In order to meet the technological requirements for the next generations of p–n junctions, highly promising methods consist of B and C ultra-low energy co-implantation in Ge pre-amorphized Si. An investigation was made of the B diffusion and the activation phenomena occurring during post-annealing of ultra-shallow junctions (USJ) obtained by spike annealing Si samples pre-amorphized by 20keV Ge and co-implanted with C at 4keV and B at 500eV. Isochronal (60s) post-annealing processes were performed in inert atmosphere (N2) by rapid thermal annealing at 500 to 1050C. It was shown that, contrary to what reported in the literature about C-free USJ, no B diffusion occurred up to 900C, and further B clustering was completely suppressed over the whole investigated temperature range. Moreover, an increase of the sheet resistance by increasing the temperature up to 900C was observed; followed by a subsequent decrease that could be easily explained on the basis of B diffusion and segregation in native SiO2 and B cluster dissolution. Finally, it was shown that C significantly reduced, by up to two orders of magnitude, the diffusion coefficient of B, that in the present experiments was present under highly extrinsic conditions. B Diffusion and Activation Phenomena during Post-Annealing of C Co-Implanted Ultra-Shallow Junctions. M.Di Marino, E.Napolitani, M.Mastromatteo, G.Bisognin, D.De Salvador, A.Carnera, S.Mirabella, G.Impellizzeri, F.Priolo, H.Graoui, M.A.Foad: Nuclear Instruments and Methods in Physics Research B, 2006, 253[1-2], 46-9