An extended transmission-electron-microscopy investigation of oxygen-implanted silicon has been carried out and has given evidence for a new precipitation mechanism. This mechanism is related to ${\mathrm{SiO}}_2$ precipitation of free oxygen involved in dense and hot collisional cascades and produces the largest precipitates in the region where oxygen concentration is still high but primary events originating the collisional cascades are no longer sufficient to guarantee the spatial covering of the silicon. This mechanism prevails at relatively low fluence, while at high fluence the conventional precipitation dominates; in the present experimental conditions (energy =100 keV, target temperature ≃250 °C) the oxygen fluence separating these two behaviors is in the interval 1×${10}^{16}$–1×${10}^{17}$ ${\mathrm{cm}}^{\mathrm{-}2}$.

• Received 5 October 1992

DOI:https://doi.org/10.1103/PhysRevB.47.10174