On the knocked oxygen contribution to low energy implanted boron diffusion retardation

Boron was implanted in crystalline silicon through oxide layers with different thicknesses. The implantation is carried out at various doses and energies of interest in Ultra Large Scale Integration (ULSI) applications. Rapid thermal annealings (RTA) are used in a way to obtain shallow junctions and electrical activation of the B atoms. However, transient enhanced diffusion induced by implantation damage can be observed on boron profiles before and after annealing obtained with secondary ion mass spectrometry (SIMS). It is found that the diffusion transient in the tail region of the boron profile increases with decreasing oxide thickness. Even more, if the implantation damage concerns mostly the oxide, i.e. when the concentration peak is located into this oxide, the oxygen knocked into the silicon substrate could play an important role in restricting the boron diffusion.