Iron and Nickel Solubilities in Heavily Doped Silicon and their Energy Levels in the Silicon Band Gap at Elevated Temperatures

We have directly measured the solubility of iron and nickel in high and low boron-doped silicon using Instrumental Neutron Activation Analysis. Boron doping levels were 1.5×10 19 and 6.5× 10 14 atoms/cm 3 . Iron and nickel impurity concentrations were measured after extended indiffusions at 800, 900, 1000 and 1100°C for iron and 600, 700 and 800°C for nickel. We have measured a significant enhancement of Fe and Ni concentrations in high boron-doped silicon as compared to low boron-doped silicon. Based on these measurements, we show the iron donor energy level shifts towards the valence band with increased temperature, e.g. at 900°C the donor level is 0.24eV above the valence band as opposed to 0.39eV at room temperature. These results demonstrate that the impurity energy level shift with temperature must be accounted for in any prediction of segregation gettering of metal impurities into heavily doped substrates and heavily implanted doping layers. Additionally, our results suggest that either Ni solubility is greatly enhanced and/or the Ni diffusivity is greatly decreased with high boron doping of silicon.