Oscillations of open-circuit potential during immersion plating of silicon in CuSO4/HF solutions

The paper analyzes the nature of oscillations of open-circuit potential (OCP) during immersion plating of copper on silicon wafers. The oscillations are observed within well-determined interval of experimental conditions (composition of the electrolyte, doping level of silicon wafers, temperature, viscosity of electrolyte, etc.). Different to other known cases of the electrochemical oscillations, in the present case, there is no external source of the electrical current. We summarize here experimental findings relevant to this phenomenon and analyze possible reasons for the occurrence of the OCP oscillations. The effect is well fit by the general phenomenology of chaos-order transitions in complex chemical systems. We present a model for the oscillatory behavior which involves simultaneous reactions of Cu deposition and oxidation of silicon wafer, generation of local mechanical stress in the system, nonlinear electrochemical etching of silicon, localization of the electric field at the etched surface, etc.