Gold diffusion into silicon during thermal annealing

Gold was found to diffuse into silicon by a complex mechanism involving a vacancy-controlled interstitial-substitutional equilibrium. We investigated the Au diffusion into silicon using differently thick Au layers on n-Si and thermal annealing in a tube furnace at 800°C for 20 h in an argon atmosphere. After thermal treatment the lateral inhomogeneity in the Au distribution has been probed by Auger electron spectroscopy (AES) scans, Scanning electron microscopy, High resolution transmission electron microscopy (HRTEM), and by Kelvin probe force microscopy (KPFM) measurements [1]. The Au diffusion led to very complex diffusion concentration profiles which deviate from the ideal ones for Au diffusion into dislocation-free silicon. The resulting depth distribution of Au in Si has been determined by AES measurements. The KPFM contrast is independent of the surface topography and reveals different long-range chemical and local electrostatic interaction between the conducting KPFM tip and sample surface. HRTEM on cross-sections prepared from the sample with a nominal 10 and 20 nm thick Au layer reveal different phases of silicide formation.
[1] C. Baumgart, A.-D. Müller, F. Müller, H. Schmidt, phys. stat. sol. (a), 2011, 208, 777-789.