Atomistic modeling of B activation and deactivation for ultra-shallow junction formation

We have investigated the physical mechanisms for the B clustering formation and dissolution for ultra-shallow junction formation. We have analyzed high-dose low-energy B implants and theoretical structures with box-shaped B profiles that are fully active. These structures could be simplifications of the situation resulting from regrowth of preamorphized or laser annealed B implants. For these conditions, we have to take into account new effects due to the high B concentration and the proximity to the surface. The simulations show that the deactivation mechanism for B implants in crystalline Si takes place through a high interstitial content path, and it happens even for low B doses. The deactivation of the B box depends on the B concentration. In the absence of excess Si interstitials, B deactivation only happens for very high B concentrations. This process is very slow for low temperature anneals. If there is a residual concentration of Si interstitials along with the B box, the deactivation will take place rapidly even at low temperatures. In the model, the reactivation mechanism takes place in all cases through the low interstitial content path, by the capture of native Si interstitial defects and the emission of B interstitials.