Thermal stability of B in poly-SiGe on SiON

Thermal stability of B atoms in in situ doped poly-SiGe films has been investigated. After annealing at 600–900 °C, the carrier concentration in the films decreased with increasing annealing time, which was due to transition from the super-saturated concentration of B for as-deposited films to the solid solubility at the annealing temperature. Thermal stability of B atoms was significantly improved by Ge doping, e.g. the stability in poly-Si0.6Ge0.4 films was four times as high as that in poly-Si films. The deactivation process of B atoms could be separated into the fast and slow processes. The time constants for both processes did not depend on the Ge fraction, while the ratio of deactivated B atoms in the fast process to those in the slow process decreased by Ge doping. The two-state model has been proposed, and explained the improved thermal stability of B atoms by Ge doping.