A quantitative analysis of stress-induced leakage currents in ultra-thin silicon dioxide films

A quantitative analysis of stress-induced leakage currents (SILCs) in ultra-thin silicon dioxide films is described, which enables the extraction of trap parameters, e.g. trap site location. Assuming a two-step trap-assisted inelastic tunneling mechanism, conduction of electrons through silicon dioxide films proceeds as follows: First, electrons tunnel from the cathode into neutral trap sites followed by an energy relaxation into the lowest available energy state of these trap sites. Finally, electrons reach the anode by a direct tunneling process. Modeling SILC characteristics of a stressed 6.8-nm-thick SiO₂ film reveal a trap site location at 4.47 nm relative to the cathode interface. SILCs in the thickness range from 5.1 to 9.6-nm can be explained by the linear increase of the trap sheet charge density on oxide thickness, which suppresses local tunneling currents between cathode interface and trap sites by a reduction of the local oxide electric field.