Line-based endpoint detection

Abstract

A method of preparing a sample for charged particle microscopy (e.g., by providing a lamella) includes removing material from a surface of the sample to provide a newly exposed surface and determining a region of interest (ROI) on the newly exposed surface. A plurality of lines are formed on the newly exposed surface of the sample, and material is removed multiple times from the processed surface of the sample (different from the newly exposed surface). A machining surface is imaged a plurality of times to capture at least a plurality of lines, and an endpoint is determined based on relative spatial characteristics between two or more lines among the plurality of lines.

Description

Technical Field

[0001] This invention generally relates to endpoint detection. More specifically, it relates to novel applications of endpoint detection on back-end (BEOL) semiconductor chips / test wafers. Background Technology

[0002] Sample preparation using charged particle microscopy (such as dual-beam microscopy, which incorporates both ion columns and electron columns) typically produces nanosheets that can be imaged, for example, in transmission electron microscopy. This preparation process is delicate, especially for sheets that are on the order of 10 nm in thickness after formation. These sheets are formed by milling material away from both sides of the sample using an ion beam. However, knowing or determining when to stop milling is a critical aspect and handling electron-based images is challenging.

[0003] As described in US11355313B2, Line Indicator Termination (LIT) is an automated process for wafer thinning in AutoTEM. LIT markers (α markers, λ markers, etc.) are milled or deposited (i.e., “placed”) on the chip surface prior to thinning. These markers are used during the thinning process to automatically determine the sample endpoint in AutoTEM (using neural networks or other processes).

[0004] However, LIT is typically used for endpoint determination / thinning of front-end processes (FEOL), where the structure is more uniform, more accessible and more imageable, and therefore easier to apply the necessary lines.

[0005] The methods and apparatus described in this paper enable the use of LIT for end-of-line (BEOL) determination / thinning. This is surprising and unexpected because BEOL structures are highly non-uniform and the region of interest (ROI) is obscured by surrounding material.

[0006] Typically, for BEOL devices, the LIT markings placed on the surface (BEOL layer / large linewidth metal layer / upper metal layer / lower metal layer) may be several micrometers to tens of micrometers perpendicular to the FEOL ROI. This significantly reduces the practicality of precisely and automatically determining the endpoint of the LIT lines.

[0007] The inverted take-out orientation places the LIT line at the bottom of the sheet, causing the LIT line to be affected by the curtain effect; both the inverted take-out orientation and the top-down take-out orientation may amplify the accidentally applied small take-out tilt angle into an excessive offset at the ROI that affects accuracy.

[0008] The method described in this paper allows for precise location of the ROI and reduces the curtain effect on the surface of the sheet caused by the surrounding material. Summary of the Invention

[0009] The present invention seeks to solve at least some of the above-mentioned problems by providing the methods and uses defined in this application.

[0010] Therefore, this application provides a method for preparing samples (e.g., by providing thin sections) for charged particle microscopy analysis, the method comprising: - Remove material from the surface of the sample to provide a newly exposed surface; - Identify the region of interest (ROI) on the newly exposed surface of the sample; - Multiple lines are formed on the newly exposed surface of the sample; - Remove material multiple times from the processed surface of the sample, where the processed surface of the sample is different from the newly exposed surface; - Image the processed surface of the sample multiple times (i.e., the surface newly exposed by removing material from the processed surface) to capture at least multiple lines; and - Determine the endpoint based on the relative spatial characteristics between two or more lines among multiple lines.

[0011] This application also provides an apparatus comprising at least an ion beam column coupled to provide an ion beam; an electron beam column coupled to provide an electron beam; a sample arranged to receive the ion beam and the electron beam; and a controller coupled to control the ion beam and the electron beam. The controller includes or is coupled to a non-transitory computer-readable medium storing instructions that, when executed by the controller, cause the apparatus to: - Remove the surface of the sample using an ion beam to provide a newly exposed surface; - Identify the region of interest on the newly exposed surface; - Use an ion beam to form multiple lines on the newly exposed surface of the sample; - Remove material multiple times from a processed surface of the sample using an ion beam, the processed surface being different from the top surface; - Image the sample multiple times with an electron beam to capture at least multiple lines, each occurrence occurring between at least one removal step; and - Determine the endpoint based on the relative spatial characteristics between two or more lines among multiple lines.

[0012] The foregoing and other features and advantages of the disclosed method will become more apparent from the following detailed description of the invention, which is illustrated in conjunction with the accompanying drawings. Brief description of the attached diagram Figure 1 – A schematic diagram of the structure of a sample that can be used in the method of the present invention.

[0013] Figure 2A – An example orientation diagram of the ion gun used in the method of the present invention, wherein the side of the sample (often referred to as the "section") (i.e. the side of the sample perpendicular to the top surface of the sample) is perpendicular to the focused ion beam (FIB).

[0014] Figure 2B – An example orientation diagram of the ion gun used in the method of the present invention, wherein the top or bottom surface (i.e., the silicon substrate layer) is perpendicular to the FIB.

[0015] Figure 3 – A schematic diagram of a charged particle microscope that can be used in the method of the present invention.

[0016] Figure 4 – A schematic diagram of how reference marks and LIT marks can be applied to devices / samples / assemblies in the method of this invention.

[0017] Figure 5A And 5B – A schematic diagram of determining endpoints (e.g., ROI edges) using the relative spatial characteristics of lines.

[0018] Figure 6A And 6B – A schematic diagram of line configuration that can be used in the disclosed methods. Invention Details The detailed description of the invention illustrates the principles of the invention by way of example rather than limitation, especially in the context of performing line-based endpoint detection techniques in dual-beam charged particle microscopy.

[0019] These techniques involve forming lines on the surface of a sample to determine when to stop removing material from the sample, i.e., endpoint detection. Such lines may have monitored and measurable relative spatial characteristics to determine the process endpoint, such as the depth of the trench forming the line, or the distance between multiple sets of lines that meet certain conditions. These techniques will be described in further detail below.

[0020] In the method of the present invention as defined herein, the method includes the step of removing material from the surface of a sample to provide a newly exposed surface.

[0021] In the method of the present invention, the sample may be an unmodified sample (i.e., a microchip that has not been milled previously), or the sample may be a microchip fragment that has been milled and extracted from the microchip.

[0022] If a sample has been previously milled from a larger sample (such as a microchip) and extracted from it, then the sample can also be referred to as a block.

[0023] Samples (e.g., microchip modules) can be at any stage of development, including partially fabricated microchips (e.g., chips that have completed FEOL to metal layer fabrication but are not yet in their final consumer form) and even fully fabricated microchips.

[0024] Therefore, the method of the present invention may include the steps of extracting a part of the device (sample / block) from the device and fixing it onto the grid (or the dual thin-film carrier support DLCH); If the sample is one that has been previously milled and extracted from a larger sample (such as a microchip), line-based endpoint detection (LIT) technology can be used to provide such a sample, for example, as a preparatory step in the method of the present invention. The LIT process is described in more detail below.

[0025] Removing material from the surface of a sample typically involves milling the material from the sample (i.e., ion beam milling, ion beam-assisted etching, or a combination thereof). Milling can be performed by any applicable method. However, milling is generally performed using focused ion beam (FIB), where the ion source can be a liquid metal ion source that typically provides a gallium ion beam, or the ion source can be a plasma-based ion source capable of providing an ion beam composed of multiple ions such as xenon, oxygen, nitrogen, argon, etc.

[0026] The surface from which material is removed from the sample will depend on the orientation of the sample relative to the milling source.

[0027] For ease of reference, the sample surfaces will be defined relative to their positions in the initial sample (i.e., in the microchip from which the sample has already been obtained).

[0028] A sample (i.e., a module) typically consists of a top surface and a bottom surface. The top surface generally corresponds to the outer surface of the sample, away from the bottom surface; typically, this could be the surface layer of a microchip. The bottom surface usually corresponds to the silicon substrate layer. This structure is shown in... Figure 1 .

[0029] The sample can be positioned such that its side surface (often referred to as the "section") (i.e., the sample side surface perpendicular to the top surface of the sample) is perpendicular to the focused ion beam (FIB) (as shown in Figure 2A). Alternatively, the sample can be positioned such that the top or bottom surface (i.e., the silicon substrate) is perpendicular to the FIB (as shown in Figure 2B).

[0030] The placement of the sample (block) may depend on the type of milling being performed.

[0031] For example, in order to peel / reverse process a sample (block) layer by layer, the beam is typically incident on the sample (block) in the following manner: perpendicular to the block cross section (or at a near-vertical angle), parallel to the block surface, and parallel to any BEOL metal wire.

[0032] This exposes a new surface parallel to the previous assembly surface, which can be used to identify the ROI location. Depending on the original device structure and removal orientation, this can be performed above or below the ROI.

[0033] When milling is used for endpoint determination and / or sample (block) thinning, FIB is typically incident on the block in the following manner: parallel to the block cross section (or at a nearly parallel angle), and perpendicular to the block surface and any BEOL metal wire; incident on the block surface or the bottom of the sample.

[0034] After the material is removed, a new sample surface is exposed. As described above, the newly exposed surface can be parallel to the original surface (i.e., the top surface) of the sample (block), thereby exposing the device structure beneath the surface (Figure 2A), or perpendicular to the original surface of the sample, thereby exposing the device structure perpendicular to and intersecting the alternative orientation (Figure 2B).

[0035] After the new surface is exposed, the region of interest (ROI) is determined on the newly exposed sample surface.

[0036] ROIs can be determined manually, based on their relative position to a feature (i.e., a computer program finds a known feature and identifies the ROI relative to it), and / or by comparing / overlapping layouts of original devices from which samples / blocks have been derived.

[0037] For example, the region of interest (ROI) can be determined using a (programmed or manual) offset positioning method, in which the ROI location is specified based on its relative position to another graphic structure. In a programmatic manner, this is often accomplished using contrast measurements, where metallic lines are bright and gaps are dark, and the light and dark pairs can be counted relative to the desired area.

[0038] Alternatively or additionally, the region of interest (ROI) can be determined using a layout diagram of the original device layer (e.g., a CAD layout diagram of the device layer), which possesses sufficient non-repeatable graphical features to clearly show the ROI location. Using a CAD layout diagram or other layout diagram of the device layer can be automated, i.e., a computer program (such as a machine learning program) trained to recognize certain graphical features in the layout diagram to locate the ROI on the device, which can then be used to identify ROIs on a sample / module. Alternatively or additionally, the layout diagram can be viewed manually and the identified ROIs can be manually applied.

[0039] Once the ROI has been identified, multiple lines can be formed on the newly exposed surface of the sample.

[0040] This can be performed using any applicable method, such as those described in US11355313, which is incorporated herein by reference. However, it may be preferred that the AutoTEM arrange the LIT lines relative to the reference and / or origin (the defined location on the block, often the center in XYZ) according to the ROI location shown in Figure 4.

[0041] Therefore, the method of the present invention may include the step of arranging a reference on the sample.

[0042] The LIT lines are offset relative to the ROI (on the X-axis). These lines are milled using FIB. Typically, the LIT lines are milled at the location shown in Figure 2B. However, other locations can be used depending on the ROI to be imaged.

[0043] Milling of LIT lines can be performed at approximately 10 kV to approximately 50 kV (preferably approximately 30 kV) and at low currents (such as approximately 5 pA to approximately 50 pA, i.e., 7 pA, 26 pA or 41 pA).

[0044] The lines were then delineated (meaning a very small amount of deposition) and filled with a compound that would provide contrast between the LIT lines and the sample surface.

[0045] For example, the lines can be outlined with tungsten (most commonly used in conjunction with FIB) and filled with TEOS (tetraethyl orthosilicate) or carbon (which can be done in FIB or SEM). This typically provides optimal contrast between the LIT lines and the sample / block while simultaneously determining the endpoint.

[0046] Multiple lines include two or more lines, such as two, three, four, five or six lines.

[0047] The number of lines used can depend on the sample type and / or ROI.

[0048] The preferred LIT line configurations are α-type and λ-type.

[0049] The α type (named for its resemblance to the letter α) consists of 5 milling lines, arranged (on the Y-axis) centered on a known ROI.

[0050] The λ type (named for its resemblance to the letter λ) consists of 3 milling lines.

[0051] The α type is primarily used when the ROI is well-positioned (e.g., on the FEOL layer) and allows thinning to be completed without knowledge of the device / sample / block itself, while the automatic endpoint determination function only samples the LIT line.

[0052] The λ type is primarily used for endpoint determination in deep linear neural networks (DLNNs) for devices / samples / modules. The endpoint determination function examines the device / sample / module structure until the front endpoint is reached, and then checks the current position relative to the LIT line. For back-end milling, the opposite side is milled rapidly to find the opposite side only relative to the LIT line, and then DLNN endpoint determination is performed, resulting in faster milling and lower machining power.

[0053] In cutaway and LIT milling, the λ marker replaces the commonly used α-type use case. The λ marker is arranged centered on the located ROI (on the Y-axis). This is based on the fact that the CAD layout can be reused and any offset between the ROI location and the LIT milling can be compensated for. In this way, the device / sample / module can be thinned using only the LIT line without a deep understanding of the ROI structure.

[0054] Examples of line configurations that can be used in the method of the present invention are shown in Figures 6A-6B.

[0055] These lines can be grooves milled into the surface or raised structures deposited on the top surface.

[0056] The lines can be arranged such that the relative spatial characteristics between at least two lines indicate the endpoint of material removal. The endpoint can be the edge of a sheet, but in other embodiments, the endpoint can be the edge of a region of interest (ROI).

[0057] Relative spatial features can be the distance between two or more lines, or a ratio of such distances. However, in both embodiments, the lines are formed on the top surface in such a way that the depth / height or distance is aligned with a desired, pre-established endpoint (such as the edge of an ROI). This is shown in Figures 5A and 5B.

[0058] For example, two lines can be formed such that they are laterally offset and overlap at their ends, so that their depth (if they are, for example, grooves) is the same in the sample area where the sample processing is expected to end.

[0059] Alternatively, lines can be formed at different angles to each other, and the constantly changing distance between lines can be monitored for certain conditions, such as equal distance. This equal distance indicates the end point of the process and, for example, is arranged at the edge of the region of interest.

[0060] These techniques facilitate automation due to their various characteristics. For example, although the absolute depth of the line will vary with the sample material and beam shape, the line depth should be equal at the line endpoint, thus providing a reference point that is insensitive to both the sample and the beam.

[0061] In this way, the marking strategy is self-calibrating and leverages the high precision of the microscope deflection system. Additionally, SEM images collected during processing (e.g., thinning) can be processed using network / machine learning pipelines for segmenting / identifying and measuring these lines, regular pattern matching type machine vision, and / or image processing algorithms. Segmented pixels can be directly analyzed, or they can be used to place edge detectors or line detectors to measure line depth. When a line depth match is achieved, the SW will instruct the system to stop milling.

[0062] As described above, after multiple lines are formed on the newly exposed sample surface, material is removed from the processed surface of the sample, which is different from the newly exposed surface.

[0063] The machined surface can form a normal angle with the newly exposed surface where the line is formed, or with some acute or obtuse angle. Material can be removed by ion beam milling, ion beam-assisted etching, or a combination thereof.

[0064] The energy of the ion beam can be adjusted as the processed surface moves closer to the desired endpoint, for example, decreasing from 30 keV to 0.5 keV.

[0065] Acquire images of the processed surface.

[0066] Images are acquired using a dotted particle microscope. Specifically, images can be acquired using a scanning electron microscope, which is part of the dual-beam system shown in Figure 3.

[0067] Finally, determine the milling endpoint. The endpoint is based on the relative spatial characteristics between two or more lines among multiple lines.

[0068] The acquired images are analyzed using algorithms or manual methods to determine whether the relative spatial features meet pre-established conditions, such as the same depth / height or isometric / distance ratio.

[0069] If the conditions are met, material removal stops. If not, additional material removal occurs.

[0070] Once the endpoint is reached, the sheet processing can be completed or further processing may be carried out, such as processing the opposite side of the sheet.

[0071] If further processing is required, applying LIT lines and material removal may be repeated once or multiple times in order to provide effective ROI imaging.

[0072] Alternatively, a high-energy ion beam, such as 30 keV, can be used to perform the first ROI and the endpoint process, wherein when using the techniques disclosed herein, material removal stops at the edge of the first ROI.

[0073] Subsequently, a second ROI can be aligned using a lower ion beam energy and other or identical endpoint lines on the top surface. The second ROI can be smaller than the first ROI, thus allowing the formation of a thinner sheet using low-energy ions. In general, the line-based endpoint detection technique disclosed herein can be reused on a single sample to obtain the desired sheet.

[0074] In the method of the present invention, the endpoint can be determined when two adjacent lines among multiple lines have the same depth on the newly exposed surface of the sample, wherein the depth of the lines is a relative spatial feature.

[0075] Alternatively, an endpoint can be determined when the distance between two of the multiple lines is equal to a predetermined distance, wherein the distance between the two lines is a relative spatial feature. For example, the predetermined distance is based on the edge location of the region of interest (ROI), and at least two of the multiple lines are formed on the newly exposed surface to be separated by the predetermined distance at the edge location of the ROI.

[0076] The endpoint can also be determined by determining the ratio of the distances between at least two of the multiple lines.

[0077] It should be noted that endpoint determination can be performed manually, or by analyzing the acquired images using a machine learning algorithm that determines the endpoint based on the relative spatial features defined above.

[0078] This application also provides an apparatus comprising at least an ion beam column coupled to provide an ion beam; an electron beam column coupled to provide an electron beam; a sample arranged to receive the ion beam and the electron beam; and a controller coupled to control the ion beam and the electron beam. The controller includes or is coupled to a non-transitory computer-readable medium storing instructions that, when executed by the controller, cause the apparatus to: - Remove the surface of the sample using an ion beam to provide a newly exposed surface; - Identify the region of interest on the newly exposed surface; - Use an ion beam to form multiple lines on the newly exposed surface of the sample; - Remove material multiple times from a processed surface of the sample using an ion beam, the processed surface being different from the top surface; - Image the sample multiple times with an electron beam to capture at least multiple lines, each occurrence occurring between at least one removal step; and - Determine the endpoint based on the relative spatial characteristics between two or more lines among multiple lines.

[0079] This description will clearly enable those skilled in the art to make and use the invention, as well as various embodiments, modifications, variations, alternatives, and uses thereof. As used herein, the terms “about” or “approximately” for any numerical value or range indicate suitable dimensional tolerances that allow portions or sets of components to function for their intended purpose as described.

[0080] For the avoidance of doubt, in this specification, when the terms "comprising" or "comprises" are used, it means that the feature being described must include the listed components, but may optionally include additional components. When the terms "consisting essentially of" or "consists essentially of" are used, it means that the feature being described must include the listed components and may also include other components, provided that no component affects the essential properties of the feature. When the terms "consisting of" or "consists of" are used, it means that the feature being described must include only the listed components.

[0081] As used herein, the term "at least one" means that a compound contains one or more of the mentioned characteristic parts. Specifically, it refers to one, two, three, or four of these characteristic parts, from one to four or from one to three.

[0082] As used in this application and in the claims, the singular forms “a”, “an” and “the” include the plural forms unless the context clearly indicates otherwise.

[0083] Additionally, the term "includes" means "contains".

[0084] Furthermore, the term "coupled" does not exclude the existence of intermediate elements between coupled items.

[0085] The systems, apparatuses, and methods described herein should not be construed as limiting in any way. Rather, this disclosure relates to all novel and non-obvious features and aspects of various disclosed embodiments, individually and in various combinations and sub-combinations of each other. The disclosed systems, methods, and apparatuses are not limited to any particular aspect or feature or combination thereof, nor are they required to have any one or more specific advantages or to solve any one or more specific problems. Any operational theory should be readily applicable, but the disclosed systems, methods, and apparatuses are not limited to such operational theories.

[0086] Although some of the disclosed methods are described in a specific order for ease of expression, it should be understood that this descriptive method encompasses rearrangement unless specifically ordered according to the language requirements below. For example, operations described sequentially may be rearranged or performed simultaneously in some cases.

[0087] Furthermore, for the sake of simplicity, the accompanying drawings may not show the various ways in which the disclosed systems, methods, and apparatuses may be used in conjunction with other systems, methods, and apparatuses. Additionally, the specification sometimes uses terms such as "produce" and "provide" to describe the disclosed methods. These terms are high-level abstractions of the actual operations performed. The actual operations corresponding to these terms will vary depending on the specific implementation and will be readily apparent to those skilled in the art.

[0088] In some examples, values, procedures, or devices are referred to as “lowest,” “best,” “smallest,” etc. It will be understood that these descriptions are intended to indicate that a choice can be made among many functional alternatives used, and that such a choice is not necessarily better, smaller, or preferred over other options.

[0089] As mentioned above, LIT is generally not possible to use in BEOL-type structures due to the sample structure.

[0090] The solution to this problem is the method and apparatus as defined in this application, which will be described in more detail below with reference to the accompanying drawings.

[0091] Figure 3 is a schematic diagram of a dual-beam system 100 for performing line endpoint determination according to an embodiment of the present disclosure.

[0092] System 100 includes a vertically mounted scanning electron microscope (SEM) column and a focused ion beam (FIB) column mounted at an angle relative to the SEM column. System 100 can be used to image and modify samples (e.g., milling or depositing onto samples). In some embodiments, system 100 is used to form a slide for imaging in a transmission electron microscope, for example, wherein the slide should have a region of interest (ROI) located therein.

[0093] However, to form a sheet containing the ROI, a milling endpoint is needed to help guide the milling operation, where the endpoint helps determine when to stop the milling process. One technique for endpoint determination is to include two or more lines on the top surface of the sample, where the relative spatial characteristics between the two or more lines are monitored.

[0094] The endpoint has been reached or will be reached in subsequent milling processes when the relative spatial characteristics equal a threshold or a pre-established condition. Although examples of suitable hardware are provided below, the disclosed techniques are not limited to implementation in any particular type of hardware.

[0095] A scanning electron microscope (SEM) 141, along with a power supply and control unit 145, is provided with the dual-beam system 100. An electron beam 143 is emitted from the cathode 152 by applying a voltage between the cathode 152 and the anode 154. The electron beam 143 is focused into a fine point by a condenser lens 156 and an objective lens 158. The electron beam 143 is scanned two-dimensionally on the sample by means of a deflection coil 160. The operation of the condenser lens 156, the objective lens 158, and the deflection coil 160 is controlled by the power supply and control unit 145.

[0096] An electron beam 143 can be focused onto a sample 122, which is located on a movable XY stage 125 inside a lower chamber 126. When electrons in the electron beam strike the sample 122, secondary electrons are emitted. These secondary electrons are detected by a secondary electron detector 140. As discussed above, a STEM detector 162 located below the TEM sample holder 124 and the stage 125 collects electrons transmitted through the sample mounted on the TEM sample holder.

[0097] The dual-beam system 100 also includes a focused ion beam (FIB) system 110, which comprises a vacuum chamber having an upper neck portion 112, within which an ion source 114 and a focusing column 116 including extraction electrodes and an electrostatic optical system are located. In some embodiments, the axis of the focusing column 116 is inclined, for example, at 52° relative to the axis of the electron column. The ion column 112 includes the ion source 114, extraction electrodes 115, focusing elements 117, deflection elements 120, and a focused ion beam 118. The focused ion beam 118 passes from the ion source 114 through the focusing column 116 and between the electrostatic deflection devices schematically shown at 120 toward a substrate 122, the substrate including, for example, semiconductor devices located on a movable XY stage 125 within a lower chamber 126.

[0098] The stage 125 is preferably movable in the horizontal plane (X and Y axes) and vertically (Z axis). The stage 125 can also be tilted approximately sixty (60) degrees and rotated about the Z axis. In some embodiments, a separate TEM sample stage (not shown) may be used. This TEM sample stage will also preferably be movable along the X, Y, and Z axes. The opening door 161 is used to insert the substrate 122 onto the XY stage 125, and if used, also for accessing the internal gas reservoir.

[0099] An ion pump 168 is used to evacuate the neck section 112. The chamber 126 is evacuated under the control of a turbomolecular pump and mechanical pump system 130, controlled by a vacuum controller 132. The vacuum system provides a vacuum within the chamber 126 between approximately 1 × 10⁻⁷ Torr and 5 × 10⁻⁴ Torr. If an etching assist gas, etching restraint gas, or deposition precursor gas is used, the chamber background pressure may increase, typically to approximately 1 × 10⁻⁵ Torr.

[0100] A high-voltage power supply provides an appropriate accelerating voltage to the electrodes in the focusing column 116 to excite and focus the ion beam 118. When the ion beam strikes the sample 122, the material is sputtered, i.e., physically ejected from the sample. Alternatively, the ion beam 118 can decompose a precursor gas to deposit material.

[0101] A high-voltage power supply 134 is connected to the appropriate electrodes in the ion source 114 and the ion beam focusing column 116 to form an ion beam 118 of approximately 0.5 keV to 60 keV and guide it to the sample. A deflection controller and amplifier 136, operating according to a prescribed pattern provided by the pattern generator 138, are coupled to a deflection plate 120, thereby allowing manual or automatic control of the ion beam 118 to trace a corresponding pattern on the upper surface of the substrate 122. As is well known in the art, in some systems, the deflection plate is positioned before the final stage lens. When a blanking voltage is applied to the blanking electrode by a blanking controller (not shown), the beam blanking electrode (not shown) within the ion beam focusing column 116 causes the ion beam 118 to strike the blanking aperture (not shown) instead of the substrate 122.

[0102] In some embodiments, ion source 114 is a liquid metal ion source that typically provides a gallium metal ion beam. This source is typically capable of focusing a beam of sub-1 / 10 micrometer width at substrate 122 for modifying substrate 122 by ion milling, enhanced etching, material deposition, or for imaging substrate 122. In other embodiments, ion source 114 is a plasma-based ion source capable of providing an ion beam 118 formed from a variety of ions (such as xenon, oxygen, nitrogen, argon ions, etc.) and can be used for the same purposes described above, such as ion milling, enhanced etching, material deposition, and / or imaging.

[0103] A charged particle detector 140, such as an Everhart Thornley or multichannel board, for detecting secondary ion or electron emissions, is connected to video circuitry 142 that supplies drive signals to a video monitor 144 and receives deflection signals from a system controller 119. The position of the charged particle detector 140 within the lower chamber 126 can vary in different embodiments. For example, the charged particle detector 140 may be coaxial with the ion beam and include apertures for allowing the ion beam to pass through. In other embodiments, secondary particles may be collected by a final-stage lens and then deflected off-axis for collection.

[0104] The micromanipulator 147 can precisely move an object within a vacuum chamber. The micromanipulator 147 may include a precision electric motor 148 positioned outside the vacuum chamber to provide X, Y, Z, and θ control of a portion 149 located inside the vacuum chamber. The micromanipulator 147 may be equipped with different end effectors for manipulating small objects.

[0105] A gas delivery system 146 extends into the lower chamber 126 for introducing and directing gaseous vapor into and onto the substrate 122. For example, iodine may be delivered to enhance etching, or a metal-organic compound may be delivered to deposit metal.

[0106] System controller 119 controls the operation of various parts of the dual-beam system 100. Through system controller 119, a user can scan the ion beam 118 or electron beam 143 in a desired manner by inputting commands in a conventional user interface (not shown). Alternatively, system controller 119 can control the dual-beam system 110 according to programming instructions stored in memory 121. In some embodiments, dual-beam system 100 incorporates image recognition software to automatically identify regions of interest, and the system can then determine the processing endpoint manually or automatically according to this disclosure. In other embodiments, for example, the acquired images can be processed using machine learning algorithms or neural networks to determine the endpoint through image segmentation and analysis. In such embodiments, the machine learning algorithm or neural network model can be executed by controller 119 or by a processing core coupled via a network or the Internet.

[0107] During operation, controller 119 can automatically or via user control establish lines on the top surface of sample 122, which are then used to determine when to stop processing sample 122 relative to sheet formation. For example, a region of interest (ROI) can be mapped onto the top surface of sample 122; the ROI may be the outline of a sheet or a region within a sheet. Two or more lines can then be formed on the top surface to establish where the edges of the ROI are located. These lines (which may be grooves milled into the surface or protrusions deposited on the top surface) can be arranged such that the relative spatial characteristics between at least two lines indicate the endpoint of material removal. In some embodiments, the endpoint may be the edge of the sheet, but in other embodiments, the endpoint may be the edge of the ROI. The sheet can then be used for further analysis, such as in transmission electron microscopy (TEM). In some embodiments, the relative spatial characteristics may be the depth or height of two adjacent lines. In other embodiments, the relative spatial characteristics may be the distance between two or more lines, or a ratio of such distances. However, in both implementations, the line is formed on the top surface in such a way that the depth / height or distance is aligned with the desired, pre-established endpoint (such as the edge of the ROI). See, for example, Figures 2 and 3.

[0108] To further illustrate, after a line is formed on the top surface of sample 122, an ion beam 118 is used to remove sample material to peel open / form the side surface of the sample (e.g., a machined surface) to form a sheet including the desired ROI. The machined surface may be at a normal angle to the top surface in which the line is formed, or at some acute or obtuse angle. Material can be removed by ion beam milling or ion beam-assisted etching, or a combination thereof. In some embodiments, the energy of the ion beam may be adjusted from 30 keV to 0.5 keV as the machined surface moves closer to the desired endpoint. In other embodiments, a high-energy ion beam, such as 30 keV, can be used to perform the first ROI and endpoint process, wherein material removal stops at the edge of the first ROI when using the techniques disclosed herein. Subsequently, a second ROI can be aligned using a lower ion beam energy and another or the same endpoint line on the top surface. The second ROI may be smaller than the first ROI, thereby forming a thinner sheet using low-energy ions. In general, the line-based endpoint detection techniques disclosed herein can be reused on a single sample 122 to obtain the desired sheet.

[0109] As sample material is removed, images of the machined surface are acquired. These images are then analyzed, either algorithmically or manually, to determine if the relative spatial features meet pre-established conditions, such as the same depth / height or equidistant / distance ratio. If not, additional material removal occurs. In some embodiments, material removal stops if the conditions are met. In other embodiments, the meeting of conditions indicates that the additional material removal step will provide the desired endpoint. For example, this material removal step may be performed with the same or lower milling energy as the previous material removal step. Once the endpoint is reached, the sheet machining can be completed, or the opposite side of the sheet can be machined subsequently.

[0110] Public paragraphs Paragraph 1 describes a method for preparing a sample for charged particle microscopy analysis, the method comprising: removing material from the surface of the sample to provide a newly exposed surface; identifying a target region (ROI) on the newly exposed surface of the sample; forming multiple lines on the newly exposed surface of the sample; removing material multiple times from a processed surface of the sample, wherein the processed surface of the sample is different from the newly exposed surface; imaging the processed surface of the sample multiple times to capture at least multiple lines; and determining the processing endpoint based on the relative spatial characteristics between two or more of the multiple marked lines.

[0111] Paragraph 2 includes the subject of paragraph 1 and further specifies that removing material from the top surface of the sample includes removing material parallel to or at an angle relative to the top surface.

[0112] Paragraph 3 includes the topic of any of paragraphs 1-2 and further specifies that determining the region of interest includes applying the layout drawing to the newly exposed surface (i.e., the CAD layout drawing).

[0113] Paragraph 4 includes the topic of any one of paragraphs 1-3 and further specifies that determining the endpoint based on the relative spatial characteristics between two or more lines among a plurality of lines includes determining when two adjacent lines among a plurality of lines have the same depth in a newly exposed surface of the sample, wherein the depth of the lines is a relative spatial characteristic.

[0114] Paragraph 5 includes the topic of any one of paragraphs 1-4, and further specifies that determining the endpoint based on the relative spatial characteristics between two or more lines among a plurality of lines includes determining when the distance between two lines among a plurality of lines equals a predetermined distance, wherein the distance between the two lines is a relative spatial characteristic.

[0115] Paragraph 6 includes the topic of any one of paragraphs 1-5, and further specifies that: the predetermined distance is based on the edge location of the region of interest (ROI), and at least two of the multiple lines are formed on the newly exposed surface to be separated by the predetermined distance at the edge location of the ROI.

[0116] Paragraph 7 includes the topic of any one of paragraphs 1-7, and further specifies that determining the endpoint based on the relative spatial characteristics between two or more lines among a plurality of lines includes determining the ratio of the distances between at least two lines among a plurality of lines.

[0117] Paragraph 8 includes the topics in paragraph 1 and further specifies that determining the endpoint based on the relative spatial features between two or more lines includes analyzing the acquired images using machine learning algorithms that determine the endpoint based on relative spatial features.

[0118] Paragraph 9 includes the subject of any one of paragraphs 1-8 and further specifies that forming multiple lines on a newly exposed surface of a sample includes forming a series of parallel and laterally offset lines, wherein at least one end of each line in the series overlaps with at least one laterally offset line in the series, and wherein the overlapping lines are of the same depth.

[0119] Paragraph 10 includes the topic of any of paragraphs 1-9 and further specifies that forming a series of lines includes forming each line in the series using the same ion beam parameters.

[0120] Paragraph 11 includes the subject matter of any one of paragraphs 1-10 and further specifies that forming multiple lines on a newly exposed surface of a sample includes forming multiple lines arranged at an angle to each other, wherein the distance between at least two sets of lines is known at least at one location along their extent.

[0121] Paragraph 12 includes the subject matter of any one of paragraphs 1-11 and further specifies: multiple removals of material from the processed surface of a sample, wherein the processed surface of the sample is different from the newly exposed surface, including: milling the material with a focused ion beam.

[0122] Paragraph 13 includes the subject matter of any one of paragraphs 1-12 and further specifies that: multiple imaging of a sample to capture the contours of at least multiple lines includes: acquiring electron beam images of the processed surface.

[0123] Paragraph 14 includes the subject matter of any one of paragraphs 1-13 and further specifies that: multiple imaging of a sample to capture the contours of at least multiple lines includes: imaging the sample while removing material or imaging the sample between material removals.

[0124] Paragraph 15 includes the subject of any of paragraphs 1-14 and further specifies that forming multiple lines on the newly exposed surface of the sample includes forming multiple lines on the newly exposed surface of the sample such that the relative spatial features are aligned with the edge of the region of interest identified in (ii).

[0125] Paragraph 16 includes the subject matter of any one of paragraphs 1-15 and further specifies that: forming multiple lines on the newly exposed surface of the sample such that the relative spatial features are aligned with the edge of the region of interest identified in (ii) includes: forming at least two of the multiple lines on the newly exposed surface such that adjacent overlapping areas are aligned with the edge of the region of interest identified in (ii).

[0126] Paragraph 17 includes the subject matter of any one of paragraphs 1-16 and further specifies that forming multiple lines on the newly exposed surface of the sample such that the relative spatial features are aligned with the edge of the region of interest identified in (ii) comprises forming at least two of the multiple lines on the newly exposed surface at different corresponding angles relative to the third line; and determining the distance between the at least two lines at the edge of the region of interest identified in (ii).

[0127] Paragraph 18 includes the topic of any of paragraphs 1-17 and further specifies that at least one of the method steps (i) to (vi) may be repeated once or more.

[0128] Paragraph 19 is an apparatus comprising: an ion beam column coupled to provide an ion beam; an ion beam column coupled to provide an ion beam; an electron beam column coupled to provide an electron beam; a sample arranged to receive the ion beam and the electron beam; and a controller coupled to control the ion beam and the electron beam, wherein the controller includes or is coupled to a non-transitory computer-readable medium storing instructions that, when executed by the controller, cause the apparatus to: remove material from a newly exposed surface of the sample with the ion beam; determine a region of origin (ROI) on the newly exposed surface of the sample; form multiple lines on the newly exposed surface of the sample with the ion beam; remove material multiple times from a processed surface of the sample with the ion beam, wherein the processed surface is different from the newly exposed surface; image the sample multiple times with the electron beam to capture at least the multiple lines; and determine an endpoint based on the relative spatial characteristics between two or more of the multiple lines.

[0129] Paragraph 20 includes the topics in paragraph 19 and further specifies that: the code executed to determine the endpoint based on the relative spatial characteristics between two or more lines among a plurality of lines includes the following code, wherein when executed by the controller, the code causes the device to: determine when two adjacent lines among a plurality of lines have the same depth in a newly exposed surface of the sample, wherein the depth of the lines is a relative spatial characteristic.

[0130] Paragraph 21 includes the subject of any one of paragraphs 19-20 and further specifies that: the code executed to determine the endpoint based on the relative spatial characteristics between two or more lines among a plurality of lines includes the following code, wherein when executed by the controller, the code causes the device to: determine when the distance between two lines among a plurality of lines is equal to a predetermined distance, wherein the distance between the two lines is a relative spatial characteristic.

[0131] Paragraph 22 includes the subject of any one of paragraphs 19-21 and further specifies that: the predetermined distance is based on the edge location of the region of interest (ROI), and at least two of the multiple lines are formed on the newly exposed surface to be separated by the predetermined distance at the edge location of the ROI.

[0132] Paragraph 23 includes the topic of any one of paragraphs 19-22 and further specifies that: the code executed to determine the endpoint based on the relative spatial features between two or more lines among a plurality of lines includes the following code, wherein when executed by the controller, the code causes the device to: analyze the acquired image using a machine learning algorithm for determining the endpoint based on the relative spatial features.

[0133] Paragraph 24 includes the subject of any one of paragraphs 19-23 and further specifies that: code executed to form multiple lines on a newly exposed surface includes code that, when executed by the controller, causes the device to: form a series of parallel and laterally offset lines, wherein at least one end of each line in the series overlaps with at least one laterally offset line in the series, and wherein the depth of each overlapping line is the same.

[0134] Paragraph 25 includes the subject of any one of paragraphs 19-24 and further specifies that: code executed to form multiple lines on a newly exposed surface includes code that, when executed by a controller, causes the device to: form multiple lines arranged at an angle to each other, wherein the distance between at least two sets of lines is known at least at one location along their range.

[0135] Paragraph 26 includes the subject matter of any one of paragraphs 19-25 and further specifies that: the code executed to form multiple lines on a newly exposed surface includes the following code, wherein when executed by the controller, the code causes the device to: form multiple lines on the newly exposed surface of the sample in such a way that they are aligned with the edges of the region of interest relative to the spatial features.

[0136] Given the many possible embodiments to which the principles of the disclosed technology may apply, it should be understood that the illustrated embodiments are merely preferred examples and should not be considered as limiting the scope of this disclosure. We claim that the entirety of the contents within the scope and spirit of the appended claims is our invention.

Claims

1. A method for preparing a sample for analysis by charged particle microscopy, comprising: (i) Remove material from the surface of the sample to provide a newly exposed surface; (ii) Determine the region of interest (ROI) on the newly exposed surface of the sample; (iii) Form multiple lines on the newly exposed surface of the sample; (iv) Remove material from the processed surface of the sample multiple times, wherein the processed surface of the sample is different from the newly exposed surface; (v) Image the sample multiple times to capture at least multiple lines; as well as (vi) Determine the endpoint based on the relative spatial characteristics between two or more lines among multiple lines.

2. The method of claim 1, wherein removing material from the top surface of the sample comprises: Remove material parallel to or at an angle relative to the top surface.

3. The method of claim 1, wherein determining the region of interest includes applying a layout map to the newly exposed surface (i.e., a CAD layout map).

4. The method of claim 1, wherein determining the endpoint based on the relative spatial characteristics between two or more lines among a plurality of lines comprises: Determine when two adjacent lines among multiple lines have the same depth in a newly exposed surface of the sample, where the depth of the lines is a relative spatial feature.

5. The method of claim 1, wherein determining the endpoint based on the relative spatial characteristics between two or more lines among a plurality of lines comprises: Determine when the distance between two lines out of a set number of lines equals a predetermined distance, where the distance between the two lines is a relative spatial feature.

6. The method of claim 5, wherein the predetermined distance is based on the edge location of the region of interest (ROI), and wherein at least two of the plurality of lines are formed on the newly exposed surface to be separated by the predetermined distance at the edge location of the ROI.

7. The method of claim 1, wherein determining the endpoint based on the relative spatial characteristics between two or more lines among a plurality of lines comprises: Determine the ratio of the distances between at least two of the multiple lines.

8. The method of claim 1, wherein determining the endpoint based on the relative spatial characteristics between two or more lines among a plurality of lines comprises: The acquired images are analyzed using a machine learning algorithm that determines the endpoint based on relative spatial features.

9. The method of claim 1, wherein forming multiple lines on the newly exposed surface of the sample comprises: A series of parallel and laterally offset lines are formed, wherein at least one end of each line in the series overlaps with at least one laterally offset line in the series, and the depth of each overlapping line is the same.

10. The method of claim 9, wherein forming a series of lines comprises forming each of the series of lines using the same ion beam parameters.

11. The method of claim 1, wherein forming multiple lines on the newly exposed surface of the sample comprises: Multiple lines are arranged at an angle to each other, wherein the distance between at least two sets of lines is known at at least one location along their range.

12. The method of claim 1, wherein material is removed multiple times from the processed surface of the sample, wherein the processed surface of the sample is different from the newly exposed surface, comprising: Materials are milled using a focused ion beam.

13. The method of claim 1, wherein imaging the sample multiple times to capture the contours of at least a plurality of lines comprises: Acquire electron beam images of the processed surface.

14. The method of claim 1, wherein imaging the sample multiple times to capture the contours of at least a plurality of lines comprises imaging the sample while removing material or imaging the sample between material removals.

15. The method of claim 1, wherein forming multiple lines on the newly exposed surface of the sample includes forming multiple lines on the newly exposed surface of the sample such that the relative spatial features are aligned with the edge of the region of interest determined in (ii).

16. The method of claim 15, wherein forming a plurality of lines on the newly exposed surface of the sample such that the relative spatial features are aligned with the edge of the region of interest determined in (ii) comprises: At least two of the multiple lines are formed on the newly exposed surface such that adjacent overlapping areas are aligned with the edge of the region of interest identified in (ii).

17. The method of claim 15, wherein forming a plurality of lines on the newly exposed surface of the sample such that the relative spatial features are aligned with the edge of the region of interest determined in (ii) comprises: At least two of the multiple lines are formed on the newly exposed surface at different corresponding angles relative to the third line; And determine the distance between at least two lines at the edge of the region of interest defined in (ii).

18. The method of claim 1, wherein at least one of steps (i) to (vi) is repeated once or more.

19. An apparatus comprising: An ion beam column coupled to provide an ion beam; Electron beam column coupled to provide an electron beam; Samples arranged to receive ion beams and electron beams; as well as A controller coupled to control an ion beam and an electron beam, wherein the controller includes or is coupled to a non-transitory computer-readable medium storing instructions that, when executed by the controller, cause the device to: Material is removed from the newly exposed surface of the sample using an ion beam; Determine the ROI on the newly exposed surface of the sample; Multiple lines are formed on the newly exposed surface of the sample using an ion beam; Material is removed multiple times from the processed surface of the sample using an ion beam, where the processed surface is different from the newly exposed surface; The sample is imaged multiple times with an electron beam to capture at least multiple lines; as well as The endpoint is determined based on the relative spatial characteristics between two or more lines among a set of multiple lines.

20. The apparatus of claim 19, wherein the controller-executable instructions executed to determine the endpoint based on the relative spatial characteristics between two or more of the plurality of lines include, when executed, controller-executable instructions causing the apparatus to determine when two adjacent lines among the plurality of lines have the same depth in a newly exposed surface of the sample, wherein the depth of the lines is a relative spatial characteristic.

21. The apparatus of claim 19, wherein executing controller executable instructions to determine an endpoint based on relative spatial characteristics between two or more of a plurality of lines includes controller executable instructions causing the apparatus to determine when two adjacent lines of the plurality of lines are equal to a predetermined distance, wherein the distance between the two lines is a relative spatial characteristic.

22. The apparatus of claim 21, wherein the predetermined distance is based on the edge location of the region of interest (ROI), and wherein at least two of the plurality of lines are formed on the newly exposed surface to be separated by the predetermined distance at the edge location of the ROI.

23. The apparatus of claim 19, wherein the controller executable instructions executed to determine the endpoint based on relative spatial features between two or more of the plurality of lines include, when executed, causing the apparatus to analyze the acquired image using a machine learning algorithm to determine the endpoint based on the relative spatial features.

24. The apparatus of claim 19, wherein the controller-executable instructions executed to form a plurality of lines on the newly exposed surface include controller-executable instructions that, when executed, cause the apparatus to: form a series of parallel and laterally offset lines, wherein at least one end of each line in the series overlaps with at least one laterally offset line in the series, and wherein the depth of each overlapping line is the same.

25. The apparatus of claim 19, wherein controller-executable instructions executed to form a plurality of lines on a newly exposed surface include controller-executable instructions that, when executed, cause the apparatus to: form a plurality of lines arranged at an angle to each other, wherein the distance between at least two sets of lines is known at at least at one location along their extent.

26. The apparatus of claim 19, wherein the controller-executable instructions executed to form multiple lines on the newly exposed surface include controller-executable instructions that, when executed, cause the apparatus to form multiple lines on the newly exposed surface of the sample such that they are aligned with the edges of the spatial features and the region of interest.

Images