Thermal stability of Cu/α-Ta/SiO2/Si structures

Abstract The thermal stability of the Cu/α-Ta/SiO 2 /Si structures is investigated. Tantalum oxides are first observed at the interface between Cu and Ta due to residual oxygen in the annealing ambient at low annealing temperatures (about 600 °C). Ternary Cu–Ta oxides and/or Ta oxides rather than Cu oxides are found at the Cu top layer on account of the out diffusion of Ta. After high temperature annealing (up to 750 °C), polycrystalline Tantalum oxides (Ta 2 O 5 ) and Ta-rich silicides (Ta 5 Si 3 ) are found as dominant products due to the dissociation of SiO 2 . A severe intermixing of Cu, Ta and SiO 2 was observed after 800 °C annealing. First a drop and then an increase in sheet resistances were observed, the former possibly resulting from grain growth and impurities removal in Cu films, and the latter from the reduction of Cu thickness and formation of high resistivity products. The α-Ta films with a thickness of 25 nm have good barrier effectiveness up to 750 °C. The degradation of α-Ta film is mainly caused by self oxidation, silicidation and bidirectional diffusion.