Dynamics of copper deposition onto silicon by galvanic displacement

Copper was deposited onto silicon rotating-disk electrodes in 3.0 M HF to determine the effects of boundary-layer mass transfer and surface reaction kinetics on Cu deposition rates. For all solution compositions tested [(CUSO4] = 0.0010 - 0.020 M, [HF] = 3.0 M), the Cu deposition rate was proportional to the concentration of Cu2+ and was under mixed diffusion and surface kinetic control. HF was used to dissolve oxidized Si, and a stoichiometry of one Cu atom deposited for each Si atom that is oxidized and dissolved was deduced from a combination of UV-visible spectroscopy and mass change experiments. These results indicate that Si dissolves as Si2+, not Si4+, as is commonly assumed for galvanic displacement. Mixed-potential theory was used to further analyze the reaction mechanism, and deposition rates and open-circuit potential values predicted from this method a.-reed well with experimental results during the initial stages of Cu deposition. Deposition rates decreased abruptly when film thicknesses exceeded 150 nm, and optical microscopy revealed buckling in these Cu films. This buckling occurred in response to compressive stresses in the films and decreased deposition rates by partially detaching Cu films from the Si substrate. (C) 2008 The Electrochemical Society.