Impact of high B concentrations and high dislocation densities on Au diffusion in Si

Abstract

We report diffusion experiments of Au in highly dislocated, undoped and homogeneously doped Si with B concentrations of 3.0×1019 and 1.7×1020 cm−3. After Au diffusion at temperatures between 800 and 1100 °C, Au profiles were measured by means of neutron-activation analysis in conjunction with serial sectioning. The diffusion of Au in dislocated Si is accurately described on the basis of the kick-out mechanism and an additional reaction which takes into account the capture of interstitial Au at dislocations. The profiles yield data for the boundary concentration CAu0 and the Au diffusion coefficient DAu whose product CAu0DAu equals the transport capacity CAuieqDAui of interstitial Aui. With increasing B doping Au diffusion increases showing that interstitial Au is singly positively charged. An enhanced boundary concentration CAu0 and simultaneously retarded Au diffusivity was observed at temperatures below 1000 °C which provides direct evidence of Au segregation at dislocations. A segregation enthalpy of 2.7 eV for the energy difference of Au atoms dissolved on substitutional lattice sites and Au atoms trapped at dislocations was determined.