Wear-out and breakdown of rf sputtered Ta₂O₅ films on silicon

Abstract

The evolution of the gate voltage during the constant current stress of Ta₂O₅ films grown on silicon exhibits an additional decreasing region, compared to the case of SiO₂ films. That phenomenon has been previously attributed to the thickness lowering of the ultrathin SiO₂ interfacial layer naturally grown during the Ta₂O₅ deposition. Based on the previously proposed method of the evolution of the capacity in accumulation with the stress time, a simplified phenomenological model of capacitors in series was developed and employed as a tool for monitoring the degradation of the insulating film. In some cases breakdown events manifested by abrupt changes of the capacity in accumulation were observed, e.g., the case with the voltage on the silicon dioxide films. In other cases, saturation of the capacity in accumulation was detected, indicating continuous degradation of the SiO₂ layer till its final destruction. The above effect was not observed in SiO₂ films and can be peculiar for Ta₂O₅/SiO₂ or similar stacked layers.