Stress Induced Degradation of High-k Gate Dielectric Ta_2O_5 Thin Films on Silicon

摘要

This work describes the influence of constant current stress induced degradation in reactively sputtered Ta_2O_5 thin film in pure argon and argon plus nitrogen within plasma. Capacitors were fabricated and the interface was characterized using I-V and C-V methods. X-ray diffraction (XRD) technique revealed the presence of N_2 content in Ta_2O_5 films. A comparison between Ta_2O_5 films doped with and without N_2 with respect to flat band shift and leakage current density is also presented. Post deposition annealing at 650° CreducesO/Ta ratio because of the formation of suboxides. It results in high quality TaO_x film with high capacitance and low leakage current. On being stressed, flat band voltage in annealed devices shifts towards negative direction as a result positive charge traps are observed in high-k thin films. Incorporation of nitrogen in Ta_2O_5 dielectric films retain the intrinsic effect that significantly diminish the electron leakage current through deactivating the V_o (oxygen vacancy) related gap states.