Leveling effects of thiourea on copper electrodeposition

Metal electrodeposition is performed to change the character of substrates in many industrial applications. The surface roughness of the electrodeposit is one of the important qualities to be considered in the electrodeposition process. In this thesis, copper electrodeposition from sulfate baths containing organic additives was studied. The study was focused on the effect of thiourea on the electrochemistry and morphology of copper upon electrodeposition.; The research was carried out by different electrochemical techniques. Cyclic voltammetry was used to study the mechanism and kinetics of the electrochemical reactions that occur on top of the copper electrode. Sensitive in-situ gravimetric measurements of the working electrode were carried out by monitoring the frequency change of a quartz crystal microbalance (QCM). To monitor the attendant changes in the morphology of the electrode surface, two optical microscopy techniques were employed. The first was phase detection interferometric microscopy (PDIM) which has a vertical resolution of about 0.6 nm. The second was confocal laser scanning microscopy (CLSM). The CLSM performs optical sectioning of the surface of a rough sample yielding a three dimensional mapping of the surface.; It was found that at low concentrations of thiourea ({dollar}{dollar}0.05 mM), the deposition rate of copper was suppressed due to the formation of a thick adsorbed layer of thiourea on the electrode surface which behaves as a barrier to the deposition process.; Photolithography was used to create a patterned copper surface to study the leveling aspect of thiourea. It was found that, geometrical leveling (the observed leveling when deposition is uniform) of the surface had a larger effect than the chemical leveling of thiourea. As a result, thiourea affects the surface morphology through surface effects rather than bulk solution effects as predicted by the diffusion-adsorption theory of surface leveling.