THEORY OF DEFECTS AND DEFECT PROCESSES IN SILICON DIOXIDE

Defects and defect processes are of particular importance in the thin SiO2 films that form an integral part of silicon-based metal-oxide-sem iconductor (MOS) electronic systems. To understand such effects, we ha ve carried out total-energy electronic structure calculations on large clusters of atoms chosen to simulate particular defects and their rea ctions. Here we consider two examples. (1) Electrical switching experi ments in thin oxides have been interpreted by a model in which a metas table state of the oxygen vacancy has a longer lifetime than seems the oretically reasonable. We suggest that this might be explained by diff erent time scales for local and longer-range atomic relaxations. (2) A serious problem occurs if boron diffuses from the polysilicon gate th rough the oxide in MOS devices. It has been found that hydrogen enhanc es and nitrogen inhibits the boron diffusion. We use the results of ou r calculations to discuss several possible explanations for these effe cts. (C) 1997 Elsevier Science B.V.