Detailed investigation of Ge–Si interdiffusion in the full range of Si1−xGex(≤x≤1) composition

Abstract

Based on the recently developed MCs2+ secondary ion mass spectrometry methodology, the Ge–Si interdiffusion has been investigated, using Ge(:B) solid sources, for Ge concentrations between 0 and 100 at. %. A strong dependence of the interdiffusion with the Ge content of SiGe alloys, formed during annealing, has been shown. The Boltzmann–Matano method was used to extract the interdiffusivity values for all the temperatures studied (750, 800, 850, and 900 °C) in the full range of SiGe compositions. Two regimes of interdiffusion have been identified, both exhibiting an exponential increase in the interdiffusion coefficient as a function of the Ge concentration. The high Ge content regime (>65 at. %) is in good agreement with the values known in the “extreme” cases of Ge diffusion in Si (0 at. %), Ge self-diffusion, and Si diffusion in Ge (100 at. %), while in the low Ge content regime (<50 at. %), the presence and evolution of misfit dislocation can explain the important values of interdiffusivity found in this work. The observed results are perfectly reproduced by a simple empirical model in which the effect of the Ge concentration and the presence of misfit dislocations are taken into account. Based on the evolution of B delta layers (in Si) and Ge depth profiles during NH3 annealing, we showed that the Ge–Si interdiffusion is predominately assisted by a vacancy mechanism with a slightly interstitial contribution in the full range of Ge concentrations. We have estimated the interstitial fraction coefficient, fGe–SiI, to ∼0.17 at 900 °C. Finally, the effect of in situ B doping is studied, which is found to induce a retardation of the Ge–Si interdiffusion.