Analysis of Leakage Current in Cu/SiO2/Si/Al Capacitors under Bias-Temperature Stress

Abstract

An investigation was carried out of the conduction mechanism by which leakage current arises in Cu/SiO2/Si/Al capacitors under bias-temperature (BT) stress. C–V measurements on the capacitors before and after BT stress revealed that the stress reduces the capacitance of the Si depletion layer and induces the formation of interface states at the SiO2/Si interface. Secondary ion mass spectroscopy (SIMS) measurements on samples after BT stress showed the presence of Cu not only in the oxide, but also at the SiO2/Si interface. These results indicate that BT stress causes Cu ions to drift through the SiO2 film as far as the Si substrate. The good linearity of the ln (I/E) versus E1/2 curve suggests that current conduction is due to Poole–Frenkel emissions. The origin of the Poole–Frenkel current is also discussed based on a study of how BT stress at a negative bias affects the gate current of the capacitors.