Electrochemistry of Ta in Aqueous HF

Abstract

Understanding of aqueous Ta electrochemistry is important due to the development of electrochemical methods for Cu seed layer deposition and the development of low-stress electrochemical methods for Ta/TaN removal. Because Ta is a highly active metal, Ta electrochemistry in aqueous electrolytes has been largely unknown. We have studied the use of HF for dissolution of the native oxide, Ta2O5. Voltammetry and impedance studies of Ta discs, Ta/Si wafers, and TaN/Si wafers are reported here. Although the native oxide can be dissolved, Ta remains covered by an ultrathin film at most potentials in 2.5 M HF. Thus although Cu electrodeposition easily occurs from 2.5 M HF, adhesion is poor. Only galvanic displacement followed by electroless Cu deposition was successful in forming an adherent Cu film on a Ta rod electrode. On the other hand, despite the presence of this interfacial film, electrochemical dissolution of both Ta and TaN is easily demonstrated.