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 solutio ns. Reaction parameters such as polarization resistance and space-char ge capacitance were evaluated using an equivalent circuit model. The e lectrochemical 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 p resent in hydrofluoric acid solutions. Both the polarization resistanc e and inductance decreased significantly as the solution Cu2+ concentr ation increased. Addition of a nonionic surfactant to hydrofluoric aci d solutions significantly altered impedance characteristics of the sil icon/solution interface. Total reflection X-ray fluorescence results s howed that illumination enhanced deposition of copper on silicon nearl y an order of magnitude.