It was demonstrated that B diffused at high concentrations during low-temperature thermal annealing in amorphous material which was pre-amorphized by Ge-ion implantation. For a typical B ultra-shallow junction doping profile, concentrations as high as 2 x 1020/cm3 appeared to be highly mobile, at 500 and 600C, in the amorphous region before recrystallization. In crystalline material at the same temperatures, the mobile B concentration was at least 2 orders of magnitude lower. It was also shown that B diffusivity in the amorphous region was similar with, and without, F. The role of F was not to enhance B diffusivity, but to slow the recrystallization rate dramatically; thus allowing the B profile to be mobile up to a concentration of 2 x 1020/cm3 for longer periods.

Boron Diffusion in Amorphous Silicon and the Role of Fluorine. R.Duffy, V.C.Venezia, A.Heringa, B.J.Pawlak, M.J.P.Hopstaken, G.C.J.Maas, Y.Tamminga, T.Dao, F.Roozeboom, L.Pelaz: Applied Physics Letters, 2004, 84[21], 4283-5