Amorphous-damage depth distributions and the amorphization of silicon by ion bombardment

Depth distributions of the radiation damage in moderately to heavily ion bombarded silicon were obtained in the following manner. The electron spin resonance signal from an ion bombarded silicon target was measured. This ESR signal was proportional to the amount of amorphous silicon present in the target. A thin oxide of specified thickness was then grown on the surface of the target by anodic oxidation, and subsequently stripped off in a HF etch. The depth of the stripped impression below the unoxidized surface was measured using a multibeam interferometer. The amorphous ESR signal was again measured, and the strip/measure process was continued until the total implanted layer was removed. These remaining-after-each-strip ESR signals were plotted versus depth removed. The experimental profiles were compared with integral profiles calculated from theoretical damage distributions. It was found that in those cases where only a small amount of nonamorphous damage was present at the critical dose, the experimental profile was in agreement with the theoretical profile. In those cases where a large amount of nonamorphous damage was present, experimental profiles at higher doses were needed to complement the critical dose profile at selected depths. This set of profiles was then compared with the theoretical results. It was also possible to deduce the energy deposited into atomic processes (damage) per incident ion from the amorphous ESR signal at the critical dose, corrected to include the nonamorphous damage. To determine this energy, a procedure for calibrating the experimental results to the theoretical results was chosen. We found that the theoretical calculations greatly overestimated the energy deposited into damage for light incident ions