An Electrochemical Preparation Method for a Three-Dimensional Silver-Based Microstructure with a High Aspect Ratio

Abstract

The present invention relates to an electrochemical preparation method for a three-dimensional silver-based microstructure with a high aspect ratio, comprising: alternately performing first-stage electroplating and second-stage electroplating to fill a three-dimensional microstructure mold to form a three-dimensional silver-based microstructure, wherein the grain size of the coating deposited by the first-stage electroplating is larger than the grain size of the coating deposited by the second-stage electroplating. This method fills a three-dimensional microstructure mold through a cyanide-free silver electroplating process with periodic alternating deposition of a low-stress electroplating system and a high-leveling electroplating system, and can prepare a three-dimensional silver-based microstructure with a high aspect ratio.

Description

Technical Field

[0001] The present invention relates to the field of microfabrication technology, and particularly to an electrochemical preparation method for a three-dimensional silver-based micro-structure with a high aspect ratio. Background Art

[0002] With the in-depth development of the diversification of functions of microelectromechanical systems (MEMS), in addition to the commonly used silicon-based materials, non-silicon-based materials represented by metals and polymers are increasingly used to construct various micro-nano devices and micro-systems with unique functions. Facing the trend of diversified development of MEMS technology functions, silver, as a metal material with the best electrical conductivity, the highest thermal conductivity, excellent reflectivity and biocompatibility at present, also has good ductility, welding performance and chemical stability, and has broad application prospects and great development potential in the fields of biomedicine, flexible electronics and micro-nano optics.

[0003] In the manufacture of micro-nano devices, the silver metallization method mainly adopts dry deposition, electroless silver plating and electroplating silver technology. The first two technologies have simple film-forming principles and high density, but slow deposition rates and high process costs, and are only suitable for preparing nano-scale thin films. In contrast, electroplating silver technology improves the thickness of the deposited coating to a certain extent on the premise of ensuring good coating quality, and broadens the application field of metallic silver. At present, cyanide-free electroplating technology has been widely used in silver metallization. However, at present, a multi-functional additive system with synergistic effects has not been developed for cyanide-free electroplating silver plating solutions. The current additives are mostly mixtures composed of aldehydes, alkynols and alkanolamines, which play an inhibitory role in the deposition process of silver ions and can achieve the effect of refining crystal grains. In a single plating solution system, metal ions and additives rely on electromigration and concentration diffusion to transfer to the bottom of the micro-structure. After long-term electroplating, defects such as uneven thickness, rough surface and void inclusion often appear in the coating. At the same time, as the deposition thickness increases, the dislocation density of the coating grains will continuously increase, which is likely to cause stress peeling of the coating. This is also an important reason why the existing electroplating silver process mainly focuses on the preparation of planar thin-layer structures and still has difficulty in realizing silver-based micro-structures with large thickness and high aspect ratio.

[0004] A preparation method for a low-cost patterned thick silver film disclosed in Chinese Patent CN 105463536A uses photolithography patterning technology and silver electroplating technology to prepare a silver film with a maximum thickness of 10 μm. Although it has initially realized a micron-scale patterned metallic silver film, it far from meets the preparation requirements of three-dimensional silver-based micro-structures. In addition, most of the existing cyanide-free silver plating solutions are alkaline solutions, which are not easily compatible with conventional patterning processes, increasing the process preparation difficulty to a certain extent. Summary of the Invention

[0005] The object of the present invention is to provide an electrochemical preparation method for a three-dimensional silver-based microstructure with a high aspect ratio. This method deposits by periodically alternating between a low-stress electroplating system and a high-planarity electroplating system, orderly regulating the grain morphology of the coating during the electroplating process, capable of preparing a three-dimensional silver-based microstructure with a high aspect ratio, overcoming the problems of stress peeling during large-thickness deposition and void entrapment in a single plating solution system, and correcting the unevenness of the coating.

[0006] Aiming at the problems existing in the prior art, the present invention provides an electrochemical preparation method for a three-dimensional silver-based microstructure with a high aspect ratio to solve, including:

[0007] Alternately performing the first-stage electroplating and the second-stage electroplating to fill a three-dimensional microstructure mold to form a three-dimensional silver-based microstructure, wherein the grain size of the coating deposited in the first-stage electroplating is larger than the grain size of the coating deposited in the second-stage electroplating.

[0008] In an embodiment of the present invention, before the step of alternately performing the first-stage electroplating and the second-stage electroplating to fill a three-dimensional microstructure mold to form a three-dimensional silver-based microstructure, it further includes:

[0009] Arranging a seed layer on the upper surface of a temporary substrate, and preparing a three-dimensional microstructure mold on the seed layer;

[0010] Pre-wetting the three-dimensional microstructure mold;

[0011] Using the temporary substrate as the cathode, setting an electrode plate as the anode, immersing the cathode and the anode in a basic silver-plating solution containing silver salt, and pre-passing a protection current between the cathode and the anode.

[0012] In an embodiment of the present invention, the first-stage electroplating includes additives added to the basic silver-plating solution, wherein the additives include one or more combinations of potassium pyrophosphate, butynediol, nicotinic acid, and saccharin, and the amount of the additives is 0-10 g / L.

[0013] In an embodiment of the present invention, the electroplating conditions of the first-stage electroplating include direct current electroplating or pulse electroplating, the average current density is 0.3-1.0 A / dm 2 , the electroplating temperature is 30-45 °C, and the stirring rate is greater than 300 r / min.

[0014] In an embodiment of the present invention, the second-stage electroplating includes: taking out the temporary substrate with the three-dimensional microstructure mold after the first-stage electroplating, rinsing it with deionized water, and then performing the second-stage electroplating to electrochemically planarize the coating of the first-stage electroplating.

[0015] In one embodiment of the present invention, the electroplating conditions for the second-stage electroplating include direct current electroplating or pulse electroplating, with an average current density of 1.0 - 2.0 A / dm 2 , the electroplating temperature is 10 - 25 °C, and the stirring rate is less than 300 r / min.

[0016] In one embodiment of the present invention, the plating solution system for the second-stage electroplating includes a silver plating solution system formed by adding additives to the basic silver plating solution, or a copper sulfate system, or a copper methyl sulfonate system, where the additives include one or more combinations of potassium pyrophosphate, butynediol, nicotinic acid, and saccharin, and the amount of the additives is 30 - 60 g / L.

[0017] In one embodiment of the present invention, the basic silver plating solution is an alkaline cyanide-free silver electroplating solution, which includes one of a succinimide silver plating solution, an ammonium iminosulfonate silver plating solution, and a 5,5-dimethylhydantoin silver plating solution.

[0018] In one embodiment of the present invention, preparing the three-dimensional microstructure mold on the seed layer includes: spin-coating a layer of negative photoresist uniformly on the seed layer, and through photolithography technology, successively performing pre-baking, photolithography, post-baking, development, and hardening to form the three-dimensional microstructure mold.

[0019] In one embodiment of the present invention, pre-wetting the three-dimensional microstructure mold includes:

[0020] Immersing the temporary substrate with the three-dimensional microstructure mold in the pre-wetting solution, and placing it in one or more combinations of a vacuum environment, an ultrasonic environment, and a megasonic oscillation environment for pre-wetting, where the pre-wetting solution is one of pure water, deionized water, and a cyanide-free silver electroplating solution with different additive ratios.

[0021] In one embodiment of the present invention, the material of the temporary substrate is a silicon substrate or a non-silicon substrate; and / or

[0022] The seed layer includes one or more combinations of chromium, titanium, copper, gold, silver, platinum, tungsten, silver oxide, and titanium oxide; and / or

[0023] The shape of the three-dimensional microstructure mold includes one or more combinations of a straight line shape, a rectangle, a triangle, a circle, a serpentine shape, and a cone shape; and / or

[0024] The depth of the three-dimensional microstructure mold is not less than 100 μm, and the depth-to-width ratio is not less than 3; and / or

[0025] The current density of the protection current is 0.1 A / dm 2 ; and / or

[0026] The area of the anode is not less than twice the area of the cathode; and / or

[0027] The anode is one of a silver plate with a purity of 99.99%, a platinum sheet electrode, and a titanium mesh electrode.

[0028] In an embodiment of the present invention, it further includes:

[0029] Removing the three-dimensional microstructure mold and the seed layer, removing the temporary substrate, and releasing the three-dimensional silver-based microstructure; and performing post-annealing treatment on the three-dimensional silver-based microstructure.

[0030] In an embodiment of the present invention, the three-dimensional microstructure mold is removed by one or a combination of mechanical physical degumming, dry chemical degumming, and wet chemical degumming, the seed layer is etched by a wet chemical method, the temporary substrate is removed, and then cleaning and drying are performed to obtain the three-dimensional silver-based microstructure.

[0031] The present invention has at least the following beneficial effects: An electrochemical preparation method of a high aspect ratio three-dimensional silver-based microstructure disclosed by the present invention. This method fills a three-dimensional microstructure mold through a cyanide-free silver electroplating process with periodic alternating deposition of a low stress electroplating system and a high leveling electroplating system, and can prepare a three-dimensional silver-based microstructure with a high aspect ratio; the periodic alternating deposition of this method affects the electrocrystallization growth mechanism of silver during electroplating and orderly regulates its grain morphology, reduces the stress of the coating, eliminates coating defects, overcomes the problems of stress peeling and void entrapment in the large-thickness deposition of a single plating solution system, flexibly uses the electrochemical planarization method during the filling process to correct the serious coating unevenness problem, improves the coating quality, and realizes the electrochemical microfabrication integrated manufacturing of a high aspect ratio three-dimensional silver-based microstructure; based on the material advantages of metallic silver, this method realizes the electrochemical forming of a high aspect ratio three-dimensional silver-based microstructure, providing a practical technical solution for the multi-field application of high-performance three-dimensional silver-based microdevices; this method is compatible with the UV-LIGA technology to prepare thick film lithography micro-molds suitable for most silver electroplating solutions, combines the cyanide-free silver electroplating process and microfabrication process technology, overcomes the problem that it is difficult to prepare a large-thickness and high aspect ratio silver-based microstructure by existing silver electroplating technologies, and lays a foundation for the establishment of the silver-based UV-LIGA process; this method first prepares the seed layer and then prepares the three-dimensional microstructure mold, enabling the coating deposited by periodic alternating deposition to grow from bottom to top. Adopting a bottom-up electroplating deposition growth mode, it avoids the problem of forming the three-dimensional microstructure mold and then performing a sputtering process to form the seed layer, and also avoids problems such as premature closure at the orifice due to a single additive system, which is conducive to realizing the dense filling of a high aspect ratio three-dimensional microstructure. Description of the Drawings

[0032] To further clarify the above and other advantages and features of the embodiments of the present invention, a more specific description of the embodiments of the present invention will be presented with reference to the accompanying drawings. It can be understood that these drawings only depict typical embodiments of the present invention and thus will not be considered as a limitation on its scope. In the drawings, for clarity, the same or corresponding components will be denoted by the same or similar reference numerals.

[0033] Figure 1 A schematic diagram showing the process of preparing a high aspect ratio three-dimensional silver-based microstructure according to an embodiment of the present invention;

[0034] Figure 2 A schematic diagram showing the alternate electroplating according to an embodiment of the present invention;

[0035] Figure 3 A schematic diagram showing the intermittent pulse electroplating according to an embodiment of the present invention; and

[0036] Figure 4 A scanning electron microscope image of a high aspect ratio silver-based microstructure according to an embodiment of the present invention. Detailed Description of the Invention

[0037] It should be noted that the components in the drawings may be exaggerated for illustration purposes and are not necessarily to scale.

[0038] In the present invention, the embodiments are only intended to illustrate the solutions of the present invention and should not be construed as restrictive.

[0039] In the present invention, unless otherwise specified, the quantifiers "a" and "one" do not exclude the scenario of multiple elements.

[0040] It should also be noted here that in the embodiments of the present invention, for clarity and simplicity, only a part of the components or assemblies may be shown, but those of ordinary skill in the art can understand that, under the teaching of the present invention, the required components or assemblies can be added according to the specific scenario requirements.

[0041] It should also be noted here that within the scope of the present invention, the terms "same", "equal", "equivalent" do not mean that the two values are absolutely equal, but allow for a certain reasonable error, that is, the terms also cover "substantially the same", "substantially equal", "substantially equivalent".

[0042] It should also be noted here that in the description of the present invention, the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than expressly or implicitly indicating that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation on the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as expressly or implicitly indicating relative importance.

[0043] In addition, the embodiments of the present invention describe the process steps in a specific order. However, this is only for the convenience of distinguishing each step and does not limit the sequence of each step. In different embodiments of the present invention, the sequence of each step can be adjusted according to the adjustment of the process.

[0044] Figure 1 The schematic diagram shows the process of preparing a high aspect ratio three-dimensional silver-based microstructure according to an embodiment of the present invention;

[0045] Figure 2 The schematic diagram shows the schematic diagram of alternating electroplating according to an embodiment of the present invention;

[0046] Figure 3 The schematic diagram shows the schematic diagram of intermittent pulse electroplating according to an embodiment of the present invention.

[0047] As Figure 1 shown, an electrochemical preparation method for a high aspect ratio three-dimensional silver-based microstructure includes the following steps:

[0048] Step 1: Provide a temporary substrate and perform pretreatment. The material of the temporary substrate can be a silicon substrate, a non-silicon substrate material such as glass, ceramic, copper sheet, titanium sheet, etc. The thickness of the temporary substrate is not less than 300 μm. The pretreatment includes sequentially ultrasonic cleaning, RCA standard cleaning, and drying treatment of the temporary substrate to obtain a cleaned temporary substrate.

[0049] Step 2: Arrange a seed layer on the upper surface of the temporary substrate. The material of the seed layer can be one or a combination of materials such as chromium, titanium, copper, gold, silver, platinum, tungsten, silver oxide, titanium oxide, etc.

[0050] Step 3: Fabricate a three-dimensional microstructural mold on the seed layer. The three-dimensional microstructural mold is an electroplating mask. Fabricating this three-dimensional microstructural mold includes: spin-coating a layer of negative photoresist evenly on the seed layer, and through photolithography techniques, successively performing processes such as pre-baking, photolithography, post-baking, development, and hardening to fabricate an electroplating mask that meets the structural design requirements. Here, the photolithography of the three-dimensional microstructural mold can adopt one of techniques such as UV photolithography, direct writing photolithography, grayscale exposure, and multiple exposures. The thickness of the negative photoresist is not less than 100 microns. The negative photoresist can be one of negative photoresists such as SU-8, BCB, and photosensitive dry film. The three-dimensional microstructural mold fabricated with a negative photoresist can be adapted to most electroplating silver solutions, especially alkaline cyanide-free electroplating silver solutions.

[0051] The shape and size of the three-dimensional microstructural mold are both controlled by the shape and size of the photomask pattern according to the structural design requirements. The shape of the three-dimensional microstructural mold includes one or a combination of shapes such as linear, rectangular, triangular, circular, serpentine, and conical. The depth of the three-dimensional microstructural mold is not less than 100 μm, and the aspect ratio is not less than 3.

[0052] Step 4: Pre-wet the three-dimensional microstructural mold. Before electroplating, the temporary substrate and the three-dimensional microstructural mold need to be pre-wetted through electroplating pretreatment. Immerse the temporary substrate with the three-dimensional microstructural mold in the pre-wetting solution and place it in one or a combination of a vacuum environment, an ultrasonic environment, and a megasonic oscillation environment for pre-wetting. The pre-wetting solution can be selected from one of solutions such as pure water, deionized water, and cyanide-free electroplating silver solutions with different additive ratios.

[0053] Step 5: Use the temporary substrate as the cathode and set an electrode plate as the anode. Immerse the cathode and the anode in a basic silver-plating solution containing silver salt, and pre-pass a protective current between the cathode and the anode. The current density of the protective current is 0.1 A / dm 2 . The surfaces of the anode and the cathode are relatively parallel, and the area of the anode is not less than twice the area of the cathode. The anode includes one of electrode plates such as a silver plate with a purity of 99.99%, a platinum sheet electrode, and a titanium mesh electrode. The basic silver-plating solution is an alkaline cyanide-free electroplating silver solution, and one of cyanide-free silver-plating solution systems such as succinimide silver-plating solution, ammonium iminodisulfonate (NS) silver-plating solution, and 5,5-dimethylhydantoin (DMH) silver-plating solution can be selected.

[0054] Step 6: Alternately perform first-stage electroplating and second-stage electroplating to fill the three-dimensional microstructure mold to form a three-dimensional silver-based microstructure. The grain size of the coating deposited by first-stage electroplating is larger than that of the coating deposited by second-stage electroplating. The thickness of the coating deposited by first-stage electroplating is greater than that of the coating deposited by second-stage electroplating. The deposition rate and time of the coating deposited by first-stage electroplating are greater than those of the coating deposited by second-stage electroplating. The surface of the coating deposited by first-stage electroplating is rough, while the surface of the coating deposited by second-stage electroplating is flat. The deposition of the coatings in both first-stage electroplating and second-stage electroplating is in a bottom-up growth mode.

[0055] During first-stage electroplating, the additive added to the basic silver plating solution is selected from one or a combination of additives such as potassium pyrophosphate, butynediol, nicotinic acid, saccharin, etc. First-stage electroplating adopts a low-stress plating solution system and its electroplating implementation conditions. During first-stage electroplating, a small amount of additive is added to the basic silver plating solution, and electroplating conditions such as low current density, high electroplating temperature, and strong external convection are set to control the crystallization growth of the coating into grains with large sizes, reduce the stress of the coating, increase the deposition rate, quickly increase the deposition thickness, and achieve low-stress rapid deposition. The amount of additive added during first-stage electroplating is 0 - 10 g / L. The strong external convection condition means that the stirring rate is greater than 300 r / min, and the stirring methods include one of magnetic stirring, air stirring, cathode swing or rotation, cathode jet, etc. The high electroplating temperature means that the electroplating temperature is 30 - 45 °C, and the low current density means that the average current density range is 0.3 - 1.0 A / dm 2 . The stirring rate of first-stage electroplating is greater than that of second-stage electroplating.

[0056] Since the crystal grains of the coating deposited by first-stage electroplating are large in size and the surface of the coating is uneven, the coating deposited by first-stage electroplating needs to be subjected to electrochemical leveling treatment. Electrochemical leveling treatment refers to using the electrochemical deposition method, flexibly applying plating solution systems and electrodeposition processes with different functions, influencing the electrocrystallization growth mechanism during the electrodeposition process, and orderly regulating the grain morphology, aiming to overcome problems such as stress peeling and void inclusion in the deposition of large thickness with a single plating solution system and correct the unevenness (flatness) of the coating.

[0057] Specifically, take out the temporary substrate with the three-dimensional microstructure mold that has completed first-stage electroplating, rinse it thoroughly with deionized water, and then perform second-stage electroplating to form a flat surface coating, thereby performing electrochemical leveling treatment on the coating of first-stage electroplating. The crystal grains of the coating deposited by second-stage electroplating are small, and the surface of the coating is flat. The coating metal of second-stage electroplating is not limited to silver and can also be other metals such as copper.

[0058] The second-stage electroplating adopts a high-leveling plating solution system and its electroplating implementation conditions. Process conditions such as high current density, low electroplating temperature, and weak external convection are set to control the crystallization growth of the coating into fine-grained crystals and reduce the deposition rate.

[0059] The plating solution system for the second-stage electroplating includes a silver plating solution system and other metal electroplating systems. A large amount of additives are added to the basic silver plating solution to form the silver plating solution system for the second-stage electroplating.

[0060] When the coating metal for the second-stage electroplating is silver, additives with a content of 30 - 60 g / L are added to the basic silver plating solution. The set electroplating conditions include: high current density, which means the average current density is 1.0 - 2.0 A / dm 2 ; low electroplating temperature, with the electroplating temperature range being 10 - 25 °C; weak external convection conditions, which means the stirring rate is less than 300 r / min, and the stirring methods include one of magnetic stirring, air stirring, cathode oscillation or rotation, cathode jet, etc.

[0061] When the coating metal for the second-stage electroplating is other non-silver metals such as copper, a composite deposition is carried out using other metal electroplating systems. The leveling treatment of the surface uniformity of the coating in the first-stage electroplating is mainly achieved by the competitive adsorption and synergistic effect between accelerators and inhibitors and other additives in the other metal electroplating systems. At the same time, intermittent deposition of a small amount of other metals in the silver-based electroplating system can further enhance certain mechanical properties of the three-dimensional silver-based microstructure, providing a research idea for realizing a three-dimensional silver-based microstructure with higher performance and high aspect ratio. The other metal electroplating systems include: one of metal electroplating systems such as copper sulfate system, copper methyl sulfonate system, etc. The electroplating conditions are the same as those for the second-stage electroplating where the coating metal is silver. The electroplating method for the first-stage electroplating and the second-stage electroplating can be selected from direct current electroplating or pulse electroplating. When depositing the coating by direct current electroplating or pulse electroplating, the coating grows from bottom to top. The current for pulse electroplating is an intermittent pulse current. The duty cycle and pulse interval of pulse electroplating can be selected to be constant or periodically changing with the electrochemistry deposition time according to the deposition effect. As Figure 3 shown, the pulse power supply can repeatedly supply and stop the current to the electroplating system. The pulse interval time can be used to allow more ions to diffuse to the bottom of the holes of the three-dimensional microstructure mold under the action of the concentration gradient, improving the situation of the reduction of metal ion concentration in the three-dimensional microstructure mold during electroplating, thereby promoting the bottom-up growth of electrochemically deposited silver. Pulse electroplating can more effectively achieve uniform and dense electroplated silver filling with high aspect ratio. Preferably, the pulse electroplating time for the first-stage electroplating is greater than the pulse electroplating time for the second-stage electroplating.

[0062] As Figure 2As shown, the first-stage electroplating and the second-stage electroplating are repeated for periodic alternating electro-deposition filling until the design requirements of the high aspect ratio three-dimensional silver-based microstructure are met, and then the electroplating filling is stopped.

[0063] Step 7: Remove the three-dimensional microstructure mold and the seed layer, remove the temporary substrate, and release the three-dimensional silver-based microstructure. After the silver plating is completed to form the three-dimensional silver-based microstructure, the three-dimensional microstructure mold is removed by one or a combination of methods such as mechanical physical degluing, dry chemical degluing, and wet chemical degluing. The seed layer is etched by a wet chemical method, and the temporary substrate is removed. Then, it is cleaned with deionized water and dried to obtain the three-dimensional silver-based microstructure. The three-dimensional microstructure mold is removed by one or a combination of methods such as mechanical physical degluing, dry chemical degluing, and wet chemical degluing.

[0064] Step 8: Perform post-annealing treatment on the three-dimensional silver-based microstructure. The high aspect ratio silver-based microstructure is subjected to high-temperature post-annealing treatment to further adjust the microcrystalline structure, reduce the residual stress, and eliminate the tendency of deformation or cracks in the periodic filling. The temperature range of the post-annealing treatment is 200-400 °C.

[0065] In this embodiment, a cyanide-free silver electroplating process is used to fill a thick photoresist micro-mold, i.e., a three-dimensional microstructure mold, to form a high aspect ratio metallic silver microstructure. By adopting the method of periodically alternating deposition of a low-stress electroplating system and a high leveling electroplating system, the electrocrystallization growth mechanism of silver during the electro-deposition process is affected and the grain morphology is orderly regulated. Finally, a high aspect ratio three-dimensional silver-based microstructure with dense deposition, good morphology, and excellent performance is prepared.

[0066] Figure 4 The scanning electron microscope image of a high aspect ratio silver-based microstructure according to an embodiment of the present invention is shown.

[0067] In this embodiment, a high aspect ratio silver-based microstructure with a thickness of 500 μm is prepared by using the above method for preparing a high aspect ratio three-dimensional silver-based microstructure. The specific process is as follows:

[0068] Step 1: Provide a temporary substrate and perform pre-treatment. Specifically, a double-polished silicon wafer with an area of 3 inches and a thickness of 1 mm is provided as the temporary substrate. The double-polished silicon wafer is sequentially subjected to ultrasonic cleaning, RCA standard cleaning, and drying treatment to obtain the cleaned temporary substrate.

[0069] Step 2: Arrange a seed layer on the upper surface of the temporary substrate. A dense and uniform Cr / Cu seed layer is sputter-deposited on the upper surface of the temporary substrate. Among them, the thickness of Cr is 20-50 nm, and the thickness of Cu is 100-300 nm.

[0070] Step 3: Fabricate a three-dimensional microstructural mold on the seed layer. Specifically, spin-coat a layer of SU-8 negative photoresist with a thickness of 500 μm uniformly on the seed layer. Using UV lithography technology, perform processes such as pre-baking, lithography, post-baking, development, and hardening film in sequence to fabricate a thick-film lithographic micro-mold that meets the structural design requirements as the three-dimensional microstructural mold. The three-dimensional microstructural mold includes multiple square holes with a hole depth of 500 μm and an aspect ratio of 3.3.

[0071] Step 4: Pre-wet the three-dimensional microstructural mold. Specifically, immerse the temporary substrate with the three-dimensional microstructural mold in pure water and place it in a vacuum environment for pre-wetting.

[0072] Step 5: Use the temporary substrate as the cathode and set an electrode plate as the anode. Immerse the cathode and anode in a basic silver plating solution containing silver salt and pre-pass a protective current between the cathode and anode. The surfaces of the anode and cathode are relatively parallel. Specifically, use a pure silver plate with a purity of 99.99% as the anode. The anode and cathode are completely immersed in a basic silver plating solution (cyanide-free silver plating solution) with 5,5-dimethylhydantoin as the complexing agent. The main components of this basic silver plating solution are: 40 - 60 g / L of 5,5-dimethylhydantoin, 15 - 25 g / L of silver nitrate, 8 - 12 g / L of potassium chloride, and the pH value is 9 - 10. In addition, pre-pass a protective current with a current density of 0.1 A / dm 2 into the tank while charging.

[0073] Step 6: Alternately perform the first-stage electroplating and the second-stage electroplating to form a three-dimensional silver-based micro-structure. Specifically, the first-stage electroplating adopts a low-stress plating solution system and its electroplating implementation conditions: add 0 - 10 g / L of saccharin and other combined additives to the basic silver plating solution, use direct current electroplating, with an average current density of 0.3 - 1.0 A / dm 2 , the electroplating temperature is 35 - 45 °C, and the stirring rate is 500 - 600 r / min to achieve low-stress rapid deposition. Take out the temporary substrate with the three-dimensional microstructural mold after the first-stage electroplating, rinse it with deionized water, and then perform the second-stage electroplating to perform electrochemical leveling treatment on the coating of the first-stage electroplating. The second-stage electroplating adopts a high-leveling plating solution system and its electroplating implementation conditions: add 30 - 50 g / L of potassium pyrophosphate and other combined additives to the basic silver plating solution, use direct current electroplating, with an average current density of 1.0 - 2.0 A / dm 2 , the electroplating temperature is 15 - 25 °C, and the stirring rate is 200 - 300 rpm to achieve compensated leveling deposition.

[0074] Repeat the first-stage electroplating and the second-stage electroplating for periodic alternating electro-deposition filling until the design requirements of the three-dimensional silver-based micro-structure with a high aspect ratio are met, and then stop the electroplating filling.

[0075] Step 7: Remove the three-dimensional microstructure mold and the seed layer, remove the temporary substrate, and release the three-dimensional silver-based microstructure. Specifically, place the temporary substrate with the three-dimensional silver-based microstructure in a stripping solution to remove the three-dimensional microstructure mold, corrode the Cr / Cu seed layer with ammonia water solution and potassium permanganate solution respectively, remove the temporary substrate, and then wash and dry with deionized water to obtain the three-dimensional silver-based microstructure. The thickness of the three-dimensional silver-based microstructure is 500 μm, the aspect ratio is 3.3, and its array unit is square.

[0076] Step 8: Perform post-annealing treatment on the three-dimensional silver-based microstructure. Specifically, perform post-annealing treatment on the silver-based microstructure with a high aspect ratio at 250 °C to further adjust the microcrystalline structure, reduce the residual stress, and eliminate the tendency of deformation or cracks in the periodic filling.

[0077] The present invention has at least the following beneficial effects: An electrochemical preparation method of a three-dimensional silver-based microstructure with a high aspect ratio disclosed by the present invention can prepare a three-dimensional silver-based microstructure with a high aspect ratio through a cyanide-free silver plating process of periodically alternating deposition of a low-stress electroplating system and a high leveling electroplating system to fill the three-dimensional microstructure mold; the periodic alternating deposition of this method affects the electrocrystallization growth mechanism of silver during the electroplating process and orderly regulates its grain morphology, reduces the stress of the coating, eliminates coating defects, overcomes the problems of stress peeling and void inclusion in the large-thickness deposition of a single plating solution system, flexibly uses the electrochemical planarization method during the filling process to correct the serious coating unevenness problem, improves the coating quality, and realizes the integrated manufacturing of electrochemical micromachining of a three-dimensional silver-based microstructure with a high aspect ratio; based on the material advantages of metallic silver, this method realizes the electrochemical forming of a three-dimensional silver-based microstructure with a high aspect ratio, providing a practical technical solution for the multi-field application of high-performance three-dimensional silver-based micro-devices; this method is compatible with the UV-LIGA technology to prepare thick-resist lithography micro-molds suitable for most silver plating solutions, combines the cyanide-free silver plating process and microfabrication process technology, overcomes the problem that it is difficult to prepare a large-thickness and high-aspect-ratio silver-based microstructure by the existing electrodeposited silver technology, and lays a foundation for the establishment of the silver-based UV-LIGA process; this method first prepares the seed layer and then prepares the three-dimensional microstructure mold, enabling the coating deposited by periodic alternating deposition to grow from bottom to top, adopting a bottom-up electroplating deposition growth mode, avoiding the problems of forming the three-dimensional microstructure mold and then performing a sputtering process to form the seed layer, and also avoiding problems such as premature closing at the orifice due to a single additive system, which is conducive to realizing the dense filling of a three-dimensional microstructure with a high aspect ratio.

[0078] Although some embodiments of the present invention have been described in this application document, those skilled in the art can understand that these embodiments are merely shown as examples. Those skilled in the art can conceive of numerous variants, alternatives, and improvement schemes under the teaching of the present invention without exceeding the scope of the present invention. The appended claims are intended to define the scope of the present invention and thereby cover the methods and structures within the scope of these claims themselves and their equivalent transformations.

Claims

1. An electrochemical preparation method for a three-dimensional silver-based microstructure with a high aspect ratio, characterized in that, Comprising: A seed layer is disposed on the upper surface of a temporary substrate, and a three-dimensional microstructure mold is prepared on the seed layer. The preparation of the three-dimensional microstructure mold on the seed layer includes: spin-coating a layer of negative photoresist uniformly on the seed layer, and through photolithography technology, successively performing pre-baking, photolithography, post-baking, development, and hardening to form the three-dimensional microstructure mold; The three-dimensional microstructure mold is filled by alternately performing the first-stage electroplating and the second-stage electroplating to form a three-dimensional silver-based microstructure, wherein the grain size of the coating deposited by the first-stage electroplating is larger than that of the coating deposited by the second-stage electroplating; The first-stage electroplating includes additives added to a basic silver plating solution, wherein the additives include one or more combinations of potassium pyrophosphate, butynediol, nicotinic acid, and saccharin, and the amount of the additives is 0 - 10 g / L; The plating solution system for the second-stage electroplating includes a silver plating solution system formed by adding additives to the basic silver plating solution, or a copper sulfate system, or a copper methyl sulfonate system, wherein the additives include one or more combinations of potassium pyrophosphate, butynediol, nicotinic acid, and saccharin, and the amount of the additives is 30 - 60 g / L; The basic silver plating solution is an alkaline cyanide-free silver plating solution; The electroplating conditions for the first-stage electroplating include direct current electroplating or pulse electroplating, with an average current density of 0.3~1.0 A / dm 2 , the electroplating temperature is 30~45 °C, and the stirring rate is greater than 300 r / min; The electroplating conditions for the second-stage electroplating include direct current electroplating or pulse electroplating, with an average current density of 1.0 - 2.0 A / dm 2 , the electroplating temperature is 10 - 25 °C, and the stirring rate is less than 300 r / min; The depth of the three-dimensional microstructure mold is not less than 100 μm, and the aspect ratio is not less than 3.

2. The electrochemical preparation method of the high aspect ratio three-dimensional silver-based microstructure according to claim 1, characterized in that, Before the step of alternately performing the first-stage electroplating and the second-stage electroplating to fill the three-dimensional microstructure mold to form a three-dimensional silver-based microstructure, it further includes: Pre-wetting the three-dimensional microstructure mold; Taking the temporary substrate as the cathode, setting an electrode plate as the anode, immersing the cathode and the anode in the basic silver plating solution containing silver salt, and pre-passing a protection current between the cathode and the anode.

3. The electrochemical preparation method of the high aspect ratio three-dimensional silver-based microstructure according to claim 2, wherein, The second-stage electroplating includes: taking out the temporary substrate with the three-dimensional microstructure mold after the first-stage electroplating, rinsing it with deionized water, and then performing the second-stage electroplating to perform electrochemical planarization treatment on the coating of the first-stage electroplating.

4. The electrochemical preparation method of the high aspect ratio three-dimensional silver-based microstructure according to claim 2, characterized in that, The basic silver plating solution includes one of a succinimide silver plating solution, an ammonium iminosulfonate silver plating solution, and a 5,5-dimethylhydantoin silver plating solution.

5. The electrochemical preparation method of the high aspect ratio three-dimensional silver-based microstructure according to claim 2, characterized in that, The pre-wetting of the three-dimensional microstructure mold includes: Immersing the temporary substrate with the three-dimensional microstructure mold in a pre-wetting solution, and placing it in one or more combinations of a vacuum environment, an ultrasonic environment, and a megasonic oscillation environment for pre-wetting, wherein the pre-wetting solution is one of pure water, deionized water, and a cyanide-free silver plating solution with different additive ratios.

6. The electrochemical preparation method of the high aspect ratio three-dimensional silver-based microstructure according to claim 2, wherein, The material of the temporary substrate is a silicon substrate or a non-silicon substrate; and / or The seed layer includes one or more combinations of chromium, titanium, copper, gold, silver, platinum, tungsten, silver oxide, and titanium oxide; and / or The shape of the three-dimensional microstructure mold includes one or more combinations of linear, rectangular, triangular, circular, serpentine, and conical; and / or The current density of the protection current is 0.1 A / dm 2 ; and / or The area of the anode is not less than 2 times the area of the cathode; and / or The anode is one of a silver plate with a purity of 99.99%, a platinum sheet electrode, and a titanium mesh electrode.

7. The electrochemical preparation method of the high aspect ratio three-dimensional silver-based microstructure according to claim 2, wherein, It further includes: Removing the three-dimensional microstructure mold and the seed layer, removing the temporary substrate, and releasing the three-dimensional silver-based microstructure; And Anneal the three-dimensional silver-based microstructure afterwards.

8. The electrochemical preparation method of the high aspect ratio three-dimensional silver-based microstructure according to claim 7, characterized in that, Remove the three-dimensional microstructure mold by one or a combination of mechanical-physical degumming, dry chemical degumming, and wet chemical degumming. Corrode the seed layer by a wet chemical method, remove the temporary substrate, and then perform cleaning and drying to obtain the three-dimensional silver-based microstructure.

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