Electrochemical Study Of Copper Electrodeposition In 1-hydroxyethylene-1, 1-diphosphonic Acid Electrolyte

The technics of Copper electroplating obtained from cyanide bathswas commonly used in industry for hundreds of years. However, cyanideiskindofthelethalchemicalsthatcausessevereenvironmentalpollution.So concerns over the biological toxicity of cyanide have stimulated anextensive research for satisfactory alternative electrolytes.1-hydroxyethylene-1, 1-diphosphonic acid (HEDPA) electrolyte wasconsidered as the most potential plating bath in non-cyanide copperplating for its marked advantages, such as simple component, stablecoordination agent, excellent bonding force with basal body of iron.While the disadvantages are also existed, such as narrow ampere densitythat technics allowed, worse strike-off power and bonding force withbasal body of iron kirksite compared with cyanide bath. At present,themajor trend was to introduce additive and a second to HEDPAelectrolytein order to obtain a better performance, but less study of theory onadditive or a second ligand was did compared with study and report ontechnics.Theelectrodeprocessofcopperelectrodepositingonastainlesssteelelectrode in HEDPA electrolyte was investigated using the test ofelectrochemistry,suchaslinearsweepvoltammetry(LSV)technique,andtest of scanning electron microscope (SEM) and calculation of apparentactivation energy. It was found that (1) the reduction reaction of copper-ioncomplexonstainlesssteelelectrodewasnonreversible;(2)theprocess of reaction was controlled by steps of electrochemistry anddispersion,anditbelongedtothetypeofmixcontrol;(3)thepeakcurrentwhich appeared at -0.72V in the curve of potential-current density wasprobablycausedbydischargeofsome copper-ioncomplex atlowligancyexisting in the bath;(4) with the increase of temperature,polarizationcurve moved to plus potential direction,cathodic polarization minishedgradually,and both the changes would make crystal grain of clad layercrassitude;(5)apparentactivationenergyvaluesofcopper-ioncomplexatlow ligancy in Tafel area were universally lower than values ofcopper-ioncomplexathighligancy.The initial electrodeposition stage of copper and the influence ofCO₃^2- ions on the nucleation and growth of copper on a glassy carbonelectrode in HEDPA electrolyte were investigated using cyclicvoltammetry (CV) and chronoamperometry (CA) techniques. It wasfound that (1) the nucleation was three-dimensional (3D) and progressivein the electrolyte without CO₃^2- ions, while as the CO₃^2- ions in theelectrolyte increased, the three-dimensional nucleation developed aninstantaneous characteristic gradually; (2) there was an increase in thenuclear number density of nuclei on the surface with the increase ofpotential.The effect of electrochemistrical behavior caused by the joining ofTEA during copper electrodepositing in HEDPA electrolyte wasinvestigated using the test of electrochemistry(such as LSV technique)andSEM.Itwasfoundthat(1)itcanexpandtheextentofcurrentdensitypermitted by cathode when the TEA reached at certain content; (2) thenucleationwas3DandprogressiveintheelectrolytewithorwithoutTEA;(3) better quality of clad layer can be obtained after TEA was introduceded into HEDPA electrolyte. Meanwhile, the mechanism wasinferred according to the infra-red spectrum, calculation of equilibriumconstant and the results of experiments ahead. It was inforred that TEAexisting as dissociation when the content of TEAintroduced into HEDPAelectrolyte was little, and CuTEA(OH)₂ gradully increased with theincrease of TEA, finally, the behavior of electrochemistry and theinfra-red spectrum changed after the certain content of TEA in HEDPAelectrolyte.