Redistribution during annealing of low-energy B implants in Si-on-insulator structures and in bulk Si was investigated by comparing secondary ion mass spectrometry and simulated profiles. All of the samples were pre-amorphized with Ge using various implantation energies in order to investigate the effects of the position of the damage upon B diffusion. Various B doses in the range of 2 x 1013 to 2 x 1015/cm2 and annealing temperatures of between 700 and 1100C were investigated. All of the secondary ion mass spectrometry profiles revealed a B pile-up in the first few nm of the Si matrix in the proximity of the Si surface. The results of the simulations, performed on samples implanted to various doses (below and above the solid solubility), indicated that the B redistribution upon annealing could be explained by a simple model which considered the presence of traps in the surface region, without considering any asymmetrical behavior of the dopant diffusion. The sink region was a few monolayers (1 to 2nm) for doses of 2 x 1013 and 2 x 1014/cm2, and it extended to about 7nm for the highest dose of 2 x 1015/cm3, in the region of very high B concentration where precipitates and clusters shrank. For the 2 lowest B doses, the amount of B trapped at the surface was a maximum at around 800C, when more than 80% of the implanted dopant was made immobile and electrically inactive. Under these experimental conditions, i.e., pre-amorphization performed with constant dose and different implantation energies, the amount of trapped B increased upon reducing the depth of the amorphous layer and it was higher in the bulk Si than in Si-on-insulator.

Uphill Diffusion of Ultralow-Energy Boron Implants in Preamorphized Silicon and Silicon-on-Insulator. M.Ferri, S.Solmi, D.Giubertoni, M.Bersani, J.J.Hamilton, M.Kah, K.Kirkby, E.J.H.Collart, N.E.B.Cowern: Journal of Applied Physics, 2007, 102[10], 103707