Copper Electrodeposition Research Articles

Numerical simulation of copper electrodeposition for Through Silicon Via (TSV) with SPS-PEG-Cl additive system

Through silicon via (TSV) technology is crucial for modern semiconductor device package, enabling high-performance integrated microsystems. This paper investigates the mechanism of the bottom-up copper deposition process in TSV, leveraging a co-adsorbed polyether-Cl-suppression layer and accelerators for optimized filling profiles. We present numerical simulations of the effects of additives (accelerator, suppressor) and chloride ions (Cl−) on the TSV filling. By varying the substance concentration, we obtain three distinct filling models, including filling with voids, conformal filling and bottom-up filling. We analyzed the distribution of various substances and current densities to elucidate the filling mechanism. Furthermore, TSV filling experiments were conducted, and the simulated profiles were in good match with the filling experiments. It is verified that the feasibility of the proposed numerical model by generalizing to 90μm × 180 μm, 50μm × 100 μm, and 10μm × 100 μm via holes of different sizes and aspect ratios.

Electrodeposition of copper on niobium for cryocooler application

The electrodeposition of copper onto niobium using commercial acidic and alkaline electrolytes was tested. The continuous dense polycrystalline copper films were successfully obtained in aqueous alkaline-type bath containing copper sulphate, sodium hydroxide and sodium gluconate. The effect of benzotriazole and sodium lauryl sulphate additives on the morphology and crystal structure of the deposited copper was investigated by optical and scanning electron microscopy, and X-ray diffraction. No copper oxides were found in the grown films. Copper films had moderate adhesion properties that would be insufficient for cryocooler application. We are currently exploring different compositions of electrolyte baths for obtaining the coatings on niobium with improved adhesion.

Aging tests of mini-modules with copper-plated heterojunction solar cells and pattern-transfer-printing of copper paste

Abstract: Mini-module aging tests with differently interconnected heterojunction solar cells having industrially viable copper metallization are presented. The plating process comprises 3 steps: firstly, screen printing of a seed-grid layout using a copper-based paste, followed by deposition of a dielectric layer over the entire wafer surface, and finally, selective copper electrodeposition on grid positions. Modules with Smartwire interconnection, fabricated with M6 half-cells, are stable in extended TC and PID tests. DH degradation is at 5% after 2700 h (glass-glass modules without edge sealing). Shingle modules, realized in collaboration with CEA INES and AMAT, exhibit notably higher fill factor compared to reference modules with screen-printed silver paste. This improvement is attributed to the superior line conductivity achieved with plated copper. TC stability of shingle modules is very good, whereas after 2000 h damp-heat aging more than 2% loss in fill factor is observed. Using pattern-transfer-printing technology narrow, high aspect-ratio lines have been obtained: with a seed-grid of pure copper paste, reinforced with electrodeposited copper. Line dimensions and line resistance as well as first cell results are presented.

(Invited) Some Observations on the History of Electrochemistry in Europe

Modern electrochemistry is generally regarded as having its origins in the work of the Italian scientists Galvani (1737 – 1798) and Volta (1745 – 1827). Their discoveries led directly to the invention (1799) by Volta of the voltaic pile, a primitive form of what we now call a battery. This invention greatly facilitated electrical experimentation and quickly led to a host of other electrochemical discoveries such as the electrolysis of water (Nicholson and Carlisle in 1800, although it was first demonstrated in 1789 by Deiman and van Troostwijk using an electrostatic generator), isolation of elemental alkali and alkaline earth metals (Davy, 1807–1808) and electroplating (Brugnatelli, 1805). The work of Davy (1778 – 1829) and of Faraday (1791 – 1867) greatly advanced the understanding of electrochemistry and Faraday’s laws of electrolysis (1833) put the field on a quantitative basis. This was followed by a long succession of electrochemical discoveries that has continued to the present.Scientists such as Daniell (1790 – 1845), Grove (1811 – 1896), Leclanché (1839 – 1882) and Planté (1834 – 1889) made early improvements to batteries; of course, research and development of batteries remains an important area of electrochemistry. Historically, batteries were the primary source of electric current until practical electric dynamos became available in about 1870. Electroplating developed as a practical technology from about 1840, initially for electrodeposition of copper on printing plates. From 1893 to 1948, the international standard for electric current was based on electrodeposition of silver. Furthermore, an electrochemical cell invented by Weston (1850 – 1936) was adopted as the reference standard for voltage in 1903 and remained so until 1990 when it was replaced by a Josephson junction standard.The science of electrochemistry experienced rapid growth from the 19th century on, with major contributions from European scientists including Kohlrausch (1840 – 1910), Ostwald (1853 – 1932), Arrhenius (1859 – 1927), Tafel (1862 – 1918), Nernst (1864 – 1941), and Heyrovský (1890 – 1967), to mention but a few. In this talk, I will attempt to trace the evolution of electrochemistry and discuss some of the major landmarks and the European scientists who made important contributions. I will also comment on how equipment and methodology have changed over the last half-century.

Effect of Pulse Parameters on Early Stage Nucleation Phenomena

Pulse electrodeposition has garnered significant attention from decades to control important parameters of the growing electrodeposits such as grain size, crystal orientation, and microhardness. Recently, pulse charging has become a major research focus due to its ability to suppress dendritic growth during the charging process for metal-anode based rechargeable batteries. In this work, we have comprehensively studied the effect of pulse duty cycle, D (D = tON/(tON+tOFF)) and frequency on the nucleation phenomena using an in-situ visualization technique (Figure 1). The nuclei density of copper electrodeposits on Indium Tin Oxide (ITO) coated glass substrate is evaluated microscopically and quantified using image processing. The pulse parameters are made equivalent to the corresponding DC voltage (VDC) by two possible ways, i) increasing the peak voltage (VPeak) based on the duty cycle applied (VPeak = VDC/D) , and ii) expanding the total deposition time, or in other words equating the cumulative reaction time (tON) in pulses to the total DC time (tDC = ∑tON). Interestingly, exactly opposite trends are observed for the two aforementioned methods. A sharp increase (∼75%) and decrease (∼80%) in nuclei density as compared to DC are observed while reducing the duty cycle till D = 1/4 for the two methods respectively. However, a decline in nuclei density is noticed while increasing in frequency in both methods. The associated pulse time scales, and the coalescence of the evolving nuclei due to merging of the diffusion zones surrounding a growing nucleus are likely to play the leading role behind this observation. The results add insights to the governing process, and will be useful in designing efficient pulse parameters to control dendritic growth. Figure 1

Microstructural effects of copper deposits on direct bonding for 3D IC integration

Cu-to-Cu direct bonding has been regarded as an important approach to achieve three-dimensional integrated circuit integration. This study aims to investigate the effects of microstructure and Xenon flash exposure on the direct bonding of copper deposits. Copper electrodeposits, along with a sputtered deposit, with various grain sizes, preferred orientations, as well as surface hardnesses, were prepared to clarify the influence of individual factors quantitatively. Experimental results show that joint strength and grain boundary density followed a positively linear relationship regardless of other microstructural differences, suggesting the dominating role of grain boundary diffusion. Grain refinement can effectively enhance bonding strength, even only one side of the directly bonded joints possessed fine grains. Considering the portable device applications which may suffer from drop shocks, drop testing of the packages comprising sputtered copper on Si chips joined with electroplated copper on Al2O3 substrates assembled by thermal compression bonding was performed for the first time. Noticeably, a proper flash irradiaiton prior to bonding brought about not only remarkable improvement in shear strength by up to 60 % but also drop resistance for direct-copper bonds. The resistance against drop shock for directly-bonded daisy chains subjected to an appropriate light exposure prior to bonding was superior than the joints bonded using impact-resistant solders.

Characterization of nanoscale pinhole defects in hydrophobic coatings using copper electrodeposition

Thin (∼ 100 nm thick) hydrophobic polymer films are used in a plethora of applications where water repellency is required. However, hydrophobic film implementation in industry is limited due to poor durability. Thin hydrophobic film blistering during condensation has been identified as one of the main mechanisms associated with failure. Yet, disagreement exists about the source of blister initiation. Furthermore, there is a lack of understanding about the physical defects or pinholes that facilitate vapor penetration pathways through thin hydrophobic films. These pinholes govern the nucleation of blisters on the interface between the hydrophobic polymer and metal substrate. Here, we use metal electrodeposition as a means to characterize these intrinsic pinholes in thin hydrophobic polymers. A facile method is demonstrated to locate pinholes and measure pinhole density on CFx and poly(2-chloro-p-xylylene) (Parylene C) films. Our work not only helps to understand the intrinsic defects associated with film deposition, it also provides design guidelines for the selection and development of efficient thin film hydrophobic coatings.

Self-organized periodic pattern dynamics of porous copper electrodeposition at the industrial large current

The formation of porous structure during metal electrodeposition not only provide new ideas for preparing advanced metal materials, but also determines the product defects in industrial electrodeposition processes. However, as for new evidence of ordered sub-structure formation within porous metal even during scalable templateless electrodeposition, existing thermodynamic reasons or exogenous-templates mechanism are under extensively controversial. Herein, we have discovered periodic self-organization behavior of porous copper at the initial stage of industrial large-current electrodeposition. Different from widely-recognized bubble-templated mechanism, the length of periodicity for Cu deposits is orders of magnitude smaller than any possible bubble template, according to in-situ observation. Coloration-tracking and in-situ electrochemical analysis experiments have been designed, to reveal the existence of a micelle-type complex intermediate and its activator effects. A self-organization mechanism has been proposed based on ordered dynamic pattern of micelle-type complex intermediate, rather than intermediate of small ions, which determines the porous structure since the very initial layer. Our findings suggest the important contribution from intrinsic self-organization dynamics of intermediate to the formation of porous metal materials with high activity or surface area in industrial scale.

Electrodeposition of Copper Coatings on Sandblasted 304 Stainless Steel Surfaces: A Characterization Study Using Computer Vision Methods

Electrodeposition is commonly employed to coat materials. The effectiveness and endurance of coatings depend on specific process conditions. The characterization of coatings is a costly endeavor, requiring specialized knowledge and expertise. This study presents a novel methodology for analyzing surfaces coated with copper, utilizing computer vision techniques to complement traditional surface characterizations such as the contact angle. The coating under investigation was produced through electrodeposition using a ChCl:2EG:0.1CuCl2·2H2O electrolyte. Our findings demonstrate the feasibility of the vision-based method for evaluating superficial copper electrodeposition on sandblasted 304 SS. The proposed vision method holds the potential to expedite the development of new coatings and facilitate the analysis of their characteristics. This, in turn, could enhance the durability of materials and devices across a range of applications.

A DFT-based FD-KMC Simulation for Electrodeposition of Copper Nanoparticles on Carbon Electrode Surface

Electrodeposition is often used to load catalysts onto electrode surfaces to enhance their electrochemical activity, thereby improving the performance of redox flow batteries. The kinetic Monte Carlo (KMC) method was used to successfully simulate the nucleation and growth of nanoparticles during the electrodeposition process. However, the reliability of KMC simulation results is closely related to the atomic kinetic parameters derived from quantum-scale calculations. Meanwhile, the electrochemical reaction behaviors during electrodeposition rely on the mass transport of electroactive ions near the electrode surface. To address these issues, density functional theory (DFT) was introduced to obtain the energy barriers required in the calculation of KMC. Simultaneously, the finite difference (FD) method was integrated into the KMC algorithm to provide the transient concentration distribution of the diffusion layer near the electrode surface. This DFT-based FD-KMC method was used to simulate the early stage of electrodeposition of copper (Cu) nanoparticles on carbon electrode surfaces and investigate the effects of bulk concentration and applied potential on the characteristics of deposition morphology of Cu nanoparticles. Additionally, carbon electrode surfaces with different defect site numbers were generated to reveal the influence of surface defect sites on the morphology of the deposited Cu nanoparticles during electrodeposition process.

Selective Copper Electrodeposition for Redistribution Layer by Varying Concentration and Agitation of Janus Green B

A fine-pitch redistribution layer (RDL) for high-performance devices in a fan-out wafer-level package (FOWLP) is required in semiconductor packaging technology. The damascene process for fine-pitch RDL has been studied for several years, which has been introduced to overcome the etching problems. Although surface planarization for removing overburden is necessary for the damascene process in RDL, it adds high cost to the FOWLP process. Selective Cu electrodeposition is a method used to prevent overburden. Janus Green B (JGB) is utilized as a leveler in Cu electrodeposition and has properties that depend on concentration and agitation. These properties affected the Cu deposition rate according to the pattern position. Thus, the electrochemical properties of JGB were investigated based on the concentration of JGB and agitation. Furthermore, the effect of JGB on the crystalline structure of the Cu film was examined. Additionally, changes in the growth behavior of the Cu nuclei caused by JGB were observed during the initial stage of chronoamperometry. Based on these results, selective Cu electrodeposition was successfully performed on the patterned substrate using the difference in the concentration of JGB and agitation.

Unveiling the potential and mechanisms of 3,3′-bicarbazole-based quaternary ammonium salts as levelers

It is important to introduce an effective leveler into electroplating bath to meet the desired requirement in the electronic industry. This work explored the impact of larger backbone structures of four 3,3′-bicarbazole quaternary ammonium salts on the performance of promising levelers in light of the ambiguous mechanism of action. For the first time, these four compounds have been functionalized and identified as promising levelers for copper electrodeposition in through holes. Electrochemical measurements, theoretical calculations, and dynamics simulations collectively revealed that among these levelers, BCz-BPD exhibits the tendency of optimal adsorption on the cathode with the strongest inhibition of copper deposition. Chronoamperometry tests were carried out to analyze the copper nucleation model during electroplating. By measuring the electrostatic potential, average local ionization energy, and planarity, the leveling mechanism of BCz-BPD leveler was analyzed. In order to confirm the high through-hole filling and excellent leveling performance of BCz-BPD in actual PCB plating, TP value measurement, SEM, and XRD tests were carried out sequentially. In addition, galvanostatic measurements were performed to study the interaction of BCz-BPD leveler with other kinds of additives.

Sequential Laser-Burned Lignin and Hydrogen Evolution-Assisted Copper Electrodeposition to Manufacture Wearable Electronics.

In the contemporary world, wearable electronics and smart textiles/fabrics are galvanizing a transformation of the health care, aerospace, military, and commercial industries. However, a major challenge that exists is the manufacture of electronic circuits directly on fabrics. In this work, we addressed the issue by developing a sequential manufacturing process. First, the target fabric was coated with a customized ink containing lignin. Next, a desired circuit layout was patterned by laser burning lignin, converting it to carbon and establishing a conductive template on the fabric. At last, using an in-house-designed printer, a devised localized hydrogen evolution-assisted (HEA) copper electroplating method was applied to metalize the surface of the laser-burned lignin pattern to achieve a very low resistive circuit layout (0.103 Ω for a 1 cm long interconnect). The nanostructure and material composition of the different layers were investigated via scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy, and Fourier-transform infrared spectroscopy (FTIR). Monitoring the conductivity change before and after bending, rolling, stretching, washing, and adhesion tests presented remarkable mechanical stability due to the entanglement of the copper nanostructure to the fibers of the fabric. Furthermore, the HEA method was used to solder a light-emitting diode to a patterned circuit on the fabric by growing copper at the terminals, creating interconnects. The presented sequential printing method has the potential for fabricating reliable wearable electronics for various applications, particularly in medical monitoring.

Electrochemical reduction of CO2 to C2 products—effect of surfactant on copper electrodeposition

Electrochemical reduction of CO2 to C2 products—effect of surfactant on copper electrodeposition

Closed-loop process for Zn and Cu selective recovery from MSWI bottom ash fine fraction

In 2019, 224 Mt of Municipal Solid Wastes (MSW) were produced in Europe. A significant proportion of this MSW is treated by incineration producing each year 20 Mt of Municipal Solid Waste Incineration (MSWI) Bottom Ashes (BA). While the coarsest fraction (>2mm) can be reemployed in construction field, this is not the case for the finest fraction <2 mm (30% wt.) which is intended to be landfilled. The challenges of the treatment of this solid residue are multiple. The metals of interest are dispersed within this complex matrix and the gangue is composed by a large proportion of carbonate based minerals which reduces the choice of possible leaching agents. Moreover, the large amounts of iron and aluminum imply to choose a highly selective recovery method and the economic constrains steer the process towards low-cost technologies. The aim of this work is to study the feasibility of a selective copper and zinc recovery, whose contents in the bottom ash fine fraction are comparable to low-grade ores. A four-step process was designed consisting of a flushing, a leaching, a precipitation and an electrowinning. A selective leaching step using ammonia-ammonium chloride solution was carried out to avoid an iron co-leaching. After the leaching step, the precipitation of zinc was achieved by addition of aluminum nitrate followed by an electrodeposition of copper from ammonia medium. Up to 70% of Cu and Zn could be recovered with minimal modifications of the leachate composition allowing thus its reuse. The developed process enables the recovery of metallic copper and zinc in a spinel form from a waste originally intended for landfilling.

The electrocatalysis of Mn-Co3O4/CeO2@C particles with different Ce content modified Ti/PbO2 anode and its application for copper electrodeposition

The electrocatalysis of Mn-Co3O4/CeO2@C particles with different Ce content modified Ti/PbO2 anode and its application for copper electrodeposition

Ni/Cu/Ag: An Electrochemically Synthesised Trimetallic Stack for CO2 Reduction

Climate change, as a result of excess atmospheric CO2 and other greenhouse gases, maintains a position, according to the United Nations as the “defining issue of our time”.1 This has led to research efforts to limit CO2 outputs as well as recycling CO2 which is already present. The electrochemical reduction of CO2 has exponentially gained interest as a possible solution since the late 1990s; if the reduction can be achieved in conjunction with a renewable energy source (e.g solar power), it could be considered carbon negative. Electrochemical CO2 reduction would remove some of the excess CO2 from the atmosphere in conjunction with providing a way for the intermittent energy generated by renewable methods to be stored as chemical bonds, both of which aid the fight against climate change.Significant focus has been placed on pure metals as electrocatalysts since Hori’s seminal discovery that Cu can uniquely reduce CO2 by more than two electrons to produce hydrocarbons.2 High overpotentials and poor selectivity remain as challenges due to the scaling relations between the simultaneous pathways of CO2 reduction.3 One approach for breaking these is alloying or the use of mixed metal phases. Bimetallic catalysts, particularly those containing Cu have gained considerable interest4, however, limited examples of trimetallic catalysts have been explored.Herein, a NiCuAg electrocatalyst has been electrochemically synthesised by copper electrodeposition on nickel, followed by galvanic replacement to produce a silver layer. The combination of Ni and Cu was proven to be promising in recent studies5,6 generating desirable non-CO and H2 products such as ethanol. Ag has been shown to promote *CO intermediate production on the Cu surface7 thus its addition to our catalyst should further promote non-CO and H2 products and increase their selectivities.Linear sweep voltammetry revealed significant activity at potentials more negative than -0.8 V vs. Ag/AgCl, thus CO2 reduction was completed in this region. Reduction products were analysed by gas chromatography and liquid products by NMR. The trimetallic stacks were characterised by XRD, and SEM/EDX before and after reduction to explore their morphology and lifetimes.

Cu Surface Chemistry in Acid Media: Vibrational Spectroscopy, Mass Spectrometry and ECSTM Measurements

Copper electrodeposition is a central process in the metallization of microelectronics and more recently copper has also found use as an important electrocatalyst in the conversion of CO2 to hydrocarbons. Gaining mechanistic insight into the reactivity of Cu surfaces requires in situ and better still in operando measurements. Herein the utility of the combination of vibrational spectroscopy (SEIRAS, SHINERS), electrochemical mass spectrometry (EC-MS) and scanning tunneling microscopy (ECSTM) to examine the competitive and co-adsorption interactions between potential dependent halide adsorption, molecular adsorption, underpotential metal deposition and hydride formation on low index Cu single crystals surface will be detailed. Further still, the emergent opportunity to study the impact of such interaction on metal deposition reactions will also be explored.1.Raciti and T.P. Moffat, “Quantification of Hydride Coverage on Cu(111) by Electrochemical Mass Spectrometry,” J. Phys. Chem., 126, 18734-18743 (2022).2.Raciti, A.R. Hight Walker, T. P. Moffat, “Mapping Surface Chemistry During Superfilling with Shell- Isolated Nanoparticle Enhanced Raman Spectroscopy and X-ray Photoelectron Spectroscopy,” J. Electrochem. Soc., 169, 082506 (2022).3.B.M. Tackett, D. Raciti, A.R. Hight Walker, T.P. Moffat, “Surface Hydride Formation on Cu (111) and its Decomposition to Form H2 in Acid Electrolytes,” J. Phys. Chem. Lett., 12, 10936-10941 (2021).4. G.Liu, S. Zou, D. Josell, L.J. Richter and T.P. Moffat, “SEIRAS Study of Chloride Mediated Polyether Adsorption on Cu,” J. Phys. Chem. C., 122, 21933-21951, (2018).

Manufacturing Millimeter-Wave Horn Antennas Using 3D Printing and Direct Electrodeposition

Additive manufacturing has undergone huge development in recent years. It has become commonplace both for the hobbyist community and industry, with important applications in several domains (e.g. biomedical, aerospace and automotive). Its main strength lies in the fact that custom parts can be quickly prototyped and manufactured, regardless of their complexity. However, many of the 3D printing techniques still have limitations in terms of strength, materials, production speed and overall usability. One of the main limitations is that most techniques utilize polymers, which are intrinsically non-conductive. This limits their use in electronics and telecommunication applications.Meanwhile, a lot of equipment used in telecommunications, such as antennas, tuners, waveguides, etc. remain very expensive due to complex and time-intensive manufacturing techniques. This leads to high prices, long lead times and limitations in the complexity of the geometries. The main goal of this research is to develop a fast and cost-effective method to produce conductive structures using additive manufacturing, more specifically fused deposition modeling (FDM) 3D printing. A special focus is put on horn antennas for microwave applications, as this application is very demanding on both the accuracy of the geometry and the conductivity of the structure.The approach in this work mainly consists of two steps: optimizing the plating conditions on flat test samples and extending this knowledge to the three-dimensional horn antenna. The chosen material is a PLA-based polymer with carbon black as an additive, which provides the polymer with some electrical conductivity (factor ~107 lower than copper). This conductivity is too low for any meaningful application but allows for the use of electrodeposition of copper directly onto the polymer to increase the conductivity. By focusing on reducing the distance from the electrical contact to the surface to be plated and by tuning the deposition parameters, high-quality uniform copper deposition is obtained on test samples. The achieved results outperform the current state-of-the-art in this field.The knowledge acquired from the test samples is then applied to the horn antenna. To this end a conductive antenna holder is developed. The antenna holder serves to keep the potential as constant as possible over the entire antenna surface in order to promote homogeneous deposition. It also aligns the electrodes, keeping the distance between electrodes as constant as possible and preventing short circuits. This method results in good partial coverage and again produces better results than can be found in the literature. However, direct deposition of a nicely uniform layer over the entire surface remains very challenging. An indirect electrodeposition method using conductive silver paint is used to produce the final version of the printed horn antenna.Measurements in an anechoic chamber demonstrate that the copper-coated version of the printed antenna has similar radiation performance as a commercial counterpart. An exponential horn antenna is made with decent performance, demonstrating the ease of production of more complexly shaped antennas. Our antennas can be produced within a couple of hours at a fraction of the price of commercial counterparts ($3 instead of $500-1500). This opens up new possibilities to quickly validate simulation results of new antenna designs. Further research focuses on the use of electroless plating to obtain more homogeneous copper deposition on three-dimensional structures, as well as extending our methodologies to more complex geometries.

Kinetic and in Situ Analysis for Ion Transport Process in Copper Electrodeposition Using Polyelectrolyte Membranes

Electrodeposition of metals has been one of the most important techniques for fabrication of microelectronics and semiconductor elements in printed circuit boards and electronics device manufacturing. From the industrial perspective, the management of electrodeposition bath is crucial to maintain product quality, productivity and long-term stability of the bath, the subject of which includes bath temperature, concentration of metal salts, supporting electrolytes, and various additives. Although these parameters have been optimized to achieve desirable deposition rate, depending on the product type and morphology, some environmental issues regarding with generating mist, sludges, and waste effluent during electrodeposition process are becoming apparent. Additionally, current electrodeposition process has been developed for substrates with large surface area and for large scale production of electronic components and could not be suitable for recent demand of small-lot, site-selective and multiproduct device microfabrication. Therefore, high-performance deposition system, allowing site-selective electrodeposition of metals without generation of large amount of effluents, needs to be developed to impact above environmental and cost perspectives. Recently, we reported a novel method for electrodeposition of metals using polyelectrolyte films attached on cathode substrate (solid electrodeposition: SED) [1]. The SED process enables one to deposit metals directly on the cathode surface from metal ions inside solid polyelectrolyte membranes and has desirable advantages including higher deposition rate, site-selectivity, and deposition using lower concentration electrolyte solution without additives. In this SED process, thin polyelectrolyte membrane sandwiched between electrodes effectively concentrates metal ions through interfacial penetration, which increases the conductance between the electrodes and realizes solid-state electrodeposition that produces no mist, sludge, or even waste effluent.In this study, we present mechanistic analysis of the SED process, including transport kinetics and equilibrium reaction of copper ions at solution/membrane interface (Figure A). We show that both detailed experimental results and theoretical calculations reveal that ion transfer in the present electrodeposition system is a penetration-controlled process at the solution/polyelectrolyte interface, providing an inherently different ion-transport mechanism compared to that of conventional diffusion-controlled electrodeposition. Several parameters including penetration rate constant, electrode geometry, and distance between polyelectrolyte and anode are varied to investigate the ion-transport process in the SED system. When the anode is slightly apart from polyelectrolyte film to introduce electrolyte layer but is closer as far as possible to it, greater current density for copper electrodeposition is achieved at steady state than that for the systemwhere the membrane is sandwiched by electrodes (Figure B). This can be due to maximum ion penetration rate and minimum resistivity of electrolyte layer, providing better deposition setup for high performance electrodeposition. Additionally, we also performed in situ analysis of concentration of copper ions inside polyelectrolyte film via visible absorption spectroscopy using a miscofiber during electrodeposition. As a result, concentration of copper in the polyelectrolyte film decreased initially and then became constant (steady state) as the deposition proceeded, a fashion of which was quite similar with that of current-time curves simultaneously acquired during constant-voltage electrodeposition.The developed deposition setup demonstrates stable electrodeposition of copper using aqueous copper sulfate solution with no supporting electrolytes and/or additives at deposition rate of few micrometers per minute. As a site-selective deposition tool, the SED process can be used to fabricate microelectronic and even semiconductor circuit elements in a manner that resembles stamping deposition, and is suitable for small-lot, on-demand, and multi-product microfabrication.Reference:[1] K. Akamatsu, S. Nakano, K. Kimura, Y. Takashima, T. Tsuruoka, H. Nawafune, Y. Sato, J. Murai, H. Yanagimoto, ACS Appl. Mater. Interfaces, 13 (2021) 13896-13906. Figure 1