Superconformal electrochemical deposition of gold for metallization in microelectronic devices

A novel process for superconformal electrochemical deposition of gold has been proposed and demonstrated using 3-mercapto-1-propanesulfonic acid sodium salt (MPS) as additive in a sulfite-based gold electrolyte. At the optimized process conditions true bottom-up gold deposition was achieved, with which aggressive features such as those that are straight-walled and even re-entrant were completely filled without voids. In the process, the additive MPS functions as a suppressor that hinders electrochemical deposition of gold, as opposed to its function as an accelerator in electrochemical deposition of copper. The results obtained appear to suggest that the driving force leading to superconformal deposition of gold with the sulfite-based gold electrolyte in the presence of the grain refiner thallium and the additive MPS may primarily stem from the depletion of MPS inside features of interest as a result of its consumption and limited supply. (c) 2006 The Electrochemical Society.