Local Atomic Structure and Electrical Activity of Arsenic Implanted in Silicon

Abstract

AbstractWe summarize the results of an extensive investigation on ion implanted arsenic in silicon after pulsed laser annealing and laser plus furnace annealing. The experiments are aimed at determining the structural and chemical environment around an arsenic impurity atom and relating that information to the electrical behavior of arsenic in silicon. We have implanted silicon with arsenic, 6×1016 As/cm2 at 100 KeV, followed by laser annealing, to obtain epitaxial regrowth with peak As concentrations of about 8 at.%. Subsequent furnace annealing at 800°C for 30 minutes reduces the apparent electrical activity of the arsenic atoms, increasing the electrical resistivity by a factor of three. We have used EXAFS, together with RBS and ion channeling, to investigate the structural and chemical origins of this deactivation. EXAFS measurements are consistent with As occupying tetrahedral sites in both laser ann-ealed and laser plus furnace annealed samples. Average As-As coordination numbers, found from fitting the EXAFS data, were 0.2 and 4.5 for nearest neighbors and for next nearest neighbors respectively. These coordination numbers suggest that there are regions with As concentrations much greater than the nominal maximum concentration mentioned above, and that the preferred local chemical order in regions of high As content resembles that in GaAs, with Si preferentially occupying Ga-sites. This short-range chemical order is unchanged by the furnace annealing. However, we find that furnace annealing does reduce the As-As second neighbor distance by approximately 0.1Å.