Mechanism of copper electrodeposition by pulse current and its relation to current efficiency

The effects of pulse periods and duty cycles on the current efficiency of acid copper plating in a wide range of pulse periods from 200 to 0.02 ms were studied. It was found the current efficiency decreased with shortening pulses in the millisecond range but increased with shortening pulses in the microsecond range. A mathematical model based on the concept of equivalent circuit was employed to simulate the potential responses. Shortening the pulse period was found to change the rate-determining step from charge transfer and surface diffusion to the first step charge transfer. In the millisecond range, the current efficiency decreases with shortening pulse period due to the disproportionation of cuprous ions and the dissolution of copper adatom. However, in the microsecond range, the current efficiency was found to increase with decreasing pulse period because the adatoms are directly incorporated into steps and kink sites, and the disproportionation of cuprous ions or the dissolution of copper adatoms has less chance to occur.     

Mass transfer and current efficiency for the electrodeposition of silver in fluorosilicic acid solution

The stripping and electrodeposition of silver in fluorosilicic acid solution are irreversible reactions as indicated by cyclic voltammetry. The rate constant for the intrinsic heterogeneous cathodic deposition of silver was obtained as k _C ⁰ =40.77 exp(1.88–29.43 E _C ⁰ ) and the diffusion coefficient of the silver ion in fluorosilicic acid solution as 5.17×10^–5 cm² s^–1. Theoretical calculations of the concentration of silver ion correlated well with experimental data. The relationship between the diffusion layer thickness and the stirring rate was also obtained. Increasing the stirring rate and temperature, and decreasing the current density and concentration of fluorosilicic acid, caused an increase in the current efficiency for silver deposition on graphite.     

抑氢剂对锌-铁合金电镀阴极电流效率的影响

为抑制碱性锌酸盐体系锌-铁合金电镀中氢气的析出,提高阴极电流效率,在分析铁族金属原子结构的基础上,筛选得到了性能优良的负二价硫族化合物抑氢剂.研究了该抑氢剂对锌-铁合金电镀的阴极电流效率及电化学行为的影响.结果表明:抑氢剂对纯锌电镀阴极电流效率的影响很小,基本上保持在80%左右;加入抑氢剂可使锌-铁合金共沉积的阴极电流效率由未加抑氢剂时的63.28%提高到83.54%;抑氢剂的最佳用量为20mL/L.     

Effect of nickel on the electrodeposition of copper

The mechanism of copper electrocrystallization from various solutions has been investigated to determine the influence of foreign cations and, particularly, of nickel. The study was performed by cyclic voltammetry and scanning electron microscopy. In sulphate solutions the Na⁺ and NH⁴⁺ cations affect the copper deposition by changing the nucleation overpotential and the presence of nickel cations makes the copper deposition easier by decreasing the nucleation overpotentials of both copper and nickel. In chloride solutions, the strong adsorption of the chloride species prevents all other influences by blocking the active sites of nucleation and growth and, therefore, Na⁺ or NH⁴⁺ addition does not modify the copper deposition. Consequently, the nickel does not modify the nucleation overpotential of copper. Whatever the solution, sulphate or chloride, the anodic behaviour of the copper-nickel codeposits are similar to the anodic behaviour of bulk Cu-Ni alloys.     

镀铜研究中的电化学方法

综述了镀铜研究中常用的电化学方法,包括恒电位技术、线性电势扫描伏安法、恒电流技术和交流阻抗技术,展望了电化学方法在镀铜研究中运用的前景.     

Transient mass transfer rate of Cu ion caused by copper electrodeposition with alternating electrolytic current

Copper electrolysis is carried out in a stagnant 0.05 M CuSO₄ aqueous electrolyte under alternating current (AC) condition. Transient mass transfer rate of Cu²⁺ ion caused by copper electrodeposition with AC is studied theoretically and experimentally with the holographic interferometer. The effect of buoyancy convection developing along the vertical plane electrodes on the transient concentration boundary layer (CBL) structure accompanying with AC is focused on. Two different electrode configurations, the horizontal cathode over anode and the vertical electrode settings, are employed for this purpose. The CBL thickness tends to increase over long duration time in the former configuration, while it converges to a steady-state value in the latter. Both calculated and measured concentration profiles in the vertical electrode configuration exhibit the characteristic transient behaviors composed of the pulsating CBL (PCBL) in the vicinity of the cathode surface and the stationary CBL (SCBL) outside the PCBL. The appearance of the SCBL is ascribed to mass transfer by advection, and the overall CBL thickness depends on the hydrodynamic conditions such as the magnitude of buoyancy convection.     

Kinetics of copper electrodeposition in citrate electrolytes

The kinetics of copper electrocrystallization in citrate electrolytes (0.5M CuSO₄, 0.01 to 2M sodium citrate) and citrate ammonia electrolytes (up to pH 10.5) were investigated. The addition of citrate strongly inhibits the copper reduction. For citrate concentrations ranging from 0.6 to 0.8 M, the impedance plots exhibit two separate capacitive features. The low frequency loop has a characteristic frequency which depends mainly on the electrode rotation speed. Its size increases with increasing current density or citrate concentration and decreases with increasing electrode rotation speed. A reaction path is proposed to account for the main features of the reduction kinetics (polarization curves, current dependence of the current efficiency and impedance plots) observed in the range 0.5 to 0.8 M citrate concentrations. This involves the reduction of cupric complex species into a compound that can be either included as a whole into the deposit or decomplexed to produce the metal deposit. The resulting excess free complexing ions at the interface would adsorb and inhibit the reduction of complexed species. With a charge transfer reaction occurring in two steps coupled by the soluble Cu(I) intermediate which is able to diffuse into the solution, this model can also account for the low current efficiencies observed in citrate ammonia electrolytes and their dependencies upon the current density and electrode rotation speed.Nomenclature b, b ₁, b ₁ ^* Tafel coefficients (V^–1) - bulk concentration of complexed species (mol cm^–3) - (si*) concentration of intermediate C^* atx=0 (mol cm^–3) - C concentration of (Cu Cit H)^2– atx=0 (mol cm^–3) - C C variation due to E - C concentration of complexing agent (Cit)^3- at the distancex (mol cm^–3) - C _o concentrationC atx=0 (mol cm^–3) - C _o C _o variation due to E - Cv _s bulk concentrationC (mol cm^–3) - (Cit H), (Cu), (Compl) molecular weights (g) - C _dl double layer capacitance (F cm^–2) - D diffusion coefficient of (Cit)^3- (cm²s^–1) - D ₁ diffusion coefficient of C^* (cm²s^–1) - E electrode potential (V) - f ₁ frequency in Equation 25 (s^–1) - F Faraday's constant (96 500 A smol^–1) - i, i ₁, i ₁ ^* current densities (A cm^–2) - i i variation due to E - Im(Z) imaginary part ofZ - j - k ₁, k ₁ ^* , K₁, K ₁ ^* , K₂, K rate constants (cms^–1) - K rate constant (s^–1) - K ₃ rate constant (cm³ A^–1s^–1) - R _t transfer resistance (cm²) - R _p polarization resistance (cm²) - Re(Z) real part ofZ - t time (s) - x distance from the electrode (cm) - Z _f faradaic impedance (cm²) - Z electrode impedance (cm²) Greek symbols maximal surface concentration of complexing species (molcm^–2) - thickness of Nernst diffusion layer (cm) - , ₁, ₂ current efficiencies - angular frequency (rads^–1) - electrode rotation speed (revmin^–1) - =K ^–1(s) - _d diffusion time constant (s) - electrode coverage by adsorbed complexing species - (in0) electrode coverage due toC _s - variation due to E     

Copper electrodeposition on pyrolytic graphite electrodes: Effect of the copper salt on the electrodeposition process

The electrodeposition of copper on pyrolytic graphite from CuSO₄ or Cu(NO₃)₂ in a 1.8 M H₂SO₄ aqueous solution was investigated. The Cu deposits were formed potentiostatically and characterized by electrochemical methods, scanning electron microscopy, energy dispersive X-ray and X-ray photoelectron spectroscopy. It was found that the deposition of copper in the presence of CuSO₄ induced the codeposition of sulfate anions. In addition, electrochemical quartz crystal microbalance revealed that the increase of the Cu mass was higher than expected from Faraday's law with the CuSO₄/H₂SO₄ solution. These results confirmed the specific adsorption of anions during the Cu deposition. On the other hand, the use of Cu(NO₃)₂ resulted in a non-contaminated surface with different surface morphologies. The Cu nuclei size, the population density and the surface coverage were monitored as a function of the deposition potential. From the analysis of the chronoamperometric curves, the nucleation kinetics was studied by using various theoretical models. Independently of the Cu source, the nucleation mechanism follows a three-dimensional (3D) process. Copper nucleates according to an instantaneous mode when the deposition potential is more negative than −300 mV versus Ag/AgCl, while the nucleation was interpreted in terms of a progressive mode at −150 mV. The nuclei population densities were also determined by using two common fitting models for 3D nucleation and growth (Scharifker-Mostany and Mirkin-Nilov-Heerman-Tarallo). Their values are reported here as a function of the deposition potential.     

Unipolar and bipolar pulsed current electrodeposition for PCB production

This paper is concerned with the study of square-wave unipolar pulse and bipolar pulse reverse electroplating and, particularly, the determination of pulse parameters to optimise through-hole plating rates and uniformity in the production of printed circuit boards (PCBs). The Wagner number, derived from cathode polarization behaviour in electroplating solutions, with and without plating additives, and under pulse plating conditions, was used to rationalize the data obtained. Fundamental predictions were found to compare favourably with results obtained from practical plating tests.     

Mechanism of copper electrodeposition in the presence of picolinic acid

The influence of picolinic acid (PA) on copper deposition from a slightly acidic sodium sulphate electrolyte has been studied over a wide range of concentration and pH by cyclic voltammetry. The mechanism by which the copper electrodeposition process in the presence of PA takes place, depends on the chemistry and electrochemistry characteristics of the additive. Depending on the PA concentration and pH of the solution, five different cathodic current peaks are obtained, which are assigned to different steps involving copper deposition from free-Cu²⁺ ions and [Cu(PA)_n]²⁺ complex species as well as H⁺ ions electroeduction. Fine-grained, highly adherent and bright copper deposits were obtained.     

The estimation of the coulombic efficiency of zinc electrodeposition by measurement of current efficiencies at a rotating ring disc electrode

The rotating ring disc electrode (RRDE) offers a simple method for the determination of the current efficiency (CE) of zinc electrodeposition in acidic zinc sulphate electrolytes. The hydrogen evolved during zinc deposition can be detected at the ring. This allows estimation of the current due to hydrogen formation at the disc and hence CE for electrodeposition of zinc can be calculated. Investigations of the conditions under which reliable measurements of CE can be obtained are described. A correlation between CE, determined using the RRDE, and the coulombic efficiency (QE), determined by weighing the zinc deposit obtained after 2 h electrodeposition at constant current, is established for a range of electrolyte compositions. It is suggested that measurement of CE at a Pt–Zn RRDE provides an efficient means of estimating QE for zinc electrolytes.     

Galvanostatic electrodeposition of aluminium nano-rods for Li-ion three-dimensional micro-battery current collectors

Constant current and pulsed current electrodeposition of aluminium nano-rods, for use as three-dimensional (3D) Li-ion micro-battery current collectors, have been studied using an ionic liquid electrolyte (1-ethyl-3-methylimidazolium chloride/aluminium chloride) and a template consisting of a commercial alumina membrane. It is shown that the homogeneity of the height of the rods can be improved significantly by inclusion of a short (i.e. 50 ms) potential pulse prior to the controlled current deposition step. The latter potential step increased the number of aluminium nuclei on the aluminium substrate and the best results were obtained for a potential of −0.9 V vs. Al/Al³⁺. The obtained nanostructured surfaces, which were characterized using electron microscopy and X-ray diffraction, consisted of parallel aligned aluminium nano-rods homogeneously distributed over the entire surface of the substrate. A narrower height distribution for the rods was obtained using a pulsed galvanostatic approach then when using a constant current, most likely due to the less favourable diffusion conditions in the latter case. The results also indicate that depletion and iR drop effects within the nano-pores result in a more homogeneous height distribution. It is concluded that the height distribution of the nano-rods is controlled by a combination of the nucleation probability in each pore at the start of the experiment, and the homogeneity of the diameters of the pores within the commercial alumina membranes employed as the electrodeposition template.     

Kinetics of copper electrodeposition in the presence of triethyl-benzyl ammonium chloride

Quasi-steady state hydrodynamic voltammetry at a rotating-disc electrode and electrochemical impedance spectroscopy were used to investigate the influence of triethyl-benzyl-ammonium (TEBA) chloride on the kinetics of copper electrodeposition from sulphate acidic electrolytes. SEM and X-ray diffraction analysis were used to examine the morphology and the structure of copper deposits. The kinetic parameters (i ₀, _c, k ₀), obtained by both Tafel and Koutecky–Levich interpretations lead to the conclusion that TEBA acts as an inhibitor of copper electrodeposition process, as a consequence of its adsorption on the electrode surface. The influence of TEBA on the kinetics of copper electrodeposition was explained in terms of a reaction model confirmed by the simulated impedance spectra. TEBA acts only as a blocking agent competing for adsorption active sites of the cathodic surface with cuprous ions without changing the reaction pathway corresponding to the absence of the additive.     

Mechanism of electrodeposition of copper from cupric pyrophosphate solutions

Cathodic polarization curves were measured for copper in cupric pyrophosphate solutions of different concentrations and temperatures. A rotating disc electrode was used to eliminate concentration polarization. For all solutions, two potential regions are distinguishable in the polarization curve; one is less negative than a critical potential E_b around ?0.75 V vs sce (Region I) and the other more negative than E_b (Region II). A weak adsorption of pyrophosphate ions and hence some inhibition of the electrodeposition of copper is expected for Region I but there is no adsorption in Region II. The exchange current density i_o for the copper deposition was obtained by extrapolating the Tafel relation observed in Region II to the rest potential corresponding to the equilibrium potential. The following reaction mechanisms are proposed to explain the dependence of i_o on the concentration of Cu(P₂O₇)^6?₂ and P₂O^4?₇ ions.

Apparent activation energies are estimated to be about 11 kcal/mol in both cases.     

HEDP溶液体系电沉积铜的电化学行为

采用循环伏安曲线法和阴极极化曲线法研究了0.388 mol/L HEDP(羟基亚乙基二磷酸)+0.160 mol/L Cu SO4·5H2O溶液体系(p H=9.3或9.5)电沉积铜的电极过程动力学规律和添加剂对阴极极化的影响。结果表明,HEDP溶液体系电沉积铜是Cu2+的一步放电还原,遵循无前置化学转化反应或前置化学转化反应很快的不可逆电极过程动力学规律。添加剂HES(含硒无机化合物)和复配添加剂HES+HEA(多胺高分子聚合物)具有促进电沉积铜和抑制析氢的双重作用,提高了HEDP溶液体系电沉积铜的阴极电流效率。     

Influence of the interaction between chloride and thiourea on copper electrodeposition

The interaction between chloride and thiourea in copper electrodeposition in a sulfate-plating bath was investigated. The sole addition of thiourea to the bath increased the polarization of the electrode potential during copper deposition, leading to very fine and smoothly structured deposit but with microscopic nodules distributed over the surface. When chloride was added to a plating solution containing thiourea, the copper deposition mechanism was changed, showing a depolarization of the electrode potential, and the copper deposits were found to have a relatively rougher microstructure, but without the formation of microscopic nodules. However, rough deposit surfaces having no distinct pattern were formed at the macroscopic scale. Observations of roughening evolution show that the rough surface was initiated from small holes formed across the deposit surface during the initial stage of deposition that eventually developed into visibly rough deposits. The copper deposition inside these holes and at other areas was expected to undergo different deposition mechanisms. Copper deposition in the areas that ultimately developed into holes was almost totally inhibited by the thiourea–Cu(I)–chloride complex film, not just in the grain growth process, but over practically the entire electrodeposition process. Conversely, copper deposition occurred in other areas under conditions where nucleation proceeded, but grain growth was inhibited to produce a fine, homogeneous microstructure. An uneven deposit surface that had different microscopic structures in different areas was then formed. The structure of the thiourea–Cu(I)–chloride film was strongly affected by the current density and appeared to break down completely if sufficiently high current density was applied to yield a fine and homogeneous microstructure that was also macroscopically smooth.     

Impedance investigation of the mechanism of copper electrodeposition from acidic perchlorate electrolyte

The mechanism of the copper electrodeposition from acidic perchlorate electrolyte has been investigated with polarization and impedance methods. The impedance of the copper electrode in copper perchlorate electrolytes has been measured as a function of frequency for different Edc overpotential values and different copper(II) ion concentrations. The relations between the shape of a complex plane impedance display and the copper electrode potential values as well as the concentration of CuII ion were analysed in terms of the electrode reaction mechanism. It is shown, that the presence of the intermediate cuprous ion and its sinusoidal change of transport rate is one of the main factors determining the depressed shape of the impedance arc. The quantitative relation between the faradaic impedance and the rates of electrode reaction rates was established. The impedance arc was simulated with a set of parameters involving: rate constants, Tafel slopes, diffusion coefficient of cuprous ion and double layer capacitance. The rate constants were calculated with respect to ECu2 + Cu00 as: k10 = 6.50 × 10−5 cm s−1, k20 = 0.139 cm s−1, k−20 = 1.88 × 10−7 mol cm−2 s−1.     

The influence of mass transport on the deposit morphology and the current efficiency in pulse plating of copper

The morphology of copper deposits formed by pulse plating from an acid sulphate electrolyte is investigated. The steady and non-steady state conditions of mass transport are controlled by use of a rotating hemispherical electrode. Below the limiting pulse current density (i _pl), granular deposits are observed. Abovei _pl, regardless of the individual values of the pulse parameters, dendritic deposits are formed. Measured current efficiencies are compared with a theoretical model, which predicts a rapid decrease of the efficiency with the increasing ofi _p/i _pl fori _p/i _pl greater than one, wherei _p is the applied pulse current density. For a given set of pulse parameters, the measured current efficiency increases with the deposit thickness due to the increase of the effective surface area. This effect is particularly important for dendritic deposits.Nomenclature A apparent (effective) surface area (cm²) - A ₀ geometrical surface area (cm²) - D diffusion coefficient (cm²s^–1) - i current density (A cm^–2) - i _l limiting current density (A cm^–2) - i _p pulse current density (A cm^–2) - i _pl pulse limiting current density (A cm^–2) - i _m average current density in pulse plating (A cm^–2) - N _p dimensionless numberN _p=i _p/i _pl - N _m dimensionless numberN _m=i _m/i _l - t _p pulse time (s) - t_p relaxation time (s) - duty cycle, =t _p/(t _p+t_p) - (steady state) diffusion layer thickness (cm) - _p pulsating diffusion layer thickness (cm) - current efficiency - kinematic viscosity (cm²s^–1) - rotation rate (rad s^–1)