Ion implantation was widely used to modify the structural, electrical and optical properties of materials. By appropriate masking, this technique could be used to define nano- and micro-structures. However, depending on the type of mask used, experiments have shown that vacancy-related substrate modification could be inferred tens of micrometers away from the edge of the mask used to define the implanted region. This could be due to fast diffusion of vacancies from the implanted area during annealing or to a geometric effect related to ion scattering around the mask edges. For quantum and single-atom devices, stray ion damage could be deleterious and must be minimized. In order to profile the distribution of implantation-induced damage, the nitrogen-vacancy color center was used as a sensitive marker for vacancy concentration and distribution following MeV He ion implantation into diamond and annealing. Results showed that helium atoms implanted through a mask clamped to the diamond surface were scattered underneath the mask to distances in the range of tens of micrometers from the mask edge. Implantation through a lithographically defined and deposited mask, with no spacing between the mask and the substrate, significantly reduces the scattering to ≤ 5μm but does not eliminate it. These scattering distances were much larger than the theoretically estimated vacancy diffusion distance of ∼ 260nm under similar conditions. This paper showed that diffusion, upon annealing, of vacancies created by ion implantation in diamond, was limited, and the appearance of vacancies many tens of micrometers from the edge of the mask was due to scattering effects.

An Upper Limit on the Lateral Vacancy Diffusion Length in Diamond. Orwa, J.O., Ganesan, K., Newnham, J., Santori, C., Barclay, P., Fu, K.M.C., Beausoleil, R.G., Aharonovich, I., Fairchild, B.A., Olivero, P., Greentree, A.D., Prawer, S.: Diamond and Related Materials, 2012, 24, 6-10