Special film structures were grown, by means of low-temperature molecular beam epitaxy, in order to investigate the properties of self-interstitials in Si. It consisted of a superlattice which was made up of B spikes which were separated from each other by 100nm of Si. After dry oxidation, the width of each spike was directly proportional to the interstitial concentration at that depth. The superlattice as a whole thus furnished a depth profile of the time-averaged interstitial concentration, and permitted direct determinations to be made of the diffusion coefficients of interstitials. The abrupt dopant concentration transitions which were achievable in low-temperature molecular beam epitaxial films permitted this type of investigation to be carried out at temperatures of between 750 and 900C. A value of 1.4 x 10-13cm2/s was found at 800C. Overall, the results (table 109) could be described by:

D(cm2/s) = 1 x 102exp[-3.1(eV)/kT]

Oxidation Enhanced Diffusion in Si B-Doping Superlattices and Si Self-Interstitial Diffusivities. H.J.Gossmann, C.S.Rafferty, H.S.Luftman, F.C.Unterwald, T.Boone, J.M.Poate: Applied Physics Letters, 1993, 63[5], 639-41

Table 109

Diffusivity of Self-Interstitials in Si