Study of inter-diffusion and defect evolution in thin film Al/Ge bilayers using SIMS and positron beam

Depth resolved investigations of defects and their evolution upon inter-dif fusion have been carried out on Al/Ge thin film bilayers, using concurrent measurements of positron beam based Doppler broadening lineshape and second ary ion mass spectrometry (SIMS) profiles. Measurements have been made on t he as-grown film and films annealed at various temperatures from 370 to 670 K. SIMS studies establish the occurrence of extensive intermixing of the A l and Ge layers beyond 370 K. It is found that there is an asymmetric diffu sion across the interface, with Ge being the dominant diffusing species. Th e intermixed Al/Ge region formed in the near-surface layers of the sample a nnealed at 670 K shows Ge precipitation, as confirmed by electron microscop y and SIMS imaging. Analysis of the Doppler broadening line shape variation , together with the SIMS concentration profiles, indicates increased produc tion of small vacancy clusters at the Al/Ge interface around 520 K, brought about by the enhanced diffusion of Ge. The interfacial vacancy structure i s inferred to be a tri-vacancy cluster. (C) 2001 Elsevier Science B.V. All rights reserved.