A new approach to the diagnostics of nanoislands in GexSi1-x/Si heterostructures by secondary ion mass spectrometry

A new approach to the diagnostics of Ge (x) Si1 - x /Si heterostructures with self-assembled nanoislands, which is based on the method of secondary ion mass spectrometry (SIMS) using secondary Ge-2 cluster ions, is discussed. Calibration dependences of the yield of atomic (Ge) and cluster (Ge-2) secondary ions on the concentration of germanium in homogeneous Ge (x) Si1 - x have been obtained for a TOF.SIMS-5 setup. It is established that, in contrast to the well-known linear dependence of Ge-74/Si-30 a << x/(1 - x), the secondary Ge-2 cluster ions obey the quadratic relation Ge-2/Si-30 a << [x/(1 - x)](2). It is shown that the proposed SIMS depth profiling using nonlinear calibration relations for Ge-2 cluster ions provides expanded information on multilayer Ge (x) Si1 - x /Si heterostructures with nanoislands. By using this approach, without additional a priori data on the sample structure, it is possible to distinguish planar layers and GeSi layers with three-dimensional nanoislands, estimate the height of islands, reveal the presence of a wetting layer, and trace the evolution of islands during their formation in a multilayer structure.