Confocal laser scanning microscopy, electrochemistry, and quartz crystal microbalance studies of leveling effects of thiourea on copper deposition

Three techniques were used to evaluate and study the effect of additives in the electrodeposition process. The evolution of surface profiles on model copper surface topography was monitored by confocal laser scanning microscopy (CLSM) in the presence of different concentrations of thiourea in copper sulfate solutions. The model surfaces were fabricated by photolithography. Along with the CLSM, concurrent measurements of electrochemistry and quartz crystal microbalance (QCM) were made. It was found that thiourea acted as a mediator in the electrochemical reactions that occurred at the electrode surface as revealed by current efficiency measurements. The cathodic consumption of thiourea was found to be negligible and it was strongly adsorbed on the surface. From the CLSM and QCM, it was found that thiourea acted as a brightening agent and did not exhibit any leveling ability.