Surface, stress, and impurity effects on room-temperature migration of ion-beam-generated point defects

We have analyzed the perturbations produced by recombination at surface, trapping at impurities, and stress fields on the room-temperature migration properties of point defects in Si. A stack consisting of a Si oxide (or a Si nitride) and a polycrystalline Si layer, deposited on Si samples, was patterned to open 2-mu m-wide, 10-mu m-spaced stripes. A 40-keV Si implantation to fluences of 1 x 10(12)-5 x 10(13)/cm(3), performed through this mask at room temperature, was used to inject point defects into the bulk of the wafer. After implants, defect-induced dopant deactivation, in the cross section orthogonal to the direction of the stripes, has been monitored using two-dimensional spreading resistance profilometry. It has been found that, in highly pure epitaxial Si samples, dopant deactivation extends in depth to several microns beyond the region (similar to 0.4 mu m) directly modified by the ions. Furthermore, the two-dimensional deactivation profiles exhibit a strong recess at the surface and a significant anisotropy, being markedly elongated in the lateral direction. Analysis of the data shows that long-range migration of defects is interrupted by trapping at impurities (C and O) or recombination at the surface, characterized by a coefficient of similar to 100 mu m(-1). Moreover, the lateral elongation of the profiles is tentatively explained assuming an anisotropy in the defect diffusivity tensor produced by the strain field under the mask.