Ionization Effects in Self-Interstitial Migration and Implant Damage Annealing in Silicon
We have attempted to induce the charge-state-dependent migration of the silicon self-interstitials (Sii) presumably produced in a shallow ion implant-damaged Si layer (160 keV O+, 1 x 1013/cm2, 300 K) by subsequently applying intense ionization from more deeply penetrating but nondamaging electron irradiations (5-20 keV e-, 7.5 x 1018/cm2 260-280 K). The samples used had been bulk doped with substitutional aluminum (Aℓs). EPR of the aluminum interstitials (Aℓi++), which are believed to be produced by replacement of Aℓs by Sii, was monitored to detect Sii migration into the bulk of the sample. We find no evidence that intense ionization following implantation causes significant enhancement of Sii migration. This result suggests a conflict between the concept of isolated Sii thermally stable at 3OO K and the hypothesis of an athermal, charge-state-dependent mechanism for Sii migration. We have also looked for ionization-stimulated annealing of the vacancy-associated lattice damage resulting from O+ implantation. Our EPR measurements show that intense ionization at 3OO K causes negligible annealing of this damage, despite the fact that significant thermal annealing does occur slightly above 3OO K. Our results suggest that ionization is not the only factor involved in implant damage annealing or in the puzzling migration of the Sii.