Wafers were pre-amorphized using 70keV Si+ and a dose of 1015/cm2 to generate a deep amorphous layer of 180nm. They were then implanted with 500eV 11B+, with and without 6keV F+, to doses of 1015 and 2 x 1015/cm2, respectively. After annealing at 550C, secondary ion mass spectroscopy revealed that the diffusivity of B in amorphous Si was significantly enhanced in the presence of F. Ellipsometry and cross-sectional transmission electron microscopy indicated that enhanced diffusion occurred only in the amorphous layer. The F increased the B diffusivity by about 5 orders of magnitude at 550C. It was proposed that the ability of F to reduce the dangling bond concentration in amorphous Si could reduce the formation energy for mobile B; thus enhancing its diffusivity.

Fluorine-Enhanced Boron Diffusion in Amorphous Silicon. J.M.Jacques, L.S.Robertson, K.S.Jones, M.E.Law, M.Rendon, J.Bennett: Applied Physics Letters, 2003, 82[20], 3469-71