Catastrophic breakdown in silicon oxides: The effect of Fe impurities at the SiO2-Si interface

Abstract

The behaviors of Fe impurities at the SiO2-Si interface of metal-oxide-semiconductor (MOS) capacitors was studied with electrical measurements and transmission electron microscopy. The MOS capacitors were fabricated on silicon wafers which had been intentionally contaminated by Fe+ ion implantation. It is confirmed that Fe impurities either scattered uniformly, or nucleated at the interface of SiO2-Si. Uniformly scattered Fe impurities lower the barrier height of the SiO2-Si interface. The nucleated Fe precipitates are in a metallic α-FeSi2 phase, penetrating both the silicon oxide and the silicon substrate. They degrade the MOS capacitors not only by reducing the barrier height of the SiO2-Si interface, but also by inducing weak spots in the silicon oxide where the electric field is strengthened and local tunneling currents are enhanced.