Microscope feedback for improved milling accuracy

Abstract

Methods and apparatus are disclosed for integrating image-based metrology into a milling workflow. A first ion beam milling operation is performed on an edge at a distance from a final target location on a sample. A SEM image of the sample is used to determine a distance between the milled edge and a reference structure on the sample. Based on the determined distance, the ion beam is adjusted to perform a second milling operation to shift the milled edge to the final target location. Extensions to the iterative process are disclosed. Various geometric configurations and corrections are disclosed. Manufacturing and analysis applications are disclosed in various fields including read-write head manufacturing and TEM sample preparation. Other combinations of imaging and milling tools can be used.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 290,438, filed December 16, 2021, and U.S. Utility Application No. 17 / 873,532, filed July 26, 2022. Technical Field

[0003] This disclosure relates to improvements in milling accuracy. Background Technology

[0004] Ion beam milling is increasingly used to machine micron- and nanon-scale devices. However, ion beam milling machines have inherent sources of positioning error, and meeting target tolerances can be challenging as device sizes continue to shrink. Therefore, there remains a need to improve techniques for precision milling of micron- and nanon-scale devices. Summary of the Invention

[0005] In simple terms, the disclosed technology combines imaging with milling. Through feedback, a milling tool with lower inherent precision can achieve the higher precision characteristics of an imaging tool. In one example, distances measured on the image are used to move the initially milled edge to the target location with a higher precision than that achievable by the milling tool alone.

[0006] In the first aspect, the disclosed technology can be implemented as an apparatus incorporating a milling tool, an imaging tool, and a controller. The milling tool is configured to mill a sample using a first particle beam. The imaging tool is configured to generate one or more images of the sample using a second particle beam. The controller is configured to cause the milling tool to mill the sample to a first edge using a first value of control parameters; and further determine a second value of the control parameters, the second value being a change from the first value based on the distance between the first edge and a target location. The distance is determined based on an image of the sample surface acquired by the imaging tool. The controller is further configured to cause the milling tool to mill the sample to a second edge using the second value of the control parameters.

[0007] In some instances, the first and second particle beams may contain different corresponding substances. The first particle beam may be a focused ion beam (FIB), and the imaging tool may be a scanning electron microscope (SEM). The image may be a first image, milling to a second edge may expose the cut surface of the sample, and the controller may be further configured to cause the imaging tool to acquire a second image of the cut surface of the sample. The imaging tool may use a common orientation of its field of view to capture the first and second images. The controller may be configured to rotate the field of view of the imaging tool relative to the sample between acquiring the first and second images. The field of view of the imaging tool may be at an angle within 10° to the surface normal when acquiring the first image, and may be at an angle in the range of 40° to 60° to the surface normal when acquiring the second image. Control parameters may determine the sweep position of the milling tool in a direction along the surface and perpendicular to the first edge.

[0008] In the second aspect, the disclosed technique can be implemented as a method. An image of the sample surface is acquired from a scanning electron microscope (SEM). Based on the relative position of the milled edge and a reference structure in the image, a distance for shifting the milling position is determined. This distance is stored. The stored distance can be used in subsequent milling operations to shift the milled edge to a predetermined spatial relationship with the reference structure.

[0009] In some instances, the distance can be a first distance, and the predetermined spatial relationship can be a tolerance range of a second distance. The second distance can be the distance from (i) a datum defined by the reference structure to (ii) a line containing the displaced milled edge. In other instances, the distance can be a first distance, and determining the first distance can further include determining a second distance from the center coordinates of the reference structure to the line containing the milled edge. Linear scaling can be applied to the second distance to obtain the first distance.

[0010] In some instances, the image may be a first image, and the method may include acquiring a second image from the SEM showing the cut surface exposed by subsequent milling operations. The reference structure may contain two distinct markers. The centroid of the reference structure can identify the location of the target device in the sample that will be exposed by subsequent milling operations. The predetermined spatial relationship may be a tolerance zone surrounding the centroid of the reference structure.

[0011] In another instance, the acquire and determine operations can be repeated after the corresponding milling operation, which includes subsequent milling operations, until a termination condition is met. Repeated operations can provide convergence to a given target location on the sample. Alternatively or additionally, repeated operations can be performed sequentially on a series of target locations on the sample.

[0012] The method may include an edge effect correction distance for the first edge. Subsequent milling operations can be performed using the same milling tool initially used to generate the milled edge. Subsequent milling operations can be performed using focused ion beam (FIB). The method can be used to generate read / write transducers from samples or thin sections for transmission electron microscopy.

[0013] In another aspect, the disclosed technology can be implemented as a computer-readable medium storing program instructions executable by one or more hardware processors. Upon execution of the instructions, the processor is activated to: (a) cause a milling tool to mill the sample to a first edge using a first value of control parameters; (b) acquire an image from a scanning electron microscope (SEM) depicting the first edge and a reference structure on the sample surface; (c) determine a second value of the control parameters based on the first value and the relative positions of the first edge and the reference structure in the image; and (d) cause the milling tool to mill the sample to a second edge using the second value of the control parameters.

[0014] In some instances, determining a second value for the control parameter may include applying a correction for the angle between the SEM's line of sight and the normal to the sample surface. The surface may be the main surface of the sample, the first edge may be the boundary between the main surface and a cut surface exposed to the first edge by milling, and the dihedral angle between the cut surface and the main surface may be in the range of 60° to 120°.

[0015] In another example, milling the sample to the first and second edges can expose the first and second cut surfaces of the sample, respectively, and the instructions can further activate the processor to apply a compensating tilt between the milling tool and the stage on which the sample is mounted before milling to the first edge. The compensating tilt can control the dihedral angle between (i) the second cut surface and (ii) the remainder of the sample surface within a predetermined range. The sample can be a first sample, the image can be a first image, and the SEM can be a first SEM. The instructions can further activate the processor to (e) cause the milling tool to mill the second sample to the third edge, thereby exposing the third cut surface of the second sample; and (f) cause the milling tool to mill the second sample to the fourth edge, thereby exposing the fourth cut surface of the second sample. The third and fourth edges can form an angle between 60° and 120° (inclusive) on the main surface of the second sample. The third and fourth cut surfaces can intersect at a fifth edge. The instructions can further activate the processor to (g) acquire a second image of the fourth cut surface from the second SEM; and (h) determine the compensating tilt angle from the relative positions of the fourth and fifth edges in the second image.

[0016] The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken with reference to the accompanying drawings. Attached Figure Description

[0017] Figure 1 It can be a diagram of an instance device through which the disclosed technology is implemented.

[0018] Figures 2A to 2B It is a diagram depicting the geometry of instances in which the disclosed technologies can be deployed.

[0019] Figure 3 This is a flowchart of a first instance method for generating image-based feedback for milling based on the disclosed technology.

[0020] Figure 4 This is a flowchart of a second example method for milling via image-based feedback, based on the disclosed technology.

[0021] Figure 5 This is a flowchart of a third instance method for milling via image-based feedback, based on the disclosed technology.

[0022] Figures 6A to 6D It is a diagram depicting a sample of operations performed according to an instance of the disclosed technology.

[0023] Figure 7 This view shows a first instance application of the disclosed technology.

[0024] Figure 8 A view showing a second instance application of the disclosed technology.

[0025] Figure 9 This section describes generalized examples of suitable computing environments in which the described embodiments, techniques, and imaging or milling-related techniques can be implemented. Detailed Implementation

[0026] Introduction and Overview

[0027] With technological advancements and the increasing applications of micromachining, focused ion beam (FIB) milling has become a preferred technique. FIB milling can provide etched shapes of arbitrary shapes with high-quality finished surfaces on a wide range of materials. FIB can be performed under program control, without the need for masks or custom tools. FIB is versatile: a single FIB tool can be used for machining, imaging, and ion implantation, allowing for efficient integration with various process flows. FIB has proven well-suited for micromachining tasks requiring precision on the order of 10 nanometers. (Although sub-10 nm precision is achievable under low beam current conditions, this may be impractical for some micromachining applications.) As an imager, some FIB milling machines today can provide resolutions of approximately 20 nm. Many factors limit the precision of FIB milling machines, including temporal and spatial variations of the beam source, beam optics, and the inherent instability of the ion beam itself.

[0028] Some micromachining applications require higher precision than that achievable with current FIB polishing machines. Two non-limiting examples include the fabrication of read / write heads for magnetic storage devices and the preparation of TEM samples of 20 nm or smaller.

[0029] Examples of the disclosed techniques utilize imaging tools with higher resolution to guide milling tools with lower inherent resolution (e.g., about 10 nm to about 50 nm for FIB). For example, a scanning electron microscope (SEM) can have a resolution of about 2 nm. For FIB, the SEM imaging resolution value can depend on precise operating conditions, and is about 2 nm for some applications of interest herein, or as low as 0.6 nm in other configurations. In particular, measurements of high-resolution SEM images can be used as feedback to the FIB milling process to achieve milling accuracy achievable solely by the milling tool.

[0030] In the experiments, it was found that the unassisted FIB milling tool had a cut position reproducibility of approximately ±9 nm (three standard deviations). By reducing or eliminating some significant sources of variability, the disclosed technique can achieve a cut position reproducibility of approximately ±5 nm (three standard deviations).

[0031] While FIB and SEM are used in combination to describe some examples, the disclosed techniques are not limited to these specific tools. Instead, any high-resolution imaging tool can be used to apply the disclosed techniques to improve the performance of any lower-resolution machining or micromachining tool.

[0032] By using the disclosed techniques, the quality and reproducibility of manufacturing apparatus, sample preparation, or cross-sectional analysis can be improved in a wide range of applications.

[0033] the term

[0034] Unless otherwise expressly stated or contradicted by the context, the usage and meaning of all terms referenced in this section apply to the entire disclosure. The following terms are extended to their relevant word forms.

[0035] "Analysis" refers to the operations used to characterize a sample. Analysis can encompass various forms of imaging, probe measurements of electrical properties, or non-contact measurements of particle or radiation scattering. Analytical operations can include delamination, electron backscattering analysis, electron microscopy, etching, imaging, mass spectrometry, materials analysis, metrology, nanoprobes, spectroscopy, or surface preparation. Analysis can be performed during or after a milling process at one or more layers exposed by the milling. Some analyses may require preparing the exposed surface prior to the analysis, for example, by polishing. Some analyses may require pausing the milling operation for analysis, while other analytical techniques can be performed in real time during milling. The equipment or instrument used to perform this operation is called an "analytical instrument" or simply an "analyzer." Some analytical instruments of interest in this paper include scanning electron microscopy (SEM).

[0036] An "azimuth" is a signed angle defined or measured about an axis from a reference plane containing the axis. This axis can be a rotation axis, and the azimuth can be changed by rotating about it. In some disclosed examples, the axis can be parallel to the rotation axis of the sample stage and perpendicular to the surface of the sample mounted thereon. Therefore, the azimuth of the incident particle beam can be changed by rotating the stage about its sample axis. The reference plane can be perpendicular to the working surface of the sample and can contain the rotation axis of the stage on which the sample is mounted. Azimuth coordinates are analogous to longitude in land locations.

[0037] The term "beam" refers to the directed flow of particles or energy. The common beam of interest in this disclosure is a particle beam, such as an electron beam or an ion beam. A beam can have a finite range transverse to its main longitudinal flow direction. The line connecting the centers of mass of two or more cross-sections of the beam is the "axis" of the beam.

[0038] A “controller” is an electronic device coupled to one or more actuators to change physical parameters, or coupled to one or more sensors to monitor physical parameters. Some controllers may contain a microprocessor that can be programmed to execute machine-readable instructions. The description of computing devices herein generally applies to this type of controller. Such controllers may contain additional electronic circuitry systems, such as filters and amplifiers. Other controllers may contain analog circuitry systems, such as filters and amplifiers, without any microprocessor.

[0039] "Coordinates" are optionally numerical units that indicate the position or orientation of a point or object in space. Common coordinates can be linear (e.g., longitudinal coordinates in the direction of the beam axis) or angular (e.g., angles in spherical coordinates). In some of the described instances, coordinates indicating the position of the milled edge can be measured along the Y-axis perpendicular to the milled edge.

[0040] A “datum” is a reference line or point defined for a sample, associated equipment, or associated coordinate system from which other features or objects can be measured. In some instances described herein, a datum may be the centroid or centerline of a reference structure.

[0041] The "dihedral angle" between two intersecting planar surfaces at their edges is a positive angle within a range (0°, 180°) measured in the planes intersecting the edges.

[0042] "Distance" is a length measure between two features on a sample or in a sample image. The two features may exist at a given time (e.g., a milled edge and a reference structure), or one of the features may be a target location (e.g., the distance from an existing milled edge to the desired location of a milled edge). The distance between two points can be the Cartesian distance between the points. The distance between a point and a line can be the perpendicular length from the point to the line. Distances to features with a finite range can be measured relative to the center location of the feature (e.g., the centroid). The measured distances can be corrected for imaging geometry (e.g., the tilt of the view axis relative to the imaging surface) or for imaging artifacts (e.g., flares).

[0043] An "edge" is a line along the intersection of two surfaces, with the surface normals discontinuous across the line. In some disclosed examples, an edge can be formed between the main surface of the sample and a cut surface exposed by milling. Continuous milling operations can move this edge.

[0044] "Edge artifacts" are artifacts in an image caused by edges on the imaged sample. In SEM images, edges may appear brighter than adjacent intersecting surfaces (sometimes called "flares").

[0045] An "electron beam" is a directed flow of electrons.

[0046] An electron microscope is a type of analytical instrument in which a sample is irradiated by an electron beam, and the resulting particles or electromagnetic radiation are used to form a spatially resolved image. Scanning electron microscopy (SEM) images the surface of a sample based on reflected, secondary, or backscattered particles or radiation from one or more surfaces of the sample. Because the beam interactions detected by SEM occur at or near this surface, SEM can operate on samples of arbitrary thickness. In contrast, transmission electron microscopy (TEM) images the sample volume based on transmitted electrons (including scattered electrons). TEM operates on samples with a thickness of approximately 10 nm to 150 nm, which can be mounted on a grid for mechanical support and thermal conduction; the grid can then be held in a sample holder. TEM can provide magnifications up to and exceeding 50 million, while the magnification of SEM is typically limited to approximately 2 million. In this disclosure, scanning transmission electron microscopy (STEM) performing transmission electron imaging is considered both SEM and TEM. The electron beam in an electron microscope can be generated in an electron gun and accelerated, focused, or directed toward the sample chamber via a series of stages.

[0047] The term “exposure” refers to the act of bringing features from inside a sample to the sample surface, for example, by removing material between previously buried features and the sample’s previous surface.

[0048] A "focused ion beam" ("FIB") is an ion beam whose focal point can be controlled to direct the beam to a point on a surface, or it can sweep across a sample in a scanning mode. FIBs can be used to analyze, deposit, or remove material at the point of incidence. Some FIBs are used for milling. Typically, FIBs include positive element ions such as Xe+ or Ga+, however these are not mandatory. For example, Ga+ ion beam materials can be derived from, for example, a liquid metal ion source (LMIS), while other ion beam materials such as Xe+ can be generated in plasma. FIBs generated using plasma sources are called plasma-focused ion beams (PFIBs).

[0049] The term "imaging" refers to the process of obtaining a two-dimensional representation (referred to as an "image") of parameter values ​​on a region of interest of a sample. In some instances, the imaging parameter may be the reflectivity of an incident particle beam (e.g., via SEM), but this is not required, and visible light or other parameters may also be used for imaging. In the disclosed instances, the image may indicate features on the sample, such as edges or reference structures. In other instances, the region of interest may encompass at least a portion of one or more surfaces of the sample.

[0050] An “imaging tool” is a device capable of imaging. In the disclosed examples, a SEM can be used as an imaging tool. However, this is not necessary, and other high-resolution imaging tools, such as atomic force microscopy or super-resolution optical microscopy (e.g., using time-varying or fluorescence techniques), can also be used. An FIB tool can perform imaging, but better spatial resolution can be achieved through SEM or other techniques. A “line of sight” is a straight line along which the imaging tool observes the region of interest. Specifically, for imaging tools that guide the beam to the region of interest being imaged, the line of sight can be a beam axis passing through the center point (e.g., the centroid) of the region of interest being imaged.

[0051] The term "iteration" refers to each instance of a given operation or sequence of operations performed multiple times. A series of iterations is called a "loop". A loop that can iterate multiple times may sometimes only perform one iteration. Iteration of a loop does not require performing all operations within the loop, but it can terminate or exit early if a termination condition is met.

[0052] A “slice” is a thin sample that is imaged in a transmission electron microscope (TEM). Slices can have a thickness ranging from 10 to 50 nm, or from 20 to 30 nm.

[0053] The term "linear scaling" refers to the operation y = A·x + B performed on the input x to obtain the output y, where A and B are constants.

[0054] Milling is a material removal process along a path guided by the movement (sometimes called "sweeping") of a milling tool relative to the sample being milled. A milling operation exposes one or more "cut surfaces" of a sample by removing material up to one side of the cut surface. Generally, the cut surface intersects the main surface of the sample: the bottom of a groove with a rectangular or trapezoidal cross-section is not called a cut surface. In practice, milling can be performed using a focused ion beam (FIB). Milling is a form of "etching," which more generally refers to any subtractive process used to remove material from a sample. Diffusion chemical etching may not be considered milling. However, ion beam-assisted chemical etching can be site-specific at the location of the ion beam and can be considered milling. A "milling tool" is a device capable of milling.

[0055] A "parameter" is a quantity that can have a specific "value". While parameters typically have numerical values, this is not required, and some parameter values ​​can be logical values, strings, or data structures. Some parameters can be control parameters, for example, set by a controller to affect a physical device or physical operation. Other parameters can be sensed parameters, for example, determined by the physical environment and evaluated by a controller or measuring device (e.g., from an image). Some control parameters of interest herein include parameters that define one or more coordinates for milling operations on a sample, which may include beam steering control, stage positioning control, etc.

[0056] A “particle beam” is a beam comprising a directed stream of particles. A “particle” is a distinct, undifferentiated unit of matter flow. Particles of common interest in this disclosure include charged particles, such as electrons or ions (e.g., Ga, Xe, or protons), however, particles are not limited to these. Although some ions contain bound electrons, electrons in an electron beam are considered distinct from ions in an ion beam. In some instances, the particles of interest are confined to matter with mass, such as electrons or ions. In other instances, the particles of interest may comprise massless photons. For illustration, a pulsed laser beam (e.g., a “femtosecond laser” with a pulse duration of less than 1 ps) can be used for milling when applying the disclosed techniques.

[0057] A “polar angle” is an unsigned angle defined or measured away from an axis. This axis can be the device axis, the beam axis, or the normal to the sample surface. The polar angle is analogous to the supplementary angle of latitude in a land location—that is, the polar angle is 0° at the North Pole (where latitude is 90°N) and 90° at the equator (where latitude is 0°). Some polar angles of interest in this paper are approximately 0° or between about 45° and 52°. Some polar angles of interest in this paper lie between the normal to the sample surface (which may be parallel to the axis of rotation of the stage supporting the sample) and the axis of the particle beam incident on the sample.

[0058] A "read / write transducer" (or "read / write head") is a device capable of reading or writing magnetically encoded data onto a magnetic storage medium. Data can be written using the magnetic field generated when a drive current passes through the transducer. Data can be read using the voltage induced in the transducer by the magnetic field provided by the magnetization domain in the magnetic storage medium. Some examples of the disclosed technology can be used to precisely mill the cut surfaces of read / write transducers for metrology or manufacturing purposes.

[0059] A "reference structure" (sometimes called a "datum") is a structure fabricated as a sample to determine the location of another structure or device within the sample. Some reference structures may contain, for example, multiple different elements (called "markers") on opposite sides of the target device. The reference structure can be visible in a structural image and can be used as a reference for measuring coordinates, distances, or angles of other features in the image. The reference structure can be a two-dimensional feature on the sample surface, or it can have a three-dimensional extent extending into the sample depth such that the reference structure remains visible when successive layers of the surface are etched away.

[0060] A “region of interest” (ROI) is a portion of a sample surface swept by an electron beam, and / or a region of the sample containing features or structures (e.g., targets) that may be the subject of subsequent analysis. The term ROI does not imply any human interest.

[0061] "Rotation" is a change in the angular orientation of an object relative to another object or relative to a fixed coordinate system. In some instances, a tool axis (e.g., the view axis or beam axis of a processing tool) can be rotated relative to a sample. Rotation can be performed by rotating all or part of the process tool, by turning the beam, by rotating the sample, or by any combination of the above. Rotation that changes the polar angle is referred to as "tilting" relative to said polar angle.

[0062] A “sample” is a physical object on which imaging, milling, or other analytical or manufacturing processes are performed. A common sample may incorporate multi-layered electrical or electronic structures, or other material structures, and undergoes fabrication or preparation for imaging or another analytical process. The “master surface” of a sample is the sample surface whose area substantially does not exceed that of any other surface of the sample. For ease of description, a sample is considered to have a top and a bottom master surface, wherein the bottom surface is supported on a stage and the top surface is exposed to one or more tools or beams.

[0063] A "spatial relationship" can be any relationship between the positions or locations of two or more objects. One or more of the spatially related objects can be a sample, a feature of a sample, a process tool or beam or a component thereof, a stage on which the sample is mounted, an axis or normal of any such physical object, or a virtual geometric entity defined by one or more such physical objects (e.g., the centroid of a sample feature, or a line joining two features). In some cases, a spatial relationship can be specified by a "tolerance," which indicates the permissible spread in the quantity defining the spatial relationship. Tolerances can be one-dimensional (referred to as a "tolerance range"), such as a distance or angle within a predetermined range, or multi-dimensional (referred to as a "tolerance zone"). Non-limiting examples of tolerance zones include: a feature being within a two-dimensional region or a three-dimensional volume relative to one or more other features; or a view axis or beam axis being within a two-dimensional pyramid relative to another direction.

[0064] A "stage" is a device on which a sample can be attached and which has actuators for adjusting the position or orientation of the sample. A "multi-axis stage" has multiple degrees of freedom, thus providing spatial adjustment of the sample in different combinations of translation or rotation.

[0065] The term "sweep" refers to spatial traversal. A common sweep in this disclosure is a one-dimensional or two-dimensional sweep of a sample's region of interest by a FIB (or other milling tool). A sweep can be performed on the region of interest in one or more passes.

[0066] The term "target" refers to the desired outcome of an analysis, preparation, or manufacturing process on a sample. Non-limiting examples of targets include: features or devices to be exposed by milling the sample; coordinates to be achieved by milling the sample; regions of interest to be imaged; or orientation of processing tools relative to the sample. In some cases, a target may not be fully achievable, but it can be successfully achieved within predetermined tolerances.

[0067] The "termination condition" is the criterion for stopping the iterative process from executing further iterations.

[0068] The exposed master surface of the horizontal sample has an upward-pointing outward normal relative to it, for example, a common configuration from which the sample can be approached by the processing tool. The terms "top," "bottom," "upward," "downward," "above," "below," "horizontal," "vertical," etc., are used for convenience. The axis of the processing tool (e.g., the line of sight of an imaging tool or the beam axis of a FIB grinder) may be substantially vertical downward onto the surface, or may be tilted relative to the normal at an angle (sometimes in the range of 40° to 60°). Those skilled in the art will understand from this disclosure that the choice of actual orientation may be altered without departing from the scope of the disclosed technology.

[0069] Example devices

[0070] Figure 1 Diagram 100 shows some features of the instance device and the environment in which the device can be deployed. Milling tool 120 and imaging tool 130 can perform corresponding operations on sample 150 while communicating with controller 110. Sample 150 can be mounted on stage 160. In some instances, sample 150 and stage 160 can be part of the environment for device components 110, 120, 130; however, in other instances, stage 160 can be included as part of the device.

[0071] For ease of description, the coordinate system is shown as having Cartesian XYZ axes 141-143 and an origin 140 (“O”) on the main top surface 152 of sample 150. As illustrated, the Z-axis 143 is the outward normal to surface 152, the X-axis 141 is parallel to the longitudinal extent of groove 154, and the Y-axis 142 forms a right triaxial (XYZ) with axes 141 and 143. An azimuth angle φ is defined about the Z-axis, with the X and Y axes at φ = 0° and φ = 90°, respectively. A polar angle θ is defined downward from the Z-axis (θ = 0°), with the XY plane at θ = 90°. For descriptive purposes, the coordinate system can be fixed in the reference frame of sample 150 such that, for example, the polar angle of the beam or the coordinate position of the milled edge changes equivalently, regardless of whether rotation or translation is applied to the beam (125, 135) or to the stage and sample (150, 160).

[0072] Milling tool 120 can be configured to mill sample 150 using particle beam 125. In the illustration, tool 120 has a milling groove 154 entering from above surface 152 in directions θM123, φM121 to expose a cut surface 156 in which the cross-section of structure 158 can be discerned. In some instances, beam 125 may be a focused ion beam (FIB); however, this is not necessary, and other beams can be used. Milling can be performed by scanning beam 125 across sample 150, by translating stage 160, or by a combination of these or other movements, to achieve relative movement between beam 125 and sample 150.

[0073] Imaging tool 130 can be configured to generate one or more images of sample 150 using particle beam 135. In the illustration, imaging tool 130 can generate an image viewed directly above sample 150 (θI = 0°); however, this is not necessary and imaging can be performed from other angles. Specifically, in some instances, imaging tool 130 can be rotated relative to sample 150 to acquire another image from tilt angles θI133, φI131, as indicated by dashed arrow 137.

[0074] Controller 110 can supervise the operation of milling tool 120 and imaging tool 130. Milling can be controlled using control parameters, which can take continuous values ​​as milling progresses. In some instances, the control parameters can control the Y coordinate of the milled surface formed by sweeping beam 125 in the X direction. Thus, the control parameters can be coordinate measurements for milling tool 120 or stage 160. Alternatively, the control parameters can be indirect position control, such as voltage applied to a steering assembly in the path of beam 125, or voltage applied to an actuator coupled to perform translation of stage 160. Using a first value of the control parameters, controller 110 can cause milling tool 120 to mill sample 150 to a first edge. For illustration, the intersection of main surface 152 and cutting surface 156 defines edge 148. As beam 125 gradually mills sample 150, the extent of groove 154 can reach a first position of edge 148 (referred to as the "first edge").

[0075] The controller 110 can also use an image of the surface 152 acquired by the imaging tool 130 to determine a second value for the control parameter that differs from the first value. That is, the distance between the edge 148 and the target location can be determined from the image, and the control parameter can be changed by an amount based on this distance to obtain the second value of the control parameter. Finally, using the second value of the control parameter, the controller 110 can cause the milling tool 120 to perform additional milling to reach a second location of the edge 148 (referred to as the "second edge"), for example, to mill away an additional sample volume between the first edge and the second edge to expose the cut surface containing the second edge.

[0076] As illustrated, the edge and target positions can be located at -55nm and +10nm in the Y coordinate, respectively, thus determining a distance of 65nm. The beam steering control parameter with a Y-direction sensitivity of 10nm / Volt can be changed by 65 / 10 = 6.5V to achieve the desired second edge. In some instances, the change in control parameter can be applied gradually, for example, 0.25V applied to each of the 26 sweeps in an additional milling operation.

[0077] Many variations and extensions can be implemented within the scope of the disclosed technology. In some instances, particle beams 125 and 135 can be different types of beams and can include particles of different substances. For illustration, milling can be performed using a focused ion beam 125 including Ga+, Xe+, or another ionic substance, while imaging can be performed using a scanning electron beam 135 including electrons. In an example, the imaging tool 130 can be a scanning electron microscope; however, this is not necessary.

[0078] After milling to the second edge 148, the controller can cause the imaging tool 130 to acquire an image of the cut surface 148. In some instances, the acquired images of the top surface 152 and the cut surface 148 can be acquired from a single line of sight of the beam 135, for example, at an angle of tilt of 137. In other instances, the controller 110 can rotate the line of sight of the imaging tool 120 between two image acquisitions. For illustration, a first image (for measuring distance) of the sample 150 can be acquired by viewing it directly from above along the line of sight of the beam 135 as illustrated, and a second image (e.g., for measuring the cut surface 148) can be acquired by viewing the line of sight along arrow 137 as illustrated. In some instances, the line of sight of the first image can have a polar angle θI ≤ 10°, while the line of sight of the second image can have a polar angle 40° ≤ θI ≤ 60°.

[0079] Figure 1 Additional variants may omit certain features, or may adopt [a specific feature]. Figure 3-5 The features described in the context of the document or elsewhere in this text.

[0080] Instance geometry

[0081] Figures 2A to 2B Figures 201 to 202 depict the geometry of instances in which the disclosed technology can be deployed. Figure 2 illustrates the geometry relative to the main (top) surface 252 of the sample and... Figure 1 The coordinate system is generally similar to the diagram of a coordinate system. Orthogonal X and Y axes 241, 242 lie in the plane of surface 252, while the Z-axis 243 is perpendicular to the outward surface of surface 252. The particle beam axis 237 (which may be the line of sight of an SEM or the beam axis of a FIB milling tool) approaches surface 252 from a polar angle θ relative to the Z-axis 273; the beam axis 237 has a projection 238 in the XY plane, which is positioned at an angle φ counterclockwise from the X-axis. Therefore, φ is the azimuth coordinate of the beam axis 237. As is customary in this document, the beam axis extending outward from the origin on the sample surface (e.g., 0° ≤ θ < 90°, as...) is described. Figure 2A As shown in the figure, although the beam particles travel in the opposite direction and toward the sample surface.

[0082] Turning Figure 2B Figure 202 is a table, where each row depicts an example device configuration that can be used with the disclosed technology. The angular coordinates in Table 202 are referenced... Figure 2A Instructions. In line 281, similar to... Figure 1The beam 135 of the imaging tool directly observes the sample surface 252 downwards. The viewing axis is oriented along θI = 0°, where φI is indeterminate. The milling tool beam axis has an orientation of θM = 45° to 52° at any azimuth angle φM. In the second row 282, both the imaging tool viewing axis and the milling tool beam axis are at polar angles θI and θM in the range of 45° to 52°, however, they can be oriented 90° apart by azimuth angles. The third row 283 can be considered the opposite of the first row 281. The milling beam axis is aligned with the surface normal (Z-axis 243) such that θM = 0°, and φM is indeterminate. The imaging viewing axis is at polar angles θI = 45°-52°, and can be at any azimuth angle φI. The fourth row has beams directly oriented downwards onto surface 252 from both the imaging tool and the milling tool. In some instances, the imaging tool and the milling tool can be spatially offset from each other in the X or Y direction, and the sample can be translated on a stage between the imaging tool and the milling tool for the corresponding operation. In other instances, beam optics can be used to combine beam paths from spatially separated beam sources onto a common axis at the sample surface.

[0083] In some instances, different configurations can be combined. For example, a vertical line of sight can be used to image surface 252 to measure or control the milling progress relative to a reference structure on surface 252. Subsequently, the imaging line of sight can be tilted to perform imaging or other analyses on the cut surface exposed by milling. That is, a configuration similar to row 281 can be used to measure the milling progress, and a configuration similar to row 282 can be used to quantify, image, or perform other analyses on the resulting cut surface.

[0084] First instance method

[0085] Figure 3 This is a flowchart 300 of a first instance method for image-based feedback for milling samples. In this method, a distance is determined so that subsequent milling operations can satisfy a target position criterion using said distance.

[0086] At box 310, an image of the sample surface is acquired from the SEM. Based on the relative positions of the milled edge and the reference structure in the SEM image, the distance to the shifted milling position can be determined at box 320. At box 330, the determined distance can be stored. This distance can be used to shift the milled edge in subsequent milling operations to achieve a predetermined spatial relationship with the reference structure.

[0087] To illustrate, the milling edge and reference structure can be determined from SEM images to have Y coordinates of -55 nm and +10 nm, respectively, in which case the determined distance can be 65 nm. Other techniques can also be used to determine distances, such as to correct for perspective shortening or edge effects, or to preferably skew subsequent milling operations toward the target coordinates, as further described herein. The milling position can be further shifted by milling to remove additional material. To illustrate, if the milling edge is parallel to the X-axis at a Y coordinate of -55 nm, each successive sweep of the milling machine can remove up to 3 nm of material in the Y direction, thereby progressively shifting the milling edge to Y = -52, -49, -46 nm, and so on. In some instances, the relative Y coordinate of the milling beam axis with respect to the stage can be changed to shift the milling position during continuous milling operations.

[0088] Many variations and extensions can be implemented within the scope of the disclosed technology. In some instances, subsequent milling operations can expose the cut surface, and the method can be extended to acquire images of the cut surface from a SEM. That is, a single SEM can be used for metrology, imaging of the top surface of the sample, and then imaging of the cut surface of the sample after milling has achieved a predetermined spatial relationship relative to a reference structure.

[0089] In another example, a reference structure can define a datum. A predetermined spatial relationship can specify the tolerance range of the distance between the shifted edge (after subsequent milling operations) and the datum. For illustration, the datum can be the centroid of the reference structure located at Y = 100 μm. The predetermined spatial relationship can specify that the shifted milled edge has a shifted Y-coordinate between 90 and 95 μm; between 95 μm and 100 μm; or between 95 μm and 102 μm. In these illustrations, the datum can be outside the tolerance zone of the shifted milled edge, can be the limit (endpoint) of the tolerance zone, or can be within the tolerance zone.

[0090] In some instances, distance determination at frame 320 can involve the application of linear scaling. For example, a non-zero polar angle of the SEM's line of sight may cause perspective shortening of distances on the top surface of the image. To illustrate, if the SEM has a line of sight along θ = 45° and φ = 90° (reference...) Figure 2AIf the distance along the Y-axis is shortened by a factor of 1 / sqrt(2) = 0.7071, then the Y-interval determined from the SEM image at box 320 can be multiplied by a factor of sqrt(2) = 1.4142 to determine the actual distance the milled edge should be shifted. In another instance, an offset can be included in linear scaling (e.g., linear scaling of the form y = A·x + B). In some cases, it may be desirable to undershoot the target position and not to overshoot the target position. In short, undershoot allows another chance to meet the specified tolerance, while overshoot may cause the sample to be discarded. Therefore, incorporating a negative offset B can increase the likelihood that the third milling operation can correct the undershoot in the tolerance area if needed and reduce the likelihood of the sample being discarded due to overshoot. This negative offset may also be beneficial when there is no perspective shortening (A = 1). Specifically, process boxes 310, 320, and 330 can be repeated after a series of milling operations that include subsequent milling operations until the predetermined spatial relationship is achieved. Furthermore, the predetermined spatial relationship can be optimized on successive iterations of boxes 310, 320, and 330. For illustration, in the first iteration, the spatial relationship can be the tolerance region [0, +100 nm] relative to the target device, which can be tightened to [0, +10 nm] and [-3 nm, +3 nm] in the second and third iterations, respectively. The iterations of boxes 310, 320, and 330 can also terminate when a termination condition is met. Continuing from the previous explanation, the termination condition can be [-3 nm, +3 nm]. If the position where +2 nm is achieved in the first iteration is determined (e.g., from an image obtained at box 310 in the second iteration), no further milling or iterations are required.

[0091] The reference structure may incorporate two markers, such as two "+" markers on either side of the target device in the sample, and the centroid of the reference structure (e.g., the midpoint between the two "+" markers) can identify the location of the target device in the sample that will be exposed by subsequent milling operations. In some instances, the centroid may be located at the position of the target structure (e.g., lateral position), while in other instances, the centroid may be a known offset distance from the target structure or a reference on the target structure. The known offset distance may be a predetermined distance or may be determined at runtime through analysis or metrology operations. The predetermined spatial relationship may be a tolerance zone around the centroid of the reference structure.

[0092] As described herein, SEM images may suffer from edge effects. Edges can appear as bright lines of finite width. The actual edge location can be offset from the centerline of the bright line. This offset can depend on geometric factors (e.g., the polar angle of the imaging axis, or the dihedral angle between the cut surface and the top surface of the sample) or the sample material. Therefore, determining the distance at box 320 can include correction for edge effects. In some applications, the amount of edge effect correction can be determined empirically, for example, by performing tests on similar samples under similar conditions.

[0093] Figure 3 The method can be applied in various applications including device fabrication or sample preparation. As an example of fabrication, the method can be applied to the fabrication of a read / write transducer, where the predetermined spatial relationship can be a tolerance range relative to a reference structure, the tolerance range indicating the position of the read / write transducer within the sample. As an example of sample preparation, the method can be applied to the preparation of a sheet for TEM analysis, where the reference structure can define a central plane of the sheet, and the method can be incorporated into the process to mill two facets of the sheet on opposite sides of the central plane. For illustration, one facet can be milled to the Y-coordinate range [+8 nm, +12 nm], while the other facet can be milled (approaching from the opposite side) to the Y-coordinate range [-12 nm, -8 nm] to prepare a sheet with a thickness of 20 ± 4 nm. The method can be extended, for example, to perform subsequent milling operations using a FIB.

[0094] Figure 3 Additional variants may omit certain features, or may adopt [a specific feature]. Figure 1 or Figure 4-5 The features described in the context of the document or elsewhere in this text.

[0095] Second instance method

[0096] Figure 4 This is a flowchart 400 of a second example method for milling via image-based feedback. In this method, two milling operations are performed on a sample. An image of the sample is used to measure the edge after the first milling operation, thereby determining the control settings for the second milling operation. The control settings are parameter values ​​used to control the position of the milling operation. The parameters can control the direction of the beam used to perform the milling, the position of the stage on which the sample is mounted, or a combination of beam and sample positioning.

[0097] At process block 410, the processor can cause a milling tool to mill the sample to a first edge using a first value of the control parameters. Subsequently, at block 420, an image of the sample surface can be acquired from the SEM, the image depicting the first edge and the reference structure. At block 430, the processor can determine a second value of the control parameters based on the first value and the relative positions of the first edge and the reference structure (in the image). For illustration, if the image shows a 25 nm offset between the first edge and the reference structure in the Y direction, the second value can be set as C2 = C1 + Δ, where C1 is the first value of the control parameters, and Δ is the adjustment of the control parameters corresponding to the 25 nm shift in the Y direction. Subsequently, at block 440, the processor can cause a milling tool to mill the sample to a second edge using the second value of the control parameters.

[0098] Many variations and extensions can be implemented within the scope of the disclosed technology. The imaging surface used for frame 420 can be the main surface of the sample. The first edge can be the boundary between the imaging surface and the cut surface exposed by milling at frame 410. The dihedral angle between the imaging surface and the cut surface can be in the range of 60° to 120° or 85° to 95°. In some instances, the determination of the second value at frame 430 can include an angle correction applied to the angle between the SEM's line of sight and the normal to the sample surface.

[0099] Compensating for sidewall slope

[0100] In some cases, the plane of the cut surface can be tilted relative to the beam axis of the milling tool; this phenomenon is sometimes referred to as "sidewall slope." This can be caused by a variety of reasons, including beam spread, sample inhomogeneity, variations in etching rate with ion beam axis orientation, anisotropic etching, or geometric misalignment. For FIB milling, control procedures expected to produce a vertical cut surface (a 90° dihedral angle between the remaining portion of the sample's top surface and the cut surface) typically produce a dihedral angle greater than 90°. However, this is not always the case, and undercuts may occur in other cases, where the dihedral angle is less than 90°.

[0101] Therefore, in some instances, prior to process block 410, the processor can also cause a compensating tilt to be applied between the milling tool and the stage on which the sample is mounted. The compensating tilt controls the dihedral angle between the second cut surface and the remainder of the sample surface within a predetermined range. For illustration, the compensating tilt can result in a dihedral angle within the range of 90°±0.2°, 90°±0.5°, 90°±1°, or 90°±2°. In other words, the compensating tilt ensures that the orientation of the second cut surface meets tolerance requirements.

[0102] In another instance, the compensation tilt can be determined by the process using a test sample. The same or different processors can result in milling the test sample to the third and fourth edges. Similar to the orientation of the first edge on the (master) sample processed in boxes 410 to 440, the third edge can be oriented on the test sample. Milling to the third edge may expose a third cut surface on the test sample. The third and fourth edges may intersect at an angle ranging from 60° to 120° on the master (top) surface of the sample. Milling to the fourth edge may expose a fourth cut surface on the test sample, where the third and fourth cut surfaces intersect at a fifth edge. Therefore, observing the fourth cut surface allows for the identification of the sidewall slope. A second SEM image of the fourth cut surface can thus be obtained. The compensation tilt angle can be determined from the relative positions of the fourth and fifth edges in the second image. In different instances, the compensation tilt can be determined using the same or different milling and imaging tools as those used for boxes 410 to 440. In some instances, the test sample can be a different physical object from the master sample, while in other instances, test sample operations and master sample operations can be performed at different locations on a common wafer.

[0103] although Figure 4 The description sometimes describes a single processor, but Figure 4 Various operations, including its extensions or variations, can be performed using multiple processors in any combination. For example, different processors can perform control of milling tools, control of imaging tools, and / or metrology of SEM images.

[0104] Figure 4 Additional variants may omit certain features, or may adopt [a specific feature]. Figure 1 , 3 The features described in the context of 5 or elsewhere in this document.

[0105] The third instance method and instance stage for sample processing

[0106] Figure 5 This is flowchart 500 of the third instance method. In this method, milling operations on the sample are performed iteratively, guided by feedback from the sample image showing the current milling state relative to the target position. (See reference) Figures 6A to 6D The third method is described in diagrams 601 to 604, which show views of a sample undergoing a series of operations.

[0107] Figure 6AAn initial top view 601 of the sample 605 is shown. Markings 606A and 606B (collectively referred to as reference structure 606) are visible in top view 601. The bow-shaped device 608 is manufactured within the sample and shown in dashed outline because, in the illustrated example, device 608 is embedded within the sample and not visible in the top view. The objective in this illustrative example may be to produce a milled edge within tolerances relative to the waist of device 608 (along the Y-axis 612). The waist is flush with the centerline connecting markings 606A and 606B (with the X-axis 611). As is common in the art, each marking is shown with a cross shape, but other shapes may be used.

[0108] The method begins at block 501 and can enter the iterative loop at process block 510. At block 510, the milling position can be set. For illustration, the milling position can be relative to... Figure 6A The Y coordinates of axes 611 and 612, wherein the axes can be similar to Figure 1 Axes 141 and 142.

[0109] At box 520, the sample can be milled from above, which can be understood as having a polar angle of less than or equal to 60° (similar to...). Figure 1 The milled beam axis of 123). Figure 6B In the top view, the milled groove 624 is shown (similar to groove 154), where edge 628 corresponds to the "first edge" described in some instances herein, or Figure 1 Edge 148. Figure 6B Other features correspond to in Figure 6A The features described in the context. In different instances, milling can be performed using FIB or another type of milling tool.

[0110] At box 530, it can be, for example, along a polar angle of less than or equal to 60° (similar to...). Figure 1 The 133) axis of view images the sample from above. The image can depict something similar to... Figure 6B The features described herein are characteristic of those described. However, in some instances, the dashed outline of device 608 may not be visible because it is buried beneath the imaging surface. In other instances, the outline of buried device 608 may be visible due to corresponding changes in surface height. In yet another instance, device 608 may be visible because the top surface has been previously etched to expose device 608.

[0111] At box 540 and refer to Figure 6CThe distance 635 from edge 628 to a target location can be measured, which may be the Y-coordinate of the centerline 631 of reference structure 606. In some instances, the distance 635 from the midpoint 630 of centerline 631 to edge 628 can be measured along perpendicular line 632. In other instances, the distance 631 from the centroid of mark 606A to the extension 638 of edge 628 can be measured along perpendicular line 636. Alternatively, other measurement techniques can be used. As described herein, one or more corrections can be applied to image perspective shortening or edge effects.

[0112] At decision box 550, the completion of the iterative milling process can be checked. In some instances, the termination criterion could be whether the distance 635 is within tolerance; however, in other instances, the termination criterion could be whether a predetermined iteration count has been reached. Composite termination criteria can be used. For illustration, the iterative loop can be terminated if the distance 631 is within [-2nm, +5nm], or after 3 iterations (whichever comes first).

[0113] When it is determined that the loop iteration is incomplete, the method may follow an N-branch path from decision box 550 to process box 560, where a new milling position may be determined. For example, the new milling position may be based on the immediately preceding milling position (e.g., at box 510) and a measured distance 635. In various instances, linear scaling or edge effect correction, as described herein, may be applied. The method may return to box 510 to set the new milling position, for example, by setting control parameters of the milling tool or the translation stage supporting the sample.

[0114] Decision box 550 can also lead to the completion of a loop iteration. In some cases, the iteration can be completed after a single pass through boxes 510 to 540, while in others, it can be performed two, three, four, or even more iterations before the loop iteration is completed. Finally, upon meeting the termination criterion, the method can follow a Y-branch from box 550 to box 560 or box 570.

[0115] Figure 6D The diagram shows a top view 651, a front cross-sectional view 652 (through section line 662), and a side cross-sectional view 653 (through section line 663) of sample 605 as it exits the iteration loop from box 550 via the Y branch. As illustrated, trench 644 has been relative to... Figure 6B The groove 624 is enlarged, and the edge 648 is aligned with the center line of the reference structure 606 (in Figure 6D Not shown in the image, see [link / reference]. Figure 6C Alignment of 631). Front sectional view 652 shows the cut surface 646 (similar to 156) of the exposure device 608 (similar to 158). These features are also visible in side sectional view 653.

[0116] In some instances, the imager used at frame 530 can be rotated at an optional process frame 560 (shown in dashed outline). For illustration, similar to visual axis 135, the visual axis of frame 530 can have a polar angle close to 0° (e.g., less than 5° or less than 10°), and at frame 570, similar to visual axis 137, the visual axis can be rotated to a polar angle ranging from 45° to 52°. In other instances, a visual axis similar to 137 can be used at frame 530, and an azimuth rotation can be performed at frame 570 to bring the visual axis of the imaging tool closer to the normal (e.g., axis 142) of the cutting plane (e.g., 156). As described herein, rotation of the visual axis relative to the sample can be performed by rotating the imaging tool 130 or by rotating the stage 150 on which the sample is mounted, or by a combination of multiple rotations. Optionally, relative translation can also be performed at frame 570. However, in other instances, a line of sight with a polar angle (e.g., 133) in the range of 40° to 60° can provide sufficient imaging accuracy and resolution for both top surface imaging at frame 530 and subsequent imaging of the cut surface. In such instances, frame 570 can be omitted.

[0117] With a suitable imaging viewpoint (with or without frame 570), the cut surface of the sample can be imaged at process frame 580. Specifically, the same imaging tool can be used at frames 530 and 580. However, this is not necessary, and in some instances, different imaging tools can be used for frames 530 and 580. In certain instances, imaging at frame 580 can be performed using a FIB tool used for milling at process frame 520. In addition to or instead of imaging, other analyses or process operations can be performed on the cut surface at frame 580.

[0118] Many variations and extensions of the third method can be implemented within the scope of the disclosed technology. In some instances, blocks 510 to 540 can be performed twice (or fewer or more times) to converge at a fixed target value. Such iterations can be performed for the manufacture or analysis of device 608.

[0119] In other instances, blocks 510 through 540 can be executed iteratively to progressively traverse a series of target locations. For example, analysis of device 608 can be performed on a series of cut surfaces along the Y direction of device 608. As an illustration, it might be desirable to analyze portions of device 608 at 20nm intervals of Y = {-60nm, -40nm, -20nm, 0nm, ..., +60nm}, with an initial milling operation reaching Y = -75nm (e.g., the first pass, blocks 510, 520). The distance to the first target location can be measured as -60nm - (-75nm) = +15nm (the first pass, blocks 530, 540), and the loop can iteratively traverse blocks 560, 510, 520 to reach Y = -62nm, which, in this illustration, is within the tolerance of Y = -60nm at the first target location. Then, in the second pass, the distance to the next target location (-40nm) can be measured between blocks 530 and 560, said distance being +22nm. Additionally, imaging or other operations similar to those in box 580 can be performed before further milling in the third pass (box 520). Illustratively, the third pass can overshoot to Y = -39 nm while remaining within the tolerance range of the second target (-40 nm). Therefore, in the third pass, a distance of +19 nm to the third target (-20 nm) can be determined (third pass, boxes 530, 540), and imaging or other operations can be performed on the second target position (-40 nm) before attempting to reach the third target position (-20 nm) in the next milling operation (fourth pass, box 520). Thus, continuous iteration can progressively traverse the desired sequence of segments in Y = {-60 nm, ... +60 nm} (within predetermined tolerances), acquiring images or performing other analyses in each segment. In different instances: fixed view axis orientation can be used for both frame 520 and imaging of continuous cut surfaces; imaging or analysis performed at each segment can be performed using a different tool than the imager used for frame 520; or the imaging tool can rotate back and forth between the optimal view axis for top surface imaging and cut surface imaging.

[0120] In another instance, additional iterations of boxes 510 to 540 can be performed to converge at the location of one or more desired segments.

[0121] Figure 5 Additional variants up to 6 may omit certain features, or may adopt [a different approach]. Figure 1 or Figures 3 to 4 The features described in the context of the document or elsewhere in this text.

[0122] Example Application

[0123] Figure 7Top view 701 and front view 702 illustrate a first application of the disclosed technology. In this application, milling is performed from one side to obtain an edge at a target location or within a tolerance zone. Sample 750 has a top surface 752 on which two markings of reference structure 706 are visible. Groove 754 has been milled to edge 748, thereby exposing cut surface 756. With the disclosed technology, edge 748 can be precisely positioned relative to reference structure 706.

[0124] Figure 7 The applications can be adapted to both manufacturing and analytical workflows. In some instances, manufacturing devices can be milled to predetermined tolerances at target locations. That is, milling according to the disclosed techniques can produce devices for the precise manufacture of products. Such products can include read / write transducers for magnetic storage devices, semiconductor lasers, or microelectromechanical systems (MEMS) such as tuned oscillators. In other instances, destructive milling can be applied to expose the interior of the device for imaging, metrology, or other analytical processes. For example, doping distribution can be measured across precisely positioned slices (cut surfaces) of the device. Analysis can be performed on active or passive electronic devices that include read / write transducers, laser modules, semiconductor chips, MEMS devices, sensors, or nanostructures.

[0125] Figure 8 Top view 801 and front view 802 illustrate a second application of the disclosed technology. In this application, milling is performed from both sides to place the edges within corresponding tolerance zones relative to a reference structure. Sample 850 has a top surface 852 on which the reference structure 806 is visible. Grooves 854 and 855 have been milled to edges 848 and 849, thereby exposing two cut surfaces, one of which, 856, is visible in front view 802. Using the disclosed technology, edges 848 and 849 can be precisely placed relative to the reference structure 806, and sheets of the desired thickness can be precisely manufactured.

[0126] Figure 8 The applications can be adapted to both manufacturing and analytical workflows. In some instances, the fabrication apparatus can be precisely milled to a predetermined thickness at specific locations within the sample 850. Such products may contain sheets or other thin films for use as MEMS resonators, thin-film sensors, or sampling probes. In other instances, milling can be destructively applied to expose and develop sheets for TEM or other analytical processes. Samples suitable for sheet preparation using the disclosed techniques can be found in many fields employing MEMS, photolithography, or epitaxial fabrication techniques. Samples may contain semiconductor, optical, optoelectronic, MEMS, or advanced materials.

[0127] General Computer Environment

[0128] Figure 9This describes a general example of a suitable computing system 900, in which the described examples, techniques, and skills can be implemented to integrate microscope feedback into the milling process, for example, by determining the amount of displacement milling position. The computing system 900 is not intended to impose any limitation on the scope or functionality of this disclosure, as innovations can be implemented in a variety of general-purpose or special-purpose computing systems. The computing system 900 can control SEM imaging tools, FIB milling tools, stages, analytical instruments, or other similar devices; can perform metrological or other analyses on images or other acquired data representing samples; can control stages, ion beam trains, or electron beam trains to apply tilt or azimuth rotation between the sample mounted on the stage and the electron or ion beam; or can acquire, process, output, or store measurement data.

[0129] refer to Figure 9 The computing environment 910 includes one or more processing units 922 and memory 924. Figure 9 In this document, the basic configuration 920 is enclosed within the dashed lines. Processing unit 922 can execute computer-executable instructions, such as those for control, measurement, or other functions as described herein. Processing unit 922 can be a general-purpose central processing unit (CPU), a processor in an application-specific integrated circuit (ASIC), or any other type of processor. In a multiprocessor system, multiple processing units execute computer-executable instructions to enhance processing power. Computing environment 910 may also include a graphics processing unit or a coprocessor unit 930. Physical memory 924 can be volatile memory (e.g., registers, cache, or RAM), non-volatile memory (e.g., ROM, EEPROM, or flash memory), or some combination thereof, accessible by processing units 922 and 930. Memory 924 stores software 980 implementing one or more innovations described herein in the form of computer-executable instructions suitable for execution by processing units 922 and 930. For example, software 980 may include software 981 for controlling SEM or other imaging tools, software 982 for controlling FIB or other milling tools, software 983 for controlling the stage supporting the sample thereon, software 984 for performing metrology or other analysis on the sample data, or other software 985 (including a user interface, host interface, or fault detection). The insertion of software 980 into storage device 940 can be similarly applied. Figure 9 The software 980 is located in other parts of the system. The memory 924 can also store control parameters, calibration data, measurement data, other database data, configuration data, or operation data.

[0130] The computing system 910 may have additional features, such as one or more of a storage device 940, an input device 950, an output device 960, or a communication port 970. Interconnection mechanisms (not shown), such as buses, controllers, or networks, interconnect the components of the computing environment 910. Typically, operating system software (not shown) provides an operating environment for other software 980 executing within the computing environment 910 and coordinates the activities of the components of the computing environment 910.

[0131] The physical storage device 940 may be removable or non-removable and includes a magnetic disk, magnetic tape or cassette tape, CD-ROM, DVD, or any other medium that can be used to store information in a non-transitory manner and can be accessed in the computing environment 910. The storage device 940 stores instructions (including instructions and / or data) for implementing one or more of the innovative software 980 described herein. The storage device 940 may also store image data, measurement data, workflow sequences, reference data, calibration data, configuration data, sample data, or other databases or data structures described herein.

[0132] Input device 950 may be a mechanical, touch-sensing, or proximity-sensing input device (e.g., a keyboard, mouse, pen, touchscreen, or trackball), a voice input device, a scanning device, or another device that provides input to computing environment 910. Output device 960 may be a display, printer, speaker, optical disc writer, or another device that provides output from computing environment 910. Input or output may also be transmitted to or from a remote device via a network connection through communication port 970.

[0133] Communication port 970 enables communication with another computing entity via a communication medium. The communication medium transmits information, such as computer-executable instructions, audio or video input or output, or other data in a modulated data signal. A modulated data signal is a signal whose characteristics are set or altered in a manner similar to encoding information in a signal. By way of example and not limitation, the communication medium may be electrical, optical, RF, acoustic, or other carriers.

[0134] The data acquisition system can be integrated into the computing environment 910 as an input device 950 or coupled to the communication port 970, and may include an analog-to-digital converter or a connection to the instrument bus. The instrument control system can be integrated into the computing environment 910 as an output device 960 or coupled to the communication port 970, and may include a digital-to-analog converter, a switch, or a connection to the instrument bus.

[0135] In some instances, the computer system 900 may also include a computing cloud 990, in which instructions implementing all or part of the disclosed technology are executed. Any combination of the memory 924, the storage device 940, and the computing cloud 990 may be used to store software instructions and data of the disclosed technology.

[0136] This invention is described in the general context of computer-executable instructions (e.g., those contained in a program module) that can be executed on a computing system on a target real or virtual processor. Typically, a program module or component includes routines, programs, libraries, objects, classes, components, data structures, etc., which perform a specific task or implement a specific data type. In various embodiments, the functionality of a program module can be combined or separated as needed. The computer-executable instructions for a program module can execute within a local or distributed computing system.

[0137] The terms “computing system,” “computing environment,” and “computing device” are used interchangeably herein. Unless the context clearly indicates otherwise, no term implies any limitation on the type of computing system, computing environment, or computing device. Generally, a computing system, computing environment, or computing device may be local or distributed and may contain any combination of dedicated hardware and / or general-purpose hardware and / or virtualized hardware, as well as software that implements the functionality described herein.

[0138] General considerations

[0139] Unless the context clearly specifies otherwise, as used in this specification and claims, the singular forms “a / an” and “the” include the plural forms. Furthermore, the term “comprising” means “including”. Additionally, the term “coupled” does not exclude the existence of intermediate elements between coupled items. Moreover, as used herein, the terms “or” and “and / or” mean any combination of one or more of the phrases.

[0140] The systems, methods, and apparatus described herein should not be construed as limiting in any way. In fact, this disclosure relates to all novel and non-obvious features and aspects of the various disclosed embodiments, whether individually or in various combinations and sub-combinations formed with each other. The disclosed systems, methods, and apparatus are not limited to any particular aspect or feature or combination thereof, nor are they required to provide any one or more specific advantages or solve any one or more specific problems. Technology from any instance may be combined with one or more of the technologies described in any other instance. Any operational theory is provided for ease of explanation, but the disclosed systems, methods, and apparatus are not limited to such operational theories.

[0141] Although some operations of the disclosed methods are described in a specific order for ease of presentation, it should be understood that this descriptive approach encompasses rearrangement unless the specific language used below requires a particular order. For example, in some cases, the operations described in sequence may be rearranged or performed simultaneously. Furthermore, for simplicity, the accompanying drawings may not show the various ways in which the disclosed systems, methods, and apparatus can be used in conjunction with other systems, methods, and apparatus. Additionally, the specification sometimes uses terms such as “acquire,” “apply,” “calibrate,” “determine,” or “produce” to describe the disclosed methods. These terms are high-level abstractions of the actual operations performed. The actual operations corresponding to these terms will vary depending on the specific implementation and are readily discernible to those skilled in the art.

[0142] In some instances, values, procedures, or devices are referred to as “lowest,” “best,” “maximum,” “optimal,” “extreme,” etc. It will be understood that such descriptions are intended to indicate that a choice can be made among several or many alternatives, and that such a choice is not necessarily better, smaller, or otherwise preferred than other unconsidered alternatives.

[0143] The operational theories, scientific principles, or other theoretical descriptions of the devices or methods referred to herein are provided for the purpose of better understanding and are not intended to be limiting in scope. The devices and methods in the appended claims are not limited to those that operate in a manner described by such operational theories.

[0144] Any of the disclosed methods can be controlled or implemented as a computer-executable instruction or computer program product stored on one or more computer-readable storage media (e.g., tangible, non-transitory computer-readable storage media) and executed on a computing device (e.g., any available computing device, including tablets, smartphones, or other mobile devices containing computing hardware). A tangible computer-readable storage medium is any available tangible medium that can be accessed in a computing environment (e.g., one or more optical media such as a DVD or CD, a volatile memory component (e.g., DRAM or SRAM), or a non-volatile memory component (e.g., flash memory or hard disk drive)). Figure 9 The computer-readable storage medium includes memory 924 and storage device 940. The term computer-readable medium or computer-readable storage medium does not include signals or carrier waves. Additionally, the term computer-readable medium or computer-readable storage medium does not include a communication port (e.g., 970).

[0145] Any of the computer-executable instructions for implementing the disclosed technology, and any data created and used during the implementation of the disclosed embodiments, may be stored on one or more computer-readable storage media. The computer-executable instructions may be, for example, part of a dedicated software application or a software application accessed or downloaded via a web browser or other software application (e.g., a remote computing application). Such software may be executed using one or more networked computers, such as on a single local computer (e.g., any suitable commercially available computer) or in a networked environment (e.g., via the Internet, a wide area network, a local area network, a client-server network, a cloud computing network, or other such networks).

[0146] For clarity, only selected aspects of software-based implementations are described. Other details well-known in the art are omitted. For example, it should be understood that the disclosed technology is not limited to any particular computer language or program. For instance, the disclosed technology can be implemented in software written in Adobe Flash, C, C++, C#, Curl, Dart, Fortran, Java, JavaScript, Julia, Lisp, Matlab, Octave, Perl, Python, Qt, R, Ruby, SAS, SPSS, SQL, WebAssembly, any derivative thereof, or any other suitable programming language, or in some instances, markup languages ​​such as HTML or XML, or any combination of suitable languages, libraries, and data packages. Similarly, the disclosed technology is not limited to any particular type of computer or hardware. Certain details of suitable computers and hardware are well-known and do not need to be elaborated in this disclosure.

[0147] Furthermore, any of the software-based embodiments (including, for example, computer-executable instructions for causing a computer to perform any of the disclosed methods) can be uploaded, downloaded, or remotely accessed via suitable communication means. Such suitable communication means include, for example, the Internet, the World Wide Web, corporate intranets, software applications, cable (including fiber optic cables), magnetic communication, electromagnetic communication (including RF, microwave, infrared, and optical communication), electronic communication, or other such communication means.

[0148] Given the many possible embodiments to which the principles of the disclosed subject matter can be applied, it should be recognized that the illustrated embodiments are merely preferred examples and should not be considered as limiting the scope of the claims. Rather, the scope of the claimed subject matter is defined by the appended claims. Therefore, we claim all that appears within the scope of these claims.

[0149] Additional instances

[0150] The following numbered paragraphs describe additional examples of the disclosed techniques. The advantages belonging to any paragraph similarly apply to any paragraph that is subordinate to it.

[0151] A1. An apparatus comprising: a milling tool configured to mill a sample using a first particle beam; an imaging tool configured to generate one or more images of the sample using a second particle beam; and a controller configured to: cause the milling tool to mill the sample to a first edge using a first value of control parameters; determine a second value of the control parameters, the second value being a change from the first value based on a distance between the first edge and a target location, wherein the distance is determined from an image of the sample surface acquired by the imaging tool; and cause the milling tool to mill the sample to a second edge using the second value of the control parameters. This apparatus can advantageously place the second edge more precisely compared to having no feedback from the imaging tool.

[0152] A2. The apparatus according to paragraph A1, wherein the first particle beam and the second particle beam comprise different corresponding materials. This apparatus can advantageously utilize the superior imaging resolution of the particle material of the second particle beam to improve the accuracy of milling using the first particle beam.

[0153] A3. The apparatus according to any one of paragraphs A1 to A2, wherein the first particle beam is a focused ion beam (FIB) and the imaging tool comprises a scanning electron microscope (SEM). This apparatus can advantageously utilize the excellent imaging resolution of the SEM to improve the accuracy of milling using the FIB.

[0154] A4. The device according to any one of paragraphs A1 to A3, wherein the image is a first image, the milling to the second edge exposes the cut surface of the sample, and the controller is further configured to cause the imaging tool to acquire a second image of the cut surface of the sample. This device can advantageously acquire the second image at a more precisely positioned cut surface compared to no feedback from the imaging tool.

[0155] A5. The apparatus according to paragraph A4, wherein the orientation of the viewing axis of the imaging tool is common to both the first and second images. This apparatus can advantageously provide feedback to the milling process and acquire the second image without requiring additional operations to change the viewing axis.

[0156] A6. The device according to paragraph A4, wherein the controller is configured to rotate the visual axis of the imaging tool relative to the sample between acquiring the first image and acquiring the second image. This device can advantageously acquire first and second images, each having an optimized visual axis.

[0157] A7. The apparatus according to paragraph A6, wherein the visual axis of the imaging tool forms an angle within 10° with the surface normal when acquiring the first image, and an angle in the range of 40° to 60° with the surface normal when acquiring the second image. This apparatus configuration advantageously reduces the solid angle required for each tool, allowing more tools to enter the sample or sample chamber through the respective ports.

[0158] A8. The device according to any one of paragraphs A1 to A7, wherein the control parameters determine the sweep position of the milling tool in a direction along the surface and perpendicular to the first edge. This device configuration advantageously improves the accuracy of the milling edge coordinates in the vertical direction.

[0159] B1. A method comprising: acquiring an image of a sample surface from a scanning electron microscope (SEM); determining a distance for shifting a milling position based on the relative position of a milled edge and a reference structure in the image; and storing the distance; wherein the stored distance can be used to shift the milled edge to a predetermined spatial relationship with the reference structure in a subsequent milling operation. This method can advantageously achieve more precise placement of a second edge compared to having no feedback from the SEM image.

[0160] B2. The method according to paragraph B1, wherein the image is a first image and the method further includes: acquiring a second image from the SEM of the cut surface exposed by the subsequent milling operation. This method can advantageously acquire the second image at a more precisely positioned cut surface compared to feedback without using the first SEM image.

[0161] B3. The method according to any one of paragraphs B1 to B2, wherein the distance is a first distance, and for a second distance from (i) a datum defined by the reference structure to (ii) a line containing a displaced milled edge, the predetermined spatial relationship is a tolerance range of the second distance. This method can advantageously satisfy a tighter tolerance range or can increase the likelihood of satisfying the tolerance range compared to having no feedback from the SEM image.

[0162] B4. The method according to any one of paragraphs B1 to B3, wherein the distance is a first distance, and determining the first distance further comprises: determining a second distance from the center coordinates of the reference structure to a line containing the milled edge; and applying linear scaling to the second distance to obtain the first distance. This method can advantageously correct for image perspective shortening or edge effects, can increase the likelihood of undershoot, or can reduce the likelihood of overshoot.

[0163] B5. The method according to any one of paragraphs B1 to B4, wherein the reference structure comprises two distinct markers, and the centroid of the reference structure identifies the location of the target device in the sample that will be exposed by the subsequent milling operation. This method can advantageously improve the accuracy of target device identification compared to using a single reference marker.

[0164] B6. According to the method described in paragraph B5, the predetermined spatial relationship is a tolerance zone around the centroid of the reference structure. This method can advantageously obtain a smaller tolerance zone or can increase the likelihood of obtaining the tolerance zone compared to having no feedback from the SEM image.

[0165] B7. The method according to any one of paragraphs B1 to B6, further comprising: repeating the acquisition and determination operation after a corresponding milling operation including the subsequent milling operation until a termination condition is met. This method can advantageously provide iterative convergence to a fixed target location, or can advantageously proceed step-by-step through a series of target locations.

[0166] B8. According to the method described in paragraph B7, the repetitive operation provides convergence to a given target location on the sample. This method can advantageously reduce the possibility of overshoot when accurately reaching the target location.

[0167] B9. The method according to paragraph B7, wherein the repetitive operation is sequentially applied to a series of target locations on the sample. This method can advantageously improve the exposure of a series of cut surfaces in the sample, for example, to the accuracy of the analysis.

[0168] B10. The method according to any one of paragraphs B1 to B9, wherein the method further comprises: correcting the distance for edge effects at the first edge. This method can advantageously provide improved accuracy in distance determination.

[0169] B11. The method according to any one of paragraphs B1 to B10, wherein the sample comprises a read / write transducer. This method can advantageously provide improved dimensional control of the manufactured read / write transducer.

[0170] B12. The method according to any one of paragraphs B1 to B11, wherein the sample comprises a thin section for transmission electron microscopy. This method can advantageously provide improved thickness control of the TEM section.

[0171] B13. The method according to any one of paragraphs B1 to B12, further comprising: performing the subsequent milling operation using a focused ion beam (FIB). This method can advantageously provide improved accuracy for the subsequent FIB milling operation.

[0172] C1. One or more computer-readable storage media, wherein executable instructions are defined, which, when executed by one or more processors, initiate the one or more processors to: cause a milling tool to mill a sample to a first edge using a first value of a control parameter; acquire an image from a scanning electron microscope (SEM) depicting the first edge and a reference structure on the surface of the sample; determine a second value of the control parameter based on the first value and the relative positions of the first edge and the reference structure in the image; and cause the milling tool to mill the sample to a second edge using the second value of the control parameter. This technique can advantageously place the second edge more precisely compared to not using the image acquired from the SEM.

[0173] C2. According to one or more computer-readable storage media as described in paragraph C1, wherein determining the second value of the control parameter includes applying a correction for the angle between the view axis of the SEM and the surface normal of the sample. This method can advantageously correct for image perspective shortening.

[0174] C3. One or more computer-readable storage media according to any one of paragraphs C1 to C2, wherein the surface is the main surface of the sample, the first edge is the boundary between the main surface and a cut surface exposed by milling to the first edge, and the dihedral angle between the cut surface and the main surface is in the range of 60° to 120°. This technique can advantageously improve the placement of cut surfaces orthogonal to the top surface of the sample, or within 30° of this orthogonality.

[0175] C4. One or more computer-readable storage media according to any one of paragraphs C1 to C3, wherein milling the sample to the first and second edges respectively exposes the first and second cut surfaces of the sample, and the instructions further activate the processor to: apply a compensating tilt between the milling tool and the stage on which the sample is mounted before milling to the first edge; wherein the compensating tilt controls (i) the dihedral angle between the second cut surface and (ii) the remainder of the surface of the sample within a predetermined range. This technique can advantageously compensate for sidewall slopes to improve the accuracy of cut surface orientation.

[0176] C5. According to one or more computer-readable storage media as described in paragraph C4, wherein the sample is a first sample, the image is a first image, the SEM is a first SEM, and the instructions further activate the processor to: cause the milling tool to mill the second sample to a third edge, thereby exposing a third cut surface of the second sample; cause the milling tool to mill the second sample to a fourth edge, thereby exposing a fourth cut surface of the second sample, wherein the third and fourth edges form an angle between 60° and 120° (inclusive) on the main surface of the second sample, and wherein the third and fourth cut surfaces intersect in a fifth edge; acquire a second image of the fourth cut surface from a second SEM; and determine the compensation tilt angle from the relative positions of the fourth and fifth edges in the second image. This technique can advantageously use the second sample to improve the accuracy of cut surface orientation.

Claims

1. An apparatus comprising: A milling tool configured to mill a sample using a first particle beam; An imaging tool configured to generate one or more images of the sample using a second particle beam; as well as The controller is configured to: The milling tool is used to mill the sample to the first edge using a first value of the control parameters; A second value for the control parameter is determined, the second value changing by an amount based on the distance between the first edge and the target location, wherein the distance is determined from an image of the surface of the sample acquired by the imaging tool, and wherein the image indicates the first edge and the target location on the surface; as well as The milling tool is used to mill the sample to the second edge using the second value of the control parameter.

2. The device according to claim 1, wherein the first particle beam and the second particle beam comprise different corresponding substances.

3. The device of claim 1, wherein the first particle beam is a focused ion beam (FIB) and the imaging tool comprises a scanning electron microscope (SEM).

4. The device according to any one of claims 1 to 3, wherein the image is a first image, the milling to the second edge exposes the cut surface of the sample, and the controller is further configured to: The imaging tool acquires a second image of the cut surface of the sample.

5. The device of claim 4, wherein the orientation of the visual axis of the imaging tool is common to both the first image and the second image.

6. The device of claim 4, wherein the controller is configured to rotate the visual axis of the imaging tool relative to the sample between acquiring the first image and acquiring the second image.

7. The device of claim 6, wherein the viewing axis of the imaging tool forms an angle of less than 10° with the normal to the surface when acquiring the first image, and forms an angle in the range of 40° to 60° with the normal to the surface when acquiring the second image.

8. The device according to any one of claims 1 to 3, wherein the control parameters determine the sweep position of the milling tool in a direction along the surface and perpendicular to the first edge.

9. A method comprising: Images of the sample surface are obtained from a scanning electron microscope (SEM). as well as The distance of the shift milling position is determined based on the relative position of the milled edge and the reference structure in the image; as well as Store the distance; The stored distance can be used to shift the milled edge to a predetermined spatial relationship with the reference structure during subsequent milling operations.

10. The method of claim 9, wherein the image is a first image and the method further comprises: A second image of the cut surface exposed by the subsequent milling operation is obtained from the SEM.

11. The method of claim 9, wherein the distance is a first distance, and for a second distance from (i) a datum defined by the reference structure to (ii) a line containing a displaced milled edge, the predetermined spatial relationship is a tolerance range of the second distance.

12. The method of claim 9, wherein the distance is a first distance, and determining the first distance further comprises: Determine a second distance from the center coordinates of the reference structure to the line containing the milled edge; as well as Linear scaling is applied to the second distance to obtain the first distance.

13. The method of claim 9, wherein the reference structure comprises two distinct markers, and the centroid of the reference structure identifies the location of the target device in the sample that will be exposed by the subsequent milling operation.

14. The method of claim 13, wherein the predetermined spatial relationship is a tolerance zone around the centroid of the reference structure.

15. The method of claim 9, further comprising: The acquisition and determination operations are repeated after the corresponding milling operation that includes the subsequent milling operation until the termination condition is met.

16. The method of claim 15, wherein the repeated operation provides convergence to a given target location on the sample.

17. The method of claim 15, wherein the repeated operations are performed sequentially on a series of target locations on the sample.

18. The method according to any one of claims 9 to 17, wherein the method further comprises: The distance is corrected to address the edge effect at the milled edge.

19. The method according to any one of claims 9 to 17, wherein the sample comprises a read / write transducer.

20. The method according to any one of claims 9 to 17, wherein the sample comprises a thin slice for transmission electron microscopy.

21. The method according to any one of claims 9 to 17, further comprising: The subsequent milling operation is performed using a focused ion beam (FIB).

22. One or more computer-readable storage media, wherein executable instructions are defined, which, when executed by one or more processors, cause the one or more processors to: The milling tool is used to mill the sample to the first edge using the first value of the control parameters; Images depicting the reference structures on the surface of the first edge and the sample were acquired using a scanning electron microscope (SEM). Based on the first value and the relative positions of the first edge and the reference structure in the image, a second value of the control parameter is determined; as well as The milling tool is used to mill the sample to the second edge using the second value of the control parameter.

23. One or more computer-readable storage media of claim 22, wherein determining the second value of the control parameter includes applying a correction for the angle between the view axis of the SEM and the normal to the surface of the sample.

24. The one or more computer-readable storage media of claim 22, wherein the surface is the main surface of the sample, the first edge is the boundary between the main surface and a cut surface exposed by milling to the first edge, and the dihedral angle between the cut surface and the main surface is in the range of 60° to 120°.

25. One or more computer-readable storage media according to any one of claims 22 to 24, wherein milling the sample to the first and second edges respectively exposes the first and second cut surfaces of the sample, and the instructions further activate the processor to: This causes a compensating tilt to be applied between the milling tool and the stage on which the sample is mounted before milling to the first edge; The compensation tilt controls the dihedral angle between (i) the second cutting surface and (ii) the remainder of the surface of the sample within a predetermined range.

26. The one or more computer-readable storage media of claim 25, wherein the sample is a first sample, the image is a first image, the SEM is a first SEM, and the instructions further activate the processor to: The milling tool is used to mill the second sample to the third edge, thereby exposing the third cutting surface of the second sample; The milling tool mills the second sample to the fourth edge, thereby exposing the fourth cutting surface of the second sample, wherein the third and fourth edges form an angle between 60° and 120° on the main surface of the second sample, and wherein the third and fourth cutting surfaces intersect at the fifth edge; A second image of the fourth cutting surface is obtained from the second SEM; as well as The compensation tilt angle is determined from the relative positions of the fourth and fifth edges in the second image.

Images