variation of the X coordinate can further reduce the total treatment time. mill is used to determine ion beam dose or other exposure parameters associated with material removal such as CPB or optical beam average power, peak power, duty cycle, repetition rate, current, current per unit area, beam energy or wavelength, or other parameters.

[0037] Example 9 Various methods can be applied to identify edges or boundaries of samples with or without coatings or sample supports. For example, Sobel filtering can be used, where a pair of convolution kernels are used to compute the gradient magnitude of the image intensity, typically identifying edges at locations with relatively large gradient magnitudes. The so-called Canny edge detection method can be used, where the image is smoothed before determining the gradient magnitude, followed by a step where non-maximum edges are suppressed, followed by hysteresis thresholding. A Laplacian of Gaussian (LoG) filter can be used, where the image is convolved with a Laplacian of Gaussian filter. Another example is the Prewitt operator method, where a convolution kernel is used to compute the gradient magnitude of the image intensity at each pixel, similar to the Sobel filter. Other methods include the use of Roberts cross operator-based zero-crossing detectors, or zero-crossing detectors based on finding zero crossings in the second derivative of the image intensity. Artificial intelligence (AI) methods such as convolutional neural networks or other deep learning methods, or other computer vision or machine learning methods can also be used.

[0038] Additional Disclosures Clause 1 is a method that includes using a processor to identify a boundary of a sample in an initial cross-section of the sample, milling the sample based on the identified boundary to reveal a subsequent cross-section, and obtaining a charged particle beam (CPB) image of at least a portion of the subsequent cross-section.

[0039] Clause 2 includes the subject matter of clause 1 and further specifies that the identified boundary of the sample at the initial cross-section of the sample is obtained based on an image of the initial cross-section.

[0040] Clause 3 includes the subject matter of any of clauses 1-2, and further specifies that identifying the boundary includes identifying at least one edge in the image of the initial cross-section of the sample, and the sample is milled to a selected depth based on the identified at least one edge.

[0041] Clause 4 includes the subject matter of any of clauses 1-3, and further specifies that identifying the boundary includes identifying a sample periphery in an image of the initial cross-section of the sample, and the sample is milled to a selected depth based on the sample periphery.

[0042] Clause 5 includes the subject matter of any of clauses 1-4, and further includes iteratively identifying edges of a previously imaged cross section using a processor, milling the sample based on the identified edges of the previously imaged cross section to reveal a subsequent cross section, and obtaining a CPB image of the subsequent cross section.

[0043] Clause 6 includes the subject matter of any of clauses 1-5, and further includes, for multiple subsequent millings of the sample based on identified edges of the previously imaged cross-sections, the sample is milled at a fixed dose.

[0044] Clause 7 includes the subject matter of any of clauses 1-6 and further specifies that the fixed dose is selected based on a cut plane height associated with a previously imaged slice.

[0045] Clause 8 includes the subject matter of any of clauses 1-7, and further specifies that for at least two of the multiple millings of the sample based on identified edges of the previously imaged cross-section, the sample is milled at different doses.

[0046] Clause 9 includes the subject matter of any of clauses 1-8 and further specifies that the different doses are based on a cut plane height associated with at least two previously acquired images of the cut plane surface.

[0047] Clause 10 includes the subject matter of any of clauses 1-9, and further includes iteratively identifying, with a processor, edges of the previously imaged cross-sections; milling the sample based on the identified edges of the previously imaged cross-sections to reveal subsequent cross-sections, where the subsequent cross-sections are not adjacent to the previously imaged cross-sections; and obtaining a CPB image of the subsequent cross-sections.

[0048] Clause 11 includes the subject matter of any of clauses 1-10, and further includes identifying the boundary includes identifying a first edge and a second edge in an image of the initial cross section of the sample, and the sample is milled to a selected depth between the first edge and the second edge.

[0049] Clause 12 includes the subject matter of any of clauses 1-11, and further specifies that the specimen is milled to a selected depth only between the first edge and the second edge.

[0050] Clause 13 includes the subject matter of any of clauses 1-12, and further specifies that at least a portion of the boundary of the sample is associated with a sample support to which the sample is attached.

[0051] Clause 14 includes the subject matter of any of clauses 1-13, and further specifies that at least a portion of the boundary of the sample is associated with a coating applied to the sample.

[0052] Clause 15 includes the subject matter of any of clauses 1-14 and further specifies that the milling is ion beam milling and the CPB image is a SEM image.

[0053] Clause 16 includes the subject matter of any of clauses 1-15, further including combining the cross-sectional CPB images to generate a three-dimensional image.

[0054] Clause 17 is a dual beam apparatus comprising ion beam optics arranged to direct an ion beam to a sample; a charged particle beam (CPB) imaging system arranged to generate an image of the sample; and a system controller coupled to the ion beam optics and the CPB imaging system and operable to control the ion beam to expose a subsequent cross-section of the sample with the ion beam based on a previous image acquired using the CPB imaging system.

[0055] Clause 18 includes the subject matter of clause 17 and further specifies that the system controller is operable to identify edges in the previous image, and the subsequent cross-sections are exposed based on the identified edges.

[0056] Clause 19 includes the subject matter of any of clauses 17-18 and further specifies that the system controller is operable to sequentially expose cross-sections of the sample with the ion beam based on at least one previous cross-sectional image obtained using the CPB imaging system.

[0057] Clause 20 includes the subject matter of any of clauses 17-19 and further specifies that the system controller is operable to identify at least one edge in a prior image acquired using the CPB imaging system and select a dose to be applied to generate the subsequent cross-sections based on the identified at least one edge.

[0058] Clause 21 includes the subject matter of any of clauses 17-20 and further specifies that the system controller is operable to expose a subsequent cross section of the sample with the ion beam based on a cut surface height associated with the previous image.

[0059] Clause 22 includes the subject matter of any of clauses 17-21 and further specifies that the system controller is operable to select a dose to be applied to expose a subsequent cross-section of the sample with the ion beam based on a cut plane height associated with a previous image, the previous image being associated with a non-adjacent cross-section.

[0060] In view of the numerous possible embodiments to which the principles of the disclosed technology may be applied, it should be recognized that the illustrated embodiments are preferred examples only and should not be construed as limiting the scope of the disclosure.

Claims

1. 1. A method comprising: using a processor to identify a boundary of the sample at an initial cross-section of the sample; milling the sample based on the identified boundaries to reveal a subsequent cross-section; obtaining a charged particle beam (CPB) image of at least a portion of the post-mortem cross-section.

2. The method of claim 1 , wherein the identified boundary of the specimen at the initial cross-section of the specimen is obtained based on an image of the initial cross-section.

3. 2. The method of claim 1, wherein the identifying the boundary comprises identifying at least one edge in the image of the initial cross-section of the sample, and the sample is milled to a selected depth based on the identified at least one edge.

4. 2. The method of claim 1 , wherein the identifying the boundary comprises identifying a sample perimeter in the image of the initial cross-section of the sample, and the sample is milled to a selected depth based on the sample perimeter.

5. iteratively identifying edges of previously imaged cross sections with said processor; milling the sample based on the identified edges of the previously imaged cross-section to reveal a subsequent cross-section; obtaining a post-mortem cross-sectional CPB image; The method of claim 1 further comprising:

6. 6. The method of claim 5, wherein the sample is milled at a fixed dose for multiple subsequent millings of the sample based on the identified edges of the previously imaged cross-sections.

7. The method of claim 6 , wherein the fixed dose is selected based on a cut plane height associated with the previously imaged cross-section.

8. 6. The method of claim 5, wherein for at least two of the multiple millings of the sample based on the identified edge of the previously imaged cross-section, the sample is milled at a different dose.

9. The method of claim 8 , wherein the different doses are based on a cut plane height associated with at least two previously acquired images of the cut plane surface.

10. iteratively identifying edges of previously imaged cross sections with said processor; milling the sample based on the identified edges of the previously imaged cross-section to reveal a subsequent cross-section, wherein the subsequent cross-section is not adjacent to the previously imaged cross-section; obtaining a post-mortem cross-sectional CPB image; The method of claim 1 further comprising:

11. 11. The method of claim 10, wherein the identifying the boundary comprises identifying a first edge and a second edge in the image of the initial cross-section of the sample, and the sample is milled to a selected depth between the first edge and the second edge.

12. The method of claim 11 , wherein the selected depth is a function of an abscissa associated with the identified edge in the previously imaged cross-section.

13. The method of claim 1 , wherein at least a portion of the boundary of the sample is associated with a sample support to which the sample is mounted.

14. 10. The method of claim 1, wherein at least a portion of the specimen boundary is associated with a coating applied to the specimen.

15. The method of claim 2 , wherein the milling is ion beam milling and the CPB image is a SEM image.

16. The method of claim 10 , further comprising combining the CPB images of the cross sections to generate a three-dimensional image.

17. 1. A dual beam device, comprising: ion beam optics arranged to direct the ion beam towards the sample; a charged particle beam (CPB) imaging system arranged to generate an image of the sample; a system controller coupled to the ion beam optics and the CPB imaging system and operable to process previous images acquired using the CPB imaging system and to control the ion beam based on the processing of the previous images to expose a subsequent cross-section of the sample with the ion beam.

18. 20. The dual beam apparatus of claim 17, wherein the system controller is operable to process the previous image to identify edges in the previous image, and the subsequent cross sections are exposed based on the identified edges.

19. 20. The dual beam apparatus of claim 17, wherein the system controller is operable to sequentially expose cross-sections of the sample with the ion beam based on processing of at least one previous cross-sectional image obtained using the CPB imaging system.

20. 20. The dual beam device of claim 17, wherein the system controller is operable to identify at least one edge in the previous image acquired with the CPB imaging system and to select a dose to be applied to generate a subsequent cross-section based on the identified at least one edge.

21. 20. The dual beam apparatus of claim 17, wherein the system controller is operable to expose a subsequent cross-section of the sample with the ion beam based on a cut plane height associated with the previous image.

22. 20. The dual beam apparatus of claim 17, wherein the system controller is operable to select a dose to be applied to expose a subsequent cross-section of the sample with the ion beam based on a cut plane height associated with the previous image, the previous image being associated with a non-adjacent cross-section.

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