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

Abstract

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 N2 gases, where Ar partial pressure was kept constant at 3.0 mTorr and N2 partial pressure was varied. When N2 partial pressure was lower than 0.5 mTorr, surface oxidation of the TaN films advanced with time. However, when N2 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 N2 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.