Electron trapping in thin gate insulators prepared using a two-step silicon oxidation procedure

Abstract

A two-step process for oxidation of silicon results in an improvement in thin silicon dioxide breakdown voltage distributions. This conclusion, previously demonstrated for approximately 8-nm-thick oxides, is shown to be valid for thicker oxides as well. However, no information was previously available concerning the trapping characteristics of gate insulators formed using the two-step oxidation process. In this work, we used the substrate hot electron effect to investigate the trapping characteristics of new insulators. Based on the degradation rate of both threshold voltage and linear transconductance of metal-oxide-semiconductor transistors, we conclude that the two-step oxidation process reduces the rate of substrate hot carrier induced degradation, in addition to improving the gate insulator integrity. We also observed a strong correlation between the degradation in linear transconductance and threshold voltage. This correlation is explained by the generation of, and trapping at, interface states and bulk oxide traps. Under our experimental conditions, the interface state density increases sublinearly with the number of electrons injected into the gate insulator. Investigation of the trapping kinetics indicates the presence of two trap species, only one of which influences the degradation in linear transconductance.