Characteristics of ultra shallow B implantation with decaborane

The characteristics of ultra shallow B implantation with mass-analyzed decaborane cluster ions (B₁₀H_x⁺) are presented. Depth profiles of B and co-implanted H were measured by SIMS, before and after annealing. Annealing results in the increase in the depth of B distribution, due to diffusion, but most of H diffuses out of Si. While the sputtering yield of Si per incoming B in a cluster was found to be comparable to the estimated sputtering yield of Si with B⁺ ions of the equivalent energy (∼ 1.2 keV), the surface effects of the two types of ions may be quite different. Atomic force microscopy revealed that the smoothing effect of the small decaborane cluster ions, observed previously by us on a surface of amorphous Si, is also present on crystalline Si and even on a much rougher surface of polycrystalline Ta film. The smoothing affects different parts of the power density spectra as functions of spatial frequency in the amorphous and crystalline materials. The smoothing on c-Si surfaces is in sharp contrast to roughening of these surfaces by irradiation with monomer Ar ions, which was done for reference, This indicates that different ion-surface interaction mechanisms are needed to describe impacts of cluster and of monomer ions. All other effects of Si implantation with B₁₀H_x⁺ measured to date were found to be the same as those with B⁺ ions of equivalent energy and dose, which confirms that decaborane implantation is an alternative to the very low energy B implantation for ultra shallow p-type junctions in Si devices.