Transient enhanced diffusion from decaborane molecular ion implantation

Transient enhanced diffusion (TED) from implantation of 5keVB10H14 and 0.5 keV B ions has been quantified and compared for nominal boron doses of 1014 and 1015cm-2. Boron diffusivity during annealing was extracted from secondary ion mass spectroscopy depth profiles of diffused marker layers in boron doping-superlattices and the actual implanted B dose was independently measured by nuclear reaction analysis. Comparable enhancements were observed from both ions. Transmission electron microscopy analysis revealed that both boron- and decaborane-implanted samples were amorphized at a nominal 1015cm-2B dose. A comparison with data from low energy Si implants revealed a similar dependence of diffusivity enhancement on implant dose. These findings are consistent with the understanding that TED is caused by the interstitial supersaturation resulting from a number of excess interstitials approximately equal to the number of implanted atoms which can become substitutional in the silicon lattice. Accordingly, no contribution to TED is expected from the hydrogen in the B10H14 ions and none is observed. Furthermore, there is no detectable effect in the diffusion profiles which can be attributed to a difference in the ion damage produced by the decaborane molecule and the boron atom. In both cases the reduction in diffusivity enhancement is due only to proximity of the implantation-induced excess interstitials to the wafer surface. copyright 1998 American Institute of Physics