Gold diffusion in silicon by Rapid Optical Annealing

Gold diffusion in silicon is investigated using Rapid Optical Annealing at temperatures in the range of 800°C to 1200°C and annealing times from 300 s down to 1 s. The resulting content of substitutional gold is determined by spreading resistance measurements and analyzed by comparison with extensive numerical simulations.The profiles obtained show a broader spectrum as compared to the U-shapes after long time diffusion. The cooling process affects the profiles significantly, since they depend on the wafer thickness. An unexpected penetration depth was found after 1200°C diffusion in thick wafers, which are subject to small cooling rates. This phenomenon is due to a special combination of reverse kick-out, deep diffusion of highly supersaturated interstitial gold, and again an incorporation in lattice sites, termed the RDI effect.Numerical calculations allow us to reproduce the experimentally observed profiles only if a sensitive balance between the different temperature dependencies is obeyed. These investigations, therefore, yield new information about the equilibrium concentration and diffusion of silicon interstitials. A best set of parameters is presented. The time constant of the kick-out process is quantified for the first time.