(449b) Interfacial Phenomena in Copper Galvanic Displacement Onto Silicon
Galvanic displacement is a selective method for depositing metals onto oxidizable substrates, such as silicon. In this process, metal ions from solution are reduced, with oxidation and dissolution of the substrate occurring simultaneously to complete the oxidation-reduction pair. Thus, metal deposition occurs only on oxidizable substrates, allowing deposition of patterned metal films on silicon, which can be used in a variety of applications, such as metal structures in microelectromechanical systems (MEMS) or metal catalysts in microreactors. In order to optimize this technique for different metals and applications, a better understanding of the deposition mechanism and the effects of solution parameters on deposition rates and film properties is needed. In this work, we examine how the deposition rate and film structure are affected by reaction kinetics and diffusion through both the external boundary layer and the porous copper. Silicon rotating disk electrodes were used to analyze the respective rates of deposition kinetics and boundary layer diffusion. Results conform well to the Koutecky-Levich equation, suggesting diffusion and reaction in series. Deposition rates decrease with the square root of time, indicating that diffusion through the growing film is one of the limiting steps in the reaction. In addition, reactant concentrations were varied in order to determine rate laws for deposition and to better understand the deposition mechanism. Deposition rates are proportional to copper sulfate concentration over the concentration range studied (0.001 ? 0.01 M), and rates also increase linearly with increasing amounts of HF for concentrations ranging from 0.05 to 0.3 M. This demonstrates that the respective driving forces for both the Cu reduction/deposition and the Si dissolution/oxidation reactions influence the deposition rate.