Thesis presented in 2006

Abstract:
In this work, we propose a CBED (Convergent Beam Electron Diffraction) procedure to characterize stress in the monocrystalline silicon substrates used for microelectronics devices through the measurement of the stress relaxation in a thin TEM lamella. This relaxation involves a bending of the atomic planes inside the sample and leads to HOLZ lines broadening observed in experimental patterns. This effect is clearly explained by coupling finite element mechanical simulation of stress relaxation in the thin lamella with diffracted intensity ca1culation. This procedure is then applied to stress quantification in reference systems Si/ Si Ge and to 3D transistors. The perfect matching between the theoretical relaxed and experimental CBED patterns is an iterative process, and so could be difficult and time-consuming. Nevertheless, it looks the only reliable way to provide strain and stresses field in the investigated device with a very good spatial resolution and an excellent sensitivity. Additionally, we have also developed a CBED software tool under MATLAB environment dedicated to the semi-automatic treatment of CBED patterns with fine HOLZ lines. This application inc1udes Hough transform to identify the exact position of experimental HOLZ lines and the automatic comparison with a quasi-kinematical simulation of HOLZ lines position via an objective function minimization on the lattice parameters. Strain and stress tensor components can then be easily derived. We use this software to characterize stress in epitaxial layer and we still underline the stress relaxation in the thin lamella which is coherent with our elastic mechanical model.