ROLE OF RECOIL IMPLANTED OXYGEN IN DETERMINING BORON-DIFFUSION IN SILICON

Annealing of silicon implanted with boron through a surface oxide results in an enhanced diffusion of boron. This enhanced diffusion is suppressed during an initial incubation period. An activation energy of 2 eV is associated with the enhanced diffusion, indicating excess silicon interstitials may be involved. On the other hand, the process leading to the onset of enhanced diffusion possesses an apparent activation energy of 3.7 eV. Two-step annealing reduces the latter value to 2.6 eV, the activation energy for interstitial oxygen diffusion. The different activation energies evaluated for the saturation process will be discussed. Transmission electron microscopy shows that the coalescence of dislocations, as well as the growth of faulted loops, proceeds rapidly after the incubation period for enhance diffusion. Precipitates along small dislocation loops are also observed after the incubation period. It is proposed that oxygen precipitation, with emission of silicon interstitials, predominates for annealing beyond the incubation period and is therefore responsible for the enhanced diffusion of boron. The enhanced diffusion sequence is initially incubated by trapping oxygen at dislocations. The real onset of the enhanced diffusion occurs when the dislocations are saturated and the oxide precipitation at the dislocations commences.