Influence of Surface Oxide of Sputtered TaN on Displacement Plating of Cu

Copper can be deposited on TaN by displacement electroless plating when a surface oxide layer is removed by wet chemical etching. For application to ultralarge-scale integrated (ULSI) interconnection technology in which very thin TaN barrier films are used, it is essential to form a stable TaN film with minimal native oxide thickness. In this study, we investigated surface oxidation of sputtered TaN films kept in air atmosphere by X-ray photoelectron spectroscopy (XPS) analysis. TaN films were sputtered in a mixture of Ar and N 2 gases, where Ar partial pressure was kept constant at 3.0 mTorr and N 2 partial pressure was varied. When N 2 partial pressure was lower than 0.5 mTorr, surface oxidation of the TaN films advanced with time. However, when N 2 partial pressure was higher than this value, oxidation of TaN film stopped at one monolayer. We confirmed that the redox potentials of TaN films formed with N 2 partial pressures higher than 0.5 mTorr are lower than that of Cu, which suggests that displacement plating of Cu is possible on TaN films with thickness smaller than 10 nm.