Activation annealing of ultra-low-energy implanted boron in silicon: a study combining experiment and process modeling

Abstract

We present our investigations on the clustering, diffusion and electrical activation of ultra-low-energy (<1 keV) implanted boron in crystalline silicon during annealing in the temperature range between 900 and 1200°C. We show that during the initial stage of the annealing, boron is bound to non-diffusing clusters. The formation and the dissolution in dependence of temperature are analyzed. We determine a dissolution time constant with an average activation energy of 2.3 eV. The depth-dependent electrical activation as measured by spreading resistance profiling was used to determine the fraction of electrically active boron. From the analysis of the time dependence of the electrically active fraction, a time constant was determined which is faster compared with the boron cluster dissolution time constant in the investigated temperature range. We have simulated the annealing process to demonstrate the influence of the boron clustering on the broadening of the boron profile.