Sodium-Induced Barrier-Height Lowering and Dielectric Breakdown on SiO₂ Films on Silicon

Electrical conduction measurements in SiC-2 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 (>1013 Na+/cm2) after bias-temperature stressing, a very substantial [formula omitted], 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 wear-out time. Moderately contaminated samples (5 x 1012 Na+/cm2) had the same limiting failure times as controls over the temperature range 100°-400°C. © 1974, The Electrochemical Society, Inc. All rights reserved.