Transmission electron microscopy study of helium implanted silicon

The structural evolution of helium-related extended defects in silicon, formed after intermediate dose helium implantation and annealing, has been investigated. It is found that the highest helium concentration (annealing at 300°C) is associated with clusters of bubbles arranged in a platelet-like morphology. At 500°c the helium concentration markedly decreases and clusters of cavities formed by a central, large cavity surrounded by small cavities (planetarylike structures) are detected. Thermal treatment at 900°c accomplishes complete helium effusion from the sample leaving behind empty cavities i.e. voids.