Evaluation of the boron activation and depth distribution using BBr₂ ⁺ implants

Ultra shallow junctions (junction depths typically 20 - 80 nm) for future generations of advanced silicon devices require either very low energy ion implantation (+, BF₂ ⁺ and BBr₂ ⁺ implants. Boron was implanted with a fluence of 2 × 10¹⁴ B⁺ cm^-2 at an energy of 5 keV using either 5 keV B⁺, 21.5 keV BF₂ ⁺ or 75 keV BBr₂ ⁺. Subsequent to implantation the samples were annealed at temperatures in the range 800-1100°C for times of between 5 and 100 seconds. The samples were analysed before and after annealing using Rutherford backscattering spectrometry (RBS) and Hall effect measurements. Molecular Dynamics simulations were also undertaken and compared with the experimental data. The experimental measurements indicate that the highest electrical activation of the B is observed for the BF₂ ⁺ implants. Above 1000°C the damage introduced during the implantation of BBr₂ ⁺ has largely been removed and the observed boron activation is higher than that for the B+ implant, although still slightly lower than that for the BF⁺ ₂ implant. Molecular dynamics simulations show that the damage introduced scales with the mass of the halide, following classic Kinchen Pease theory. The bromine distribution does not appear to change significantly during annealing.