Direct observation of indium precipitates in silicon following high dose ion implantation

We present electron microscopy, electrical measurement and secondary ion mass spectroscopy (SIMS) characterization of silicon doped with indium to concentrations well above the assumed solid solubility. Samples have been prepared using ion implantation at an energy of 40 keV to achieve as-implanted indium concentrations up to 1 × 1020 cm−3, with post-implantation annealing performed at temperatures between 600 and 1050 °C. We provide direct evidence for nano-scale indium precipitates in the silicon matrix and on the sample surface after annealing. Precipitates having a tetragonal crystal structure and a rectangular shape were observed in all of the samples implanted at the highest dose of 1 × 1015 cm−2, and some of the samples implanted with a lower dose. Comparing SIMS and electron microscopy data allows us to conclude a solid solubility of ≈1018 cm−3, consistent with previously published work (Solmi et al 2002 J. Appl. Phys. 92 1361–6). This paper determines the limitations of indium utility as a dopant in silicon with regard to solid solubility and dose loss. The latter is in excess of 75% for samples annealed at temperatures at and above 750 °C.