Wafer aluminum-based UBM electroless plating process, electroless plating pretreatment agent and its preparation method

Abstract

This application provides a wafer aluminum-based UBM electroless plating process, a pretreatment agent for electroless plating, and a method for preparing the same. The pretreatment agent includes a cleaning agent and a micro-etching agent. The cleaning agent includes: sodium carbonate 8-35 g / L, pH adjuster 8-30 g / L, surfactant 1-10 g / L, dispersant 5-20 g / L, and auxiliary corrosion inhibitor 2-10 g / L. The solvent is deionized water. The surfactant contains at least C8-C20 alkyl sulfonates, and the auxiliary corrosion inhibitor contains at least one compound with the general chemical formula HO-[CH2-CH2-O]. n The micro-etching agent consists of 68% nitric acid (290-580 ml / L), an accelerator (10-40 g / L), a protectant (5-30 g / L), and an ion complexing agent (5-30 g / L). The solvent is deionized water, the accelerator is a fluorinated compound, and the protectant is a polyphosphate. By adding an auxiliary corrosion inhibitor to the cleaning agent to help regulate the cleaning intensity, efficient and moderate cleaning is achieved, reducing surface height differences. Within the micro-etching agent, the accelerator synergistically accelerates the decomposition of the passivation layer with nitric acid, while the protectant and complexing agent synergistically compete for adsorption sites of active elemental aluminum, achieving uniform roughening.

Description

Technical Field

[0001] This application relates to the field of semiconductor chip electroless plating technology, and in particular to a wafer aluminum-based UBM electroless plating process, an electroless plating pretreatment agent, and a method for preparing the same. Background Technology

[0002] With the development of fifth-generation mobile communication technology and the arrival of the 5G / 6G era, semiconductor devices are moving towards higher frequencies, higher power, and higher quality. Against this backdrop, aluminum-based materials, with their excellent thermal conductivity, electrical conductivity, and processability, have become the core substrate for components such as power module substrates. However, due to aluminum's reactive chemical properties, it easily forms a dense alumina film in the natural environment. Furthermore, its surface readily absorbs contaminants such as grease during processing and transportation, which can lead to quality defects such as incomplete plating and discoloration in the aluminum-based under-bump metal layer (UBM) during subsequent nickel and gold plating processes. Therefore, reliable pretreatment processes are essential to ensure the reliability and yield of high-performance aluminum-based module devices.

[0003] Traditional pretreatment processes using a single acid or alkali washing process are difficult to precisely control the roughening degree of aluminum-based UBM surfaces. This often leads to defects and quality problems in subsequent plating layers, such as blistering, delamination, and discoloration, caused by uneven roughening, over-etching, or under-etching. These issues severely affect the yield and lifespan of semiconductor device end products.

[0004] To address the aforementioned single processing techniques, a pretreatment process using a compound system of hydrochloric acid-oxidant and sodium persulfate is proposed. This process employs hydrochloric acid-oxidant cleaning agents, such as hydrochloric acid-hydrogen peroxide, to powerfully remove the natural oxide layer and metallic impurities from the aluminum surface. Then, sodium persulfate is used for micro-etching and activation, forming a hydrophilic and activated surface state. This achieves uniform roughening of the aluminum-based UBM surface to approximately 0.5 μm. The dense micropore array on the roughened surface increases the effective specific surface area to 3–5 times the original area, providing a strong mechanical interlocking anchor point for subsequent coating. The coating exhibits excellent adhesion to the aluminum-based UBM substrate, making this a common mainstream process in the pretreatment of aluminum-based materials.

[0005] However, as electronic manufacturing moves towards miniaturization and integration, the precision requirements for pretreatment of aluminum-based UBMs are constantly increasing. When processing aluminum-based UBMs with high-end semiconductor chips and precision circuit structures, the aforementioned pretreatment processes suffer from several problems. Firstly, the cleaning and micro-etching processes lack corresponding corrosion inhibition and control methods. With uneven Al2O3 passivation layer thickness, the initially exposed elemental aluminum areas, due to their active chemical properties, experience heightened corrosion from the active components of the cleaning or micro-etching processes, leading to over-cleaning or over-etching in some areas, increased surface roughness, and macroscopically, uneven morphology. Secondly, the cleaning and micro-etching processes lack treatment for impurity metal ions. When impurity metal ions such as copper ions adhering to the aluminum-based UBM surface are introduced into the solution system, reactions such as 2Al + 3Cu²⁺ occur. + → 2Al³ + The reaction of +3Cu↓ leads to irregular pitting and red speckled corrosion on the aluminum substrate surface. Furthermore, the stability of the aforementioned hydrochloric acid-oxidant cleaning system and sodium persulfate micro-etching system is limited. In practical applications, aluminum ions accumulate in the solution, causing problems such as decreased solution stability and turbidity. Therefore, there is an urgent need to develop a cleaning and micro-etching pretreatment process that can effectively remove grease and oxide layers from the aluminum surface while ensuring a clean and uniform surface, to meet the high-performance requirements of aluminum-based semiconductor chip modules. Summary of the Invention

[0006] Based on this, the first aspect of this application provides an aluminum-based UBM electroless plating pretreatment agent that can achieve efficient cleaning of the aluminum-based surface to be plated, high-precision micro-etching and roughening of the aluminum-based surface to be plated, and has a long service life.

[0007] The second aspect of this application provides a method for preparing a pretreatment agent for electroless plating of aluminum-based UBM wafers. The method involves preparing the cleaning agent and micro-etching agent in the aforementioned pretreatment agent to efficiently clean and micro-etch the aluminum-based UBM surface to be plated, thereby obtaining a uniformly roughened, colorless aluminum-based surface to be plated.

[0008] The third aspect of this application provides a chemical plating process for aluminum-based UBM wafers, wherein the aforementioned chemical plating pretreatment agent is used in the pretreatment step to clean and micro-etch the surface of the aluminum-based UBM wafer to be plated, resulting in a uniformly roughened, colorless aluminum-based surface to be plated.

[0009] The specific technical solution of this application is as follows: In a first aspect, this application provides a pretreatment agent for electroless plating of aluminum-based UBM wafers, including a cleaning agent and a micro-etching agent; The cleaning agent comprises the following components at the following mass concentrations: sodium carbonate 8-35 g / L, pH adjuster 8-30 g / L, surfactant 1-10 g / L, dispersant 5-20 g / L, and auxiliary corrosion inhibitor 2-10 g / L. The solvent is deionized water. The surfactant contains at least an alkyl sulfonate with the general chemical formula R–SO3M, wherein R is a long-chain alkyl group between C8 and C20. The auxiliary corrosion inhibitor contains at least one component with the general chemical formula HO-[CH2-CH2-O]. n Organic alcohols with -H, where 4≤n≤13; The micro-etching agent comprises the following components by volume or mass concentration: 68% nitric acid 290-580 ml / L, accelerator 10-40 g / L, protectant 5-30 g / L, ion complexing agent 5-30 g / L, with deionized water as the solvent. The accelerator is a fluorinated compound, and the protectant is a polyphosphate.

[0010] The pretreatment agent for electroless plating of aluminum-based UBM wafers provided in the first aspect of this application has at least the following beneficial effects: Cleaning agents are produced by adding chemicals with the general formula HO-[CH2-CH2-O]. n The -H organic alcohol-based auxiliary corrosion inhibitor and the alkyl sulfonate surfactant with the general chemical formula R–SO3M slow down the alkaline degreasing process while improving the physical degreasing activity, providing a smoother surface foundation for the subsequent process of roughening the surface with micro-etching agents. Specifically, the active ether oxygen atoms in the organic alcohol-based auxiliary corrosion inhibitor naturally tend to adsorb onto the aluminum-based UBM surface to be plated, forming a physical shielding layer and slowing down the corrosion of the aluminum-based surface by sodium carbonate. The hydrophobic long-chain alkyl groups in the surfactant readily combine with grease and impurities on the aluminum-based UBM surface to be plated, encapsulating the grease and impurities to form tiny micelles insoluble in water. Under the action of sulfonic acid groups and dispersants, these micelles detach from the surface to be plated and remain relatively stably suspended in the water-based solvent system, thus achieving a non-strongly alkaline degreasing effect while effectively protecting the substrate surface. Furthermore, the cleaning agent system of this application does not introduce silicate substances, avoiding the problem of silicate ions spontaneously condensing into colloidal particles and forming white precipitates during long-term use, significantly extending the lifespan. Experiments show that the cleaning agent of this application has a lifespan of more than 6 months.

[0011] The micro-etching agent uses a fluorinated compound compounded with polyphosphate. The fluorinated compound dissociates into F... - As an oxide film disruptor, it preferentially attacks the natural Al2O3 passivation layer, releasing the underlying active aluminum metal as a high-energy site, and polyphosphate ions (P...) n O （3n+1） (n+2)-It plays a regulating role, preferentially adsorbing onto the high-energy region of exposed active aluminum, protecting the high-energy region from excessive corrosion. The two work synergistically to achieve a leveling effect, resolving the discoloration problem caused by uneven etching and roughness. Furthermore, the appropriately added ionic complexing agent can effectively complex Al in the solution. 3+ Prevent it from being related to F - After extensive complexation, the etchant adheres to the aluminum-based UBM surface to be plated, causing secondary corrosion and thus avoiding uneven etching and hazy appearance on the roughened surface. Simultaneously, it strongly complexes any impurity ions such as copper ions that may appear in the solution, preventing in-situ corrosion on the aluminum surface and avoiding phenomena such as surface reddening. Experiments have shown that aluminum-based surfaces pretreated with the cleaning agent and micro-etchant of this application exhibit no uneven etching, discoloration, pitting, or hazy appearance.

[0012] Furthermore, the long-chain alkyl group of the surfactant can be a straight-chain or branched saturated hydrocarbon group, or an alkyl group with a terminal aromatic ring.

[0013] In some embodiments, the cleaning agent satisfies at least one of the following conditions: a: the pH adjuster is sodium bicarbonate with a mass concentration of 10-20 g / L; b: the surfactant is sodium dodecyl sulfonate with a mass concentration of 5-10 g / L; c: the dispersant is trisodium phosphate; d: the auxiliary corrosion inhibitor is PEG400.

[0014] A saturated solution of pure sodium carbonate has a pH close to 12, while a saturated solution of sodium bicarbonate has a pH of approximately 9. Using sodium carbonate as the main alkaline raw material and sodium bicarbonate as an auxiliary pH adjuster, without introducing other impurity ions, they work together to maintain a stable alkaline environment. Furthermore, without introducing new substances, the slow hydrolysis of sodium bicarbonate buffers the trend of pH decrease in the solution, further increasing the stability of the alkaline environment of the detergent.

[0015] Sodium dodecyl sulfonate is a common industrial preparation with mature technology and economical cost.

[0016] Trisodium phosphate acts as an auxiliary degreasing agent, synergistically working with surfactants to achieve a powerful grease removal effect; on the other hand, it exerts its complexing ability, with phosphate ions (PO4) forming a complex. 3- It possesses oxygen coordination sites and a certain ability to chelate with metal ions, strongly complexing them with metal ions such as calcium and magnesium in hard water. This enhances the cleaning agent system's resistance to metal ion contamination and extends the cleaning agent's lifespan. Furthermore, during the degreasing process, it can synergistically work with organic alcohol-assisted corrosion inhibitors to preferentially adsorb at the grain boundary defects with the highest activation energy on the aluminum-based surface to be plated, mitigating excessive corrosion to some extent and providing a smoother surface foundation for subsequent micro-etching and roughening processes.

[0017] The PEG400 has a moderate intramolecular active ether oxygen atom density, which balances good solubility and fluidity, enabling rapid dispersion in solvent systems and stable adsorption on the aluminum-based UBM surface to be plated, thus exerting a corrosion inhibition effect and suppressing excessive etching.

[0018] In some embodiments, the micro-etching agent satisfies at least one of the following conditions: e: the accelerator is ammonium fluoride with a mass concentration of 10-30 g / L; f: the protective agent is sodium tripolyphosphate with a mass concentration of 10-20 g / L; g: the ion complexing agent is ethylenediaminetetraacetic acid with a mass concentration of 5-20 g / L.

[0019] Ammonium fluoride was chosen as the accelerator because it offers a safer and more controllable etching process compared to the traditionally used ammonium bifluoride. Ammonium bifluoride relies on the high concentration of H+ ions ionized in water. + and F - Strong corrosion roughening is rapid but uncontrollable, often resulting in rough, large particles on the surface. The low-concentration nitric acid and a small amount of ammonium fluoride normal salt used in this application have a mild effect. Nitric acid has a certain passivation effect on aluminum-based substrates. At low concentrations, the formation of the passivation layer is almost negligible, but the reaction with alumina is slow. At this time, under the synergistic effect of a small amount of fluoride ions in the system, the removal of alumina is significantly accelerated.

[0020] Sodium tripolyphosphate was selected as the protective agent. It has a moderate chain length, strong resistance to hydrolysis in nitric acid environments, stable chemical properties, and excellent ion chelating ability. The tripolyphosphate ion P3O3 is particularly effective in this process. 10 5- It possesses oxygen coordination sites, enabling it to chelate with metal ions, significantly enhancing the micro-etchant's resistance to metal ion contamination and extending its service life. Furthermore, sodium tripolyphosphate preferentially adsorbs onto grain boundary defects on the aluminum surface, where activation energy is highest, thus mitigating corrosion to some extent and improving uneven etching and haze.

[0021] The ion-complexing agent ethylenediaminetetraacetic acid (EDTA) forms a hexadecanal coordination cage with four carboxyl oxygen groups and two amino nitrogen groups, exhibiting strong complexing ability for metal ions and effectively complexing Al in solution. 3+ Prevent it from being related to F - After extensive complexation, it adheres to the aluminum metal surface, causing uneven secondary corrosion and fogging; at the same time, it strongly complexes impurity ions such as copper ions that may appear in the solution, preventing them from causing in-situ corrosion on the aluminum surface and resulting in a reddish surface.

[0022] Furthermore, the simultaneous use of ammonium fluoride and sodium tripolyphosphate revealed a synergistic effect between the two during long-term experiments. - With free Al 3+ It will generate [AlF6] 3-This causes the solution to become turbid and precipitate out. Sodium tripolyphosphate can chelate free aluminum ions, preventing the formation of precipitates and thus protecting the long-term stability of the system. At the same time, its multiple oxygen atom coordination sites make it easy to adsorb onto the active sites of the aluminum-based surface to be plated, and preferentially complex with Al. 3+ Further control of F - It has a corrosive effect on the metal surface, achieving the effect of removing the aluminum oxide layer without damaging the aluminum metal layer.

[0023] Furthermore, the combined use of ethylenediaminetetraacetic acid and sodium tripolyphosphate can, on the one hand, synergistically complex free metal ions in the solution system to improve the long-term stability of the micro-etchant, and on the other hand, synergistically adsorb the active sites on the aluminum-based surface to be plated to optimize the corrosion inhibition effect and effectively prevent excessive corrosion.

[0024] In some embodiments, the cleaning agent comprises the following components at mass concentrations: sodium carbonate: 30 g / L, sodium bicarbonate: 20 g / L, sodium dodecyl sulfonate: 10 g / L, trisodium phosphate: 20 g / L, PEG400: 10 g / L; the solvent is deionized water; the micro-etching agent comprises the following components at volume or mass concentrations: 68% nitric acid: 290 ml / L, ammonium fluoride: 20 g / L, sodium tripolyphosphate: 20 g / L, ethylenediaminetetraacetic acid: 20 g / L; the solvent is deionized water.

[0025] The cleaning agent uses sodium dodecyl sulfate as the main cleaning component and trisodium phosphate as an auxiliary cleaning component, achieving a powerful removal effect of grease and other impurities. Furthermore, trisodium phosphate has complexing capabilities, strongly complexing metal ions such as calcium and magnesium in hard water, preventing uneven reactions caused by impurities during operation. It also avoids the introduction of silicate substances, preventing the spontaneous aggregation of silicate ions into colloidal particles and the formation of white precipitates over long-term use, thus significantly extending its lifespan. The organic alcohol-based auxiliary corrosion inhibitor forms a physical shielding layer on the aluminum-based UBM surface through the adsorption of active ether oxygen atoms, preventing over-cleaning from damaging the surface smoothness.

[0026] The content of nitric acid and ammonium fluoride in the micro-etching solution is far below the industry's conventional application range. Reducing the use of corrosive agents helps ensure safety in large-scale industrial production. Specifically, nitric acid is used to decompose the oxide film on the surface of aluminum-based UBM, but the reaction rate is slow, while F... - The addition of [a specific ingredient] can effectively accelerate the decomposition rate of nitric acid and improve the roughening efficiency. Furthermore, ammonium fluoride ortho-salt has a higher ionization rate than ammonium bifluoride. -The etching rate is more moderate and controllable, avoiding excessive reaction that could lead to uneven etching. Furthermore, the use of ethylenediaminetetraacetic acid (EDTA) as a complexing agent effectively complexes free metal ions in the solution, ensuring the long-term stability of the micro-etching solution. Sodium tripolyphosphate, as a protective agent, has a moderate chain length, is more resistant to nitric acid environments, and possesses ion chelating ability. When used in conjunction with EDTA, it synergistically exerts ion complexation and corrosion inhibition effects, both complexing impurity metal ions to eliminate contamination and adsorbing onto the exposed aluminum substrate surface to protect high-energy potential areas and optimize corrosion inhibition.

[0027] Secondly, this application provides a method for preparing a pretreatment agent for aluminum-based UBM electroless plating on wafers. The preparation of the cleaning agent includes the following steps: S001: Take a portion of deionized water as solvent, add a measured amount of sodium carbonate and the pH adjuster, and fully dissolve to form a weakly alkaline solvent environment; S002: Add the surfactant and stir until uniform; S003: Add the dispersant and the auxiliary corrosion inhibitor in sequence and stir until uniform; S004: Add deionized water dropwise to bring the solution to the required volume, shake well, and obtain the cleaning agent; The preparation of the micro-etching agent includes the following steps: S005: Take a portion of deionized water as solvent, measure a measured volume of 68% nitric acid, and slowly dilute the nitric acid in the deionized water; S006: Slowly add the accelerator and stir until uniform; S007: Add the protective agent and the ion complexing agent in sequence and stir until uniform; S008: Bring the solution to the required volume with deionized water and shake well to obtain the micro-etching agent.

[0028] The preparation method described herein is simple in procedure and easy to operate, making it suitable for industrial-grade automated production.

[0029] Thirdly, this application provides a chemical plating process for aluminum-based UBM wafers, including a pretreatment step, wherein the pretreatment step uses the chemical plating pretreatment agent as described above or the chemical plating pretreatment agent obtained by the preparation method described above to treat the surface of the aluminum-based UBM wafer to be plated. The pretreatment step includes the following steps: S1: ultrasonically washing the aluminum-based UBM wafer to remove surface-adhered particles; S2: plasma treatment of the ultrasonically washed aluminum-based UBM wafer to remove surface residue; S3: immersing the aluminum-based UBM wafer in the cleaning agent at 20-65°C for 1-2 minutes and shaking it to eliminate air bubbles and remove surface impurities; S4: placing the cleaned aluminum-based UBM wafer in the micro-etching agent at 40-60°C for 1-2 minutes to remove the surface oxide layer; S5: spraying deionized water to wash the aluminum-based UBM wafer, completing the pretreatment of the surface of the aluminum-based UBM wafer to be plated.

[0030] Furthermore, the immersion temperature of the aluminum-based UBM wafer in the cleaning agent is preferably 50°C.

[0031] Because of the aforementioned beneficial effects of the pretreatment agent for electroless plating, the pretreatment process of the electroless plating process provided in this application can efficiently clean and uniformly etch aluminum-based UBM, resulting in a roughened, uniform, and colorless aluminum-based surface to be plated, providing uniform and firm mechanical interlocking anchors for the subsequent electroless plating layer, and improving the adhesion between the subsequent plating layer and the aluminum-based UBM substrate.

[0032] In some embodiments, step S2 further includes: S21: immersing the aluminum-based UBM wafer in acidic sodium citrate for 1-3 minutes to clean surface impurities; S22: treating the acid-washed aluminum-based UBM wafer surface with Ar plasma, setting the pressure to 150-250 mTorr, the power to 80-120 W, the gas flow rate to 80-120 sccm, and the time to 20-40 s.

[0033] In some implementations, the sum of the time intervals between adjacent steps S1-S5 is ≤5 min. This avoids secondary oxidation of the newly formed exposed aluminum metal surface during the process flow, which would affect the chemical plating activity of the aluminum-based surface to be plated.

[0034] In some embodiments, the electroless plating process for aluminum-based UBM wafers further includes an electroless gold plating step, which includes the following steps: S6: The aluminum-based UBM wafers that have completed the pretreatment step are placed in a zinc replacement solution for a first zinc plating, with a plating time of 1-3 min; S7: After the first zinc plating, the aluminum-based UBM wafers are washed and immersed in dilute nitric acid for 5-20 s to remove zinc; S8: After the zinc removal, the aluminum-based UBM wafers are washed and placed in a zinc replacement solution again for a second zinc plating, with a plating time of 1-3 min; S9: After the electroless zinc plating, the aluminum-based UBM wafers are washed and electroless nickel and / or electroless palladium plating is performed. After washing, they are placed in an electroless gold plating solution for electroless gold plating for 5-20 min to complete the electroless gold plating on the surface of the aluminum-based UBM wafers.

[0035] In some implementations, the temperature for electroless zinc plating is 20-40℃; the temperature for electroless nickel plating is 50-70℃, and the plating time is 10-30 min; the temperature for electroless palladium plating is 40-60℃, and the plating time is 5-20 min; and the temperature for electroless gold plating is 30-50℃. 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 250x magnified micrograph of the surface morphology of an aluminum-based UBM wafer before chemical gold plating following pretreatment.

[0038] Figure 2 This is a magnified micrograph of the surface of the electroless gold plating layer on the aluminum-based UBM wafer of Example 1 after the pretreatment process, magnified 250 times.

[0039] Figure 3 This is a magnified 2500x microscopic image of the surface of the electroless gold plating layer on the aluminum-based UBM wafer of Example 1 after the pretreatment process.

[0040] Figure 4 This is a magnified micrograph of the surface of the electroless gold plating layer on the aluminum-based UBM wafer of Example 2 after the pretreatment process, magnified 250 times.

[0041] Figure 5 This is a magnified micrograph of the surface of the electroless gold plating layer on the aluminum-based UBM wafer of Example 3 after the pretreatment process, magnified 250 times.

[0042] Figure 6 This is a magnified micrograph of the surface of the electroless gold plating layer on the aluminum-based UBM wafer of Example 4 after the pretreatment process, magnified 250 times.

[0043] Figure 7 This is a magnified micrograph of the surface of the electroless gold plating layer on the aluminum-based UBM wafer of Example 5 after the pretreatment process, magnified 250 times.

[0044] Figure 8 This is a magnified micrograph of the surface of the electroless gold plating layer on the aluminum-based UBM wafer of Example 6 after the pretreatment process, magnified 250 times.

[0045] Figure 9 This is a magnified 250x micrograph of the surface morphology of the aluminum-based UBM wafer in Comparative Example 1 after the pretreatment process and chemical gold plating.

[0046] Figure 10 This is a magnified micrograph of the surface of the aluminum-based UBM wafer in Comparative Example 2 after the pretreatment process, showing the chemical gold plating layer.

[0047] Figure 11 This is a magnified micrograph of the surface of the aluminum-based UBM wafer in Comparative Example 3 after the pretreatment process, showing the chemical gold plating layer.

[0048] Figure 12 This is a flowchart of the pretreatment steps for an aluminum-based UBM electroless plating process for wafers according to this application. Detailed Implementation

[0049] 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.

[0050] 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 "8-35 g / L" should be considered to include any and all subranges that begin with a minimum value of 8 g / L or greater and end with a maximum value of 35 g / L or less, such as 8 to 12 g / L, or 20 to 30 g / L, or 15 to 35 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 290 and 580," "290 to 580," or "290-580" should generally be considered to include the endpoints 290 and 580.

[0051] Unless otherwise specified, in this article, ratio refers to mass ratio and percentage refers to mass percentage.

[0052] 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.

[0053] This application addresses the shortcomings of existing pretreatment processes for aluminum-based UBM wafers. When processing high-end semiconductor chips and precision circuit structures, the lack of etching control and management of impurity metal ion removal leads to defects such as over-cleaning or over-etching in certain areas, increased surface roughness, and discoloration and speckling caused by the deposition of colored metal ions. It also addresses the poor stability of existing cleaning agent and micro-etching agent systems. This application proposes a chemical plating pretreatment agent that effectively removes grease impurities and oxide layers from the surface of aluminum-based UBM wafers, ensuring a clean and uniformly roughened aluminum surface, thus meeting the high-performance requirements of aluminum-based semiconductor chip modules.

[0054] The first aspect of this application provides a pretreatment agent for electroless plating of aluminum-based UBM wafers, including a cleaning agent and a micro-etching agent; The cleaning agent comprises the following components at the following mass concentrations: sodium carbonate 8-35 g / L, pH adjuster 8-30 g / L, surfactant 1-10 g / L, dispersant 5-20 g / L, and auxiliary corrosion inhibitor 2-10 g / L. The solvent is deionized water. The surfactant contains at least an alkyl sulfonate with the general chemical formula R–SO3M, wherein R is a long-chain alkyl group between C8 and C20. The auxiliary corrosion inhibitor contains at least one component with the general chemical formula HO-[CH2-CH2-O]. n Organic alcohols with -H, where 4≤n≤13; The micro-etching agent comprises the following components by volume or mass concentration: 68% nitric acid 290-580 ml / L, accelerator 10-40 g / L, protectant 5-30 g / L, ion complexing agent 5-30 g / L, with deionized water as the solvent. The accelerator is a fluorinated compound, and the protectant is a polyphosphate.

[0055] The pretreatment agent for electroless plating of aluminum-based UBM wafers provided in the first aspect of this application has at least the following beneficial effects: Cleaning agents are produced by adding chemicals with the general formula HO-[CH2-CH2-O]. n The -H organic alcohol-based auxiliary corrosion inhibitor and the alkyl sulfonate surfactant with the general chemical formula R–SO3M slow down the alkaline degreasing process while improving the physical degreasing activity, providing a smoother surface base for subsequent surface roughening processes using micro-etching agents. Specifically, the active ether oxygen atoms in the organic alcohol-based auxiliary corrosion inhibitor naturally tend to adsorb onto the aluminum-based UBM surface to be plated, forming a physical shielding layer that slows down the corrosion of the aluminum-based surface by sodium carbonate. The hydrophobic long-chain alkyl groups in the surfactant readily combine with grease and impurities on the aluminum-based UBM surface to be plated, encapsulating the grease and impurities to form tiny micelles insoluble in water. Under the action of the sulfonic acid groups and dispersants, these micelles detach from the surface to be plated and remain relatively stably suspended in the water-based solvent system, thus achieving a non-strongly alkaline degreasing effect while effectively protecting the substrate surface.

[0056] Furthermore, the cleaning agent system of this application does not introduce silica-based substances, thus avoiding the problem of silicate ions spontaneously condensing into colloidal particles and forming white precipitates during long-term use, and the lifespan can be significantly extended.

[0057] The micro-etching agent uses a fluorinated compound compounded with polyphosphate. The fluorinated compound dissociates into F... - As an oxide film disruptor, it preferentially attacks the natural Al2O3 passivation layer, releasing the underlying active aluminum metal as a high-energy site, and polyphosphate ions (P...) n O （3n+1） (n+2)- It plays a regulating role, preferentially adsorbing onto the high-energy region of exposed active aluminum, protecting the high-energy region from excessive corrosion. The two work synergistically to achieve a leveling effect, solving the discoloration problems caused by uneven etching and uneven roughness. Furthermore, the appropriately added ionic complexing agent can effectively complex Al in the solution. 3+ Prevent it from being related to F - After extensive complexation, the etchant adheres to the aluminum-based UBM surface to be plated, causing secondary corrosion and thus avoiding uneven etching and hazy appearance on the roughened surface. Simultaneously, it strongly complexes any impurity ions such as copper ions that may appear in the solution, preventing in-situ corrosion on the aluminum surface and avoiding phenomena such as surface reddening. Experiments have shown that aluminum-based surfaces pretreated with the cleaning agent and micro-etchant of this application exhibit no uneven etching, discoloration, pitting, or hazy appearance.

[0058] Furthermore, experiments have shown that the lifespan of both the cleaning agent and the micro-etching agent in this application is greater than 6 months.

[0059] Furthermore, the long-chain alkyl group of the surfactant can be a straight-chain or branched saturated hydrocarbon group, or an alkyl group with a terminal aromatic ring.

[0060] It should be noted that 68% nitric acid is a common specification for commercially available nitric acid reagents, specifically referring to a nitric acid content of 68 wt%.

[0061] In some embodiments, the cleaning agent satisfies at least one of the following conditions: a: the pH adjuster is sodium bicarbonate; b: the surfactant is sodium dodecyl sulfonate; c: the dispersant is trisodium phosphate; d: the auxiliary corrosion inhibitor is PEG400.

[0062] A saturated solution of pure sodium carbonate has a pH close to 12, while a saturated solution of sodium bicarbonate has a pH of approximately 9. Using sodium carbonate as the main alkaline raw material and sodium bicarbonate as an auxiliary pH adjuster, without introducing other impurity ions, they work together to maintain a stable alkaline environment. Furthermore, without introducing new substances, the slow hydrolysis of sodium bicarbonate buffers the trend of pH decrease in the solution, further increasing the stability of the alkaline environment of the detergent.

[0063] Sodium dodecyl sulfonate is a common industrial preparation with mature technology and economical cost.

[0064] Trisodium phosphate acts as an auxiliary degreasing agent, synergistically working with surfactants to achieve a powerful grease removal effect; on the other hand, it exerts its complexing ability, with phosphate ions (PO4) forming a complex. 3- It possesses oxygen coordination sites and a certain ability to chelate with metal ions, strongly complexing them with metal ions such as calcium and magnesium in hard water. This enhances the cleaning agent system's resistance to metal ion contamination and extends the cleaning agent's lifespan. Furthermore, during the degreasing process, it can synergistically work with organic alcohol-assisted corrosion inhibitors to preferentially adsorb at the grain boundary defects with the highest activation energy on the aluminum-based surface to be plated, mitigating excessive corrosion to some extent and providing a smoother surface foundation for subsequent micro-etching and roughening processes.

[0065] The PEG400 has a moderate intramolecular active ether oxygen atom density, which balances good solubility and fluidity, enabling rapid dispersion in solvent systems and stable adsorption on the aluminum-based UBM surface to be plated, thus exerting a corrosion inhibition effect and suppressing excessive etching.

[0066] In some embodiments, the micro-etching agent satisfies at least one of the following conditions: e: the accelerator is ammonium fluoride; f: the protective agent is sodium tripolyphosphate; g: the ion complexing agent is ethylenediaminetetraacetic acid.

[0067] Ammonium fluoride was chosen as the accelerator because it offers a safer and more controllable etching process compared to the traditionally used ammonium bifluoride. Ammonium bifluoride relies on the high concentration of H+ ions ionized in water. + and F - Strong corrosion roughening is rapid but uncontrollable, often resulting in rough, large particles on the surface. The low-concentration nitric acid and a small amount of ammonium fluoride normal salt used in this application have a mild effect. Nitric acid has a certain passivation effect on aluminum-based substrates. At low concentrations, the formation of the passivation layer is almost negligible, but the reaction with alumina is slow. At this time, under the synergistic effect of a small amount of fluoride ions in the system, the removal of alumina is significantly accelerated.

[0068] Sodium tripolyphosphate was selected as the protective agent. It has a moderate chain length, strong resistance to hydrolysis in nitric acid environments, stable chemical properties, and excellent ion chelating ability. The tripolyphosphate ion P3O3 is particularly effective in this process. 10 5- It possesses oxygen coordination sites, enabling it to chelate with metal ions, significantly enhancing the micro-etchant's resistance to metal ion contamination and extending its service life. Furthermore, sodium tripolyphosphate preferentially adsorbs onto grain boundary defects on the aluminum surface, where activation energy is highest, thus mitigating corrosion to some extent and improving uneven etching and haze.

[0069] The ion-complexing agent ethylenediaminetetraacetic acid (EDTA) forms a hexadecanal coordination cage with four carboxyl oxygen groups and two amino nitrogen groups, exhibiting strong complexing ability for metal ions and effectively complexing Al in solution. 3+ Prevent it from being related to F - After extensive complexation, it adheres to the aluminum metal surface, causing uneven secondary corrosion and fogging; at the same time, it strongly complexes impurity ions such as copper ions that may appear in the solution, preventing them from causing in-situ corrosion on the aluminum surface and resulting in a reddish surface.

[0070] Furthermore, the simultaneous use of ammonium fluoride and sodium tripolyphosphate revealed a synergistic effect between the two during long-term experiments. - With free Al 3+ It will generate [AlF6] 3- This causes the solution to become turbid and precipitate out. Sodium tripolyphosphate can chelate free aluminum ions, preventing the formation of precipitates and thus protecting the long-term stability of the system. At the same time, its multiple oxygen atom coordination sites make it easy to adsorb onto the active sites of the aluminum-based surface to be plated, and preferentially complex with Al. 3+ Further control of F - It has a corrosive effect on the metal surface, achieving the effect of removing the aluminum oxide layer without damaging the aluminum metal layer.

[0071] Furthermore, the combined use of ethylenediaminetetraacetic acid and sodium tripolyphosphate can, on the one hand, synergistically complex free metal ions in the solution system to improve the long-term stability of the micro-etchant, and on the other hand, synergistically adsorb the active sites on the aluminum-based surface to be plated to optimize the corrosion inhibition effect and effectively prevent excessive corrosion.

[0072] Furthermore, the mass concentration of the pH adjuster is 10-20 g / L.

[0073] Furthermore, the mass concentration of the surfactant is 5-10 g / L.

[0074] Furthermore, the mass concentration of the accelerator is 10-30 g / L.

[0075] Furthermore, the mass concentration of the protective agent is 10-20 g / L.

[0076] Furthermore, the mass concentration of the ionic complexing agent is 5-20 g / L.

[0077] In specific implementation, taking an ammonium fluoride addition of 30 g / L as an example, compared with micro-etching agents without ammonium fluoride, the pretreatment time is reduced from the minimum value of 20 min to 3-5 min, and the total time for subsequent chemical gold plating is also reduced from the minimum value of 40 min to 25 min, significantly improving production efficiency.

[0078] In some embodiments, the cleaning agent comprises the following components at mass concentrations: sodium carbonate: 30 g / L, sodium bicarbonate: 20 g / L, sodium dodecyl sulfonate: 10 g / L, trisodium phosphate: 20 g / L, PEG400: 10 g / L; the solvent is deionized water; the micro-etching agent comprises the following components at volume or mass concentrations: 68% nitric acid: 290 ml / L, ammonium fluoride: 20 g / L, sodium tripolyphosphate: 20 g / L, ethylenediaminetetraacetic acid: 20 g / L; the solvent is deionized water.

[0079] The cleaning agent uses sodium dodecyl sulfate as the main cleaning component and trisodium phosphate as an auxiliary cleaning component, achieving a powerful removal effect of grease and other impurities. Furthermore, trisodium phosphate has complexing capabilities, strongly complexing metal ions such as calcium and magnesium in hard water, preventing uneven reactions caused by impurities during operation. It also avoids the introduction of silicate substances, preventing the spontaneous aggregation of silicate ions into colloidal particles and the formation of white precipitates over long-term use, thus significantly extending its lifespan. The organic alcohol-based auxiliary corrosion inhibitor forms a physical shielding layer on the aluminum-based UBM surface through the adsorption of active ether oxygen atoms, preventing over-cleaning from damaging the surface smoothness.

[0080] The content of nitric acid and ammonium fluoride in the micro-etching solution is far below the industry's conventional application range. Reducing the use of corrosive agents helps ensure safety in large-scale industrial production. Specifically, nitric acid is used to decompose the oxide film on the surface of aluminum-based UBM, but the reaction rate is slow, while F... - The addition of [a specific ingredient] can effectively accelerate the decomposition rate of nitric acid and improve the roughening efficiency. Furthermore, ammonium fluoride ortho-salt has a higher ionization rate than ammonium bifluoride. -The etching rate is more moderate and controllable, avoiding excessive reaction that could lead to uneven etching. Furthermore, the use of ethylenediaminetetraacetic acid (EDTA) as a complexing agent effectively complexes free metal ions in the solution, ensuring the long-term stability of the micro-etching solution. Sodium tripolyphosphate, as a protective agent, has a moderate chain length, is more resistant to nitric acid environments, and possesses ion chelating ability. When used in conjunction with EDTA, it synergistically exerts ion complexation and corrosion inhibition effects, both complexing impurity metal ions to eliminate contamination and adsorbing onto the exposed aluminum substrate surface to protect high-energy potential areas and optimize corrosion inhibition.

[0081] Secondly, this application provides a method for preparing a pretreatment agent for aluminum-based UBM electroless plating on wafers. The preparation of the cleaning agent includes the following steps: S001: Take a portion of deionized water, add a measured amount of sodium carbonate and the pH adjuster, and dissolve them completely to form a weakly alkaline solvent environment; S002: Add the surfactant and stir until uniform; S003: Add the dispersant and the auxiliary corrosion inhibitor in sequence and stir until uniform; S004: Add deionized water dropwise to bring the solution to the required volume, shake well, and obtain the cleaning agent; The preparation of the micro-etching agent includes the following steps: S005: Take a portion of deionized water, measure a measured volume of 68% nitric acid, and slowly dilute the nitric acid in the deionized water; S006: Slowly add the accelerator and stir until uniform; S007: Add the protective agent and the ion complexing agent in sequence and stir until uniform; S008: Bring the solution to the required volume with deionized water and shake well to obtain the micro-etching agent.

[0082] The preparation method described herein is simple in procedure and easy to operate, making it suitable for industrial-grade automated production.

[0083] Thirdly, see Figure 12 This application provides a chemical plating process for aluminum-based UBM wafers, including a pretreatment step. In the pretreatment step, the surface of the aluminum-based UBM to be plated is treated with a chemical plating pretreatment agent as described above or a chemical plating pretreatment agent obtained by the preparation method described above. The pretreatment step includes the following steps: S1: ultrasonically washing the aluminum-based UBM wafer to remove surface-adhered particles; S2: plasma treatment of the ultrasonically washed aluminum-based UBM wafer to remove surface residue; S3: immersing the aluminum-based UBM wafer in the cleaning agent at 20-65°C for 1-2 minutes and shaking it to eliminate air bubbles and remove surface impurities; S4: placing the cleaned aluminum-based UBM wafer in the micro-etching agent at 40-60°C for 1-2 minutes to remove the surface oxide layer; S5: spraying deionized water to wash the aluminum-based UBM wafer, completing the pretreatment of the surface of the aluminum-based UBM wafer to be plated.

[0084] Furthermore, the preferred immersion temperature of the aluminum-based UBM wafer in the cleaning agent is 50°C, and the immersion time is 2 minutes; the preferred immersion temperature in the micro-etching agent is 50°C, and the immersion time is 2 minutes.

[0085] Because the pretreatment agent for electroless plating has the beneficial effects described above, the pretreatment process of the electroless plating process provided in this application can efficiently clean and uniformly etch aluminum-based UBM, resulting in a roughened, uniform, and colorless aluminum-based surface to be plated (see...). Figure 1 This provides uniform and robust mechanical interlocking anchors for subsequent chemically deposited coatings, improving the adhesion between the subsequent coatings and the aluminum-based UBM substrate.

[0086] In some embodiments, step S2 further includes: S21: immersing the aluminum-based UBM wafer in acidic sodium citrate for 1-3 minutes to clean surface impurities; S22: treating the acid-washed aluminum-based UBM wafer surface with Ar plasma, setting the pressure to 150-250 mTorr, the power to 80-120 W, the gas flow rate to 80-120 sccm, and the time to 20-40 s.

[0087] In some implementations, the sum of the time intervals between adjacent steps S1-S5 is ≤5 min. This avoids secondary oxidation of the newly formed exposed aluminum metal surface during the process flow, which would affect the chemical plating activity of the aluminum-based surface to be plated.

[0088] In some embodiments, the electroless plating process for aluminum-based UBM wafers further includes an electroless gold plating step, which includes the following steps: S6: The aluminum-based UBM wafers that have completed the pretreatment step are placed in a zinc replacement solution for a first zinc plating, with a plating time of 1-3 min; S7: After the first zinc plating, the aluminum-based UBM wafers are washed and immersed in dilute nitric acid for 5-20 s to remove zinc; S8: After the zinc removal, the aluminum-based UBM wafers are washed and placed in a zinc replacement solution again for a second zinc plating, with a plating time of 1-3 min; S9: After the electroless zinc plating, the aluminum-based UBM wafers are washed and electroless nickel and / or electroless palladium plating is performed. After washing, they are placed in an electroless gold plating solution for electroless gold plating for 5-20 min to complete the electroless gold plating on the surface of the aluminum-based UBM wafers.

[0089] The surface grains are refined through a secondary, rapid, and loose zinc deposition process, which enhances the adhesion between the subsequent plating material and the aluminum substrate surface.

[0090] In the specific implementation process, the zinc replacement solution, electroless nickel plating solution, electroless palladium plating solution, and electroless gold plating solution used are all commercially available products.

[0091] In some implementations, the temperature for electroless zinc plating is 20-40℃; the temperature for electroless nickel plating is 50-70℃, and the plating time is 10-30 min; the temperature for electroless palladium plating is 40-60℃, and the plating time is 5-20 min; and the temperature for electroless gold plating is 30-50℃.

[0092] The following examples will further illustrate this application.

[0093] The reagents and raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0094] Examples 1-6 and Comparative Examples 1-3 of this application each include the following three experimental procedures and one testing procedure. The experimental procedures are performed according to steps one through three below, respectively, for sample preparation, pretreatment, and chemical gold plating. The testing procedure is performed according to step four below. The microstructure diagrams obtained from the testing can be found in [reference needed]. Figure 2-11 : I. Preparation of pretreatment agent for chemical plating: Add the cleaning agent components in the following order and stir thoroughly to dissolve in deionized water: Sodium carbonate: 8-35 g / L, pH adjuster sodium bicarbonate 8-30 g / L, surfactant sodium dodecyl sulfonate 1-10 g / L, dispersant trisodium phosphate 5-20 g / L, auxiliary corrosion inhibitor PEG400 2-10 g / L, solvent is deionized water; 1. Take an appropriate amount of deionized water, and first add measured amounts of sodium carbonate and sodium bicarbonate to provide a stable, weakly alkaline environment; 2. Then add the surfactant and stir until well mixed; 3. Add dispersant and auxiliary corrosion inhibitor in sequence; 4. Add deionized water to the required volume and shake until the solution is fully homogeneous.

[0095] The components of the micro-etching agent should be added in the following order and thoroughly stirred to dissolve in deionized water: The ingredients are: 68% nitric acid 290 ml / L, accelerator ammonium fluoride 10-40 g / L, protectant sodium tripolyphosphate 5-30 g / L, ion complexing agent ethylenediaminetetraacetic acid 5-20 g / L, and solvent deionized water.

[0096] 1. Take a portion of the solvent, deionized water, and measure out a measured volume of 68% nitric acid. Add this to the deionized water and dilute slowly. 2. Then slowly add the accelerator and stir until homogeneous; 3. Add the protective agent and ionic complexing agent in sequence, and stir until homogeneous; 4. Add deionized water to the required volume and shake until the solution is fully homogeneous.

[0097] II. Pre-treatment process (1) Ultrasonic water washing of aluminum-based UBM wafers for 30 seconds to remove surface particles; (2) The aluminum-based UBM wafers after ultrasonic water washing are subjected to acid cleaning and Ar plasma treatment to remove aluminum-based residues and water-soluble contaminants. (3) Immerse the aluminum-based UBM wafer in the above cleaning agent for 1-2 minutes, set the temperature to 50°C, and remove surface grease; (4) After cleaning, place the aluminum-based UBM wafer into the above micro-etching agent for 1-2 min, set the temperature to 50℃, and remove the surface oxide layer.

[0098] III. Chemical Gold Plating Process The specific steps are as follows: The above-mentioned cleaned and micro-etched aluminum-based UBM wafers were cleaned with deionized water. 1. Zinc plating: The cleaned aluminum-based UBM wafer is immersed in a zinc displacement solution for a first zinc plating process, with a plating time of 3 minutes. It is then rinsed and immersed in dilute nitric acid for 10 seconds to remove zinc. After rinsing, it is immersed again in the zinc displacement solution for a second zinc plating process, with a plating time of 3 minutes. The zinc plating is performed at room temperature (25°C) using a displacement plating method.

[0099] 2. Electroless nickel plating: After cleaning the zinc-plated aluminum-based UBM wafers, immerse them in an electroless nickel plating solution for nickel plating. The electroless nickel plating temperature is 60℃ and the plating time is 30 min. Optionally, a palladium plating step can be added after electroless nickel plating, with the palladium plating temperature at 50°C and the plating time at 20 minutes.

[0100] 3. Electroless gold plating: After cleaning the nickel-plated aluminum-based UBM wafers, place them in an electroless gold plating solution. The electroless gold plating temperature is 40℃ and the plating time is 10 min.

[0101] 4. Post-processing: After the gold plating is completed, the aluminum-based UBM wafer is removed, thoroughly cleaned by spraying with deionized water, and then dried with nitrogen or oven to obtain the finished product.

[0102] IV. Testing and Evaluation Methods To verify the effectiveness of the technical solution of this application, the following methods were used to characterize the chemically plated samples: 1. Microstructure and structural defects: The surface morphology of the aluminum-based UBM coating on the gold-plated wafer was observed using a scanning electron microscope (SEM) to check for microstructural defects such as voids and cracks.

[0103] 2. Roughness: The surface roughness of the aluminum-based UBM wafer after gold plating was measured using a roughness profiler.

[0104] 3. Adhesion: Tested using the cross-cut adhesion test.

[0105] 4. Thermal stability: The sample was placed in a constant temperature and humidity test chamber and heat-treated at 350℃. The surface morphology changes were then observed again using SEM.

[0106] 5. Cleaning agent and micro-etching agent lifespan: Record the duration for which the cleaning agent and micro-etching agent can maintain the above performance indicators after continuous use.

[0107] V. Examples The following six specific embodiments further illustrate the wafer aluminum-based UBM electroless plating pretreatment agent and pretreatment process of this application.

[0108] Example 1 The cleaning agent contains the following components at the following mass concentrations: Sodium carbonate: 30 g / L, sodium bicarbonate: 20 g / L, sodium dodecyl sulfonate: 5 g / L, trisodium phosphate: 20 g / L, PEG400: 2 g / L; solvent: deionized water; The micro-etching agent comprises the following components in volume or mass concentration: 68% nitric acid: 290 ml / L, ammonium fluoride 30 g / L, sodium tripolyphosphate 10 g / L, ethylenediaminetetraacetic acid 20 g / L; solvent is deionized water.

[0109] Pretreatment steps: After ultrasonically washing the aluminum-based UBM wafers with water, immerse them in acidic sodium citrate solution for 2 minutes. Then, treat the sample surface with Ar plasma at a pressure of 200 mTorr, a power of 100 W, a gas flow rate of 100 sccm, and a time of 30 seconds. After the treatment, immerse the treated aluminum-based UBM wafers in the aforementioned cleaning agent for further cleaning at 50°C for 2 minutes. Afterward, rinse the cleaned aluminum-based UBM wafers and immerse them in a micro-etching agent at 50°C for 2 minutes to complete the pretreatment. Finally, rinse with deionized water.

[0110] Chemical gold plating process: After pretreatment, the aluminum-based UBM wafer is immersed in a zinc displacement solution for 3 minutes, then rinsed and immersed in nitric acid for 10 seconds to remove zinc. After rinsing, it is immersed in the zinc displacement solution again for 3 minutes, rinsed with water, and then immersed in a chemical nickel plating solution for 30 minutes. After rinsing clean, it is placed in a chemical gold plating solution for 10 minutes. After completion, it is cleaned and dried for testing.

[0111] Result: As Figures 2-3 As shown in Table 1, the coating obtained in Example 1 has a rough surface, contains discolored oil stains, and has an oxide layer on the uncoated surface. This indicates that the pretreatment process in this example was not uniform in degreasing, and the surface oxide layer and surface contaminants hindered subsequent micro-etching. The roughness is >1μm, the cross-cut adhesion test is grade 0B, and the adhesion is poor.

[0112] Example 2: The only difference between Example 2 and Example 1 is that the composition of the cleaning agent is different.

[0113] The cleaning agent contains the following components at the following mass concentrations: Sodium carbonate: 30 g / L, sodium bicarbonate: 20 g / L, sodium dodecyl sulfonate: 10 g / L, trisodium phosphate: 20 g / L, PEG400: 2 g / L; solvent is deionized water.

[0114] Result: As Figure 4 As shown in Table 1, the surface roughness was improved, there was no oil stain, the surface was dark and had no discoloration, indicating that the pretreatment process was excessively corroded in this case, the cleaning effect was good, the overall appearance was frosted with a slight gloss, the roughness was <0.25μm, the cross-cut adhesion test was 5B grade, and the adhesion was good.

[0115] Example 3 The only difference between Example 3 and Example 1 is that the composition of the cleaning agent is different.

[0116] The cleaning agent comprises the following components at the following mass concentrations: Sodium carbonate: 30 g / L, sodium bicarbonate: 20 g / L, sodium dodecyl sulfonate: 10 g / L, trisodium phosphate: 20 g / L, PEG400: 10 g / L; solvent is deionized water.

[0117] Result: As Figure 5 As shown in Table 1, the surface is slightly rough, without oil stains or discoloration, indicating that the pretreatment in this case was basically qualified, with a roughness of <0.2μm and a cross-cut adhesion test grade of 5B.

[0118] Example 4 The only difference between Example 4 and Example 3 is that the composition of the micro-etching agent is different.

[0119] The micro-etching agent comprises the following components in volume or mass concentration: 68% nitric acid: 290 ml / L, ammonium fluoride 20 g / L, sodium tripolyphosphate 10 g / L, ethylenediaminetetraacetic acid 20 g / L; solvent is deionized water.

[0120] Result: As Figure 6 As shown in Table 1, the surface is relatively smooth, with a reflective effect, and is generally bright. There are no discolored oil stains, the roughness is <0.08μm, and the cross-cut adhesion test is 5B.

[0121] Example 5 The only difference between Example 5 and Example 3 is the composition of the micro-etching agent.

[0122] The micro-etching agent comprises the following components in volume or mass concentration: 68% nitric acid: 290 ml / L, ammonium fluoride 10 g / L, sodium tripolyphosphate 10 g / L, ethylenediaminetetraacetic acid 20 g / L; solvent is deionized water.

[0123] Result: As Figure 7 As shown in Table 1, the surface is smooth with a mirror-like reflective effect, with no plating defects, no oil stains, no discoloration, roughness <0.02μm, and a cross-cut adhesion test grade of 5B.

[0124] Example 6 The only difference between Example 6 and Example 3 is that the composition of the micro-etching agent is different.

[0125] The micro-etching agent comprises the following components in volume or mass concentration: 68% nitric acid: 290 ml / L, ammonium fluoride 10 g / L, sodium tripolyphosphate 20 g / L, ethylenediaminetetraacetic acid 20 g / L; solvent is deionized water.

[0126] Result: As Figure 8 As shown in Table 1, the surface is smooth and mirror-reflective, free of discolored oil stains, with a roughness of <0.03μm and a cross-cut adhesion test grade of 5B.

[0127] VI. Comparative Example To highlight the high-quality surface treatment effect of the cleaning agent and micro-etching agent in this application, the following comparative examples are set up.

[0128] Comparative Example 1 The only difference between Comparative Example 1 and Example 3 is that the composition of the cleaning agent and the micro-etching agent are different.

[0129] The cleaning agent comprises the following components at the following mass concentrations: Sodium carbonate: 30 g / L, sodium bicarbonate: 20 g / L, sodium dodecyl sulfonate: 10 g / L, trisodium phosphate: 0 g / L, PEG400: 10 g / L; solvent: deionized water; The micro-etching agent comprises the following components in volume or mass concentration: 68% nitric acid: 290 ml / L, ammonium fluoride 10 g / L, sodium tripolyphosphate 10 g / L, ethylenediaminetetraacetic acid 20 g / L; solvent is deionized water.

[0130] Result: As Figure 9 As shown in Table 1, the surface is rough with a roughness of <0.07μm, and the surface has a dark discoloration. There is no oil stain, and the cross-cut adhesion test is grade 5B.

[0131] Comparative Example 2 The only difference between Comparative Example 2 and Example 3 is the composition of the micro-etching agent.

[0132] The micro-etching agent comprises the following components in volume or mass concentration: 37% hydrochloric acid: 290 ml / L, ammonium fluoride 10 g / L, sodium tripolyphosphate 10 g / L, ethylenediaminetetraacetic acid 20 g / L; solvent is deionized water.

[0133] Result: As Figure 10 As shown in Table 1, the surface is rough with a roughness greater than 1 μm, and there are reddish spots. The cross-cut adhesion test is grade 5B. After heating, residual chloride ions on the surface lead to increased chlorine corrosion, resulting in surface abnormalities and the appearance of more severe and dense reddish spots.

[0134] Comparative Example 3 The only difference between Comparative Example 3 and Example 3 is the composition of the micro-etching agent.

[0135] The micro-etching agent comprises the following components in volume or mass concentration: 68% nitric acid: 290 ml / L, ammonium fluoride 0 g / L, sodium tripolyphosphate 10 g / L, ethylenediaminetetraacetic acid 20 g / L; solvent is deionized water.

[0136] Result: As Figure 11 As shown in Table 1, the surface is rough with a roughness of <0.2μm, there is no discolored oil stains, the surface oxide layer is not completely removed, resulting in extremely poor adhesion of the subsequent coating, and the cross-cut adhesion test is grade 0B.

[0137] It should be noted that: Insufficient cleaning leads to: colored circular contamination areas on the sample surface, ion intrusion pitting corrosion, and red spots on the gold-plated surface (red spots also appear on unplated surfaces, but are difficult to observe on gray surfaces). Additionally, conventional acidic degreasing solutions easily cause insufficient adhesion.

[0138] Insufficient micro-etching leads to: surface plating defects, incomplete oxide layer removal, inability to plate in oxide areas or uneven plating, discoloration, or false plating on the oxide layer surface, resulting in easily detached plating and "insufficient adhesion." Over-etching, on the other hand, easily causes surface roughness, uneven corrosion resulting in streaks and discoloration, and localized excessive corrosion. Although the aluminum-based material surface may not show obvious abnormalities macroscopically, significant differences in metal ion deposition rates may occur during subsequent nickel and gold plating processes. These differential depositions, magnified microscopically, result in uneven corrosion, leading to noticeable streaks and discoloration after gold plating. Therefore, over-etching can easily lead to a situation where the pretreatment is normal but the finished product is abnormal. Thus, the quality of the pretreatment is verified by reverse verification through the quality of the gold plating layer.

[0139] As can be seen from the above embodiments and comparative examples, this application successfully solves the problems of over-etching, under-etching, surface roughness, and uneven coloring in the pretreatment process of aluminum-based UBM by using specific pretreatment cleaning micro-etching processes, clearly defined cleaning micro-etching agent combinations, and matched pretreatment process parameters. The electroless plating surface of the aluminum-based UBM after the pretreatment process in this application is dense and uniform, possessing good conductivity, mechanical strength, and thermal stability, which can meet the high reliability requirements of high-performance chip aluminum-based UBMs, and has the advantages of high production efficiency and controllable cost.

[0140] 1. Microstructure and structural defects: The surface morphology of the chemical gold plating layer on the aluminum-based UBM surface was observed using a scanning electron microscope (SEM) to examine microstructural defects such as voids and cracks.

[0141] 2. Roughness: The surface roughness of the UBM after gold plating was measured by a roughness profiler; among them, a roughness > 0.5 μm is a matte surface, a roughness between 0.5 and 0.02 μm is a semi-gloss surface, and a roughness ≤ 0.02 μm is a reflective surface.

[0142] 3. Adhesion: Tested and rated using the cross-cut adhesion test.

[0143] 4. Thermal stability: The sample was placed in a constant temperature and humidity test chamber and heat-treated at 350℃. The surface morphology changes were then observed again using SEM.

[0144] 5. Cleaning agent and micro-etching agent lifespan: Record the duration for which the cleaning agent and micro-etching agent can maintain the above performance indicators after continuous use.

[0145] Table 1 shows the parameter settings and performance indicators such as surface quality and adhesion of the gold-plated layer after electroless gold plating for each embodiment and comparative example. To simplify the table, sodium dodecyl sulfonate is simplified to SDS, trisodium phosphate to TSP, ammonium fluoride to NH4F, and sodium tripolyphosphate to STPP.

[0146] Table 1. Parameter settings and performance indicators for Examples 1-6 and Comparative Examples 1-3 Based on Examples 1-2, it can be seen that increasing the amount of sodium dodecyl sulfate surfactant added to the cleaning agent enhances the cleaning ability of the cleaning agent to remove surface oil stains, resulting in good cleanliness of the surface to be plated on aluminum-based UBM wafers and eliminating colored contamination patterns.

[0147] Based on Examples 2 and 3, it can be seen that increasing the amount of organic alcohol-based auxiliary corrosion inhibitors added to the cleaning agent can effectively slow down the corrosion of amphoteric aluminum oxide by the alkaline reagent environment during the cleaning process. At the same time, the emulsification effect removes grease and helps ensure a smooth and clean surface.

[0148] Combining Example 5 and Comparative Example 1, it can be seen that increasing the amount of trisodium phosphate dispersant added to the cleaning agent helps to ensure a uniform dispersion effect on the surface and prevents discoloration of the surface pattern.

[0149] Based on Examples 3-5 and Comparative Example 3, it can be seen that increasing the amount of ammonium fluoride accelerator added to the micro-etching agent accelerates the removal of the surface oxide layer, providing a strong anchor point for the adhesion of the subsequent coating. Without addition, the residual surface oxide layer results in extremely poor adhesion, while excessive addition leads to excessive corrosion and defects such as rough and dark surface.

[0150] Combining Example 5 and Comparative Example 2, it can be seen that nitric acid in the micro-etching agent can provide an acidic environment and play a certain leveling effect, eliminating the potential for subsequent pitting corrosion.

[0151] In summary, the cleaning agent of this application uses sodium dodecyl sulfonate as the main cleaning component and trisodium phosphate as the auxiliary cleaning component, which can achieve a powerful removal effect of impurities such as grease, remove oil stains that hinder subsequent micro-etching and roughening, and the nitric acid and ammonium fluoride in the micro-etching solution synergistically accelerate the decomposition of the passivation layer. Sodium tripolyphosphate quickly adsorbs and occupies the exposed highly active aluminum sites, inhibiting further corrosion of aluminum metal by nitric acid and ammonium fluoride, improving the height difference of the surface to be plated, and improving the roughening uniformity.

[0152] 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 pretreatment agent for aluminum-based UBM electroless plating on wafers, characterized in that, The product includes a cleaning agent and a micro-etching agent. The cleaning agent comprises the following components at mass concentrations: sodium carbonate 8-35 g / L, pH adjuster 8-30 g / L, surfactant 1-10 g / L, dispersant 5-20 g / L, and auxiliary corrosion inhibitor 2-10 g / L. The solvent is deionized water. The surfactant contains at least an alkyl sulfonate with the general chemical formula R–SO3M, wherein R is a long-chain alkyl group between C8 and C20. The auxiliary corrosion inhibitor contains at least one component with the general chemical formula HO-[CH2-CH2-O]. n -H organic alcohol, wherein 4≤n≤13; the micro-etching agent comprises the following components by volume or mass concentration: 68% nitric acid 290-580 ml / L, accelerator 10-40 g / L, protectant 5-30 g / L, ion complexing agent 5-30 g / L, the solvent being deionized water, the accelerator being a fluorinated compound, and the protectant being a polyphosphate.

2. The wafer aluminum-based UBM electroless plating pretreatment agent according to claim 1, characterized in that, The cleaning agent meets at least one of the following conditions: a: the pH adjuster is sodium bicarbonate with a mass concentration of 10-20 g / L; b: the surfactant is sodium dodecyl sulfonate with a mass concentration of 5-10 g / L; c: the dispersant is trisodium phosphate; d: the auxiliary corrosion inhibitor is PEG400.

3. The wafer aluminum-based UBM electroless plating pretreatment agent according to claim 1, characterized in that, The micro-etching agent satisfies at least one of the following conditions: e: the accelerator is ammonium fluoride with a mass concentration of 10-30 g / L; f: the protective agent is sodium tripolyphosphate with a mass concentration of 10-20 g / L; g: the ion complexing agent is ethylenediaminetetraacetic acid with a mass concentration of 5-20 g / L.

4. The wafer aluminum-based UBM electroless plating pretreatment agent according to claim 1, characterized in that, The cleaning agent comprises the following components at mass concentrations: sodium carbonate: 30 g / L, sodium bicarbonate: 20 g / L, sodium dodecyl sulfonate: 10 g / L, trisodium phosphate: 20 g / L, PEG400: 10 g / L; the solvent is deionized water. The micro-etching agent comprises the following components at volume or mass concentrations: 68% nitric acid: 290 ml / L, ammonium fluoride: 20 g / L, sodium tripolyphosphate: 20 g / L, ethylenediaminetetraacetic acid: 20 g / L; the solvent is deionized water.

5. A method for preparing a wafer aluminum-based UBM electroless plating pretreatment agent as described in any one of claims 1-4, characterized in that, The preparation of the cleaning agent includes the following steps: S001: Take a portion of deionized water as solvent, add a measured amount of sodium carbonate and the pH adjuster, and dissolve them completely to form a weakly alkaline solvent environment; S002: Add the surfactant and stir until homogeneous; S003: Add the dispersant and the auxiliary corrosion inhibitor sequentially and stir until homogeneous; S004: Add deionized water dropwise to bring the solution to the required volume, shake well, and the cleaning agent is obtained; The preparation of the micro-etching agent The process includes the following steps: S005: Take a portion of deionized water as solvent, measure a metered volume of 68% nitric acid, and slowly dilute the nitric acid in the deionized water; S006: Slowly add the accelerator and stir until homogeneous; S007: Add the protective agent and the ion complexing agent sequentially and stir until homogeneous; S008: Adjust the volume to the required level with deionized water, shake well, and the micro-etching agent is obtained.

6. A wafer aluminum-based UBM electroless plating process, characterized in that, The process includes a pretreatment step, wherein the electroless plating pretreatment agent as described in any one of claims 1-4 or the electroless plating pretreatment agent obtained by the preparation method of claim 5 is used to treat the surface of the aluminum-based UBM wafer to be plated in the pretreatment step. Includes the following steps: S1: Ultrasonic water washing is performed on aluminum-based UBM wafers to remove surface-adhered particles; S2: Plasma treatment is performed on the ultrasonically washed aluminum-based UBM wafer to remove surface adhesive residue; S3: Immerse the aluminum-based UBM wafer in the cleaning agent at 20-65°C for 1-2 minutes and shake it to eliminate air bubbles and remove surface impurities; S4: Place the cleaned aluminum-based UBM wafer into the micro-etching agent at 40-60℃ for 1-2 minutes to remove the surface oxide layer; S5: Rinse the aluminum-based UBM wafer with deionized water to complete the pretreatment of the surface of the aluminum-based UBM wafer to be plated.

7. The wafer aluminum-based UBM electroless plating process according to claim 6, characterized in that, Step S2 further includes: S21: Immersing the aluminum-based UBM wafer in acidic sodium citrate for 1-3 minutes to clean surface impurities; S22: Treating the surface of the acid-washed aluminum-based UBM wafer with Ar plasma, setting the pressure to 150-250 mTorr, the power to 80-120 W, the gas flow rate to 80-120 sccm, and the time to 20-40 s.

8. The wafer aluminum-based UBM electroless plating process according to claim 6, characterized in that, The sum of the time intervals between adjacent steps S1-S5 is ≤5 min.

9. The wafer aluminum-based UBM electroless plating process according to any one of claims 6-8, characterized in that, The wafer aluminum-based UBM electroless plating process also includes an electroless gold plating step, which further... Includes the following steps: S6: Place the aluminum-based UBM wafer that has completed the pretreatment process into a zinc replacement solution for zinc plating once. The plating time is 1-3 min. S7: After cleaning the aluminum-based UBM wafers that have completed one zinc plating, immerse them in dilute nitric acid for 5-20 seconds to remove zinc; S8: After cleaning the aluminum-based UBM wafers that have completed zinc removal, immerse them again in the zinc replacement solution for a second zinc plating, with a plating time of 1-3 minutes. S9: After cleaning the aluminum-based UBM wafer that has undergone electroless zinc plating, perform electroless nickel plating and / or electroless palladium plating. After cleaning, immerse it in an electroless gold plating solution for 5-20 minutes to complete the electroless gold plating on the surface of the aluminum-based UBM wafer.

10. The wafer aluminum-based UBM electroless plating process according to claim 9, characterized in that, The temperature for electroless zinc plating is 20-40℃; the temperature for electroless nickel plating is 50-70℃, and the plating time is 10-30 min; the temperature for electroless palladium plating is 40-60℃, and the plating time is 5-20 min; the temperature for electroless gold plating is 30-50℃.

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