Energy Distribution of Positive Charges in Gate Dielectric: Probing Technique and Impacts of Different Defects

Positive charges (PCs) in gate dielectric shift the threshold voltage and cause a time-dependent device variability. To assess their impact on circuits, it is useful to know their distribution for a wide energy range both within and beyond silicon bandgap. Such a distribution is still missing, and a technique for its extraction has not been demonstrated yet. The central objective of this paper is, for the first time, to develop a new fast technique and to demonstrate its capability for probing the energy distribution of PCs over such a wide energy range. Results show that PCs can vary significantly with energy level. The PCs in different energy regions clearly originate from different defects. The PCs below the valence band edge are as-grown hole traps that are insensitive to stress time and temperature, and substantially higher in thermal SiON. The PCs above the valence-band edge are from created defects. The PCs within the bandgap have a peak near Ev + 0.8 eV and saturate for either longer stress time or higher stress temperature. In contrast, the PCs above a conduction band edge, namely the antineutralization positive charges, do not saturate, and their generation is clearly thermally accelerated.