Low-energy ion damage in semiconductors: A progress report

There has been steady progress in understanding the propagation of low-energy, ion-induced damage into semiconductor substrates. The availability of specifically designed heterostructure substrates allows us to trace the profile of damage into the material. A number of experiments, together with theoretical simulations, have confirmed the important role played by fortuitous channeling of ions, deep into the material (e.g., >1000 Angstrom deep for incident ions energies similar to 300 eV). Recent experiments have also shown the importance of rapid diffusion of ion-created defects. Using a model that includes the effects of both channeling and defect diffusion, channeling and diffusion in ion damage (CHANDID), we have deduced a room-temperature diffusion constant of D similar to 1 x 10(-15) cm(2)/s. This is an extremely high value for diffusion at room temperature, and is more characteristic of diffusion taking place at temperatures of a few hundred to a few thousand degrees centigrade. One cause of this high value of D may be attributed to radiation enhanced diffusion: the creation of excess electrons and holes during the etch process whose subsequent nonradiative recombination transfers momentum to the defects. Preliminary experiments, which monitor the effects of above band-gap illumination during ion bombardment, validate this picture. Such understanding, of intrinsic importance, can be used to design material and device structures in which the effects of ion damage may be mitigated. (C) 1996 American Vacuum Society.