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

A sequence of three boron spikes, grown in silicon by molecular beam epitax y (MBE) and characterized by secondary-ion mass spectrometry, has been empl oyed to investigate the mechanisms of boron diffusion during irradiation wi th 2.5 MeV protons at an elevated sample temperature of 570 degreesC. The e nergy of the proton beam has been chosen so that the generation rate of poi nt defects can be considered as uniform throughout the boron delta-doped si licon. The influence of the B concentration (ranging from 5 x 10(15) to 3 x 10(18) cm(-3) in different samples) on the enhanced diffusion of boron hav e been studied in detail. For each concentration the B diffusion coefficien t is increased by a factor greater than 5 x 10(4) under irradiation as comp ared to the B diffusion coefficient at 570 degreesC in unirradiated areas. In the first approximation this enhancement is independent on the depth pos ition of the boron spike but depends on the boron concentration. The diffus ion of boron under irradiation exhibits an exponential behavior. This kind of diffusion has already been reported in the literature for boron diffusio n in silicon during oxidation experiments at 600 degreesC. The direct compa rison with oxidation experiments where Si self-interstitials are injected i n a non-uniform way provides further information on the basics of the boron diffusion mechanisms in silicon. (C) 2001 Elsevier Science B.V. All rights reserved.