Sample preparation method

Abstract

A sample preparation method. The invention relates to the field of sample analysis, such as morphological analysis and micro / nano analysis, in particular to a method for preparing a powder sample cross section for charged particle microscopy analysis.

Description

Technical Field

[0001] This invention relates to the field of sample analysis, such as morphological analysis and micro / nano analysis, and specifically to a method for preparing a cross-section of a powder sample for charged particle microscopy analysis. Background Technology

[0002] The development of electron and scanning probe microscopy in the latter half of the 20th century has yielded spectacular images of the internal structure and composition of matter at nanoscale, molecular, and atomic resolution. This progress has been largely made possible by computer-aided methods for microscope manipulation, data acquisition, and analysis. At the beginning of the 21st century, advancements in imaging technology have opened the well-known floodgates to obtaining highly accurate information on structure and function. From a hardware perspective, high-resolution imaging methods now typically resolve atomic positions with sub-angstrom precision, enabling in-depth understanding of the atomic structure and dynamics of materials.

[0003] Various types of microscopy examinations may be relevant to this invention, such as electron microscopy, charged particle microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM), as well as various sub-species, such as so-called "dual-beam" tools (e.g., FIB-SEM), which additionally employ a focused ion beam (FIB) to allow supporting activities such as ion beam milling or ion beam induced deposition (IBID) or ion-based imaging. This is a non-exclusive list of high-performance microscopy methods.

[0004] As an alternative to using electrons as the irradiation beam, other types of charged particles can be used for charged particle microscopy. In this regard, the phrase "charged particles" should be interpreted broadly to include, for example, electrons, positive ions (e.g., Ga or He ions), negative ions, protons, and positrons.

[0005] Regarding ion-based microscopy, for example, some further information can be gathered from sources such as: WHEscovitz, TRFox and R. Levi-Setti, Scanning Transmission Ion Microscope with a Field Ion Source, Proc. Nat. Acad. Sci. USA, 72(5), pp. 1826-1828 (1975).

[0006] The listing or discussion of a clearly prior art document in this specification should not necessarily be construed as an admission that the document is part of the prior art or common general knowledge.

[0007] It should be noted that, in addition to imaging, charged particle microscopes (CPMs) can also perform other functions, such as performing spectral analysis, examining diffraction patterns, and performing (local) surface modifications (e.g., milling, etching, deposition).

[0008] Another method of microscopy involves site-specific analysis, deposition, and ablation of materials using a focused ion beam (FIB). This is a technique particularly used in the semiconductor industry, materials science, and increasingly in the biological field. An FIB device is a scientific instrument similar to a scanning electron microscope (SEM). However, while SEM uses a focused electron beam to image samples in a chamber, an FIB device uses a focused ion beam. FIB can also be combined in systems with both electron beam columns and ion beam columns, allowing the use of either beam to study the same features.

[0009] The most widely used instruments employ liquid metal ion sources (LMIS), such as gallium ion sources. In a gallium LMIS, metallic gallium is brought into contact with a tungsten needle. The heated gallium wets the tungsten and flows to the needle tip. Under the interaction of surface tension and an electric field, the gallium forms a pointed tip at the needle tip, called a Taylor cone. The large electric field (greater than 1 × 10⁸ volts / cm) at the small tip causes the gallium atoms to ionize and emit field radiation.

[0010] The source ions are then typically accelerated to energies of 1–50 keV (kiloelectron volts) and focused onto the sample using an electrostatic lens. LMIS generates a high-current-density ion beam by dispersing the beam with very small energies. Modern FIBs can deliver tens of nanoamps of current to the sample, or image the sample with a spot size on the order of a few nanometers.

[0011] Focused ion beam (FIB) systems have been commercially produced for about 20 years, primarily for use by large semiconductor manufacturers. FIB systems operate similarly to scanning electron microscopes (SEMs), but the difference is that FIB systems do not use an electron beam. As the name suggests, they use a fine focused ion beam (typically gallium) that can operate at low beam currents for imaging or at high beam currents for sputtering or grinding at specific locations.

[0012] High-current plasma FIB systems are now indispensable in the semiconductor industry and materials research to improve material removal rates and the final surface quality of cross-sectional or 3D tomographic samples.

[0013] However, plasma FIB milling can also produce artifacts, such as curtains. The presence of these artifacts makes it more difficult to identify defects or other features. The invention described herein addresses at least some of these problems during powder sample analysis. Summary of the Invention

[0014] This invention provides a method for preparing a powder sample, wherein the method includes: (a) Provide a section of silicon to provide uneven edges; (b) Place the silicon segment on the aluminum foil, bringing the uneven edge close to the aluminum foil; (c) Place the powder sample on the aluminum foil; (d) Sliding / pushing the silicon segment on the powder sample (particles) such that the uneven edge contacts / moves above / traps the powder; and (e) Cover the powder trapped in the uneven edges with a sealant (i.e., silver paint or carbon paint) to encapsulate the particles.

[0015] This should be referred to as the method of the present invention in the following text.

[0016] The present invention also provides a silicon segment comprising a powder sample encapsulated with a sealant (such as silver paint and / or carbon paint).

[0017] The present invention also provides silicon segments obtained by the methods described herein.

[0018] A method for analyzing powder samples is also provided. Attached Figure Description

[0019] To gain a more complete understanding of the invention and its advantages, the following description is now taken in conjunction with the accompanying drawings, in which: Figure 1 A schematic diagram of an example silicon segment located on an aluminum foil is shown, indicating its direction of travel relative to the powder sample and sealant.

[0020] Figure 2 A schematic diagram is shown, including a silicon segment of a powder sample encapsulated by a sealant.

[0021] The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown in different figures is indicated by similar reference numerals. For clarity, not every component may be labeled in every drawing. Detailed Implementation

[0022] In this detailed description of various embodiments, numerous specific details are set forth for illustrative purposes to provide a thorough understanding of the disclosed embodiments. However, those skilled in the art will appreciate that these various embodiments may be practiced with or without these specific details. Furthermore, those skilled in the art will readily understand that the specific order in which the methods are presented and performed is illustrative, and that such order may be altered while still remaining within the spirit and scope of the various embodiments disclosed herein.

[0023] Figure 1 An overview of the placement and travel direction of the silicon segment (101) on the aluminum foil (103) relative to the uneven edge (102), the powder sample (104), and the sealant (105) in an embodiment of the present invention is shown.

[0024] As described above, the method of the present invention provides a silicon segment (101) with uneven edges (102).

[0025] The silicon segment (101) is typically roughly cuboid in shape, comprising a top surface (101a), a bottom surface (101b), and four sides perpendicular to the top and bottom surfaces. However, other shapes / geometry configurations are permitted to achieve the same effect.

[0026] As used herein, the term “uneven surface” in relation to a silicon segment generally refers to a silicon segment (101) whose upper surface (101a) extends beyond the lower surface (101b) in the longitudinal direction, i.e., the upper surface (101a) is suspended above the lower surface (101b).

[0027] The upper surface (101a) may extend beyond the lower surface (101b) by any suitable distance to accommodate the powder sample (104). The distance may include, but is not limited to, about 10 μm to about 1000 μm, such as about 50 μm to about 500 μm or about 100 μm to about 250 μm.

[0028] When the upper surface (101a) extends beyond the lower surface (101b), the thickness of the upper surface (101a) can be from about 5 μm to about 100 μm, for example, from about 10 μm to about 50 μm or from about 20 μm to about 30 μm. The thickness of the upper surface (101a) can be constant or variable. For example, the thickness at the end of the upper surface (101a) where the lower surface (101b) terminates can be greater than the thickness at a more distant location on the upper surface, and vice versa.

[0029] The uneven edge (102) in silicon can be obtained by any technique known to those skilled in the art. Typically, silicon can be cut using a diamond scribing tool, and then the scribing segment can be broken using physical force (e.g., by pressing down with a thumb). Therefore, the method of the present invention may include a pre-step of breaking the silicon to obtain the uneven edge.

[0030] The upper surface (101a) of silicon is typically polished and free of dust or particles.

[0031] The lower surface (101b) is usually unpolished.

[0032] The uneven edge (102) may include a microcavity in which powder particles may be placed.

[0033] In the method of the present invention, a silicon segment (101) having uneven edges (102) is placed on an aluminum foil (103), such as an aluminum foil sheet.

[0034] Importantly, in this step, the silicon segment (101) is placed on the aluminum foil with the upper surface (101a) at the very top.

[0035] The powder sample (104) is also placed on the aluminum foil. The powder sample (104) can be placed on the aluminum foil (103) before or after the silicon segment (101) is placed on the aluminum foil (103).

[0036] That is, steps (b) and (c) in this invention can be performed in any order, i.e., (b) before (c) or (c) before (b). In either case, the silicon segment (101) is positioned with its uneven edge (102) close to the powder sample (104). For example, when the silicon segment (101) is placed on the aluminum foil (103) before the powder sample (104), the powder sample will be positioned close to the uneven edge (102). Or when the powder sample (104) is placed on the aluminum foil (103) before the silicon segment (101), the silicon segment (101) will be positioned on the aluminum foil (103) with its uneven edge (102) close to the powder sample (104).

[0037] The powder sample (104) can be any powder sample suitable for charged particle microscopy analysis. Specifically, the powder sample (104) can be cathode particles and / or anode particles. A non-limiting list of example powder samples includes: - Ceramic powder used in all-solid-state batteries; - Graphite, hard graphite, and Si / SiO2 / graphite mixed powders for lithium-ion battery anodes; - LFP, NMC and LMN particles for lithium-ion battery cathodes; - Hard material particles: BN, SiC, Al2O3, diamond, WC.

[0038] The powder sample (104) can be placed on the aluminum foil (103) by any suitable means, such as by manual operation using a scraper or by automatic operation by a machine. The powder sample (104) can be gently tapped to distribute it evenly on the aluminum foil (103).

[0039] Then move the silicon segment (101) so that the uneven edge (102) passes through / through the powder sample.

[0040] The silicon segment (101) can be moved by any suitable means, such as pushing and / or sliding the silicon segment on the powder sample (104). However, the preferred method is to move the silicon segment (101) in a gentle manner so as not to disturb the powder sample (104) during the movement. Therefore, the preferred method is to manually push / slide the silicon segment (101) on the aluminum foil (103) using tweezers or gloved fingers. Alternatively, the silicon segment (101) can be moved automatically, for example by a robotic arm or robotic tweezers.

[0041] Depending on the sensitivity of the powder sample, such as its sensitivity to air or water, the movement of the silicon segment (101) through / through the powder sample (104) can be carried out in a glove box or similar chamber where atmospheric conditions can be controlled.

[0042] Push and / or slide a silicon segment (101) on the powder sample (104) so ​​that an uneven edge (102) passes through / through the powder sample (104) and collects at least some of the powder sample (104) in the area formed by the upper surface (101a) extending beyond the lower surface (101b).

[0043] After the silicon segment (101) is pushed / or slid past the powder sample (104), the uneven edge (102) now filled with the powder sample (104) is covered with a sealant (105) (such as silver paint and / or carbon paint) in order to hold / fix the powder sample (104) within the uneven edge (102).

[0044] The powder sample (104) can be covered with sealant (105) in any manner. However, a preferred method may be to cover the powder sample (104) with sealant using the same pushing / sliding motion as when collecting the powder sample (104) within the uneven edge (102). In this case, sealant (105) can be placed on aluminum foil (103) close to the powder sample (104) such that after the silicon segment (101) passes / throughs the powder sample (104), the powder sample (now located in the uneven edge of the silicon segment) passes through the sealant (105) and thus comes into contact with the sealant, thereby covering the powder sample (104). This is in Figure 1 As shown in the image.

[0045] In the method of the present invention, the preferred method is that the sealant (105) covers only the powder sample (104). For example, the preferred method is that the powder sample (104) does not extend to cover the upper surface (101a) of the silicon segment (101), but only covers the side surface of the silicon segment (101), including the uneven edge (102).

[0046] Then, the silicon segment (101) of the powder sample (104) encapsulated by sealant (105) (as shown) Figure 2 The sample (shown) can be used for further preparation (e.g., obtaining a cross-section), analysis (which may include obtaining a cross-section), or can be stored for use when needed. Therefore, the present invention also provides a silicon segment (101) comprising a powder sample (104) encapsulated with a sealant (105).

[0047] In the method of the present invention, the powder sample (104) is typically a sample that can be analyzed by charged particle microscopy, particularly focused ion beam microscopy or plasma focused ion beam microscopy for cross-sectional morphology analysis, i.e., scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS) or focused ion beam secondary ion mass spectrometry (FIB-SIMS).

[0048] Encapsulating the powder sample (104) in the uneven edge (102) of the silicon segment (101) allows the upper surface (101a) of the silicon segment to act as a beam tail blocker during further milling (e.g., milling using a focused ion beam), thereby reducing or eliminating the formation of milling curtains and / or other milling artifacts.

[0049] Therefore, the method of the present invention may include step (f): milling a silicon segment (101) to provide a cross-section. The cross-section can then be analyzed.

[0050] Because of the presence of the upper surface (101a), milling can be performed at beam currents higher than those typically used. For example, beam currents exceeding 200 nA, such as about 200 nA to about 1000 nA, or about 400 nA to about 800 nA. This is because the large beam tail strikes the upper surface first, meaning the powder sample (104) is protected from direct exposure to the beam tail. Since milling curtains are typically caused by such direct exposure, the powder sample (104) prepared by the method of the present invention significantly reduces milling curtains, thereby improving sample analysis.

[0051] During the method of the present invention, the preferred approach is to keep the upper surface (101a) of the silicon segment (101) substantially free of particles (particles can cause milling curtains). Therefore, throughout the method of the present invention, additional cleaning steps may be included between each step to ensure that the upper surface (101a) remains substantially free of particles. The cleaning steps can be performed in any suitable manner and can vary depending on the type of particles to be removed. For example, the cleaning steps may include examining particles and / or airborne dust using an optical microscope.

[0052] Therefore, the method of the present invention may further include step (g), wherein the cross-section is analyzed using a charged particle microscope.

[0053] Plasma FIB cross-section preparation: using our improved method for silicon fracture samples.

[0054] Traditional plasma FIB cross-section preparation typically involves a multi-step process, including GIS deposition and oscillating milling. However, the method of this invention provides a simplified approach that eliminates these steps and reduces the presence of a milling curtain.

[0055] Method 1: Traditional Method ● GIS deposition: FIB deposition using Pt and carbon gas at low kV to protect the caprock. ● High-current milling: Initial milling is performed under high current. ● Rotary milling: Rotate the stage to reduce curtain formation; for larger cross-sections, reduce the current. The current should be 60 nA or less.

[0056] Our Improvement Methods ● Prepare powder samples according to the method of the present invention. ● No GIS deposition: Our silicon fracture edges provide natural protection, eliminating the need for a capping layer. ● No shaking milling: Silicon single crystals effectively mitigate the beam tail effect, thus allowing high-current milling without forming a curtain. ● Higher final current: We can use a final grinding current of up to 200 nA or even greater.

[0057] Advantages of our method ● Simple: Our method is more direct and reduces processing time. ● Efficiency: Eliminating GIS deposition and oscillating milling improves efficiency. ● High quality: We achieved a high-quality curtainless cross-section with no artifacts associated with the capping layer.

[0058] Our innovative silicon fracture method, combined with an improved plasma-fusible interphase (FIB) cross-section preparation method, offers significant advantages over conventional approaches. This method is particularly suitable for beam-sensitive and ultrahard materials, which are typically difficult to process using conventional techniques. Eliminating GIS deposition and rocking milling minimizes damage and deformation, resulting in higher-quality cross-sections.

Claims

1. A method for preparing a powder sample, the method comprising: Provide a section of silicon to provide uneven edges; Place the silicon segment on the aluminum foil, so that the uneven edge is placed close to the aluminum foil; Place the powder sample on the aluminum foil; Slide / push the silicon segment on the powder sample (particles) such that the uneven edge contacts / moves above / retains the powder; and The powder trapped in the uneven edges is covered with a sealant (i.e., silver paint or carbon paint) to encapsulate the particles.

2. The method according to claim 1, wherein the powder sample comprises anode particles and / or cathode particles.

3. The method of claim 1, further comprising milling the packaged particles to provide a cross-section.

4. The method of claim 3, wherein the milling is performed at a beam current of about 200 nA to about 1000 nA.

5. The method of claim 1, wherein the method is performed under controlled atmospheric conditions.

6. The method according to claim 1, wherein the sealant is silver paint and / or carbon paint.

7. A silicon segment comprising a powder sample encapsulated with a sealant.

8. The silicon segment of claim 7, wherein the powder sample (cathode particles / anode particles) is encapsulated in an uneven edge.

9. The silicon segment according to claim 7 or 8, wherein the sealant is silver paint and / or carbon paint.

10. A silicon product obtained by the method of claim 1.

11. A method for performing analysis of a powder sample using charged particle analysis, wherein the method comprises: (a) Provide a beam of charged particles; (b) The method of claim 1 provides a powder sample within an uneven edge of a silicon sample; (c) Orient the beam toward the silicon segment; (d) Detecting particles emitted from the silicon segment.

12. The method of claim 11, wherein the silicon segment is a milled cross-section.

13. The method of claim 12, wherein the silicon is milled at a beam current of about 200 nA to about 1000 nA.

14. The method of claim 11, wherein the uneven edge is a tail blocker.

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