Effects of post-nitridation anneals on radiation hardness in rapid thermal nitrided gate oxides

Abstract

Effects of post-nitridation anneals on radiation hardness of metal-oxide-semiconductor (MOS) capacitors with rapid thermal nitrided (RTN) gate oxides have been studied. Post-nitridation anneals consisted of either rapid thermal reoxidation (RTO) in pure O2 or rapid thermal anneals (RTA) in pure N2 ambient. The radiation was performed by exposing devices to x rays at doses of 0.5–5.0 Mrad (Si). Comparing RTO and RTA anneals at the same temperature and time for given nitrided oxides, it was found that RTO enhanced the radiation hardness while RTA in N2 had detrimental effects, in terms of interface-state generation (ΔDit) and flatband voltage shift (ΔVfb). The strainless interfacial oxide regrowth during RTO of RTN oxides is responsible for the enhanced interface ‘‘hardness’’ of RTN/RTO oxides. A physical mechanism is described to account for the observation.