RBS-channeling analysis of ion-irradiation effects in heavily-doped Si : As

Structural modification of heavily-doped, laser annealed Si:As induced by 2 MeV Si+ irradiation, is investigated by the Rutherford backscattering-channeling (RBS-C) technique. Aligned (001) spectra, (001) to {110} angular scans and electrical activation measurements are compared with results previously obtained in silicon-on-insulator layers containing the same concentration of As, but activated by furnace instead of laser. Defects injected by ion bombardment interact with As, leading in laser annealed sample to strong electrical deactivation and to an increase in As RBS-C yield much larger than the one of Si. Comparison of samples with different initial location of As, shows that the distribution of dopant among the different kinds of lattice arrangements (schematized as substitutional, slightly displaced and random/incoherent) is nearly the same after irradiation. This result can be explained with the achievement under MeV irradiation, of a stationary state in the near-surface region, characterized by a dynamic equilibrium of intrinsic and extrinsic defects, in which the memory of As location before irradiation is substantially lost.