A nickel plating solution and plating method for wafer-level packaging

Abstract

This application provides a nickel plating solution and electroplating method for wafer-level packaging. The nickel plating solution contains the following components and their concentrations: nickel sulfamate 60-150 g / L, nickel chloride 10-30 g / L, boric acid 20-60 g / L, leveling agent 0.1-1 g / L, wetting agent 0.01-0.5 g / L, complexing agent 0.1-5 g / L, stabilizer 0.01-0.1 g / L, stress reliever 0.5-2 g / L, cobalt ions with a mass concentration of 2-21 g / L, and deionized water as the solvent. The stress reliever has a molecular formula with at least a segment of the general chemical formula Ar-SO2-N-X1X2. The leveling agent is a quaternary ammonium salt cationic compound. The mass relationship between the cobalt ions A, the stress reliever B, and the leveling agent C simultaneously satisfies: 6.67≤A / B≤10, 20≤A / C≤33.33, and 2≤B / C≤5. By using cobalt salt as a functional additive as a dopant metal in the nickel alloying process, and by adding a specific ratio of stress relievers and leveling agents, the electroplated nickel layer has high hardness, corrosion resistance, and good heat dissipation, meeting the reliability requirements of high heat density and high computing power chips.

Description

Technical Field

[0001] This application relates to the field of advanced packaging electroplating technology, and in particular to a nickel plating solution and plating method for wafer-level packaging. Background Technology

[0002] As the computing power requirements of various chips continue to increase, the power density of chip operation is also getting higher and higher. The power density of some high-computing chips has exceeded 200 W / cm². The significant temperature rise during operation will generate strong thermal stress in the material. The traditional nickel-plated protective layer on the wafer will cause thermomechanical fatigue after long-term thermo-mechanical coupling cycle, and is prone to surface cracking and electrochemical corrosion, making it difficult to meet the reliability requirements of high-computing chips for long-term service.

[0003] In existing technologies, a common way to improve the mechanical strength, thermal stability, and corrosion resistance of nickel protective layers is to dope them with other elements to form nickel-based alloys. Among these, nickel-copper alloys can optimize heat dissipation and exhibit good thermal stability, but they are susceptible to selective phase corrosion in strongly oxidizing acidic environments such as nitric acid and sulfuric acid, resulting in insufficient corrosion resistance. Furthermore, the soft metal nature of copper leads to insufficient hardness and weak mechanical strength in nickel-copper alloys, making them unable to effectively buffer stress under thermo-mechanical coupling cycles. This easily induces bulk cracking and open circuits, ultimately limiting their large-scale application on wafers.

[0004] Furthermore, the most common nickel alloy is the nickel-phosphorus alloy. Compared to nickel-copper alloys, nickel-phosphorus alloys have a wider range of hardness capabilities, with a hardness of approximately 500-600 HV in the deposited state. After the formation of the hard Ni3P phase, the hardness can further increase to 900-1100 HV, or even higher. However, the internal stress control mechanism of nickel-phosphorus alloys is complex, making them prone to brittleness. Moreover, their resistance to chemical corrosion depends on the phosphorus content. Too low a phosphorus doping level cannot provide effective corrosion resistance, while too high a phosphorus doping level will affect the heat dissipation capacity of the nickel-phosphorus alloy coating, failing to meet the thermal stability requirements of wafer products and the basic application conditions of high-performance chip protective casings.

[0005] To address the problems existing in the above technologies, there is an urgent need to develop a nickel plating solution and plating process with high mechanical strength, strong thermal stability and corrosion resistance for wafer-level packaging, so as to adapt to the high thermal stress operating environment of high computing power chips and meet the requirements of high hardness and strong corrosion resistance of the protective layer. Summary of the Invention

[0006] Based on this, the first aspect of this application provides a nickel plating solution for wafer-level packaging, which uses cobalt salt as a functional additive as a dopant metal to participate in the nickel alloying process, so that the electroplated nickel layer has high hardness, corrosion resistance and good heat dissipation, meeting the reliability requirements of high-heat-density, high-computing-power chips.

[0007] The second aspect of this application provides a method for electroplating nickel at the wafer level, wherein a high-quality nickel plating layer with strong adhesion is obtained by electroplating the aforementioned nickel plating solution on the wafer surface, and the adhesion grade is 5B as determined by cross-cut adhesion testing.

[0008] The specific technical solution of this application is as follows: In a first aspect, this application provides a nickel plating solution for wafer-level packaging, the nickel plating solution comprising the following components at the following mass concentrations: nickel sulfamate 60-150 g / L, nickel chloride 10-30 g / L, boric acid 20-60 g / L, leveling agent 0.1-1 g / L, wetting agent 0.01-0.5 g / L, complexing agent 0.1-5 g / L, stabilizer 0.01-0.1 g / L, stress reliever 0.5-2 g / L, and deionized water as the solvent; the nickel plating solution further comprises a functional additive cobalt salt, and the mass concentration of cobalt ions is 2-21. The stress reliever has a molecular formula of at least one segment with the general chemical formula Ar-SO2-N-X1X2, where Ar is a group containing an aromatic ring, and X1 and X2 are selected from H, metal ions, carboxyl groups, ester groups, acyl groups, and carbonyl groups, respectively. The leveling agent is a quaternary ammonium salt cationic compound. The mass relationship between the cobalt ion A, the stress reliever B, and the leveling agent C simultaneously satisfies the following conditions: 6.67≤A / B≤10, 20≤A / C≤33.33, and 2≤B / C≤5.

[0009] The nickel plating solution for wafer-level packaging described in this application has at least the following beneficial effects: First, this application utilizes cobalt salts as functional additives in conjunction with nickel sulfamate for alloying electrodeposition. During electroplating, cobalt ions enter the nickel growth lattice, inducing local lattice distortion and hindering dislocation movement, thereby effectively improving the hardness and chemical corrosion resistance of the nickel plating layer. Furthermore, by combining stress-relieving agents with specific molecular chain segments with quaternary ammonium salt cationic compounds, the negative impacts of cobalt introduction, such as an overly hard and brittle nickel plating layer and poor adhesion to the wafer surface, are eliminated. The combined action of sulfonyl and imino groups allows stress-relieving agent molecules to selectively adsorb onto specific crystal faces of the wafer, achieving grain refinement. The ammonium cation [R4N] of the leveling agent... + It can diffuse and adsorb onto the cathode surface, preferentially covering microscopic protrusions with higher surface energy, thus achieving a coating leveling effect. At the same time, quaternary ammonium salt cationic compounds and stress-relieving agent molecules can also form large ion pairs through electrostatic attraction, covering the convex surface area of ​​the wafer as a whole, blocking the preferential growth of coating grains at the protrusions, and forcing the coating surface to deposit uniform crystal nuclei. Compared with single application, it can achieve a better leveling effect of 1+1>2.

[0010] Secondly, based on the molecular-level synergistic effect among the aforementioned functional additives, stress relievers, and leveling agents, this application further constrains the addition ratio of functional additives, stress relievers, and leveling agents to balance the performance of the nickel plating layer in terms of hardness, surface quality, and adhesion between the nickel plating layer and the wafer surface. Specifically, within a concentration range of 2-21 g / L, the higher the concentration of cobalt ions in the nickel plating solution, the greater the hardness of the nickel plating layer, but the thermal conductivity and corrosion resistance will deteriorate. Within a concentration range of 0.5-2 g / L, the higher the concentration of stress relievers, the better the control of deposition internal stress, the higher the surface quality of the nickel plating layer, and the less cracking and brittleness, but the hardness will decrease. Excessive addition of stress relievers will over-adsorb onto the plating surface, interfering with the normal deposition of metal ions, weakening the adhesion between the plating layer and the wafer, and easily causing peeling and flaking during subsequent machining or use, resulting in a significant decrease in adhesion. Within a concentration range of 0.1-1 g / L, a higher concentration of leveling agent results in better pre-leveling of the wafer surface and higher surface quality of the nickel plating layer. However, excessive leveling agent can over-adsorb onto the plating surface, interfering with metal ion deposition. Furthermore, stress relievers exhibit a similar stress-relieving effect on cobalt ions as they do on nickel ions. There is also competition between leveling agents and stress relievers for adsorption sites. When the mass ratios of cobalt ions (A), stress reliever (B), and leveling agent (C) simultaneously satisfy 6.67 ≤ A / B ≤ 10, 20 ≤ A / C ≤ 33.33, and 2 ≤ B / C ≤ 5, the hardness, surface quality, and good adhesion to the wafer of the nickel plating layer can be balanced.

[0011] In some embodiments, the cobalt salt is at least one selected from cobalt sulfate, cobalt chloride, cobalt aminosulfonate, cobalt alkylsulfonate, cobalt citrate, cobalt tartrate, cobalt gluconate, and cobalt acetate.

[0012] All of the above cobalt salts are compatible with water-based nickel plating solutions, achieving the effect of co-deposition of nickel and cobalt metal grains. Preferably, the cobalt salt is cobalt sulfate.

[0013] When the concentration of cobalt ions added is 2 g / L as in Example 1, the hardness of the final nickel plating layer is insufficient. When the concentration of cobalt ions added reaches 20 g / L as in Example 3, the uniformity of the deposition of the plating metal becomes worse, the surface of the resulting nickel plating layer is rough, and the adhesion to the wafer also becomes worse.

[0014] In some embodiments, the stress reliever is at least one of o-benzoylsulfonylimide and its alkali metal salt, p-toluenesulfonamide, and benzenesulfonamide.

[0015] All the aforementioned compounds contain the Ar-SO2-N-X1X2 chain segment. It is understood that X1 and X2 can be the same group or different groups. Specifically, in o-benzoylsulfonamide, the Ar group is phenyl, and one of the X1 and X2 groups is an H group while the other is a carbonyl group. Furthermore, in its corresponding alkali metal salt, one of the H groups needs to be replaced with an alkali metal ion. In p-toluenesulfonamide, the Ar group is tolyl, and both X1 and X2 groups are H groups. In benzenesulfonamide, the Ar group is phenyl, and both X1 and X2 groups are H groups. Using these specific compounds as stress relievers demonstrates good stability in the plating bath system, uses simple raw materials, and has controllable costs.

[0016] In some embodiments, the nickel plating solution satisfies at least one of the following conditions: a: the wetting agent is a perfluoroepoxy alkyl nonionic surfactant; b: the stabilizer is a thiazole compound.

[0017] Perfluoroepoxy alkyl nonionic surfactants are used to improve surface tension, accelerate the escape of surface bubbles, and prevent surface plating defects. Thiazole compounds contain thiazole rings with lone pairs of electrons that can form coordination bonds with the metal surface, covering the active surface of free nickel, blocking its reaction with reducing agents, and inhibiting spontaneous decomposition of the plating bath. Perfluoroepoxy alkyl nonionic surfactants and thiazole stabilizers synergistically create a favorable plating environment, achieving uniform plating rate and stable plating bath.

[0018] In some embodiments, the leveling agent satisfies at least one of the following conditions: c: the leveling agent is bis(dodecyl)dimethylammonium chloride; d: the mass concentration of the leveling agent is 0.1-0.5 g / L.

[0019] Using large-molecule didodecyl dimethyl ammonium chloride as a leveling agent, when the cathode current flows through the wafer, the strong charge adsorption effect drives the didodecyl dimethyl ammonium chloride to be adsorbed on the surface of the wafer to be plated. The long chain of didodecyl carbon significantly increases the molecular volume of the leveling agent, which can more efficiently cover the growth high sites of the plating surface, prevent the local excessively rapid growth of the plating grains, enhance the leveling effect and refine the grains, and improve the adhesion between the nickel plating layer and the wafer.

[0020] In some embodiments, the complexing agent satisfies at least one of the following conditions: e: the complexing agent is ethylenediaminetetraacetic acid; f: the mass concentration of the complexing agent is 0.1-3 g / L.

[0021] Ethylenediaminetetraacetic acid (EDTA) is slightly acidic and has a multidentate chelate structure, which has a strong ability to complex nickel and cobalt metal ions. The complex formed is stable and soluble in solution. The cathodic polarization of nickel and cobalt ions after complexation is enhanced, the ion reduction rate is optimized, which helps to improve the uniformity and density of the coating. At the same time, it provides a stable solution environment for leveling agents and stress relievers.

[0022] In some embodiments, the wetting agent satisfies at least one of the following conditions: g: the wetting agent is a hexafluoropropylene oxide oligomer; h: the mass concentration of the wetting agent is 0.01-0.15 g / L.

[0023] The strong oleophobic and hydrophobic properties of fluorocarbon chains give them extremely low surface energy, which can significantly reduce the surface tension of the plating solution system, accelerate the rapid wetting of the wafer surface by the plating solution, effectively eliminate air bubbles attached to the plating surface, and prevent phenomena such as missed plating, pitting, or uneven plating.

[0024] Insufficient wetting agent will result in poor wetting effect, while exceeding the upper limit will only slow down the improvement of plating uniformity and cause unnecessary cost increases. In the concentration range of 0.01-0.15 g / L, both wetting effect and cost control can be achieved.

[0025] In some embodiments, the stabilizer also satisfies at least one of the following conditions: j: the stabilizer is mercaptobenzothiazole; k: the mass concentration of the stabilizer is 0.01-0.05 g / L.

[0026] Mercaptobenzothiazole was selected for two purposes: firstly, as a stabilizer, the thiazole ring coordinates and complexes with free nickel, inhibiting reductive decomposition; secondly, as an accelerator, the -SH group has a certain adsorption effect on the cathode surface, while the C=S group can improve the catalytic activity of the wafer surface, accelerate the deposition rate of metal grains, shorten the electroplating time, improve production efficiency, and reduce manufacturing costs.

[0027] The concentration window for adding stabilizer is 0.01-0.05 g / L. Insufficient addition of stabilizer is not conducive to the stability of free nickel, while when the addition of stabilizer exceeds the upper limit, free nickel is excessively captured, the plating rate drops significantly, and even incomplete plating occurs.

[0028] In some embodiments, the nickel plating solution comprises the following components in mass concentrations: nickel aminosulfonate solution 60-150 g / L, nickel chloride 10-30 g / L, boric acid 20-60 g / L, dodecyl dimethyl ammonium chloride 0.1-0.5 g / L, hexafluoropropylene oxide oligomer 0.01-0.15 g / L, ethylenediaminetetraacetic acid 0.1-5 g / L, mercaptobenzothiazole 0.01-0.05 g / L, o-benzoylsulfonyl imide 0.5-2 g / L, anhydrous cobalt sulfate 5.3-55 g / L, and deionized water as the solvent.

[0029] The nickel plating solution with the above composition produces a nickel plating layer with high hardness, corrosion resistance, and good heat dissipation, meeting the reliability requirements of high-heat-density, high-computing-power chips.

[0030] Secondly, this application provides a method for electroplating nickel at the wafer level for packaging, wherein the electroplating method uses the nickel electroplating solution described in any of the preceding claims, and the electroplating method includes the following steps: S1: Perform surface cleaning and plasma treatment on the wafer to enhance the surface hydrophilicity and active sites of the wafer; S2: The activated wafer is placed in the nickel plating solution for electroplating, and the nickel plating solution is circulated and stirred during the electroplating process; S3: After electroplating, the wafer is cleaned and dried to obtain a nickel plating layer.

[0031] The wafer-level packaging nickel plating method of this application has at least the following beneficial effects: This method first removes impurities or passivation layers from the wafer plating surface, then uses plasma treatment to create active sites, effectively improving the activity of the wafer plating surface. Specifically, the physical bombardment of the plating surface by plasma forms a high density of active sites, while the chemical action of plasma introduces highly active functional groups, enhancing the surface energy and hydrophilicity of the plating surface. Through the chemical bonding between the highly active functional groups and the precipitated nickel-cobalt metal, the mechanical stability of the nickel plating layer is improved at the microscopic molecular level. Moreover, the plating layer achieves a grade of 5B in the cross-cut adhesion test. The good adhesion between the obtained nickel plating layer and the plating surface can adapt to the operating environment of high-performance chips with high-intensity thermal cycling, ensuring the long service life of high-performance chips.

[0032] In some embodiments, step S1 further includes: S11: immersing the wafer in an acidic sodium citrate solution for 1-3 minutes; S12: subjecting the acid-immersed wafer to Ar plasma treatment under the following conditions: pressure 150-250 mTorr, power 80-120 W, gas flow rate 80-120 sccm, time 20-40 seconds; S13: subjecting the Ar plasma-treated wafer to N2 plasma treatment under the following conditions: pressure 150-250 mTorr, power 180-220 W, gas flow rate 80-120 sccm, time 50-70 seconds.

[0033] First, acid leaching removes surface contaminants, providing a clean substrate for subsequent plasma treatment. Then, chemically inert Ar plasma treatment physically bombards the wafer surface, further removing residual trace contaminants, adsorbed layers, and weak boundary layers. Simultaneously, it increases surface roughness and surface energy at the nanoscale. Ion bombardment also breaks surface chemical bonds, creating dangling bonds and placing the surface in a highly activated state. Finally, N2 plasma treatment with active nitrogen introduces nitrogen-containing polar functional groups, such as amino and imine groups, into the wafer surface, significantly enhancing surface hydrophilicity and chemical activity, which is beneficial for subsequent nickel and cobalt deposition. If N2 plasma treatment is performed first, poor surface cleanliness and roughness may lead to uneven functional group grafting or poor adhesion, and subsequent Ar bombardment may damage the introduced functional groups.

[0034] In some embodiments, step S2 further includes: S21: placing the prepared nickel plating solution for 1-10 minutes and stirring rapidly at 100 r / min with a magnetic stirrer to homogenize the components in the nickel plating solution; S22: placing the wafer into the nickel plating solution, reducing the stirring speed, lifting it out of the liquid surface 2-5 times, and then letting it stand in the nickel plating solution for 30-60 seconds to fully wet the surface; S23: placing the fully wetted wafer face the anode plate and performing room temperature electroplating under a stirring cycle at a speed of 20-100 r / min, controlling the pH of the plating solution to be ≤4.5, the current density to be 0.5-2 A / dm², and the plating time to be 15-45 minutes to complete the nickel plating operation on the wafer surface.

[0035] Setting electroplating conditions with low current density, controlled pH, and moderate stirring, and finely regulating the electrocrystallization process, is beneficial for forming a dense, uniform, low-stress, and well-adhesive high-quality coating. Attached Figure Description

[0036] To more clearly illustrate the technical solution of this application, the accompanying drawings used in the description of this application will be briefly introduced below.

[0037] Figure 1 This is a magnified micrograph of the surface of the nickel plating layer in Example 1, magnified one thousand times.

[0038] Figure 2 This is a magnified micrograph of the surface of the nickel plating layer in Example 2, magnified one thousand times.

[0039] Figure 3 This is a magnified micrograph of the surface of the nickel plating layer in Example 3, magnified one thousand times.

[0040] Figure 4 This is a magnified micrograph of the surface of the nickel plating layer in Example 4, magnified one thousand times.

[0041] Figure 5 This is a magnified micrograph of the surface of the nickel plating layer in Example 5, magnified one thousand times.

[0042] Figure 6 This is a magnified micrograph of the surface of the nickel plating layer in Example 6, magnified one thousand times.

[0043] Figure 7 This is a magnified micrograph of the surface of the nickel plating layer in Example 7, magnified one thousand times.

[0044] Figure 8 This is a magnified microscopic image of the surface of the nickel plating layer in Comparative Example 1, magnified one thousand times.

[0045] Figure 9 This is a magnified microscopic image of the surface of the nickel plating layer in Comparative Example 2, magnified one thousand times.

[0046] Figure 10 This is a magnified microscopic image of the surface of the nickel plating layer in Comparative Example 3, magnified one thousand times.

[0047] Figure 11 This is a flowchart illustrating the steps of an optional implementation of the nickel plating method for wafer-level packaging according to this application. Detailed Implementation

[0048] The embodiments of this implementation are described in detail below. These embodiments are only used to explain this implementation and should not be construed as limiting this implementation.

[0049] In the description of the embodiments of this application, it should be noted that all ranges disclosed in this application are to be understood to encompass any and all subranges included therein. For example, the stated range "60-150 g / L" should be considered to include any and all subranges that begin with a minimum value of 60 g / L or greater and end with a maximum value of 150 g / L or less, such as 60 to 120 g / L, or 90 to 140 g / L, or 100 to 130 g / L. Furthermore, all ranges disclosed in this application are also considered to include the endpoints of the ranges, unless otherwise expressly stated. For example, the ranges "between 10 and 30," "10 to 30," or "10-30" should generally be considered to include the endpoints 10 and 30.

[0050] Unless otherwise specified, in this article, ratio refers to mass ratio and percentage refers to mass percentage.

[0051] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0052] This application addresses the high-performance thermal stress environment of high-computing-power chips by using cobalt salt as a functional additive in conjunction with nickel sulfamate for alloy electrodeposition, effectively improving the hardness and chemical corrosion resistance of the nickel plating layer. Simultaneously, it incorporates stress-relieving agents with specific molecular chain segments to molecularly regulate the spatial distribution of nickel and cobalt ions within the nickel plating solution system, as well as their binding rate, binding strength, and positional preference with active sites on the wafer surface. Ultimately, this results in a high-quality alloy nickel plating layer with uniform grain size, smooth and flat surface, low internal stress, and excellent adhesion to the wafer substrate.

[0053] In summary, the inventors of this case selected cobalt salt as a functional additive. The addition of cobalt refines the grain size of the plating layer, promotes the formation of a denser and more stable passivation film on the surface, and improves the hardness and corrosion resistance of the nickel plating layer. Furthermore, by compounding a stress reliever with a specific molecular structure, the nickel-cobalt deposition process is regulated, thereby improving the surface quality of the nickel plating layer and its adhesion to the wafer surface. At the same time, the complex mechanism of action of alloying functional additives and stress relievers in electroplating solutions with nickel sulfamate as the main nickel source has been understood, and a scheme for controlling the ratio of alloying functional additives and stress relievers has been provided to avoid the effects of excessive cobalt on the thermal conductivity and corrosion resistance of the plating layer, as well as the effects of excessive stress relievers on the adhesion.

[0054] The first aspect of this application provides a nickel plating solution for wafer-level packaging, comprising the following components and their concentrations: nickel sulfamate 60-150 g / L, nickel chloride 10-30 g / L, boric acid 20-60 g / L, leveling agent 0.1-1 g / L, wetting agent 0.01-0.5 g / L, complexing agent 0.1-5 g / L, stabilizer 0.01-0.1 g / L, stress reliever 0.5-2 g / L, and deionized water as the solvent. The nickel plating solution also includes a functional additive, cobalt salt, with a cobalt ion mass concentration of 2-21 g / L. The stress reliever has a molecular formula with at least a chain segment of the general chemical formula Ar-SO2-N-X1X2, where Ar is a group containing an aromatic ring, and X1 and X2 are selected from one of H groups, metal ions, carboxyl groups, ester groups, acyl groups, and carbonyl groups, respectively. The leveling agent is a quaternary ammonium salt cationic compound. The mass relationship between the cobalt ion A, the stress reliever B, and the leveling agent C simultaneously satisfies the following conditions: 6.67≤A / B≤10, 20≤A / C≤33.33, and 2≤B / C≤5.

[0055] Cobalt salts were selected as functional additives to synergistically alloy nickel sulfamate for electrodeposition. Compared to Watt's nickel, nickel sulfamate exhibits lower stress during deposition and a wider process window, making it suitable for industrial production. During electroplating, cobalt ions enter the nickel growth lattice, inducing local lattice distortion and hindering dislocation movement, thereby effectively improving the hardness and chemical corrosion resistance of the nickel plating layer. Furthermore, the negative impacts of cobalt introduction, such as an overly hard and brittle nickel plating layer and poor adhesion to the wafer surface, were mitigated by combining stress-relieving agents with specific molecular chain segments with quaternary ammonium salt cationic compounds. Specifically, the conjugated electron system of the Ar groups containing aromatic rings in the stress-relieving agent, the strong electron-withdrawing properties of the sulfonamide groups, and the strong charge adsorption of the quaternary ammonium salt cationic compounds all preferentially anchor the metal active sites on the cathode wafer surface within the electroplating solution, forming an initial oriented adsorption layer, reducing internal stress in the plating layer, and effectively enhancing surface adhesion. The combined action of the sulfonyl group and the imino group allows the stress reliever molecules to selectively adsorb onto specific crystal faces of the wafer, achieving a grain refinement effect. The leveling agent contains ammonium cations [R4N]. + It can diffuse and adsorb onto the cathode surface, preferentially covering microscopic protrusions with higher surface energy, thus achieving a coating leveling effect. Simultaneously, the quaternary ammonium salt cationic compound and stress-relieving agent molecules can form large ion pairs through electrostatic attraction, covering the convex surface region of the wafer and blocking the preferential growth of coating grains at protrusions, forcing the deposition of uniform crystal nuclei. Compared to single applications, this achieves a superior leveling effect (1+1>2). Specifically, the lone pair of electrons in the sulfonyl group forms a coordinate bond with the empty d orbital of the nickel atom, further enhancing the adsorption capacity for nickel and cobalt ions. Furthermore, the directional arrangement of polar bonds in the amide group enhances the adsorption force while dispersing internal stress within the grains. The stress-relieving agent molecules not only relieve stress on nickel but also on cobalt. After charge bonding with the quaternary ammonium salt cationic compound, the molecular volume increases, and the two work synergistically to achieve a low-stress and strong leveling effect.

[0056] In some embodiments, the cobalt salt is at least one selected from cobalt sulfate, cobalt chloride, cobalt aminosulfonate, cobalt alkylsulfonate, cobalt citrate, cobalt tartrate, cobalt gluconate, and cobalt acetate. All of these cobalt salts are compatible with water-based nickel plating solutions, achieving the effect of co-deposition of nickel and cobalt metal grains. Optionally, the cobalt salt is cobalt sulfate. The addition of cobalt refines the grain structure of the plating layer, promotes the formation of a denser and more stable passivation film on the surface, and improves the hardness and corrosion resistance of the nickel plating layer.

[0057] Furthermore, the mass concentration of the cobalt salt is preferably 2-20 g / L. If the concentration of the cobalt salt added is 2 g / L as in Example 1, the hardness of the final nickel plating layer is insufficient; when the concentration of the cobalt salt added reaches 20 g / L as in Examples 3 and 4, the uniformity of the deposition of the plating metal becomes worse, the surface of the resulting nickel plating layer is rough, and the adhesion to the wafer also becomes worse.

[0058] In some embodiments, the stress reliever is at least one of o-benzoylsulfonylimide and its alkali metal salt, p-toluenesulfonamide, and benzenesulfonamide. Within the electroplating solution system, the sulfonamide groups form strong electron-withdrawing centers that preferentially adsorb onto the wafer surface to be electroplated. Furthermore, the polar sites of the sulfonamide groups can electrostatically interact with positively charged cobalt and nickel ions, resulting in uniform dispersion of cobalt and nickel ions on the cathode surface. During deposition, the weak coordination of the sulfonamide sites with the metal ions dynamically adjusts the co-deposition potential of cobalt and nickel ions, reducing the deposition potential difference between the two metal ions, ensuring uniform precipitation of nickel-cobalt grains, and avoiding internal stress concentration caused by grain segregation. Further, nickel, as the base plating material, has a much higher concentration in the electroplating solution than cobalt. Therefore, nickel aminosulfonate is selected as the main nickel source. The aminosulfonate group can also form intermolecular hydrogen bonds with the sulfonamide groups in the stress reliever, further enhancing the dispersion effect on the nickel salt and inhibiting excessive local nickel grain growth. Furthermore, hydrogen bonding is stronger than electrostatic interactions, which facilitates the solvation of nickel ions, further homogenizing the concentration distribution of nickel ions on the cathode surface and preventing rapid accumulation of nickel ions due to local concentration polarization, thus reducing lattice distortion caused by uneven deposition. Based on this, the strongly electron-withdrawing sulfonamide groups selectively adsorb onto high-energy crystal planes and micro-protrusions on the wafer surface, blocking the preferential growth of nickel grains at these sites. This forces the deposition process to continuously generate new uniform crystal nuclei, resulting in a refined nanocrystalline structure. Simultaneously, molecular occupancy relaxes dislocation accumulation during lattice growth, preventing the accumulation of internal stress caused by dislocation entanglement. Ultimately, a high-quality nickel plating layer with uniform grain size, a smooth and flat surface, low internal stress, and excellent adhesion to the wafer substrate is obtained.

[0059] Further, the leveling agent is bis(dodecyl)dimethylammonium chloride; the mass concentration of the leveling agent is 0.1-0.5 g / L.

[0060] A high-molecular-weight didodecyl dimethyl ammonium chloride is selected as the leveling agent. When the cathode current flows through the wafer, the strong charge adsorption drives the didodecyl dimethyl ammonium chloride to be adsorbed onto the wafer surface to be plated. The long chain of the didodecyl carbon significantly increases the molecular volume of the leveling agent, enabling it to more efficiently cover the growth high sites on the plating surface, preventing excessively rapid local growth of the plating grains, enhancing the leveling effect, refining the grains, and improving the adhesion between the nickel plating layer and the wafer. The optimal addition window for the leveling agent is 0.1-0.5 g / L. Insufficient addition will result in poor leveling effect, while excessive addition will lead to over-adsorption onto the plating surface, interfering with metal ion deposition.

[0061] Furthermore, the mass relationships of the cobalt ions A, the stress reliever B, and the leveling agent C simultaneously satisfy: 6.67≤A / B≤10, 20≤A / C≤33.33, and 2≤B / C≤5.

[0062] Based on the molecular-level synergistic effect among functional additives, stress relievers, and leveling agents, the addition ratios of these additives, stress relievers, and leveling agents are further constrained to balance the performance of the nickel plating layer in terms of hardness, surface quality, and adhesion between the nickel plating layer and the wafer surface. Specifically, within a concentration range of 2-21 g / L, a higher concentration of cobalt ions in the nickel plating solution results in greater hardness of the nickel plating layer, but deteriorates thermal conductivity and corrosion resistance. Within a concentration range of 0.5-2 g / L, a higher concentration of stress relievers leads to better control of deposition stress, higher surface quality of the nickel plating layer, and fewer cracking and brittleness phenomena, but a decrease in hardness. Excessive addition of stress relievers can lead to over-adsorption of the plating surface, interfering with the normal deposition of metal ions, weakening the adhesion between the plating layer and the wafer, and easily causing peeling and flaking during subsequent machining or use, resulting in a significant reduction in adhesion. Within a concentration range of 0.1-1 g / L, a higher concentration of the leveling agent results in better pre-leveling of the wafer surface and higher surface quality of the nickel plating layer. However, excessive leveling agent can lead to over-adsorption of the plating surface, interfering with metal ion deposition. Furthermore, stress relievers exhibit similar stress-relieving effects on cobalt ions as they do on nickel ions. There is also competition between leveling agents and stress relievers for adsorption sites. When the mass ratios of cobalt ions (A), stress reliever (B), and leveling agent (C) simultaneously satisfy the following conditions: 6.67 ≤ A / B ≤ 10, 20 ≤ A / C ≤ 33.33, and 2 ≤ B / C ≤ 5, the hardness, surface quality, and good adhesion to the wafer of the nickel plating layer are balanced.

[0063] In some embodiments, the wetting agent is a perfluoroepoxy alkyl nonionic surfactant.

[0064] Perfluorinated epoxy alkyl nonionic surfactants are used to improve surface tension, accelerate the escape of surface bubbles, and eliminate surface plating defects.

[0065] Furthermore, the stabilizer is a thiazole compound.

[0066] Thiazole rings in thiazole compounds have lone pairs of electrons that can form coordination bonds with metal surfaces, covering the active surface of free nickel, blocking its reaction with reducing agents, and preventing its reduction and deposition in the plating bath.

[0067] Understandably, the combined use of perfluoroepoxy alkyl nonionic surfactants and thiazole stabilizers synergistically creates a favorable plating environment, achieving uniform plating speed and stable plating solution.

[0068] Furthermore, the mass concentration of the hexafluoropropylene oxide oligomer is 0.01-0.15 g / L. The strong oleophobic and hydrophobic properties of the fluorocarbon chain give it extremely low surface energy, which significantly reduces the surface tension of the plating solution system, accelerates the rapid wetting of the wafer surface, effectively removes adhering air bubbles, and prevents incomplete plating, pitting, or uneven coating.

[0069] The concentration of wetting agent added is 0.01-0.15 g / L. If the addition is insufficient, the wetting effect will be poor, while if the upper limit is exceeded, the improvement on the uniformity of the plating will be slow, which will cause unnecessary cost increases.

[0070] Furthermore, the stabilizer is mercaptobenzothiazole with a mass concentration of 0.01-0.05 g / L.

[0071] Mercaptobenzothiazole was selected for two purposes: firstly, as a stabilizer, the thiazole ring coordinates and complexes with free nickel, inhibiting reductive decomposition; secondly, as an accelerator, the -SH group has a certain adsorption effect on the cathode surface, while the C=S group can improve the catalytic activity of the wafer surface, accelerate the deposition rate of metal grains, shorten the electroplating time, improve production efficiency, and reduce manufacturing costs.

[0072] The concentration window for adding stabilizer is 0.01-0.05 g / L. Insufficient addition of stabilizer is not conducive to the stability of free nickel, while when the addition of stabilizer exceeds the upper limit, free nickel is excessively captured, the plating rate drops significantly, and even incomplete plating occurs.

[0073] In some embodiments, the nickel plating solution comprises the following components in mass concentrations: nickel aminosulfonate solution 60-150 g / L, nickel chloride 10-30 g / L, boric acid 20-60 g / L, dodecyl dimethyl ammonium chloride 0.1-0.5 g / L, hexafluoropropylene oxide oligomer 0.01-0.15 g / L, ethylenediaminetetraacetic acid 0.1-5 g / L, mercaptobenzothiazole 0.01-0.05 g / L, anhydrous cobalt sulfate 5.3-55 g / L, o-benzoylsulfonyl imide 0.5-2 g / L, and deionized water as the solvent.

[0074] The nickel plating solution with the above composition produces a nickel plating layer with high hardness, corrosion resistance, and good heat dissipation, meeting the reliability requirements of high-heat-density, high-computing-power chips.

[0075] On the other hand, see Figure 11 This application also provides a method for nickel plating at the wafer level, comprising preparing a nickel plating solution according to the aforementioned formula and injecting it into an electroplating apparatus. The electroplating method includes the following steps: S1: Perform surface cleaning and plasma treatment on the wafer to enhance the surface hydrophilicity and active sites of the wafer; S2: The activated wafer is placed in the nickel plating solution for electroplating, and the nickel plating solution is circulated and stirred during the electroplating process; S3: After electroplating, the wafer is cleaned and dried to obtain a nickel plating layer.

[0076] Impurities or passivation layers are removed through surface cleaning, and plasma treatment is used to physically bombard the electroplated surface to form active sites. The physical and chemical effects of plasma are then used to introduce highly active functional groups, enhancing surface energy and hydrophilicity, strengthening the chemical bonding with the deposited nickel and cobalt metal, and improving the mechanical stability of the nickel plating layer. Furthermore, the nickel plating layer is rated as 5B after cross-cut adhesion testing. Its excellent adhesion is suitable for the high-intensity thermal cycling operating environment of high-performance chips, ensuring the long service life of high-performance chips.

[0077] In some implementations, the pretreatment step S1 before wafer electroplating further includes: S11: immersing the wafer in an acidic sodium citrate solution for 1-3 minutes; S12: subjecting the acid-immersed wafer to Ar plasma treatment under the following conditions: pressure 150-250 mTorr, power 80-120 W, gas flow rate 80-120 sccm, and time 20-40 seconds; S13: subjecting the Ar plasma-treated wafer to N2 plasma treatment under the following conditions: pressure 150-250 mTorr, power 180-220 W, gas flow rate 80-120 sccm, and time 50-70 seconds.

[0078] First, acid leaching removes contaminants from the wafer surface, providing a clean substrate for subsequent plasma treatment. Then, chemically inert Ar plasma treatment physically bombards the wafer surface, further removing residual trace contaminants, adsorbed layers, and weak boundary layers. Simultaneously, it increases surface roughness at the nanoscale, raising surface energy. Ion bombardment also breaks surface chemical bonds, creating dangling bonds and placing the surface in a highly activated state. Finally, N2 plasma treatment with active nitrogen introduces nitrogen-containing polar functional groups, such as amino and imine groups, into the wafer surface, significantly enhancing surface hydrophilicity and chemical activity, which is beneficial for subsequent nickel and cobalt deposition. If N2 plasma treatment is performed first, poor surface cleanliness and roughness may lead to uneven functional group grafting or poor adhesion, and subsequent Ar bombardment may damage the introduced functional groups.

[0079] In some implementations, the electroplating of the wafer also includes: S21: Let the prepared nickel plating solution stand for 1-10 minutes, and stir it rapidly with a magnetic stirrer at 100 r / min to homogenize the components of the nickel plating solution system. S22: Place the wafer into the nickel plating solution, reduce the stirring speed, lift it out of the liquid surface 2-5 times, and then let it stand in the nickel plating solution for 30-60 seconds to allow the surface to be fully wetted. S23: After the wafer is fully wetted, place it face the anode plate and perform room temperature electroplating under stirring and circulation at a speed of 20-100 r / min. Control the pH of the electroplating solution to ≤4.5, the current density to be 0.5-2 A / dm², and the electroplating time to be 15-45 min to complete the nickel plating operation on the wafer surface. S24: After electroplating, the wafer is removed, thoroughly rinsed with deionized water, and then dried with nitrogen or oven to obtain the finished product.

[0080] Setting electroplating conditions with low current density, controlled pH, and moderate stirring, and finely regulating the electrocrystallization process, is beneficial for forming a dense, uniform, low-stress, and well-adhesive high-quality coating.

[0081] In some implementation schemes, the pH of the electroplating solution during the electroplating process is ≤4.5. The slightly acidic electroplating solution environment can effectively inhibit the precipitation of cobalt and nickel ions as hydroxides due to local pH increases, thus avoiding the inclusion of impurity phases or a loose structure in the coating. On the other hand, the acidic environment reduces the precipitation potential difference between nickel and cobalt, inhibiting excessive abnormal co-deposition and ensuring uniform nickel and cobalt composition and consistent performance in the coating.

[0082] The following examples will further illustrate this application.

[0083] The reagents and raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0084] Examples 1-7 and Comparative Examples 1-3 of this application all include the following four parts of experimental and testing processes: I. The preparation of nickel electroplating solution includes the following steps: 1. First, add the measured amount of nickel sulfamate to provide nickel ions, and stir until homogeneous.

[0085] 2. Adding nickel chloride increases conductivity.

[0086] 3. Add a measured amount of boric acid to provide a stable acid-base environment.

[0087] 4. Add leveling agent, wetting agent, complexing agent, stabilizer, functional additive, and stress reliever in sequence.

[0088] 5. Add deionized water to the required volume and stir continuously until the solution is fully homogeneous.

[0089] II. Pretreatment and Activation Process for Wafer Surface To achieve optimal coating adhesion and surface smoothness, the wafer (or carrier) must be cleaned and activated before electroplating. The steps are as follows: 1. Acidic cleaning: Immerse the wafer to be treated in a 5-10 wt% acidic sodium citrate aqueous solution at room temperature for 2 minutes to remove the surface oxide layer and residual metal ions. After removal, rinse with deionized water.

[0090] 2. Ar plasma treatment: The cleaned wafer is placed in a plasma treatment device, Ar gas is introduced, and the treatment lasts for 30 seconds under conditions of 200 mTorr pressure, 100 W power, and 100 sccm gas flow rate. This physical bombardment further cleans the surface organic matter and creates active sites.

[0091] 3. N2 plasma treatment: Within the same chamber, N2 gas was switched and treated for 60 seconds at a pressure of 200 mTorr, a power of 200 W, and a gas flow rate of 100 sccm. Through physical and chemical reactions, highly active nitrogen-containing functional groups were introduced onto the sample surface, significantly enhancing surface energy and hydrophilicity. After treatment, the samples were ready for use.

[0092] III. Electroplating Process The DC electroplating method is used, and the specific operation is as follows: 1. Plating solution homogenization: Before immersing the wafer, let the prepared nickel plating solution stand for 1-10 minutes and stir it rapidly with a magnetic stirrer at 100 r / min to homogenize the composition of the plating solution before the experiment.

[0093] 2. Immersion treatment: After the first step of homogenizing the plating solution is completed, the wafer is placed in the nickel plating solution, the stirring speed is reduced, and it is lifted out of the liquid surface 2-5 times. Then, it is left to stand in the nickel plating solution for 30-60 seconds to allow the surface to be fully wetted.

[0094] 3. DC electroplating: Position the fully wetted wafer directly onto the anode plate. Perform room temperature electroplating with a stirring cycle of 20-100 r / min, a current density of 0.5-2 A / dm², and an electroplating time of 15-45 min to complete the nickel plating operation on the wafer surface.

[0095] 4. Post-processing: After electroplating, the wafer is removed, thoroughly rinsed with deionized water, and then dried with nitrogen or oven to obtain the finished product.

[0096] IV. Testing and Evaluation Methods To verify the effectiveness of this application, the following methods were used to characterize the electroplated finished product: Nickel plating thickness and plating speed: Use an X-ray thickness gauge to measure whether the plating reaches 6μm within half an hour and the speed reaches 12μm / h or more.

[0097] Surface structure and defects: The surface microstructure was observed using scanning electron microscopy (SEM).

[0098] Hardness test: The surface hardness is tested using a hardness tester.

[0099] Bonding strength: Tested using the 100-grid test.

[0100] Plating solution life: The duration for which the plating solution can maintain the above performance indicators after continuous use and regular replenishment of nickel sulfamate and functional additives.

[0101] Thermal conductivity test: Laser flash method, using 50 microsecond pulses to heat the wafer surface, and the thermal diffusivity is calculated using the following formula: Thermal diffusion rate: λ = α·ρ·C p ; in: λ α: Thermal conductivity, unit W / (m·K); α: Thermal diffusivity, unit m 2 / s; ρ: Material density, unit kg / m³ 3 C p Specific heat capacity, in J / (kg·K).

[0102] Roughness test: Roughness test is performed using a step tester, and the average roughness Ra is used to reflect the degree of roughness.

[0103] V. Examples The present invention is further illustrated below through seven specific embodiments.

[0104] Example 1 This embodiment provides a nickel plating solution for wafer-level packaging. The specific composition of the nickel plating solution is: 150 g / L nickel sulfamate solution, 30 g / L nickel chloride, 20 g / L boric acid, 0.1 g / L dodecyl dimethyl ammonium chloride, 0.1 g / L hexafluoropropylene oxide oligomer, 5 g / L ethylenediaminetetraacetic acid, 0.015 g / L mercaptobenzothiazole, 5.3 g / L cobalt sulfate (cobalt ions 2 g / L), 0.5 g / L o-benzoylsulfonyl imide, and deionized water as the solvent. The ratios of cobalt ions (A), stress reliever (B), and leveling agent (C) are: A / B = 4, A / C = 20, and B / C = 5. The measured pH value of the nickel plating solution is 4.4.

[0105] Electroplating process: After immersing the wafer in acidic sodium citrate for 2 minutes, the sample surface is treated with Ar plasma at a pressure of 200 mTorr, power of 100 W, gas flow rate of 100 sccm, and time of 30 s. Then, it is treated with N2 plasma at a power of 200 W, gas flow rate of 100 sccm, time of 60 s, and pressure of 200 mTorr. After this, the treated wafer is placed in the aforementioned A-plating solution equipment for electroplating at room temperature, with a stirring speed of 30 r / min and a current density of 2 A / dm³. 2 The electroplating time is 15 minutes. After the wafer electroplating is completed, it is rinsed with water and dried before testing.

[0106] Results: See Figure 1 As shown in Table 1 below, the hardness of the nickel plating layer obtained under low concentration of cobalt ions is 350 HV, the surface roughness is greater than 1μm, and the adhesion under the cross-cut adhesion test is grade 5B. The low leveling agent leads to surface roughness, and the low cobalt ion content leads to insufficient plating hardness.

[0107] Example 2: The only difference between Example 2 and Example 1 is the content of functional additives in the nickel electroplating solution: cobalt sulfate 25 g / L (cobalt ions 10 g / L), cobalt ions A, stress reliever B, and leveling agent C: A / B=20, A / C=100, B / C=5.

[0108] Results: See Figure 2 As shown in Table 1 below, the hardness of the nickel plating layer increased to 600 HV under higher concentrations of cobalt ions, the surface roughness was greater than 1 μm, the adhesion under the cross-cut adhesion test was grade 3B, and a certain area of ​​peeling occurred, indicating that the stress was too strong during the electroplating process in this case, and the proportion of functional additives, stress relievers and leveling agents was unbalanced.

[0109] Example 3 The only difference between Example 3 and Example 1 is the content of functional additives in the nickel electroplating solution: 50 g / L cobalt sulfate (20 g / L cobalt ions), and in cobalt ions A, stress reliever B, and leveling agent C: A / B=40, A / C=200, B / C=5.

[0110] Results: See Figure 3 As shown in Table 1 below, the hardness of the nickel plating layer under high cobalt ion concentration further increased to 650 HV, the surface roughness was greater than 1 μm, and the adhesion under the cross-cut adhesion test was 0B grade, with complete peeling. This indicates that the cobalt ion concentration in this case was significantly too high, the addition ratio of stress reliever was insufficient, and the addition ratio of cobalt ions, stress reliever and leveling agent was seriously unbalanced.

[0111] Example 4 The only difference between Example 4 and Example 1 is that the content of some components in the nickel electroplating solution is different. Specifically, the solutions are: 25 g / L cobalt sulfate (10 g / L cobalt ions), 1 g / L o-benzoylsulfonylimide, 0.3 g / L dodecyl dimethyl ammonium chloride, and the ratios of cobalt ions A, stress reliever B, and leveling agent C are: A / B=10, A / C=33.33, and B / C=3.33.

[0112] Results: See Figure 4 As shown in Table 1 below, the nickel plating layer with high concentration of cobalt ions has a hardness of up to 650 HV, a surface roughness of less than 0.5 μm, and an adhesion grade of 5B under the cross-cut adhesion test, with no surface peeling. This indicates that the stress of the electroplated layer is optimized and the adhesion to the substrate is enhanced. It can be seen that with the same concentration of cobalt salt, adding a certain proportion of stress reliever and leveling agent can improve the adhesion between the final nickel plating layer and the wafer. The proportion of the three components of functional additive, stress reliever and leveling agent is set reasonably.

[0113] Example 5 The difference between Embodiment 5 and Example 1 lies only in the content of some components in the nickel electroplating solution. Specifically, the content of cobalt sulfate is 25 g / L (cobalt ions 10 g / L), o-benzoylsulfonylimide is 2 g / L, and bis(dodecyl)dimethylammonium chloride is 0.3 g / L. In cobalt ions A, stress reliever B, and leveling agent C, the ratios are: A / B = 5, A / C = 33.33, and B / C = 6.67.

[0114] Results: See Figure 5 As shown in Table 1 below, the hardness of the nickel plating layer under high concentration of cobalt ions is 600 HV, the surface roughness is less than 0.5 μm, the adhesion is grade 4B under the cross-cut adhesion test, and very little peeling occurs, which confirms that when the proportion of stress relieving agent is too high, it will weaken the adhesion of the metal plating.

[0115] Example 6 The only difference between Example 6 and Example 1 is that the content of some components in the nickel electroplating solution is different. Specifically, the content of cobalt sulfate is 25 g / L (cobalt ions 10 g / L), o-benzoylsulfonylimide is 1 g / L, and bis(dodecyl)dimethylammonium chloride is 0.5 g / L. In cobalt ions A, stress reliever B, and leveling agent C, the ratios are: A / B=10, A / C=20, and B / C=2.

[0116] Results: See Figure 6 As shown in Table 1 below, the nickel plating layer with cobalt ions at this concentration has a hardness of 600 HV, a surface roughness of less than or equal to 0.05 μm, a cross-cut adhesion test grade of 5B, and no surface peeling, indicating that the ratio of cobalt ions, stress reliever, and leveling agent in this embodiment is reasonable.

[0117] Example 7 The only difference between Example 7 and Example 1 is that the content of some components in the nickel electroplating solution is different. Specifically, the solutions are: cobalt sulfate 25 g / L (cobalt ions 10 g / L), o-benzoylsulfonylimide 1.5 g / L, and didodecyl dimethyl ammonium chloride 0.3 g / L. In cobalt ions A, stress reliever B, and leveling agent C, the ratios are: A / B = 6.67, A / C = 33.33, and B / C = 5.

[0118] Results: See Figure 7 As shown in Table 1 below, the hardness of the nickel plating layer at this cobalt ion concentration is 610 HV, the surface roughness is less than or equal to 0.08 μm, the cross-cut adhesion test grade is 5B, and there is no surface peeling, indicating that the proportions of cobalt ions, stress relievers, and leveling agents added in this embodiment are appropriate.

[0119] VI. Comparative Example To highlight the advantages of this invention, the following comparative examples are provided.

[0120] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that some components and their contents in the nickel plating solution are different. Specifically, copper sulfate is used instead of cobalt sulfate, and the contents of copper ions are: 10 g / L, o-benzoylsulfonylimide 1 g / L, and bis(dodecyl)dimethylammonium chloride 0.5 g / L.

[0121] Results: See Figure 8 As shown in Table 1 below, the hardness of the nickel plating layer is 300 HV, grade 5B in cross-cut adhesion testing, and there is no surface peeling, which does not fully meet the high hardness requirement.

[0122] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that some components and their contents in the nickel plating solution are different. Specifically, zinc sulfate is used instead of cobalt sulfate, and the zinc ion content is 10 g / L, o-benzoylsulfonylimide 1 g / L, and bis(dodecyl)dimethylammonium chloride 0.5 g / L.

[0123] Results: See Figure 9 Compared with Table 1 below, Comparative Example 1 shows better strength and wear resistance. The addition of zinc increases the hardness of the nickel plating layer to 400 HV, but it still lags behind cobalt, with an adhesion grade of 2B.

[0124] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that some components and their contents in the nickel plating solution are different. Specifically, ferric sulfate is used instead of cobalt sulfate, and the contents of iron ions are: 10 g / L, o-benzoylsulfonylimide 1 g / L, and bis(dodecyl)dimethylammonium chloride 0.5 g / L.

[0125] Results: See Figure 10 As shown in Table 1 below, although the hardness of the obtained nickel plating layer can reach over 600 HV, the plating layer is brittle, has poor adhesion, and achieves a 1B cross-cut adhesion rating, resulting in large-area peeling. This proves that the overall performance of other metal ion plating solutions is insufficient and cannot achieve a stable and reliable protective effect.

[0126] As can be seen from the above embodiments and comparative examples, this application successfully solves the problems of insufficient hardness, weak adhesion, and poor heat dissipation of wafer electroplating protective layers by adding specific proportions of functional additives, stress relievers, and leveling agents, and matching them with corresponding DC electroplating process parameters. The coating obtained by this nickel electroplating solution system and electroplating process is dense and uniform, with good mechanical strength, thermal stability, and corrosion resistance, which can meet the high reliability requirements of high-computing-power wafers, and has the advantages of high production efficiency and controllable cost.

[0127] Based on the production requirements of a plating speed of 12μm / h (nickel layer thickness of 6μm in half an hour), no cracks, no discoloration, no missing plating on the wafer surface after plating, hardness greater than 600 HV, and adhesion of 5B or above, it can be determined that Examples 4, 6 and 7 meet the above requirements.

[0128] Table 1. Parameter settings and experimental results for each embodiment and comparative example. (Continued from the table above) In conjunction with Examples 1-3, as the cobalt ion content increases, the hardness of the nickel plating layer steadily increases, but the adhesion gradually decreases. Consequently, the results of heat resistance tests, salt spray corrosion tests, and thermal conductivity also gradually deteriorate, indicating that cobalt ions have the optimal addition window for a plating solution system containing a fixed amount of stress reliever and leveling agent.

[0129] Further, in conjunction with Examples 4-7, the mass ratios of cobalt ions A, stress reliever B, and leveling agent C need to be adjusted to simultaneously satisfy the following ratios: 6.67≤A / B≤10, 20≤A / C≤33.33, and 2≤B / C≤5. This will result in a nickel plating layer that meets the application requirements. Furthermore, if the proportion of any single component among the aforementioned three reagents is too high or too low, the electroplating effect will decrease. The proportional relationships proposed in this application are of guiding significance for controlling the electroplating quality of nickel electroplating solutions.

[0130] Based on Comparative Examples 1-3, it is demonstrated that cobalt salts have a natural property of being suitable for nickel plating solutions compared to copper, zinc, and iron salts. Assuming that the functions of copper, zinc, and iron ions are exactly the same as those of cobalt ions, even if the ratio of functional additives (measured by the metal ions), stress relievers, and leveling agents satisfies the above pairwise component quantitative relationships, there are still several indicators that do not meet the actual requirements.

[0131] Although embodiments of this implementation have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this implementation, the scope of which is defined by the claims and their equivalents.

Claims

1. A nickel plating solution for wafer-level packaging, characterized in that, The nickel plating solution comprises the following components at the following mass concentrations: nickel sulfamate 60-150 g / L, nickel chloride 10-30 g / L, boric acid 20-60 g / L, leveling agent 0.1-1 g / L, wetting agent 0.01-0.5 g / L, complexing agent 0.1-5 g / L, stabilizer 0.01-0.1 g / L, stress reliever 0.5-2 g / L, and deionized water as the solvent; the nickel plating solution also includes a functional additive: cobalt salt, and the mass concentration of cobalt ions is 2-21. The stress reliever has a molecular formula of at least one segment with the general chemical formula Ar-SO2-N-X1X2, where Ar is a group containing an aromatic ring, and X1 and X2 are selected from H, metal ions, carboxyl groups, ester groups, acyl groups, and carbonyl groups, respectively. The leveling agent is a quaternary ammonium salt cationic compound. The mass relationships of the cobalt ion A, the stress reliever B, and the leveling agent C simultaneously satisfy: 6.67≤A / B≤10, 20≤A / C≤33.33, and 2≤B / C≤5.

2. The nickel plating solution for wafer-level packaging according to claim 1, characterized in that, The cobalt salt is at least one of cobalt sulfate, cobalt chloride, cobalt aminosulfonate, cobalt alkylsulfonate, cobalt citrate, cobalt tartrate, cobalt gluconate, and cobalt acetate; the stress reliever is at least one of o-benzoylsulfonamide and its alkali metal salt, p-toluenesulfonamide, and benzenesulfonamide.

3. The nickel plating solution for wafer-level packaging according to claim 1, characterized in that, The nickel plating solution meets at least one of the following conditions: a. the wetting agent is a perfluoroepoxy alkyl nonionic surfactant; b. the stabilizer is a thiazole compound; c. the leveling agent is didodecyl dimethyl ammonium chloride; d. the mass concentration of the leveling agent is 0.1-0.5 g / L.

4. The nickel plating solution for wafer-level packaging according to claim 1, characterized in that, The complexing agent satisfies at least one of the following conditions: e. The complexing agent is ethylenediaminetetraacetic acid; f. The mass concentration of the complexing agent is 0.1-3 g / L.

5. The nickel plating solution for wafer-level packaging according to claim 3, characterized in that, The wetting agent satisfies at least one of the following conditions: g: the wetting agent is a hexafluoropropylene oxide oligomer; h: the mass concentration of the wetting agent is 0.01-0.15 g / L.

6. The nickel plating solution for wafer-level packaging according to claim 3, characterized in that, The stabilizer also satisfies at least one of the following conditions: i: the stabilizer is mercaptobenzothiazole; j: the mass concentration of the stabilizer is 0.01-0.05 g / L.

7. The nickel plating solution for wafer-level packaging according to claim 1, characterized in that, The nickel plating solution comprises the following components in the indicated mass concentrations: nickel aminosulfonate solution 60-150 g / L, nickel chloride 10-30 g / L, boric acid 20-60 g / L, dodecyl dimethyl ammonium chloride 0.1-0.5 g / L, hexafluoropropylene oxide oligomer 0.01-0.15 g / L, ethylenediaminetetraacetic acid 0.1-5 g / L, mercaptobenzothiazole 0.01-0.05 g / L, o-benzoylsulfonylimide 0.5-2 g / L, anhydrous cobalt sulfate 5.3-55 g / L, and deionized water as the solvent.

8. A method for electroplating nickel at the wafer-level packaging stage, characterized in that, The electroplating method uses the nickel electroplating solution according to any one of claims 1-7. Includes the following steps: S1: Perform surface cleaning and plasma treatment on the wafer to enhance the surface hydrophilicity and active sites of the wafer; S2: The activated wafer is placed in the nickel plating solution for electroplating, and the nickel plating solution is circulated and stirred during the electroplating process; S3: After the electroplating is completed, the wafer is cleaned and dried to obtain a nickel plating layer.

9. The electroplating method according to claim 8, characterized in that, Step S1 further includes: S11: Immersing the wafer in an acidic sodium citrate solution for 1-3 minutes; S12: Treating the wafer after acid immersion with Ar plasma under the following conditions: pressure 150-250 mTorr, power 80-120 W, gas flow rate 80-120 sccm, time 20-40 seconds; S13: Treating the wafer after Ar plasma treatment with N2 plasma under the following conditions: pressure 150-250 mTorr, power 180-220 W, gas flow rate 80-120 sccm, time 50-70 seconds.

10. The electroplating method according to claim 8, characterized in that, Step S2 further includes: S21: Let the prepared nickel plating solution stand for 1-10 minutes and stir it rapidly at 100 r / min with a magnetic stirrer to homogenize the components in the nickel plating solution; S22: Put the wafer into the nickel plating solution, reduce the stirring speed, lift it out of the liquid 2-5 times, and then let it stand in the nickel plating solution for 30-60 seconds to fully wet the surface; S23: Place the fully wetted wafer facing the anode plate and perform room temperature electroplating under a stirring cycle of 20-100 r / min, controlling the pH of the plating solution to be ≤4.5, the current density to be 0.5-2 A / dm², and the plating time to be 15-45 minutes to complete the nickel plating operation on the wafer surface.

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