Detection of Cs2Ge+ clusters for the quantification of germanium atoms by secondary ion mass spectrometry: Application to the characterization of Si1−xGex layers (⩽x⩽1) and germanium diffusion in silicon

Abstract

We have studied the matrix effects in Si1−xGex structures under O2+ and Cs+ bombardments. Matrix effects are practically suppressed with Cs2Ge+ secondary ions, for Ge concentrations between 0 and 100at.%. A procedure for the accurate quantification of the Ge concentration in Si1−xGex alloys using Cs2Ge+ and CsGe+ clusters has been proposed. For structures in which the Ge content is constant over several hundreds of nanometers, both methods provide very similar results, with an excellent agreement between the Ge concentrations measured by secondary ions mass spectrometry and x-ray diffraction. However, for continuously varying Ge concentration profiles, the nonlinear response of the CsGe+ normalized intensity and the persistence of strong matrix effects for CsSi+ ions lead to differences between the Ge concentration profiles measured with the CsGe+ method compared to the Cs2Ge+ one. The latter is therefore the only reliable method for the study of Ge indiffusion into Si from a pure Ge layer grown by chemical vapor deposition. An application of this method to the analysis of Ge indiffusion in Si at 900°C is also reported.