IRON GETTERING MECHANISMS IN SILICON

Boron implantation into silicon offers a unique system for studying th e gettering mechanisms of Fe. Using deep level transient spectroscopy to monitor the remaining Fe in the gettered region and secondary-ion-m ass spectroscopy to measure the concentration of Fe redistributed to t he B region, we show that the gettering mechanisms can be quantitative ly described. A combination of Fermi-level-induced Fe+ charge-state st abilization 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 10(6 ) at a p+/p interface at temperatures below approximate to 400 degrees 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 neutra l 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 f or Cr and Mn. (C) 1996 American Institute of Physics.