Copper drift in high-dielectric-constant tantalum oxide thin films under bias temperature stress

Abstract

The use of high-dielectric-constant (high-κ) materials for embedded capacitors is becoming increasingly important. Tantalum oxide (Ta2O5) is a prominent candidate as a high-κ material for embedded capacitor use. Metal drift in Ta2O5 (κ∼25) was investigated by bias temperature stress and triangular voltage sweep testing techniques on metal/Ta2O5∕SiO2∕Si structures. At a temperature of 300°C and 0.75MV∕cm bias conditions, Al, Ta, and Ti do not diffuse in Ta2O5, but Cu clearly showed a drift. The Cu drift is attributed to the lack of a stable Cu oxide which can limit Cu ion generation and penetration.