Micro gap measuring method and device based on nano additive manufacturing

Abstract

The invention discloses a micro gap measurement method and device based on nano additive manufacturing, and belongs to the field of micro-nano scale measurement. According to the method, a gap reverse mold is formed in a micro gap on a substrate material through electrochemical additive manufacturing; non-destructive demolding is realized through thermal circulation by utilizing the difference of thermal expansion coefficients of a reverse mold material and a substrate material; performing sequence slicing on the demolded reverse mold by using a focused ion beam, and imaging the exposed surface to obtain a series of two-dimensional images; and finally, based on the two-dimensional image sequence, performing three-dimensional reconstruction on the geometrical morphology of the gap. According to the invention, high-resolution, three-dimensional quantitative and low-damage measurement can be carried out on buried tiny gaps with complex three-dimensional shapes or high depth-to-width ratios, and the method is suitable for various substrate material systems. The non-contact reverse mode duplication strategy is especially suitable for a gap structure which is difficult to apply by a traditional measurement method or a sample is easy to damage, and has scientific research universality and industrialization popularization value; the method can be widely applied to structural analysis scenes such as semiconductors, micro electro mechanical systems, material science, packaging, nano electronics, flexible electronics, biochips, energy devices, microfluidics, biological tissue interfaces and aerospace composite materials, and has remarkable interdisciplinary adaptability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of micro-nano scale three-dimensional structure measurement and characterization, and particularly relates to a micro-scale gap geometry reconstruction method based on electrochemical deposition, thermal demolding and focused ion beam analysis. The method is suitable for three-dimensional non-destructive characterization and high-precision measurement of micro-nano scale gaps in complex internal structures, buried, encapsulation layers or heterogeneous material interface regions. BACKGROUND

[0002] In scientific research and industrial production, accurate measurement of micro-scale gaps (e.g. from sub-micron to tens of microns) is crucial for device performance evaluation, process control, failure analysis and research and development of new materials and structures. These gaps may exist between multiple layers, micro-cracks, pores, inside device packaging or complex three-dimensional structures.

[0003] Currently, existing micro-gap measurement techniques mainly include:

[0004] Capacitance method: the gap distance is calculated by measuring the capacitance change formed on both sides of the gap. This method has relatively simple structure, high sensitivity, but usually only provides one-dimensional or two-dimensional average information, and has limited characterization ability for complex three-dimensional topography, and is easily affected by environmental interference and installation conditions.

[0005] Optical measurement method: confocal microscopy, white light interferometry, optical coherence tomography and X-ray micro-computed tomography. These methods can realize non-contact measurement, and some techniques can provide three-dimensional information. However, confocal microscopy and interferometry are difficult to measure the buried gap inside the optically opaque material; the resolution and penetration depth of OCT are mutually restricted; Micro-CT can perform three-dimensional imaging, but its spatial resolution is usually in the micron level, and it has insufficient precision measurement capability for sub-micron or nanometer scale, and the imaging effect of the gap of the material with low density contrast is not good.

[0006] Mechanical probe method: such as atomic force microscope, scanning probe profilometer, etc. These methods can provide nanoscale surface topography information, but the scanning range is small, the speed is slow, and it is difficult to measure high aspect ratio or buried gaps. The profilometer may damage the sample surface, and the probe size limits its measurement capability for micro-complex structures.

[0007] Direct FIB cross-section analysis: The sample is cut by FIB to expose the gap cross-section, and then imaged by SEM or other methods. This method can obtain high-resolution local cross-section information, but it is destructive and may cause serious curtain effect on the edge of the gap during FIB milling. In addition, for some materials sensitive to ion beam or prone to severe deformation, amorphization or selective sputtering under FIB processing, the accuracy and reliability of direct FIB analysis will be affected.

[0008] Other indirect methods: Use soft polymer to replicate the surface microstructure and then perform microscopic analysis. This method is usually used for surface topography replication, and the soft polymer reverse mold is prone to deformation or shrinkage during demolding and subsequent operations, affecting the measurement accuracy, and is not suitable for precise three-dimensional structure analysis.

[0009] In summary, the existing technology has limitations in measuring complex three-dimensional structures, buried gaps, high aspect ratio gaps, or gaps in materials sensitive to FIB processing. Therefore, there is an urgent need for a new method that can overcome the above limitations and achieve high-precision, high-resolution three-dimensional quantitative characterization of such complex micro gaps. SUMMARY

[0010] The present application aims to overcome the shortcomings of existing micro gap measurement techniques in high-resolution three-dimensional characterization, complex structure adaptability, material system compatibility, and non-destructive analysis. It proposes a micro-nano gap measurement method that can be applied to various material systems and can achieve high-fidelity reverse mold replication, demolding, and sequential slice reconstruction of buried or deep and narrow gaps. This method integrates electrochemical deposition, thermal expansion differential demolding, focused ion beam sequential slicing, and image reconstruction into a unified indirect measurement scheme. It can accurately obtain the three-dimensional geometric information of the gap region without directly interfering or damaging the original sample structure.

[0011] TECHNICAL SCHEME

[0012] To solve the above problems, the present application proposes a micro gap measurement method and device based on nano additive manufacturing, which includes the following steps:

[0013] Step 1: Electrochemical deposition of a metal inverse mold in a micro-gap. A micro-gap (3) in a substrate material (1) to be measured is placed as the cathode in an electrolyte (2) containing metal ions corresponding to the intended inverse mold material. A metal (4) corresponding to the intended inverse mold material is placed as the anode. A direct current power supply (5) is connected with the positive terminal to the anode and the negative terminal to the micro-gap (3) in the substrate material (1) as the cathode. The corresponding metal is deposited in the micro-gap by electrochemical deposition to form a metal inverse mold (8) in the micro-gap.

[0014] Step 2: Thermal cycling of the sample with the metal inverse mold (8) in a precision temperature-controlled furnace (7). During thermal cycling, due to the difference in the coefficient of thermal expansion between the inverse mold material and the substrate material, the inverse mold shrinks more than the substrate when heated to 150-250 degrees Celsius and cooled, resulting in radial peeling stress and axial tensile stress at the interface. When the stress exceeds the interfacial adhesion, the metal inverse mold (8) separates from the substrate, forming a non-destructive separation.

[0015] Step 3: Processing and analysis of the metal inverse mold (8) successfully separated from the micro-gap. A focused ion beam generator is used to serially mill the metal inverse mold (8) to expose the internal morphology layer by layer. A series of image data (17) are obtained through microscopic observation equipment, and finally a high-precision three-dimensional model (18) of the micro-gap is established using three-dimensional image reconstruction methods.

[0016] Preferably, the inverse mold material is selected from metals or their alloys that have good electrical conductivity, good FIB processing performance, and suitable coefficients of thermal expansion, such as copper, nickel, gold, or their alloys.

[0017] Preferably, the substrate material is selected from materials that have a significant difference in the coefficient of thermal expansion from the inverse mold material, such as silicon, glass, ceramic, or metallic glass.

[0018] Preferably, in the electrochemical deposition step, the composition, pH, temperature, deposition potential or current density, and deposition time of the electrolyte are controlled to ensure the formation of a high-fidelity, low-defect (e.g., void-free) gap inverse mold.

[0019] Preferably, in the thermal demolding step, the temperature cycle curve is precisely controlled, including the heating rate, peak temperature, holding time, and cooling rate, to ensure that the inverse mold is cleanly separated from the substrate without plastic deformation or damage.

[0020] Preferably, before the FIB serial section analysis step, a protective layer (platinum, tungsten, or carbon) can be deposited on the surface of the inverse mold to protect the top surface features and reduce the curtain effect during FIB milling.

[0021] Preferably, in the FIB sequence section analysis step, the FIB milling parameters and SEM imaging parameters are optimized to obtain high-quality, low-noise, high-contrast two-dimensional cross-sectional images. It is possible to consider using a non-perpendicular tilt angle relative to the sample surface for FIB milling to further reduce processing defects.

[0022] Preferably, in the three-dimensional image reconstruction step, the image processing adopted includes image alignment, noise reduction, contrast enhancement, and precise anti-mold boundary segmentation, region growing algorithm and machine learning-based segmentation algorithm.

[0023] Advantages

[0024] Compared with the prior art, the present application has the following advantages:

[0025] 1. High-resolution three-dimensional characterization capability: combined with the high spatial resolution of FIB-SEM and the sequence sectioning technique, it can realize the accurate three-dimensional topography reconstruction and size measurement of micro gaps (including sub-micron and even nanometer level features).

[0026] 2. Suitable for buried and difficult-to-access gaps: through the indirect strategy of "copy-mold-analysis anti-mold", it can effectively measure those gaps that are deeply buried in the material or cannot be touched by traditional direct observation or detection methods due to complex structure.

[0027] 3. Wide material applicability: in theory, as long as a suitable anti-mold material for electrodeposition can be found, and there is enough difference in the thermal expansion coefficient between the material and the substrate, this method can be applied to a variety of different types of substrate materials.

[0028] 4. Potential low damage to the original sample: the main destructive analysis step is carried out on the anti-mold after demolding, and the original sample is theoretically less damaged after the anti-mold is formed and demolded, which is beneficial to preserve the original sample for other analysis or archiving.

[0029] 5. Overcome the limitations of FIB direct analysis of difficult materials: for some original materials that perform poorly under FIB direct processing (easy to charge, easy to damage, heterogeneous, etc.), this method analyzes the metal anti-mold with uniform properties and good FIB processing performance, avoiding the challenge of directly processing these difficult materials, and improving the accuracy and reliability of the measurement results.

[0030] 6. Synergistic effect improves overall performance: this invention combines electrochemical additive manufacturing, thermal demolding, FIB-SEM sequence sectioning and three-dimensional reconstruction in four stages, through cross-stage material selection and process parameter optimization, producing a synergistic effect beyond the simple combination of each independent technology, achieving efficient and accurate measurement of complex micro gaps. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a schematic diagram of a micro gap measurement method and device based on nano additive manufacturing proposed by the present application;

[0032] Figure 2 : schematic diagram of the thermal expansion driven inverse mold demolding stage;

[0033] Figure 3 : schematic diagram of the FIB sequential section analysis stage of the inverse mold;

[0034] Figure 4 : example diagram of the high-precision three-dimensional model of the inverse mold reconstructed from a series of two-dimensional cross-sectional images.

[0035] The label names in the figure are: 1, base material; 2, electrolyte; 3, micro gap; 4, metal block; 5, direct current power supply; 6, beaker; 7, precision temperature control furnace; 8, micro gap inverse mold; 9, microscopic observation equipment; 10, position signal; 11, DSP; 12, PC; 13, control signal; 14, controller; 15, focused ion beam generator; 16, circulating stepping motor; 17, series of microscopic observation images; 18, high-precision three-dimensional model of the micro gap. DETAILED DESCRIPTION

[0036] The technical solutions of the present application will be described in detail below in combination with the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and not to limit the present application.

[0037] Example 1: Measurement of micron-scale trench gap on silicon substrate

[0038] This embodiment aims to illustrate how to apply the method of the present application to measure the micron-scale trench gap with known design size prepared on the silicon substrate by photolithography and etching process.

[0039] Step one: select P-type single crystal silicon wafer as base material (1). Through standard photolithography and deep reactive ion etching process, arc-shaped trenches with a width of 2 μm, a depth of 5 μm and a length of 100 μm are made on the surface of the silicon substrate as micro gaps (3). Clean the silicon wafer to remove organic matter and particle contamination. Select copper as the inverse mold material. Copper has good electrical conductivity, mature electrodeposition process, significantly different thermal expansion coefficient from silicon, and good FIB processing performance. Acidic copper sulfate electrolyte is used, 200-250 g / L, sulfuric acid (H2SO4) 50-70 g / L.

[0040] Step two: Use silicon wafer with trenches as cathode, and select copper as anode material. Electrochemical additive manufacturing is carried out at 25°C. A constant current density of 10-30 mA / cm2 is used. The processing time is controlled to ensure that the copper can completely fill the trenches and form a dense, hollow, and accurate replication of the trench morphology of the metal reverse mold (8).

[0041] Step three: Use thermal expansion to drive the demolding of the metal reverse mold (8). Place the substrate material (1) with the metal reverse mold (8) in a precision temperature-controlled furnace (7). The heating rate is 5-10°C / min, and the temperature is slowly raised to avoid thermal shock. The peak temperature is 150-250°C. The temperature is kept at the peak temperature for 10-30 minutes to ensure uniformity. The cooling rate is 5-10°C / min, and the temperature is slowly lowered. During the cooling process, due to the large shrinkage of copper compared to silicon, shear stress and normal stress will be generated at the interface between the reverse mold (7) and the silicon substrate (1). When these stresses exceed the interfacial bonding strength, the copper reverse mold will be peeled off or separated from the silicon substrate. Take out the demolded copper reverse mold. At this time, the reverse mold (7) has a protruding structure that is a precise inverse of the original silicon trench.

[0042] Step four: Use FIB to analyze the sequence of cross-sections of the reverse mold. Fix the demolded copper reverse mold on the sample stage of the FIB-SEM. Deposit a thin protective layer (platinum, thickness 100 nm) on the surface of the reverse mold using the FIB in-situ gas injection system to protect the top surface features of the reverse mold and reduce the curtain effect during FIB milling.

[0043] Step five: Use a dual-beam FIB-SEM system. Position the area on the reverse mold (8) that represents the protruding structure of the original trench. Use Ga + ions with an ion beam energy of 5 keV for fine slicing and a 30 nA ion beam current with a slicing thickness of 20 nm.

[0044] Use automatic sequence slicing software to set the milling area, slicing thickness, and number of slices. Use FIB milling at a certain angle (5°-15°) relative to the sample surface normal to obtain a smoother cross-section. After each FIB slicing, immediately use SEM to image the newly exposed cross-section. The image resolution is 1024x768 pixels, and a series of (100-300) consecutive two-dimensional cross-sectional SEM images (17) are recorded.

[0045] Step six: Gap measurement by 3D image reconstruction. The obtained SEM image (17) sequence is imported into image processing software. The sequence images are precisely aligned to correct the slight drift or jitter that may occur during the FIB slicing process. The automatic alignment tool based on feature points is used. The images are filtered to remove noise. The brightness and contrast of the whole image are adjusted to make the boundary of the inverse mold clearer. In each two-dimensional cross-sectional image, the profile boundary of the inverse mold material representing the original gap is precisely segmented. The segmented binary image sequence is input into the 3D reconstruction module. The volume rendering algorithm is used to generate a 3D digital model of the copper inverse mold (18).

[0046] On the reconstructed 3D model, the built-in measurement tool of the software is used to accurately measure the size of the inverse mold protruding structure representing the original trench.

[0047] The details of the present application are known to the art.

[0048] The above examples are only to illustrate the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made in accordance with the spirit and essence of the present application shall be covered within the protection scope of the present application.

Claims

1. A method and apparatus for measuring microslit based on nanometer additive manufacturing, characterized in that, The method comprises the following steps: Step one: placing a micro-gap (3) with a substrate material (1) to be measured as a cathode in an electrolyte (2) containing metal ions corresponding to a predetermined counter-mold material, while setting a metal (4) corresponding to the predetermined counter-mold material as an anode, and performing electrochemical additive manufacturing by a direct current power supply (5) with its positive electrode connected to the anode and its negative electrode connected to the micro-gap (3) as the cathode, so that the corresponding metal fills the micro-gap and forms a metal counter-mold (8) of the micro-gap; Step two: placing the sample with the metal counter-mold (8) into a precision temperature control furnace (7) for at least one thermal cycle treatment. During the thermal cycle, due to the difference in the thermal expansion coefficients between the counter-mold material and the substrate material, when heated to 150-250 degrees Celsius and cooled, the volume shrinkage of the counter-mold is greater than that of the substrate, resulting in radial peeling stress and axial positive tensile stress at the interface. When the stress exceeds the interfacial adhesion, the metal counter-mold (8) separates, forming a non-destructive separation; Step three: processing and analyzing the metal counter-mold (8) successfully separated from the micro-gap, using a focused ion beam generator (15) to perform a series of grinding on the metal counter-mold (8) to expose the internal topography layer by layer, obtaining multiple image data (17) through a microscopic observation device (9), and finally establishing a high-precision three-dimensional model (18) of the micro-gap using a three-dimensional image reconstruction method.

2. The method of claim 1, wherein, The material of the metal counter-mold (8) is one or more of copper, nickel, gold, silver, platinum or their alloys; wherein the material of the substrate material (1) is one or more of silicon, glass, ceramic or metallic glass.

3. The method of claim 1, wherein, The preset temperature change of the thermal cycle treatment in step two mainly includes cooling the sample to a predetermined low temperature and then warming it to near the initial temperature.

4. The method according to claim 1 or 3, characterized in that, The thermal expansion coefficient of the material of the metal counter-mold (8) is greater than the thermal expansion coefficient of the substrate material.

5. The method of claim 1, wherein, After step two and before step three, an auxiliary separation step is also included for the loosened or partially separated metal counter-mold (8), which includes ultrasonic treatment or clean gas blowing to ensure complete removal of the metal counter-mold (8).

6. The method of claim 1, wherein, The electrochemical additive manufacturing process in step one is performed by precisely controlling one or more parameters such as the composition, pH value, operating temperature, potential or current density of the electrolyte, and total deposition time.

7. The method of claim 1, wherein, The thermal cycle treatment in step two can also include a combined process of heating, holding and cooling, wherein the peak temperature of any heating process is set below the threshold temperature at which irreversible damage occurs to the material of the metal counter-mold (8) and the substrate material, and is intended to assist or achieve the demolding of the metal counter-mold (8).

8. The method of claim 1, wherein, In step three, the slice thickness of the FIB series grinding is set to be between 20 nanometers and 50 nanometers, the ion species used is gallium ion, the ion beam energy is set to be between 5 kiloelectron volts and 30 kiloelectron volts, the ion beam current is set to be between 10 picoamperes and 1000 picoamperes, and the incident angle of FIB cutting relative to the cross section to be observed is set to be between 5 degrees and 15 degrees.

9. The method of claim 1, wherein, In the step three, the microscopic observation equipment is a scanning electron microscope, and a secondary electron detector or a backscattered electron detector is used for imaging.

10. The method of claim 1, wherein, The process of establishing the three-dimensional distribution map in the step three includes image alignment, image enhancement, target region segmentation and three-dimensional modeling steps on the obtained multiple image data; wherein the target region segmentation can use a neural network algorithm based on deep learning.

11. The method of claim 1, wherein, The finally established three-dimensional model of the micro gap is used for further analysis of one or more parameters of the micro gap, such as geometric size, volume size, internal topographic features and surface roughness.

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