Sodium-Induced Barrier-Height Lowering and Dielectric Breakdown on SiO[sub 2] Films on Silicon

Abstract

Electrical conduction measurements in films showed that the injecting barrier height was uniformly reduced by a small amount (<1 eV) in proportion to the level of Na contamination. However, at high contamination levels after bias‐temperature stressing, a very substantial (≈3 eV), localized barrier lowering was observed. Since this second type of lowering was eliminated after exposure of the film to moisture (in air) and was also seen in uncontaminated samples, it was not attributed to sodium. Accelerated dielectric breakdown measurements at low fields (<2 MV/cm) showed that even a monolayer of Na did not appreciably decrease the wearout time. Moderately contaminated samples had the same limiting failure times as controls over the temperature range 100°–400°C.