Hole Trapping in Reoxidized Nitrided Silicon Dioxide.

摘要

The nitridation of silicon dioxide gate dielectrics for metal-oxide-semiconductor (MOS) devices has been reported to reduce interface state generation by ionizing radiation, and also to reduce midgap or threshold voltage shift due to hole trapping. However, nitridation is also known to introduce substantial numbers of large cross-section electron traps. These are eliminated by a reoxidation step. In this paper we report an investigation of the hole trapping behavior of reoxidized nitrided oxides. Radiation-induced hole trapping in nitrided oxides and reoxidized nitrided oxides was investigated. Midgap voltage shift in reoxidized nitrided oxide capacitors was observed to saturate rapidly with dose, while the voltage shift nitrided oxide capacitors continues to increase. Reoxidized nitrided oxide capacitors exhibited the unusual characteristic of greater voltage shifts when irradiated under negative bias. It is proposed that a high density of small cross section traps exists in the nitrided oxide, while the traps in reoxidized samples are larger in cross section and concentrated in the upper half of the dielectric. An etch-off experiment demonstrated that the majority of these traps lie within approx. 7 nm of the gate. Reprints. (kt)