Transient enhanced diffusion from implantation of molecular decaborane ions

The transient enhanced diffusion (TED) from implantation of 5-keV B₁₀H₁₄ and 0.5-keV B ions has been quantified and compared at nominal boron doses of 10¹⁴ and 10¹⁵ cm^-2. The B diffusivity during annealing was extracted from SIMS of marker layers in boron doping-superlattices and the actual B dose implanted was independently measured by nuclear reaction analysis. Comparable enhancements were observed from both ions. TEM analysis revealed that both boron- and decaborane-implanted samples were amorphized at a nominal B dose of 10¹⁵ cm^-2. A comparison with data from low energy Si implants revealed a similar dependence of diffusivity enhancements 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 B₁₀H ₁₄ 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