Ge fraction dependent improved thermal stability of in situ doped boron in polycrystalline Si_(1-x)Ge_x (0≤x≤0.5) films on SiON

摘要

Postannealing characteristics of in situ doped B atoms in poly-Si_(1-x)Ge_x (x ≤0.5) films on SiON have been investigated. Supersaturated electrically active B (2 X 10~(20) cm~(-3)) is obtained for as-chemical vapor deposition samples, and their thermal stability is significantly improved by increasing Ge fraction, e.g., the stability for poly-Si_(0.6)Ge_(0.4) is ten times as high as that for poly-Si at 700-800℃. Such a Ge induced improvement will be a powerful tool to achieve poly-SiGe gate electrode for the next generation ultralarge scale integrated circuits. In addition, the deactivation process of electrically active B has been analyzed. Results indicated that deactivation processes consist of fast and slow processes. The former is due to movement of B atoms from substitutional to interstitial sites, which is enhanced by a local strain induced by the difference in atomic radii between Si and B atoms. The slow process was due to trapping of B at grain boundaries during grain growth. The two-state model based on the local strain compensation by Ge doping is proposed, which can well explain the Ge dependent thermal stability of electrically active B atoms.