Kinetics of large B clusters in crystalline and preamorphized silicon

We present an extended model for B clustering in crystalline or in preamorphized Si and with validity under conditions below and above the equilibrium solid solubility limit of B in Si. This model includes boron-interstitial clusters (BICs) with BnIm configurations-complexes with n B atoms and m Si interstitials-larger (n > 4), and eventually more stable, than those included in previous models. In crystalline Si, the formation and dissolution pathways into large BICs configurations require high B concentration and depend on the flux of Si interstitials. In the presence of high Si interstitial flux, large BICs with a relatively large number of interstitials (m >= n) are formed, dissolving under relatively low thermal budgets. On the contrary, for low Si interstitial flux large BICs with few interstitials (m << n) can form, which are more stable than small BICs, and whose complete dissolution requires very intense thermal budgets. We have also investigated the kinetics of large BICs in preamorphized Si, both experimentally and theoretically. B was implanted at a high-dose into preamorphized Si, and the B precipitation was studied by transmission electron microscopy and by sheet resistance and Hall measurement techniques. A simplified model for B clustering and redistribution in amorphous Si is proposed, including the experimental value for the B diffusivity in amorphous Si and the energetics of BICs. Our model suggests that B-2, B3I, B4I and B4I2 clusters are the most energetically favored configurations, with relative abundance depending on B concentration. After recrystallization, thermal anneals up to 1100 degrees C evidence that BICs evolve under very low flux of Si interstitials under the particular experimental conditions considered. Simulations indicate that for very high B concentrations and low Si interstitial flux a significant fraction of the initial small BICs evolves into larger and very stable BIC configurations that survive even after intense thermal budgets, as confirmed by energy filtered transmission electron microscopy analyses. The correlation between simulations and Hall measurements on these samples suggest that hole mobility is significantly degraded by the presence of a high concentration of BICs. (C) 2011 American Institute of Physics. [doi:10.1063/1.3639280]

We present an extended model for B clustering in crystalline or in preamorphized Si and withvalidity under conditions below and above the equilibrium solid solubility limit of B in Si. Thismodel includes boron-interstitial clusters (BICs) with BnIm configurations—complexes with n Batoms and m Si interstitials—larger (n>4), and eventually more stable, than those included in previousmodels. In crystalline Si, the formation and dissolution pathways into large BICs configurationsrequire high B concentration and depend on the flux of Si interstitials. In the presence of highSi interstitial flux, large BICs with a relatively large number of interstitials (m n) are formed, dissolvingunder relatively low thermal budgets. On the contrary, for low Si interstitial flux large BICswith few interstitials (mn) can form, which are more stable than small BICs, and whose completedissolution requires very intense thermal budgets. We have also investigated the kinetics oflarge BICs in preamorphized Si, both experimentally and theoretically. B was implanted at a highdoseinto preamorphized Si, and the B precipitation was studied by transmission electron microscopyand by sheet resistance and Hall measurement techniques. A simplified model for B clusteringand redistribution in amorphous Si is proposed, including the experimental value for the B diffusivityin amorphous Si and the energetics of BICs. Our model suggests that B2, B3I, B4I and B4I2clusters are the most energetically favored configurations, with relative abundance depending onB concentration. After recrystallization, thermal anneals up to 1100 C evidence that BICsevolve under very low flux of Si interstitials under the particular experimental conditions considered.Simulations indicate that for very high B concentrations and low Si interstitial flux a significantfraction of the initial small BICs evolves into larger and very stable BIC configurations thatsurvive even after intense thermal budgets, as confirmed by energy filtered transmission electronmicroscopy analyses. The correlation between simulations and Hall measurements on these samplessuggest that hole mobility is significantly degraded by the presence of a high concentration ofBICs.