Capacitance effect on Co-layer dissolution during pulse potentiostatic deposition of Co-Cu/Cu multilayers

Electrodepositon of Co-Cu/Cu multilayer was carried out employing two-pulse potentiostatic method from a sulphate based single solution electrolyte. Dissolution characteristics of thin Co-layer preceding a Cu-layer, were investigated using chronoamperometry, chronocolumetry and electrochemical quartz crystal microbalance (EQCM) techniques. Both galvanic displacement due to Cu²⁺ ions and cell capacitance effect were found to be responsible for the dissolution of Co-layer during pulse switchover from Co to Cu-discharge. Competitive effect of these two factors on Co-dissolution was found to depend solely on the choice of discharge potential pair of Cu and Co. Co-layer dissolution could be prevented on application of Cu-discharge potential very close to the point of onset of Co-reduction potential. An effort has been made to understand the thickness loss due to capacitance effect by adopting a double layer model. It was also seen that the Cu-layer formed due to galvanic displacement reaction was porous in nature, and allows the Co-layer underneath to corrode for several nanometers upon allowance.