Copper electrodeposition from a pH 3 sulfate electrolyte

Kinetics and growth modes of copper electrodeposited from copper sulfate 0.8 M, pH 3 electrolytes are studied and compared to those for standard acidic sulfate baths. The influence of chlorides and three different additives (polyethylene glycol, a thiocompound and a quaternary ammonium salt) on steady state and transient electrokinetic behaviour, structure and morphology is investigated. Chlorides behave as a surface stabilizing agent, promoting epitaxy and contributing to the electrolyte microlevelling power. Each organic additive shows a specific effect which, however, may change substantially in the presence of other additives. Polyethylene glycol is a suppresser with the strongest action on copper electrodeposition, as shown by its effects on discharge kinetics and growth behaviour. The main role of the brightener (thiocompound) and the leveller (quaternary ammonium salt) consists in mitigating or tuning the surfactant blocking action respectively, realising the best balance between catalytic and suppressing factors. The pH 3 electrolyte is shown to be a valuable alternative to the standard acid bath, allowing higher deposition rates and promising improvements with regard to microthrowing power and growth control of thin films.