Defect engineering

Although the presence of defects usually has detrimental effects, sometimes defects are intentionally created to improve device performance. High energy implantation (MeV) or nitridation (annealing in a NH3 ambient) can be used to create vacancy reservoirs. The excess of vacancies reduce the interstitial concentration, and therefore the interstitial-mediated diffusion of some dopants. Impurity co-implantation during the doping process may also result in less dopant diffusion during subsequent thermal treatments. This is the case of fluorine co-implantation with boron inside an amorphous layer, in which the reduced boron diffusion is attributed to the formation of fluorine-vacancy clusters during solid phase epitaxial (SPE) recrystallization. Additionally, implant and annealing conditions can be tuned to obtain defect clusters with some relevant characteristics, for example for photoluminescence applications, since some small defect clusters may be optically active

Our kinetic Monte Carlo simulations revealed the beneficial effect of a vacancy profile induced by MeV irradiation on B diffusion and activation. We have also developed a model that reproduces the interaction of fluorine with point defects and therefore its effect on B diffusion. Our experience on defect engineering also includes the analysis of the effect of Si self-implantation conditions and B background concentrations on the formation of optically active defect clusters.

Boron profiles after SPE (black symbols and line), and after SPE and 60s anneal at 1000°C with (blue symbols and lines) or without (green symbols and lines) the presence of F. Symbols and dashed lines represent experimental data and solid lines simulation results (P. López et al., Materials Science and Engineering B 154-155, 207 (2008) - Atomistic modeling of FnVm complexes in pre-amorphized Si).