Iron gettering mechanisms in silicon

Abstract

Boron implantation into silicon offers a unique system for studying the gettering mechanisms of Fe. Using deep level transient spectroscopy to monitor the remaining Fe in the gettered region and secondary-ion-mass spectroscopy to measure the concentration of Fe redistributed to the B region, we show that the gettering mechanisms can be quantitatively described. A combination of Fermi-level-induced Fe+ charge-state stabilization and Fe+–B− pairing acts to lower the free energy of Fe in p+ regions. This can lead to Fe partition coefficients as high as 106 at a p+/p interface at temperatures below ≊400 °C. The dynamic response of the system is diffusion limited during the cooling cycle. B gettering is more effective than gettering produced by Si implantation damage and more effective than trapping by a neutral impurity such as C. These mechanisms also make a large contribution to the effective gettering of Fe by p/p+ epitaxial silicon wafers. The Fermi-level/pairing gettering mechanism is also expected to operate for Cr and Mn.