Secondary defect formation in self-ion irradiated silicon

Abstract

A detailed experimental study has been made of the evolution of extended secondary decondary defects which form during rapid thermal anneals of 0.5 MeV energy self-ion irradiated silicon. The implant fluence (2 × 10 15 ions/cm 2), flux and substrate temperature (91°C) were chosen so that primary damage levels were well below saturation. Cross-sectional transmission electron microscopy (X-TEM), Rutherford backscattering-channeling spectroscopy (RBS-C) and variable-energy positron annihilation techniques (VEP) have been used to allow partial discrimination between vacancy- and interstitial-type defects. The growth and development of the defect band and of specific types of extended defects within the band has been followed up to anneal temperatures of 1000°C, where the majority are shown to have dissipated. X-TEM has revealed the formation of a previously unreported tubular defect which is found in a narrow temperature range of 700–765°C. The occurrence of this defect correlates with the positron annihilation analysis which shows that a small concentration of defects with vacancy character is present after annealing in the same temperature range. In addition, positron annihilation analysis has allowed an assessment of the role played by defects lying in regions appearing defect-free by the other techniques (RBS-C and TEM). The implications of these findings to existing models involving secondary defect production are discussed.