Clustering of ultra-low-energy implanted boron in silicon during activation annealing

The clustering kinetics and the electrical activation of boron during the post-implantation activation annealing of ultra-low-energy implanted boron (<1 keV) in silicon has been investigated. By analyzing the boron concentration profiles obtained by means of secondary ion mass spectroscopy (SIMS) non-diffusing boron clusters dissolving with a temperature dependent time constant have been found which exhibit a thermal activation energy of 2.3 eV. The formation of the boron clusters shows at 900°C an incorporation efficiency of boron atoms into clusters of approximately 1. The incorporation efficiency is decreasing with increasing temperature and shows an activation energy of 0.9 eV. The depth profiles of the active boron concentration as measured by spreading resistance profiling was analyzed. The comparison of electrical activation and boron clustering shows that the boron clusters are determining the electrical activation.