Copper deposition onto silicon by galvanic displacement: Effect of silicon dissolution rate

The rates of Cu deposition onto rotating Si electrodes were measured to probe the effects of mass transfer, Cu2+ reduction, and Si oxidation and dissolution on deposition dynamics. Cu deposition rates were proportional to CuSO4 concentration and limited by Cu2+ diffusion and subsequent reduction at high HF concentrations ([HF]/[CuSO4]> 20). In contrast, Si dissolution limited film growth at low HF concentrations ([HF]/[CuSO4]< 10), and HF2- was identified as the most active Si etchant. The observed effects of rotation rate indicate that mass transfer of Cu2+ limits deposition rates, but mass transfer of HF does not. Open-circuit potential measurements and mixed-potential theory were used to develop a reaction-transport model that accurately predicts deposition rates over a broad range of Cu and HF concentrations. The structure of the films formed was probed by atomic force microscopy. The roughness of the Cu films decreased with increasing [HF]/[CuSO4] ratios, as Si surfaces became less oxidized, and lateral connectivity between Cu nuclei increased. (c) 2008 The Electrochemical Society.