Leakage currents and dielectric breakdown of Si 1− x− yGe xC y thermal oxides

Abstract

A detailed study of the leakage currents and dielectric wear-out of thermal oxides grown on Si 1− x Ge x , Si 1− y C y and Si 1− x− y Ge x C y epilayers to determine their quality and reliability for Si 1− x− y Ge x C y MOS technology is presented. After applying electrical stress to the samples, we have determined the conduction mechanisms and the dependence of leakage currents upon epilayer composition (Ge and C content). Conduction takes place mainly via Fowler–Nordheim tunneling injection. Ge and C introduce traps in the oxide which assist injection and thus lower the effective height of the tunneling barrier. We have also monitored the oxide reliability, focusing on time-dependent dielectric breakdown (TDDB). The nature of trapped charge in the oxide depends on the initial epilayer composition. We have found that the formation of defects induced by the presence of C leads to extrinsic oxide failure. While the presence of Ge in the oxide does not seem to introduce significant differences with respect to Si breakdown statistics, C in the oxide truly modifies the statistical profile.