In situ TEM study of the transitions between crystalline Si and nonstoichiometric amorphous oxide under bipolar voltage bias

The electrical responses, either structurally or chemically, at the interface between a SiO₂ thin film and a single crystalline Si substrate are an important research subject in Si-based devices. Dielectric breakdown-induced epitaxial migration of Si into SiO₂ has been reported as a degradation mechanism in field effect transistors. Here, we show a direct observation of electric field induced conversion of single crystalline Si to nonstoichiometric amorphous oxide starting from the Si/native oxide interface using in situ transmission electron microscopy. We further show that nanocrystalline Si can form in the amorphous oxide under a voltage bias of reversed polarity. Electron energy loss spectroscopy and energy dispersive X-ray spectroscopy analyses indicate that the observed amorphization process was caused by the oxidation of Si and the recrystallization process was caused by the reduction of nonstoichiometric amorphous silicon oxide. Both transitions are a result of field-driven directional migration of oxygen which originally comes from its native oxide layer.