Oxide thickness dependence of nitridation effects on TDDB characteristics

Abstract

Wet oxide thicknesses dependence of nitridation effects on electrical characteristics, charge trapping properties and TDDB (Time Dependent Dielectric Breakdown) characteristics have been investigated. It is found that the difference of conduction current between the wet and nitrided wet oxide increases with increasing oxide thickness both for negative and positive bias to the gate until constant current stress is applied. After the stress, with decreasing oxide thickness both in wet and nitrided wet oxide leakage current increases. Up to ∼ 60 Å no difference was observed between the wet and nitrided wet oxide but at ∼ 50 Å nitrided wet oxide has less increase of current comparing to the wet oxide for the same stress. In wet oxide with increasing stress current density initial hole trap decreases but electron trap increases whereas in nitrided wet oxide has less initial hole trap and also electron trap is less comparing to the wet oxide. Both in wet and nitrided wet oxide for negative bias stress, time to 50 % breakdown decreases with decreasing thickness but at ∼ 50 Å a turn-around effect was observed due to nitridation i.e., the 50 % breakdown time is greater for nitrided wet oxide comparing to the wet oxide. On the contrary, for positive bias stress 50 % breakdown time increases with decreasing oxide thickness both in wet and nitrided wet oxide. For positive bias also a turn-around effect is observed at ∼ 50 Å i.e., 50% breakdown time is less in nitrided wet oxide comparing to the wet oxide. The improved reliability of nitrided wet oxide at the thin region of ∼ 50 Å seems to be due to the increase of more SiN bond to the interface of oxide and Si comparing to the thick oxide of above ∼ 60 Å for the same nitridation conditions.