Electron microscopy characterization of monoclinic SiAs precipitates in heavily As+-implanted silicon

Silicon wafers have been implanted with As+ ions at an energy of 100 keV and a dose of 1 × 1017 cm−2 and subsequently annealed at 1050°for 15 min. This results in a peak As concentration of 7 × 1021 cm−3, which is far beyond the solid solubility value of arsenic in silicon at this annealing temperature. Rod-like precipitates, dislocations, and small precipitate-like defects have been observed by transmission electron microscopy. From the analysis of several diffraction patterns taken on a number of rod-like particles at different tilt angles, it has been unambiguously found that they have the structure of the monoclinic SiAs compound previously reported in literature. The stoichiometry of the precipitates has been confirmed by x-ray microanalysis. To our knowledge, this is the first time that this SiAs phase is detected in As+-implanted silicon.