Influence of boron concentration on the enhanced diffusion observed after irradiation of boron delta-doped silicon at 570°C

Abstract

A sequence of three boron spikes, grown in silicon by molecular beam epitaxy (MBE) and characterized by secondary-ion mass spectrometry, has been employed to investigate the mechanisms of boron diffusion during irradiation with 2.5 MeV protons at an elevated sample temperature of 570°C. The energy of the proton beam has been chosen so that the generation rate of point defects can be considered as uniform throughout the boron delta-doped silicon. The influence of the B concentration (ranging from 5×10 15 to 3×10 18 cm −3 in different samples) on the enhanced diffusion of boron have been studied in detail. For each concentration the B diffusion coefficient is increased by a factor greater than 5×10 4 under irradiation as compared to the B diffusion coefficient at 570°C in unirradiated areas. In the first approximation this enhancement is independent on the depth position of the boron spike but depends on the boron concentration. The diffusion of boron under irradiation exhibits an exponential behavior. This kind of diffusion has already been reported in the literature for boron diffusion in silicon during oxidation experiments at 600°C. The direct comparison with oxidation experiments where Si self-interstitials are injected in a non-uniform way provides further information on the basics of the boron diffusion mechanisms in silicon.