Wafer copper electroplating method

Abstract

This application provides a method for copper electroplating on wafers. First, the wafer surface is cleaned. Then, a conductive copper layer is deposited on the wafer surface by sputtering, and the conductive copper layer is activated. During electroplating, a copper sulfate plating solution is used. A titanium substrate with a catalytic coating is used as the anode, and the wafer with the deposited conductive copper layer is used as the cathode. Under pulsed current control, the plating solution is atomized into droplets using an ultrasonic atomizer and sprayed onto the wafer surface to be plated through an array of multiple concentric nozzles propelled by nitrogen gas. The surface to be plated is positioned below the surface of the plating solution. The catalytic coating on the anode is formed by a mixture of graphene-coated nickel-cobalt spinel particles and precious metal powder. Furthermore, the concentration of nickel-cobalt spinel particles on the surface of the catalytic coating is greater than that in the inner layer. The plating layer prepared in this way has the advantages of uniform conductivity and high-efficiency production, meeting the requirements of high-quality wafer manufacturing.

Description

Technical Field

[0001] This application belongs to the field of semiconductor manufacturing process technology, and more specifically, relates to a method for copper electroplating on wafers. Background Technology

[0002] Wafer copper plating is a core metallization technology in semiconductor manufacturing. It involves electrochemically depositing a copper layer on the surface of a silicon wafer to form interconnect structures, supporting the electrical interconnection and performance optimization of integrated circuits. In recent years, with the rise of 5G and AI chips, electronic products are developing towards miniaturization, high density, and high-frequency, high-speed transmission, placing increasingly stringent quality requirements on wafer copper plating processes. Traditional wafer copper plating processes rely on chemical additives to improve conductivity, but still face problems such as poor coating uniformity, low catalytic activity of the plating solution, and low production efficiency.

[0003] To address the aforementioned shortcomings, there is an urgent need to develop a wafer copper electroplating process that balances uniform conductive layer deposition with high catalytic performance, in order to meet the technical requirements of high quality and high efficiency. Summary of the Invention

[0004] The purpose of this application is to provide a method for electroplating copper on wafers to solve the technical problems of poor coating uniformity and low catalytic activity of plating solution in the prior art.

[0005] To achieve the above objectives, the technical solution adopted in this application is: to provide a method for electroplating copper on a wafer, comprising the following steps:

[0006] Preprocessing steps: The wafer surface is cleaned, and then a conductive copper layer is deposited on the wafer surface by sputtering, and the conductive copper layer is activated;

[0007] Atomized pulse electroplating steps: A copper sulfate plating solution is used. A titanium substrate with a catalytic coating is used as the anode, and a wafer with a conductive copper layer is used as the cathode. Under the control of pulsed current, the plating solution is atomized into droplets by an ultrasonic atomizer and sprayed onto the surface of the wafer to be plated by a nozzle array arranged in multiple concentric circles under the propulsion of nitrogen gas. The surface of the wafer to be plated is located below the liquid surface of the plating solution. The catalytic coating of the anode is formed by a mixture of nickel-cobalt spinel particles with graphene coating and precious metal powder. Moreover, the concentration of nickel-cobalt spinel particles on the surface of the catalytic coating is greater than the concentration of nickel-cobalt spinel particles in the inner layer of the catalytic coating.

[0008] In one embodiment, the preparation steps of the nickel-cobalt spinel particles with graphene coating include:

[0009] A GO aqueous solution with a concentration of 1-5 mg / mL was ultrasonically treated to disperse GO into a monolayer.

[0010] Nickel-cobalt spinel undergoes acid pickling to remove the surface oxide layer;

[0011] Nickel-cobalt spinel particles were added to a GO dispersion, and the GO was uniformly adsorbed onto the particle surface by magnetic stirring.

[0012] Hydrazine hydrate is added as a reducing agent to reduce GO to graphene, thus forming a coating layer, followed by washing and filtration.

[0013] In one embodiment, the anode fabrication step includes:

[0014] The precious metal powder was mixed with 0.5-1 wt% silane coupling agent and ball-milled.

[0015] By using plasma spraying, the powder feeding ratio is controlled by independently controlled precious metal powder channels and graphene-coated nickel-cobalt spinel particle channels, and a catalytic coating with a gradient concentration of nickel-cobalt spinel particles is sprayed onto the surface of a titanium substrate.

[0016] In one embodiment, the anode preparation step further includes: laser irradiating the sprayed coating.

[0017] In one embodiment, during the atomized pulse electroplating step, the wafer is continuously rotated, causing droplets to diffuse radially across the surface of the wafer.

[0018] The nozzle array is integrated in the electroplating tank and is 10-15 mm away from the wafer. The central axis of the nozzle array coincides with the central axis of the wafer, and the orifice diameter of the nozzle is 0.1-0.3 mm.

[0019] In one embodiment, the nozzle spray direction forms a tangential angle of 30°-45° with the surface of the wafer.

[0020] In one embodiment, the copper sulfate concentration is 80-120 g / L, and 0.05-0.1 g / L of sodium polydisulfide dipropane sulfonate and 0.1-0.3 g / L of sodium dodecyl sulfate are added to the plating solution.

[0021] In one embodiment, the parameters of the pulse current are:

[0022] Forward current density 3-5A / dm², pulse width 5-10ms;

[0023] Reverse current density 0.5-1A / dm², pulse width 2-5ms;

[0024] Pulse frequency 50-100Hz, duty cycle 10%-25%.

[0025] Compared with the prior art, the wafer copper electroplating method provided in this application can more uniformly disperse the plating solution and improve the uniformity of the coating by combining atomized electroplating and pulsed current regulation. In addition, the anode material of pulse electroplating is a titanium substrate with a catalytic coating on its surface. The catalytic coating is formed by mixing noble metal powder and nickel-cobalt spinel particles coated with graphene. In this way, the nickel-cobalt spinel particles can provide abundant catalytic active sites, improve catalytic activity and coating stability, and improve electroplating efficiency. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 A flowchart illustrating a wafer copper electroplating method provided in an embodiment of this application. Detailed Implementation

[0028] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0029] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0030] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0031] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0032] The wafer copper electroplating method provided in this application embodiment will now be described. The wafer copper electroplating method includes the following steps:

[0033] Preprocessing steps: The wafer surface is cleaned, and then a conductive copper layer is deposited on the wafer surface by sputtering, and the conductive copper layer is activated;

[0034] Atomized pulse electroplating steps: A copper sulfate plating solution is used. A titanium substrate with a catalytic coating is used as the anode, and a wafer with a conductive copper layer is used as the cathode. Under the control of pulsed current, the plating solution is atomized into droplets by an ultrasonic atomizer and sprayed onto the surface of the wafer to be plated by a nozzle array arranged in multiple concentric circles under the propulsion of nitrogen gas. The surface of the wafer to be plated is located below the liquid surface of the plating solution. The catalytic coating of the anode is formed by a mixture of nickel-cobalt spinel particles with graphene coating and precious metal powder. Moreover, the concentration of nickel-cobalt spinel particles on the surface of the catalytic coating is greater than the concentration of nickel-cobalt spinel particles in the inner layer of the catalytic coating.

[0035] Specifically, in the pretreatment step, plasma cleaning and RCA cleaning can be used sequentially to remove organic contaminants, particles, and metallic impurities from the wafer surface. RCA cleaning is a wet cleaning process used to remove organic matter, metal ions, and other contaminants from the wafer surface. Specifically, RCA cleaning includes two main steps: SC-1 cleaning and SC-2 cleaning. SC-1 cleaning mainly uses a mixture of NH4OH (ammonium hydroxide), H2O2 (hydrogen peroxide), and H2O (water); SC-2 cleaning mainly uses a mixture of HCl (hydrochloric acid), H2O2, and H2O. Then, a thin conductive copper layer can be formed on the wafer surface using DC magnetron sputtering. This conductive copper layer serves as a seed layer, providing a conductive basis for subsequent electroplating. Before electroplating, the conductive copper layer needs to be activated to remove the oxide film on its surface, thereby exposing fresh metallic copper, optimizing surface properties, and ensuring uniform and continuous copper deposition in subsequent electroplating, avoiding defects such as voids, peeling, or "islands." Specifically, a 0.1-1% dilute hydrochloric acid solution is used. The wafer is immersed in the dilute hydrochloric acid solution for 5-30 seconds at 20-25°C, while the solution is stirred to activate the conductive copper layer on the wafer surface.

[0036] In the atomized pulse electroplating step, a conventional copper sulfate (CuSO4) plating solution is used, and surfactants and other additives can also be added to the solution. A titanium substrate with a catalytic coating serves as the anode, and a wafer with a deposited conductive copper layer serves as the cathode. In high-precision electroplating applications such as wafer copper interconnects and precision electronic components, pulse electroplating, by periodically changing the on / off state of the current (or voltage), such as following a cycle of "pulse on-reverse pulse-stop," significantly improves coating uniformity and optimizes physical properties compared to traditional DC electroplating. Furthermore, pulse electroplating can reduce plating energy consumption.

[0037] Specifically, the plating solution is dispersed into tiny droplets by an ultrasonic atomizer and then directionally sprayed into the plating tank through a nozzle array under the propulsion of nitrogen gas, dispersing onto the surface of the wafer to be plated. Simultaneously, the plating solution in the tank can be circulated back to the ultrasonic atomizer and sprayed back into the tank. This ensures a more uniform ionic composition in the plating solution and maximizes the even distribution of the plating solution onto the wafer surface, thereby improving the uniformity of the coating. It should be noted that during the electroplating process, the surface of the wafer to be plated remains below the liquid surface in the plating tank, ensuring that the wafer surface is always covered by the liquid. The continuous plating solution on the wafer surface can form a conductive circuit with the anode and cathode. However, the depth of the wafer surface in the plating solution is relatively small, generally not exceeding 5 mm. This shallower plating solution on the wafer surface has better fluidity, maximizing the uniformity of the plating solution. Furthermore, ultrasonic vibration can break down ion clusters in the plating solution, reducing local concentration polarization, inhibiting dendrite growth, reducing coating porosity, and improving coating quality. In addition, nitrogen, as a carrier gas, can isolate oxygen, inhibit the oxidation of metal ions, reduce the accumulation of impurities in the plating solution, and extend the service life of the plating solution; the use of atomized electroplating can also improve the utilization rate of the plating solution.

[0038] Furthermore, the ultrasonic atomizer is equipped with multiple nozzles arranged in concentric circles to form a nozzle array. This allows the plating solution to be sprayed onto different locations on the wafer from the center to the edge through multiple different nozzles, resulting in more uniform dispersion of the plating solution and thus improving the uniformity of the coating. The area covered by the nozzle array is slightly larger than the area of ​​the wafer, enabling the plating solution to be sprayed onto all areas of the wafer through the nozzles, reducing concentration polarization and further improving the uniformity of the coating.

[0039] Furthermore, in the atomized pulse electroplating process, a titanium substrate coated with a catalytic coating serves as the anode. This catalytic coating is formed by mixing nickel-cobalt spinel coated with graphene and noble metal powder. Noble metal powder is commonly used as a component in titanium-based catalytic coatings. Nickel-cobalt spinel (NiCo2O4) is a transition metal oxide with a stable spinel framework structure. It is a typical p-type semiconductor with a room temperature conductivity reaching 10⁻⁶. 2 -10 3With a conductivity of S / m, it can transport electrons without the need for additional conductive agents. Graphene is a two-dimensional material composed of a single layer of carbon atoms, possessing extremely high electrical conductivity and a very large specific surface area. When graphene is coated on the surface of nickel-cobalt spinel, it can construct a "three-dimensional conductive network," compensating for the conductivity disadvantage of nickel-cobalt spinel. This facilitates the rapid transfer of electrons to the active sites of nickel-cobalt spinel and noble metals, reducing electron transport resistance and minimizing reaction overpotential.

[0040] Nickel-cobalt spinel itself contains multivalent metal ions (Ni 2+ / Ni 3+ / Ni 4+ Co 2+ / Co 3+ / Co 4+ These ions can participate in electron transfer through reversible redox reactions, serving as "active centers" for catalytic reactions and thus providing abundant redox active sites. For example, in the oxygen evolution reaction (OER), Co... 3+ It can be oxidized to Co 4+ Simultaneously triggering OH - →O - +e - →Electron transfer of O2. Ni 2+ / Ni 3+ The redox reaction can help regulate the electron density on the spinel surface, enhancing its adsorption capacity for reactants and forming a synergistic effect with the active sites of Co. Nickel-cobalt spinel also has a high specific surface area, exposing more redox active sites. Furthermore, the defect sites on the graphene surface (such as edges and vacancies) can also assist in the adsorption of reactants (such as H₂O, OH⁻). - This enhances the contact efficiency between reactants and active sites. The catalytic coating consists of graphene-coated nickel-cobalt spinel and noble metal powder. The two achieve highly efficient catalytic reactions through shared electron conduction networks and complementary active sites, greatly improving catalytic performance and significantly reducing the activation energy of the reaction.

[0041] It is worth mentioning that graphene also protects nickel-cobalt spinel from electrolyte corrosion due to its strong mechanical properties and chemical stability. This means that it prevents nickel-cobalt spinel from dissolving in a high-oxidation environment, while also inhibiting the agglomeration of nickel-cobalt spinel particles and maintaining a high specific surface area.

[0042] Specifically, the concentration of nickel-cobalt spinel particles on the surface of the catalytic coating is greater than that in the inner layer of the catalytic coating. Since the catalytic reaction mainly occurs on the surface and near-surface of the coating, the concentration of nickel-cobalt spinel particles exhibits a gradient design, with a higher concentration on the surface. This means that more nickel-cobalt spinel active sites are distributed at the interface between the coating and the electrolyte, allowing for direct interaction with reactants in the electrolyte (such as OH-). -First, the high concentration and stable structure of nickel-cobalt spinel (coated with graphene) forms a denser "reaction barrier" on the coating surface. This barrier exhibits excellent oxidation and corrosion resistance, preferentially withstanding electrolyte erosion and reducing direct exposure of the inner precious metal powder and titanium substrate, thus lowering the corrosion rate. Therefore, this gradient design is based on precise optimization of catalytic reaction kinetics, mass transfer efficiency, and coating stability.

[0043] Compared with the prior art, the wafer copper electroplating method provided in this application can more uniformly disperse the plating solution and improve the uniformity of the coating by combining atomized electroplating and pulsed current regulation. In addition, the anode material of pulse electroplating is a titanium substrate with a catalytic coating on its surface. The catalytic coating is formed by mixing noble metal powder and nickel-cobalt spinel particles coated with graphene. In this way, the nickel-cobalt spinel particles can provide abundant catalytic active sites, improve catalytic activity and coating stability, and improve electroplating efficiency.

[0044] In one embodiment, the preparation steps of the nickel-cobalt spinel particles with graphene coating include:

[0045] A GO aqueous solution with a concentration of 1-5 mg / mL was ultrasonically treated to disperse GO into a monolayer.

[0046] Nickel-cobalt spinel undergoes acid pickling to remove the surface oxide layer;

[0047] Nickel-cobalt spinel particles were added to a GO dispersion, and the GO was uniformly adsorbed onto the particle surface by magnetic stirring.

[0048] Hydrazine hydrate is added as a reducing agent to reduce GO to graphene, thereby forming a coating layer, followed by washing and filtration.

[0049] Specifically, firstly, an aqueous solution of graphene oxide (GO) with a concentration of 1-5 mg / mL is prepared. This solution is then ultrasonically treated for 20-30 minutes. The cavitation effect of ultrasound breaks down the π-π stacking of the GO sheets, allowing them to be uniformly dispersed in water as a monolayer, forming a stable GO dispersion. Next, nickel-cobalt spinel particles are acid-washed in a dilute hydrochloric acid or dilute sulfuric acid solution. The acidic environment dissolves the oxide layer (such as NiO, Co3O4, etc.) on the surface of the nickel-cobalt spinel particles. After acid washing, the particles are repeatedly rinsed with ultrapure water and centrifuged to obtain clean, active particles. Finally, the treated nickel-cobalt spinel particles are added to the GO dispersion and incubated at 200-400 rpm at room temperature. The mixture was magnetically stirred at a high speed for 4-6 hours. Utilizing hydrogen bonding and electrostatic adsorption between the polar groups (hydroxyl and carboxyl groups) on the particle surface and the oxygen-containing functional groups (such as epoxy and hydroxyl groups) of the GO sheets, GO sheets uniformly coated the surface of the nickel-cobalt spinel particles. Finally, an aqueous solution of hydrazine hydrate (N2H4•H2O) was added dropwise to the system at a mass ratio of hydrazine hydrate to GO of 1:(5-10). The reaction was continuously stirred at 60-80℃ for 2-3 hours. The hydrazine hydrate removed the oxygen-containing functional groups on the GO sheets through a reduction reaction, transforming them into highly conductive graphene. Simultaneously, the π-π conjugation and mechanical flexibility of the graphene sheets formed a continuous coating layer on the surface of the nickel-cobalt spinel particles. After the reaction, the product was collected by centrifugation and washed alternately with ethanol and ultrapure water 3-5 times to remove residual reducing agent and unadsorbed graphene fragments, ultimately obtaining nickel-cobalt spinel particles coated with graphene.

[0050] The nickel-cobalt spinel particles with graphene coating prepared by the above method have excellent uniformity and continuity of the coating layer, ensuring electron transfer efficiency; the spinel active sites are fully retained, maximizing catalytic performance; and the process is simple and controllable.

[0051] In one embodiment, the anode fabrication step includes:

[0052] The precious metal powder was mixed with 0.5-1 wt% silane coupling agent and ball-milled.

[0053] By using plasma spraying, the powder feeding ratio is controlled by independently controlled precious metal powder channels and graphene-coated nickel-cobalt spinel particle channels, and a catalytic coating with a gradient concentration of nickel-cobalt spinel particles is sprayed onto the surface of a titanium substrate.

[0054] Specifically, precious metal powders such as platinum powder and iridium powder (particle size 200-500 nm) are mixed with 0.8 wt% silane coupling agent (KH-550) and ball-milled for 4 hours (300 rpm) to improve dispersibility. After vacuum drying at 60°C, the mixture is passed through a 400-mesh sieve to reduce particle agglomeration. Finally, a catalytic coating is sprayed onto a titanium substrate using a plasma spraying system. One powder feeding channel is used to transport graphene-coated nickel-cobalt spinel particles, while the other is used to transport the precious metal powder. The powder feeding rate is independently controlled by the two channels. When spraying to form the inner layer of the catalytic coating, the amount of graphene-coated nickel-cobalt spinel particles fed is relatively low, while when spraying to form the outer layer of the catalytic coating, the amount of graphene-coated nickel-cobalt spinel particles fed is higher than that of the inner layer, thus obtaining a catalytic coating with a gradient concentration of nickel-cobalt spinel particles. The catalytic coating on the anode surface prepared by the above process possesses catalytic activity, conductivity, and corrosion resistance.

[0055] In one embodiment, the anode preparation step further includes: laser irradiating the sprayed coating. By adjusting the laser power (50-200W) and scanning speed (1-5mm / s), the coating adhesion strength can be optimized, reducing the risk of coating peeling during electroplating.

[0056] In one embodiment, the nozzle's spray direction forms a tangential angle of 30°-45° with the surface of the wafer. The liquid flow flows along the tangential direction of the wafer surface, spreading outward from the spray point. The flow velocity distribution in the radial direction (from center to edge) is more gradual, avoiding the edge buildup effect caused by vertical spraying, reducing uneven deposition due to differences in mass transfer rate, and improving the coating consistency in planar areas.

[0057] In one embodiment, during the atomized pulse electroplating step, the wafer continues to rotate, causing the droplets to diffuse radially across the wafer. Specifically, when the plating solution in the nozzle is sprayed out at a tangential angle, the wafer is kept rotating during the electroplating process by a rotating mechanism. This causes the plating solution sprayed onto the wafer surface to form a vortex. Under the combined action of rotational centrifugal force and tangential impact force, the liquid flow diffuses from the spray point outwards, resulting in a more even distribution of flow velocity radially (from center to edge). This further accelerates the radial diffusion of the plating solution on the wafer, reduces concentration polarization, improves the phenomenon of thicker plating solution accumulation at the edges and thinner accumulation at the center, and promotes uniform coating thickness.

[0058] In one embodiment, in the atomized pulse electroplating step, a nozzle array is integrated in the electroplating tank and is 10-15 mm away from the wafer. The central axis of the nozzle array coincides with the central axis of the wafer, and the orifice diameter of the nozzle is 0.1-0.3 mm.

[0059] It is understandable that the central axis of the nozzle array coincides with the central axis of the wafer, and the symmetrical layout achieves uniform radial diffusion of the droplets. The tangential impact force of the droplets promotes the flow of the plating solution along the spiral direction, accelerates the radial diffusion of the plating solution on the wafer, and reduces concentration polarization.

[0060] The nozzle features a small orifice design, generating tiny droplets through ultrasonic atomization. This ensures droplet size and distribution density, enhances the wettability of the plating solution, and improves the density of the coating.

[0061] The nozzle array has a small vertical distance from the wafer, which ensures sufficient droplet kinetic energy, avoids droplet evaporation or dispersion caused by long-distance transmission, and enhances the wettability of the plating solution on the wafer surface.

[0062] In one embodiment, the copper sulfate concentration is 80-120 g / L, and 0.05-0.1 g / L of sodium polydisulfide dipropane sulfonate and 0.1-0.3 g / L of sodium dodecyl sulfate are added to the plating solution.

[0063] The copper ion concentration range is 80-120 g / L to ensure sufficient Cu. 2+ Supply should be adjusted to avoid insufficient deposition rate and thin coating due to excessively low concentration, or excessively high concentration causing grain coarsening and increased porosity, thereby optimizing coating density and conductivity.

[0064] Sodium polydisulfide dipropane sulfonate is adsorbed onto the active sites of copper deposition, regulating the microstructure of the coating, inhibiting excessively rapid local growth and dendrite growth, reducing the grain size of the coating, improving surface smoothness, and reducing signal transmission loss.

[0065] Sodium dodecyl sulfate, as an anionic surfactant, improves the dispersibility and compositional uniformity of atomized droplets, enhances the wetting ability of the plating solution, reduces surface tension, and synergistically improves the smoothness of the coating.

[0066] In one embodiment, the parameters of the pulse current are: forward current density 3-5 A / dm², pulse width 5-10 ms; reverse current density 0.5-1 A / dm², pulse width 2-5 ms; pulse frequency 50-100 Hz, duty cycle 10%-25%.

[0067] The relatively low forward current density and short pulse width provide high instantaneous energy, driving rapid migration of copper ions. The reverse current density periodically dissolves the protruding parts of the copper plating, exposing more active sites and inhibiting dendrite growth. Furthermore, the pulse frequency of 50-100Hz combined with a duty cycle of 10%-25% controls the diffusion rate of metal ions through intermittent power-off, suppressing grain coarsening through high-frequency pulses and achieving a dense nanocrystalline structure.

[0068] Example 1

[0069] A method for electroplating copper on wafers includes the following steps:

[0070] The wafer surface was sequentially subjected to plasma cleaning and RCA cleaning; then a 400nm conductive copper layer was formed on the wafer surface by DC magnetron sputtering; the wafer was immersed in 0.5% dilute hydrochloric acid for 20s at 20-25℃, while the dilute hydrochloric acid solution was stirred to activate the conductive copper layer.

[0071] A copper sulfate plating solution with a concentration of 100 g / L was used, with 0.08 g / L of sodium polydisulfide dipropane sulfonate and 0.2 g / L of sodium dodecyl sulfate added. A titanium substrate with a catalytic coating was used as the anode, and a wafer with a conductive copper layer was used as the cathode. The catalytic coating of the anode was formed by mixing nickel-cobalt spinel particles coated with graphene and iridium (Ir) powder. The concentration of nickel-cobalt spinel particles in the surface layer (5 μm) of the catalytic coating was 80%, and the concentration in the inner layer (10 μm) was 20%. Ultrasonic atomization was used under pulsed current control. The device atomizes the plating solution into droplets and, propelled by nitrogen, sprays them onto the substrate surface at a tangential angle of 30° through a nozzle array integrated in the electroplating tank and arranged in a concentric circular structure. Simultaneously, a motor drives the wafer to rotate continuously during the atomization electroplating process. The vertical distance between the nozzle array and the wafer is 15 mm, the central axis of the nozzle array coincides with the central axis of the substrate, and the nozzle orifice diameter is 0.2 mm. The pulse current parameters are: forward current density 4 A / dm², pulse width 8 ms; reverse current density 1 A / dm², pulse width 2 ms; pulse frequency 90 Hz, duty cycle 10%.

[0072] Example 2

[0073] A method for electroplating copper on wafers includes the following steps:

[0074] The wafer surface was sequentially subjected to plasma cleaning and RCA cleaning; then a 400nm conductive copper layer was formed on the wafer surface by DC magnetron sputtering; the wafer was immersed in 0.5% dilute hydrochloric acid for 20s at 20-25℃, while the dilute hydrochloric acid solution was stirred to activate the conductive copper layer.

[0075] A copper sulfate plating solution with a concentration of 100 g / L was used, with 0.08 g / L of sodium polydisulfide dipropane sulfonate and 0.2 g / L of sodium dodecyl sulfate added. A titanium substrate with a catalytic coating was used as the anode, and a wafer with a conductive copper layer was used as the cathode. The catalytic coating of the anode was formed by mixing nickel-cobalt spinel particles coated with graphene and iridium (Ir) powder. The concentration of nickel-cobalt spinel particles in the surface layer (5 μm) of the catalytic coating was 80%, and the concentration in the inner layer (10 μm) was 20%. Ultrasonic atomization was used under pulsed current control. The device atomizes the plating solution into droplets and, propelled by nitrogen, sprays them onto the surface of the wafer at a tangential angle of 40° through a nozzle array integrated in the electroplating tank and arranged in a concentric circular structure. Simultaneously, a motor drives the wafer to rotate continuously during the atomization electroplating process. The vertical distance between the nozzle array and the wafer is 15 mm, the central axis of the nozzle array coincides with the central axis of the wafer, and the nozzle orifice diameter is 0.2 mm. The pulse current parameters are: forward current density 4 A / dm², pulse width 8 ms; reverse current density 1 A / dm², pulse width 2 ms; pulse frequency 90 Hz, duty cycle 10%.

[0076] Example 3

[0077] A method for electroplating copper on wafers includes the following steps:

[0078] The wafer surface was sequentially subjected to plasma cleaning and RCA cleaning; then a 400nm conductive copper layer was formed on the wafer surface by DC magnetron sputtering; the wafer was immersed in 0.5% dilute hydrochloric acid for 20s at 20-25℃, while the dilute hydrochloric acid solution was stirred to activate the conductive copper layer.

[0079] A copper sulfate plating solution with a concentration of 100 g / L was used, with 0.08 g / L of sodium polydisulfide dipropane sulfonate and 0.2 g / L of sodium dodecyl sulfate added. A titanium substrate with a catalytic coating was used as the anode, and a wafer with a conductive copper layer was used as the cathode. The catalytic coating of the anode was formed by mixing nickel-cobalt spinel particles coated with graphene and iridium (Ir) powder. The concentration of nickel-cobalt spinel particles in the surface layer (5 μm) of the catalytic coating was 80%, and the concentration in the inner layer (10 μm) was 20%. Ultrasonic atomization was used under pulsed current control. The device atomizes the plating solution into droplets and, propelled by nitrogen, sprays them onto the surface of the wafer at a tangential angle of 40° through a nozzle array integrated in the electroplating tank and arranged in a concentric circular structure. Simultaneously, a motor drives the wafer to rotate continuously during the atomization electroplating process. The vertical distance between the nozzle array and the wafer is 15 mm, the central axis of the nozzle array coincides with the central axis of the wafer, and the nozzle orifice diameter is 0.1 mm. The pulse current parameters are: forward current density 4 A / dm², pulse width 8 ms; reverse current density 1 A / dm², pulse width 2 ms; pulse frequency 90 Hz, duty cycle 10%.

[0080] Comparative Example 1

[0081] A method for electroplating copper on wafers includes the following steps:

[0082] The wafer surface was sequentially subjected to plasma cleaning and RCA cleaning; then a 400nm conductive copper layer was formed on the wafer surface by DC magnetron sputtering; the wafer was immersed in 0.5% dilute hydrochloric acid for 20s at 20-25℃, while the dilute hydrochloric acid solution was stirred to activate the conductive copper layer.

[0083] A copper sulfate plating solution with a concentration of 100 g / L was used, with 0.08 g / L of sodium polydisulfide dipropane sulfonate and 0.2 g / L of sodium dodecyl sulfate added. A titanium substrate with a catalytic coating was used as the anode, and a wafer with a conductive copper layer was used as the cathode. The catalytic coating of the anode was formed by mixing nickel-cobalt spinel particles coated with graphene and iridium (Ir) powder. The concentration of nickel-cobalt spinel particles in the surface layer (5 μm) of the catalytic coating was 80%, and the concentration in the inner layer (10 μm) was 20%. Under the control of the pulse current, the plating solution is sprayed onto the surface of the wafer at a tangential angle of 40° through a nozzle array integrated in the electroplating tank and arranged in a concentric circular structure. At the same time, the wafer is continuously rotated by a motor. The vertical distance between the nozzle array and the wafer is 15 mm, the central axis of the nozzle array coincides with the central axis of the wafer, and the orifice diameter of the nozzle is 0.2 mm. The parameters of the pulse current are: forward current density 4 A / dm², pulse width 8 ms; reverse current density 1 A / dm², pulse width 2 ms; pulse frequency 90 Hz, duty cycle 10%.

[0084] Comparative Example 2

[0085] A method for electroplating copper on wafers includes the following steps:

[0086] The wafer surface was sequentially subjected to plasma cleaning and RCA cleaning; then a 400nm conductive copper layer was formed on the wafer surface by DC magnetron sputtering; the wafer was immersed in 0.5% dilute hydrochloric acid for 20s at 20-25℃, while the dilute hydrochloric acid solution was stirred to activate the conductive copper layer.

[0087] A copper sulfate plating solution with a concentration of 100 g / L was used, with 0.08 g / L of sodium polydisulfide dipropane sulfonate and 0.2 g / L of sodium dodecyl sulfate added. A titanium substrate with a catalytic coating was used as the anode, and a wafer with a conductive copper layer deposited on it was used as the cathode. The catalytic coating on the anode was formed by mixing nickel-cobalt spinel particles coated with graphene and iridium (Ir) powder. The concentration of nickel-cobalt spinel particles in the surface layer (5 μm) of the catalytic coating was 80%, and the concentration in the inner layer (10 μm) was... The concentration of nickel-cobalt spinel particles is 20%; electroplating is performed using direct current, and the plating solution is atomized into droplets by an ultrasonic atomizer and sprayed onto the surface of the wafer at a tangential angle of 40° under the impingement of nitrogen through a nozzle array of multiple concentric circles integrated in the electroplating tank. During atomization electroplating, the wafer is continuously rotated by a motor; the vertical distance between the nozzle array and the wafer is 15 mm, the central axis of the nozzle array coincides with the central axis of the wafer, and the orifice diameter of the nozzle is 0.2 mm.

[0088] Comparative Example 3

[0089] A method for electroplating copper on wafers includes the following steps:

[0090] The wafer surface was sequentially subjected to plasma cleaning and RCA cleaning; then a 400nm conductive copper layer was formed on the wafer surface by DC magnetron sputtering; the wafer was immersed in 0.5% dilute hydrochloric acid for 20s at 20-25℃, while the dilute hydrochloric acid solution was stirred to activate the conductive copper layer.

[0091] A copper sulfate plating solution with a concentration of 100 g / L was used, with 0.08 g / L of sodium polydisulfide dipropane sulfonate and 0.2 g / L of sodium dodecyl sulfate added. A titanium substrate with a catalytic coating was used as the anode, and a wafer with a conductive copper layer was used as the cathode. The catalytic coating on the anode was an iridium (Ir) coating. Under the control of pulsed current, the plating solution was atomized into droplets by an ultrasonic atomizer and propelled by nitrogen gas through multiple nozzles arranged in a concentric circle structure integrated in the electroplating tank. The array sprays the nozzles onto the surface of the wafer at a tangential angle of 40°, and simultaneously performs atomization electroplating while driving the wafer to rotate continuously via a motor. The vertical distance between the nozzle array and the wafer is 15 mm, the central axis of the nozzle array coincides with the central axis of the wafer, and the orifice diameter of the nozzle is 0.2 mm. The parameters of the pulse current are: forward current density 4 A / dm², pulse width 8 ms; reverse current density 1 A / dm², pulse width 2 ms; pulse frequency 90 Hz, duty cycle 10%.

[0092] The following are the test data for the coating thickness at the center and edge of the wafer and the OER overpotential of the anodic catalyst coating in the three embodiments and comparative examples above:

[0093] Table 1. Coating thickness and OER overpotential test data in the three examples and comparative examples.

[0094]

[0095] As can be seen from the above, compared with Comparative Example 1, the wafer copper electroplating method provided in this application adopts an atomized spray plating solution, which makes the plating solution distribution more uniform, the thickness difference of the copper plating layer at the center and edge of the wafer is smaller, and the plating layer uniformity is higher. Compared with Comparative Example 2, the wafer copper electroplating method provided in this application adopts a pulse electroplating method, which can significantly improve the plating layer uniformity by periodically changing the current on and off state. Compared with the pure noble metal coating used for the catalytic coating of the anode in Comparative Example 3, the catalytic coating of the anode in the wafer copper electroplating method provided in this application uses a mixture of nickel-cobalt spinel particles with graphene coating and noble metal iridium (Ir) powder. The OER overpotential of this composite catalytic coating is only slightly higher than that of the pure noble metal coating, and the difference between the two is no more than 30mV. It can be seen that in this composite catalytic coating, the noble metal can make up for the difference in activity of nickel-cobalt spinel, and nickel-cobalt spinel can compensate for the lack of activity by having a high specific surface area (specific surface area > 100m² after graphene coating). 2 / g) disperses precious metal particles, making the activity of the composite catalytic coating close to that of the pure precious metal catalytic coating. However, the composite catalytic coating can reduce the amount of precious metal used, reduce costs, and nickel-cobalt spinel can inhibit the sintering of precious metal particles, thereby improving stability.

[0096] In summary, this application combines a three-in-one innovative approach of atomized electroplating, pulsed current regulation, and catalytic activity optimization, which improves the catalytic activity and uniformity of the coating and solves the core problems of limited mass transfer and poor coating uniformity in the prior art. The coating uniformity, density, and reliability are significantly better than traditional processes, and it is suitable for wafer manufacturing in high-density interconnect and high-frequency and high-speed scenarios.

[0097] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for electroplating copper on wafers, characterized in that, Includes the following steps: Preprocessing steps: The wafer surface is cleaned, and then a conductive copper layer is deposited on the wafer surface by sputtering, and the conductive copper layer is activated; Atomized pulse electroplating steps: A copper sulfate plating solution is used. A titanium substrate with a catalytic coating is used as the anode, and a wafer with a conductive copper layer is used as the cathode. Under the control of pulsed current, the plating solution is atomized into droplets by an ultrasonic atomizer and sprayed onto the surface of the wafer to be plated by a nozzle array arranged in multiple concentric circles under the propulsion of nitrogen gas. The nozzle array is integrated in the electroplating tank and the vertical distance between it and the wafer is 10-15 mm, so that the surface of the wafer to be plated is below the liquid surface of the plating solution. The catalytic coating of the anode is formed by a mixture of nickel-cobalt spinel particles with graphene coating and precious metal powder. Moreover, the concentration of nickel-cobalt spinel particles on the surface of the catalytic coating is greater than the concentration of nickel-cobalt spinel particles in the inner layer of the catalytic coating.

2. The wafer copper electroplating method as described in claim 1, characterized in that, The preparation steps of the nickel-cobalt spinel particles with graphene coating include: A GO aqueous solution with a concentration of 1-5 mg / mL was ultrasonically treated to disperse GO into a monolayer. Nickel-cobalt spinel undergoes acid pickling to remove the surface oxide layer; Nickel-cobalt spinel particles were added to a GO dispersion, and the GO was uniformly adsorbed onto the particle surface by magnetic stirring. Hydrazine hydrate is added as a reducing agent to reduce GO to graphene, thus forming a coating layer, followed by washing and filtration.

3. The wafer copper electroplating method as described in claim 2, characterized in that, The anode preparation steps include: The precious metal powder was mixed with 0.5-1 wt% silane coupling agent and ball-milled. By using plasma spraying, the powder feeding ratio is controlled by independently controlled precious metal powder channels and graphene-coated nickel-cobalt spinel particle channels, and a catalytic coating with a gradient concentration of nickel-cobalt spinel particles is sprayed onto the surface of a titanium substrate.

4. The wafer copper electroplating method as described in claim 3, characterized in that, The anode preparation step further includes: laser irradiating the sprayed coating.

5. The wafer copper electroplating method as described in claim 1, characterized in that, In the atomized pulse electroplating step, the wafer is continuously rotated, causing droplets to diffuse radially on the surface of the wafer. The central axis of the nozzle array coincides with the central axis of the wafer, and the orifice diameter of the nozzle is 0.1-0.3 mm.

6. The wafer copper electroplating method as described in claim 5, characterized in that, The nozzle spray direction forms a tangential angle of 30°-45° with the surface of the wafer.

7. The wafer copper electroplating method according to any one of claims 1-6, characterized in that, The copper sulfate concentration is 80-120 g / L, and 0.05-0.1 g / L of sodium polydisulfide dipropane sulfonate and 0.1-0.3 g / L of sodium dodecyl sulfate are added to the plating solution.

8. The wafer copper electroplating method according to any one of claims 1-6, characterized in that, The parameters of the pulse current are: Forward current density 3-5A / dm², pulse width 5-10ms; Reverse current density 0.5-1A / dm², pulse width 2-5ms; Pulse frequency 50-100Hz, duty cycle 10%-25%.

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