Full-nanotwinned silver deposition layer with high {111} preferred orientation and method of making

Abstract

This invention discloses a fully nanotwinned silver deposition layer with a highly {111}-preferred orientation. The grains contain nanotwin lamellae, and there is no transition layer between the deposition layer and the copper substrate. The grain size and orientation are identical to those of the copper substrate. During fabrication, an electrodisplacement deposition technique is employed. By optimizing the solution composition, deposition parameters, and the microstructure of the copper substrate, the nanotwin lamellae and their orientation within the silver deposition layer are controlled. This invention overcomes the shortcomings of existing methods, such as the need for additional photolithography processes, the inability to avoid the formation of transition layers in the silver layer, and low deposition rates. It enables selective deposition at a high deposition rate on the copper substrate surface, resulting in a layer without a transition layer, strong adhesion, high thermal stability, uniform thickness, and a highly {111}-preferred orientation. The method is simple and easy to implement, perfectly compatible with existing copper fabrication processes, and at a lower cost.

Description

Technical Field

[0001] This invention relates to the field of microelectronic materials and their preparation technology, and in particular to a silver deposition layer with a highly {111}-preferred orientation and its preparation method. Background Technology

[0002] In recent years, with the emergence of new application fields such as 5G, artificial intelligence, autonomous driving, and metaverse, traditional copper pillar bump bonding technology can no longer meet the high interconnect density requirements of future microelectronic devices. Copper-copper direct bonding technology has attracted much attention due to its high conductivity, high electromigration resistance, and low cost, and is considered one of the most promising methods for achieving ultra-high density interconnects. Although copper-copper bonding has advantages, copper is easily oxidized, requiring bonding temperatures exceeding 400°C or chemical pretreatment under specific conditions (H. Hu, K. Chen, Development of low temperature CuCu bonding and hybrid bonding for three-dimensional integrated circuits (3DIC), Microelectronics Reliability, 127, 2021, 114412). The high thermal budget and stringent processing conditions of copper-copper bonding processes limit its widespread acceptance in the industry.

[0003] Various attempts have been made to lower the bonding temperature of copper-copper bonding. One promising solution is the use of nanotwinned copper with a highly {111}-preferred orientation. Thanks to the fastest surface diffusion rate and the lowest oxidation rate of the {111}-oriented surface, the copper-copper bonding temperature can be reduced to 150-250 °C under vacuum and air atmosphere conditions (Y. Liu, Y. Lu, K. Tu, Low temperature interfacial reaction in 3D IC nanoscalematerials, Materials Science and Engineering: R: Reports, 151, 2022, 100701). Furthermore, the nanotwinned structure has been found to enhance copper atom transport, further strengthening copper-copper bonding. However, despite the particularly low oxidation rate of nanotwinned copper with a highly {111}-preferred orientation, copper oxidation cannot be completely avoided from pretreatment to bonding.

[0004] Metal passivation is considered a promising technical approach to address the aforementioned challenges. Compared to copper, silver exhibits better oxidation resistance (it hardly oxidizes at room temperature, and its surface oxides decompose at 180°C) and possesses the highest electrical and thermal conductivity among metals. By sputtering a silver passivation layer onto the electroplated copper surface, the entire internal electroplated copper area can be effectively protected from oxidation, and it exhibits good compatibility with existing copper fabrication processes (T. Chou, S. Huang, P. Chen, et al., Electrical and Reliability Investigation of Cu-to-Cu Bonding With Silver Passivation Layer in 3-D Integration, IEEE Transactions on Components, Packaging and Manufacturing Technology, 11, 2021, 2156-3985). However, silver is typically soft, thus limiting its application in microelectronic devices. To address this, researchers have attempted to introduce nanotwin structures with a highly {111}-preferred orientation to improve the mechanical properties of silver and further reduce the bonding heat budget. In 2022, researchers from National Tsing Hua University and National Chiao Tung University in Taiwan (L. Chang, J. Wang, T. Hung, K. Chen, F. Ouyang, Direct metal bonding using nanotwinned Ag films with {111} surface orientation under air atmosphere for heterogeneous integration, Applied Surface Science, 576, 2022, 151845) successfully prepared nanotwinned silver with a highly {111} preferred orientation using magnetron sputtering. Direct bonding of silver to silver in an air atmosphere was achieved within 3-60 minutes at temperatures of 150-250°C. Shear tests showed a bonding strength as high as 70 MPa, which is 2-3 times that of traditional solder joints.

[0005] Despite these advantages, large-scale production of highly {111}-preferred-orientation nanotwinned silver deposits via sputtering remains a challenge. Compared to mainstream electroplating techniques, magnetron sputtering requires advanced and expensive equipment and has a relatively low deposition rate. Furthermore, it necessitates additional photolithography processes to accommodate existing copper fabrication processes (sponging silver onto copper). More importantly, the formation of randomly oriented, non-twinned transition regions at the bottom of sputtered silver materials remains a significant challenge. These transition layers can induce abnormal grain growth during subsequent bonding, altering silver orientation and grain morphology, leading to bonding failure (Y. Lai, P. Wu, T. Chuang, Thermal stability of grain structure for Ag nanotwinned films sputtered with substrate bias, Materialsia, 20, 2021, 101215). These factors limit its practical application, thus necessitating a method for preparing a highly {111}-preferred-orientation fully nanotwinned silver deposit compatible with existing copper fabrication processes. Summary of the Invention

[0006] In view of the above, the technical problem to be solved by the present invention is to address the problems mentioned in the background art by providing a fully nanotwinned silver deposition layer with a highly {111}-preferred orientation and its preparation method. The main objective is to comprehensively utilize the principle of electrodisplacement reaction between silver and a copper substrate, and to optimize the solution composition, deposition parameters, and microstructure of the copper substrate in the electrodisplacement deposition process to control the nanotwinned crystalline layers and their orientation in the silver deposition layer. This allows for the selective deposition at a high deposition rate on the copper substrate surface to obtain a fully nanotwinned silver deposition layer with no transition layer, high thermal stability, good adhesion, uniform thickness, and a highly {111}-preferred orientation, thus providing the possibility for industrial production and widespread application.

[0007] To achieve the above objectives, the present invention mainly provides the following technical solutions:

[0008] On one hand, embodiments of the present invention provide a silver deposition layer with a highly {111}-preferred orientation and a fully nanotwinned structure, wherein, in the microstructure of the silver deposition layer with a highly {111}-preferred orientation, the grains contain nanotwin wafer layers, there is no transition layer between the deposition layer and the substrate copper material, and the grain size and orientation are the same as those of the substrate copper material.

[0009] Preferably, the thickness of the silver deposition layer with a highly {111}-preferred orientation and a fully nanotwinned structure is 15-400 nanometers.

[0010] Preferably, the average thickness of the nanotwin wafer layer in the silver deposition layer with a highly 111 preferred orientation is 2-150 nanometers.

[0011] Preferably, the ratio of the diffraction intensity of the {111} orientation to the {200} orientation of the silver deposition layer with a highly {111} preferred orientation is not less than 10:1.

[0012] Preferably, the silver deposition layer with a highly preferred {111} orientation exhibits good thermal stability. After annealing in a vacuum atmosphere at 400 degrees Celsius for 2 hours, the nanotwin crystal layer does not completely disappear, and the ratio of the {111} orientation to the {200} orientation diffraction intensity of the silver deposition layer with a highly preferred {111} orientation is not less than 10:1.

[0013] As a further optimization of the silver deposition layer with a highly {111}-preferred orientation and its preparation method, the substrate copper material is copper with a highly {111}-preferred orientation, preferably columnar nanotwinned copper with a highly {111}-preferred orientation.

[0014] Preferably, the ratio of the diffraction intensity of the {111} to {200} oriented crystal planes in the substrate copper material is not less than 10:1.

[0015] Preferably, the proportion of {111} oriented crystal planes in the substrate copper material is not less than 80%.

[0016] On the other hand, embodiments of the present invention provide a method for preparing a fully nanotwinned silver deposition layer with a highly {111} preferred orientation as described in any of the above claims, wherein the fully nanotwinned silver deposition layer with a highly {111} preferred orientation is deposited on the surface of a copper substrate using an electrodisplacement technique, comprising the following steps:

[0017] Step a), Pretreatment of substrate copper material: First, the surface of the substrate copper material to be deposited is degreased, rinsed with deionized water, then immersed in the pretreatment solution to remove the surface oxide film, and finally dried with nitrogen gas;

[0018] Step b), prepare the electrodisplacement solution and adjust the pH;

[0019] Step c), adjust the temperature of the electrodisplacement solution to 30-60℃;

[0020] Step d) Immerse the substrate copper material in a flowing electrodisplacement solution for 10-300 seconds;

[0021] Step e) Remove the copper substrate material that has undergone electro-displacement from the electro-displacement solution, thoroughly wash it in flowing deionized water, dry it with clean nitrogen gas, and seal it for storage.

[0022] As a further optimization of the silver deposition layer with a highly {111} preferred orientation and its preparation method, the temperature of the electrodisplacement solution in step c) is adjusted to 45-55℃.

[0023] As a further optimization of the silver deposition layer with a highly {111}-preferred orientation and its preparation method, the electrodisplacement solution in step b) contains silver ions and a silver complexing agent. 、 Silver plating additive, pH adjuster and pure water.

[0024] As a further optimization of the silver deposition layer with a highly {111} preferred orientation and its preparation method, in step d), one or more of the following means are used to achieve the electrodisplacement solution in a flowing state: controlled flow rate flushing, ultrasonic disturbance, magnetic stirring, aeration, spraying, substrate rotation or reciprocating motion.

[0025] As a further optimization of the silver deposition layer with a highly {111} preferred orientation and its preparation method, the pretreatment solution in step a) is one or more of dilute hydrochloric acid aqueous solution, citric acid aqueous solution, and copper material chemical polishing solution.

[0026] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects:

[0027] 1. This invention provides a fully nanotwinned silver deposition layer with a highly {111}-preferred orientation. The microstructure contains nanotwin wafers within its grains, and there is no transition layer between the deposition layer and the copper substrate. Furthermore, the grain orientation is the same as that of the copper substrate. Due to the absence of a transition layer and the highly {111}-preferred orientation, the fully nanotwinned silver deposition layer exhibits high thermal stability. Even after annealing at 400 degrees Celsius in a vacuum atmosphere for 2 hours, the nanotwin wafers do not completely disappear, and the ratio of the {111} orientation to the {200} orientation diffraction intensity of the fully nanotwinned silver deposition layer is not less than 10:1, which meets the requirements of metal bonding processes.

[0028] 2. This invention provides a method for preparing a fully nanotwinned silver deposition layer with a highly {111}-preferred orientation. It utilizes the unique electrodisplacement reaction principle between silver and a copper substrate, employing electrodisplacement deposition technology to selectively deposit a fully nanotwinned silver deposition layer of a certain thickness on the surface of a copper substrate. Furthermore, by optimizing the solution composition, deposition parameters, and the microstructure of the copper substrate in the electrodisplacement deposition process, the nanotwin wafer layers and their orientation within the silver deposition layer can be controlled. The method is simple and easy to implement, requires no additional photolithography process, offers a fast deposition rate, good adhesion, and lower cost. It is also perfectly compatible with existing copper fabrication processes (such as photolithography, electroplating, and chemical mechanical polishing), thus enabling industrial production and widespread application. Attached Figure Description

[0029] Figure 1 This is a cross-sectional microstructure diagram of the silver deposition layer with a highly {111}-preferred orientation and its substrate copper in Embodiment 1 of the present invention.

[0030] Figure 2 This is the X-ray diffraction pattern of the silver deposition layer with a highly {111} preferred orientation and its substrate copper in Embodiment 1 of the present invention.

[0031] Figure 3 This is a cross-sectional morphology image of the silver deposition layer with a highly {111} preferred orientation, exhibiting a fully nanotwinned structure, under a transmission electron microscope in Embodiment 1 of the present invention.

[0032] Figure 4 This is a selected area electron diffraction pattern of the interface region between the silver deposition layer with a highly {111}-preferred orientation and the substrate copper material in Embodiment 1 of the present invention.

[0033] Figure 5 This is a cross-sectional image of the silver deposition layer with a highly {111} preferred orientation, exhibiting a fully nanotwinned structure, as shown in Embodiment 1 of the present invention, after being annealed for 2 hours in a vacuum atmosphere at 400 degrees Celsius.

[0034] Figure 6 This is a cross-sectional image of the silver deposition layer with a highly {111} preferred orientation, exhibiting a fully nanotwinned structure, as shown in Embodiment 1 of the present invention, after annealing for 2 hours in a vacuum atmosphere at 600 degrees Celsius.

[0035] Figure 7 The X-ray diffraction pattern of the silver deposition layer with a highly {111} preferred orientation and its substrate copper after annealing is shown in Example 1.

[0036] Figure 8This is an electron backscattering diffraction pattern of the surface of the silver deposition layer with a highly {111}-preferred orientation in Embodiment 1 of the present invention.

[0037] Figure 9 This is the {111} pole figure of the silver deposition layer with a highly {111} preferred orientation and a fully nanotwinned structure in Embodiment 1 of the present invention;

[0038] Figure 10 This is a cross-sectional morphology image of the silver deposition layer with a highly {111} preferred orientation, exhibiting a fully nanotwinned structure, under a transmission electron microscope in Embodiment 2 of the present invention.

[0039] Figure 11 This is a high-resolution cross-sectional image of the silver deposition layer with a highly {111}-preferred orientation and an all-nanotwin structure in Embodiment 2 of the present invention, under a transmission electron microscope.

[0040] Figure 12 This is a cross-sectional image of the silver deposition layer with a highly {111} preferred orientation, exhibiting a fully nanotwinned structure, under a transmission electron microscope after annealing for 2 hours in a vacuum atmosphere at 400 degrees Celsius in Embodiment 2 of the present invention.

[0041] Figure 13 This is an electron backscattering diffraction pattern of the surface of the silver deposition layer with a highly {111}-preferred orientation in Embodiment 3 of the present invention.

[0042] Figure 14 This is the {111} pole figure of the surface of the silver deposition layer with a highly {111} preferred orientation and a fully nanotwinned structure in Embodiment 3 of the present invention;

[0043] Figure 15 This is a histogram of grain boundary orientation difference distribution of the silver deposition layer with a highly {111} preferred orientation in the fully nanotwinned structure of the present invention, in Embodiment 3 of the present invention;

[0044] Figure 16 This is the X-ray diffraction pattern of the silver deposit and its substrate copper in Comparative Example 3. Implementation

[0045] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings:

[0046] This invention can be implemented in many different forms and should not be considered as limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully express the scope of the invention to those skilled in the art.

[0047] This invention discloses a silver deposition layer with a highly {111}-preferred orientation and its preparation method. Utilizing the higher electromotive force of silver compared to copper, a silver deposition layer of a certain thickness with a fully nanotwinned structure is selectively deposited on the surface of a copper substrate using electrodisplacement deposition technology. There is no transition layer between the silver deposition layer and the copper substrate, and the grain orientation is identical to that of the copper substrate. Control over the nanotwin crystalline layers and their orientation within the silver deposition layer can be achieved simply by optimizing the solution composition, deposition parameters, and the microstructure of the copper substrate during the electrodisplacement deposition process. Examples and comparative figures are provided below for illustration.

[0048] Example 1

[0049] In this embodiment, a 250-nanometer-thick silver deposition layer with a highly {111}-preferred orientation and an all-nanotwin structure is deposited on a 4-inch copper substrate wafer. Figure 1 As shown, where:

[0050] The ratio of the {111} orientation to the {200} orientation diffraction intensity of the fully nanotwinned silver deposition layer with a highly {111}-preferred orientation is greater than 100:1. Figure 2 The substrate copper material is a highly {111}-preferred oriented columnar nanotwinned copper with a grain size of 5 micrometers. The ratio of the diffraction intensity of the {111} to {200} oriented crystal planes is higher than 100:1. Figure 2 The proportion of {111} oriented crystal planes is higher than 97%.

[0051] Figure 3 The image shows the cross-sectional morphology of the silver deposition layer with a highly {111}-preferred orientation and a fully nanotwinned structure in Example 1 under a transmission electron microscope. Statistical analysis shows that the thickness of the nanotwin wafers in the silver deposition layer ranges from 2 to 55 nanometers, with an average twin thickness of 30 nanometers. No transition layer was found at the bottom of the deposition layer. Figure 4 Selected area electron diffraction (SEED) patterns at the interface between the silver deposit and the copper substrate further confirm the epitaxial relationship between the silver deposit and the copper substrate, exhibiting the same crystal orientation. After annealing at 400°C in a vacuum atmosphere for 2 hours... Figure 5 The nanotwin layer in the silver deposition layer did not disappear, and the average thickness of the nanotwin layer did not change significantly. After annealing for 2 hours in a vacuum atmosphere at 600 degrees Celsius, the average thickness of the nanotwin layer increased slightly. Figure 6 ).

[0052] Figure 7The image shows the X-ray diffraction patterns of the silver deposition layer with a highly {111}-preferred orientation and its copper substrate after annealing, as described in Example 1. After annealing for 2 hours in a vacuum atmosphere at 400 degrees Celsius, the ratio of the {111}-oriented to the {200}-oriented diffraction intensity of the silver deposition layer is higher than 50:1; after annealing for 2 hours in a vacuum atmosphere at 600 degrees Celsius, the ratio of the {111}-oriented to the {200}-oriented diffraction intensity of the silver deposition layer is also higher than 50:1. The silver deposition layer still exhibits a highly {111}-preferred orientation, indicating that the silver deposition layer has high thermal stability.

[0053] Figure 8 The image shows the electron backscattering diffraction pattern of the silver deposition layer with a highly {111}-preferred orientation and an all-nanotwin structure in Example 1. Grain boundaries of ordinary sizes are marked in white. It can be seen that no grain boundaries other than twin boundaries (55°-63.5°, marked in black) were observed within the silver deposition layer grains. Figure 9 The {111} pole figure of the sample shows that the silver deposition layer has a highly {111} preferred orientation. The results also indicate that the grain size and orientation of the silver deposition layer are the same as those of the substrate copper material.

[0054] The specific preparation method of the silver deposition layer with a highly {111}-preferred orientation and a fully nanotwinned structure in this embodiment includes the following steps:

[0055] Step a), Pretreatment of substrate copper material: First, the surface of the substrate copper material to be deposited is degreased, rinsed with deionized water, then immersed in commercially available copper material polishing to remove the surface oxide film, and finally dried with nitrogen gas.

[0056] Step b), prepare the electrodisplacement solution and adjust the pH;

[0057] Step c), adjust the temperature of the electrodisplacement solution to 50°C;

[0058] Step d) Immerse the substrate copper material in a flowing electrodisplacement solution for 150 seconds;

[0059] Step e) Remove the copper substrate material that has undergone electro-displacement from the electro-displacement solution, thoroughly wash it in flowing deionized water, dry it with clean nitrogen gas, and seal it for storage.

[0060] In this embodiment, the concentration of silver ions in the electrodisplacement solution is 0.9 g / L, the total concentration of complexing agent and additives is 0.03 M, and the pH range is 0.8-1. Silver nitrate is used as the silver ions, 68% nitric acid is used as the pH adjuster, and commercially available products are used for both the complexing agent and additives. Magnetic stirring is used to keep the electrodisplacement solution in a flowing state.

[0061] To briefly explain the principle of the electrodisplacement deposition technique used in this invention, since the electromotive force of copper (+0.34V) is lower than that of silver (+0.79V), when the copper substrate is immersed in a silver electrodisplacement solution, the copper substrate material dissolves to form copper ions. This dissolution process also generates electrons, at which point the copper substrate becomes a reducing agent, promoting the reduction of silver ions in the solution and forming adsorbed atoms on the copper substrate. Subsequently, the adsorbed atoms grow to eventually form a silver deposition layer. Compared with traditional electroplating techniques, there is no so-called edge effect in the electrodisplacement process, so the deposited layer often has better thickness uniformity. In addition, since the electrodisplacement reaction requires the dissolution of the copper substrate, silver atoms may enter and occupy copper lattice positions, and adapt to lattice mismatch by introducing periodically distributed mismatched dislocations, ultimately exhibiting the same orientation as the copper substrate to minimize the total interface energy. In summary, this invention utilizes the special electrodisplacement reaction principle between silver and copper to achieve the deposition of a certain thickness of a fully nanotwinned silver deposition layer with a highly {111}-preferred orientation on the surface of a copper substrate material.

[0062] Example 2

[0063] In this embodiment, a 400-nanometer-thick silver deposition layer with a highly {111}-preferred orientation and an all-nanotwin structure is deposited on a 4-inch copper substrate wafer, wherein:

[0064] The silver deposition layer with a highly {111}-preferred orientation exhibits a diffraction intensity ratio of {111} to {200} orientation exceeding 50:1. The substrate copper material is a highly {111}-preferred orientation columnar nanotwinned copper with a grain size of 5 micrometers, a diffraction intensity ratio of {111} to {200} orientations of 80:1, and a {111} orientation accounting for no less than 95% of the total.

[0065] Figure 10 The image shows the cross-sectional morphology of the silver deposition layer with a highly {111}-preferred orientation and a fully nanotwinned structure as described in Example 2, under a transmission electron microscope. The thickness of the nanotwin lamellae in the silver deposition layer ranges from 10 to 150 nanometers, with an average thickness of 50 nanometers at room temperature. No transition layer was found at the bottom of the deposition layer. High-resolution transmission electron images also confirm that the twin boundaries in the silver deposition layer are coherent twin boundaries. Figure 11 After annealing in a vacuum atmosphere at 400 degrees Celsius for 2 hours, the nanotwin crystal layer did not disappear, and the twin thickness remained essentially unchanged. Figure 12 ).

[0066] The specific preparation method of the silver deposition layer with a highly {111}-preferred orientation and a fully nanotwinned structure in this embodiment includes the following steps:

[0067] Step a), Pretreatment of substrate copper material: First, the surface of the substrate copper material to be deposited is degreased and rinsed with deionized water. Then, it is immersed in a 20% dilute hydrochloric acid aqueous solution to remove the surface oxide film. Finally, it is dried with nitrogen gas.

[0068] Step b), prepare the electrodisplacement solution and adjust the pH;

[0069] Step c), adjust the temperature of the electrodisplacement solution to 60°C;

[0070] Step d) Immerse the substrate copper material in a flowing electrodisplacement solution for 300 seconds;

[0071] Step e) Remove the copper substrate material that has undergone electro-displacement from the electro-displacement solution, thoroughly wash it in flowing deionized water, dry it with clean nitrogen gas, and seal it for storage.

[0072] In this embodiment, the concentration of silver ions in the electrodisplacement solution is 1 g / L, the total concentration of complexing agent and additives is 320 g / L, and the pH range is 1-1.5. Silver sulfate is used as the silver ions, 20% dilute hydrochloric acid is used as the pH adjuster, a halide salt is used as the complexing agent, and polyethylene glycol 400 and isomeric tridecyl alcohol polyoxyethylene ether are used as additives. Magnetic stirring is employed to ensure the electrodisplacement solution is in a flowing state.

[0073] Example 3

[0074] This embodiment is at 1cm 2 A 200 nm thick silver deposition layer with a highly {111}-preferred orientation and an all-nanotwinned structure was deposited on a copper substrate, wherein:

[0075] The silver deposition layer with a highly {111}-preferred orientation and a fully nanotwinned structure exhibits a diffraction intensity ratio of {111} to {200} orientation exceeding 500:1. The substrate copper material is commercially available copper with a highly {111}-preferred orientation, a grain size of 1 cm, a diffraction intensity ratio of {111} to {200} orientation exceeding 500:1, and a {111} orientation accounting for 100% of the crystal planes.

[0076] Figure 13 The image shows the electron backscattering diffraction pattern of the silver deposition layer with a highly {111}-preferred orientation and an all-nanotwin structure in Example 3. No grain boundaries other than twin boundaries (55°–63.5°, marked in black) were observed in the silver deposition layer. Figure 14 The {111} texture diagram of the sample shows six equally bright spots in a hexagonal pattern with a Chi angle of ~70.5°, indicating that the silver deposition layer has a highly {111} preferred orientation and the presence of twins. Figure 15The histogram of grain boundary orientation difference distribution shows that the twin content in the silver deposition layer exceeds 90% and no ordinary grain boundaries at any other angle are observed. This also proves that the silver deposition layer has the same grain size as the substrate copper material and does not produce a fine equiaxed transition layer with random orientation.

[0077] The specific preparation method of the silver deposition layer with a highly {111}-preferred orientation and a fully nanotwinned structure in this embodiment includes the following steps:

[0078] Step a), Pretreatment of substrate copper material: First, the surface of the substrate copper material to be deposited is degreased and rinsed with deionized water. Then, it is immersed in a 20% citric acid aqueous solution to remove the surface oxide film and finally dried with nitrogen.

[0079] Step b), prepare the electrodisplacement solution and adjust the pH;

[0080] Step c), adjust the temperature of the electrodisplacement solution to 50°C;

[0081] Step d) Immerse the substrate copper material in a flowing electrodisplacement solution for 120 seconds;

[0082] Step e) Remove the copper substrate material that has undergone electro-displacement from the electro-displacement solution, thoroughly wash it in flowing deionized water, dry it with clean nitrogen gas, and seal it for storage.

[0083] In this embodiment, the concentration of silver ions in the electrodisplacement solution is 0.9 g / L, the total concentration of complexing agent and additives is 0.03 M, and the pH range is 0.8-1. Silver nitrate is used as the silver ions, 68% nitric acid is used as the pH adjuster, and commercially available products are used for both the complexing agent and additives. Magnetic stirring is used to keep the electrodisplacement solution in a flowing state.

[0084] Comparative Example 1

[0085] In 2020, the team led by T.H. Chuang at National Taiwan University deposited 8-micrometer-thick nanotwin silver layers on silicon substrates with a 100-nanometer titanium deposition layer using magnetron sputtering. The twin layer thickness was 8-12 nanometers, and the deposition rate was 1.35-1.795 nanometers / second (T. Chuang, P. Wu, Y. Lin, Lattice buffer effect of Ti film on the epitaxial growth of Ag nanotwins on Si substrates with various orientations, Materials Characterization, 167, 2020, 110509). They found that the transition layer thicknesses in the nanotwin silver layers sputtered on {100}, {110}, and {111} oriented single-crystal silicon substrates were 1.22, 2.16, and 1.78 micrometers, respectively.

[0086] In 2021, Zhuang Donghan's team continued their research on the thermal stability of magnetron sputtered nanotwinned silver (Y. Lai, P. Wu, T. Chuang, Thermal stability of grain structure for Ag nanotwinned films sputtered with substrate bias, Materialia, 20, 2021, 101215). They discovered that some nanotwinned silver layers exhibited severe abnormal grain growth (starting from the transition layer) after annealing at 250℃ for 1 hour. The nanotwinned crystalline layers disappeared, and the grain orientation changed from a {111} preferred orientation to a {200} preferred orientation. Clearly, nanotwinned silver layers prepared by magnetron sputtering often contain a transition layer, and their thermal stability needs further improvement.

[0087] Comparative Example 2

[0088] In 2021, the team led by T.H. Chuang at National Taiwan University also reported the fabrication of 2-micrometer-thick {111}-oriented nanotwinned silver nanolayers on a titanium-coated {100}-oriented silicon substrate using plasma-assisted electron beam evaporation (P. Wu and T. Chuang, Evaporation of ag nanotwinned films on sisubstrates with ion beam assistance, IEEE Transactions on Components, Packaging and Manufacturing Technology, 11, 2021, 2222-2228.). Although the deposition rate of electron beam evaporation is higher than that of magnetron sputtering, a transition layer of over 400 nanometers still exists at the bottom of the silver layer.

[0089] Comparative Example 3

[0090] In this comparative example, a 400-nanometer-thick silver deposition layer was deposited on a 4-inch copper substrate. The only difference from Example 2 is that the substrate copper material is copper with a highly {220} preferred orientation, with a grain size of 5 micrometers. The ratio of the diffraction intensity of the {111} to {200} oriented crystal planes is close to 1:1, but the ratio of the diffraction intensity of the {220} to {200} oriented crystal planes is higher than 100:1.

[0091] Figure 16 The X-ray diffraction patterns of the silver deposited layer and its copper substrate in Comparative Example 3 show that the ratio of the diffraction intensity of the {111} orientation to the {200} orientation of the silver deposited layer is 1:1, but the ratio of the diffraction intensity of the {220} orientation to the {200} orientation is higher than 150:1, indicating that the silver deposited layer has the same {220} preferred orientation as the substrate.

[0092] Based on Examples 1-3, it can be seen that by optimizing the solution composition, deposition parameters, and microstructure of the substrate copper material in the electrodisplacement deposition process, the control of the nanotwin layer and crystal orientation in the silver deposition layer can be achieved.

[0093] Considering that the stacking fault energy of silver is very small (17 mJ / m) 2This allows for the formation of wider, stable stacking faults, which is beneficial for the formation of nanotwin lamellae layers in silver that are denser and longer than those in other metals. According to the thermodynamic model of nanotwin growth proposed by Professor Xinghang Zhang et al. of Purdue University (D. Bufford, H. Wang, X. Zhang, Highstrength, epitaxial nanotwinned Ag films, Acta Materialia, 59, 2011, 93-101), a higher deposition rate can further reduce the critical nucleation radius for twin formation to a value comparable to the critical radius for defect-free nucleation, thereby promoting twin nucleation. Furthermore, the silver deposition rate in this invention is relatively fast (1.2-2.2 nm / s), higher than that reported in the literature for magnetron sputtering and electron beam evaporation (0.2-1.8 nm / s). This can preliminarily explain the formation of the nanotwin lamellae layer structure in the silver deposition layer and the influence of the deposition rate on the thickness of the twin lamellae layer.

[0094] Furthermore, in order to evaluate the bonding strength between the silver deposition layer with a highly {111} preferred orientation and the copper substrate material in this invention, the bonding strength of the silver deposition layer on the copper substrate material in this invention was studied by tape test according to the relevant standard of ASTM D3359-02. The results showed that in Examples 1-3, no peeling or removal of the silver deposition layer was observed along the cut, indicating that the method proposed in this invention can ensure a stable bond between the silver deposition layer and the copper substrate material.

[0095] Finally, it should be emphasized that the method proposed in this invention does not require expensive equipment and can be carried out in a simple beaker or a homemade tank, requiring only a heating system and a solution stirring device or motion mechanism. Taking the deposition of 25 nm and 250 nm thick silver deposits with a highly {111}-preferred orientation and a fully nanotwinned structure on a 4-inch wafer as an example, the cost of using the method of this invention was simply evaluated and compared with magnetron sputtering. According to current market research results, without considering the cost of equipment and substrate copper materials, the cost of magnetron sputtering 25 nm thick silver (and without guaranteeing a fully nanotwinned structure) is 250-450 yuan per wafer; the cost of magnetron sputtering 250 nm thick silver with a twinned structure is 350-550 yuan per wafer. In comparison, the cost of configuring 5 liters of the electrodisplacement solution in Example 1 of this invention is approximately 1000 yuan. Without considering the costs of equipment, substrate copper material, and solution maintenance, 5 liters of solution can prepare 20-35 silver wafers with a 25 nm thick fully twinned structure, thus the cost per wafer is 28-50 yuan; 5 liters of solution can prepare 10-15 silver wafers with a 250 nm thick fully twinned structure, thus the cost per wafer is 67-100 yuan. In fact, by performing necessary maintenance on the electrodisplacement solution (e.g., using an ion exchange membrane to remove excess copper ions, and adding silver ions, complexing agents, and additives), the service life of the electrodisplacement solution can be greatly extended, further reducing production costs. Therefore, the method proposed in this invention has a greater advantage in terms of production cost.

[0096] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0097] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. The above description is only for specific embodiments of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a silver deposition layer with a highly {111}-preferred orientation and a fully nanotwinned structure, wherein the microstructure of the silver deposition layer with a highly {111}-preferred orientation and a fully nanotwinned structure contains nanotwin wafers inside the grains, there is no transition layer between the deposition layer and the substrate copper material, and the grain size and orientation are the same as those of the substrate copper material. The substrate copper material is copper with a highly {111} preferred orientation; The ratio of the diffraction intensity of the {111} orientation to that of the {200} orientation in the copper substrate material is not less than 10:1; The proportion of {111} oriented crystal planes in the copper substrate material is not less than 80%; Its features are, A method for preparing a silver deposition layer with a highly {111}-preferred orientation fully nanotwinned structure utilizes electrodisplacement technology to deposit the silver deposition layer with a highly {111}-preferred orientation fully nanotwinned structure on the surface of a copper substrate, comprising the following steps: Step a), Pretreatment of substrate copper material: First, the surface of the substrate copper material to be deposited is degreased, rinsed with deionized water, then immersed in the pretreatment solution to remove the surface oxide film, and finally dried with nitrogen gas; Step b), prepare the electrodisplacement solution and adjust the pH; Step c), adjust the temperature of the electrodisplacement solution to 30-60℃; Step d), immerse the substrate copper material in a flowing electrodisplacement solution for 10-300 seconds; Step e) Remove the copper substrate material that has undergone electro-displacement from the electro-displacement solution, thoroughly wash it in flowing deionized water, dry it with clean nitrogen gas, and seal it for storage.

2. The method for preparing a silver deposition layer with a highly {111}-preferred orientation and an all-nanotwinned structure according to claim 1, characterized in that, The thickness of the all-nanotwinned silver deposition layer is 15-400 nanometers; and / or The thickness of the nanotwin wafer layer in the fully nanotwinned silver deposition layer is 2-150 nanometers; and / or The ratio of the {111} orientation to the {200} orientation diffraction intensity of the fully nanotwinned silver deposition layer is not less than 10:1; and / or The fully nanotwinned silver deposition layer exhibits thermal stability. After annealing in a vacuum atmosphere at 400 degrees Celsius for 2 hours, the nanotwinned crystalline layer does not completely disappear, and the ratio of the diffraction intensity of the {111} orientation to the {200} orientation of the silver deposition layer is not less than 10:

1.

3. The method for preparing a silver deposition layer with a highly {111}-preferred orientation and an all-nanotwin structure according to claim 1, characterized in that, The substrate copper material is nanotwinned copper with a highly {111} preferred orientation.

4. The method for preparing a silver deposition layer with a highly {111}-preferred orientation and an all-nanotwinned structure according to claim 1, characterized in that, In step c), the temperature of the electrodisplacement solution is adjusted to 45-55℃.

5. A method for preparing a fully nanotwinned silver deposition layer with a highly {111}-preferred orientation as described in claim 1, characterized in that, The electrodisplacement solution contains silver ions, complexing agents, additives, pH adjusters, and pure water.

6. A method for preparing a fully nanotwinned silver deposition layer with a highly {111}-preferred orientation as described in claim 1, characterized in that, In step d), the electrodisplacement solution is kept in a flowing state by one or more of the following methods: controlled flow rate flushing, ultrasonic agitation, magnetic stirring, aeration, spraying, substrate rotation or reciprocating motion; and / or In step a), the pretreatment solution for the copper substrate is one or more of the following: dilute hydrochloric acid aqueous solution, citric acid aqueous solution, and copper material chemical polishing solution.

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