Undissociated Dislocations in Ion Damaged Silicon

Abstract

Ion implantation in recent years has become an integral part of fabricating electronic devices in Si, e.g., shallow source and drain pockets in FET devices may be fabricated by implanting As+ions at ~ 100 keV to a dose of ~ 1016/cm2. For such implanting conditions, the top layer of the material becomes amorphous and during subsequent heat treatment it grows back epitaxially into a single crystal layer containing dislocations. For several reasons dislocations may be generated in the recrystallized layer. If a high concentration of substitutional species whose atomic radius is sufficiently different from the Si atom radius is incorporated, the strain in this layer may exceed the Si elastic limit and a misfit dislocation network, situated close to the implanted - unimplanted material interface, may form. Certain implanting species may tend to form small clusters with Si atoms and thus causing stacking errors to occur in the growing Si crystal, i.e., dislocations may now be nucleated within the recrystallized layer. However, it is also known that V-shaped dislocation half loops form even for Si+ implanted Si.1 They are apparently nucleated from positions close to the initial amorphous-crystalline Si interface, indicating that certain dislocation nuclei in the crystalline Si beneath the amorphous layer were already generated during implantation. We have presently analyzed the defects in the crystalline material right beneath the amorphous layer by the lattice imaging technique. Among others, the defects of primary interest are undissociated 60° dislocation dipoles of small sizes.