Nucleation Of Copper Research Articles

Copper electrocrystallization from acidic sulfate electrolyte containing MPS additive

Copper electrodeposition and nucleation on a glassy carbon electrode from acid sulfate electrolytes in the presence of 3-mercapto-1-propanesulfonate sodium salt (MPS) and its combinations with chloride ions (Cl) or/and polyethylene glycol (PEG) were investigated by utilizing cyclic voltammetry (CV), chronoamperometry (CA) and scanning electron microscopy (SEM). CV results indicate that MPS and MPS–PEG inhibit whereas MPS–Cl and MPS–PEG–Cl accelerate copper deposition. CA and SEM results suggest that copper nucleation follows an instantaneous nucleation mechanism with three-dimensional growth from all baths at the studied deposition potentials. The copper nucleation rate and nuclei number density are increased greatly in the MPS–Cl and MPS–PEG–Cl baths.

Formicary-like carbon nanotube/copper hybrid nanostructures for carbon fiber-reinforced composites by electrophoretic deposition

An electrophoretic deposition process has been applied to produce unique carbon nanotube (CNT)/copper nanostructures on the carbon fiber surfaces. During the deposition process, ionized copper and positively charged CNTs are accelerated towards the carbon fiber under applied electric fields. An interconnected formicary-like network of nanotubes and nanoparticles is formed where copper nucleation and growth occurs predominantly at nanotube crossing and edge-contact locations. When embedded in a structural composite the CNT/copper structures create a highly conductive and strongly bonded network shown by significant enhancements in both electrical conductivity and interlaminar shear strength as compared to composites without the CNT/copper nanostructures.

Simulation of electrochemical nucleation in the presence of additives under galvanostatic and pulsed plating conditions

Galvanostatic nucleation of copper onto pretreated ruthenium is investigated using experimental methods and numerical simulations in the presence of two different suppressor molecules; polyethylene glycol (PEG) and ethylene glycol–propylene glycol–ethylene glycol block copolymer (EPE). The model parameters have been largely determined from electrochemical characterization. Results suggest that a fast adsorption rate of the suppressor results in higher nucleus densities. Simulation results provide insight why EPE is more effective than PEG at increasing nucleus density. In addition, the simulations are used to predict the impact of pulse plating paramaters, showing that both the properties of the additive and the waveform need to be considered to optimize nucleus density enhancement.

Tailoring Copper Island Density for Copper Plating on a RuTa Substrate

The electrochemical nucleation and growth of copper on a ruthenium-tantalum (RuTa) alloy has been studied using galvanostatic methods. The experimental results show that the island density is highly dependent on the bath composition and deposition parameters. High island density was achieved with higher applied current, addition of suppressor and low copper concentration in the plating bath.

Seedless Copper Electrodeposition onto Tungsten Diffusion Barrier

Copper was electrodeposited directly onto a sputter-deposited tungsten diffusion barrier layer in an acidic copper–ammonium–citrate bath. The nucleation characteristic of copper deposits according to applied cathodic potential was investigated. The nucleation mode, nuclei density, and dominant copper species to be preferentially reduced were critically dependent on the applied cathodic potential. Pure instantaneous or progressive nucleation of copper was not observed, but instead, mixed nucleation mechanisms appeared. For low cathodic potentials, the copper deposits, which were reduced mainly from cupric ions, showed consequently a progressive nucleation characteristic despite initial instantaneous nucleation. For large cathodic potentials, the instantaneous nucleation of copper was achieved from the reduction of copper complexes following the early stage of progressive nucleation. The copper nuclei density of calculated for filling the sub-70 nm damascene structures was approached by applying large cathodic potentials.

On the mechanism of nucleation of copper precipitates upon aging of Fe-Cu alloys

Structure of the Fe-5.5% Cu alloy has been studied after aging at 500°C to show that the lattice of copper precipitates changes with increasing time of holding at a temperature from bcc to 9R to fcc. The free energy of the solid solutions and the phase-separation diagrams of the bcc and fcc phases of copper have been calculated. Barriers for the nucleation of copper particles with the bcc and fcc lattices have been evaluated. Factors that favor the appearance of intermediate structural forms of copper, which precede the formation of the stable fcc phase, are discussed.

Metallic Nanostructure Formation Limited by the Surface Hydrogen on Silicon

Constant miniaturization of electronic devices and interfaces needed to make them functional requires an understanding of the initial stages of metal growth at the molecular level. The use of metal-organic precursors for metal deposition allows for some control of the deposition process, but the ligands of these precursor molecules often pose substantial contamination problems. One of the ways to alleviate the contamination problem with common copper deposition precursors, such as copper(I) (hexafluoroacetylacetonato) vinyltrimethylsilane, Cu(hfac)VTMS, is a gas-phase reduction with molecular hydrogen. Here we present an alternative method to copper film and nanostructure growth using the well-defined silicon surface. Nearly ideal hydrogen termination of silicon single-crystalline substrates achievable by modern surface modification methods provides a limited supply of a reducing agent at the surface during the initial stages of metal deposition. Spectroscopic evidence shows that the Cu(hfac) fragment is present upon room-temperature adsorption and reacts with H-terminated Si(100) and Si(111) surfaces to deposit metallic copper. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) are used to follow the initial stages of copper nucleation and the formation of copper nanoparticles, and X-ray energy dispersive spectroscopy (XEDS) confirms the presence of hfac fragments on the surfaces of nanoparticles. As the surface hydrogen is consumed, copper nanoparticles are formed; however, this growth stops as the accessible hydrogen is reacted away at room temperature. This reaction sets a reference for using other solid substrates that can act as reducing agents in nanoparticle growth and metal deposition.

Effect of sulfate ion adsorption on the rate of copper electrocrystallization on Ag(111) face

The process of copper electrocrystallization on the Ag(111) face was studied in acidic perchlorate-sulfate electrolytes. Enhanced rate of charge transfer in the course of nucleation and growth of epitaxial copper crystallites was observed in the solutions with additives of sulfate ion as a result of local electrostatic effects under specific adsorption of anions. Copper nucleation parameters were estimated in the framework of the diffusion models and atomistic theory of electrochemical nucleation.

A Novel Mathematical Model for the Study of Electrochemical Nucleation of Metals on Foreign Substrates from the Analysis of Potentiostatic Current Transients

A numerical model has been developed in order to characterize the kinetics of electrochemical nucleation processes using chronoamperometric techniques. The main purpose has been to overcome the limitations of the Scharifker-Mostany model which is currently used to determine kinetics parameters and to reproduce current density profiles. The proposed model was validated using chronoamperometric data obtained for copper nucleation on gold electrodes in CuSO4 - H2SO4 solutions at pH 1.0, 25 ºC with 0.05 M copper concentrations for overpotentials in the range -100 and -300 mV.

Selective Nucleation and Growth of Cu and Ni Core/Shell Nanoparticles

A simple synthesis of core−shell nanoparticles (CSNPs) is reported using a modified polyol process. We found that it is possible to control the nucleation kinetics of nickel and copper salts in ethylene glycol by manipulating the boiling temperature of the solution. It is hypothesized that a 10 °C temperature difference is sufficient to separate out the nucleation of elemental copper and nickel nanoparticles.

Direct Cu Wet Seed on Barrier of TSV Wafer

Through Silicon Vias (TSVs) promise to provide shorter interconnect length and higher electrical connection density with reduced signal delay and power consumption for both multichip interconnection and packaging. To achieve void free electrolytic TSV gapfill, continuous seed is critical. While the TSV dimension scales down and the aspect ratio increases, continuous Cu seed coverage is harder to achieve by conventional PVD process. Giving the conformal nature of electrochemical process, direct electrolytic Cu deposition on barrier is an alternative to enable continuous seed coverage. The challenges for direct wet seed are: (1) the barrier layer, typically TiN and TaNx, is too resistive to achieve uniform thickness distribution by conventional copper plating processes. (2) the nucleation of copper on barrier oxides is difficult and the copper growth is dendritic. Designed for direct seeding on barriers, a novel chemistry has been developed. This alkaline (pH 9~10) bath has been demonstrated with TSV wafers with different barriers including Ta, TaNx, Ti, TiN. The process has shown to provide high nucleation density (10Exp11~10Exp12 nuclei/cm2) and continuous seed coverage can be achieved between 10 and 25nm thickness on most barriers. The deposition takes place at very negative plating potential while the current efficiency is maintained at >90%. The strong polarization enables in-situ barrier oxide reduction for some barriers, and pretreatment becomes not necessary. Elimination of oxides along with high nucleation density significantly enhanced the bonding strength between copper and barriers. The wet seed on all barriers including Ta, TaNx, Ti, TiN has passed ASTM D3359 cross-cut tape test. Electrolytic TSV gapfill on the wet seed is demonstrated for patterned TiN barrier TSV wafer. Void-free fills are achieved for the features with dimensions between 20 and 200 microns. In summary, the novel chemistry for direct copper wet seed deposition on barriers has been demonstrated to yield high nucleation density and uniform seed distribution with adequate adhesion, and the wet seed enables subsequent void free TSV gapfill.

Analysis of the Copper Electrodeposition Current Transients in Nitrates Media

This work deals with the kinetic changes originated by nitrate presence on copper nucleation. From analysis of experimental potentiostatic current transients recorded during copper electrodeposition from aqueous solutions, with and without nitrate ions, it is shown that when NO3- are present, the copper nucleation rate increases while the number density of active site almost remains constant for every applied potential considered.

Shape and size controlled fabrication of copper nanopowders from industrial electrolytes by pulse electrodeposition

In the present paper a novel approach to control size and shape of deposited copper particles and nanoparticles from industrial electrolytes at the ultramicroelectrodes (UME) is presented. The copper nanopowders were pulse deposited on different metallic substrates from copper electrorefinery electrolytes. The SEM and electrochemical measurements showed that the morphology and structure of copper deposit can be precisely controlled by using different substrates and kind of chronoamperometric pulses. By choosing appropriate UME metal it is possible to get either the growth of copper spherical clusters, nano-wires or smooth flat films of copper. It was found that increasing deposit potentials produces smaller nuclei and higher nuclei copper population density. The kinetics and mechanism of copper nucleation was studied as well. It should be noted that very high nucleation rates and apparent cathodic current densities can be obtained at the ultramicroelectrodes.

A simple electrochemical strategy for the characterisation of defects in alumina-coated metal substrates

A simple electrochemical procedure is proposed to obtain defect information in alumina-coated platinum substrates prepared by r.f. magnetron sputtering. The method makes use of cyclic voltammetry, chronoamperometry and scanning electrochemical microscopy (SECM), the alumina-coated samples being the working electrodes. Cyclic voltammograms, performed in solutions containing Ru ( NH 3 ) 6 3 + and Cu 2+ ions, indicated that the systems investigated, due to the presence of defects in alumina layers, behaved as arrays of recessed microelectrodes with no overlap of individual diffusion layers. These features, along with data obtained from steady-state voltammetry, nucleation of metallic copper in the defect sites and SECM images of copper-decorated defects, provided information on defect density and spatial distribution, as well as on average defect sizes.

Methodical aspects of studying the electroreduction of nitrate on modified single crystal Pt(hkl) + Cu electrodes

Technique of modification of basal faces Pt(hkl) by adatoms and epitaxial copper deposits is developed. Analysis of potentiostatic current transients of copper deposition/dissolution and atomic force microscopy showed that the activity of Pt(hkl) faces regarding the processes of copper nucleation and epitaxial growth increases in the sequence of Pt(111) < Pt(110) < Pt(100). The reaction of nitrate anion reduction is sensitive towards the surface structure, not only in the case of platinum, but also in the case of copper deposits (including a monolayer of adatoms). The highest process rate is observed for the Pt(100) electrode modified by a monolayer of adatoms or islands of bulk copper; nitrate reduction at the lowest rate occurs at Pt(111) + Cu electrodes. Structure-sensitive competitive adsorption of background electrolyte and nitrate anions is the factor that largely determines the kinetics of nitrate reduction on different faces of platinum single crystal and copper deposits.

Electrochemical Behavior of Copper(I) Oxide in Urea-Choline Chloride Room-Temperature Melts

The physicochemical properties of urea-salt based melts such as the 66.7-33.3 mol % mixture of urea and choline chloride are com-parable to those of many room-temperature ionic liquids. Copper (I) oxide dissolves in this melt to form complex ions. The standard heterogeneous rate constants and transfer coefficients for the Cu(I)/Cu(II) and Cu(I)/Cu(0) electrode reactions were determined in this melt at both glassy carbon and platinum electrodes by using cyclic and rotating disk electrode voltammetric methods. The elec-trodeposition of copper was investigated on glassy carbon by using chronoamperometry. Comparison of the dimensionless data with the corresponding theoretical models for three-dimensional nuclea-tion indicated that the copper nucleation process was intermediate between the limiting cases for instantaneous and progressive nuc-leation. This suggests that nucleation of copper on glassy carbon proceeded at a finite number of active sites.

Numerical simulation of solidification morphologies of pure copper by vacuum continuous casting using cellular automaton model and its experimental verification

The purpose of this study was to predict the morphologies of the solidification process for pure copper using vacuum continuous casting (VCC) and to verify its accuracy by comparing these findings with observed experimental results. A finite differential method and a cellular automaton (CA) model were used to simulate the macro-temperature field for nucleation and grain growth of pure copper using real data from actual casting operations. From the observed experimental results, the drawing speed of the VCC process was considered as the fundamental parameter. With the increase of drawing speed, morphologies of the copper changed and the position of the liquid–solid zone moved closer to the orifice of the mould. The solidification morphologies simulated with the CA model were in good agreement with the results from the actual casting experiment.

Electroreduction of cupric(II) ions at the ultramicroelectrodes from concentrated electrolytes – Comparison of industrial and laboratory prepared aqueous solutions of copper(II) ions in sulfuric acid electrolytes

The electroreduction of cupric ions has always attracted considerable attention because of its importance for both fundamental and applied aspects. In this paper, the electrodeposition of copper from concentrated real refinery and laboratory prepared electrolytes is investigated. The influence of the complex matrix present in industrial electrolytes (from which active animal glue and thiourea were removed) on the copper electrodeposition mechanism and kinetics was not sufficiently studied in the past. The same can be stated regarding the copper electroreduction investigations in concentrate electrolytes. The influence of potential and temperature on potentiostatic reduction of copper ions at gold ultramicroelectrodes in both electrolytes is studied by chronoamperometric methods. In both studied electrolytes the mechanism of copper nucleation was found to be diffusion controlled, 3D and progressive. The values of apparent bulk diffusion coefficients and the rates of copper nuclei formation in both industrial and synthetic electrolytes are estimated and compared. In both solutions the rate of nucleation increases with absolute value of potential and temperature. Increasing deposit potentials produces smaller nuclei and higher nuclei copper population density. In the whole studied temperatures and potentials ranges AN ∞ changes from 3.30 × 10 9 to 2.50 × 10 13 cm −2 s −2 in industrial and from 1.77 × 10 10 to 1.49 × 10 13 cm −2 s −2 in laboratory prepared electrolytes. The values of diffusion coefficients obtained for industrial and for laboratory prepared solutions do not differ markedly.

Electrodeposition of copper composites from deep eutectic solvents based on choline chloride

Here we describe for the first time the electrolytic deposition of copper and copper composites from a solution of the metal chloride salt in either urea-choline chloride, or ethylene glycol-choline chloride based eutectics. We show that the deposition kinetics and thermodynamics are quite unlike those in aqueous solution under comparable conditions and that the copper ion complexation is also different. The mechanism of copper nucleation is studied using chronoamperometry and it is shown that progressive nucleation leads to a bright nano-structured deposit. In contrast, instantaneous nucleation, at lower concentrations of copper ions, leads to a dull deposit. This work also pioneers the use of the electrochemical quartz crystal microbalance (EQCM) to monitor both current efficiency and the inclusion of inert particulates into the copper coatings. This technique allows the first in situ quantification or particulate inclusion. It was found that the composition of composite material was strongly dependent on the amount of species suspended in solution. It was also shown that the majority of material was dragged onto the surface rather than settling on to it. The distribution of the composite material was found to be even throughout the coating. This technology is important because it facilitates deposition of bright copper coatings without co-ligands such as cyanide. The incorporation of micron-sized particulates into ionic liquids has resulted, in one case, in a decrease in viscosity. This observation is both unusual and surprising; we explain this here in terms of an increase in the free volume of the liquid and local solvent perturbation.

Effect of composition of combined sensitization/activation solutions on chemical deposition of Cu-TiO2 ultrafine-grained composite coatings on diamond powders

We study the effect of combined sensitization/activation solutions on chemical deposition of ultrafine-grained composite coatings based on copper and anatase titania on diamond powders. The surface sensitization/ activation parameters influence the deposition kinetics of copper and composite coatings, determining the copper nucleation rate and making a special contribution to the predetermination of the dispersivity of components and the morphology of coatings.