Formation and growth of nanocavities and cavities induced by He+ implantation in silicon

My Anh Nguyen, Marie-Odile Ruault and Franck Fortuna

Abstract

Nanocavities and cavities are known to be efficient gettering sites for metallic impurities in silicon. Here, we report results from implanted 100 silicon at room temperature with 50 keV helium ions at a dose of 3×10¹⁶ cm⁻². Due to its low solubility, He segregates in gas-vacancy complexes and forms nanobubbles. Then, during an N₂ ambient annealing at 800 °C using either rapid thermal annealing (RTA) or conventional furnace annealing, nanobubbles grow and He is released from the nanobubbles by gas exodiffusion, leading to (nano)cavities' formation. (Nano)cavities and residual defects were observed by transmission electron microscopy (TEM). The fraction of retained helium was shown to decrease with annealing time according to the first-order gas release model. Two nucleation-growth mechanisms involved in the growth of these (nano)cavities have been studied. A remarkable result shows evidence about the balance-time dependence of the two mechanisms involved in the growth process of (nano)cavities. At the very beginning (30 s) of the annealing, the main mechanism is the migration-coalescence including nanobubbles and vacancy-helium complexes leading to the cavities' formation. Then, the Ostwald ripening mechanism, related to the helium exodiffusion, between the nanocavities and cavities appeared.