Damage evolution in low-energy ion implanted silicon

Abstract

The annealing of damage generated by low-energy ion implantation in polycrystalline silicon (poly-Si) and amorphous silicon (a-Si) is compared. The rate of heat release between implantation temperature and $350--500\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ for Si implanted in both materials and for different ions implanted in poly-Si shows a very similar shape, namely, a featureless signal that is characteristic of a series of processes continuously distributed in terms of activation energy. Nanocalorimetry signals differ only by their amplitude, a smaller amount of heat being released after light ion implantation compared to heavier ones for the same nominal number of displaced atoms. This shows the importance of dynamic annealing of the damage generated by light ions. A smaller amount of heat is released by implanted poly-Si compared to a-Si, underlining the effect of the surrounding crystal on the dynamic annealing and the relaxation of the defects. Damage accumulation after $30\text{\ensuremath{-}}\mathrm{keV}$ Si implantation is also characterized by Raman scattering and reflectometry, featuring a similar trend in a-Si, poly-Si, and monocrystalline silicon (c-Si) with a saturation around $4\phantom{\rule{0.3em}{0ex}}\mathrm{Si}∕{\mathrm{nm}}^{2}$. Considering these results together with other recent experiments in c-Si and molecular dynamic simulations, it is concluded that the damage generated by low-energy ion implantation that survives dynamic annealing is structurally very similar if not identical in both crystalline and amorphous silicon, giving rise to the same kind of processes during a thermal anneal. However, the damage peak obtained by channeling saturates only above $10\phantom{\rule{0.3em}{0ex}}\mathrm{Si}∕{\mathrm{nm}}^{2}$. This suggests that between 4 and $10\phantom{\rule{0.3em}{0ex}}\mathrm{Si}∕{\mathrm{nm}}^{2}$, further damage occurs by structural transformation without the addition of more stored energy.