A kinetic study of direct copper plating via Pd catalyst and S ligand

A dual-reaction model has been proposed to explain the mechanism of direct copper plating on a nonconductor with the assistance of PdS. The reaction i n which charge passes through the sulfur ligand is responsible for the late ral growth of copper on the surface. The other reaction is the conventional cupric/copper deposition, which is responsible for the vertical growth of copper deposit. The exchange current density and rest potential of these tw o reactions have been evaluated via the potentiostatic method. When the [Cu 2+] is above 0.3 M, the exchange current densities of these two reactions w ere found comparable. However, for a low [Cu2+], the i(0) of lateral reacti on is significantly higher than that of vertical reaction. Furthermore, the slope partial derivative log i(0)/partial derivative log a(Cu2+) is about 0.58 for the vertical reaction, which is similar to that for the common cop per deposition reaction, but is only about one-third of that for the latera l reaction, which implies the occurrence of a different reaction. Regarding the effect of copper concentration on the equilibrium potential, partial d erivative E/partial derivative log a(Cu2+) is about 28 mV/dec, which is rea sonable based on the Nernst equation. However, in the case of lateral react ion induced by sulfet ligand, the slope is only 18 mV/dec, indicating again the existence of a different reaction. (C) 1999 The Electrochemical Societ y. S0013-4651(98)04-055-5. All rights reserved.