Comparison of elemental boron and boron halide implants into silicon

This paper investigates the electrical activation of boron halide molecular implants into silicon and compares them to boron implants at the same effective energy. The implanted species: B⁺, BF2+, BCl2+ and BBr2+ were implanted to doses of 2 × 10¹⁴ and 1 × 10 ¹⁵ B cm^-2 the energy of the molecular implants was calculated to give an effective boron implant energy of 5 keV. Samples cut from the wafers were annealed for 30 s at temperatures ranging from 800 °C to 1100 °C. Hall effect measurements were used to compare and contrast the electrical activation of the boron between the different halide species and doses. It was found that molecular implants of BBr2+ and BCl2+ do not enhance the electrical activation of boron to the same extent that BF2+ implants do. The BBr2+ implants are only comparable with boron after annealing at high temperatures (above 1000 °C). The BF2+ implants show enhanced electrical activation with respect to boron for all the annealing temperatures and doses studied. Rutherford backscattering spectroscopy (RBS) of silicon implanted with BBr2+ to a dose of 1 × 10¹⁵ boron atoms cm^-2, shows that an amorphous region is created during the implantation. This region fully re-grows after annealing at 1100 °C; lower temperature anneals remove only part of the amorphous layer. RBS channelling shows that a fraction of the bromine takes up substitutional lattice sites upon implantation, and that this fraction increases as the samples are annealed at temperatures above 600 °C with 40% of the B being in substitutional sites after annealing at 1050 °C.