Dual role of fluorine at the Si-SiO2 interface

Fluorine is known to have both a beneficial and adverse role on the characteristics of Si-SiO2-based devices. Here we report the results of first-principles calculations in terms of which we elucidate this dual behavior. On one hand, we find that Si-F interfacial bonds are resistant to depassivation by hydrogen species, with the process being shut down in the presence of holes. However, we also show that any excess of fluorine has a negative effect since it either creates stretched bonds, which can act as carrier traps, or disrupts an abrupt interface by cleavage of Si-Si bonds. (C) 2004 American Institute of Physics.