Microscopic feedback for improved milling accuracy

Abstract

To disclose a method and a device for unifying measurements of an image base in a milling work flow.SOLUTION: First ion beam milling operation is performed on an edge located at a distance from a final target position on a sample. Using an SEM image of the sample, a distance between a milled edge of the sample and a reference structure is determined. An ion beam is adjusted so that second milling operation is performed to shift the milled edge to the final target position on the basis of the determined distance. Extension of a repeating procedure is disclosed. Various different geometrical structures and corrections are disclosed. There are disclosed a manufacturing application and an analysis application in various different fields, including manufacturing of a reading / writing head and preparation of a TEM sample. Another combination of an imaging tool and a milling tool can be used.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Cross - reference to Related Applications 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.

[0002] This disclosure relates to improving milling accuracy.

Background Art

[0003] Ion beam milling is increasingly being used for machining micro - scale devices and nano - scale devices. However, ion beam mills have inherent causes of positioning errors and may become difficult to meet target tolerances as device sizes continue to shrink. Therefore, improved techniques for precision milling of micro - scale devices and nano - scale devices are still needed.

Summary of the Invention

[0004] Briefly stated, the disclosed technology combines imaging and milling. Through feedback, higher accuracy specific to the imaging tool can be achieved with a milling tool having lower inherent accuracy. In an embodiment, the measured distance on an image is used to shift a pre - milled edge to a target position with an accuracy higher than that achievable with only the milling tool.

[0005] In a 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 use a first value of a control parameter to cause the milling tool to mill the sample to a first edge, and further to determine a second value of the control parameter, which is changed from the first value by an amount based on the distance between the first edge and a target position. The distance is determined from an image of the sample surface acquired by the imaging tool. The controller is further configured to use the second value of the control parameter to cause the milling tool to mill the sample to a second edge.

[0006] In some embodiments, the first and second particle beams can incorporate different species. The first particle beam can be a focused ion beam (FIB), and the imaging tool can incorporate a scanning electron microscope (SEM). The image can be a first image, and milling up to the second edge can expose the cross-section of the sample. The controller may be further configured to cause the imaging tool to acquire a second image of the cross-section of the sample. The imaging tool for acquiring the first and second images can use a common orientation of the visual axis. The controller may be configured to rotate the visual axis of the imaging tool relative to the sample between acquiring the first image and acquiring the second image. The visual axis of the imaging tool may be within 10° of the surface normal for acquiring the first image, and within 40° to 60° of the surface normal for acquiring the second image. Control parameters can determine the sweep position of the milling tool along the surface and perpendicular to the first edge.

[0007] In a second embodiment, the disclosed technique can be implemented as a method. An image of the sample surface is acquired from a scanning electron microscope (SEM). The distance to shift the milling position is determined based on the relative position of the milled edge in the image and the relative position of the reference structure. The distance is stored. The stored distance can be used during subsequent milling operations to shift the milled edge to a predetermined spatial relationship with the reference structure.

[0008] In some embodiments, the distance may be a first distance, and a given spatial relationship may be a tolerance range for the second distance. The second distance may be the distance from (i) a datum defined by the reference structure to (ii) a line containing a shifted and milled edge. In other embodiments, the distance may be a first distance, and determining the first distance may further include determining the second distance from the center coordinates of the reference structure to a line containing a milled edge. The first distance may be obtained by applying linear scaling to the second distance.

[0009] In certain embodiments, the image may be a first image, and the method may include obtaining a second image from the SEM of the cross-section exposed by a subsequent milling operation. The reference structure may include two distinct markings. The centroid of the reference structure can identify the location of the target device in the sample that will be exposed by the subsequent milling operation. A given spatial relationship may be a tolerance zone with respect to the centroid of the reference structure.

[0010] In further embodiments, the acquisition and determination operations can be repeated after each milling operation, including subsequent milling operations, until a termination condition is met. The repeated operations can provide convergence to a given target location on the sample. Alternatively or additionally, the repeated operations can successively target a series of target locations on the sample.

[0011] This method may include distance correction for edge effects at the first edge. Subsequent milling operations can be performed using the same milling tool used to create the initial milling edge. Subsequent milling operations can be performed using a focused ion beam (FIB). This method can be used to create read / write transducers or lamellae for transmission electron microscopy from a sample.

[0012] In another embodiment, the disclosed technology can be implemented as a computer-readable medium storing executable program instructions by one or more hardware processors. Upon execution of an instruction, the processors are activated to (a) use a first value of a control parameter to cause a milling tool to mill the sample to a first edge; (b) acquire an image from a scanning electron microscope (SEM) depicting the first edge and a reference structure on the surface of the sample; (c) 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 (d) use the second value of the control parameter to cause the milling tool to mill the sample to a second edge.

[0013] In some embodiments, determining the second value of the control parameter may involve applying an angle correction between the SEM's viewing axis and the normal to the sample surface. The surface may be the primary surface of the sample, the first edge may be the boundary between the primary surface and the cut surface exposed by milling up to the first edge, and the dihedral angle between the cut surface and the primary surface may be in the range of 60° to 120°.

[0014] In additional embodiments, milling a sample to a first and second edge can expose the first and second cross-sections of the sample, and the instruction may further activate the processor to apply a compensatory slope between the milling tool and the stage on which the sample is placed before milling to the first edge. The compensatory slope can be controlled so that the dihedral angle between (i) the second cross-section and (ii) the rest of the sample surface is within a predetermined range. The sample may be the first sample, the image may be the first image, and the SEM may be the first SEM. The instruction may further activate the processor to (e) mill the second sample to a third edge, thereby exposing the third cross-section of the second sample, and (f) mill the second sample to a fourth edge, thereby exposing the fourth cross-section of the second sample. The third and fourth edges can form an angle of 60° to 120° (including both endpoints) on the main surface of the second sample. The third and fourth cross-sections can intersect at the fifth edge. The instruction further activates the processor to (g) acquire a second image of the fourth cross-section from the second SEM, and (h) determine the compensation tilt angle from the relative positions of the fourth and fifth edges in the second image.

[0015] The aforementioned and other purposes, features, and advantages of this disclosure will become apparent from the following detailed description with reference to the accompanying drawings. [Brief explanation of the drawing]

[0016] [Figure 1] This is a diagram of an exemplary apparatus capable of carrying out the disclosed technology. [Figure 2A] This is a diagram showing exemplary geometry that allows the disclosed technology to be deployed. [Figure 2B] This is a diagram showing exemplary geometry that allows the disclosed technology to be deployed. [Figure 3]This is a flowchart of a first exemplary method for generating image-based feedback for milling using the disclosed technology. [Figure 4] This is a flowchart of a second exemplary method of milling using image-based feedback, based on the disclosed technology. [Figure 5] This is a flowchart of a third exemplary method of milling using image-based feedback, based on the disclosed technology. [Figure 6A] This figure shows the state of a sample during a series of operations, as illustrated by an example of the disclosed technology. [Figure 6B] This figure shows the state of a sample during a series of operations, as illustrated by an example of the disclosed technology. [Figure 6C] This figure shows the state of a sample during a series of operations, as illustrated by an example of the disclosed technology. [Figure 6D] This figure shows the state of a sample during a series of operations, as illustrated by an example of the disclosed technology. [Figure 7] A diagram illustrating the first example of use of the disclosed technology is shown. [Figure 8] A diagram illustrating a second application example of the disclosed technology is shown. [Figure 9] A generalized example of a suitable computing environment in which the described embodiments, techniques, and technologies related to imaging or milling can be carried out is illustrated. [Modes for carrying out the invention]

[0017] Introduction and Overview As technology evolves and the use of microfabrication applications increases, focused ion beam (FIB) milling has become the optimal technology. FIB milling can provide etching of any shape with a good finish over a variety of materials. FIB can be executed under program control without using a mask or custom tooling. FIB has a wide range of applications and a single FIB tool can be used for machining, imaging, and ion implantation, and various process workflows can be effectively integrated with FIB. FIB has proven to be well-suited for microfabrication tasks that require accuracy on the order of several tens of nanometers. (Accuracy below 10 nm can be achieved under low beam current conditions, but such conditions may not be practical for some microfabrication applications.) As an imaging device, some current FIB mills can provide a resolution of about 20 nm. The accuracy of FIB mills is limited by many factors, including temporal and spatial variations of the beam source, beam optics, and instabilities of the ion beam itself.

[0018] In some microfabrication applications, higher accuracy is required than can be achieved with current FIB mills. Two non-limiting examples include the manufacture of read / write heads for magnetic storage devices and the preparation of TEM samples below 20 nm.

[0019] Examples of the disclosed technology use an imaging tool with higher resolution to guide a milling tool with a lower native 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 value of the SEM imaging resolution may depend on the exact operating conditions and can be about 2 nm for some of the applications of interest in this specification or as low as 0.6 nm in other configurations. In particular, measured values of high-resolution SEM images can be used as feedback to the FIB milling process to achieve milling accuracies that are not achievable with only the milling tool.

[0020] Tests showed that the self-propelled FIB milling tool had a reproducibility of approximately ±9 nm (three standard deviations) for the cleavage sequence. By reducing or eliminating several key causes of variability, the disclosed technology was able to achieve a reproducibility of approximately ±5 nm (three standard deviations) for the cleavage sequence.

[0021] While some embodiments are described using a combination of FIB and SEM, the disclosed techniques are not limited to these specific tools. Rather, the disclosed techniques can be applied with any high-resolution imaging tool to improve the performance of any low-resolution machining or micro-machining tool.

[0022] By using the disclosed technology, the quality and reproducibility of analysis of manufactured devices, prepared samples, or cross-sections can be improved in a wide range of applications.

[0023] term The usage and meaning of all terms cited in this section apply to the entire disclosure unless otherwise explicitly indicated or contrary to the context. The following terms are extended to their related forms.

[0024] "Analysis" refers to the action used to characterize a sample. Analysis may include various forms of imaging, probe measurements of electrical properties, or non-contact measurements of particles or radiation scattering. Analytical actions may include delayering, electron backscatter analysis, electron microscopy, etching, imaging, mass spectrometry, material analysis, metrology, nanoprobing, spectroscopy, or surface treatment. Analysis can be performed on one or more layers exposed by milling during or after a milling procedure. Some analyses may require treatment of the exposed surface (e.g., by polishing) before the analysis is performed. Some analyses may require pausing the milling operation for the analysis to be performed, while other analytical techniques can be performed on the fly during milling. The instruments or equipment used to perform such operations are referred to as "analytical instruments" or simply "analytical apparatus." Some analytical instruments of interest herein incorporate scanning electron microscopes (SEMs).

[0025] The "azimuth angle" is a signed angle defined or measured around an axis from a reference plane that includes the axis. The axis may also be a rotation axis, and the azimuth angle can be changed by rotating around the axis. In some disclosed embodiments, the axis may be parallel to the rotation axis of the sample stage and perpendicular to the surface of the sample placed on the stage. Thus, the azimuth angle of the incident particle beam can be changed by rotating the stage around its sample axis. The reference plane may be perpendicular to the working surface of the sample and may include the rotation axis of the stage on which the sample is placed. Azimuth coordinates are analogous to longitude of a location on Earth.

[0026] A “beam” is a directed flow of particles or energy. Typical beams of interest in this disclosure are particle beams, such as electron beams or ion beams. A beam may have a finite range transversely to the main longitudinal direction of the flow. The “axis” of the beam is the line connecting the centroids of two or more cross-sections of the beam.

[0027] A "controller" is an electronic device coupled to one or more actuators for making changes to physical parameters, or to one or more sensors for monitoring physical parameters. Some controllers may include a microprocessor that can be programmed to execute machine-readable instructions. The descriptions of computing devices herein are generally applicable to such controllers. Such controllers may include additional electronic circuits, such as filters and amplifiers. Some controllers may include analog circuits, such as filters and amplifiers, without using a microprocessor.

[0028] A "coordinate" is a numerical value, optionally having units, that indicates the position or orientation of a point or object in space. Common coordinates can be linear (e.g., longitudinal coordinate in the direction of the beam axis) or angular (e.g., an angle in spherical coordinates). In some of the embodiments described, the coordinate indicating the position of a milled edge can be measured along the Y-axis perpendicular to the milled edge.

[0029] A "datum" is a reference line or reference point defined with respect to a sample, associated equipment, or associated coordinate system from which other features or objects can be measured. In some embodiments of this specification, the datum may be the centroid or centerline of a reference structure.

[0030] The "dihedral angle" between two planes that intersect at an edge is a positive angle within the range (0°, 180°) measured on a plane perpendicular to the edge.

[0031] "Distance" is a measure of the length between two features on or within an image of a sample. Both 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 location of a desired milled edge). The distance between two points may be the Cartesian distance between the points. The distance between a point and a line may be the length of the perpendicular from the point to the line. Distances to features with a finite range can be measured relative to the center position of the feature (e.g., the centroid). Measured distances can be corrected for imaging geometry (e.g., the tilt of the visual axis relative to the imaged surface) or for imaging artifacts (e.g., flare).

[0032] An "edge" is a line along the intersection of two surfaces where the surface normals are discontinuous. In some disclosed embodiments, an edge can be formed between the main surface of a sample and the cut surface exposed by milling. Such an edge may move due to continuous milling operations.

[0033] "Edge effect" is an artifact in an image that arises from the edges of the imaged sample. In SEM images, edges may appear brighter than adjacent intersecting surfaces (sometimes called "flare").

[0034] An "electron beam" is a directional flow of electrons.

[0035] An electron microscope is a type of analytical instrument that irradiates a sample with an electron beam and uses the resulting particles or electromagnetic radiation to form a spatially resolved image. A scanning electron microscope (SEM) images the sample surface based on reflected particles, secondary particles, or backscattered particles or radiation from one or more surfaces of the sample. Because the beam interaction detected by the SEM occurs at or near this surface, the SEM can operate on samples of any thickness. In contrast, a transmission electron microscope (TEM) images the sample volume based on transmitted electrons (including scattered electrons). TEMs operate on samples with a thickness of approximately 10–150 nm. The sample can be placed on a grid for mechanical support and thermal conductivity, and the grid can then be held in a sample holder. TEMs can provide magnifications of 50 million times or more, while the magnification of an SEM is typically limited to about 2 million times. In this disclosure, a scanning transmission electron microscope (STEM) that images transmitted electrons is considered to be both an SEM and a TEM. The electron beam in an electron microscope is generated by an electron gun and can be accelerated, focused, or manipulated through a series of stages toward the sample chamber.

[0036] The term "exposure" refers to the action of bringing the internal features of a sample to the surface of the sample by removing the material between the pre-embedded features of the sample and the surface.

[0037] A focused ion beam ("FIB") is an ion beam whose focus can be controlled to direct the beam to a spot on a surface, or which can be swept over a sample in a sweep pattern. FIBs can be used for the analysis, deposition, or removal of materials at an incident spot. Some FIBs are used for milling. Typically, FIBs contain positive elemental ions such as Xe+ or Ga+, but these are not requirements. Ion beam species such as Ga+ can be supplied from, for example, a liquid metal ion source (LMIS), while other ion beam species such as Xe+ can be generated in a plasma. FIBs generated in a plasma source can be called plasma focused ion beams (PFIBs).

[0038] The term “imaging” refers to the process of obtaining a two-dimensional representation (called an “image”) of parameter values ​​across a region of interest of a sample. In some embodiments, the imaged parameter may be the reflectance of an incident particle beam (e.g., by a SEM), but this is not a requirement, and visible light or other parameters can also be imaged. In the disclosed embodiments, the image may show features such as edges or reference structures on the sample. In further embodiments, the region of interest may include at least a portion of one or more surfaces of the sample.

[0039] The “imaging tool” is an imaging device. In the disclosed embodiments, a SEM can be used as the imaging tool. However, this is not a requirement, and other high-resolution imaging tools can also be used, such as an atomic force microscope or a super-resolution optical microscope (e.g., using time-varying or fluorescence techniques). While a FIB tool can perform imaging, a SEM or other techniques can achieve better spatial resolution. The “visual axis” is the straight line through which the imaging tool views the imaged region of interest. Specifically, in the case of an imaging tool that directs a beam over the imaged region of interest, the visual axis can be the beam axis passing through the center point (e.g., the centroid) of the imaged region of interest.

[0040] The term "iteration" refers to each of the multiple times a given action, or a series of actions, is performed. A series of iterations is called a "loop." Loops that can be repeated multiple times may sometimes be able to be repeated only once. In a loop iteration, it is not necessary to perform all the actions within the loop, but the loop can terminate or exit early if the termination condition is met.

[0041] A "lamella" is a thin sample imaged using a transmission electron microscope (TEM). Lamellars can have a thickness in the range of 10–50 nm or 20–30 nm.

[0042] The term "linear scaling" refers to the operation y = A·x + B, which is performed on the input x to obtain the output y, where A and B are constants.

[0043] Milling is a process of removing material along a path, guided by the movement (sometimes called sweeping) of a milling tool relative to the sample being milled. The milling operation can expose one or more "cut surfaces" of a sample by removing material up to one side of the cut surface. Generally, cut surfaces intersect the main surface of the sample. The bottom of a trench with a rectangular or trapezoidal cross-section is not called a cut surface. In examples, milling can be performed using a focused ion beam (FIB). Milling is a form of etching, and more generally, refers to a removal process for removing material from a sample. Diffusion chemical etching may not be considered milling. However, ion beam-assisted chemical etching can be considered milling because it may be site-specific in terms of the ion beam's position. A "milling tool" is a device capable of milling.

[0044] A "parameter" is a quantity that can have a specific "value". Often, parameters are numerical, but this is not a requirement; 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 sensing 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, and may include beam steering control, stage positioning control, and the like.

[0045] A “particle beam” is a beam that includes a directed flow of particles. A “particle” is an unrefined, distinct unit of a flow of matter. In this disclosure, particles of common interest include, but are not limited to, charged particles such as electrons or ions (such as Ga, Xe, or protons). Electrons in an electron beam are considered a different species from ions in an ion beam, despite some ions containing bound electrons. In some embodiments, particles of interest are limited to species with mass, such as electrons or ions. In other embodiments, particles of interest may include photons with zero mass. For example, a pulsed laser beam (e.g., a “femtosecond laser” with a pulse duration of less than 1 picosecond) can be used for milling in applications of the disclosed technology.

[0046] A "polar angle" is an unsigned angle defined or measured away from an axis. The axis can be the instrument axis, the beam axis, or the normal to the sample surface. The polar angle is analogous to the complement of latitude for a location on Earth; that is, the polar angle is equal to 0° at the North Pole (latitude 90°N) and equal to 90° at the equator (latitude 0°). Some polar angles of interest in this specification are about 0°, or about 45°–52°. Some polar angles of interest in this specification are between the normal to the sample surface (which may be parallel to the rotation axis of the stage supporting the sample) and the axis of the particle beam incident on the sample.

[0047] A “read / write transducer” (or “read / write head”) is a device capable of reading and writing magnetically encoded data on a magnetic storage medium. Data can be written using the magnetic field generated when an electric current is driven through the transducer. Data can be read using a voltage induced in the transducer by the magnetic field provided by the magnetized domains of the magnetic storage medium. Some embodiments of the disclosed technology can be used to precisely mill the cross-section of a read / write transducer for measurement or manufacturing purposes.

[0048] A "reference structure" (sometimes called a "reference") is a structure fabricated on a sample for use in determining the location of another structure or device within the sample. Some reference structures may include multiple distinct elements (called "markings"), for example, on the opposite side of a target device. Reference structures can be seen in images of the structure and can be used as a reference for measuring the coordinates, distances, or angles of other features in the image. Reference structures can be two-dimensional features on the sample surface or they may have a three-dimensional extension to the depth of the sample, so that the reference structure remains visible even if a continuous layer of the surface is etched away.

[0049] A "Region of Interest" (ROI) is a portion of the sample surface scanned by an electron beam, and / or an area of ​​the sample that includes features or structures, such as a target, i.e., the object of subsequent analysis. The term ROI does not refer to any human interest.

[0050] "Rotation" is a change in the angular orientation of an object relative to another object or a fixed coordinate system. In some embodiments, the tool axis (e.g., the visual axis or beam axis of a process tool) can be rotated relative to the sample. Rotation can be performed by rotating all or part of the process tool, manipulating the beam, rotating the sample, or any combination of the above. A rotation that changes the polar angle is called "tilting" with respect to that polar angle.

[0051] A “sample” is a physical object on which imaging, milling, or other analytical or manufacturing procedures are performed. A typical sample may incorporate multilayer electrical or electronic structures or other material structures and is manufactured or prepared for imaging or another analytical procedure. The “primary surface” of a sample is the surface of the sample whose area does not substantially exceed that of any other surface of the sample. For convenience of explanation, a sample is considered to have a top primary surface and a bottom primary surface, with the bottom surface supported on a stage and the top surface exposed to one or more tools or beams.

[0052] A “spatial relationship” can be any relationship between the positions or orientations of two or more objects. One or more of the spatially related objects may be a sample, a feature of a sample, a process tool or its beam or components, a stage on which the sample is placed, an axis or normal to such a physical object, or a hypothetical geometric essence defined by one or more such physical objects (e.g., the centroid of a sample feature, or a line connecting two features). In some cases, a “tolerance” can be used to specify a range of tolerance for the quantity defining the spatial relationship. A tolerance may be one-dimensional (called a “tolerance range”) or multi-dimensional (called a “tolerance zone”), such as distance or angle, within a given range. Non-restrictive examples of tolerance zones include a feature in a two-dimensional area or three-dimensional volume relative to one or more other features, or a visual axis or beam axis in a two-dimensional pyramid with respect to another direction.

[0053] A "stage" is a device on which a sample can be mounted and which has actuators for adjusting the position or orientation of the sample. A "multi-axis stage" has multiple degrees of freedom and provides spatial adjustment of the sample through various combinations of translation and rotation.

[0054] The term "sweep" refers to spatial traversal. A typical sweep in this disclosure is a one-dimensional or two-dimensional sweep of a FIB (or other milling tool) over a region of interest of a sample. The sweep can be performed in one or more passes over the region of interest.

[0055] The term "target" refers to the desired object of an analysis, preparation, or manufacturing procedure for a sample. Non-limiting examples of targets include features or devices exposed by milling the sample, coordinates reached by milling the sample, regions of interest to be imaged, and orientations for setting process tools relative to the sample. In some cases, the target may not be precisely achieved, but may be successfully achieved within a given tolerance.

[0056] A "termination condition" is the criterion by which an iterative process stops executing further iterations.

[0057] Terms such as “top,” “bottom,” “up,” “down,” “above,” “below,” “horizontal,” and “vertical” are used for convenience for common configurations where the exposed main surface of a horizontal sample has an upward outward normal, for example, when the sample is easily accessible from above for a process tool. The axis of the process tool (e.g., the visual axis of an imaging tool, or the beam axis of a FIB mill) may be substantially perpendicular downward to the surface, or it may be tilted at some angle (possibly in the range of 40° to 60°) with respect to the normal. Those skilled in the art will understand from this disclosure that the actual choice of orientation can be modified without departing from the scope of the disclosed art.

[0058] Exemplary device Figure 1 is a diagram of an exemplary apparatus, shown with some features of the environment in which the apparatus can be deployed. Communicating with the controller 110, the milling tool 120 and the imaging tool 130 can perform their respective operations on the sample 150. The sample 150 can be placed on the stage 160. In some embodiments, the sample 150 and the stage 160 may be part of the environment for the apparatus components 110, 120, and 130, and in other embodiments, the stage 160 may be included as part of the apparatus.

[0059] For the sake of clarity, a coordinate system is shown on the main top surface 152 of sample 150, having Cartesian XYZ axes 141-143 and the origin 140 ("O"). As illustrated, the Z axis 143 is the outward normal to surface 152, the X axis 141 is parallel to the longitudinal direction of slot 154, and the Y axis 142, together with axes 141 and 143, forms an orthogonal triad (XYZ). The azimuth angle φ is defined around the Z axis, with the X and Y axes having φ=0° and φ=90°, respectively. The polar angle θ is defined downward from the Z axis (θ=0°), with the XY plane having θ=90°. For illustrative purposes, the coordinate system can be fixed to the reference frame of sample 150, so that, for example, the polar angle of the beam, or the coordinate position of the milled edge, changes equally regardless of whether rotation or translation is applied to the beam (125, 135), or the stage (160) and sample (150).

[0060] The milling tool 120 may be configured to mill a sample 150 using a particle beam 125. In the illustrative figure, the tool 120 has a milled slot 154 that enters from above the surface 152 from a direction θM123, φM121, exposing a cut surface 156 that can identify a cross-section of the structure 158. In some embodiments, the beam 125 may be a focused ion beam (FIB), but this is not a requirement and other beams can be used. Milling can be performed by translating the stage 160 by scanning the beam 125 across the sample 150 to achieve relative motion between the beam 125 and the sample 150, or by any combination of these motions or other motions.

[0061] The imaging tool 130 may be configured to generate one or more images of the sample 150 using the particle beam 135. In the illustrative diagram, the imaging tool 130 can generate an image viewed from directly above the sample 150 (θI=0°), but this is not a requirement, and imaging can be performed from other angles. Specifically, in some embodiments, the imaging tool 130 can be rotated relative to the sample 150 to acquire another image from an oblique angle θI133, φI131, as indicated by the dashed arrow 137.

[0062] The controller 110 can monitor the operation of the milling tool 120 and the imaging tool 130. Milling can be controlled using a control parameter that can take continuous values ​​as milling progresses. In some embodiments, the control parameter can control the Y coordinate of the milled surface formed by sweeping the beam 125 in the X direction. Thus, the control parameter can be a coordinate scale of either the milling tool 120 or the stage 160. Alternatively, the control parameter can be an indirect position control, such as a voltage applied to a steering component in the path of the beam 125, or a voltage applied to an actuator coupled to perform translation of the stage 160. Using a first value of the control parameter, the controller 110 can cause the milling tool 120 to mill the sample 150 to a first edge. For example, the intersection of the main surface 152 and the cutting plane 156 defines the edge 148. As beam 125 gradually mills sample 150, the range of slot 154 can reach a first position on edge 148 (referred to as the "first edge").

[0063] The controller 110 can also use the image of the surface 152 acquired by the imaging tool 130 to determine a second value for the control parameter, which is different from the first value. That is, the distance between the edge 148 and the target position 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 for the control parameter. Finally, using the second value for the control parameter, the controller 110 can cause the milling tool 120 to perform additional milling to reach a second position of the edge 148 (referred to as the "second edge"), and, for example, mill away an additional sample volume between the first and second edges to expose the cross-section containing the second edge.

[0064] As an example, the edge and target positions may be at Y-coordinates -55nm and +10nm, respectively, and therefore a distance of 65nm can be determined. With a Y-direction sensitivity of 10nm / volt, the beam steering control parameter can be varied by 65 / 10 = 6.5 volts to bring about the desired second edge. In some embodiments, the change to the control parameter is applied gradually; for example, 0.25V can be applied to each of the 26 sweeps of an additional milling operation.

[0065] Numerous modifications and extensions can be implemented within the scope of the disclosed technology. In some embodiments, the particle beams 125 and 135 may be different types of beams and may contain different species of particles. For example, milling may be performed with a focused ion beam 125 containing Ga+, Xe+, or another ion species, and imaging may be performed with a scanning electron beam 135 containing electrons. In embodiments, the imaging tool 130 may be a scanning electron microscope, but this is not a requirement.

[0066] After milling up to the second edge 148, the controller can cause the imaging tool 130 to acquire an image of the cross-section 148. In some embodiments, the acquired images of the top surface 152 and the cross-section 148 can be acquired from a single viewing axis of the beam 135, at an oblique angle such as 137. In other embodiments, the controller 110 can rotate the viewing axis of the imaging tool 120 between the two image acquisitions. For example, the first image (for measuring distance) can be acquired on a viewing axis along the beam 135, as shown in the figure, while viewing the sample 150 from directly above, and the second image (for measuring the cross-section 148, for example) can be acquired on a viewing axis along arrow 137, as shown in the figure. In some embodiments, the viewing axis of the first image can have a polar angle θI ≤ 10°, and the viewing axis of the second image can have a polar angle 40° ≤ θI ≤ 60°.

[0067] Further modifications of Figure 1 may omit certain features or adopt features described in Figures 3-5 or in relation to other parts of this specification.

[0068] Exemplary Geometry Figures 2A–2B are diagrams 201–202 illustrating exemplary geometries from which the disclosed technology can be deployed. Figure 2 illustrates a coordinate system for the main (upper) surface 252 of the sample, which is substantially similar to the coordinate system in Figure 1. The orthogonal X-axis 241 and Y-axis 242 lie in the plane of the surface 252, and the Z-axis 243 is the outer surface perpendicular to the surface 252. The particle beam axis 237 (which may be the SEM's viewing axis or the beam axis of the FIB milling tool) approaches the surface 252 from a polar angle θ with respect to the Z-axis 273. The beam axis 237 has a projection 238 located in the XY plane at an angle φ counterclockwise from the X axis. Thus, φ is the azimuthal coordinate of the beam axis 237. By convention in this specification, even though the beam particles are traveling in opposite directions and toward the sample surface, the beam axis is described as extending outward from the origin on the sample surface (for example, 0° ≤ θ < 90°, as shown in Figure 2A).

[0069] Referring to Figure 2B, Table 202 is a table in which each row shows an exemplary instrument configuration in which the disclosed technology can be used. The angular coordinates in Table 202 are shown with reference to Figure 2A. In the first row 281, the imaging tool looks directly down at the sample surface 252, similar to beam 135 in Figure 1. The orientation of the visual axis is along θI=0°, where φI is indeterminate. The beam axis of the milling tool has an orientation θM=45°~52° at an arbitrary azimuth angle φM. In the second row 282, both the visual axis of the imaging tool and the beam axis of the milling tool can have azimuth orientations that are 90° apart, but at polar angles θI, θM in the range of 45°~52°. The third row 283 can be considered the inverse 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 axis is at a polar angle θI = 45° to 52° and can be at any azimuth angle φI. The fourth row has beams for both the imaging tool and the milling tool, oriented directly downward on surface 252. In some embodiments, 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 their respective operations. In other embodiments, a beam optics system can be used to integrate beam paths from spatially separated beam sources onto a common axis on the sample surface.

[0070] In some embodiments, different configurations can be combined. For example, the surface 252 can be imaged using the vertical viewing axis to measure or control the progress of milling relative to a reference structure on the surface 252. Subsequently, the viewing axis of the image can be tilted to perform imaging or other analysis on the cross-section exposed by the milling. In other words, a configuration similar to row 281 can be used to measure the progress of milling, and a configuration similar to row 282 can be used for measurement, imaging, or other analysis of the resulting cross-section.

[0071] First exemplary method Figure 3 is a flowchart 300 of a first exemplary method for providing image-based feedback for milling a sample. In this method, a distance is determined such that a subsequent milling operation can satisfy a target position criterion.

[0072] In block 310, an image of the sample surface is acquired from the SEM. In block 320, the distance to shift the milled position can be determined based on the relative position of the milled edge in the SEM image and the relative position of the reference structure. In block 330, the determined distance can be stored. This distance can be used to shift the milled edge during subsequent milling operations to achieve a predetermined spatial relationship with the reference structure.

[0073] For example, the milled edge and reference structure can be determined from the SEM image to have Y coordinates of -55 nm and +10 nm, respectively. In this case, the determined distance may be 65 nm. As further described herein, other techniques can be used to determine the distance, for example, by shortening or correcting for edge effects, or by shifting subsequent milling operations toward the target coordinates in preference. The milling position can be shifted by further milling, removing additional material. For example, if the milled edge is parallel to the X axis at a Y coordinate of -55 nm, each of the continuous sweeps of the mill can remove up to 3 nm of material in the Y direction, gradually shifting the milled edge to Y = -52, -49, -46 nm, etc. In some embodiments, the Y coordinate of the milling beam axis relative to the stage can be changed to shift the milling position when a continuous milling operation is performed.

[0074] Numerous modifications and extensions can be implemented within the scope of the disclosed technology. In some embodiments, a subsequent milling operation can expose the cross-section, and this method can be extended to acquiring images of the cross-section from a SEM. That is, a single SEM can be used to perform measurements, image the top surface of the sample, and then image the cross-section of the sample after the milling has reached a predetermined spatial relationship with respect to a reference structure.

[0075] In further embodiments, the reference structure can define a datum. A given spatial relationship can specify a tolerance range for the distance between shifted edges (following a subsequent milling operation) relative to the datum. For example, the datum may be the centroid of the reference structure at Y=100μm. The given spatial relationship can specify that the shifted and milled edges have shifted Y coordinates of 90μm–95μm, 95μm–100μm, or 95μm–102μm. In these illustrative diagrams, the datum may be outside the tolerance zone of the shifted and milled edges, at the limit of the tolerance zone (endpoint), or within the tolerance zone.

[0076] In some embodiments, distance determination in block 320 may involve the application of linear scaling. For example, a non-zero pole angle of the SEM's visual axis may result in a shortened distance on the imaged upper surface. To illustrate, if the SEM has a visual axis along θ=45° and φ=90° (see Figure 2A), the distance along the Y axis can be shortened by a coefficient of 1 / sqrt(2) = 0.7071. Therefore, to determine the true distance at which the milled edge should be shifted, the Y distance determined from the SEM image in block 320 may be multiplied by a coefficient of sqrt(2) = 1.4142. In further embodiments, the offset may be included in linear scaling (e.g., linear scaling of the form y=A·x+B). In some scenarios, it may be desirable to undershoot the target position, and it may be undesirable to overshoot the target position. Simply put, undershoot gives another opportunity to meet a specified tolerance, while overshoot may result in the sample being discarded. Therefore, incorporating a negative offset B increases the likelihood that a third milling operation can correct undershoot of the tolerance zone as needed, and reduces the likelihood of sample discard due to overshoot. Such a negative offset may also be beneficial when there is no shortening (A=1). Specifically, processing blocks 310, 320, and 330 can be repeated after a series of milling operations, including subsequent milling operations, until a predetermined spatial relationship is achieved. Furthermore, the predetermined spatial relationship can be improved through successive iterations of blocks 310, 320, and 330. For example, in the first iteration, the spatial relationship may be a tolerance zone [0, +100 nm] for the target device, narrowed to [0, +10 nm] in the second iteration, and to [-3 nm, +3 nm] in the third iteration. The iterations of blocks 310, 320, and 330 can also be terminated when termination conditions are met. Continuing from the previous example, the termination condition could be [-3nm, +3nm]. If it is determined that the position +2nm is achieved in the first iteration (for example, from the image acquired in block 310 of the second iteration), no further milling or iterations are necessary.

[0077] The reference structure can incorporate two markings. For example, two "+" markings on either side of a target device in a sample, and the centroid of the reference structure (e.g., the midpoint between the two "+" markings) can identify the position of the target device in the sample, which will be exposed by a subsequent milling operation. In some embodiments, the centroid may be at the position of the target structure (e.g., lateral position), and in other embodiments, the centroid may be at a known offset distance from the target structure or a datum on the target structure. The known offset distance may be a predetermined distance or may be determined at runtime by an analysis or measurement operation. The predetermined spatial relationship may be a tolerance zone with respect to the centroid of the reference structure.

[0078] As described herein, SEM images may be subject to edge effects. Edges may appear as emission lines with finite width. The actual edge position may be offset from the center line of the emission line. The offset may depend on geometric factors (e.g., the polar angle of the imaging axis, or the dihedral angle between the cross-section and the top surface of the sample) or the sample material. Therefore, determining the distance in block 320 may include correcting for edge effects. In some applications, the amount of edge effect correction can be determined empirically, for example, by tests performed on similar samples under similar conditions.

[0079] The method shown in Figure 3 can be applied to a variety of applications, including device manufacturing or sample preparation. As an example of manufacturing, the method can be applied to the manufacture of a read / write transducer, where a given spatial relationship can be a tolerance range relative to a reference structure 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 lamellae for TEM analysis, where a reference structure can define the central plane of the lamellar, and the method can be incorporated into a procedure for milling two cross-sections of the lamellar opposite the central plane. For example, one cross-section can be milled to a Y-coordinate range [+8nm, +12nm], and the other surface (approaching from the opposite side) can be milled to a Y-coordinate range [-12nm, -8nm] to prepare a lamellar with a thickness of 20±4nm. The method can be extended to perform subsequent milling operations using, for example, a FIB.

[0080] Further variations of Figure 3 may omit certain features or adopt features described in relation to Figure 1, or Figures 4-5, or other parts of this specification.

[0081] Second exemplary method Figure 4 is a flowchart 400 of a second exemplary method of milling using image-based feedback. In this method, two milling operations are performed on a sample. Using an image of the sample, the edges are measured 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 steering of the beam used to perform the milling, the position of the stage on which the sample is placed, or a combination of beam and sample positioning.

[0082] In processing block 410, the processor can use a first value of the control parameter to instruct the milling tool to mill the sample up to a first edge. Next, in block 420, an image of the sample surface can be acquired from the SEM, which depicts the first edge and the reference structure. In block 430, the processor can determine a second value of the control parameter based on the first value, as well as the relative positions of the first edge and the reference structure (in the image). For example, if the image shows a 25 nm offset in the Y direction between the first edge and the reference structure, the second value can be set to C2 = C1 + Δ, where C1 is the first value of the control parameter and Δ is the adjustment amount of the control parameter corresponding to the 25 nm shift in the Y direction. Next, in block 440, the processor can use the second value of the control parameter to instruct the milling tool to mill the sample up to a second edge.

[0083] Numerous modifications and extensions can be implemented within the scope of the disclosed technology. The surface imaged in block 420 may be the primary surface of the sample. The first edge may be the boundary between the primary surface and the cross-section exposed by milling in block 410. The dihedral angle between the imaged surface and the cross-section may be in the range of 60° to 120°, or 85° to 95°. In some embodiments, determining the second value in block 430 may include applying an angle correction between the SEM's viewing axis and the normal to the sample's surface.

[0084] Compensation for side wall inclination In some scenarios, the plane of the cut surface may be inclined with respect to the beam axis of the milling tool; this phenomenon is sometimes called "sidewall inclination." This can occur for a variety of reasons, including beam spreading, sample heterogeneity, variations in etching rate due to ion beam axis orientation, anisotropic etching, or geometric misalignment. In the case of FIB milling, a control program aimed at producing a perpendicular cut surface (e.g., a 90° dihedral angle between the rest of the sample's top surface and the cut surface) can typically result in dihedral angles greater than 90°. However, this is not always the case, and in other instances, undercuts with dihedral angles less than 90° may occur.

[0085] Therefore, in some embodiments, the processor may also apply a compensatory slope between the milling tool and the stage on which the sample is placed, prior to the processing block 410. The compensatory slope can control the dihedral angle between the second cut surface and the rest of the sample surface to be within a predetermined range. For example, the compensatory slope may result in a dihedral angle in the range of 90°±0.2°, 90°±0.5°, 90°±1°, or 90°±2°. In other words, the compensatory slope can enable tolerance requirements to be met regarding the orientation of the second cut surface.

[0086] In further embodiments, the compensatory slope can be determined by a procedure using a test sample. The same or different processors can be used to mill the test sample up to the third and fourth edges. The third edge can be oriented on the test sample in the same way as the orientation of the first edge on the (main) sample processed in blocks 410-440. Milling up to the third edge can expose a third cross-section on the test sample. The third and fourth edges can intersect at an angle in the range of 60° to 120° on the main (upper) surface of the sample. Milling up to the fourth edge can expose a fourth cross-section on the test sample, with the third and fourth cross-sections intersecting at the fifth edge. Thus, the sidewall slope can be identified by observing the fourth cross-section. Thus, a second SEM image of the fourth cross-section can be obtained. The compensatory slope angle can be determined from the relative positions of the fourth edge and the fifth edge in the second image. In various embodiments, the determination of the compensatory slope can be performed using the same or different milling and imaging tools used in blocks 410-440. In some embodiments, the test sample may be a separate physical object from the main sample, and in other embodiments, the test sample operation and the main sample operation can be performed at separate locations on a common wafer.

[0087] While the explanation in Figure 4 sometimes describes a single processor, the various operations in Figure 4, and some of its extensions or variations, can be performed using multiple processors in any combination. For example, separate processors may perform tasks such as controlling milling tools, controlling imaging tools, and / or measuring SEM images.

[0088] Further variations of Figure 4 may omit certain features or adopt features described in relation to Figures 1, 3, or 5, or elsewhere in this specification.

[0089] Third exemplary method and exemplary step of sample processing Figure 5 is a flowchart of the third exemplary method. In this method, the milling operation on the sample is performed iteratively and guided by feedback from an image of the sample indicating the current milling state relative to the target position. The third method is described with reference to Figures 6A-6D, which are Figures 601-604, showing a diagram of the sample on which the series of operations are performed.

[0090] Figure 6A shows the first top view 601 of sample 605. Markings 606A and 606B (collectively, reference structure 606) can be seen in top view 601. In the illustrated embodiment, device 608 is embedded within the sample and may not be visible in the top view; therefore, the bow-tie shaped device 608 is fabricated within the sample and indicated by a dashed contour line. The objective of this illustrated embodiment may be to generate a mill edge within a tolerance range (along the Y-axis 612) for the neck of device 608. The neck is at the same height as the center line connecting markings 606A and 606B (coinciding with the X-axis 611). Each marking is shown to have a cross shape, as is common in the art, but other shapes may also be used.

[0091] This method starts in block 501, and from there, it can enter an iterative loop in processing block 510. In block 510, the milling position can be set. For example, the milling position may be the same as axes 141 and 142 in Figure 1, or it may be the Y coordinate relative to axes 611 and 612 in Figure 6A.

[0092] In block 520, the sample can be milled from above, which can be understood as a milling beam axis having a polar angle of 60° or less (similar to 123 in Figure 1). In Figure 6B, the milled trench 624 (similar to slot 154) appears in the top view along with edge 628, which corresponds to the “first edge” described in the specific example herein, or edge 148 in Figure 1. Other features of Figure 6B correspond to features described in relation to Figure 6A. In various embodiments, milling can be performed using a FIB or another type of milling tool.

[0093] In block 530, for example, the sample can be imaged from above along a visual axis having an extreme angle of 60° or less (similar to 133 in Figure 1). The image can depict features similar to those illustrated in Figure 6B. However, in some embodiments, the device 608 with the dashed contour may not be visible because it is embedded beneath the imaged surface. In other embodiments, the contour of the embedded device 608 may be visible due to corresponding surface height variations. In further embodiments, the device 608 may be visible because the top surface is pre-etched to expose the device 608.

[0094] Referring to Figure 6C, in block 540, a distance 635 can be measured from edge 628 to a target position which can be the Y-coordinate of the centerline 631 of the reference structure 606. In some embodiments, the distance 635 can be measured along a perpendicular 632 from the midpoint 630 of the centerline 631 to edge 628. In other embodiments, the distance 631 can be measured along a perpendicular 636 from the centroid of marking 606A to the extension 638 of edge 628. Alternatively, other measurement techniques may be used. As described herein, one or more corrections can be applied to the image for shortening or edge effects.

[0095] The decision block 550 can be used to check whether the iterative milling procedure is complete. In some embodiments, the termination criterion may be whether the distance 635 is within tolerance, and in other embodiments, the termination criterion may be whether a predetermined number of iterations has been reached. A combined termination criterion can be used. For example, the iterative loop can be terminated if the distance 631 is within [-2nm, +5nm] or after 3 iterations, whichever comes first.

[0096] If it is determined that the loop iteration is not complete, the method can follow N branches from the decision block 550 to the processing block 560, where a new milling position can be determined. For example, the new milling position can be based on the previous milling position (e.g., in block 510) and the measurement distance 635. In various examples, linear scaling or edge effect correction can be applied, as described herein. The method can return to block 510 and set the new milling position, for example, by setting the control parameters of the milling tool or the control parameters of the translation stage supporting the sample.

[0097] Decision block 550 can also determine that the loop iteration is complete. In some cases, the iteration may be completed after passing through blocks 510-540 once, but in other cases, it may take two, three, four, or more iterations before the loop iteration is complete. When the termination criteria are finally met, the method can follow a Y branch from block 550 to either block 560 or block 570.

[0098] Figure 6D shows a top view 651, a front section view 652 (through cutting line 662), and a side section view 653 (through cutting line 663) of sample 605 as it exits the iterative loop via a Y branch from block 550. As illustrated, trench 644 is enlarged relative to trench 624 in Figure 6B, and edge 648 is aligned with the centerline of reference structure 606 (see 631 in Figure 6C, not shown in Figure 6D). Front section view 652 shows a cross section 646 (similar to 156) with device 608 (similar to 158) exposed. These features can also be seen in side section view 653.

[0099] In some embodiments, the imaging device used in block 530 can be rotated in an optional processing block 560 (indicated by a dashed outline). For example, the viewing axis of block 530, like viewing axis 135, can have a polar angle close to 0° (e.g., less than 5° or less than 10°), and the viewing axis in block 570, like viewing axis 137, can be rotated to a polar angle in the range of 45° to 52°. In other embodiments, block 530 can use a viewing axis similar to 137, and block 570 can perform azimuth rotation to bring the viewing axis of the imaging tool closer to the normal (e.g., axis 142) of the cross-section (e.g., 156). As described herein, rotation of the viewing axis can be performed relative to the sample by rotating the imaging tool 130, rotating the stage 150 on which the sample is placed, or by a combination of multiple rotations. Relative translation can also be optionally performed in block 570. However, in other embodiments, a visual axis having a polar angle in the range of 40° to 60° (e.g., 133) can provide sufficient imaging accuracy and resolution for both top imaging in block 530 and subsequent imaging of the cross-section. In such embodiments, block 570 can be omitted.

[0100] Once a suitable imaging axis (with or without block 570) is obtained, the cross-section of the sample can be imaged in processing block 580. Specifically, the same imaging tool can be used in blocks 530 and 580. However, this is not a requirement, and in some embodiments, different imaging tools can be used in blocks 530 and 580. In certain embodiments, imaging in block 580 can be performed by the FIB tool used for milling in processing block 520. Additional or alternative to imaging, other analytical or process operations can be performed on the cross-section in block 580.

[0101] Within the scope of the disclosed technology, numerous modifications and extensions of the third method can be implemented. In some embodiments, blocks 510-540 can be run twice (or fewer or more times) to converge to a fixed target value. Such iterations can be performed for the manufacture or analysis of device 608.

[0102] In other embodiments, blocks 510-540 can be iteratively executed to step through a series of target positions. For example, the analysis can be performed on a series of cross-sections of device 608 along the Y direction of device 608. For example, it may be desired to analyze cross-sections of device 608 at 20 nm intervals Y = {-60 nm, -40 nm, -20 nm, 0 nm, ..., +60 nm}, and a preliminary milling operation can reach Y = -75 nm (e.g., first pass, block 510, block 520). The distance to the first target position can be measured as -60 nm - (-75 nm) = +15 nm (first pass, block 530, block 540), and the loop can be repeated through blocks 560, 510, and 520 to reach Y = -62 nm. In this example, this is within the tolerance range of the first target position Y = -60 nm. Next, in the second pass, the distance to the next target position (-40nm) can be measured between block 530 and block 560, which is +22nm. In addition, imaging or other operations similar to those in block 580 can be performed in the third pass, block 520, before continuing further milling. Illustratively, the third pass can overshoot up to Y=-39nm while remaining within the tolerance range of the second target (-40nm). Thus, in the third pass, a distance of +19nm to the third target (-20nm) can be determined (third pass, block 530, block 540), and imaging or other operations on the second target position (-40nm) can be performed before the next milling operation (fourth pass, block 520) attempts to reach the third target position (-20nm). Therefore, in successive iterations, a desired series of cross-sections can be stepped through at Y = {-60nm, ... +60nm} (within a given tolerance), and an image can be acquired or other analysis performed at each cross-section. In various embodiments, a fixed axial orientation can be used for both the imaging of block 520 and the imaging of successive cross-sections. The imaging or analysis performed at each cross-section can use a different tool than the imaging device used for block 520, or the imaging tool can be rotated forward or backward between the optimal axial axes for imaging the top surface and the cross-sections.

[0103] In further embodiments, additional iterations of blocks 510-540 can be performed to converge at one or more locations of the desired cross-sections.

[0104] The additional variations in Figures 5-6 may omit certain features or adopt features described in relation to Figure 1 or Figures 3-4, or elsewhere in this specification.

[0105] Application example Figure 7 shows a top view 701 and an elevation view 702 of a first application of the disclosed technology. In this application, milling is performed from one side to obtain an edge within a tolerance zone at or from a target location. Sample 750 has a top view 752 in which two markings of a reference structure 706 are visible. The slot 754 is milled up to an edge 748, exposing the cut surface 756. The disclosed technology allows the edge 748 to be precisely positioned relative to the reference structure 706.

[0106] The applications shown in Figure 7 may be suitable for both manufacturing and analytical workflows. In some embodiments, the manufactured device can be milled to within a predetermined tolerance of the target location. That is, milling by the disclosed technique can produce precisely manufactured devices for use in products. Such products may include read / write transducers for magnetic memory devices, semiconductor lasers, or microelectromechanical structures (MEMS) such as tuned oscillators. In other embodiments, milling can be applied destructively to expose the interior of a device for imaging, measurement, or other analytical procedures. For example, doping profiles can be measured across precisely positioned slices (cross-sections) of a device. Analysis can be performed on active or passive electronic devices, including read / write transducers, laser modules, semiconductor chips, MEMS devices, sensors, or nanostructures.

[0107] Figure 8 shows a top view 801 and an elevation view 802 of a second application of the disclosed technology. In this application, milling is performed from two sides to position the edges within their respective tolerance zones relative to a reference structure. Sample 850 has a top view 852 in which the reference structure 806 is visible. Slots 854 and 855 are milled to edges 848 and 849, exposing two cut surfaces, one of which 856 can be seen in the elevation view 802. With the disclosed technology, edges 848 and 849 can be precisely positioned relative to the reference structure 806, and lamellae of the desired thickness can be precisely produced.

[0108] The applications shown in Figure 8 may be suitable for both manufacturing and analytical workflows. In some embodiments, the manufactured device can be precisely milled to a predetermined thickness at a specific location within the sample 850. Such products may include lamellae or other films for MEMS resonators, thin-film sensors, or sampling probes. In other embodiments, milling can be applied destructively to expose and develop lamellae for TEM procedures or other analytical procedures. Suitable samples for lamellar preparation using the disclosed techniques may arise in many fields using MEMS manufacturing techniques, photolithography manufacturing techniques, or epitaxial manufacturing techniques. Samples may include semiconductor materials, optical materials, optoelectronic materials, MEMS materials, or advanced materials.

[0109] Generalized computer environment Figure 9 illustrates a generalized example of a preferred computing system 900 that can implement the described embodiments, techniques, and technologies to integrate microscopic feedback into the milling procedure, for example, by determining the amount to shift the milling position. Since the computing system 900 can implement the technological innovation in a variety of general-purpose or dedicated computing systems, it is not intended to imply any limitation on the scope of use or functionality of this disclosure. The computing system 900 can control SEM imaging tools, FIB milling tools, stages, analytical instruments, or other similar instruments; can perform measurements or other analyses on images or other acquired data representing a sample; can control stages, ion beam columns, or electron beam columns to apply tilt or azimuthal rotation between a sample placed on a stage and an electron beam or ion beam; or can acquire, process, output, or store measurement data.

[0110] Referring to Figure 9, the computing environment 910 includes one or more processing units 922 and memory 924. In Figure 9, this basic configuration 920 is enclosed within the dashed lines. The processing unit 922 can execute computer executable instructions for control, measurement, or other functions described herein. The processing unit 922 may 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 multi-processing system, multiple processing units execute computer executable instructions to increase processing capacity. The computing environment 910 may also include a graphics processing unit or a co-processing unit 930. The tangible memory 924 may be volatile memory (e.g., registers, cache, or RAM), non-volatile memory (e.g., ROM, EEPROM, or flash memory), or a combination thereof, accessible by the processing units 922 and 930. The memory 924 stores software 980 that implements one or more technological innovations described herein in the form of computer executable instructions suitable for execution by the processing units 922 and 930. For example, software 980 may include software 981 for controlling the SEM or other imaging tools, software 982 for controlling the FIB or other milling tools, software 983 for controlling the stage on which the sample is supported, software 984 for measuring sample data or performing other analyses, or other software 985 (including a user interface, host interface, or fault detection). The inset showing software 980 in storage device 940 is similarly applicable to software 980 elsewhere in Figure 9. Memory 924 may also store control parameters, calibration data, measurement data, other database data, configuration data, or operation data.

[0111] The computing system 910 may have additional functions, such as one or more of the following: 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 to other software 980 running on the computing environment 910 and coordinates the operation of the components of the computing environment 910.

[0112] The tangible storage device 940 may be removable or non-removable and may include magnetic disks, magnetic tapes or cassettes, CD-ROMs, DVDs, or any other media that can be used to store information in a non-temporary manner and are accessible within the computing environment 910. The storage device 940 stores instructions (including instructions and / or data) for software 980 that implement one or more of the technological innovations described herein. The storage device 940 may also store image data, measurement data, workflow programs, reference data, calibration data, configuration data, sample data, or other databases or other data structures described herein.

[0113] The input device 950 may be a mechanical, touch-sensitive, or proximity-sensitive input device such as a keyboard, mouse, pen, touchscreen, or trackball, an audio input device, a scanning device, or another device that provides input to the computing environment 910. The output device 960 may be a display, printer, speaker, optical disc writer, or another device that provides output from the computing environment 910. The input or output may also communicate with a remote device via a network connection through the communication port 970.

[0114] Communication port 970 enables communication to another computing entity via a communication medium. The communication medium transmits information such as computer executable instructions, audio input / output or video input / output, or other data in a modulated data signal. A modulated data signal is a signal having one or more characteristics that are set or modified in a manner that encodes the information in the signal. The communication medium may be an electrical carrier, optical carrier, RF carrier, acoustic carrier, or other carrier, but is not limited to these.

[0115] The data acquisition system can be integrated into the computing environment 910 either as an input device 950 or coupled to a communication port 970, and may include connections to an analog-to-digital converter or an instrumentation bus. The instrumentation control system can be integrated into the computing environment 910 either as an output device 960 or coupled to a communication port 970, and may include connections to an analog-to-digital converter, a switch, or an instrumentation bus.

[0116] In some embodiments, the computer system 900 may also include a computing cloud 990 on which instructions for performing all or part of the disclosed technology are implemented. Any combination of memory 924, storage device 940, and computing cloud 990 can be used to store software instructions and data of the disclosed technology.

[0117] This technological innovation can be described in the general context of computer-executable instructions, such as instructions contained in program modules, that are executed on a computing system on a target physical or virtual processor. Generally, a program module or program component includes routines, programs, libraries, objects, classes, components, data structures, etc., that perform a specific task or implement a specific data type. The functionality of program modules can be combined or divided among program modules as desired in various embodiments. The computer-executable instructions of program modules can be executed within a local computing system or a distributed computing system.

[0118] The terms “computing system,” “computing environment,” and “computing device” are used interchangeably herein. Unless explicitly indicated otherwise in the context, none of these terms limit 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 include any combination of dedicated hardware and / or general-purpose hardware and / or virtualized hardware, along with software that implements the functions described herein.

[0119] General Considerations As used in this application and claims, the singular forms "a," "an," and "the" include the plural form unless otherwise explicitly indicated in the context. In addition, the term "includes" means "equipped with." Furthermore, the term "combined" does not exclude the existence of intermediate elements between combined items. Furthermore, as used herein, the terms "or" and "and / or" mean any one item or combination of items in the phrase.

[0120] The systems, apparatus, and methods described herein should not be construed as restrictive in any way. Rather, this disclosure covers all novel and non-obvious features and aspects of the various disclosed embodiments, both individually and in various combinations and partial combinations. The disclosed systems, methods, and apparatus are not limited to any particular aspect or feature or combination thereof, nor are they required to have any one or more particular advantages or to solve any problem. The technology of any embodiment can be combined with the technology described in any one or more of the other embodiments. Any operating theory is provided for ease of explanation, but the disclosed systems, methods, and apparatus are not limited to such operating theories.

[0121] Some operations of the disclosed methods are described in a particular order for convenience; however, it should be understood that this style of description is inclusive of reordering unless a specific order is required by the specific terminology described below. For example, operations described sequentially may, in some cases, be reordered or performed simultaneously. Furthermore, for simplification, the accompanying diagrams may not show the various ways in which the disclosed systems, methods, and apparatus can be used with other systems, methods, and apparatus. In addition, the description may use terms such as “obtain,” “apply,” “correct,” “determine,” or “generate” to describe the disclosed methods. These terms are high-level abstractions of the actual operations performed. The actual operations corresponding to these terms vary depending on the particular embodiment and are readily recognizable to those skilled in the art.

[0122] In some embodiments, values, procedures, or devices are described with terms such as “minimum,” “best,” “maximum,” “optimal,” or “extreme.” Such descriptions are intended to indicate that a choice is possible from a small or large number of alternatives, and it will be understood that such a choice does not necessarily have to be lower, better, less, or otherwise preferable to other options.

[0123] The operating theories, scientific principles, or other theoretical explanations presented herein with reference to the apparatus or method of this disclosure are provided for the purpose of understanding and are not intended to limit the scope. The apparatus and method in the claims set forth separately are not limited to apparatus and method that operate in the manner described by such operating theories.

[0124] Any of the disclosed methods may be controlled by, or implemented as, computer executable instructions or computer program products, stored in one or more computer-readable storage media, such as tangible non-temporary 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). Tangible computer-readable storage media are available tangible media that can be accessed within a computing environment (e.g., one or more optical media discs such as DVDs or CDs, volatile memory components (such as DRAM or SRAM), or non-volatile memory components (such as flash memory or hard drives)). Referring to Figure 9 as an example, the computer-readable storage media includes memory 924 and storage device 940. The terms computer-readable media or computer-readable storage media do not include signals and carriers. Furthermore, the terms computer-readable media or computer-readable storage media do not include communication ports (e.g., 970).

[0125] Any data created and used during the implementation of the disclosed embodiments, as well as any computer executable instructions for implementing the disclosed technology, can be stored on one or more computer-readable storage media. Computer executable instructions may be, for example, a dedicated software application, or part of a software application accessed or downloaded via a web browser or other software application (such as a remote computing application). Such software may run, for example, on a single local computer (e.g., any suitable commercial computer) or in a network environment using one or more network computers (e.g., via the Internet, a wide area network, a local area network, a client-server network, a cloud computing network, or other such network).

[0126] For clarity, only specific selected embodiments 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 example, the disclosed technology may be implemented by 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 embodiments by markup languages ​​such as HTML or XML, or any combination of suitable languages, libraries, and packages. Similarly, the disclosed technology is not limited to any particular computer or hardware type. Specific details of suitable computers and hardware are well known and do not need to be described in detail in this disclosure.

[0127] Furthermore, any of the software-based embodiments (including, for example, computer-executable instructions for causing a computer to perform any of the disclosed methods) may be uploaded, downloaded, sideloaded, or remotely accessed through preferred means of communication. Such preferred means of communication include, for example, the Internet, the World Wide Web, intranets, software applications, cables (including fiber optic cables), magnetic communications, electromagnetic communications (including RF communications, microwave communications, infrared communications, and optical communications), electronic communications, or other such means of communication.

[0128] Given the numerous possible embodiments to which the principles of the subject matter of this disclosure may be applied, it should be recognized that the illustrated embodiments are merely preferred examples and should not be construed as limiting the scope of the claims. Rather, the scope of the claimed subject matter is defined by the following claims. Accordingly, the applicant claims all that is included in these claims.

[0129] Additional examples The following numbered paragraphs describe additional embodiments of the disclosed technology. Any advantages belonging to any paragraph are equally applicable to any paragraphs subordinate thereto.

[0130] 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 a sample using a second particle beam; and a controller configured to: use a first value of a control parameter to cause the milling tool to mill the sample up to a first edge; determine a second value of the control parameter which is changed from the first value by an amount based on the distance between the first edge and a target position, the distance being determined from an image of the sample surface acquired by the imaging tool; and use the second value of the control parameter to cause the milling tool to mill the sample up to a second edge. The apparatus can position the second edge more accurately and advantageously than without feedback from the imaging tool.

[0131] A2. The apparatus described in paragraph A1, wherein the first and second particle beams each contain different species. This apparatus can improve the accuracy of milling by the first particle beam by taking advantage of the superior imaging resolution of the particle species in the second particle beam.

[0132] A3. The apparatus described in paragraph A1 or A2, wherein the first particle beam is a focused ion beam (FIB) and the imaging tool is a scanning electron microscope (SEM). This apparatus can improve the accuracy of milling by FIB by taking advantage of the superior imaging resolution of the SEM.

[0133] A4. The apparatus described in any one of paragraphs A1 to A3, wherein the image is the first image, milling up to the second edge exposes the cross-section of the sample, and the controller is further configured to cause the imaging tool to acquire a second image of the cross-section of the sample. This apparatus can advantageously acquire the second image at a more precisely positioned cross-section than without feedback from the imaging tool.

[0134] A5. The apparatus described in paragraph A4, wherein the orientation of the optical axis of the imaging tool is common to the first and second images. This apparatus can provide advantageous feedback to the milling procedure and can acquire the second image without the extra operation of changing the optical axis.

[0135] A6. The apparatus described in paragraph A4, wherein the controller is configured to rotate the viewing axis of the imaging tool relative to the sample between the acquisition of the first image and the acquisition of the second image. This apparatus can advantageously acquire the first and second images, each having an optimized viewing axis for each image.

[0136] A7. The apparatus described in paragraph A6, wherein the viewing axis of the imaging tool is within 10° of the normal to the surface for acquiring the first image, and within 40° to 60° of the normal to the surface for acquiring the second image. This apparatus configuration advantageously reduces the solid angle required for each tool, allowing more tools to access the sample or sample chamber through their respective ports.

[0137] A8. The apparatus described in 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 apparatus configuration advantageously improves the accuracy of the vertical mill edge coordinates.

[0138] B1. A method comprising: acquiring an image of the surface of a sample from a scanning electron microscope (SEM); determining a distance to shift the milling position based on the relative position of the milled edge in the image and the relative position of a reference structure; and storing the distance, wherein the stored distance can be used during a subsequent milling operation to shift the milled edge to a predetermined spatial relationship with the reference structure. This method can advantageously position the second edge more accurately than without feedback from the SEM image.

[0139] B2. The method according to paragraph B1, wherein the image is a first image, and the method further comprises acquiring a second image of a section exposed by a subsequent milling operation from the SEM. The method can advantageously acquire the second image with a more precisely positioned section than without feedback using the first SEM image.

[0140] B3. The method according to paragraph B1 or B2, wherein the distance is a first distance, and for a second distance, (i) from a datum defined by a reference structure to (ii) a line containing a shifted and milled edge, a given spatial relationship is the tolerance range of the second distance. This method can favorably meet tighter tolerance ranges or increase the likelihood of meeting tolerance ranges compared to the absence of feedback from the SEM image.

[0141] B4. The method according to any one of paragraphs B1 to B3, further comprising: the distance being a first distance; determining the first distance; 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 favorably correct image shortening or edge effects, increase the possibility of undershoot, or decrease the possibility of overshoot.

[0142] B5. The method according to any one of paragraphs B1-B4, wherein the reference structure includes two distinct markings, and the centroid of the reference structure is exposed by a subsequent milling operation, thereby locating the target device within the sample. This method can advantageously improve the accuracy of identifying the target device compared to using a single reference marking.

[0143] B6. The method according to paragraph B5, wherein a given spatial relationship is a tolerance zone with respect to the centroid of a reference structure. This method can favorably achieve a smaller tolerance zone or increase the likelihood of achieving a tolerance zone compared to the absence of feedback from SEM images.

[0144] B7. The method according to any one of paragraphs B1 to B6, further comprising repeating the acquisition and determination operations after each milling operation, including subsequent milling operations, until the termination condition is met. This method can advantageously provide iterative convergence to a fixed target position, or advantageously step through a series of target positions.

[0145] B8. The method of paragraph B7, wherein repeated motion provides convergence to a given target position on the sample. This method can advantageously reduce the possibility of overshoot when accurately reaching the target position.

[0146] B9. The method according to paragraph B7, wherein repeated motions successively target a series of target locations on the sample. This method can advantageously improve the accuracy of exposing a series of cross-sections within the sample for analysis, for example.

[0147] B10. The method according to any one of paragraphs B1 to B9, further comprising correcting the distance for edge effects at the first edge. This method can advantageously provide improved accuracy in distance determination.

[0148] B11. The method according to any one of paragraphs B1-B10, wherein the sample includes a read / write transducer. This method can advantageously provide improved dimensional control of the manufactured read / write transducer.

[0149] B12. The method according to any one of paragraphs B1 to B11, wherein the sample includes lamellae for transmission electron microscopy. This method can advantageously provide improved thickness control of TEM lamellae.

[0150] B13. The method according to any one of paragraphs B1-B12, further comprising using a focused ion beam (FIB) to perform a subsequent milling operation. This method can advantageously improve the accuracy of the subsequent FIB milling operation.

[0151] C1. One or more computer-readable storage media having internally defined executable instructions, wherein when an executable instruction is executed by one or more processors, one or more processors are activated to perform the following actions: use a first value of a control parameter to cause a milling tool to mill a sample up to a first edge; 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 use the second value of the control parameter to cause the milling tool to mill the sample up to a second edge. This technique can advantageously position the second edge more accurately than when images acquired from an SEM are not used.

[0152] C2. One or more computer-readable storage media as described in paragraph C1, wherein determining a second value of a control parameter involves applying an angle correction between the SEM's viewing axis and the normal to the surface of the sample. This method can favorably correct image shortening.

[0153] C3. One or more computer-readable storage media as described in paragraph C1 or C2, wherein the surface is the main surface of the sample, the first edge is the boundary between the main surface and the cut surface exposed by milling up 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 arrangement of the cut surface that is perpendicular to the top surface of the sample or within 30° of such orthogonality.

[0154] C4. One or more computer-readable storage media as described in any one of paragraphs C1 to C3, wherein the instruction further activates the processor to apply a compensatory slope between the milling tool and the stage on which the sample is placed before milling to the first edge, and the compensatory slope is controlled so that the dihedral angle between (i) the second cut surface and (ii) the rest of the surface of the sample is within a predetermined range. This technique can favorably compensate for sidewall inclination and improve the accuracy of the orientation of the cut surface.

[0155] C5. One or more computer-readable storage media as described in paragraph C4, wherein sample is the first sample, image is the first image, SEM is the first SEM, and instruction further activates a processor to cause a milling tool to mill the second sample to the third edge, thereby exposing the third cross-section of the second sample, and the milling tool to mill the second sample to the fourth edge, thereby exposing the fourth cross-section of the second sample, wherein the third and fourth edges form an angle of 60° to 120° (including both endpoints) on the main surface of the second sample, and the third and fourth cross-sections intersect at the fifth edge, and a second image of the fourth cross-section is obtained from the second SEM, and a compensation tilt angle is determined from the relative positions of the fourth edge and the fifth edge in the second image. This technique can improve the accuracy of the orientation of the cross-section by advantageously using a second sample.

Claims

1. It is a device, 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, It is a controller, Using a first value of the control parameter, the milling tool is made to mill the sample up to a first edge, Determining a second value of the control parameter that is changed from the first value by an amount based on the distance between the first edge and the target position, wherein the distance is determined based on the relative positional relationship between the first edge and the target position in the image of the sample surface acquired by the imaging tool, and the image shows the first edge and the target position on the surface. An apparatus comprising: a controller configured to use the second value of the control parameter to cause the milling tool to mill the sample up to a second edge; and

2. The apparatus according to claim 1, wherein the first particle beam and the second particle beam each comprise different species.

3. The apparatus according to 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 above image is the first image, and the milling up to the second edge exposes the cut surface of the sample, and the controller, The apparatus according to claim 1, wherein the imaging tool is further configured to acquire a second image of the cross-section of the sample.

5. The apparatus according to claim 4, wherein the orientation of the optical axis of the imaging tool is common to the first image and the second image.

6. The apparatus according to claim 4, wherein the controller is configured to rotate the viewing axis of the imaging tool with respect to the sample between the acquisition of the first image and the acquisition of the second image.

7. The apparatus according to claim 6, wherein the viewing axis of the imaging tool is within 10° of the normal to the surface for acquiring the first image, and within 40° to 60° of the normal to the surface for acquiring the second image.

8. The apparatus according to claim 1, wherein the control parameter determines the sweep position of the milling tool in a direction along the surface and perpendicular to the first edge.

9. It is a method, This involves obtaining images of the sample surface from a scanning electron microscope (SEM), and Based on the relative position of the milled edge in the image and the reference structure in the image, the distance to shift the milling position is determined. This includes storing the aforementioned distance, The stored distance can be used during a subsequent milling operation to shift the milled edge to a predetermined spatial relationship with the reference structure, in a method.

10. The aforementioned image is the first image, and the method is The method according to claim 9, further comprising obtaining a second image of the cross-section exposed by the subsequent milling operation from the SEM.

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

12. The aforementioned distance is a first distance, and determining the aforementioned first distance is Determining a second distance from the center coordinates of the reference structure to the line containing the milled edge, The method according to claim 9, further comprising applying linear scaling to the second distance to obtain the first distance.

13. The method according to claim 9, wherein the reference structure includes two distinct markings, and the center of gravity of the reference structure identifies the location of a target device in the sample that will be exposed by the subsequent milling operation.

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

15. The method according to claim 9, further comprising repeating the acquisition operation and the determination operation after each milling operation, including the subsequent milling operation, until the termination condition is met.

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

17. The method according to claim 15, wherein the repeated operation continuously targets a series of target positions on the sample.

18. The method described above is The method according to claim 9, further comprising correcting the distance for edge effects at the first edge.

19. The method according to claim 9, wherein the sample includes a read / write transducer.

20. The method according to claim 9, wherein the sample includes lamellae for transmission electron microscopy.

21. The method according to claim 9, further comprising using a focused ion beam (FIB) to perform the subsequent milling operation.

22. One or more computer-readable storage media having internally defined executable instructions, wherein when the executable instructions are executed by one or more processors, the one or more processors are activated. The first value of the control parameter is used to cause the milling tool to mill the sample up to the first edge, The scanning electron microscope (SEM) is used to obtain an image depicting the first edge and reference structure on the surface of the sample. Based on the first value and the relative position between the first edge in the image and the reference structure in the image, a second value of the control parameter is determined. A computer-readable storage medium that, using the second value of the control parameter, causes the milling tool to mill the sample up to a second edge.

23. The computer-readable storage medium according to claim 22, wherein determining the second value of the control parameter includes applying an angle correction between the viewing axis of the SEM and the normal to the surface of the sample.

24. The computer-readable storage medium according to claim 22, wherein the surface is the main surface of the sample, the first edge is the boundary between the main surface and the cut surface exposed by the milling up 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. Milling the sample to the first and second edges exposes the first and second cut surfaces of the sample, respectively, and the executable instruction further activates the processor, Before milling up to the first edge, a compensatory inclination is applied between the milling tool and the stage on which the sample is placed. The computer-readable storage medium according to claim 22, wherein the compensating slope controls the dihedral angle between (i) the second cross-section and (ii) the remaining portion of the surface of the sample to be within a predetermined range.

26. The sample is the first sample, the first edge and the second edge are on the first sample, the image is the first image, the SEM is the first SEM, and the instruction further activates the processor, The milling tool is used to mill the second sample up to the first edge of the second sample, thereby exposing the first cut surface of the second sample. The milling tool is used to mill the second sample up to the second edge of the second sample, thereby exposing the second cut surface of the second sample, wherein the first and second edges of the second sample form an angle of 60° to 120° on the main surface of the second sample, and the first and second cut surfaces of the second sample intersect at the third edge of the second sample. Obtain an image of the second cross-section of the second sample from the second SEM, The computer-readable storage medium according to claim 25, wherein the compensating tilt angle is determined from the relative position of the second edge and the relative position of the third edge of the second sample in the image of the second cross-section of the second sample.

Images