He and O ion implantation induced defects in Si crystal studied using slow positron annihilation spectroscopy

Abstract

Open volume defect profiles have been obtained in He, O and (He + O) ion implanted silicon crystal 〈1 0 0〉 using slow positron beam measurements. The p-type Si samples have been implanted with He (30 keV), O (120 keV) and both the ions [He (30 keV) + O(120 keV)] with the dose of 1 × 1015 and 1 × 1017 ions/cm2. The average range of these ions in Si is estimated ∼280 nm. The depth dependent defect profiles have also been studied after isochronal annealing (100–900 °C) of the ion implanted Si crystals. On annealing at temperatures (>500 °C), an increase (decrease) in S-parameter was observed in the He (O) ion implanted samples. The variations observed in the S-E profiles indicate that large size open volume defects are created in He irradiated Si followed by annealing at 700 °C. In the case of O and (He + O) implanted samples, variations in S-E and W-E profiles indicate the formation of oxygen-vacancy clusters, a buried silicon oxide layer or oxygen decorated cavities. The S-E (W-E) profiles have been fitted using a program ‘Variable Energy Positron fit’ to evaluate the characteristic S- and W- parameter values of different regions. It is observed through S-W correlation plots that He ions as well as vacancy defects diffuse out of the silicon crystal at higher annealing temperatures. Oxygen-vacancy cluster defects are identified in O implanted (1 × 1015 ions/cm2) and annealed at 700 and 900 °C. In case of O implanted (1 × 1017 ions/cm2) and co-implanted samples (1 × 1015 ions/cm2 and 1 × 1017 ions/cm2) annealed at 700 and 900 °C, formation of oxygen decorated cavities is proposed.