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)