Electrochemical impedance spectroscopy of copper deposition on silicon from dilute hydrofluoric acid solutions

Electrochemical impedance spectroscopy was used to probe the mechanism of copper deposition on silicon from dilute hydrofluoric acid solutions. Reaction parameters such as polarization resistance and space-charge capacitance were evaluated using an equivalent circuit model. The electrochemical impedance technique was found to be sensitive to parts per billion levels of Cu²⁺ ion in dilute hydrofluoric acid solutions. An inductive loop appeared in Nyquist plots only when Cu²⁺ ions were present in hydrofluoric acid solutions. Both the polarization resistance and inductance decreased significantly as the solution Cu²⁺ concentration increased. Addition of a nonionic surfactant to hydrofluoric acid solutions significantly altered impedance characteristics of the silicon/solution interface. Total reflection X-ray fluorescence results showed that illumination enhanced deposition of copper on silicon nearly an order of magnitude.