The chemical effect of fluorine on boron transient enhanced diffusion

The role of fluorine in suppressing boron diffusion is studied by comparing the diffusion of boron from 5 keV BF₂⁺ implants versus 1.1 keV ¹¹B⁺ implants with varying 1.9 keV F⁺ implant doses. Prior to B⁺, F⁺ or BF₂⁺ implantation, the surface was amorphized to a depth of 1450 Å using a 70 keV Si⁺ 1×10¹⁵/cm² implant. By implanting the boron, fluorine or BF₂ into pre-amorphized silicon, the differences in damage are factored out of the experiment. In addition, the pre-amorphizing implant provides a source of silicon interstitials for studying boron transient-enhanced diffusion (TED). Secondary Ion Mass Spectrometry (SIMS) profiles indicate negligible reduction in boron diffusion, even with higher fluorine doses corresponding to F:B ratios>that for BF₂. Transmission electron microscopy (TEM) analysis shows no effect of the presence of F on the evolution of the source of the interstitials, except at F doses>2×10¹⁴ /cm². Earlier studies also using pre-amorphized substrates, but higher dose B implants, showed a significant effect of F on B TED. By comparing our results on lower dose B to these earlier results on higher dose B, a mechanism for the observed reduction in B TED at high B doses is proposed