ABSTRACT
This chapter investigates the structural evolution of helium-related extended defects in silicon, formed after intermediate dose helium implantation and annealing. A possible explanation of the overall process starts from the accepted points that single vacancies cannot trap helium and that at high fluence the concentration of vacancy clusters attains a value sufficient to stabilize around them a helium atmosphere generating a complex invisible by transmission electron microscope. Different types of helium-related intrinsic defects have been found depending on annealing temperature which, in turn, determines the amount of helium remaining in the sample. First, bubble clusters arranged in a plate-like shape are detected at T=300°C, when almost the total helium implanted dose is still present in the sample. Second, planetary-like cavity clusters, at T=500°C, when the helium concentration is markedly decreased and voids for T=900°C, when annealing accomplishes complete gas effusion from the cavities.
