Gold gettering in silicon by phosphorous diffusion and argon implantation: Mechanisms and limitations

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Abstract
The ability of phosphorus diffusion or argon implantation to remove gold from a silicon wafer has been studied. Both the gettering layer and the gettered substrate have been analyzed for their gold content by complementary techniques such as Rutherford backscattering, neutron activation analysis, and deep level transient spectroscopy. Phosphorus diffusion allows a very efficient gold removal when surface concentration CS and temperature T are kept in a well-defined domain (high CS , low T). On the contrary, the gettering is ineffective in the low CS , high T domain. The boundary between these two domains is found to be an iso-Fermi level curve corresponding to Ec −EF = 0.15 eV. These results are explained by the formation of a negatively charged (P, Au) pair. Argon implantation induces a damaged layer which is found to accomodate large amounts of metal. However, at annealing temperatures higher than 800 °C, gold is found to remain in the bulk at noticeable concentrations which increase with temperature. Such a behavior is attributed to a weak binding energy between gold atoms and the implantation-induced defects. Finally, as low temperatures are found to prevail in both cases, it is emphasized that the duration of the gettering step must be long enough so that gold can travel across the wafer. For example, in the case of argon implantation, a quite efficient gold removal is obtained at 800 °C only after 10 h.