A method for microstructure testing of metal filaments, ribbons or coatings

Abstract

The application discloses a microstructure testing method for metal filaments, thin strips or platings, and applies to the technical field of material physical and chemical detection. The method uses an ion beam with a specific beam intensity after being focused by an electromagnetic lens and accelerated by a specific intensity electric field to continuously scan a sample testing surface at a specific scanning speed and scanning times. The ion beam has a stripping effect on atoms in the nanometer-thickness surface layer of the sample testing surface and excites a secondary electron signal. The principle of obtaining a contrast image containing crystal orientation information by using the characteristics that the stripping effect and the secondary electron signal excitation intensity are influenced by different crystal face orientations of polycrystalline metal materials is used to obtain the microstructure information of the sample testing surface. The microstructure information of the metal filaments, thin strips and platings which is difficult to obtain by traditional metallographic corrosion methods can be directly, quickly and accurately obtained, the detection difficulty of the microstructure of commonly used bonding wires, connecting pieces and platings in the microelectronic field is solved, and the blank of the testing method is filled.

Description

Technical Field

[0001] This invention relates to the technical field of material physicochemical property testing, and in particular to a microstructure testing method for metal wires, strips, or coatings. Background Technology

[0002] In the field of microelectronics, metal bonding wires and connectors with diameters or thicknesses of hundreds or even tens of micrometers are frequently used to achieve electrical connections or signal transmissions. These typically require gold or nickel plating layers of one to tens of micrometers for surface conductivity and corrosion protection in the packaged structure. The quality of these bonding wires, connectors, and plating layers directly affects the lifespan and reliability of microelectronic components and assemblies. To verify whether the performance of these bonding wires, connectors, and plating layers meets the usage requirements, verification tests are necessary. These tests typically include assessments of chemical composition, mechanical properties (including plating adhesion), microstructure, and environmental adaptability (resistance to salt spray, damp heat, etc.).

[0003] For samples with diameters or thicknesses ranging from a few micrometers to hundreds of micrometers, chemical composition can be tested using instruments such as energy dispersive spectrometers, wave spectrometers, electron probe microanalyzers, X-ray photoelectron spectrometers, and Auger electron spectrometers. Mechanical properties can be tested using instruments such as microhardness testers, nanoindentation, and nanoscratching. Environmental adaptability can be tested using salt spray chambers and damp heat chambers to simulate service environments, followed by analysis of surface corrosion and damage after environmental testing using instruments such as stereomicroscopes and scanning electron microscopes. However, the microstructure field, especially the microstructure field, is still limited by the small sample size, which makes it impossible to perform conventional metallographic sample preparation operations such as resin embedding and mechanical polishing. High-purity samples with strong corrosion resistance (such as pure gold bonding wires and coatings, pure aluminum bonding wires, etc.) are difficult to display grain boundaries with chemical or electrolytic etching solutions, or may produce many pits or artifacts that affect observation. As a result, there is still a lack of effective microstructure testing methods for bonding wires, connecting sheets, and coating materials. In the fields of production, R&D, and failure analysis of bonding wires, connecting sheets, and coatings, the inability to conduct microstructure tests makes it impossible to explain changes in macroscopic properties from the perspective of the essential characteristics of the material's microstructure, which is detrimental to product improvement and the upgrading of production technology. There is an urgent need in related fields to find a convenient, fast, and effective microstructure testing method. Summary of the Invention

[0004] This invention provides a method for testing the microstructure of metal wires, strips, or coatings. The purpose is to obtain, intuitively, quickly, and accurately, the microstructure information of metal wires, strips, and coatings that is difficult to obtain by traditional metallographic etching methods. This solves the problem of detecting the microstructure of bonding wires, connecting sheets, coatings, and other materials and material products commonly used in the microelectronics field, and fills the gap in testing methods.

[0005] In a first aspect, a method for microstructural testing of metal wires, strips, or coatings is provided, comprising:

[0006] Place the sample in the vacuum chamber, adjust the position of the test surface to be perpendicular to the incident direction of the ion beam, and adjust the distance between the test surface and the ion beam generator so that the ion beam can be focused on the test surface.

[0007] Set the ion beam acceleration voltage, first magnification, and first beam current; set the first scanning speed for continuous scanning, focus, and adjust the contrast and brightness until the image is clear;

[0008] Positioned near the area to be observed on the test surface, based on the first magnification and the first beam current, the first beam current is shifted to the second beam current. The second beam current satisfies the following: at the expected magnification, after focusing and adjusting the contrast and brightness, the image contrast of the grain orientation can be obtained after up to N scans, where the first magnification is less than the expected magnification.

[0009] Set the first magnification and the first beam current, focus and adjust the contrast and brightness until the image is clear, locate the area to be observed, magnify to the expected magnification, shield the beam current and pause scanning;

[0010] Set the ion beam acceleration voltage, second beam current, first scan speed, contrast, and brightness. Remove the beam shield and start scanning. After N scans are completed, set the scan speed to the second scan speed and then perform M scans to obtain a clear image, where N>M and the second scan speed is slower than the first scan speed.

[0011] In conjunction with the first aspect, in certain implementations of the first aspect, the method satisfies at least one of the following:

[0012] The first beam current is below 80 pA;

[0013] The second beam current ranges from 80 pA to 0.23 nA;

[0014] The first or second scan rate is 100 ns to 30 μs;

[0015] N is 5–25;

[0016] M is 1 to 5.

[0017] In conjunction with the first aspect, in certain implementations of the first aspect, the method satisfies at least one of the following:

[0018] The first beam current intensity is 1 pA to 65 nA;

[0019] The first scan rate is 200ns to 500ns;

[0020] The first scan rate is 3 μs to 30 μs.

[0021] In conjunction with the first aspect, in some implementations of the first aspect, the first beam current used for samples less than 1 μm thick is 1 pA to 40 pA.

[0022] In conjunction with the first aspect, in certain implementations of the first aspect, the step of converting the first beam to the second beam based on the first magnification and the first beam includes:

[0023] Based on the first magnification, the magnification is gradually increased to the second magnification. The second magnification satisfies the requirement that after focusing and adjusting the contrast and brightness, the image contrast of the grain orientation can be obtained after N scans. The second magnification at this time is recorded as Z.

[0024] If Z is lower than the expected magnification, the beam current is reduced based on the first beam current. The adjusted second beam current satisfies that when magnified to the expected magnification, the image contrast of the grain orientation can be obtained after focusing and adjusting the contrast and brightness within N scans.

[0025] If Z is not lower than the expected magnification, then adjust to the expected magnification. If, after focusing and adjusting contrast and brightness, image contrast of grain orientation can be obtained after N scans, then no beam current adjustment is performed based on the first beam current used. If, after focusing and adjusting contrast and brightness, image contrast of grain orientation cannot be obtained after N scans, then the beam current is increased based on the first beam current. The adjusted second beam current satisfies the requirement that, at the expected magnification, image contrast of grain orientation can be obtained after focusing and adjusting contrast and brightness within N scans.

[0026] In conjunction with the first aspect, in some implementations of the first aspect, the first magnification factor is 60 to 1000 times.

[0027] In conjunction with the first aspect, in some implementations of the first aspect, the method further includes:

[0028] The test surface is pretreated to obtain a smooth surface with no organic contaminants adhering to the observation area and a roughness equal to or better than Ra0.2. The pretreatment includes at least one of the following: wire cutting, mechanical cutting, mechanical grinding, vibratory polishing, chemical polishing, electrolytic polishing, solvent cleaning, and ion beam cutting.

[0029] In conjunction with the first aspect, in some implementations of the first aspect, the preprocessing of the test surface satisfies at least one of the following:

[0030] When the test surface is the cross-section of a thin metal wire, the cross-section is prepared by ion beam cutting;

[0031] When the test surface is a cross-section in the thickness direction of a thin strip, the cross-section is obtained by cutting with a scalpel, and the edges of the mechanically cut surface are trimmed by ion beam cutting based on the cut surface;

[0032] When the test surface is a cross-section in the direction of coating thickness, the cross-section is cut out using wire cutting, followed by mechanical grinding, mechanical polishing and / or vibration polishing, and then the polished surface is trimmed using ion beam cutting.

[0033] Cold-drawn filaments, cold-rolled strips, or the original surfaces of coatings that have not undergone mechanical processing can be used directly for testing after solvent cleaning.

[0034] In conjunction with the first aspect, in some implementations of the first aspect, after determining the value of the second beam, the method further includes:

[0035] Based on the ion beam accelerating voltage, second beam current, first scan speed, contrast and brightness, all relevant parameters were recorded;

[0036] Keeping the magnification constant, move to a nearby area to verify whether the parameter settings are appropriate.

[0037] In conjunction with the first aspect, in certain implementations of the first aspect, the method satisfies at least one of the following:

[0038] The vacuum environment of the vacuum chamber is equivalent to or better than 7×10⁻⁶. -3 Pa;

[0039] The ion beam accelerating voltage is 5kV to 30kV.

[0040] Compared with the prior art, the solution provided by the present invention has at least the following beneficial technical effects:

[0041] (1) This invention can obtain the microstructure of metal bonding wires, connecting sheets, and coatings with diameters or thicknesses of several hundred or even tens of micrometers without the traditional metallographic sample preparation process of resin embedding, mechanical grinding and polishing, and etching. After simple pretreatment (mainly solvent cleaning), the remaining sample preparation and microstructure display work can be completed simultaneously in the vacuum chamber of the focused ion beam scanning electron microscope. It is simple to operate, highly efficient, and does not require the use of corrosive chemicals or contact with high-speed rotating equipment (such as mechanical grinding and polishing equipment). It solves the problems of small-sized samples (diameter or thickness) that are difficult to handle, high-purity samples that are resistant to corrosion (chemical corrosion or electrolytic corrosion), and pitting or artifacts that may affect observation during metallographic sample preparation. It is particularly suitable for the microstructure testing of bonding wires, connecting sheets, and coating materials widely used in the microelectronics field, and can solve the long-standing problem of lacking effective microstructure testing methods for the above materials.

[0042] (2) Unlike traditional ion beam cutting and ion beam imaging methods, in the microstructure test of this invention, the ion beam is incident perpendicular to the sample surface to be tested. The ion beam scans the sample surface under the applicable and controlled combination parameters of ion beam incident direction, ion beam acceleration voltage, ion beam current, scanning time, number of scans, contrast and contrast adjustment, and focus adjustment obtained through pre-experiment. At the same time, the material in the nanoscale depth region of the surface layer is uniformly removed. The contrast image containing crystal orientation information can be obtained by utilizing the characteristics of ion stripping and the intensity of secondary electron signals excited by ions being affected by the different crystal orientations of polycrystalline metal materials. Thus, the microstructure information of the sample test surface can be obtained.

[0043] (3) Unlike existing ion etching techniques that can only remove material, the method described in this invention, although also using an ion beam, employs a relatively small ion beam etching amount concentrated in the region of interest. The ion stripping depth is nanometer-level and relatively uniform, avoiding the formation of pores or raised effects due to differences in the etching properties of local material defects caused by ion etching. Furthermore, this invention allows for in-situ observation within a vacuum chamber, avoiding oxidation and contamination during sample processing and transfer, and enabling direct microscopic imaging observation of the region of interest. Ion etching can also be used as a pretreatment method when the sample surface roughness does not meet the requirements of this invention. Attached Figure Description

[0044] Figure 1 This is for copper foil ion beam imaging (the central area is the microstructure test area).

[0045] Figure 2 Electron beam imaging of copper foil (the central area is the microstructure test area).

[0046] Figure 3 This refers to the boundary between the copper foil microstructure test area and the surrounding sample (the peeling of the surface layer of the test area at a nanometer depth).

[0047] Figure 4 The microstructure of the cross-section of the aluminum-silicon bonding wire.

[0048] Figure 5 The image shows the morphology of the aluminum-silicon bonding wire after ion etching.

[0049] Figure 6 Microstructure of a sample on the surface of an electrolytic copper foil (10μm thick) connecting sheet.

[0050] Figure 7 Microstructure of a cross-sectional sample of electrolytic copper foil (10μm thick) connecting sheet.

[0051] Figure 8 The microstructure of the surface sample of an aluminized polyester film (aluminum coating thickness less than 1 μm).

[0052] Figure 9Microstructure of a sample on the surface of a gold-plated layer (1.5 μm thick) on the housing of a plastic-encapsulated device. Detailed Implementation

[0053] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0054] refer to Figures 1 to 3 The present invention provides a method for microstructure testing of metal wires, strips or coatings, and the specific steps are as follows.

[0055] Step (1): Check whether the sample test surface is smooth (roughness and cleanliness).

[0056] If the test surface is too rough or there are contaminants covering the test area, wire cutting and / or mechanical cutting and / or mechanical grinding and polishing and / or vibratory polishing and / or chemical polishing and / or electrolytic polishing and / or solvent cleaning and / or ion beam cutting are required to obtain a smooth surface with no organic contaminants adhering to the test area and a roughness equal to or better than Ra0.2.

[0057] In some embodiments, when the test surface is a cross-section of a metal filament (with a diameter of less than 200 μm), the cross-section can be prepared by ion beam cutting.

[0058] In some embodiments, when the test surface is a cross-section in the thickness direction of the thin strip (thickness less than 200 μm), the cross-section can be obtained by mechanical cutting methods such as scalpel cutting. If necessary, ion beam cutting can be used on the cut surface to trim the edges of the mechanical cut to remove the local plastic deformation area caused by mechanical cutting.

[0059] In some embodiments, when the test surface is a cross-section in the coating thickness direction (thickness less than 200 μm), the cross-section can be cut out using wire cutting, followed by mechanical grinding, and if necessary, mechanical polishing and / or vibration polishing. Then, the polished surface can be trimmed using ion beam cutting to remove the localized plastic deformation areas caused by polishing.

[0060] In some embodiments, the original surfaces of cold-drawn filaments, cold-rolled strips, or coatings that have not undergone mechanical processing can be directly used for testing after solvent cleaning.

[0061] Based on the experience summarized by the applicant during the research process, oxide layers, deformation layers, or contamination layers on the sample surface can prevent the ion beam from uniformly stripping metal atoms when etched down to the underlying substrate. This can lead to a lack of grain orientation information in certain areas or artifacts caused by uneven etching. Therefore, the surface condition of the sample should be checked before testing, and pretreatment should be performed if necessary.

[0062] Step (2): Place the sample in the vacuum chamber, adjust the position of the test surface so that it is perpendicular to the incident direction of the ion beam, and adjust the distance between the test surface and the ion beam generator so that the ion beam can be focused on the test surface.

[0063] The working principle of a focused ion beam scanning electron microscope (FEM) is similar to that of a scanning electron microscope (SEM). The difference is that FEM uses ions (such as gallium and helium) while SEM uses electrons. FEM is more inclined to perform micro- and nano-scale surface processing (cutting and deposition), while SEM can only perform surface imaging.

[0064] The sample test surface is perpendicular to the ion beam incident direction to ensure uniform etching (exfoliation) of the sample during ion beam scanning, thereby laying the foundation for displaying grain orientation contrast. In some embodiments, the vacuum chamber of a focusing particle beam scanning electron microscope achieves an equivalent or better 7×10⁻⁶ Ω·cm. -3 A vacuum environment of Pa is required; too low a vacuum level will affect the ion beam intensity and focusing effect.

[0065] Step (3): Set the ion beam acceleration voltage, first magnification, and first beam current; set the first scanning speed for continuous scanning, focus, and adjust the contrast and brightness until the image is clear. This step is used to reduce sample surface damage.

[0066] In some embodiments, the ion beam accelerating voltage is from 5 kV to 30 kV. This allows for adaptation to samples of varying thicknesses. Lower electric field strengths result in weaker ion stripping, which can protect the sample and may be used for preliminary positioning of experimental locations. Higher electric field strengths enhance ion stripping and increase the depth and intensity of the excited secondary electron signal, which is beneficial for obtaining orientation information of the sample substrate regardless of surface roughness.

[0067] In some embodiments, the first magnification is 60x to 1000x.

[0068] In some embodiments, the first beam current does not exceed 80 pA. The intensity of the first beam current obtained after the ion beam is accelerated by an electric field can be adjustable from 1 pA to 65 nA. Samples less than 1 μm thick should use a smaller beam current, such as 1 pA to 40 pA. Lower beam current intensities result in weaker ion stripping, which can protect the sample and can be used for preliminary positioning of the test location. Higher beam current intensities enhance ion stripping and increase the intensity of the excited secondary electron signal, which is beneficial for improving the signal-to-noise ratio of obtaining orientation information of the sample substrate, but excessively high beam current intensities will reduce image resolution.

[0069] In some embodiments, the ion source of the ion beam is, for example, gallium (Ga) ions.

[0070] In some embodiments, the resolution of the focused image can be equivalent to or better than 5 nm. This ensures that the image obtained by line-by-line, frame-by-frame scanning has nanometer-level spatial resolution.

[0071] In some embodiments, the first scan rate is from 100 ns to 30 μs. Further, the first scan rate is a moderately fast scan rate, ranging from 200 ns to 500 ns.

[0072] Step (4): Position the device near the area to be observed on the test surface. Based on the first magnification in step (3), gradually increase the magnification to the second magnification. The second magnification is such that after focusing and adjusting the contrast and brightness, the image contrast of the grain orientation can be obtained after N scans. Record the second magnification at this time as Z, and N is more than 1 scan (or 1 frame, each frame consists of multiple reciprocating scan lines).

[0073] If Z is lower than the expected magnification (at the expected magnification, the area to be observed is fully displayed and the percentage of the area occupied by the image exceeds the preset area percentage), then the beam current is reduced based on the first beam current used in step (3). The adjusted second beam current satisfies that when magnified to the expected magnification, the image contrast of the grain orientation can be obtained after focusing and adjusting the contrast and brightness within N scans.

[0074] If Z is not lower than the expected magnification, then adjust to the expected magnification. If the image contrast of the grain orientation can be obtained after N scans after focusing and adjusting the contrast and brightness, then no beam adjustment is required based on the first beam used in step (3). If the image contrast of the grain orientation still cannot be obtained after 20 consecutive scans after focusing and adjusting the contrast and brightness, then the beam current is increased based on the first beam current used in step (3). The adjusted second beam current satisfies that, at the expected magnification, the image contrast of the grain orientation can be obtained after N scans after focusing and adjusting the contrast and brightness.

[0075] This step is a preliminary experiment to obtain the final specific parameters, so as to quickly obtain the optimal combination of parameters applicable to the sample.

[0076] In some embodiments, N scans are 5 to 20 consecutive scans.

[0077] In some embodiments, the experimentally validated recommended second beam current for imaging is 80 pA to 0.23 nA (ensuring 15,000 times image clarity).

[0078] Step (5): Based on the ion beam accelerating voltage, beam current, scanning speed, contrast, and brightness obtained in step (4), record all relevant parameters. If necessary, move to an adjacent area while keeping the magnification constant to verify whether the parameter settings are appropriate. This step is to verify the combined parameters obtained in step (4) to ensure that the formal experiment can achieve satisfactory results.

[0079] Step (6): Set the magnification and beam current back to the first magnification and first beam current from step (3), focus and adjust the contrast and brightness until the image is clear, locate the area to be observed, magnify to the expected magnification, shield the beam current and pause scanning. This step is used to locate the test area.

[0080] Step (7) sets the ion beam accelerating voltage, beam current, scanning speed, contrast, and brightness to the parameters recorded in step (5). This step is used to set the parameter combination verified in (5).

[0081] Step (8): Remove the beam shield and start scanning. After N scans are completed, set the scanning speed to the second scanning speed, and then perform M more scans to obtain a clear image (microstructure).

[0082] During scanning, the focused ion beam continuously sweeps across the sample surface line by line. The initial medium-to-fast first scan speed, used in multiple scans, ensures the ion beam reacts as uniformly as possible with the sample surface. Slow scanning would result in prolonged contact between the ion beam and the sample surface, potentially causing material damage and producing uneven, streak-like or localized pitting. During imaging, a medium-to-slow second scan speed is beneficial for obtaining a clear image. Using a fast scan during imaging will result in a blurry image.

[0083] If necessary, refocus and adjust contrast and brightness. Excessive scanning of some samples, especially those less than 1 μm thick, may affect the test results; in such cases, operation should be performed as quickly as possible to minimize the total number of scans. This step is the formal test of the sample test surface. By using validated combined parameters, the surface ion removal and grain orientation display are simultaneously achieved, obtaining a contrast image containing information about the sample's microstructure. The ion beam exfoliates the nanometer-thick atoms on the surface of the sample test surface while simultaneously exciting secondary electron signals. Utilizing the characteristic that both the exfoliation effect and the intensity of the secondary electron signal excitation are affected by the different crystal orientations of polycrystalline metal materials, a contrast image containing crystal orientation information is obtained, thus revealing the microstructure information of the sample test surface. The image contrast displays microstructure information, including: grain boundaries, twin boundaries, grain size and shape, differences in grain orientation, inclusions, and the distribution of other material defects.

[0084] In some embodiments, the second scan rate is from 100 ns to 30 μs. Further, the second scan rate is a moderately slow scan rate, ranging from 3 μs to 30 μs.

[0085] In some embodiments, M scans are 1 to 5 scans.

[0086] Step (9), if necessary, repeat (2) to (8) to obtain microstructure information of other areas of the sample test surface or at a magnification.

[0087] Step (10) is repeated if other samples need to be tested.

[0088] When an ion beam acts on a sample surface, it excites secondary electron and secondary ion signals. Image information can be obtained by collecting and processing the secondary electron signals. This invention, through a specific combination of parameters, including the ion beam incident direction, ion beam accelerating voltage, ion beam current, scanning time, number of scans, contrast and contrast adjustment, focus adjustment, and initial sample surface condition processing, can simultaneously achieve uniform removal of material in the shallow nanometer-deep region during continuous ion beam scanning of the sample surface. Furthermore, it can utilize the characteristic that both ion exfoliation and the intensity of ion-excited secondary electron signals are affected by the different crystal orientations of polycrystalline metal materials to obtain images with contrast including crystal orientation information, thereby obtaining the microstructure information of the sample test surface.

[0089] The present invention provides a microstructure testing method, wherein an ion beam (5) with a specific beam intensity (4) after being focused by an electromagnetic lens (2) and accelerated by a specific electric field (3) is used to scan the pre-treated sample test surface (8) at a specific scanning speed (6) and scanning times (7) under a high vacuum testing environment (1) to generate image contrast (10) and thereby obtain the microstructure information of the sample test surface (11).

[0090] (1) A vacuum chamber using a focused particle beam scanning electron microscope achieves a performance equivalent to or better than 7×10⁻⁶. -3 A vacuum environment of Pa is required; too low a vacuum level will affect the ion beam intensity and focusing effect.

[0091] (2) The image resolution after aggregation is equivalent to or better than 5nm. This is to ensure that the image obtained by scanning line by line and frame by frame has a spatial resolution at the nanometer level.

[0092] (3) The ion accelerating electric field strength (ion beam accelerating voltage) is adjustable from 5kV to 30kV to accommodate samples of different thicknesses. The ion stripping effect is weaker at lower electric field strengths, which can protect the sample and can be used for preliminary positioning of the test location. At higher electric field strengths, the ion stripping effect is enhanced and the depth and intensity of the excited secondary electron signal are increased, which is beneficial for obtaining the orientation information of the sample substrate without being affected by surface roughness.

[0093] (4) After the ion beam is accelerated by the electric field described in (2), the beam current intensity is adjustable from 1 pA to 65 nA. Lower beam current intensities result in weaker ion stripping, which can protect the sample and can be used for preliminary positioning of the experimental location. Higher beam current intensities enhance ion stripping and increase the intensity of the excited secondary electron signal, which is beneficial for improving the signal-to-noise ratio of the sample substrate orientation information. However, excessively high beam current intensities will reduce image resolution. Experimental verification has shown that the recommended imaging beam current is 80 pA to 0.23 nA (ensuring 15,000x image clarity).

[0094] (5) Gallium (Ga) ions. A commonly used and readily available ion source.

[0095] (6) Scan time per line: 100 ns to 30 μs. Shorter scan times result in weaker ion stripping, which can protect the sample and can be used for preliminary positioning of the test location, but the image resolution is poor. Longer scan times result in stronger ion stripping and stronger excitation signals, which is beneficial for improving the signal-to-noise ratio of obtaining orientation information of the sample substrate, but excessively high scan times will lead to differences in the degree of stripping per line, affecting the uniformity of the image contrast. Recommended commonly used scan speeds are 300 ns (fast), 500 ns (medium), and 10 μs (slow).

[0096] (7) More than 1 scan (or 1 frame, each frame consists of multiple reciprocating scan lines), with 5 to 20 scans recommended. If the number of scans is too few, the surface oxide layer, deformation layer or contamination layer will not be removed sufficiently and crystal orientation information cannot be obtained. If the scan time is too long, unevenness will occur due to the difference in ablation rate for different orientations, or even artifacts will be generated due to ion implantation.

[0097] (8) The original state and / or the smooth surface obtained after wire cutting and / or mechanical cutting and / or mechanical grinding and polishing and / or chemical polishing and / or electrolytic polishing and / or vibratory polishing and / or solvent cleaning and / or ion beam cutting. If the surface has an excessively thick oxide layer, deformation layer or contamination layer, the ion beam will not be able to uniformly strip metal atoms when etched to the underlying substrate, which will result in the inability to obtain grain orientation information in some areas or the generation of artifacts due to uneven etching.

[0098] (9) The ion beam conforms to the settings in (2)(3)(4) and the incident direction is perpendicular to the test surface for reciprocating scanning. The scanning parameters conform to the settings in (6)(7).

[0099] (10) The ion beam exfoliates the atoms of the nanometer-thick surface layer of the sample test surface while exciting the secondary electron signal. The principle of obtaining a contrast image containing crystal orientation information is obtained by utilizing the property that both the exfoliation effect and the excitation intensity of the secondary electron signal are affected by the different crystal orientations of the polycrystalline metal material. Thus, the microstructure information of the sample test surface is obtained.

[0100] This principle differs from traditional ion beam cutting, which focuses solely on material removal. Traditional ion beam cutting typically uses a larger beam current, such as 40nA to 65nA, for coarse cutting, followed by a medium beam current, such as 0.23nA to 2.5nA, for trimming. The test surface is perpendicular to the ion beam direction, and the ion beam only serves to remove the material by stripping it away. Although the cutting process also involves scanning line by line, the large beam current and cutting depth result in uneven ion stripping between different scan lines. This leads to a large surface roughness after stripping, and the contrast formed by the grain orientation of the ion beam is completely masked by the roughness and cannot be obtained.

[0101] This principle differs from traditional ion beam imaging, which often uses a smaller beam current, such as 4pA to 80pA, to minimize the effect of ion stripping on the sample surface in order to observe the original morphological information of the sample surface. Furthermore, the observation of sample surface information more commonly uses an electron beam with lower energy as the incident source. Ion beam imaging is usually only used for auxiliary positioning before ion beam cutting.

[0102] This invention obtains a clean surface with a surface thickness not exceeding Ra0.2 by pre-treating the sample. Then, by using a specific combination of parameters, including ion beam incident direction, ion beam accelerating voltage, ion beam current, scanning time, number of scans, contrast and contrast adjustment, and focus adjustment, it can simultaneously achieve uniform removal of material in the shallow nanometer-deep region during continuous ion beam scanning of the sample surface. It can also utilize the characteristics that both ion exfoliation and the intensity of ion-excited secondary electron signals are affected by the different crystal orientations of polycrystalline metal materials to obtain images with contrast containing crystal orientation information, thereby obtaining the microstructure information of the sample test surface.

[0103] (11) Use the image contrast of (10) to display microstructure information, including: grain boundaries, twin boundaries, grain size and shape, differences in orientation of different grains, distribution of inclusions and other material defects, etc.

[0104] Example 1: Cross-sectional microstructure of aluminum-silicon bonding wire

[0105] (1) The sample was inspected and found to be suitable for testing. A bonding wire sample about 10 mm long was cut and prepared into a cross-sectional sample using a focused particle beam.

[0106] (2) Place the cross-sectional sample of the bonding wire obtained in (1) into the vacuum chamber and adjust the cross-section to be perpendicular to the direction of ion beam incident.

[0107] (3) Based on the experience accumulated from previous experiments, the ion beam acceleration voltage was set to 30kV, the magnification was set to 3000 times to cover the entire cross-section of the bonding wire, the beam current was set to 80pA, the scanning speed was set to 200ns for continuous scanning, and the focus, contrast and brightness were adjusted until the image was clear.

[0108] (4) Position the image center so that it basically coincides with the center of the cross-section of the gold bonding wire. Adjust the magnification to 3965 times so that the image covers the entire cross-section. Shield the beam current, set the beam current to 2.5nA, and set the scanning speed to 10μs.

[0109] (5) After removing the beam shield and adjusting the contrast and brightness, perform five consecutive scans to obtain clear images of the microstructure (see...). Figure 4 ).

[0110] Samples after ion etching (see) Figure 5 In contrast, the method of this invention can clearly display the grains, while samples processed by ion etching technology only show cross-sections with many pits and cannot display grain information. This may be due to factors such as excessive etching of areas with poor corrosion resistance and oxidation of the sample upon contact with air after etching. This also verifies that the present invention has significant advantages over etching techniques that also use ion beams.

[0111] Example 2: Microstructure of electrolytic copper foil (10μm thickness) connecting sheet

[0112] (1) After inspection, the sample was cleaned with anhydrous ethanol for 5 minutes and dried before being used for testing. A thickness section specimen (approximately 5 mm in height and 7 mm in length) was prepared by scalpel cutting, and a surface specimen with a size of approximately 10 mm × 8 mm was cut by scissors.

[0113] (2) Place the cross-sectional sample and surface sample described in (1) into the vacuum chamber. Adjust the position of the surface sample so that it is perpendicular to the incident direction of the ion beam, and adjust the distance between the test surface and the ion beam generating device so that the ion beam can be focused on the test surface.

[0114] (3) Set the ion beam acceleration voltage to 30kV, the magnification to 100 times, the beam current to 80pA, and the scanning speed to 200ns for continuous scanning. Focus and adjust the contrast and brightness until the image is clear.

[0115] (4) Position the device near the area to be observed on the test surface. Based on the magnification in (3), gradually increase the magnification until the image contrast of the grain orientation can be obtained within 5 to 20 consecutive tests after focusing and adjusting the contrast and brightness. Record the magnification at this time as 15000 times.

[0116] Since the expected magnification was 6500 times, which was lower than 15000 times, the magnification was adjusted to the expected magnification of 6500 times. After focusing and adjusting the contrast and brightness, the image contrast of the grain orientation could not be obtained after 20 consecutive scans. Therefore, the beam current was increased to 0.23nA based on (3). After focusing and adjusting the contrast and brightness, the image contrast of the grain orientation could be obtained after 15 consecutive scans.

[0117] (5) Based on the ion beam accelerating voltage, beam current, scanning speed, contrast, and brightness obtained in (4) to achieve satisfactory grain orientation image contrast within 15 consecutive scans, record all relevant parameters. Keeping the magnification constant, move to an adjacent area to verify that the parameter settings are appropriate and can reproduce satisfactory results.

[0118] (6) Set the magnification to the lower magnification and smaller beam current in (3) again, focus and adjust the contrast and brightness until the image is clear, locate the area to be observed, magnify to the expected magnification, shield the beam current and pause the scan.

[0119] (7) Set the ion beam accelerating voltage, beam current, scanning speed, contrast and brightness to the parameters recorded in (5): magnification 15000 times, beam current 0.23nA, ion beam accelerating voltage 30kV, scanning time 200ns.

[0120] (8) Remove the beam shield and start scanning. After 15 scans, set the scanning speed to 10 μs and scan once more to obtain a clear image (see surface sample microstructure). Figure 6 ).

[0121] (9) Repeat steps (2) to (8) to obtain a clear image of the cross-sectional sample. Change the expected magnification to 8000x. After verification, the parameters in (7) are usable. Therefore, after changing the position, at a magnification of 8000x, directly follow step (8) to complete the scanning imaging (see the cross-sectional sample microstructure). Figure 7 ).

[0122] Example 3: Microstructure of a sample on the surface of an aluminized polyester film (aluminum coating thickness less than 1 μm)

[0123] (1) The sample was inspected and found to be ready for use. Cut a sample to a size of approximately 10mm × 10mm using scissors.

[0124] (2) Attach and fix the sample on the platform and place it in the vacuum chamber. Adjust the position of the test surface so that it is perpendicular to the incident direction of the ion beam. Adjust the distance between the test surface and the ion beam generator so that the ion beam can be focused on the test surface.

[0125] (3) Set the ion beam acceleration voltage to 5kV, the magnification to 100 times, the beam current to 40pA, and the scanning speed to 300ns for continuous scanning. Focus and adjust the contrast and brightness until the image is clear.

[0126] (4) Position the device near the area to be observed on the test surface. Based on the magnification in (3), gradually increase the magnification until the image contrast of the grain orientation can be obtained within 10 consecutive tests after focusing and adjusting the contrast and brightness. Record the magnification at this time as 15000 times.

[0127] Since 15,000 times is lower than the expected magnification of 30,000 times, the beam current is reduced to 24 pA based on the beam current used in (3) and magnified to the expected magnification of 30,000 times. After focusing and adjusting the contrast and brightness, the image contrast of the grain orientation can be obtained after five consecutive scans.

[0128] (5) Based on the ion beam accelerating voltage, beam current, scanning speed, contrast and brightness obtained in (4) to obtain satisfactory grain orientation image contrast in 5 consecutive scans, record all relevant parameters.

[0129] (6) Set the magnification to the lower value and smaller beam current in (3) again, focus and adjust the contrast and brightness until the image is clear, locate the area to be observed, block the beam current and pause the scan.

[0130] (7) Set the magnification to 30,000 times, the ion beam acceleration voltage to 30 kV, the beam current to 24 pA, the scanning speed to 200 ns, and the contrast and brightness to the parameters recorded in (5).

[0131] (8) Remove the beam shield and start scanning. After one image scan is completed, set the scanning speed to 5 μs and scan again to obtain a clear image (see microstructure). Figure 8 ).

[0132] Example 4: Microstructure of a sample sample on the surface of a gold-plated layer (1.5 μm thick) on a plastic-encapsulated device housing

[0133] (1) Upon inspection, the sample is ready for use.

[0134] (2) Place the sample in the vacuum chamber, adjust the position of the test surface so that it is perpendicular to the incident direction of the ion beam, and adjust the distance between the test surface and the ion beam generator so that the ion beam can be focused on the test surface.

[0135] (3) Set the ion beam acceleration voltage to 30kV, the magnification to 200 times, the beam current to 80pA, and the scanning speed to 500ns for continuous scanning. Focus and adjust the contrast and brightness until the image is clear.

[0136] (4) Position the device near the area to be observed on the test surface. Based on the magnification in (3), gradually increase the magnification until the image contrast of the grain orientation can be obtained after 20 consecutive tests with focusing and adjustment of contrast and brightness. Record the magnification at this time as 12500 times, which is basically consistent with the expected magnification. Record the parameters.

[0137] (5) Set the magnification to the lower magnification and smaller beam current in (3) again, focus and adjust the contrast and brightness until the image is clear, locate the area to be observed, magnify to the expected magnification, shield the beam current and pause the scan.

[0138] (6) Set the ion beam acceleration voltage to 30kV, beam current to 80pA, scanning speed to 500ns, and contrast and brightness to the same parameters as (4).

[0139] (7) Remove the beam shield and start scanning. After 20 scans, set the scanning speed to 10 μs and scan once more to obtain a clear image (see surface sample microstructure). Figure 9 ).

[0140] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims of the present invention.

Claims

1. A method for microstructure test of metal filaments, ribbons or coatings, characterized by, The method comprises: placing the sample in a vacuum chamber, adjusting the position of the test surface to be perpendicular to the incident direction of the ion beam, and adjusting the distance between the test surface and the ion beam generating device to enable the ion beam to focus on the test surface; setting the ion beam acceleration voltage, the first magnification, and the first beam current; setting the first scanning speed for continuous scanning, focusing, and adjusting the contrast and brightness to obtain a clear image; positioning near the observation area of the test surface, and based on the first magnification and the first beam current, adjusting the first beam current to the second beam current, which satisfies that after N times of scanning after focusing and adjusting the contrast and brightness at the expected magnification, the image contrast of the grain orientation can be obtained, wherein the first magnification is less than the expected magnification; setting the first magnification and the first beam current, focusing, and adjusting the contrast and brightness to obtain a clear image, positioning to the observation area, magnifying to the expected magnification, shielding the beam current, and pausing the scanning; setting the ion beam acceleration voltage, the second beam current, the first scanning speed, the contrast, and the brightness, unshielding the beam current, and starting the scanning, and after N times of scanning, setting the scanning speed to the second scanning speed, and then performing M times of scanning to obtain a clear image, wherein N>M, and the second scanning speed is slower than the first scanning speed.

2. The method of claim 1, wherein, The method satisfies at least one of the following conditions: the first beam current is less than 80 pA; the second beam current is 80 pA to 0.23 nA; the first scanning speed or the second scanning speed is 100 ns to 30 μs; N is 5 to 25; M is 1 to 5.

3. The method of claim 2, wherein, The method satisfies at least one of the following conditions: the first beam current is 1 pA to 65 nA; the first scanning speed is 200 ns to 500 ns; the first scanning speed is 3 μs to 30 μs.

4. The method of claim 3, wherein, The first beam current used for a sample with a thickness of less than 1 μm is 1 pA to 40 pA.

5. The method of claim 1, wherein, The method of adjusting the first beam current to the second beam current based on the first magnification and the first beam current comprises: gradually increasing the magnification from the first magnification to the second magnification based on the first magnification, the second magnification satisfying that after N times of scanning after focusing and adjusting the contrast and brightness, the image contrast of the grain orientation can be obtained, and recording the second magnification at this time as Z; if Z is lower than the expected magnification, then reducing the beam current based on the first beam current, and the adjusted second beam current satisfies that when magnified to the expected magnification, the image contrast of the grain orientation can be obtained after N times of scanning after focusing and adjusting the contrast and brightness; if Z is not lower than the expected magnification, then adjusting to the expected magnification, and if the image contrast of the grain orientation can be obtained after N times of scanning after focusing and adjusting the contrast and brightness, then not adjusting the beam current based on the first beam current; and if the image contrast of the grain orientation cannot be obtained after N times of scanning after focusing and adjusting the contrast and brightness, then increasing the beam current based on the first beam current, and the adjusted second beam current satisfies that at the expected magnification, the image contrast of the grain orientation can be obtained after N times of scanning after focusing and adjusting the contrast and brightness.

6. The method of claim 5, wherein, The first magnification is 60 times to 1000 times.

7. The method of claim 1, wherein, The method further comprises: The test surface is pretreated to obtain a smooth surface with no organic contaminants attached to the observation area with roughness equal to or better than Ra0.2, the pretreatment including at least one of the following: wire cutting, mechanical cutting, mechanical polishing, vibration polishing, chemical polishing, electrolytic polishing, solvent cleaning, ion beam cutting.

8. The method of claim 7, wherein, The pretreatment of the test surface satisfies at least one of the following: When the test surface is a cross section of a metal filament, the cross section is prepared using ion beam cutting; When the test surface is a cross section in the thickness direction of a thin strip, the cross section is obtained using a scalpel, and the edges of the mechanical cutting are trimmed using ion beam cutting on the basis of the cutting surface; When the test surface is a cross section in the thickness direction of a plated layer, the cross section is cut using wire cutting, then mechanically polished, and then polished and / or vibration polished, and then the polished surface is trimmed using ion beam cutting; The cold-drawn filament, cold-rolled strip or plated original surface without mechanical processing is directly used for testing after solvent cleaning.

9. The method of claim 1, wherein, After determining the value of the second beam current, the method further comprises: On the basis of the ion beam acceleration voltage, the second beam current, the first scanning speed, the contrast and the brightness, all relevant parameters are recorded; The magnification is kept unchanged to move to the adjacent area to verify whether the parameter settings are appropriate.

10. The method of claim 1, wherein, The method satisfies at least one of the following: The vacuum environment of the vacuum chamber is equivalent to or better than 7 x 10 -3 Pa; The ion beam acceleration voltage is 5kV to 30kV.

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