Range and damage distributions in ultra-low energy boron implantation into silicon

An ultra high vacuum, low energy ion implanter was used in conjunction with a range of analytical techniques to study the range and damage distributions of B⁺ ions implanted at normal incidence into Si(100) samples held at room temperature. Samples were implanted over a dose range from 1E14 ions/cm² with and without a surface oxide layer and those implanted at 1 keV and below were capped with a nominal 20 nm layer of ²⁸Si by ion beam deposition in situ in order to produce an oxygen equilibration layer for subsequent secondary ion mass spectrometry depth profiling. The samples were analysed using secondary ion mass spectroscopy, medium energy ion scattering, spectroscopic ellipsometry, spreading resistance profiling and high resolution, cross section transmission electron microscopy to obtain the range and damage distributions and junction depths. The general observations were that channelling occurs at all energies studied, and that the relationship between the damage and range distributions depends strongly on bombardment energy. Comparison of the range and damage profiles was carried out to ascertain the role of the surface in determining the behaviour of defects produced very close to it by the low energy implants required for the production of junctions at depths in the 20 to 50 nm range. The role of the surface or silicon/silicon dioxide interface as a defect sink significantly influences the B redistribution behaviour during rapid thermal annealing