Sample preparation method for microscopic characterization of sample profile

Abstract

The invention relates to the technical field of sample preparation, and discloses a sample preparation method for microscopic characterization of a sample profile. The method comprises the steps of sample pretreatment, specific position positioning, profile preparation, sample separation, carrier transfer and fixation and the like, cutting parameters are accurately controlled through a focused ion beam (FIB), and a silicon wafer carrier and Pt / C / W welding and fixing technology is combined. The problems that in an existing sample preparation method, sample preparation precision is low, conductivity is poor, fixation is unstable, and multi-characterization combination adaptability is insufficient are solved. Nondestructive preparation of a small-size micro-area profile at a specific position is realized, the sample stability is high, various characterization means such as nano infrared and nano SIMS are compatible, the accuracy and relevance of analysis data are ensured, and the method is suitable for microscopic characterization requirements in the fields of semiconductor integrated circuits, nano coatings, biomedical materials and the like.

Description

Technical Field

[0001] This invention belongs to the field of sample preparation technology, specifically relating to a sample preparation method for microscopic characterization of sample profiles. It is applicable to scenarios in fields such as semiconductor integrated circuits, nano-coatings, biomedical materials, geology and archaeology, where it is necessary to perform microscopic morphology and trace element analysis on specific locations at the micrometer or nanometer level on block samples. Background Technology

[0002] Microscopic characterization techniques, such as optical microscopy, scanning electron microscopy, transmission electron microscopy, nano-infrared spectroscopy, and nano-SIMS, are widely used in many fields due to their extremely high resolution and sensitivity. These characterization methods place extremely stringent requirements on sample preparation; the sample's vacuum tolerance, conductivity, surface smoothness, and firmness on the supporting substrate directly affect the accuracy of the analytical results.

[0003] In existing sample preparation techniques, powder samples can be prepared by dispersing in conductive adhesives or using wet dispersion methods, biological samples can be prepared using ultrathin sectioning methods, and large bulk materials can be directly fixed with conductive adhesives. However, for specific micron- or nanometer-scale morphological regions on bulk samples, when high-precision analysis such as nano-infrared or nano-SIMS is required, existing techniques have significant limitations:

[0004] Traditional mechanical cutting methods are prone to stress damage and structural deformation in the sample profile, which cannot meet the high-precision preparation requirements of micron and submicron level micro-region samples.

[0005] Small-sized samples in specific locations are difficult to prepare, lack stable support, and are prone to positional displacement or structural breakage during transfer due to tweezers or airflow disturbances, which can cause subsequent characterization to fail to align with the target profile.

[0006] Traditional temporary carriers have inherent defects. Although copper mesh has excellent conductivity, its mesh structure easily obscures the cross-section and has insufficient support. Glass slides are not compatible with the vacuum ion beam environment of SIMS, and none of them can meet the needs of multi-characterization coupling.

[0007] Therefore, there is an urgent need for a sample preparation method that can accurately locate samples, achieve good conductivity, high flatness, and stable fixation, in order to meet the requirements of high-precision microscopic characterization. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies by proposing a sample preparation method for microscopic characterization of sample profiles.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A sample preparation method for microscopic characterization of sample profiles specifically includes the following steps:

[0011] (1) Sample pretreatment: Fix the sample to be analyzed on the FIB stage;

[0012] (2) Specific location positioning: Identify and locate the target structure or morphology of the sample under SEM;

[0013] (3) Profile preparation: The target position is cut and trimmed by FIB equipment to expose the profile of the target structure and meet the flatness requirements. The flatness requirement is that the roughness of the sample profile is ≤10RMS.

[0014] (4) Sample separation: Control the FIB parameters to cut off the connection between the sample and the parent body, so that the sample in the area to be analyzed is completely separated from the parent body;

[0015] (5) Carrier transfer: Transfer the separated sample to the preset substrate, with the target profile of the sample facing upwards;

[0016] (6) Sample fixation: The sample is firmly connected to the substrate by depositing conductive material to complete the sample preparation.

[0017] Preferably, the profile preparation in step (3) includes: flipping the sample stage to 52-56° and depositing Pt, C or W as a protective layer on the sample surface. The protective layer has a thickness of 1~2 μm, a length of 10~20 μm, and a width of 1~4 μm.

[0018] Preferably, the FIB cutting parameters in step (3) include: initial cutting voltage of 30kV and current of 7~65nA, cutting a rectangular area above and below the target position, the reference size of the rectangular area is 40×30μm, which can be adaptively adjusted according to the size of the target analysis area of ​​the sample; subsequent trimming cutting voltage of 30kV and current of 500~3000pA.

[0019] Preferably, step (3) further includes: adjusting the sample stage to 0°, setting the FIB parameters to voltage 5~30kV and current 20~700pA to continue cutting, so that the sample thickness is retained to 0.5~2μm, and rotating the sample stage 1~4 degrees according to the cutting state to compensate for the slope, ensuring that the roughness of the sample profile is ≤10RMS.

[0020] Preferably, in step (4), the FIB cutting parameters are voltage 30kV and current 20~100pA, cutting off the connection between the sample and the mother body on both sides.

[0021] Preferably, the substrate in step (5) is a clean silicon wafer of 1×1cm, and the sample is transferred to the center of the silicon wafer using a glass needle of a pick-up transfer system.

[0022] Preferably, the conductive material deposited in step (6) is Pt, C or W, the deposition thickness is 0.5~2μm, the deposition location is the bottom of the sample sidewall below half of the substrate in contact with the substrate, and the thickness of the conductive material deposition layer does not exceed the height of the sample surface.

[0023] Preferably, after the sample is transferred to a preset substrate, the substrate and sample are placed back into the FIB-SEM dual-beam apparatus, the sample stage is adjusted to 0° for dual-beam alignment, and then conductive material deposition and fixation are performed.

[0024] Preferably, before sample separation in step (4), the bottom of the sample is cut off and the sidewall is partially cut off so that the sample is in a state of incomplete separation from the parent body, and then the subsequent complete separation operation is carried out.

[0025] Preferably, the sample to be analyzed is a micron- or nano-scale specific morphological region on a bulk material, which can be adapted to the requirements of multiple characterization applications such as nano-infrared spectroscopy and nano-SIMS that require high conductivity, high flatness and vacuum environment after sample preparation.

[0026] This invention provides a sample preparation method for microscopic characterization of sample profiles, which, compared with existing technologies, offers the following advantages:

[0027] High precision fabrication: By precisely controlling cutting voltage, current and other parameters through FIB equipment, combined with protective layer deposition and slope compensation technology, non-destructive fabrication of small-sized (10×10μm) micro-area profiles of specific structures is achieved, with a profile roughness ≤10RMS, effectively avoiding structural damage and deformation caused by traditional mechanical cutting.

[0028] High sample stability: Using a 1×1cm silicon wafer as the support substrate and welding it with Pt / C / W conductive material not only solves the problems of positional displacement and structural breakage during the transfer of small-sized samples, but also ensures that the sample does not deform during subsequent characterization, ensuring that the characterization process can be accurately aligned with the target profile.

[0029] Good characterization adaptability: Silicon wafers have good electrical conductivity and chemical inertness, which are compatible with the optical detection requirements of nano-infrared spectroscopy and can also be adapted to the vacuum and ion beam environment of nano-SIMS. Multiple characterizations can be combined without changing the carrier, thus improving the characterization efficiency.

[0030] Excellent data accuracy: The stable carrier fixation method reduces interference factors in the sample characterization process, and samples on the same silicon wafer can be continuously characterized in multiple ways, ensuring that all analytical data come from the same profile, which significantly improves the correlation and accuracy of the data and provides a reliable sample basis for microscopic analysis. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0032] Example 1

[0033] Profile preparation of semiconductor nanocoating samples (adapted for nano-SIMS characterization)

[0034] 1. Sample pretreatment: Select a block sample of nano-coating on the surface of a semiconductor chip (coating thickness 5μm), fix it to the FIB stage with conductive adhesive, and press the edge of the sample to ensure that it is firmly fixed without loosening or displacement.

[0035] 2. Specific location positioning: Activate the SEM imaging function of the FIB-SEM dual-beam device, adjust the magnification to 5000x, find the interface position between the nano-coating and the substrate through high-resolution imaging, and use the device's marking function to delineate the target analysis area (10×10μm).

[0036] 3. Profile preparation:

[0037] (1) Flip the sample stage to 55° and deposit W as a protective layer on the surface of the marked area using a FIB device. The protective layer is 1.8 μm thick, 18 μm long and 3 μm wide to avoid damage to the coating structure during subsequent cutting.

[0038] (2) Set the FIB ion beam parameters: voltage 30kV, current 50nA, and cut a rectangular area of ​​40×30μm above and below the marked position to fully expose the interface profile between the coating and the substrate;

[0039] (3) Adjust the FIB parameters to 30kV voltage and 2500pA current, and perform preliminary trimming on the exposed profile to remove any protruding impurities remaining from the surface cutting.

[0040] (4) Adjust the sample stage to 0°, set the FIB parameters to voltage 25kV and current 500pA, continue to cut the sample until the thickness is 1.2μm, observe the cutting status during the process, rotate the sample stage 3 degrees to compensate for the slope, and finally make the sample profile roughness reach 7RMS.

[0041] 4. Sample Separation: Set the FIB parameters to 30kV voltage and 80pA current, and disconnect the connection between the sample and the substrate on both sides. Before this, cut the bottom of the sample and partially cut the sidewalls with 30kV voltage and 6nA current to keep the sample in a partially separated state from the substrate, avoiding direct separation that could cause the coating to peel off.

[0042] 5. Carrier transfer: Prepare a clean silicon wafer of 1×1cm as the substrate. Using the glass needle of the Pick-up transfer system, transfer the separated sample to the center of the silicon wafer under real-time SEM observation, ensuring that the interface profile between the coating and the substrate is facing upwards and is placed flat without tilting or contamination.

[0043] 6. Sample fixation: Place the silicon wafer with the sample back into the FIB-SEM dual-beam apparatus, adjust the sample stage to 0° dual-beam alignment, locate the sample, and deposit W at the bottom of the sample sidewall below the contact position with the silicon wafer. The deposition thickness is 1.2 μm, and the thickness of the deposition layer does not exceed the height of the sample surface, thus completing the firm fixation.

[0044] After sample preparation, the silicon wafer and sample were transferred to the nano-SIMS device for trace element analysis. The test results showed that the target profile was clear and undamaged, the elemental distribution boundary between the coating and the substrate was clear, and the analysis data was highly accurate, meeting the stringent requirements of nano-SIMS for sample conductivity, flatness and stability.

[0045] Example 2: Preparation of micro-area profiles of biomedical materials (characterized using nano-infrared spectroscopy and scanning electron microscopy)

[0046] 1. Sample pretreatment: Select a block sample with bioceramic coating on the surface of medical titanium alloy, fix it on the FIB stage, and ensure that the sample surface is free of oil, dust and other impurities.

[0047] 2. Specific location positioning: Activate the SEM imaging function of the FIB-SEM dual-beam device, adjust the magnification to 3000x, locate the defect area (micron-level crack location) of the bioceramic coating, and mark the target profile range (8×8μm).

[0048] 3. Profile preparation:

[0049] (1) Flip the sample stage to 53° and deposit C as a protective layer using a FIB device. The layer is 1.2 μm thick, 12 μm long and 2 μm wide, covering the defect area and its surroundings.

[0050] (2) Set the FIB ion beam parameters: voltage 30kV, current 35nA, and cut a rectangular area of ​​40×30μm above and below the marked position to expose the longitudinal profile of the crack defect;

[0051] (3) Adjust the FIB parameters to 30kV voltage and 1500pA current, and perform preliminary trimming on the profile;

[0052] (4) Adjust the sample stage to 0°, set the FIB parameters to voltage 15kV and current 300pA, cut the sample to a thickness of 0.8μm, and flip the sample stage 2 degrees to compensate for the slope according to the cutting state. The final cross-sectional roughness reaches 9RMS.

[0053] 4. Sample Separation: Set the FIB parameters to 30kV voltage and 50pA current, and disconnect the sample from the parent material on both sides. Before separation, cut the bottom of the sample and partially cut the sidewalls with 30kV voltage and 4nA current to ensure the integrity of the sample structure.

[0054] 5. Carrier transfer: Using a clean 1×1cm silicon wafer as the substrate, the sample is transferred to the center of the silicon wafer using the glass needle of the Pick-up transfer system, with the crack profile facing upwards, and the sample edges are gently pressed to ensure flatness.

[0055] 6. Sample fixation: Place the silicon wafer and sample back into the FIB-SEM dual-beam apparatus. After aligning the dual beams at 0°, deposit C at the contact point between the bottom of the sample sidewall and the silicon wafer, with a thickness of 0.8 μm. The deposited layer should not exceed the height of the sample surface to complete the fixation.

[0056] After sample preparation, nano-infrared spectroscopy and scanning electron microscopy were performed sequentially. The combined tests could be completed without changing the carrier: nano-infrared spectroscopy clearly captured the changes in chemical composition in the crack area, and scanning electron microscopy imaging showed that the crack morphology was intact and undeformed, verifying the adaptability of the sample preparation method to the combined use of multiple characterization methods.

[0057] Example 3: Sample preparation of micron-sized inclusions in geological minerals (adapted to transmission electron microscopy + nano-infrared spectroscopy)

[0058] 1. Sample pretreatment: Select geological mineral block samples containing micron-sized fluid inclusions, fix them on the FIB stage, and ensure that the area where the inclusions are located is unobstructed.

[0059] 2. Specific location positioning: Activate the SEM imaging function of the FIB-SEM dual-beam device, adjust the magnification to 8000x, and accurately locate the fluid inclusion (approximately 2μm in diameter) through backscattered electron imaging, marking the center of the inclusion and the surrounding 10×10μm target area.

[0060] 3. Profile preparation:

[0061] (1) Flip the sample stage to 52° and deposit Pt as a protective layer with a thickness of 1 μm, a length of 15 μm and a width of 2 μm to precisely cover the inclusion area;

[0062] (2) Set the FIB ion beam parameters: voltage 30kV, current 20nA, and cut a rectangular area of ​​40×30μm above and below the marked position to expose the cross-section of the fluid inclusion;

[0063] (3) Adjust the FIB parameters to 30kV voltage and 1000pA current, and preliminarily trim the profile;

[0064] (4) Adjust the sample stage to 0°, set the FIB parameters to voltage 10kV and current 200pA, cut the sample to a thickness of 0.5μm, and rotate the sample stage 1 degree to compensate for the slope according to the cutting state. The final profile roughness reaches 6RMS.

[0065] 4. Sample Separation: Set the FIB parameters to 30kV voltage and 30pA current, and disconnect the sample from the parent material on both sides. Before separation, cut the bottom of the sample and partially cut the sidewalls with a voltage of 30kV and a current of 5nA to prevent the inclusions from rupturing.

[0066] 5. Carrier transfer: Using a clean 1×1cm silicon wafer as the substrate, the sample is gently transferred to the center of the silicon wafer using the glass needle of the Pick-up transfer system, ensuring that the cross-section of the inclusion is facing upwards and free of contamination.

[0067] 6. Sample fixation: Place the silicon wafer and sample back into the FIB-SEM dual-beam apparatus. After aligning the dual beams at 0°, deposit Pt at the contact point between the bottom of the sample sidewall and the silicon wafer. The thickness of Pt is 0.5 μm. The deposited layer does not exceed the height of the sample surface, thus completing the firm fixation.

[0068] After sample preparation, transmission electron microscopy (TEM) and nano-infrared spectroscopy were used for characterization: TEM clearly observed the internal structure of the fluid inclusions, and nano-infrared spectroscopy accurately analyzed the chemical composition of the inclusions, proving that the sample preparation method can meet the requirements of high-precision microscopic characterization of geological samples.

[0069] In summary, this sample preparation method for microscopic characterization of sample profiles is as follows:

[0070] High precision fabrication: By precisely controlling cutting voltage, current and other parameters through FIB equipment, combined with protective layer deposition and slope compensation technology, non-destructive fabrication of small-sized (10×10μm) micro-area profiles of specific structures is achieved, with a profile roughness ≤10RMS, effectively avoiding structural damage and deformation caused by traditional mechanical cutting.

[0071] High sample stability: Using a 1×1cm silicon wafer as the support substrate and welding it with Pt / C / W conductive material not only solves the problems of positional displacement and structural breakage during the transfer of small-sized samples, but also ensures that the sample does not deform during subsequent characterization, ensuring that the characterization process can be accurately aligned with the target profile.

[0072] Good characterization adaptability: Silicon wafers have good electrical conductivity and chemical inertness, which are compatible with the optical detection requirements of nano-infrared spectroscopy and can also be adapted to the vacuum and ion beam environment of nano-SIMS. Multiple characterizations can be combined without changing the carrier, thus improving the characterization efficiency.

[0073] Excellent data accuracy: The stable carrier fixation method reduces interference factors in the sample characterization process, and samples on the same silicon wafer can be continuously characterized in multiple ways, ensuring that all analytical data come from the same profile, which significantly improves the correlation and accuracy of the data and provides a reliable sample basis for microscopic analysis.

[0074] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A sample preparation method for micro-characterization of sample cross-sections, characterized in that, Specifically comprising the following steps: (1) Sample pretreatment: fixing the sample to be analyzed on the FIB stage; (2) Positioning: identifying and positioning the target structure or topography position of the sample under SEM; (3) Cross-section preparation: cutting and trimming the target position by FIB equipment to expose the target structure cross-section and meet the flatness requirement, the flatness requirement is that the sample cross-section roughness is less than or equal to 10RMS; (4) Sample separation: controlling the FIB parameters to cut off the connection between the sample and the parent body, so that the sample to be analyzed and the parent body are completely separated; (5) Carrier transfer: transferring the separated sample to the pre-set substrate, so that the target cross-section of the sample is placed upward; (6) Sample fixation: fixing the sample and the substrate by depositing conductive material, and completing the sample preparation.

2. A sample preparation method for microscopical profiling of a sample according to claim 1, characterized in that, In step (3), the cross-section preparation includes: turning the sample stage to 52-56°, depositing Pt, C or W as a protective layer on the sample surface, the thickness of the protective layer is 1-2μm, the length is 10-20μm, and the width is 1-4μm.

3. A sample preparation method for micro-characterization of sample profile according to claim 1, characterized in that, In step (3), the FIB cutting parameters include: first cutting voltage 30kV, current 7-65nA, cutting the rectangular area above and below the target position, the reference size of the rectangular area is 40×30μm, which can be adjusted adaptively according to the size of the sample target analysis area; subsequent trimming cutting voltage 30kV, current 500-3000pA.

4. A sample preparation method for micro-characterization of sample profile according to claim 1, characterized in that, In step (3), it also includes: adjusting the sample stage to 0°, setting the FIB parameters voltage 5-30kV, current 20-700pA for further cutting, so that the sample thickness is retained 0.5-2μm, and according to the cutting state, the sample stage is turned 1-4 degrees for slope compensation, to ensure that the sample cross-section roughness is less than or equal to 10RMS.

5. A sample preparation method for micro-characterization of sample profile according to claim 1, characterized in that, In step (4), the FIB cutting parameters are voltage 30kV, current 20-100pA, and the connection between the sample and the parent body on both sides is cut off.

6. A sample preparation method for microscopical profiling of a sample according to claim 1, characterized in that, In step (5), the substrate is a clean 1×1cm silicon wafer, and the sample is transferred to the center position of the silicon wafer using the glass needle of the Pick up transfer system.

7. A sample preparation method for microscopical profiling of a sample according to claim 1, characterized in that, In step (6), the deposited conductive material is Pt, C or W, the deposition thickness is 0.5-2μm, the deposition position is the bottom of the sample sidewall below half, and the contact position with the substrate, and the thickness of the deposited conductive material layer does not exceed the height of the sample surface.

8. A sample preparation method for microscopical profiling of a sample according to claim 7, characterized in that, After the sample is transferred to the pre-set substrate, the substrate and the sample are again placed in the FIB-SEM dual-beam equipment, the sample stage is adjusted to 0° for dual-beam centering, and then the conductive material is deposited and fixed.

9. A sample preparation method for microscopical profiling of a sample according to claim 1, characterized in that, Before the sample is separated in step (4), the bottom of the sample is cut off and the sidewall is partially cut off, so that the sample and the parent body are in an incomplete separation state, and then the subsequent complete separation operation is performed.

10. A sample preparation method for microscopical profiling of a sample according to claim 1, characterized in that, The sample to be analyzed is a micron or nanometer level specific topography area on a block material, which can adapt to the needs of multi-characterization combination such as nanometer infrared spectroscopy, nano SIMS, etc. which require high conductivity, high flatness and vacuum environment.