The effect of B atoms upon F diffusion was demonstrated by experiments on pre-amorphized samples, uniformly doped with B, during 3 annealing stages. In the pre-annealing stage, during and after implantation at room temperature, F diffusion was significantly retarded by the high background B concentrations. In the second stage of annealing, at 550C, the substrate condition remained amorphous and F migration was suppressed in the presence of B. It was suggested that negatively charged F atoms were trapped at dangling bonds, positively charged by B atoms due to the Coulomb attractive force. In the third stage of annealing, at 800C, F atoms migrated anomalously and accumulated - at the 0.8 projected range of F - only in samples doped with B. This suggested that the background B enhanced F migration via the dissolution of small defects or the prevention of the formation of small defects in the recrystallized region; resulting in F accumulation in the damaged area associated with implantation.

Role of Boron Atoms on Fluorine Diffusion under Various Stages of Annealing. M.Tachi, H.Tsuji, M.Furuhashi, K.Taniguchi: Japanese Journal of Applied Physics, 2005, 44[5A], 2902-4

Figure 3

Diffusivity of B in Si

(from the top: pure Si with interstitial injection, C-doped Si with interstitial injection,

pure Si with no injection, C-doped Si with no injection)