The formation, migration, agglomeration and annealing of vacancy-type defects in self-implanted Si

The evolution of vacancy-type defects has been studied by variable-energy positron annihilation spectroscopy (VEPAS) in samples of high-quality FZ p-type (001) silicon wafers implanted with 4 MeV Si2+ ions at room temperature to doses of 1012–1014 cm−2. The average vacancy concentration increases as (ion dose)0.70 ± 0.06. Progressive isochronal annealing measurements show that open-volume point defects (having a VEPAS signature close to that for divacancies) anneal between 500–600°C. VEPAS with enhanced depth sensitivity (via progressive etching) verified that single 30 min anneals to 550 and 600°C lead to the formation of buried clusters V N with an average N of 3.5 lying between depths of 2.2 and 3.6 μm (both ± 2 μm), close to the peak of vacancy damage just shallower than the ion range predicted by simulation. The concentration of these clusters increases as (ion dose)2.6 ± 0.1. Single anneals to higher temperatures reduce all open-volume point defect concentrations to below the limit detectable by VEPAS.