A method and system for refining the microstructure of a copper surface of a RDL

Abstract

The application discloses a kind of RDL copper surface microstructure detailed processing method and system, for the problems such as grain coarsening, high surface roughness, poor process stability of traditional electroplating copper process, the method is realized optimization by four-step core process: first by micro-current cathode electrolytic cleaning, complex acid-based microetching and in-situ reduction complete synergistic pretreatment;Then controlled multi-pulse electroplating is carried out using a specific formula plating solution and "nucleation pulse-relaxation-growth pulse" multi-stage waveform, cooperate with flow field optimization;Subsequently implement in-situ infrared transient thermal annealing;Finally, the process parameters are dynamically adjusted by multi-module online monitoring and AI closed-loop feedback.The application can obtain equiaxed grain structure with an average grain size of <300 nm, the surface roughness of copper layer Ra≤10nm, significantly improve the electrical performance and process robustness (Cpk>1.67), while eliminating the post-polishing / long-time annealing step, optimizing the production cycle and cost, suitable for mass production.

Description

Technical Field

[0001] This invention belongs to the field of advanced semiconductor packaging manufacturing technology, and relates to a method and system for improving the surface microstructure of copper conductors and enhancing their uniformity, density and electrical reliability in the redistribution layer (RDL) metallization process for fan-out wafer-level / panel-level packaging. Background Technology

[0002] With Moore's Law approaching its physical limits, advanced packaging technologies, such as fan-out packaging, have become a key path for industry development by achieving system integration through epitaxial interconnects. The redistribution layer (RDL), as its core interconnect structure, bears the heavy responsibility of signal transmission and power distribution. RDLs are typically formed using copper plating, and the quality of their surface and interfaces directly determines the electrical performance, mechanical reliability, and long-term service life of the final product.

[0003] The main problems facing current technology Grain coarsening and poor uniformity: Traditional DC electroplating processes tend to form coarse columnar crystals in areas with uneven current density distribution, with obvious grain boundaries, resulting in uneven resistivity distribution of the conductors, causing severe skin effect and signal integrity loss during high-frequency signal transmission.

[0004] High surface roughness: The kinetic imbalance between additive adsorption and desorption during electroplating easily forms nodular or lumpy protrusions on the copper layer surface, increasing surface roughness. This not only exacerbates local electric field concentration during subsequent dielectric layer deposition, leading to an increased risk of dielectric layer breakdown, but also affects the line resolution in the photolithography process.

[0005] Narrow process window and poor stability: Existing improvement solutions (such as using complex additives and pulse electroplating) are extremely sensitive to fluctuations in process parameters (temperature, current waveform, solution stirring), and there is a lack of coordination and feedback between process steps, making it difficult to guarantee yield and consistency during mass production.

[0006] Limitations of existing solutions Existing technologies largely focus on optimizing single process points, such as developing novel electroplating additives or improving electroplating power supply modes. While these methods can refine grain size to some extent, they often have the following limitations: additive decomposition products contaminate the plating bath, pulse electroplating equipment is expensive and has low throughput, and subsequent annealing or polishing processes increase steps and costs. There is a lack of a systematic, monitorable, and feedback-enabled integrated solution encompassing pretreatment, core deposition, and post-treatment. Summary of the Invention

[0007] The purpose of this invention is to provide a method and system for refining the microstructure of RDL copper surfaces. The method adopts a systematic and closed-loop controlled process for refining RDL copper surfaces, treating the copper deposition process as a precisely controllable "crystallization project". Through the synergistic effect of multiple physical fields and online monitoring feedback, the method actively guides copper ions to achieve a deposition mode of "high nucleation density and low preferential growth" on the seed layer, thereby obtaining a high-quality copper layer with fine grains, random orientation, and smooth surface.

[0008] The objective of this invention is achieved through the following technical solution: A method for refining the microstructure of RDL copper surfaces includes the following steps: S1: Synergistic pretreatment and surface activation For a substrate that has already had a passivation layer opening and a physical vapor deposition seed layer completed, wherein the substrate is a wafer or a panel, the following steps are performed sequentially: a) Microcurrent cathodic electrolytic cleaning: In a weakly alkaline electrolyte, a weak reverse current lower than the electroplating current is applied to remove oxides and organic contaminants from the surface of the seed layer. b) Complex acid-based micro-etching: A mixed solution of organic acids containing corrosion inhibitors is used to form nanoscale pit-like micro-roughness on the surface of the copper seed layer. c) In-situ reduction treatment: Before being transferred into the electroplating bath, the substrate surface is treated in an inert or reducing atmosphere to make the copper atoms on the surface in a zero-valence state. S2: Controlled Multipulse Electroplating and Flow Field Optimization The substrate treated with S1 was placed in the electroplating solution for deposition. The electroplating process adopted a multi-order pulse current waveform of "nucleation pulse-relaxation period-growth pulse". The flow field in the electroplating tank was optimized into a uniform and stable laminar flow through computational fluid dynamics simulation. S3: In-situ thermal excitation and microstructure relaxation Note: Relaxation is a core concept widely found in physics, chemistry, and materials science. It refers to the dynamic process by which a system gradually recovers from a non-equilibrium state to a new equilibrium state after being subjected to external disturbances (such as changes in temperature, stress, electric field, or magnetic field).

[0009] After electroplating is completed or at a specific interval in the electroplating cycle, a non-contact infrared radiation source is used to perform in-situ infrared transient thermal annealing on the substrate being plated, followed by a short-term rapid heating and natural cooling; by inducing microstructure relaxation through heat treatment, the mechanical and thermal stability of the electroplated metal can be effectively improved.

[0010] S4: Online monitoring and closed-loop feedback control The coating thickness and uniformity, on-chip resistance, and surface roughness are monitored in real time by a multi-wavelength laser interferometer, a contact probe resistor, and an optical scattering instrument, respectively. The monitoring data is transmitted to the central process control system with a built-in artificial intelligence algorithm model. Based on the correlation between historical production data and the final performance of the product, the artificial intelligence algorithm model dynamically adjusts the processing time of S1, the pulse waveform parameters of S2, and the thermal annealing conditions of S3, forming a closed loop of "monitoring-analysis-adjustment".

[0011] As a further improvement of the present invention, the parameters of the multi-order pulse current waveform in step S2 satisfy: Nucleation pulse: current density of 5-10 ASD, pulse width in milliseconds; Relaxation period: The current returns to zero, and strong convection of the solution is achieved through jet flow or ultrasonic-assisted stirring; Growth pulse: current density of 1-3 ASD, pulse width longer than nucleation pulse; The above three stages are alternated and cycled until the target coating thickness is achieved.

[0012] As a further improvement of the present invention, the peak temperature of the in-situ infrared transient thermal annealing in step S3 is 200-350°C.

[0013] As a further improvement of the present invention, in step S1: The electrolyte for microcurrent cathode electrolytic cleaning is an ammonium aminosulfonate solution with pH=9.5, the applied current is 0.05ASD, and the treatment time is 30 seconds; The complex acid-based micro-etching uses a citric acid-hydrogen peroxide etching system at 25°C and a processing time of 20 seconds. The atmosphere used in the in-situ reduction process is nitrogen containing 5% hydrogen, and the processing time is 10 seconds.

[0014] As a further improvement of the present invention, the electroplating solution in step S2 is formulated by mass percentage as follows: 220 g / L copper sulfate, 50 g / L sulfuric acid, and 50 ppm chloride ions; the flow field adopts a vertical jet flow with a flow rate of 2 m / s.

[0015] As a further improvement of the present invention, in step S3, an in-situ infrared transient thermal annealing is performed after every 2μm layer deposition, with a peak temperature of 280°C and a duration of 500ms.

[0016] A microstructure refinement system for RDL copper surfaces using the above-mentioned processing method includes: Collaborative pretreatment module: used to perform the microcurrent cathode electrolytic cleaning, complex acid micro-etching, and in-situ reduction treatment described in step S1 of claim 1, including a weak alkaline electrolytic cleaning device, an organic acid micro-etching device, and an atmosphere reduction device. Controlled multi-pulse electroplating module: includes an electroplating tank containing the electroplating solution of claim 1, a pulse power supply that outputs multi-stage pulse current, and a jet flow or ultrasonic-assisted stirring device to achieve flow field optimization, wherein the flow field of the electroplating tank is optimized by computational fluid dynamics simulation. In-situ thermal excitation module: Employs a non-contact infrared radiation source to perform the in-situ infrared transient thermal annealing described in step S3 of claim 1; Online monitoring module: Composed of a multi-wavelength laser interferometer, a contact probe resistor meter, and an optical scattering meter, used to monitor coating thickness and uniformity, on-chip resistance, and surface roughness, respectively; Central process control module: It has a built-in artificial intelligence algorithm model and communicates with the online monitoring module, collaborative pretreatment module, controlled multi-pulse electroplating module, and in-situ thermal excitation module. It is used to receive monitoring data and dynamically adjust the process parameters of each module.

[0017] As a further improvement of the present invention, the pulse power supply can output nucleation pulses with a current density of 5-10 ASD and a pulse width in the millisecond range, as well as growth pulses with a current density of 1-3 ASD.

[0018] As a further improvement of the present invention, the infrared radiation source of the in-situ thermal excitation module can achieve peak temperature adjustment of 200-350°C, and the processing time can be set in the range of milliseconds to seconds.

[0019] The above technical solution has the following beneficial effects: 1. Significant grain refinement effect: By adopting a synergistic strategy of "high-density nucleation + suppression of vertical growth", an equiaxed crystal structure with an average grain size of less than 300 nanometers is finally obtained. Compared with the traditional DC electroplating process, the grain refinement degree exceeds 50%, which greatly improves the uniformity of copper layer grain size.

[0020] 2. Excellent surface quality: Through the controlled multi-pulse electroplating flat growth mode, combined with subsequent in-situ thermal relaxation treatment, the surface roughness (Ra value) of the copper layer can be stably controlled below 10nm, meeting the stringent requirements of the most advanced interconnect technology for surface flatness and avoiding the problems of nodular protrusions in traditional processes.

[0021] 3. Significantly improved electrical performance: On the one hand, the refined equiaxed crystal structure reduces electron scattering at grain boundaries, making the resistivity of the coating closer to the theoretical value of pure copper and reducing the resistance of the wires; on the other hand, the excellent surface flatness effectively reduces the insertion loss during high-frequency signal transmission (e.g., an improvement of 0.15dB / cm at 1GHz), thus improving signal integrity.

[0022] 4. Strong process robustness and production stability: The closed-loop feedback control system can automatically compensate for interference factors such as fluctuations in incoming materials and changes in equipment status, which greatly expands the process window and significantly improves the product yield and consistency in batch production (Cpk>1.67), solving the pain points of traditional solutions being sensitive to process parameters and having poor stability.

[0023] 5. Achieving an optimal balance between cost and efficiency: Although an online monitoring and closed-loop control system has been introduced, the complex post-process polishing or long furnace tube annealing steps in the traditional process have been eliminated, which shortens the overall production cycle, reduces the overall production cost, and takes into account both technical performance and industrialization feasibility.

[0024] 6. Improved reliability: High temperature and high humidity bias tests have verified that the average failure time of RDL copper wires treated with this process is significantly better than that of traditional processes. The grain boundary structure is more stable, the electroplating stress is effectively released, and the long-term service life of the product is extended. Attached Figure Description

[0025] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0026] The structures, proportions, sizes, etc. shown in this specification are only used to complement the content disclosed in the specification for those skilled in the art to understand and read, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportional relationships, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0027] Figure 1 This is a schematic diagram of the process for refining the microstructure of RDL copper surfaces provided by the present invention.

[0028] Figure 2 This is a schematic diagram of the RDL copper surface microstructure refinement system provided by the present invention.

[0029] In the picture: 1. Collaborative pretreatment module; 2. Controlled multi-pulse electroplating module; 3. Central process control module; 4. In-situ thermal excitation module; 5. Online monitoring module. Detailed Implementation

[0030] In this invention, unless otherwise stated, directional terms such as "upper," "lower," "top," and "bottom" are generally used in relation to the direction shown in the accompanying drawings, or in relation to the vertical, perpendicular, or gravitational direction of the component itself; similarly, for ease of understanding and description, "inner" and "outer" refer to the inner and outer contours of each component itself, but the above directional terms are not intended to limit this invention.

[0031] like Figure 1 As shown, a method for refining the microstructure of an RDL copper surface includes the following steps: S1: Synergistic pretreatment and surface activation For a substrate that has already had a passivation layer opening and a physical vapor deposition seed layer completed, wherein the substrate is a wafer or a panel, the following steps are performed sequentially: a) Microcurrent cathodic electrolytic cleaning: In a weakly alkaline electrolyte, a weak reverse current lower than the electroplating current is applied to precisely remove oxides and organic contaminants from the surface of the seed layer without causing excessive damage to the seed layer. b) Complex acid-based micro-etching: A short-time treatment with a mixed solution of organic acids containing corrosion inhibitors is used to form a uniform and moderate micro-roughness (nanoscale pits) on the surface of the copper seed layer, which greatly increases the density of effective nucleation sites for subsequent copper deposition. c) In-situ reduction treatment: Before being transferred into the electroplating bath, the substrate surface is treated in an inert or reducing atmosphere to make the copper atoms on the surface in a zero-valence state. S2: Controlled Multipulse Electroplating and Flow Field Optimization The substrate treated with S1 was placed in an electroplating solution for deposition. The electroplating solution was formulated by mass percentage as follows: 220 g / L copper sulfate, 50 g / L sulfuric acid, and 50 ppm chloride ions. The flow field adopted a vertical jet flow with a flow rate of 2 m / s.

[0032] The electroplating process employs a multi-order pulsed current waveform consisting of a nucleation pulse, a relaxation period, and a growth pulse. The flow field within the electroplating tank is optimized through computational fluid dynamics simulation to achieve a uniform and stable laminar flow. The parameters of the multi-order pulsed current waveform satisfy the following: The first stage (nucleation pulse): A high current density (e.g., 5-10 ASD) pulse with a pulse width in the millisecond range is applied to instantly induce a large number of non-selective nucleations of copper on the ultra-high density active sites created in step S1. The second stage (relaxation period): the current returns to zero, and under the action of strong solution convection (achieved through optimized jet flow or ultrasonic-assisted stirring), the concentration gradient of copper ions and additives near the electrode interface is restored, while concentration polarization is eliminated. The third stage (growth pulse): Apply a pulse with a medium current density (e.g., 1-3 ASD) and a pulse width longer than the nucleation pulse to drive the already formed crystal nuclei to grow laterally and merge, while inhibiting the preferential growth in the vertical direction. This process is repeated cyclically until the target coating thickness is achieved. Throughout the process, the flow field within the electroplating tank is optimized through computational fluid dynamics simulation to ensure a uniform and stable laminar flow on the wafer / panel surface, avoiding uneven thickness caused by eddies.

[0033] S3: In-situ thermal excitation and microstructure relaxation After electroplating, or at specific intervals during the electroplating cycle, the substrate undergoes "in-situ infrared transient thermal annealing." A non-contact infrared radiation source is used to rapidly heat the copper surface for milliseconds to seconds (peak temperature 200-350℃), followed by natural cooling. This process provides sufficient atomic migration energy, prompting small grains to migrate and merge at grain boundaries, growing to a stable submicron size. Simultaneously, it releases electroplating stress, making the grain boundary structure more stable without causing excessive grain coarsening. By inducing microstructure relaxation through heat treatment, the mechanical and thermal stability of the electroplated metal can be effectively improved.

[0034] Note: Relaxation is a core concept widely found in physics, chemistry, and materials science. It refers to the dynamic process by which a system gradually recovers from a non-equilibrium state to a new equilibrium state after being subjected to external disturbances (such as changes in temperature, stress, electric field, or magnetic field).

[0035] S4: Online monitoring and closed-loop feedback control The following online monitoring modules are integrated throughout the process: Multi-wavelength laser interferometer: Real-time monitoring of coating growth thickness and surface profile, and calculation of growth rate and uniformity.

[0036] Contact probe resistor meter: measures the on-chip resistance of specific test bonds, indirectly reflecting the density and grain size of the coating.

[0037] Optical scattering instrument: to assess the macroscopic and microscopic roughness variations of the deposited surface.

[0038] The aforementioned monitoring data is transmitted to the central process control system in real time. The control system has a built-in artificial intelligence algorithm model. By learning the correlation between historical production data and final performance (such as grain size, resistivity, and reliability), the artificial intelligence algorithm model can dynamically adjust the processing time in S1, the pulse waveform parameters (current, pulse width, and frequency) in S2, and the thermal annealing conditions in S3, forming a closed loop of "monitoring-analysis-adjustment" to achieve adaptive optimization of the process.

[0039] A system for refining the microstructure of RDL copper surfaces using the above-mentioned processing method, such as... Figure 2 As shown, it includes: Collaborative pretreatment module 1: used to perform the microcurrent cathode electrolytic cleaning, complex acid micro-etching, and in-situ reduction treatment described in step S1, including a weak alkaline electrolytic cleaning device, an organic acid micro-etching device, and an atmosphere reduction device. Controlled multi-pulse electroplating module 2: includes an electroplating tank containing the electroplating solution, a pulse power supply that outputs multi-stage pulse current, and a jet flow or ultrasonic-assisted stirring device to achieve flow field optimization, and the flow field of the electroplating tank is optimized by computational fluid dynamics simulation. In-situ thermal excitation module 4: Employs a non-contact infrared radiation source to perform the in-situ infrared transient thermal annealing described in step S3; Online monitoring module 5: It consists of a multi-wavelength laser interferometer, a contact probe resistor meter, and an optical scattering meter, which are used to monitor the coating thickness and uniformity, on-chip resistance, and surface roughness, respectively. Central process control module 3: It has a built-in artificial intelligence algorithm model and communicates with the online monitoring module, collaborative pretreatment module, controlled multi-pulse electroplating module, and in-situ thermal excitation module to receive monitoring data and dynamically adjust the process parameters of each module.

[0040] Example 1: Fabrication of RDL copper layer for 12-inch wafer Fan-out WLP 1. Substrate preparation: A 12-inch reconstructed wafer with a pre-formed PI-1 passivation layer and a 50nm Ti / 100nm Cu seed layer sputtered was used.

[0041] 2. S1 Collaborative Preprocessing: Microcurrent cathodic electrolytic cleaning: Apply a current of 0.05 ASD to an ammonium aminosulfonate solution at pH 9.5 and treat for 30 seconds.

[0042] Complex acid micro-etching: Immersion in a citric acid-hydrogen peroxide etching system at 25°C for 20 seconds to form a uniform nano-rough surface.

[0043] In-situ reduction treatment: Treat in a nitrogen atmosphere containing 5% hydrogen for 10 seconds.

[0044] 3.S2 Controlled Multi-Pulse Electroplating: Electroplating solution: copper sulfate 220 g / L, sulfuric acid 50 g / L, chloride ions 50 ppm.

[0045] Pulse parameters: nucleation pulse (8 ASD, 5 ms) → relaxation (0 ASD, 20 ms) → growth pulse (2 ASD, 50 ms). Cycled for a total deposition time of 25 minutes and a target thickness of 8 μm.

[0046] Flow field: Vertical jet flow with a velocity of 2 m / s is used.

[0047] 4. S3 In-situ thermal excitation: After every 2 μm of deposition, infrared transient annealing is performed, with a peak temperature of 280℃ and a duration of 500 ms.

[0048] 5. S4 Online Monitoring and Feedback: The interferometer displays the thickness uniformity in real time within ±3%. When a measurement shows that the growth rate in the edge region is too low, the control system automatically fine-tunes the flow rate of the nozzle corresponding to the edge region and slightly increases the pulse width of the growth pulse in the next pulse cycle, so that the non-uniformity is corrected in subsequent deposition.

[0049] 6. Post-processing and Results: After electroplating, photoresist stripping and seed layer etching were performed to form the RDL pattern. FIB-SEM cross-section analysis revealed that the copper conductors contained equiaxed crystals with an average grain size of approximately 280 nm and a smooth surface. Compared to the comparative example (conventional DC electroplating), the conductor resistance was reduced by approximately 8%, and the insertion loss at 1 GHz was improved by 0.15 dB / cm.

[0050] In summary, the embodiments of the present invention achieve the following technical effects: 1. Significant grain refinement effect: By adopting the strategy of "high-density nucleation + suppression of vertical growth", an equiaxed crystal structure with an average grain size of less than 300 nanometers can be obtained, which is more than 50% finer than the traditional process.

[0051] 2. Excellent surface quality: The smooth growth pattern and subsequent in-situ thermal relaxation can stably control the surface roughness Ra value of the copper layer below 10 nm, meeting the requirements of the most advanced interconnect technology.

[0052] 3. Improved electrical performance: The refined equiaxed crystal structure reduces electron scattering at grain boundaries, making the resistivity of the coating closer to the theoretical value of pure copper. At the same time, the excellent surface flatness reduces high-frequency transmission loss.

[0053] 4. Strong process robustness: The closed-loop feedback control system can automatically compensate for interference caused by factors such as fluctuations in incoming materials and changes in equipment status, which greatly broadens the process window and improves the yield and consistency of mass production (Cpk > 1.67).

[0054] 5. Cost and efficiency balance: Although an online monitoring and control system has been introduced, the complex post-polishing or long furnace tube annealing steps have been eliminated, thus optimizing the overall production cycle and comprehensive cost.

[0055] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0056] It should be noted that the terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in sequences other than those illustrated or described herein.

[0057] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for refining the microstructure of RDL copper surfaces, characterized in that, Includes the following steps: S1: Synergistic pretreatment and surface activation For a substrate that has already had a passivation layer opening and a physical vapor deposition seed layer completed, wherein the substrate is a wafer or a panel, the following steps are performed sequentially: a) Microcurrent cathodic electrolytic cleaning: In a weakly alkaline electrolyte, a weak reverse current lower than the electroplating current is applied to remove oxides and organic contaminants from the surface of the seed layer. b) Complex acid-based micro-etching: A mixed solution of organic acids containing corrosion inhibitors is used to form nanoscale pit-like micro-roughness on the surface of the copper seed layer. c) In-situ reduction treatment: Before being transferred into the electroplating bath, the substrate surface is treated in an inert or reducing atmosphere to make the copper atoms on the surface in a zero-valence state. S2: Controlled Multipulse Electroplating and Flow Field Optimization The substrate treated with S1 was placed in the electroplating solution for deposition. The electroplating process adopted a multi-order pulse current waveform of "nucleation pulse-relaxation period-growth pulse". The flow field in the electroplating tank was optimized into a uniform and stable laminar flow through computational fluid dynamics simulation. S3: In-situ thermal excitation and microstructure relaxation After electroplating is completed or at a specific interval in the electroplating cycle, a non-contact infrared radiation source is used to perform in-situ infrared transient thermal annealing on the substrate being plated, followed by rapid heating and natural cooling. S4: Online monitoring and closed-loop feedback control The coating thickness and uniformity, on-chip resistance, and surface roughness are monitored in real time by a multi-wavelength laser interferometer, a contact probe resistor meter, and an optical scattering meter, respectively. The monitoring data is transmitted to the central process control system with a built-in artificial intelligence algorithm model. Based on the correlation between historical production data and the final performance of the product, the artificial intelligence algorithm model dynamically adjusts the processing time of S1, the pulse waveform parameters of S2, and the thermal annealing conditions of S3, forming a closed loop of "monitoring-analysis-adjustment".

2. The method for refining the microstructure of RDL copper surface according to claim 1, characterized in that, The parameters of the multi-order pulse current waveform described in step S2 satisfy: Nucleation pulse: current density of 5-10 ASD, pulse width in milliseconds; Relaxation period: The current returns to zero, and strong convection of the solution is achieved through jet flow or ultrasonic-assisted stirring; Growth pulse: current density of 1-3 ASD, pulse width longer than nucleation pulse; The above three stages are alternated and cycled until the target coating thickness is achieved.

3. The method for refining the microstructure of RDL copper surface according to claim 1, characterized in that, The peak temperature of the in-situ infrared transient thermal annealing in step S3 is 200-350℃.

4. The method for refining the microstructure of RDL copper surface according to claim 1, characterized in that, In step S1: The electrolyte for microcurrent cathode electrolytic cleaning is an ammonium aminosulfonate solution with pH=9.5, the applied current is 0.05ASD, and the treatment time is 30 seconds; The complex acid-based micro-etching uses a citric acid-hydrogen peroxide etching system at 25°C and a processing time of 20 seconds. The atmosphere used in the in-situ reduction process is nitrogen containing 5% hydrogen, and the processing time is 10 seconds.

5. The method for refining the microstructure of RDL copper surface according to claim 1, characterized in that, The electroplating solution in step S2 is formulated by mass percentage as follows: 220 g / L copper sulfate, 50 g / L sulfuric acid, and 50 ppm chloride ions; the flow field adopts a vertical jet flow with a flow rate of 2 m / s.

6. The method for refining the microstructure of RDL copper surface according to claim 3, characterized in that, In step S3, after every 2μm of coating deposition, an in-situ infrared transient thermal annealing is performed, with a peak temperature of 280℃ and a duration of 500ms.

7. A system for refining the microstructure of RDL copper surfaces using the method described in claim 1, characterized in that, include: Collaborative pretreatment module: used to perform the microcurrent cathode electrolytic cleaning, complex acid micro-etching, and in-situ reduction treatment described in step S1 of claim 1, including a weak alkaline electrolytic cleaning device, an organic acid micro-etching device, and an atmosphere reduction device. Controlled multi-pulse electroplating module: includes an electroplating tank containing the electroplating solution of claim 1, a pulse power supply that outputs multi-stage pulse current, and a jet flow or ultrasonic-assisted stirring device to achieve flow field optimization, wherein the flow field of the electroplating tank is optimized by computational fluid dynamics simulation. In-situ thermal excitation module: Employs a non-contact infrared radiation source to perform the in-situ infrared transient thermal annealing described in step S3 of claim 1; Online monitoring module: Composed of a multi-wavelength laser interferometer, a contact probe resistor meter, and an optical scattering meter, used to monitor coating thickness and uniformity, on-chip resistance, and surface roughness, respectively; Central process control module: It has a built-in artificial intelligence algorithm model and communicates with the online monitoring module, collaborative pretreatment module, controlled multi-pulse electroplating module, and in-situ thermal excitation module. It is used to receive monitoring data and dynamically adjust the process parameters of each module.

8. The method for refining the microstructure of RDL copper surface according to claim 7, characterized in that, The pulse power supply can output nucleation pulses with a current density of 5-10 ASD and a pulse width in the millisecond range, as well as growth pulses with a current density of 1-3 ASD.

9. The method for refining the microstructure of RDL copper surface according to claim 7, characterized in that, The infrared radiation source of the in-situ thermal excitation module can achieve peak temperature adjustment of 200-350℃, and the processing time can be set in the range of milliseconds to seconds.

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