Relationship between hole trapping and interface state generation in metal-oxide-silicon structures

We have discovered a general relationship between the location of trapped holes and the subsequent generation of interface states. Experimentally, we find that a hole can become an interface state, but it must first be trapped between 20 and 70 Å from the Si/SiO₂ interface (near-interfacial hole trap) and then transfer to within 18 Å of the interface (interfacial trapped holes). Finally, the hole captures an electron and becomes an interface state. The transfer process between near-interfacial and interfacial trapped holes does not seem to be a simple release-capture process. Rather it appears to involve a complicated migration of the trapped hole defect towards the interface. Radiation-hardened oxides are shown to have a similar number of near-interfacial traps, but these traps are shallower than those in the soft oxides.