(449a) Electrochemistry of Active Metals in Aqueous Hf

Removal of the native oxide from Ta and TaN and from Ti and TiN surfaces is required for electrochemical ULSI processing, including both direct electrodepositon onto these materials and electrochemical planarization (ECP). We have shown by cyclic voltammetry and electrochemical impedance spectroscopy (EIS) that aqueous HF can dissolve the native oxide from Ta and TaN. HF is similarly effective in removing the native oxide from Ti surfaces. Electrochemical impedance spectroscopy (EIS) of Ta at different fluoride concentrations illustrates that the native oxide dissolves at low pH, as shown by the dramatic reduction in the charge transfer resistance (Rct). However, EIS studies also reveal a low frequency inductive loop, suggesting that although the native oxide has been removed, an ultrathin thin passive film of unknown origin remains. Applications of HF electrochemistry to both direct electrodepositon of Cu onto Ta/TaN and electrochemical planarization (ECP) of Ta/TaN will be discussed. Applications to direct electrodeposition onto Ti and to Ti ECP will also be discussed. The use of fluoride-containing solutions also allows W electrodeposition.